Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
MT versus Hartzell
- Thread starter fodrv7
- Start date
MT vs. Hartzell
The following is from an e-mail by Jim Ayers (MT Distributor):
I have done propeller cruise testing using a Harmon Rocket 2 with a stock Lycoming 540 engine, and on a RV-6A with a stock Lycoming O-360 180 hp engine. In normal cruise conditions, the MT 3 blade propeller for that aircraft at least matched the performance of the 2 blade Hartzell propeller for that aircraft on the same airplane with the same pilot under the same flight conditions.
The 4 blade MT Propeller on the HR2 that John Starn is talking about was a custom design for John Harmon's HR3 with a special Lycon 540 engine dyno'd at 380 hp.
Tom Gummo's HR2 has a stock Lycoming 540 engine, and the HR3 propeller is not designed for that engine. However, the price was right, and they were willing to give up the performance.
In my opinion, the 3 blade MT RV-10 propeller and spinner would be an excellent choice for your aircraft.
Next: The following is a posting from the Matronics RV E-mail postings:
Subject: Prop test 2-blade, 3-blade, 4-blade
From: JOHN STARN ([email protected])
Date: Fri Jan 28 - 11:09 AM
--> RV-List message posted by: "JOHN STARN" <[email protected]>
Very long and anecdotal.
Sent from Jack computer - Tom Gummo
do not archive
There has been a lot of talk lately on different props for the RV and Rocket
series aircraft. I have flown with three different props on my plane. I
have been asked to comment on my experiences.
First let me say that I am a pilot (OK, I like to think of myself as a
Fighter Pilot). I would build again in a heartbeat if the money and time
issue would occur again but I don't think of myself as a builder.
Second, I don't have the training of Kevin Horton or the wordsmith skills of
Doug R. but here is my story.
I have the slowest Rocket build with an IO-540 with 250 HP. (Isn't there a
Rocket with the 235 hp version of the engine?). With that said, it PUTS A
GIANT SMILE on my face each time I fly it. I started with a two blade
Hartzell that John Harmon sells for the Rocket. The six verses
four-cylinder engine different can be felt. I total believe the
six-cylinder is smoother.
Here is my flight test experience (note I don't say data). First, I don't
know the max speed at sea level. I just don't fly that way. I takeoff (at
22 GPH), climb to altitude and bring the fuel flow back to a reasonable 10
to 12 GPH and fly around at 140 to 150 Knots indicated. The speeds seen on
my gauges agree with the GPS but not tested in any real manner. At 11,500
or 12,500, the altitudes I go X-country, full throttle, RPM at 2100 or 2200,
fuel flow around 11.5-12.0 GPH, the 140 Knots indicated produced 180 Knots
True.
I let some dumb-guy fly my plane and he had to stop quickly while taxing
back to the hangar and put the plane on it's nose. NEW PROP required.
Enter Jim Ayers; I met Jim several years ago as my EAA chapter helps ACS run
the Copperstate Dash race, which started at APV my home airport. He ran his
RV-3 a couple of times. Turns out that he was building a Rocket too. So we
talked by email helping each other with building problems. By this time, I
knew he was dealer for MT props. So, I gave him a call. Let me say again,
I am a pilot. I didn't want to wait 6 months, 6 weeks, 6 days or even 6
minutes for a new prop. I want to fly. He told me that John Harmon had a
FOUR bladed MT prop he tried on his new HR-III and the Reno Air Races. It
didn't fit John's requirements. John made me a deal and I had a new prop
for my rocket. I knew up front, both Jim and John, told me that, it would
slow me down. As I wanted a military paint scheme (WW-II), the four bladed
prop just looked too good.
(My 250 HP isn't enough to use the prop properly)
The four bladed prop was notability smoother. While it wasn't really
"Turbine like", but except for the noise, it was hard to tell if the engine
was running (he said with tongue in cheek). As predicted, I lost some
speed. The same partial throttle 10 GPH fuel flows, now produce only 140
Knots indicated and at altitude, the GPS is now reporting 170 Knots true.
Sure looks good thou.
I let another dumb-guy fly my plane and as he was putting the plane back
into the hangar, he hit the prop on the hangar door. (Turns out someone
moved the hangar door while he was flying but he didn't check before moving
the plane.) I contacted Jim and we determined that the prop had to be
returned to MT-Germany to fix the ding. He then said something I never
expected. Jim said, "I have a three bladed prop you can use while your prop
is being fixed." Jack and I took off the prop, drove to Jim's house,
returned with the other prop, and was flying the next day.
I couldn't tell the difference in smoothness between the three bladed or
four bladed props. But the 10 knots lost were back.
Here is my summary:
All the MT props were smoother than the Hartzell prop. I don't have all the
model numbers here.
The two bladed Hartzell and three bladed MT produced the best speeds. I
didn't do enough testing to be able to tell if there was any difference.
But it wouldn't be more than one or two knots, so get the one you want.
The four bladed MT prop caused a lost of 10 knots of speed. However, MT
believes that they have a new design and at 250-300 HP ranges, a four bladed
prop will produce the same speeds as the three bladed prop. So far, MT
props have produced what they told me they would so I would like to believe
them. They want another 2200 dollars to change out the new blades for my
old ones so we won't know. 2200 dollars buys lots of gas.
As for Jim, he comes off as a MT dealer because he is. I also believe that
he is willing to help other builders, etc. He sure helped me out this time.
I am sure that he makes money when he gets group buys for MT props, but at
the same time, where are you going to get those prices if you want one. I
for one will give Jim a little slack on his emails.
Tom Gummo
HR-II, N561FS, 240 hours
Apple Valley, CA
P.S. - All those dumb guys were me.
I currently have the new MT 3 blade prop designed for the RV-10/IO-540. Once I get my RV-10 flying, I will post the flight test results. My hanger buddy, and fellow RV-10 builder, has an IO-540 and a two blade Hartzell and when we both have our 10's flying we are going to do a "race test". Won't those results be interesting!!
Regards,
The following is from an e-mail by Jim Ayers (MT Distributor):
I have done propeller cruise testing using a Harmon Rocket 2 with a stock Lycoming 540 engine, and on a RV-6A with a stock Lycoming O-360 180 hp engine. In normal cruise conditions, the MT 3 blade propeller for that aircraft at least matched the performance of the 2 blade Hartzell propeller for that aircraft on the same airplane with the same pilot under the same flight conditions.
The 4 blade MT Propeller on the HR2 that John Starn is talking about was a custom design for John Harmon's HR3 with a special Lycon 540 engine dyno'd at 380 hp.
Tom Gummo's HR2 has a stock Lycoming 540 engine, and the HR3 propeller is not designed for that engine. However, the price was right, and they were willing to give up the performance.
In my opinion, the 3 blade MT RV-10 propeller and spinner would be an excellent choice for your aircraft.
Next: The following is a posting from the Matronics RV E-mail postings:
Subject: Prop test 2-blade, 3-blade, 4-blade
From: JOHN STARN ([email protected])
Date: Fri Jan 28 - 11:09 AM
--> RV-List message posted by: "JOHN STARN" <[email protected]>
Very long and anecdotal.
Sent from Jack computer - Tom Gummo
do not archive
There has been a lot of talk lately on different props for the RV and Rocket
series aircraft. I have flown with three different props on my plane. I
have been asked to comment on my experiences.
First let me say that I am a pilot (OK, I like to think of myself as a
Fighter Pilot). I would build again in a heartbeat if the money and time
issue would occur again but I don't think of myself as a builder.
Second, I don't have the training of Kevin Horton or the wordsmith skills of
Doug R. but here is my story.
I have the slowest Rocket build with an IO-540 with 250 HP. (Isn't there a
Rocket with the 235 hp version of the engine?). With that said, it PUTS A
GIANT SMILE on my face each time I fly it. I started with a two blade
Hartzell that John Harmon sells for the Rocket. The six verses
four-cylinder engine different can be felt. I total believe the
six-cylinder is smoother.
Here is my flight test experience (note I don't say data). First, I don't
know the max speed at sea level. I just don't fly that way. I takeoff (at
22 GPH), climb to altitude and bring the fuel flow back to a reasonable 10
to 12 GPH and fly around at 140 to 150 Knots indicated. The speeds seen on
my gauges agree with the GPS but not tested in any real manner. At 11,500
or 12,500, the altitudes I go X-country, full throttle, RPM at 2100 or 2200,
fuel flow around 11.5-12.0 GPH, the 140 Knots indicated produced 180 Knots
True.
I let some dumb-guy fly my plane and he had to stop quickly while taxing
back to the hangar and put the plane on it's nose. NEW PROP required.
Enter Jim Ayers; I met Jim several years ago as my EAA chapter helps ACS run
the Copperstate Dash race, which started at APV my home airport. He ran his
RV-3 a couple of times. Turns out that he was building a Rocket too. So we
talked by email helping each other with building problems. By this time, I
knew he was dealer for MT props. So, I gave him a call. Let me say again,
I am a pilot. I didn't want to wait 6 months, 6 weeks, 6 days or even 6
minutes for a new prop. I want to fly. He told me that John Harmon had a
FOUR bladed MT prop he tried on his new HR-III and the Reno Air Races. It
didn't fit John's requirements. John made me a deal and I had a new prop
for my rocket. I knew up front, both Jim and John, told me that, it would
slow me down. As I wanted a military paint scheme (WW-II), the four bladed
prop just looked too good.
(My 250 HP isn't enough to use the prop properly)
The four bladed prop was notability smoother. While it wasn't really
"Turbine like", but except for the noise, it was hard to tell if the engine
was running (he said with tongue in cheek). As predicted, I lost some
speed. The same partial throttle 10 GPH fuel flows, now produce only 140
Knots indicated and at altitude, the GPS is now reporting 170 Knots true.
Sure looks good thou.
I let another dumb-guy fly my plane and as he was putting the plane back
into the hangar, he hit the prop on the hangar door. (Turns out someone
moved the hangar door while he was flying but he didn't check before moving
the plane.) I contacted Jim and we determined that the prop had to be
returned to MT-Germany to fix the ding. He then said something I never
expected. Jim said, "I have a three bladed prop you can use while your prop
is being fixed." Jack and I took off the prop, drove to Jim's house,
returned with the other prop, and was flying the next day.
I couldn't tell the difference in smoothness between the three bladed or
four bladed props. But the 10 knots lost were back.
Here is my summary:
All the MT props were smoother than the Hartzell prop. I don't have all the
model numbers here.
The two bladed Hartzell and three bladed MT produced the best speeds. I
didn't do enough testing to be able to tell if there was any difference.
But it wouldn't be more than one or two knots, so get the one you want.
The four bladed MT prop caused a lost of 10 knots of speed. However, MT
believes that they have a new design and at 250-300 HP ranges, a four bladed
prop will produce the same speeds as the three bladed prop. So far, MT
props have produced what they told me they would so I would like to believe
them. They want another 2200 dollars to change out the new blades for my
old ones so we won't know. 2200 dollars buys lots of gas.
As for Jim, he comes off as a MT dealer because he is. I also believe that
he is willing to help other builders, etc. He sure helped me out this time.
I am sure that he makes money when he gets group buys for MT props, but at
the same time, where are you going to get those prices if you want one. I
for one will give Jim a little slack on his emails.
Tom Gummo
HR-II, N561FS, 240 hours
Apple Valley, CA
P.S. - All those dumb guys were me.
I currently have the new MT 3 blade prop designed for the RV-10/IO-540. Once I get my RV-10 flying, I will post the flight test results. My hanger buddy, and fellow RV-10 builder, has an IO-540 and a two blade Hartzell and when we both have our 10's flying we are going to do a "race test". Won't those results be interesting!!
Regards,
Last edited by a moderator:
f1rocket
Well Known Member
Interesting story on this topic....
At Airventure last year, I was trying to make my prop choice. It came down to a three-bladed MT versus a three-bladed Hartzell. Since Hartzell is in my backyard and a quick drive, I had just always assumed that I'd go with Hartzell.
That was until I talked to the Hartzell cronies manning their display in one of the exhibition halls. When asked for a comparison, all I got was put downs about MT. When I politely tried to re-diect the conversation back to their prop and its performance, all I got was put downs about the MT.
My MT prop is due to arrive any day now.
At Airventure last year, I was trying to make my prop choice. It came down to a three-bladed MT versus a three-bladed Hartzell. Since Hartzell is in my backyard and a quick drive, I had just always assumed that I'd go with Hartzell.
That was until I talked to the Hartzell cronies manning their display in one of the exhibition halls. When asked for a comparison, all I got was put downs about MT. When I politely tried to re-diect the conversation back to their prop and its performance, all I got was put downs about the MT.
My MT prop is due to arrive any day now.
randylervold
moderator
fodrv7 said:
Yes. One of our local guys installed the 3-bladed MT on his RV-8A. His speeds were down compared to all the other guys around here. He then bought and installed a Whirl Wind 200RV and his speeds came back up. Sorry, I don't have the specific speed increases but he's no longer compaining.
gmcjetpilot
Well Known Member
MT vs Hartzell
A comment of why performance is down with the MT prop.
First it is known by the "aero guy's" that multi blades interfere with each other and reduce efficiency. THe differnce in efficency is small but speed is not the reason to go with more blades necessarily. I know Jim thinks a 4 blade prop will be the ultimate, but I really don't see 4 blades making much practical sense on a 200hp RV or 270hp Rocket. Planes I flew with multi blades: Ted Smith Aerostar (later PA60) 350hp turbo charged twin 3 blades; 1200hp commuter (Metro Liner) 4 blades.
Why go with multi blades. For one, to absorb high horsepower, requires more blades, but I am talking about 500-1000HP, not 200-250HP. Also, multi blades allows for reduce overall diameter, which improves prop tip ground clearance and lowers tip speeds, which can reduce noise. The big turbo-props (+2000hp) use multi blades (up to 6) with large twist and turn much slower than we do (2000 rpm).
Blade thickness also effects efficiency. Metal blades tend to be thinner than wood or wood core/composite props. Thinner the blade the more efficient.
As far as impact resistance, metal is better and a gouge can be easily blended with a file on the ramp. However wood/composite has vibration dampen qualities that are better. Does that make it smoother? That is debatable. Most of the vibrations we feel are from the engine. A well-balanced metal prop will be fairly smooth. Will a well-balanced composite prop be smoother? Slightly I suppose it could be precieved as smoother but it is a trade off.
Than there is cost: The MT is more expensive and repair is harder to get.
Cheers George
Impact resistance, I agree a metal prop is more likely to damage the crank in an accident, where a wood/composite prop would fragment. However I was referring to more benign rock impacts, which leave a nick in the leading edge. A dent or impact to the leading edge of a MT may cause more damage or damage that requires extensive repair methods than a metal prop blade.
Cost: my first RV had an overhauled Hartzell made from used parts for $2,500. A new one today is around $5,500. You will pay over $2,000, up to $5000 more to get a composite version. Hartzell overhauls go for about $1,500 on a TBO of 2000 hours.
Weight: We are talking about 20lbs average differance in weight between Hartzell and other c/s props with composite blades.
Service life: it is 20,000 hours or 8,700 hours on the original HC-C2YK/F7666 with lightspeed ignition and/or HC pistons. That is a lot of flying. If you flew 200 hours a year that would be over 40 years with electronic ignition. What would a MT wood/composite prop blade would look like in 8,700 hours or 40 years?
Speed: We are talking about 2-8 mph depending on models (see below).
** The RVator, 1st issue, 2004, pg 5, test of 8 prop's at 8,500', full throt,2500 rpm.
Hartzell C2YR (2 metal blade) = 208.9**
Whirlwind 200RV (2 comp blade) = 206.9
Whirlwind 200C (2 comp blade) = 205.6
Hartzell C2YK (2 metal blade) = 205.4**
Aerocomposite ((2 comp blade) = 204.6
Whrilwind 150 (3 comp blade) = 201.9
MT 12B (3 wood / comp blade) = 200.7**
A comment of why performance is down with the MT prop.
First it is known by the "aero guy's" that multi blades interfere with each other and reduce efficiency. THe differnce in efficency is small but speed is not the reason to go with more blades necessarily. I know Jim thinks a 4 blade prop will be the ultimate, but I really don't see 4 blades making much practical sense on a 200hp RV or 270hp Rocket. Planes I flew with multi blades: Ted Smith Aerostar (later PA60) 350hp turbo charged twin 3 blades; 1200hp commuter (Metro Liner) 4 blades.
Why go with multi blades. For one, to absorb high horsepower, requires more blades, but I am talking about 500-1000HP, not 200-250HP. Also, multi blades allows for reduce overall diameter, which improves prop tip ground clearance and lowers tip speeds, which can reduce noise. The big turbo-props (+2000hp) use multi blades (up to 6) with large twist and turn much slower than we do (2000 rpm).
Blade thickness also effects efficiency. Metal blades tend to be thinner than wood or wood core/composite props. Thinner the blade the more efficient.
As far as impact resistance, metal is better and a gouge can be easily blended with a file on the ramp. However wood/composite has vibration dampen qualities that are better. Does that make it smoother? That is debatable. Most of the vibrations we feel are from the engine. A well-balanced metal prop will be fairly smooth. Will a well-balanced composite prop be smoother? Slightly I suppose it could be precieved as smoother but it is a trade off.
Than there is cost: The MT is more expensive and repair is harder to get.
Cheers George
Regarding prop smoothness, impressions of other builders, MT vs. others, such as Hartzell or Whirlwind report a little difference with the MT but not as dramatic as reports of "turbine smooth", but I agree with Penguin-Pete, a composite/wood prop should reduce vibes over a metal blade. I still contend the engine is shaking and the prop is only going to do so much. Builder?s preference.penguin said:
Impact resistance, I agree a metal prop is more likely to damage the crank in an accident, where a wood/composite prop would fragment. However I was referring to more benign rock impacts, which leave a nick in the leading edge. A dent or impact to the leading edge of a MT may cause more damage or damage that requires extensive repair methods than a metal prop blade.
Cost: my first RV had an overhauled Hartzell made from used parts for $2,500. A new one today is around $5,500. You will pay over $2,000, up to $5000 more to get a composite version. Hartzell overhauls go for about $1,500 on a TBO of 2000 hours.
Weight: We are talking about 20lbs average differance in weight between Hartzell and other c/s props with composite blades.
Service life: it is 20,000 hours or 8,700 hours on the original HC-C2YK/F7666 with lightspeed ignition and/or HC pistons. That is a lot of flying. If you flew 200 hours a year that would be over 40 years with electronic ignition. What would a MT wood/composite prop blade would look like in 8,700 hours or 40 years?
Speed: We are talking about 2-8 mph depending on models (see below).
** The RVator, 1st issue, 2004, pg 5, test of 8 prop's at 8,500', full throt,2500 rpm.
Hartzell C2YR (2 metal blade) = 208.9**
Whirlwind 200RV (2 comp blade) = 206.9
Whirlwind 200C (2 comp blade) = 205.6
Hartzell C2YK (2 metal blade) = 205.4**
Aerocomposite ((2 comp blade) = 204.6
Whrilwind 150 (3 comp blade) = 201.9
MT 12B (3 wood / comp blade) = 200.7**
Last edited:
Metal vs Composite props
I would like to offer a different opinion to George concerning vibration. I believe that composite bladed props (wood or glass/carbon) will always result in a smoother engine installation, so would would be loath to fit a Hartzell, although it is cheaper initially. In my opinion the smoothness is worthwhile.
Also, Hatzells are not so tolerant to propstrikes, have finite overhaul lives, and are heavier than MTs (which are heavier than Whirlwind carbon props). Following a prop strike your Hartzell will bend and stop the engine quickly, with the possibility (probability?) of engine damage. Wooden (MT) and composite (Whirlwind) props often break the blades causing less damage to the engine. Result to the prop in all cases is the same (new blades)! There is a good MT service network built up now (although Hartzell is better).
In my opinion the only benefit of a Hartzell is price and may be a couple of mph.
Pete
I would like to offer a different opinion to George concerning vibration. I believe that composite bladed props (wood or glass/carbon) will always result in a smoother engine installation, so would would be loath to fit a Hartzell, although it is cheaper initially. In my opinion the smoothness is worthwhile.
Also, Hatzells are not so tolerant to propstrikes, have finite overhaul lives, and are heavier than MTs (which are heavier than Whirlwind carbon props). Following a prop strike your Hartzell will bend and stop the engine quickly, with the possibility (probability?) of engine damage. Wooden (MT) and composite (Whirlwind) props often break the blades causing less damage to the engine. Result to the prop in all cases is the same (new blades)! There is a good MT service network built up now (although Hartzell is better).
In my opinion the only benefit of a Hartzell is price and may be a couple of mph.
Pete
Bill Dicus
Well Known Member
Props
Planning to go Hartzell for my RV-8. It'll have a lycon parallel valve IO-360 with 10:1 pistons. Anybody heard of experience with the Blended Airfoil prop on an engine such as this? Bill
Planning to go Hartzell for my RV-8. It'll have a lycon parallel valve IO-360 with 10:1 pistons. Anybody heard of experience with the Blended Airfoil prop on an engine such as this? Bill
Romeo Victor
Member
fodrv7 said:
I made the same experience. I have an IO360 with 200 HP on my 8 and cruise maximum 163 kts at 8000 ft with an MT 3-blade. When I asked they told me it depends on the way I build my aeroplane. Other RVs wouldn't have that problem. I still have the propeller but sell the plane in July. My next is a RV7 with an Aero Composite, probably 2 blade.
Stephan
gmcjetpilot
Well Known Member
Why Aero Composite
http://www.lazy8.net/proptest.htm (click on Aero Composites story)
Not that I think there is anything wrong with Aero Composite, just they are more complicated blades made up of many bonded parts. My big complaint is the size of the company (small), where you can get it overhauled, cost and any blade repair will involve removal from plane and shipping it to the manufacture. The faster composite prop, the RV200 from Whirl Wind, would be an alternative to the Aero composite, but they are having issues with their other models. Although the issues are not with the RV200, the RV200 has a very low TBO. Whirl Wind like Aero Composite, is in the same small company with factory only repair/overhaul boat. Hartzells support can repair or support world wide.
That is why Hartzell has the advantage in every way but weight IMHO. However late model RV's (RV-7/8) can take the extra weight on the nose from a metal prop. I know composites are sexy and an undeniable attraction, but practically speaking $6,000 on a Hartzell BA 7497 bladed prop is hard to beat. Also with the new blade there are no or less restrictions (depending on engine & ignition).
Why Aero composite. They are crazy expensive. They may be faster than MT but not faster than the Hartzell BA prop. Weight I grant you is better but you should read this guys experience with Aero composite.Romeo Victor said:
http://www.lazy8.net/proptest.htm (click on Aero Composites story)
Not that I think there is anything wrong with Aero Composite, just they are more complicated blades made up of many bonded parts. My big complaint is the size of the company (small), where you can get it overhauled, cost and any blade repair will involve removal from plane and shipping it to the manufacture. The faster composite prop, the RV200 from Whirl Wind, would be an alternative to the Aero composite, but they are having issues with their other models. Although the issues are not with the RV200, the RV200 has a very low TBO. Whirl Wind like Aero Composite, is in the same small company with factory only repair/overhaul boat. Hartzells support can repair or support world wide.
That is why Hartzell has the advantage in every way but weight IMHO. However late model RV's (RV-7/8) can take the extra weight on the nose from a metal prop. I know composites are sexy and an undeniable attraction, but practically speaking $6,000 on a Hartzell BA 7497 bladed prop is hard to beat. Also with the new blade there are no or less restrictions (depending on engine & ignition).
Last edited:
"First it is known by the "aero guy's" that multi blades interfere with each other and reduce efficiency." Only un-knowledgeable aero guys. Each blade follows its own individual helical path through the air.
"Blade thickness also effects efficiency. Metal blades tend to be thinner than wood or wood core/composite props. Thinner the blade the more efficient." Sorry! Wrong statement #2. Thin blades have much lower L/D than thick blades, and higher induced drag.
In a multi-blade prop with the correct AOA and lift distribution along the blade, the only reason for less speed is if the blades have a klunky shape in the root region that sticks out into the airstream causing drag; this and the big openings in the spinner around the blades. Seal the blades to the spinner or provide streamlined fairings around the root and that drag goes away, leaving lower blade loading the more blades that are present. Lower blade loading equates to the lower span loading of higher aspect-ratio wings. It's a shame that this same mis-information keeps making the rounds. So Tom Aberle's Reno Gold winning biplane's 15% thick four-blade shouldn't have given him the 10 mph speed increase over the previous year's 15% thick three-blade. What stuff and nonsense! Are these the same "aero guys" who keep repeating the nostrum that a single-blade prop is the most efficient. In which galaxy? Put one on your plane and see how long it takes the thrust un-balance to rip the engine off the mounts!
"Blade thickness also effects efficiency. Metal blades tend to be thinner than wood or wood core/composite props. Thinner the blade the more efficient." Sorry! Wrong statement #2. Thin blades have much lower L/D than thick blades, and higher induced drag.
In a multi-blade prop with the correct AOA and lift distribution along the blade, the only reason for less speed is if the blades have a klunky shape in the root region that sticks out into the airstream causing drag; this and the big openings in the spinner around the blades. Seal the blades to the spinner or provide streamlined fairings around the root and that drag goes away, leaving lower blade loading the more blades that are present. Lower blade loading equates to the lower span loading of higher aspect-ratio wings. It's a shame that this same mis-information keeps making the rounds. So Tom Aberle's Reno Gold winning biplane's 15% thick four-blade shouldn't have given him the 10 mph speed increase over the previous year's 15% thick three-blade. What stuff and nonsense! Are these the same "aero guys" who keep repeating the nostrum that a single-blade prop is the most efficient. In which galaxy? Put one on your plane and see how long it takes the thrust un-balance to rip the engine off the mounts!
randylervold
moderator
I'd debate that
Certainly the Hartzell BA and the WW 200RV are the acknowledged contenders for fastest prop, can't we find a way to have an owner of one or the the other borrow a prop and do some testing? C'mon guys, let's settle this, someone step up for the good of the community.
I would argue that and submit that the WW 200RV is. Unfortunately the only comparative data available is extrapolated by Van's from two different aircraft, their Dilbert and my RV-8. As one who was involved in collecting the data, and one who has participated in quite a few RV run-offs with RVs equipped with various props, that is my unfortunately non-scientific gut feel.osxuser said:
Certainly the Hartzell BA and the WW 200RV are the acknowledged contenders for fastest prop, can't we find a way to have an owner of one or the the other borrow a prop and do some testing? C'mon guys, let's settle this, someone step up for the good of the community.
gmcjetpilot
Well Known Member
You may be right but.....
There's more to number of blades, than one is best. It's only best for a 40 hp 60 mph planes. However there are a dozen other design factors that go into it, besides blade number.
The more HP (thrust) the greater the blade area is needed, like the heaver a plane, the bigger the wing. More blade area requires you make it wider or the diameter longer, or you can add blades, which allows smaller dia and slower tip speeds. That is the pay off, but if you don't have the greater HP or top speed to justify multi-multi blades, it's like a red flame paint job on a Hyundai or mini van, it will not make it faster or better.
One word: compromises, applies to total HP and airplane speed. The faster you go the smaller diameter (or slower RPM) you need to keep the prop tip speed. Multi blades allow smaller diameters and slower RPM's, needed for high speed aircraft. They may lose some efficiency in one way but gain it in others.
The early J2 cubs and self launch gliders use one-blade counter weighted props. Of course the single blade system below is primarily because it fits so well in a glider. You would think or I do at least, even dynamically balanced the center of thrust is offset and would not be too smooth aerodynamically with one blade. However it's reported to be fairly smooth. Again we are talking slow 40 hp or so planes.
Early P51's had three blades at first and only went to 4-later. I suspect due to the higher HP engines and altitudes they eventually grew to. The P-51 ended with the H model at +2000HP and 487 mph. A RV-X with 200 hp and top speed of 225 mph does not need three or four blades, practically speaking. There are trade offs to blade numbers, but in general less is more, when it comes to speed alone with in reason.
Reno Gold winning biplane? Of course one blade is ridiculous because it could not have enough area to absorb the HP. The 10 MPH came from what, other 100 mods he made from the previous year? May be 4-blades are better at the HP and SPEEDS he operates at. It's more complicated than one blade is best. A Reno Racer may need four blades? He may have upped the HP from the previous year? You are right one blade is not workable for most planes over 40 HP.
Seems that the P-51 had many different props but note the roots.
Negative, have you ever seen a thick jet wing. Look at a super-sonic jet fighter wing. All very thin relative to sub-sonic planes. Props and jet wings are working in the mach 0.70-0.90 range, transonic. Thick blades or wings are only for when you are drunk, oh..........that is chicks, but same thing, stay thin go fast.elippse said:
Yea, how dare they repeat the facts.
There's more to number of blades, than one is best. It's only best for a 40 hp 60 mph planes. However there are a dozen other design factors that go into it, besides blade number. The more HP (thrust) the greater the blade area is needed, like the heaver a plane, the bigger the wing. More blade area requires you make it wider or the diameter longer, or you can add blades, which allows smaller dia and slower tip speeds. That is the pay off, but if you don't have the greater HP or top speed to justify multi-multi blades, it's like a red flame paint job on a Hyundai or mini van, it will not make it faster or better.
One word: compromises, applies to total HP and airplane speed. The faster you go the smaller diameter (or slower RPM) you need to keep the prop tip speed. Multi blades allow smaller diameters and slower RPM's, needed for high speed aircraft. They may lose some efficiency in one way but gain it in others.
The early J2 cubs and self launch gliders use one-blade counter weighted props. Of course the single blade system below is primarily because it fits so well in a glider. You would think or I do at least, even dynamically balanced the center of thrust is offset and would not be too smooth aerodynamically with one blade. However it's reported to be fairly smooth. Again we are talking slow 40 hp or so planes.
Early P51's had three blades at first and only went to 4-later. I suspect due to the higher HP engines and altitudes they eventually grew to. The P-51 ended with the H model at +2000HP and 487 mph. A RV-X with 200 hp and top speed of 225 mph does not need three or four blades, practically speaking. There are trade offs to blade numbers, but in general less is more, when it comes to speed alone with in reason.
You make great points about spinner cutouts and klunky blade roots for structural reasons. Good point. Look at a P-51 blade, its an airfoil right to the spinner and than its sealed around the round root.
Reno Gold winning biplane? Of course one blade is ridiculous because it could not have enough area to absorb the HP. The 10 MPH came from what, other 100 mods he made from the previous year? May be 4-blades are better at the HP and SPEEDS he operates at. It's more complicated than one blade is best. A Reno Racer may need four blades? He may have upped the HP from the previous year? You are right one blade is not workable for most planes over 40 HP.
Seems that the P-51 had many different props but note the roots.
Last edited:
Until someone does some scientific tests (the Van's ones are not, even by their own admission), let's wait and see which prop is the fastest.
The root of the prop is mainly support for the outer portion of the blade which provides the majority of thrust.
Before anyone here shoots down elippse, maybe you should find out who he is. He is THE MAN on props at Reno in the lighter classes. He is a pretty clever guy with the results to show he knows more than most of the other "experts" out there.
Finally, I've never bought the one blade, two blade theory being most efficient and the crazy explanations about wake interference on adjacent blades. Watch a wind tunnel test on a rotating prop or votices on a really humid day. Paul is right on this one.
The root of the prop is mainly support for the outer portion of the blade which provides the majority of thrust.
Before anyone here shoots down elippse, maybe you should find out who he is. He is THE MAN on props at Reno in the lighter classes. He is a pretty clever guy with the results to show he knows more than most of the other "experts" out there.
Finally, I've never bought the one blade, two blade theory being most efficient and the crazy explanations about wake interference on adjacent blades. Watch a wind tunnel test on a rotating prop or votices on a really humid day. Paul is right on this one.
Another thing about thin blades is that they have a very small diameter LE which will cause separation at less departure from design angle of attack. Look at the polars on the 6% thick 65-206 for example. Its CL peaks at 1.0, and its minimum profile drag is at a CL of 0.2. For a prop blade to be efficient it needs a CL of 0.5-0.6 where the 65-206's CD is.006, and its drag bucket of 0.004 is 0.2 CL wide at 0.1 to 0.3 CL. The 15% thick 652-415 CL peak is about 1.6, and its drag bucket of 0.0045 extends from 0.1 to 0.6 CL. Obviously this section will be superior at design CL and several degrees AOA removed from that. When a thin LE gets pitting from rain or rocks, it seriously degrades the drag and lift. The same pitting on the 15% blade, with its rounder LE, suffers less degradation, since it represents a lesser percentage of the LE. My propeller designs have the same thrust/ torque ratio from the root to almost the tip. There it drops off due to the higher drag at high Mach. The two places prop blades throw away power is tip drag and klunky, low thrust/high drag root sections. Letting the root sections develop thrust, which they will even at a pitch angle of 70 deg, is half of the battle. Keep in mind that this 70 deg is the helix angle the blade advances through the air; its not moving flat-wise through the air. There is no thrust at the tip, since there can be no pressure differential at and near the tip. However, any chord at the tip will develop profile drag for an L/D of zero. And that drag CD at M0.85 is about 6-8 times as great as it is at M0.65. so the tip makes only drag based on its chord at the extremely high dynamic pressure at the high tip Mach, and that drag force is multiplied through the radius to give reverse torque, and so HP loss. One of the worst blade planforms you can have is a rounded tip, and next to it is a wide square tip. Remember, the larger the tip chord, the more drag it creates. You can statically balance a single blade prop, but you can't balance it against its thrust on a single side. The higher the power input, the greater the unbalanced thrust acting against the crankshaft. For that you need a blade or blades arranged symmetrically. And how much drag does that counter-balance weight develop in whirling around, and how much dead weight does it contribute. It's a dumb idea based on poor engineering analysis. And what about those GE, Rolls, and P&W engines with their 18-or-more blade fixed pitch prop(fan) at the front which develops most of the thrust. Why don't those "aero guys" show these engine people the error of their ways! According to their theory, those fans are extremely inefficient, non?
David-aviator
Well Known Member
Sonic and sub sonic
Absolutely fascinating discussion!
The disconnect on skinny blades vrs fat blades must be due to tip speed. Look at WWII photos of 51's and they had fat blades all the way to the hub.
Look at a P&W fan and they are skinny, very skinny. For sure they are super sonic in flight and they work. The difference in efficiency from the non fan engines to the later fans was incredible. And those little suckers are tough...took a huge sea gull out of Newark one morning that caused a compressor stall that coughed the bird forward bending one blade at the tip for about 4 inches. After landing at ORD, maintence got into the book and they took an old fashioned hack saw and sawed the bent tip off, filed it even and the engine was ok for service for a number of hours. For sure the harmonics of the engine changed but the trusty JT3 ran just fine.
Yes, I know slightly off topic, but I think you are both right.
Absolutely fascinating discussion!
The disconnect on skinny blades vrs fat blades must be due to tip speed. Look at WWII photos of 51's and they had fat blades all the way to the hub.
Look at a P&W fan and they are skinny, very skinny. For sure they are super sonic in flight and they work. The difference in efficiency from the non fan engines to the later fans was incredible. And those little suckers are tough...took a huge sea gull out of Newark one morning that caused a compressor stall that coughed the bird forward bending one blade at the tip for about 4 inches. After landing at ORD, maintence got into the book and they took an old fashioned hack saw and sawed the bent tip off, filed it even and the engine was ok for service for a number of hours. For sure the harmonics of the engine changed but the trusty JT3 ran just fine.
Yes, I know slightly off topic, but I think you are both right.
In the Unlimited Class, more effort has been expended to simply cut down tip mach numbers by installing very high reduction gear ratios, even custom made ones as low as .38 on Dago. Almost all high hp turboprops also use very low rpms to increase efficiency, turning only 750-1000 rpm. Naturally this is a must to some degree with props in the 15 to 20 foot diameter range as well.
I think you'll see the redrive equipped Lancair and Thunder Mustang eventually come out on top in the Sport Class due to high hp capability and higher prop efficiency than their direct drive competitors.
It's always interesting to hear the theorists on this forum continue to sprout the same old stuff- even in the face of flight test results. This reminds me of Paul Lamar's statement that the IVO prop could never exceed 200mph due to his "analysis" of the blade producing "negative thrust". He continued to support this nonsense even after several people had flown the IVO well past 200mph. I'd prefer to see more flight testing results and less conjecture here. Real science gives us facts and either shatters or confirms preconceived ideas.
Back to the MT/ Hartzell question. MT was helpful if a bit slow in responding to my questions and of course very slow in providing the propeller due to production backlogs. If you are in a rush, Hartzell will certainly offer quicker service.
Advantages of the MT would be lower weight, smoother operation and an electric option. Disadvantages will be higher cost and less service centers close by in the event of damage.
From a composite prop perspective, MT has far more experience than any other manufacturer currently in this area. Blade retention being by the vastly proven lag screw method compared to others with bonded/wrapped ferrules.
It is interesting that many RVs are equipped with MTs these days despite higher cost and perceived lower performance. Why are all these people not installing Hartzells? The choice just seems so clear to many here.
For those contemplating an MT and not buying from Van's or Eggenfellner, I had good experiences with Bob Honig from American Propeller whom I met at Reno in '05. Although I did not end up buying from him, I have heard good things about AP from others as well.
I think you'll see the redrive equipped Lancair and Thunder Mustang eventually come out on top in the Sport Class due to high hp capability and higher prop efficiency than their direct drive competitors.
It's always interesting to hear the theorists on this forum continue to sprout the same old stuff- even in the face of flight test results. This reminds me of Paul Lamar's statement that the IVO prop could never exceed 200mph due to his "analysis" of the blade producing "negative thrust". He continued to support this nonsense even after several people had flown the IVO well past 200mph. I'd prefer to see more flight testing results and less conjecture here. Real science gives us facts and either shatters or confirms preconceived ideas.
Back to the MT/ Hartzell question. MT was helpful if a bit slow in responding to my questions and of course very slow in providing the propeller due to production backlogs. If you are in a rush, Hartzell will certainly offer quicker service.
Advantages of the MT would be lower weight, smoother operation and an electric option. Disadvantages will be higher cost and less service centers close by in the event of damage.
From a composite prop perspective, MT has far more experience than any other manufacturer currently in this area. Blade retention being by the vastly proven lag screw method compared to others with bonded/wrapped ferrules.
It is interesting that many RVs are equipped with MTs these days despite higher cost and perceived lower performance. Why are all these people not installing Hartzells? The choice just seems so clear to many here.
For those contemplating an MT and not buying from Van's or Eggenfellner, I had good experiences with Bob Honig from American Propeller whom I met at Reno in '05. Although I did not end up buying from him, I have heard good things about AP from others as well.
Last edited:
Bill Dicus
Well Known Member
2 vs. 3 blade
Not an RV, but our Lance's prop had to be replaced at this annual (bad old hub).... but so did the engine! We couldn't get a 2 blade Hartzell for several months but Hartzell would sell us right away a three blade "top prop" which they say climbs better and doesn't lose cruise speed (which 3 blades have a rep for) and encouraged us with a $1000 discount. Despite an obviously stronger new engine and a climb rate that seems at least 300 fpm better than before, we have lost a few knots (about 3) in cruise. I don't have exact numbers at identical DA's etc but after 20 years of flying the plane think this is about right. Our TAS's are consistently lower at comparable DA's and power settings/fuel flows at peak EGT than they were with the 2 blade and the old presumably weaker engine, despite Hartzell's claims. We didn't notice any increse in smoothness, just a different vibration character. Sometimes the three blade actually felt rougher. So we had the prop balance check. Our prop just as it came out of the annual (new install) was 1.17 ips, too little out of balance to expend effort and weights on to improve. Sure like the climb and the increased ground clearance (slight). The 3 blader does limit access to cowl and engine compared to 2 blades and is a little heavier. My partner loves the looks, though. My -8 will be 2 blade BA. Bill
Not an RV, but our Lance's prop had to be replaced at this annual (bad old hub).... but so did the engine! We couldn't get a 2 blade Hartzell for several months but Hartzell would sell us right away a three blade "top prop" which they say climbs better and doesn't lose cruise speed (which 3 blades have a rep for) and encouraged us with a $1000 discount. Despite an obviously stronger new engine and a climb rate that seems at least 300 fpm better than before, we have lost a few knots (about 3) in cruise. I don't have exact numbers at identical DA's etc but after 20 years of flying the plane think this is about right. Our TAS's are consistently lower at comparable DA's and power settings/fuel flows at peak EGT than they were with the 2 blade and the old presumably weaker engine, despite Hartzell's claims. We didn't notice any increse in smoothness, just a different vibration character. Sometimes the three blade actually felt rougher. So we had the prop balance check. Our prop just as it came out of the annual (new install) was 1.17 ips, too little out of balance to expend effort and weights on to improve. Sure like the climb and the increased ground clearance (slight). The 3 blader does limit access to cowl and engine compared to 2 blades and is a little heavier. My partner loves the looks, though. My -8 will be 2 blade BA. Bill
Questions for the prop design experts here
Two questions from my curious mind:
- ellippse suggests that thrust is available even at the root, where a helix angle of 70? would give you an effective 0? AoA. That might be true, but surely most of your lift - 94% of it - even at best L/D will resolve to a reaction torque rather than thrust. What criteria is used to determine whether it's better to have 0? AoA or something else? I guess this must make a large spinner a good thing? Maybe a radial engine isn't so bad after all?
- why do we not see intersection fairings / fillets at the propellor roots? The aerofoil is moving at some considerable rate of knots, even at the blade root, so surely it's worthy of a healthy intersection fillet?
Two questions from my curious mind:
- ellippse suggests that thrust is available even at the root, where a helix angle of 70? would give you an effective 0? AoA. That might be true, but surely most of your lift - 94% of it - even at best L/D will resolve to a reaction torque rather than thrust. What criteria is used to determine whether it's better to have 0? AoA or something else? I guess this must make a large spinner a good thing? Maybe a radial engine isn't so bad after all?
- why do we not see intersection fairings / fillets at the propellor roots? The aerofoil is moving at some considerable rate of knots, even at the blade root, so surely it's worthy of a healthy intersection fillet?
The prop needs to be at an AOA, relative to the induced flow, that will give a CL of 0.5 to 0.6 for best efficiency. Remember, too, you have to take into account the zero-lift AOA of the airfoil in determining its lift. Root thrust-to-torque? OK! Resolve the lift force vector perpendicular to the induced angle of attack into its forward, thrust, direction, 0.34, and into its tangential direction, 0.939, which acts against the engine. Now multiply the the tangential force by the radius in ft. Guess what happens at 6" radius? The tangential force becomes 0.47 lb-ft. Divide this into the thrust and what do you get? 0.73 thrust-torque ratio! See! What most forget is that to get torque, you have to multiply the tangential force by the radius to get torque. That's why the tip drag from the high CD values at high Mach can make the prop so inefficient. Root fairings? You bet! I have them on my prop, and I tell everyone who will listen that you need to streamline the prop root section, and even on a CS, find a way to form a rotating seal so the root section doesn't have the drop-off in lift as at the tip! Good thinking!!!!
gmcjetpilot
Well Known Member
Aerodynamics is not everything, practically speaking
I agree 100% that prop blade roots are blunt. The "2-by-4" shape of a fixed pitch prop blade root or baseball bat shape of a C/S prop blade root are aerodynamically like a barn door, terrible; however its done for practical structural and design reasons, aka to bolt to a crankshaft or attach to a hub that varies blade pitch angle.
All props have "twist distribution", which tailors the blade angle of attack along the span for the difference in speed from root to tip. Also airfoil shape, chord (width), thickness and tip shape (square, round, shear) are varied along the length to account for the +600 mph tip speed to root, only going about 200 mph. Most of the thrust of course is at about 2/3rds span. The roots are just beating the air to death.
Mach drag at tips is not an issue. Tip drag is not a factor at the speeds we work at, which is well below the super critical Mach 0.90. Sure there's drag, but that's the cost of doing business, making lift/thrust. Efficiency is a function of RPM and forward airspeed, HP and even air density. It's a challenge to design a prop blade, especially over a wide operating range of conditions.
It's impossible to make a perfect prop blade; it's impossible to make a perfect airplane wing for all conditions. However with wings we can add leading and trailing edge slats and flaps to change the effective size and shape of the wing (airfoil). Of course prop geometry is fixed, but it would be cool if we could vary prop dimensions and shapes in flight, besides just blade pitch angle. Aerodynamics and practicality run into each other again.
The idea of any prop is to get max thrust for HP input. Most props have efficiency percentages in the high 70's to low 80's. That means for 100 hp you are only getting 80% or 80 HP thrust out of it. You are throwing 20 HP away. So your fire breathing 200HP RV is only a 160HP may be 166 HP on a good day. It would be nice to get back more HP with higher prop efficiency, but they have been trying and like I said, success has been measure in a few percent.
In the prop design world, props really only vary by a handful of percentage points. On paper it does not look like a big deal. However a fraction of a percent is golden and not easy to achieve. 2% or 4% difference in efficiency is really a big deal, especially to fast and fairly high HP planes like the RV. Only the Hartzell's BA and Sensenich's blades have been tailored to RV's. God bless American Engineering. To only way to squeeze those few precentage points out is work to a specific airframe.
Hartzell gained 1.5% with their BA prop, which was tailored for the RV, over an already excellent performing prop. The HC-C2YK/F7666-4 was designed in the late 60's for Mooney's and Piper Comanches. Fast planes with similar HP so the match was good. The new BA prop is about 3.5 mph faster. The F7666 blade is no slouch and still quite a bit faster than a MT. However this does point out how hard it is to get more performance out a blade. In this case about 1.5% and required optimization for a specific airframe. The BA prop was tuned to the RV airframe, including the conditions we mostly operate in. To get almost 1.5% is amazing, part physics and part black magic. The magic is choosing the compromises to make.
My hat is off to Hartzell and making a RV specific BA prop that is getting into the +85% range of efficiency (max). It's no small accomplishment and does not make MT bad, only that Hartzell really sharpened their pencils and went after the RV market. Most other props (except Sensenich) are "generic" props not necessarily optimized for a RV airframe, HP, performance range and flight operations.
Material of blade is a small but important part of the blade design. MT's fiberglass laminated wood cores have pros and cons, but thin and high speed efficiency is not one of the pros. Thickness is a factor. You can't make wood/fiberglass blades as thin as a metal ones, yet. The high end carbon/carbon prop blades are thinner yet, but they also cost more and are still not as thin as aluminum blades, I believe. Plus you lose the smoothness of wood/glass props. Carbon/Carbon are super stiff. (Smooth is a relative and totally subjective term. A well balanced engine and Hartzell prop is smooth to me.)
Carbon/Carbon is what's called "Black Aluminum". It's super stiff, strong but not as light as you expect from typical composite construction. Of course the weak link is the blade retainer fitting, transitioning to metal. Also you still need leading edge erosion strips. Making it all smooth and thin is hard (expensive). Scrap rate can be costly and the cost is absorbed by the product cost. Composites are not a panacea for every structure (yet), especially when you put cost, maintenance and service support into the equation.
For most folks in my opinion the Hartzell is the best value, giving best performance, service and reliability. I mean the RV is the best homebuilt plane, right, and its made of metal, Nuff said.
I appreciate facts and figures as much of anyone but, What?elippse said:
I agree 100% that prop blade roots are blunt. The "2-by-4" shape of a fixed pitch prop blade root or baseball bat shape of a C/S prop blade root are aerodynamically like a barn door, terrible; however its done for practical structural and design reasons, aka to bolt to a crankshaft or attach to a hub that varies blade pitch angle.
-How do you propose you fair in or seal the root?
-How much "Gain" would you see or did you see?
-What prop did you do this to and do you have any pictures?
-How much "Gain" would you see or did you see?
-What prop did you do this to and do you have any pictures?
All props have "twist distribution", which tailors the blade angle of attack along the span for the difference in speed from root to tip. Also airfoil shape, chord (width), thickness and tip shape (square, round, shear) are varied along the length to account for the +600 mph tip speed to root, only going about 200 mph. Most of the thrust of course is at about 2/3rds span. The roots are just beating the air to death.
Mach drag at tips is not an issue. Tip drag is not a factor at the speeds we work at, which is well below the super critical Mach 0.90. Sure there's drag, but that's the cost of doing business, making lift/thrust. Efficiency is a function of RPM and forward airspeed, HP and even air density. It's a challenge to design a prop blade, especially over a wide operating range of conditions.
It's impossible to make a perfect prop blade; it's impossible to make a perfect airplane wing for all conditions. However with wings we can add leading and trailing edge slats and flaps to change the effective size and shape of the wing (airfoil). Of course prop geometry is fixed, but it would be cool if we could vary prop dimensions and shapes in flight, besides just blade pitch angle. Aerodynamics and practicality run into each other again.
The idea of any prop is to get max thrust for HP input. Most props have efficiency percentages in the high 70's to low 80's. That means for 100 hp you are only getting 80% or 80 HP thrust out of it. You are throwing 20 HP away. So your fire breathing 200HP RV is only a 160HP may be 166 HP on a good day. It would be nice to get back more HP with higher prop efficiency, but they have been trying and like I said, success has been measure in a few percent.
In the prop design world, props really only vary by a handful of percentage points. On paper it does not look like a big deal. However a fraction of a percent is golden and not easy to achieve. 2% or 4% difference in efficiency is really a big deal, especially to fast and fairly high HP planes like the RV. Only the Hartzell's BA and Sensenich's blades have been tailored to RV's. God bless American Engineering. To only way to squeeze those few precentage points out is work to a specific airframe.
Hartzell gained 1.5% with their BA prop, which was tailored for the RV, over an already excellent performing prop. The HC-C2YK/F7666-4 was designed in the late 60's for Mooney's and Piper Comanches. Fast planes with similar HP so the match was good. The new BA prop is about 3.5 mph faster. The F7666 blade is no slouch and still quite a bit faster than a MT. However this does point out how hard it is to get more performance out a blade. In this case about 1.5% and required optimization for a specific airframe. The BA prop was tuned to the RV airframe, including the conditions we mostly operate in. To get almost 1.5% is amazing, part physics and part black magic. The magic is choosing the compromises to make.
My hat is off to Hartzell and making a RV specific BA prop that is getting into the +85% range of efficiency (max). It's no small accomplishment and does not make MT bad, only that Hartzell really sharpened their pencils and went after the RV market. Most other props (except Sensenich) are "generic" props not necessarily optimized for a RV airframe, HP, performance range and flight operations.
Material of blade is a small but important part of the blade design. MT's fiberglass laminated wood cores have pros and cons, but thin and high speed efficiency is not one of the pros. Thickness is a factor. You can't make wood/fiberglass blades as thin as a metal ones, yet. The high end carbon/carbon prop blades are thinner yet, but they also cost more and are still not as thin as aluminum blades, I believe. Plus you lose the smoothness of wood/glass props. Carbon/Carbon are super stiff. (Smooth is a relative and totally subjective term. A well balanced engine and Hartzell prop is smooth to me.)
Carbon/Carbon is what's called "Black Aluminum". It's super stiff, strong but not as light as you expect from typical composite construction. Of course the weak link is the blade retainer fitting, transitioning to metal. Also you still need leading edge erosion strips. Making it all smooth and thin is hard (expensive). Scrap rate can be costly and the cost is absorbed by the product cost. Composites are not a panacea for every structure (yet), especially when you put cost, maintenance and service support into the equation.
For most folks in my opinion the Hartzell is the best value, giving best performance, service and reliability. I mean the RV is the best homebuilt plane, right, and its made of metal, Nuff said.
Last edited:
Maybe someone can measure a Hartzell at about 2/3rds blade span. My MT has an 8% thickness at 20 inches from the spinner on a 31 inch blade. Thicker or thinner than a Hartzell?
GMC may be right on the RV specific design of the Hartzell compared to MT. MTs have consistently shown relatively better performance at lower rpms than Hartzells. Of course with a lycoming, hp will fall off at these lower rpms, hurting cruise. Now with a turbo Sube and a reduction gear, I can pull that rpm way down and restore power by increasing manifold pressure. Maybe the MT will be happier doing this.
GMC may be right on the RV specific design of the Hartzell compared to MT. MTs have consistently shown relatively better performance at lower rpms than Hartzells. Of course with a lycoming, hp will fall off at these lower rpms, hurting cruise. Now with a turbo Sube and a reduction gear, I can pull that rpm way down and restore power by increasing manifold pressure. Maybe the MT will be happier doing this.
My fixed-pitch, three-blade prop has an efficiency of 82% in a climb at 2410rpm, 110mph IAS, at 1000' dalt, 1500 fpm, 1350 lb, 125 HP at sea-level at 2800 rpm, 77 sq. ft wing area, 8.05 AR, almost a strait-line approximation of an elliptical wing, Oswald efficiency factor of 0.82. Peter Garrison, given the same numbers, came up with 84%, but I think the 82% is more realistic. My cruise efficiency is at least 90%!!! The Phantom biplane, using the four-blade prop I designed for it for Reno 2006, won at 252 mph at the same rpm at which he qualified at 221 mph in 2003. That's an outrageous 48% improvement in efficiency! 'Don't believe it? Check the results for 2003-2007. They are available in the Fall editions of Sportsman Pilot for those years. www.sportsmanpilot.com. BTW; my prop roots do not "beat the air to death"; they are an integral part of the lift production of the blade. If not, I would not be able to predict the performance of a plane using my design to within 1 mph. Most of the thrust is not at 2/3 span; it is elliptically-distributed along the span from the widest chord out to the tip. Mach tip drag is one of the major issues! My props make very little noise; they throw away very little power at the tip. There is very little tip chord to generate the drag and noise. BOY! Old wive's tales die really hard!!!
What? A 4 blade prop beating 2 blade ones. How is that possible? The "experts" here say that just can't be. Cough...cough.
When I saw the Biplane speeds last year I couldn't believe it. Keep up the good work Paul. Hope to see you at Reno this year. Do you know Mike Dacey by chance? He is based in your area. I'm helping him out with EFI this year.
When I saw the Biplane speeds last year I couldn't believe it. Keep up the good work Paul. Hope to see you at Reno this year. Do you know Mike Dacey by chance? He is based in your area. I'm helping him out with EFI this year.
Kevin Horton
Well Known Member
I'm not sure I understand what you are saying here. I assume the prop for 2007 is not the same prop that was used in 2003. Are you sure there were no changes to the engine or its induction system that would have increased the power available at a given rpm? No changes to induction air inlet, etc?elippse said:
And were there no changes to the airframe to reduce drag between 2003 and 2007?
Even with no changes to the engine, the increase in speed would allow for more ram pressure recovery, so the manifold pressure for 2007 was probably higher than it was in 2003. Hence I really doubt that the speed increase was solely due to an increase in prop efficiency. I don't doubt that you make a great prop, but it is only part of the reason for the speed that any given aircraft achieves.
If you follow air racing Kevin and look at the Biplane speeds historically, Paul's props have raised speeds more than any other single thing in this class. Even more than the radical design "Sorceress" back in the mid '70s. Paul's ideas are revolutionary.
Can't have increased ram pressure in the induction system without getting there first somehow in the speed department. MP rise due to even 20 more mph would be relatively insignificant as hp required varies as the cube of the speed.
Can't have increased ram pressure in the induction system without getting there first somehow in the speed department. MP rise due to even 20 more mph would be relatively insignificant as hp required varies as the cube of the speed.
Well, Kevin! There was a small power increase from in the engine from 2005 to 2006, but the major speed increas was from the higher rpm the four-blade prop allowed. The original three-blade I designed for Phantom for 2004, where he qualified at 241 mph, was with the same engine, drag, whatever as he had with the two-blade in 2003 when he qualified at 221 mph, but it did it at 250 rpm less!!! That's a 40% improvement!!! The engine builder told people that the engine was different, but when I asked Tom, he said that was not true. Apparently they were telling people that in order to take credit for the performance increase. Are you really trying to say I'm not telling the whole story? If you have any doubts about my veracity, I'd suggest you get in touch with Tom Aberle himself to verify what I write. [email protected] Have you taken the time to calculate the increase in dynamic pressure in going from 241 to 252 and the power increase you would get? or from 221 mph to 252 mph? Since you bring that up as a salient point, I think you should do that and present the results for all of us on this forum to see, and also include in your calculations the percentage of speed increase you will see from this effect, keeping in mind the cubic relation between power increase and speed increase, i.e. it takes 3% more power to get 1% more speed. The density altitude at Reno is 7000' typically.We are all awaiting your analysis! BTW, Tom would tell you that the prop was the ONLY reason for the increase from 2003 to 2004.
Kevin Horton
Well Known Member
Hey, I don't want to get into a pissing contest here. I was just a bit baffled that a Reno racer would go several years without making any attempt to reduce the drag of his aircraft, or get more power from his engine. It seems that perhaps the engine power did increase between 2003 and 2006.elippse said:
I agree with your calculation that if there were no changes that reduced drag, approximately 48% more installed power (i.e. engine power times prop efficiency) should be required to go from 221 mph to 252 mph (assuming the same density altitude for both years).
elippse said:
I only mentioned the increase in ram air pressure recovery as one effect that was likely not the same between the two cases. I never claimed it would be responsible for a significant proportion of the speed increase. At a density altitude of 7000 ft, 221 mph TAS = 199.5 mph CAS. The ram air pressure at 199.5 mph CAS is 1.95" HG. At 252 mph TAS (227.6 mph CAS) we have a ram air pressure of 2.55" HG. If we assume that extreme care has been taken to recover as much of this ram air pressure as possible, perhaps 80% of that pressure would be seen as an increase in MP. I don't know what engine is used, nor would I have access to any dyno charts that would be valid at the rpm you would be running. As a point of reference, on a Lycoming IO-360-A series engine, at 2700 rpm at 5100 ft pressure altitude and 21.5 deg C (which gives a density altitude of 7000 ft), an extra 0.48" HG (80% of 2.55-1.95) would give a power increase of about 2%, which would be worth about an extra 1.5 mph. So this effect might explain perhaps 5% of the speed increase.
Anyone who has his props on the top Reno racers obviously knows how to make a prop that is efficient at high speed and high rpm. I'm not questioning your ability to design a very high performance prop.
BTW - how do you determine the efficiency of your props? By analysis, or flight test? 90% prop efficiency is a very, very impressive number. Why are your props so much better than those from Sensenich, etc? Is it because you can do a point design, while they need to have a prop that has decent efficiency over a wider range of conditions? Or, are they using older design concepts, and you are using newer ideas? Would it be possible to design a fixed pitch prop that had better performance than the Sensenich props over the range of conditions used by RVs, while still having acceptable life, and no issues with errosion in rain?
Last edited:
Paul, thanks for your response. An interesting discussion here!
Next question - transonic jets gain some considerable efficiency by winglets - why don't we see them on prop tips? I'm assuming that tip vortices are a fundamental loss mechanism to props as to wings. Is it for structural reasons or is it that the added section drag at the tip doesn't yield any net benefits?
A
Next question - transonic jets gain some considerable efficiency by winglets - why don't we see them on prop tips? I'm assuming that tip vortices are a fundamental loss mechanism to props as to wings. Is it for structural reasons or is it that the added section drag at the tip doesn't yield any net benefits?
A
osxuser
Well Known Member
The Q-tip hartzells provide better efficiency over the standard blade of the same length, that is the contention. Either that, or they say that they provide the same or slightly better performance with better ground clearance. Whichever way you want to think about it. Doesn't really matter does it? The are quieter, and look really neat, thats all I know.
Bob Brown
Well Known Member
another speed test needed
Not to get back on topic, but I'll offer my MTV15B (2 blade aluminum blended airfoil prop) to speed test to anyone who already has done speed testing on a Hartzell BA prop. The 3 or 4 airplanes here that are running the (MT) MTV15B prop seem to be running faster than the Hartzell BA's. One guy has the MTV15B on an 8 and swears it is faster than the Hartzell BA prop it replaced. Randy Lervold, are you interested in putting another data point on the chart?
Not to get back on topic, but I'll offer my MTV15B (2 blade aluminum blended airfoil prop) to speed test to anyone who already has done speed testing on a Hartzell BA prop. The 3 or 4 airplanes here that are running the (MT) MTV15B prop seem to be running faster than the Hartzell BA's. One guy has the MTV15B on an 8 and swears it is faster than the Hartzell BA prop it replaced. Randy Lervold, are you interested in putting another data point on the chart?
Well, Andy, I don't know about other prop designers, but I design my props for M0.85 at the tip, so I really can't extend them. The tip shape is a point, since that is how an elliptical section ends, and has minimum radial flow, minimum tip vortex, and no extra unwanted tip induced loss, all as explained by Prandtl about wing shape. This shape is already about the best you can get, although I recently read where someone has come up with something better than elliptical, but haven't yet seen it. Any chord at the tip will not produce lift but only drag. As I showed before, the drag at the tip, which is considerable at M0.85 and is proportional to chord, is multiplied by the radius to give torque loading to the engine.
RVjim
Well Known Member
rv6ejguy said:This is what we need, an actual test, not conjecture. A back to back test on the same airframe/ engine combo. Good of you to offer this up.
I have a RV-6A with a Lyc. O-360 180 hp engine.
I have a Hartzell prop with the 7666-4 blades, a MTV-15-B/183-402 2 blade aluminum propeller, a MTV-12-B/183-59b 3 blade propeller and access to a Hartzell 72" diameter blended airfoil prop.
I have started collecting data. Mostly at 8,000 foot DENSITY altitude. Although 4,000, 12,000 and 16,000 foot DENSITY altitudes have been used.
I am using full throttle and varing the RPM in 100 RPM increments from 2000 to 2700 RPM. It takes over an hour at each altitude to obtain this data set.
So far I have concentrated on the techniques required to get repeatable data. Of the eight data points at one altitude, I have been able to repeat six of the eight data points exactly, and the other two data points within one knot. I expect to be able to do better than this.
I am doing this over the Pacific Ocean from 5 miles off of Oxnard CA to 45 miles west of Oxnard. The 4,000' density altitude testing is NOT my favorite test altitude (about 3,000 MSL). I like the 12,000' & 16,000 density altitude a lot better.
I have recently obtained test data at 65% power at 8,000' density altitude with the RPM varied from 2100 to 2400 RPM. The slower the RPM the faster the RV-6A.
(Does the propeller actually have less drag at the lower RPM?)
Before I start changing propellers, what testing would be of interest to you?
Jim Ayers
RVjim
Well Known Member
With regards to the 65% power testing and the possibility of spark advance affecting the performance, I have dual mags. No spark advance that I know of.
Basic aerodynamics can be used in understanding what the propeller is doing.
Turn the propeller slower, less drag. Turn the propeller faster, more drag.
My perception of the propeller has all of the engine horsepower being used to match the drag of the propeller (horsepower required to turn the propeller). The horsepower produced by the engine creates no thrust at the propeller flange. The propeller creates the thrust.
The relationship of the drag of the propeller to the thrust of the propeller could be referred to as the "propeller efficiency".
Jim Ayers
Basic aerodynamics can be used in understanding what the propeller is doing.
Turn the propeller slower, less drag. Turn the propeller faster, more drag.
My perception of the propeller has all of the engine horsepower being used to match the drag of the propeller (horsepower required to turn the propeller). The horsepower produced by the engine creates no thrust at the propeller flange. The propeller creates the thrust.
The relationship of the drag of the propeller to the thrust of the propeller could be referred to as the "propeller efficiency".
Jim Ayers
osxuser
Well Known Member
But engine HP output is also a function of engine RPM. For instance, with the new 3-blade on our Cardinal. I can fly along at 2300-2500 rpm with no change in TAS, but below that it starts to drop off for any given MP. I'm guessing in that range the reduction in turning and blade drag makes up for the loss in HP. But past that it doesn't.
Kevin Horton
Well Known Member
Jim,RVjim said:
I'm looking forward to seeing the results. It will take a lot of flying to get a good data set on each prop. The first question in my mind is "what is the purpose of the testing?" The answer will drive the test requirements. For example, do we care about climb performance, or only cruise performance? I think most CS prop RV guys cruise at full throttle, and control power with rpm. But, do we want to also gather partial throttle data to cover the guys who want to do that?
Personally, I am much more interested in cruise performance than in climb performance. Full throttle cruise performance is much more interesting to me than partial throttle cruise performance (assuming that the engine/prop limitations allow low enough rpm to get 65% power at 8000 ft.
I am interested in the following data for each condition for the full throttle cruise points:
Pressure altitude
Density altitude
OAT
IAS
CAS (assuming that you know the relationship between IAS and CAS)
TAS (either calculated from CAS, or from GPS ground speed, using a solid test method).
rpm
MP
fuel flow
aircraft weight
test point comments (e.g. comments on air stability, quality of the point, etc).
I am glad that you intend to repeat each test on other days until you have repeatable results. This adds significantly to the time required, but makes a huge difference in the credibilty of the results. Note: expect some variation in speed at the same DA and rpm as the OAT changes. Engine power is not constant with DA, unfortunately, at least if we believe the Lycoming power chart.
I will assume that the Lycoming power chart is correct, and that you have accurately followed it to set 65% power. If so, your test results suggest that the prop efficiency increases as the rpm decreases. This is not surprising. For any given power and altitude, there will be an rpm where the prop efficiency is greatest, and hence were the speed will be highest.RVjim said:
RVjim said:
This is great Jim. I think many are getting carried away with what you need to do here while you are paying for fuel. Let's keep it simple here.
Do all the tests at WOT with both props, just vary the rpm with pitch and use a target EGT. Record IAS- forget TAS, CAS for the time being as you will repeat the same test with the Hartzell on the same airframe right? If you can, record OAT and altitude and do all the runs at the same DA. Maybe at 6000, 8000 and 10,000 are good enough to settle the argument as these are typical mission altitudes for RVs. We don't care much about climb here as all C/S RVs are more than adequate in this area.
Eagerly awaiting your data. Anyone who can do similar tests with a composite MT out there?
OH! And while we are looking at the small effects which can have an effect on engine power with a change in speed, don't forget to take into account the stagnation temperature rise in the induction system which will give about a 1% reduction in inlet density for each 5.2F rise. Tom's biplane, in going from 221 to 252, would have had an additional 2.6F rise, which would have dropped his power 1/2%. So many things to consider, but sometimes you can get lost in the minutiae while overlooking the big picture. He still had to go faster in order to get more induction pressure; the pressure didn't come first and then the speed followed it.
"Turn the propeller slower, less drag. Turn the propeller faster, more drag."
Not necessarily! There are two types of drag, of course, parasite drag and induced "drag". Induced "drag" is a consequence of producing lift, and should be the same for a given planform, thrust, and angle distribution. But parasite drag has a component that is affected by the Reynolds number. As Re decreases, lower speed and same chord, the parasite drag CD increases. Depending on the type of airfoil used on the prop, laminar or turbulent, there is a crossover between these two that occurs at an Re of about 600,000, with the laminar being better above this value and the turbulent better below it. Since our props are somewhat narrow, the Re can often be quite low where CD is greater. Another thing is twist distribution. One of the CS props used by the Reno Sport class that I evaluated actually peaked in efficiency at the rpm and power for about 250 mph, and showed a steady decrease in efficiency above that speed. Many prop makers compromise twist to get better low speed thrust, which then proves to be a detriment at cruise. I've often heard people say about their props that they increased the rpm and didn't go any faster. Sometimes that's a case of not recognizing that the small HP increase associated with higher rpm was not sufficient to bring about an increase that you couldn't see without careful testing. How many times have you heard someone say that they still had about an inch of throttle remaining, not realizing that on a throttle valve, that last inch only moved the disc through a very small angle, with almost no power change! Other times it is because they are operating at the point where the efficiency is falling off rapidly, since the twist is wrong for their speed and rpm, and part of the prop is making reverse thrust!
Not necessarily! There are two types of drag, of course, parasite drag and induced "drag". Induced "drag" is a consequence of producing lift, and should be the same for a given planform, thrust, and angle distribution. But parasite drag has a component that is affected by the Reynolds number. As Re decreases, lower speed and same chord, the parasite drag CD increases. Depending on the type of airfoil used on the prop, laminar or turbulent, there is a crossover between these two that occurs at an Re of about 600,000, with the laminar being better above this value and the turbulent better below it. Since our props are somewhat narrow, the Re can often be quite low where CD is greater. Another thing is twist distribution. One of the CS props used by the Reno Sport class that I evaluated actually peaked in efficiency at the rpm and power for about 250 mph, and showed a steady decrease in efficiency above that speed. Many prop makers compromise twist to get better low speed thrust, which then proves to be a detriment at cruise. I've often heard people say about their props that they increased the rpm and didn't go any faster. Sometimes that's a case of not recognizing that the small HP increase associated with higher rpm was not sufficient to bring about an increase that you couldn't see without careful testing. How many times have you heard someone say that they still had about an inch of throttle remaining, not realizing that on a throttle valve, that last inch only moved the disc through a very small angle, with almost no power change! Other times it is because they are operating at the point where the efficiency is falling off rapidly, since the twist is wrong for their speed and rpm, and part of the prop is making reverse thrust!
gmcjetpilot
Well Known Member
For practical and useful purposes, good enough
For pilots that are flying and especially those with constant speed props if you can cruise at 2450 rpm or 2,600 rpm you will be more efficient at slower RPM. Now efficiency and speed are separate. Less RPM, you will have less thrust and thus speed. Of course your engine does make the same HP at different RPM, unless you can increase the Torque with say more manifold pressure. Therefore lower RPM and higher MP is more efficient than higher RPM and lower MP. Yes you can run higher MP about one inch "over square".
There is an interrelation of engine efficiency, airframe efficiency, prop efficiency and atmosphere. The prop does not work isolated from the engine, airframe or atmosphere. My comment is generically correct and useful to pilots.
Prop characteristics are a function of:
propeller diameter - d
propeller rotation speed - n
torque - Q
thrust - T
fluid density - ρ
fluid viscosity - ν
fluid bulk elasticity modulus - K
flight velocity - V
efficiency - η prop
The key term J, "propeller advance ratio":
J = "propeller advance ratio" =
;
Note the below plot (generic prop/plane) says it all.
NOTE:
V (flt velocity) goes up J goes up
n (prop revs) go down J goes up
d (dia) J goes up
It says it all you want a higher advance ratio to a certain point, depending on the pitch angle. This is also for one unspecified tip speed. It gets better. You can calculate our "J" is 0.95 to 1.35 cruise, 0.42 to 0.7 in climb.
Efficiency can also be expressed as:
Where Cp and Ct are coefficient of power and thrust, the more thrust per power input the more efficient. The Ct and Cp terms are complicated and will not get into it, but they look like this:
You can see air-density, engine power, thrust and J (a function of airframe drag) also figure into these factors. P is power such as HP = [ Q (torque) * n (rpm) ] / 5252.
To put it simply as I said, try to run your RPM as low as practical or possible. Of course takeoff, climb or desired airspeed demands more RPM. With a constant speed prop we have more options with choosing RPM; with a fixed pitch prop its academic.
I have Hartzell data that gives me efficiency for given parameters and can estimate efficiency. You can get real technical but in general lowering RPM increases efficiency.
However because our engines make more power with higher RPM in general (e.g., about 4-6 HP per 100 rpm), the increased RPM means our speed goes up, even though efficiency (aka miles per gallon) goes down, thrust goes up. In other words the increase in power dominates over loss in prop efficiency.
All the parameters above are moving targets and interrelated; changing one changes almost everything else. It's complicated and any one can take a simple statement and poke holes in it. However MOST pilots are not calculating theoretical prop efficiency; they just want to know a rule of thumb. When choosing RPM, smoothness comes into play for me, at least with my Hartzell/Lycoming. There are "nodes" every 250-300 rpms where the prop feels smoother, so I pick my RPM just to get that smoother feel sometimes.
Well if you had Hartzell data like I do, you would agree. A better way to put it: "Turn the propeller slower, more efficiency. Turn the propeller faster, less efficiency."elippse said:
For pilots that are flying and especially those with constant speed props if you can cruise at 2450 rpm or 2,600 rpm you will be more efficient at slower RPM. Now efficiency and speed are separate. Less RPM, you will have less thrust and thus speed. Of course your engine does make the same HP at different RPM, unless you can increase the Torque with say more manifold pressure. Therefore lower RPM and higher MP is more efficient than higher RPM and lower MP. Yes you can run higher MP about one inch "over square".
There is an interrelation of engine efficiency, airframe efficiency, prop efficiency and atmosphere. The prop does not work isolated from the engine, airframe or atmosphere. My comment is generically correct and useful to pilots.
Prop characteristics are a function of:
propeller diameter - d
propeller rotation speed - n
torque - Q
thrust - T
fluid density - ρ
fluid viscosity - ν
fluid bulk elasticity modulus - K
flight velocity - V
efficiency - η prop
The key term J, "propeller advance ratio":
J = "propeller advance ratio" =
Note the below plot (generic prop/plane) says it all.
NOTE:
V (flt velocity) goes up J goes up
n (prop revs) go down J goes up
d (dia) J goes up
It says it all you want a higher advance ratio to a certain point, depending on the pitch angle. This is also for one unspecified tip speed. It gets better. You can calculate our "J" is 0.95 to 1.35 cruise, 0.42 to 0.7 in climb.
Efficiency can also be expressed as:
Where Cp and Ct are coefficient of power and thrust, the more thrust per power input the more efficient. The Ct and Cp terms are complicated and will not get into it, but they look like this:
You can see air-density, engine power, thrust and J (a function of airframe drag) also figure into these factors. P is power such as HP = [ Q (torque) * n (rpm) ] / 5252.
To put it simply as I said, try to run your RPM as low as practical or possible. Of course takeoff, climb or desired airspeed demands more RPM. With a constant speed prop we have more options with choosing RPM; with a fixed pitch prop its academic.
I have Hartzell data that gives me efficiency for given parameters and can estimate efficiency. You can get real technical but in general lowering RPM increases efficiency.
However because our engines make more power with higher RPM in general (e.g., about 4-6 HP per 100 rpm), the increased RPM means our speed goes up, even though efficiency (aka miles per gallon) goes down, thrust goes up. In other words the increase in power dominates over loss in prop efficiency.
All the parameters above are moving targets and interrelated; changing one changes almost everything else. It's complicated and any one can take a simple statement and poke holes in it. However MOST pilots are not calculating theoretical prop efficiency; they just want to know a rule of thumb. When choosing RPM, smoothness comes into play for me, at least with my Hartzell/Lycoming. There are "nodes" every 250-300 rpms where the prop feels smoother, so I pick my RPM just to get that smoother feel sometimes.
Last edited:
