[whifof100ll]

props, IFR, and pitch stability

Maybe this should be on a different thread but I have to ask, why does a CS prop make IFR flight more stable?

Good question. Two reasons.

The first is that up/down drafts cause fluctuations in RPM. Since power is a function of MP and RPM, you will get fluctuations in power with FP. If you get a disturbance that causes in increase in RPM, the plane will produce more power and tend to speed up or climb. A CS prop will regulate the disturbance out and maintain a more constant power.

Reason 2 has more to do with weight than CS vs. FP, but FP props are generally lighter, especially comparing a wood or composite FP prop to a metal CS. A more forward CG is more stable in pitch.
I just completed my IFR recurrency in my RV with a light prop, and it was not too bad, but hand flying it takes more attention than my buddies CS RV-7 that I also fly. Way more challenging than my Cardinal. IFR flight in my RV makes me love Tru Trak. Plus/Minus 100 feet in the soup takes attention without the autopilot.

Landing
Unless loaded far aft, my plane is easy to land and can land really slow. An RV loaded near the aft CG limit can be a challenge to land well, so a light prop and a lot of bags or heavy back seater can cause some interesting landings. During AFT CG tests, I pogoed my first few big time! I learned to cope with this from my buddy who has an RV-4 with a wood prop. He just carries about five exrta knots when loaded near the aft limit and wheel lands, flying it onto the runway. This works fine at aft CG.

Agility
The pitch sensitivity due to CG change is also a factor in handling. Some prefer a more forward CG. Some prefer the lighter less stable but more aglile feel a light prop offers. A Hartzell equipped RV still handles great and is a real hoot to fly.

Again, I strongly encourage those with a choice to make to try both before you buy if at all possible. Many will choose CS, many will not, but all will be correct in their choice because they will have bought what they want rather than what someone told them they needed.

 

[N941WR]

Dale,

I have to disagree with your reason 1, up/down drafts may cause fluctuations in RPM but not power. Just like when coasting downhill in your car, you may accelerate even with your foot off the gas pedal doesn't mean you are putting out more power. Back when I was taking instrument training in a Archer, we just set the power and didn't worry about it.

As for reason 2, I don't understand. The airplane may be a bit more stable but that also has to do with passenger and baggage compartment loading. As long as you are w/in CG and W&B this should be the same between similar airplanes.

Agility has to do with mass, simple as that. If you have less mass then it is easier to accelerate that mass in a different direction. It is also best if that mass is in the center of the airplane. Therefore, a heavy prop will adversely impact roll, yaw, and pitch. It is kind of like a race car with heavy wheels and tires. They accelerate slower, turn in slower, and stop slower. All bad stuff. ?Agility? is a subject measure and means different things to different people. A very light plane may seem twitchy to some while a heavy version of the same plane may seem stable.

 

[Sid Lambert]

I agree that a CS prop makes your speed much more stable in rough air. When we fly in tight (tight for our standards) the CS guys are always complaining about us fixed pitch guys changing speeds even when we don't move the throttle. Also, minor alt changes (200') effect speed much more on a fixed pitch prop than CS.

I have no idea how that correlates with IFR as I'm a clear and a million, winds at 3 knots kinda guy.

 

[Bryan Wood]

Trust Your Own Gut

how much speed do you loose. surely the take off distance and climb is not as good with a fixed prop, as if the rv family has a problem with that. i guess what i am looking for is input from you guys that have been through this already.

You should find somebody in your area with a constant speed prop on an 8 and go for a ride. You will know right away what is right for you after a couple times around the pattern. Have the 1st take off be full throttle, 2,700 rpm, and then on downwind set up the prop for 2,300 rpm and just leave it that way during the landing and taxi back. With this setting for the next takeoff you will get a full throttle and 2,300 rpm departure similar to what the fixed pitch prop will give you. Feeling, seeing, hearing, and just overall experiencing the difference will give you the ability to make an infomed decision to the difference. The point of this is not to push the constant speed, but to give you the ability to see the difference in the same airframe and then you can choose what is right for you based on what you experience. If it is a budget thing there is nothing to apologize for flying with a fixed pitch propeller. As you can see from the previous responses they are the choice of people who can have anything they choose.

But on the other hand, to argue that having the ability to alter an airfoil to fit the current flight regime isn't an advantage, well frankly they are doing you a dis-service. You simply need to actually see if this advantage is worth the cost, and extra weight.

Good luck, see you in the nose wheel, tail wheel debate.

 

[Barry]

Stability In IFR Flight

RVs are airplanes that quickly accelerate when the nose is pointing down.
In the case of a decent in IMC through clouds the airspeed can quickly build up, this usually follows by tending to over control with a "chase the needles" syndrome quickly building up. Following good advice I once received from Alex De Dominicis it helps when one has a RV fitted with a CS prop to pull the power back to say 18 inches of MP. With the engine MP set to 18 inches MP it is much easier to fly a stabilize 500 ft minute decent whithout ending up chasing the airspeed. With a fixed pitch prop you would not have this advantage.
I am not a professional pilot however I am sure those that fly F16s and Jumbo Jets for a living will have no difficulty flying a stabilized 500 ft per minute decent with the pedal to the metal whether or not they have a CS prop!!

Just my 2 cents worth.

Barry RV6A

 

[David-aviator]

I thought this thread would end a long time ago but it seems to have a life of its own with a new perspective every day.

I just came off 4+ years behind a CS prop and it is the cat's meow - as long as it works. Take off performance is a rush some days when there's a bit of head wind and the temps are moderate, no denying that. But I came near putting one in a field one day when the thing failed in the fine pitch mode. It doesn't matter what engine you have, if it fails in the fine pitch mode, you don't have much thrust while trying to stay under the engine/prop rpm read line.

When I switched engines, I decided to accept the down side of FP in favor of getting rid of a failure mode. In fact I got rid of several failure modes going to the old technology - like a PSRU, an ECU, liquid cooling system, a manditory alternator, and the CS prop.

That's my perspective for the day. I like the Catto for its simplicity and no sweat operation, to each his own. I been forced down one to many times and getting very conservative or something.

 

[JHines]

I thought this thread would end a long time ago but it seems to have a life of its own with a new perspective every day.

I just came off 4+ years behind a CS prop and it is the cat's meow - as long as it works. Take off performance is a rush some days when there's a bit of head wind and the temps are moderate, no denying that. But I came near putting one in a field one day when the thing failed in the fine pitch mode. It doesn't matter what engine you have, if it fails in the fine pitch mode, you don't have much thrust while trying to stay under the engine/prop rpm read line.

<SNIP>

I'll second that. The first time I ever flew behind a C/S prop, in an old Arrow, I had a runaway prop (it had just come out of an overhaul, BTW). Fortunately it happened near the pattern, but to stay under the redline there was no way I had enough power available for a go-around. Oh and it goverened just fine on the ground during the runup and after landing.

 

[burgundyja]

8a catto or hartzel c/s

my 2 main concerns are weight and acro. should i go with the catto for the weight and money or a used c/s hartzel? i dont have the budget for new c/s. is there a large gain for acro in the c/s prop?

 

[Finley Atherton]

But I came near putting one in a field one day when the thing failed in the fine pitch mode. It doesn't matter what engine you have, if it fails in the fine pitch mode, you don't have much thrust while trying to stay under the engine/prop rpm read line.

I can see the point you are making. However I would have thought that if the low pitch stops are set correctly for max static rpm on the ground, then you would still be able to use considerable throttle without exceeding red line rpm in flight especially at slower airspeeds even if it fails in full fine.

Fin
9A

Edit: The low pitch stops on my new Hartzell as delivered from Vans were set a long way too fine. I can believe that had I not adjusted them, then little throttle would have been available if I had lost oil pressure to the prop.

 

[Rick6a]

Today, the weather finally cooperated so I seized the moment and took my Sensenich FP equipped RV up for a bit of airwork. This thread has morphed into a sort of FP versus CS dialog and some of the bull it has generated was still fresh in my mind. Upon takeoff on runway 27, I made a right hand departure and headed north. A few miles north of the airport I did a 180 and headed back in. Crossing the field WOT at pattern altitude the run generated a GPS ground speed of 178 MPH. The number represents a typical RV cruise speed. That's important. After crossing directly over the runway at pattern altitude, I reduced the power and made a left downwind for 27. At no time while in the traffic pattern did I range farther than 1.5 miles from the center of the airport . This is a much tighter pattern than many of the spam can drivers around here use I can tell ya. Guess what? The RV slowed down enough to allow the first few degrees of flap deployment when the airspeed indicator flirted with 100 MPH at the corner of downwind and base. As anybody who flys RV's knows, the airspeed can drop off dramatically once the flaps are even slightly deployed. Soon thereafter, final approach proved as normal as normal can be and 30 feet or so above the numbers, I shoved the throttle forward and climbed out to repeat the exercise once again. The second run WOT at pattern altitude proved a bit faster and produced a 184 MPH groundspeed directly over the runway. This time I ended the exercise with a completely uneventful squeaker of a full stop landing.

As I taxied back to the hangar at the end of the two runs, I just had to shake my head at those naysayers who insist on spreading the false, misleading, inaccurate poppycock that when piloting a FP equipped RV, the pilot (as opposed to his CS brethern) must start slowing down some miles from the airport. Those guys probably had trouble with proseal and canopy cutting too.

 

[Finley Atherton]

Its true my Catto requires closer attention to speed management in the pattern. On the other hand, glide ratio is much better than with a CS prop. So, if glide ratio is included in the performance equation, it is not at all clear that CS has better performance.

Steve,
I agree that a FP prop would give a better glide ratio. However, I would guess that in the majority of engine failure situations, the engine would be windmilling and producing oil pressure. In this case, a C/S prop can most likely be put in full coarse pitch and that will greatly increase the glide ratio. It would be interesting to compare glide ratios of FP V C/S with the C/S in full coarse. As a point of reference, my 0-320 9A at 9,000 ft DA has a sink rate of 857 f/min at 80 kts IAS with the engine dead (mixture at idle cutoff) and the prop windmilling at full coarse pitch.

Fin
9A

 

[whifof100ll]

Dale,

I have to disagree with your reason 1, up/down drafts may cause fluctuations in RPM but not power. Just like when coasting downhill in your car, you may accelerate even with your foot off the gas pedal doesn't mean you are putting out more power. Back when I was taking instrument training in a Archer, we just set the power and didn't worry about it.

As for reason 2, I don't understand. The airplane may be a bit more stable but that also has to do with passenger and baggage compartment loading. As long as you are w/in CG and W&B this should be the same between similar airplanes.
of the same plane may seem stable.

An FP Warrior is more stable than an RV, so it is not as noticable, reason 1 does apply.

To disprove your car analagy, when I point my RV downhill without reducing the throttle, the RPM's pick up. The MP stays the same. The fuel burn goes up. This is easy to see with my AFS. Fuel burn is an indication of power, so there goes your car dowhill argument. When you go down hill in your car, you slightly decrease throttle (manifold pressure) to maintain speed. If you did not, the speed would pick up and the power would pick up. Look at the power charts for your lycoming or most internal combustion engines and you will see that unless you are way up on the power curve, power output increases with RPM for any given MP. When you point a CS RV downhill, the speed goes up, but as long as the MP does not appreciably change, the RPM, power, and fuel burn will be the same.


Reason 2, Let me reword this one a bit. Airplanes with down flying tails have less dynamic stabiltity as CG moves aft. Dynamic stability is defined as the ability to restore pitch attitude after a pitch upset. As you go past the aft CG limit, you can pull the nose up, and as the speed decreases the nose will rise instead of fall (pitch instability). Neutral dynamic stability means that if you pull the nose up, it will stay there as speed falls of. Draw a free body diagram (showing the forces at work) of your RV in flight and you can figure out why.

As a plane gets near neutral dynamic stabilty, it is more of a handfull to land as relaxing back pressure does not have the same affect has with more dynamic stability.

 

[Steve Brown]

IMO: FP verses CS negligeable factor in fuel efficiency

......
I don't want to start an argument, just some of you who have flow both please enlighten me on fuel burn at same speed and LOP with each?
jeff h

I have run LOP in a couple of different Mooneys, but they are so different than and RV I don't think its a good comparison.

The M20E (injected) that I had in the 90s seemed to burn about 0.5-1.0 GPH less than an M20C (carburetor) I rented occasionally at roughly the same airspeed (or more). Not a very scientific comparison, but I'm convinced injection is the way to go.

Obviously having CS prop gives RPM options and these engines do burn less fuel at lower RPMs, even for the same power setting. On the other hand, they weigh more, which decreases efficiency because you have to drag them up to altitude. Depending on specifics, it may be a wash, or go either way.

I run my O320 / FP LOP all the time. It can be quite economical. Check this link to a non stop tip I did last year:
http://www.vansairforce.com/community/showthread.php?t=31715

I don't know if I'll do it again unless I've got a stiff tail wind, because staying on top of the fuel management was just too stressful, but the point is that it can be done.

I doubt that having CS prop would make that trip less stressful, but fuel injection might tip the balance.

 

[penguin]

Obviously having CS prop gives RPM options and these engines do burn less fuel at lower RPMs, even for the same power setting. On the other hand, they weigh more, which decreases efficiency because you have to drag them up to altitude. Depending on specifics, it may be a wash, or go either way.

Everyone's entitled to an opinion, but I'm not sure this is accurate. With a C/S prop you can run at an rpm that will burn less fuel for a given power setting/speed. 2200/24" burns less fuel than 2300/23, and both will likely burn less fuel than the size engine with a FP prop. If these engines are O-360s they will again burn less fuel (up to 1.5 gph less) than an FP O-320 going the same speed (I realize that the 360s will be producing less % power). Injecting the 360s will reduce the fuel burn if the pilots are prepared to work at it (run LOP, etc). Using a 200hp IO-360 will further reduce the fuel burn (by up to a further 1 gph) at the same speed (again less % power than the O-360s). This is fuel consumption at the pump - all start off with full tanks, all climb together to cruise alt (8000' for sake or arguement), although C/S airplanes will get there much quicker, and all fly at same speed. An FP 150hp O-320 will burn around 9 gph, chock to chock flying WOT when cruising. The (I)O-360s will use less over (say) a 2 hr flight. I believe the C/S props used sensibly - max MP and control speed on rpm - are responsible for most of the fuel savings.

If the larger engined airplanes were to fly at the same power settings (% power) I have no idea what the result would be.

Pete

 

[n5lp]

The theoretical reasons that a constant speed prop airplane should be more efficient are certainly valid but advantages like that are often overpowered by operation techniques.

Way back before the advent of 200 HP IO-360s on RVs, I took a trip with three other airplanes. The group had a good cross-section of the recommended powerplant propeller combinations of the time and all the airplanes were RV-6s or RV-6As.

Fuel burn results (from my website):

The two tankfuls where everyone flew together gave a little opportunity to compare the fuel efficiency of the four RVs. The fuel burn order was consistent, but three of the airplanes were very close on fuel usage. The order was, from least burned to most:

180 HP O-360, fixed pitch Sensenich

160 HP O-320, constant speed

160 HP O-320, wood (lightest airplane)

180 HP O-360, constant speed (heaviest airplane by quite a bit)

My airplane (O-360 F/P, carb, mags) burned the least fuel. That is just because of leaning technique. I lean according to the Lycoming guidelines which results in one cylinder lean of peak, one quite rich of peak and a couple of cylinders near peak. The whole business is a theoretical mess.

For the entire trip, covering large parts of the western US, my fuel burn was 7.4 GPH.

 

[Steve Brown]

I don't think so

......With a C/S prop you can run at an rpm that will burn less fuel for a given power setting/speed. 2200/24" burns less fuel than 2300/23, and both will likely burn less fuel than the size engine with a FP prop.

What I wrote is that this is probably true, but (expanding) depends on the specifics in terms of FP prop pitch and aerodynamic / propulsive efficiency of each prop.

If these engines are O-360s they will again burn less fuel (up to 1.5 gph less) than an FP O-320 going the same speed (I realize that the 360s will be producing less % power).
Injecting the 360s will reduce the fuel burn if the pilots are prepared to work at it (run LOP, etc). Using a 200hp IO-360 will further reduce the fuel burn (by up to a further 1 gph) at the same speed (again less % power than the O-360s).

Why would a larger engine burn less fuel at same absolute power setting?

This does not make sense to me. First assume either both FP or both CS, and also assume 360s and 320s are leaned the same way. In that case they should be roughly equivalent, except that the larger engine would be expected to have more internal friction resulting in slightly less efficiency at low power settings at the same RPM. The injected engine burns less because because of better mixture control/distribution, not because it is running at lower percentage of its maximum HP.
If you reduce RPM on the larger engine to get the equivalent power, you might be able to offset the increased friction of its larger size. The slower turning prop is probably a bigger contributor due to decreased drag. Could the balance be tipped the other way? I don't know, but I'll guess the difference is relatively small either way between 320 & 360.
Anyway, fuel efficiency verses engine size is an interesting topic, but I think a different topic than FP verses CS.

This is fuel consumption at the pump - all start off with full tanks, all climb together to cruise alt (8000' for sake or argument), although C/S airplanes will get there much quicker, and all fly at same speed. An FP 150hp O-320 will burn around 9 gph, chock to chock flying WOT when cruising. The (I)O-360s will use less over (say) a 2 hr flight. I believe the C/S props used sensibly - max MP and control speed on rpm - are responsible for most of the fuel savings.................

Pete

Raising the extra weight of a heavier engine and prop to the same altitude takes more energy.

In this case the tables have turned on CS verses FP because in climb the FP will typically be turning lower RPM than CS, reducing friction & prop drag. The CS pilot could decrease the RPMs even further, but then would definitely NOT out climb the FP pilot since he will be using less power to raise more weight.

Assuming:

• Equivalent aerodynamic & propulsive efficiency
• CS somewhat more efficient at cruise power settings because of running at lower RPM
• CS somewhat less efficient at cruise power settings due to extra weight resulting in greater angle of attack, resulting in more drag.
• CS takes more energy in climb due to greater weight
• FP somewhat more efficient in climb due to turning lower RPMs

Those more knowledgeable than me could probably put numbers on those relationships. Which would win overall would depend on the time in climb, verses time in cruise, specific weight differences, specific prop efficiency differences, and possibly the phase of the moon.

I would not want to bet on the outcome, but if I had to bet, I would go with the FP prop.

 

[L.Adamson]

What I wrote is that this is probably true, but (expanding) depends on the specifics in terms of FP prop pitch and aerodynamic / propulsive efficiency of each prop.



Raising the extra weight of a heavier engine and prop to the same altitude takes more energy.

In this case the tables have turned on CS verses FP because in climb the FP will typically be turning lower RPM than CS, reducing friction & prop drag. The CS pilot could decrease the RPMs even further, but then would definitely NOT out climb the FP pilot since he will be using less power to raise more weight.

Assuming:

• Equivalent aerodynamic & propulsive efficiency
• CS somewhat more efficient at cruise power settings because of running at lower RPM
• CS somewhat less efficient at cruise power settings due to extra weight resulting in greater angle of attack, resulting in more drag.
• CS takes more energy in climb due to greater weight
• FP somewhat more efficient in climb due to turning lower RPMs

Those more knowledgeable than me could probably put numbers on those relationships. Which would win overall would depend on the time in climb, verses time in cruise, specific weight differences, specific prop efficiency differences, and possibly the phase of the moon.

I would not want to bet on the outcome, but if I had to bet, I would go with the FP prop.

I do believe that you'll find..............

That a C/S prop will beat a F/P prop to altitude nearly every time. Unless of course, the F/P prop is pitched for best climb, in which cruise would suffer. With a C/S, we can generate full RPM on takeoff. RPM translates to available horsepower. Fly two similar RV's with C/S & F/P, and you'll easily notice the difference between the two.

L.Adamson --- RV6A Hartzell C/S

 

[Pallet]

Maybe this has already been dicussed, but with a fixed prop set up for cruise, I'm wondering how much longer ground roll this would take.
Anyone with experience that has kept track?
I'm thinking possible grass strip.

 

[RV6_flyer]

I would like to see some FACTs on what is being discussed. Can anyone point me to ACTUAL independent DATA showing the performance deltas?

I will post a link to the FIRST REAL HARD DATA on this thread.

You need to be an EAA member and login to their members only web site. You are looking for "Sport Aviation" November 1990 issue article on "The First Annual CAFE Propeller Competition". If the link I inserted works, it will take you directly to the PDF version of the article.

If the hyperlink does not work, the link is:
http://members.eaa.org/home/saarchive/eaa_articles/013474.pdf
The article was written by Dick VanGrunsven of Van's Aircraft.

I have been flying my RV-6 160 HP with Constant Speed prop for almost 11.5 years. I would like to know what EXPENSE there is operating a Constant Speed prop that everyone keeps talking about. The only operating expense has been grease every year. If you go to RVproject.com and look up the weight and balance issue, you will see that without the constant speed prop, my useful load would be reached at a lower weight becasue I would hit the AFT CG limit much sooner. As for the weight of a CS prop vs a fixed pitch, go to Van's web site and compare the difference in performance of any of the RVs at solo weight and gross weight. IIRC, the rate of climb on an RV-6 goes down 1 FPM for every pound increase in weight at the same HP. (Assuming a straight line function.)

I hope this is the FIRST of MANY posts with LINKS to FACTS that can be verified and not OPINION. I have Lycoming Copywrited material on 320 and 360 that are power charts. These charts show that the 360 burns less pounds of fuel per hour per HP produced. Yes the 360 will burn more fuel at full power but it is making more horsepower so that should be expected. If someone has a link to charts can be shared on the web that shows this, please post them.

Lets see some posts to articles on LIKE aircraft with Fixed and CS props showing RACE results or economy runs?

MY OPINION:
"I would rather walk than own an RV that does not have a Constant Speed prop." I have over 2,000 PIC hours in RVs when I make that statement. How many RV hours do you have to backup your opinion?

 

[David-aviator]

I would like to see some FACTs on what is being discussed. Can anyone point me to ACTUAL independent DATA showing the performance deltas?

I will post a link to the FIRST REAL HARD DATA on this thread.

You need to be an EAA member and login to their members only web site. You are looking for "Sport Aviation" November 1990 issue article on "The First Annual CAFE Propeller Competition". If the link I inserted works, it will take you directly to the PDF version of the article.


.....Lets see some posts to articles on LIKE aircraft with Fixed and CS props showing RACE results or economy runs?

MY OPINION:
"I would rather walk than own an RV that does not have a Constant Speed prop." I have over 2,000 PIC hours in RVs when I make that statement. How many RV hours do you have to backup your opinion?

Gary,

Gary Hertzler won the CAFE 400 in 1990 with his VEZ and a FP prop. Klaus Savier has recorded 100 mpg with his VEZ, also with a FP prop. The efficiency gurus can not afford the weight of the CS system. For all out speed, the CS wins. For efficiency it loses.

If you'd rather walk than fly behind a fixed pitch prop, have at it. I'd rather fly anything than walk.

 

[RV6_flyer]

Gary,

Gary Hertzler won the CAFE 400 in 1990 with his VEZ and a FP prop. Klaus Savier has recorded 100 mpg with his VEZ, also with a FP prop. The efficiency gurus can not afford the weight of the CS system. For all out speed, the CS wins. For efficiency it loses.

If you'd rather walk than fly behind a fixed pitch prop, have at it. I'd rather fly anything than walk.

We are talkng about RVs not EZs. Lets compare RVs to RVs and EZs to EZs. Show me links to the RESULTS I do not want to take your WORD for it.

How may RV PIC flying hours do you have to backup your statement: "I'd rather fly anything than walk." ?

 

[pierre smith]

Hi Todd....

Maybe this has already been dicussed, but with a fixed prop set up for cruise, I'm wondering how much longer ground roll this would take.
Anyone with experience that has kept track?
I'm thinking possible grass strip.

....I have over 440 hours on my 0-360 powered -6A and its Catto. I've flown quite a few other RV's with 360's and CS props and the acceleration is phenomenal compared to my airplane and climb is much better. That said, however, the weight on the nose is definitely notable, as is the reduced glide at idle. FWIW, a FP RV anything is no slouch considering that I still climb at near 2000 FPM solo and use around 650 feet takeoff roll. The CS airplanes get off in about half that.

Regards,

 

[David-aviator]

We are talkng about RVs not EZs. Lets compare RVs to RVs and EZs to EZs. Show me links to the RESULTS I do not want to take your WORD for it.

How may RV PIC flying hours do you have to backup your statement: "I'd rather fly anything than walk." ?

You win with more RV PIC time, but I'd still rather fly anything than walk.

The CAFE 400 results are on their web site. Do a search on Klaus Savier, that's how I found the 100 mpg effort. He is also mentioned at CAFE with his Lightspeed stuff when they did the ignition testing. I've sat in on one of his lectures at OSH and he is one of my favorite guys in this business. Very interesting mountain of data on electronic ignition at CAFE, in fact more than my mind can absorb in one sitting. One conclusion was clear with regard to magnetos, they are OK up to about 8500', I liked that.

Gary, the CS speed prop is good. The FP prop is also very good for those on a short budget and/or a fetish about weight. My NG weight has been reduced from 364 to 244 pounds, I love it notwithstanding the slightly reduced take off performance. The RV is a delight to fly with either prop system.

(This thread should have died a week ago - every square inch of ground has been plowed on the subject at least one time)

 

[L.Adamson]

The FP prop is also very good for those on a short budget and/or a fetish about weight.

Regarding weight..........

I seen the words "light & nimble" used. Yes a lightweight RV is kind of like a Cub, and a heavier RV, thanks to a larger displacement engine and C/S prop is more comparible to a P-51 fighter. And the F1/Rockets are even closer!

And BTW, I have been in both Cub's and Mustangs for comparison sake...

L.Adamson

 

[Steve Brown]

Hours don't equate to being right

.................
MY OPINION:
"I would rather walk than own an RV that does not have a Constant Speed prop." I have over 2,000 PIC hours in RVs when I make that statement. How many RV hours do you have to backup your opinion?

Except in being clear on what you like to fly behind. I'm not questioning your choice. These decisions, like everything else in an airplane, are about trades between one feature or another. The extra few hundred FPM are not worth it to me, they are to you. No problemo.

I don't need empirical data to know that it takes less energy to lift a lighter airplane. That is immutable fact. Likewise that it takes more energy to cruise in a heavier airplane.

That CS will outperform FP in takeoff and climb is not being disputed. However, it cannot have greater fuel efficiency when doing so because it weighs more. Unless you have found a way to violate the laws of physics, that is fact not opinion.

Does the 360 have greater fuel efficiency than the 320? If so, fine, but it is not relevant to FP verses CS, since either can use either. In fact, I can fly FP and 360 with less weight than CS and 320.

 

[dhammer]

The big question is - What kind of primer did you use on your prop?

 

[penguin]

Raising the extra weight of a heavier engine and prop to the same altitude takes more energy.

In this case the tables have turned on CS verses FP because in climb the FP will typically be turning lower RPM than CS, reducing friction & prop drag. The CS pilot could decrease the RPMs even further, but then would definitely NOT out climb the FP pilot since he will be using less power to raise more weight.

Assuming:

• Equivalent aerodynamic & propulsive efficiency
• CS somewhat more efficient at cruise power settings because of running at lower RPM
• CS somewhat less efficient at cruise power settings due to extra weight resulting in greater angle of attack, resulting in more drag.
• CS takes more energy in climb due to greater weight
• FP somewhat more efficient in climb due to turning lower RPMs

Those more knowledgeable than me could probably put numbers on those relationships. Which would win overall would depend on the time in climb, verses time in cruise, specific weight differences, specific prop efficiency differences, and possibly the phase of the moon.

I would not want to bet on the outcome, but if I had to bet, I would go with the FP prop.

I think you have convinced yourself that an FP would win out over a CS when all of the data this is available suggests otherwise. The weight difference between a FP O-320 and a CS IO-360 is probably around 50lb, or about 3%, if all other factors are equal. If you can measure the increased fuel burn due to that 3% then that's really good data collection! The CS is more efficient in the cruise because the pilot can set the engine to operate at the rpm where the prop is most efficient, the FP cannot. Assuming the FP is optimised for the cruise, any advantage in the climb through lower revs may be negated due running at sub-optimum conditions.

All I can tell you is that in my experience CS is more ecomomic than FP, and bigger engines are more economic than smaller engines, when flying at the same speed, (which is as fast as the slowest airplane will go).

Pete

 

[WyoDave]

shows how much I know...

I saw the original post when it was new. I figured this subject had been beat up enough that someone would just refer the poster to a previous thread, and it would fade away. But, danged if it hasn't turned into quite the soap opera! And all over whether, on a scale of 1-10, an RV with a FP only rates a 9.6 and the CS is a 9.8. Or is it the other way around?
I read somewhere about a guy, years ago, with an RV-3 with something like a dinky little O-290/wood prop. I guess there were some uninformed folks around that thought even that was pretty cool.
BTW, I don't think we've heard from the original poster lately. He probably ran for cover.

 

[Bryan Wood]

Anybody remember Lindbergh?

Gary,

I did a quick search for Lindbergh and oversquare and came up with this, as well as many other links. There didn't seem to be a reason to read any farther, but then you convinced me years ago and my Hartzell was planned into the budget.

http://www.experimentalaircraft.info/flight-planning/aircraft-engine.php

Oh good Lord, here's another. I love this stuff. Here Deakin goes into the friction thing as well as tons of other info, but on his IO-550 he claims a 20 horsepower loss to friction by spinning the prop up from 2,100 to 2,700 rpm's. For those unfamiliar he has done extensive dyno testing and puts on seminars on engine management.

http://www.avweb.com/news/pelican/182583-1.html

 

[pierre smith]

Hi Dave....

....I'm 63 and built a Cassutt in '73 when a dollar was....sho 'nuff, a dollar and fresh out of the Army poor but I wanted a) a fast airplane, or b) aerobatic, if not fast. Fortunately, my 12 G airplane was both.

Van came along then and offered a super deal, near 200 MPH airplane, aerobatic for a bargain price, cheap engines and a wood prop. Nowadays, high tech has radically changed everything and steam is out, glass is in...albeit at a price. It stands to reason then, a $75-$100,000 airplane must have a CS prop, no?

An RV can still be built in the $30's but that wouldn't include a CS prop, would it?

My .02c

 

[JonJay]

Absolutely

....I'm 63 and built a Cassutt in '73 when a dollar was....sho 'nuff, a dollar and fresh out of the Army poor but I wanted a) a fast airplane, or b) aerobatic, if not fast. Fortunately, my 12 G airplane was both.

Van came along then and offered a super deal, near 200 MPH airplane, aerobatic for a bargain price, cheap engines and a wood prop. Nowadays, high tech has radically changed everything and steam is out, glass is in...albeit at a price. It stands to reason then, a $75-$100,000 airplane must have a CS prop, no?

An RV can still be built in the $30's but that wouldn't include a CS prop, would it?

My .02c

I thought my 6 would be the only and last airplane I ever built. At the time, I could not imagine not having the latest and greatest of everything, C/S, EFIS, AP, Elec. Flaps, all the "right" stuff. I have no regrets.
Now that I am building my 3, I could not imagine having any of that stuff, except maybe the EFIS/EM, as it simplifies things.
It all comes down to your personal preference and your mission. I dont see anyone arguing that here, only arguing the points that some are making about one choice or another.
Make your own choice, you wont regret either.

 

[Tangier Sunset]

Fixed

My 9A has a Catto prop with 400hrs. My home turf is Idaho and my runway is 3500' long. In the winter I am airborn in less than a 1000' and in the summer I am off in less than 1500. (airport elevation 4700'). I took off from Leadville, Colorado last June weighing 1650 lbs and the density alt was around 11000'. Take off roll was between 2000 and 3000. I've landed at a few of Idaho's backcountry strips and it gets in and out with 2 people and camping gear.
Slowing down in the pattern is a non issue. I often enter downwind at 150mph, cut the power at midpoint, raise the nose a bit and have flap speed abeam the numbers.
The only argument I've heard in favor of a constant speed on an RV is if you plan to do lots of aerobatic flying. Why spend the extra $, save it for fuel and/or instruments. An RV isn't a 152 or a 172. It's a sports car! and I am still grinning.

 

[L.Adamson]

Slowing down in the pattern is a non issue. I often enter downwind at 150mph, cut the power at midpoint, raise the nose a bit and have flap speed abeam the numbers.

Then it's a double non issue with the C/S! There really is quite a difference in what can be accomplished between fixed and C/S in regards to slowing down. We have plenty of RV's around here with both F/P & C/S to note the differences. As to my landings, I drop from pattern altitude in a steep descending arc from abeam the numbers, to straightening out as I'm over the threshold. Checking at the mid-point for traffic of course... .
And then I'll be off the first taxiway. The arc itself is very close to the runway. I'd say the Cessnas around here, take about five times as long as I do. At least it seems like it!

FWIW --- the above description is a rather steep descent, and usually power off, before the threshold. In my 6A, the flare has to be timed perfectly, as to not fall through the flare, because the airspeed seems to dump in micro-seconds. If there are cross-winds, I'll usually use some power through the flare to be completely stabilized. More than not, I only use half flaps.

L.Adamson --- formally of Twin Falls, Idaho

 

[Rick6a]

I like being able to enter a pattern area without having to slow down miles ahead of time....

yup yup yup..... ..the Cs is tops on my list. Makes flying very fun.

I am fortunate to have it both ways. I agree a CS is more fun but a FP is no slouch either. Apparently some people seem to have great difficulty slowing down a FP so in their case a CS is a more suitable fit.

 

[L.Adamson]

I am fortunate to have it both ways. I agree a CS is more fun but a FP is no slouch either. Apparently some people seem to have great difficulty slowing down a FP so in their case a CS is a more suitable fit.

It's just "simple physics"! Any airplane with a lot of built in drag..............will slow down quickly with a fixed pitch prop........too!

L.Adamson

P.S. -- I hate the term "simple physics"..

edit----------------- Is that your "8" with a C/S ?

 

[allbee]

Lets just look at it this way. There are two different ways to fly an airplane.

If you just want to go out and tootle around with comfort in mind. Take the take off and landing with simplicity, use the flaps, watch your landing speed, do the pattern ruetine. Not care about the g's on take off, take the grandmother along. Than the FP prop is just fine for you.

On the other hand, you want a rush, want to have fun in the pattern, want to tailer your prop at any given moment. Have instant air brake cus that's just the way you fly. Most important, have the mulla to support your addiction. Than go with the CS prop.

What is neat is we have a choice.

 

[Webb]

Got the answer

I have the answer....and it's medically related.

It's called wallet thickness. Sitting on too fat a wallet causes pressure on the sciatic nerve which can cause pain and numbess in the leg on the side the wallet is kept.

Now that this is clear.....ff your wallet is too thick to sit on it while flying, you definate should thin it out and put a CS on the plane.

 

[SteinAir]

I'm kinda like Rick...been there done that both ways and with both 320 and a 360. I LOVE my 360 with a C/S on it in my jeep of an RV6, but I flew for many years and hundreds of hours in my old RV6 with a FP prop on it behind a 360. If you're willing to throw them over on their side and learn how to slip aggressively, and also learn how to slow them down, the FP is no big deal either. You can come blasting into the pattern a full bore midfield, and still do a nice turning/slip to roll out and flare....just takes practice! With the C/S it's of course easier and you can be a bit more aggressive, but to say the FP makes you fly huge patterns would be untrue. You just gotta learn how to lose a lot of speed fast (which isn't hard in any RV, CS or FP), and while doing it dump out flaps, throw 'em over on their side and slip aggressively all the way in....easy peasy!

I don't knock either choice because the both have their place. My old FP RV6 flew fine out of the grass strip it lived on, and also landed fine with super tight patterns. The C/S allows you to be a bit more aggressive but both work well in almost any situation. I happen to like my C/S enough to keep it and no change back to a FP, but I won't knock anyone flying a FP either.

Cheers,
Stein

 

[gasman]

Why would you BLAST into the pattern at 160 mph when 90% of the aircraft that might be in that pattern are flying at about 115 mph or less???

And, yes......... if you cut the power at flap speed abeam the numbers with a FP prop, you can make a tight steep approch and land with ease in 600 feet. 6A............

 

[L.Adamson]

The C/S allows you to be a bit more aggressive but both work well in almost any situation. I happen to like my C/S enough to keep it and no change back to a FP, but I won't knock anyone flying a FP either.

It's not a case of knocking for anyone for using a F/P, but some enlightenment for anyone considering using a constant speed. It appears that many F/P users write of little justification for using C/S. Just more money, weight, and maintenance they say..............with little additional benefit. Of course, that is a "crock"!

Yes, it's true, you can slip the **** out of your RV to add tremendous amounts of fuselage drag, while making those turns to final. That will work. You've now covered 1 out of 3 advantages that a C/S provides. But you're still stuck with the compromises of a fixed pitch when it comes to climb and cruise. The F/P is always stuck somewhere in the middle; or at worse, towards one end or the other. Less power to climb, or less airspeed on the top end. And more than not, it's a classic case of winding up to red-line and having to reduce throttle or get the prop re-pitched. As we've noticed, there are many threads regarding F/P prop re-pitches on this website.

Therefor, I have no problem with those who use a F/P. I'm only stating the facts and advantages of a C/S.

L.Adamson --- RV6A, Hartzell C/S

 

[L.Adamson]

Why would you BLAST into the pattern at 160 mph when 90% of the aircraft that might be in that pattern are flying at about 115 mph or less???

And, yes......... if you cut the power at flap speed abeam the numbers with a FP prop, you can make a tight steep approch and land with ease in 600 feet. 6A............

If, for numerous reasons, it's an advantage to "blast" to the pattern...........you can easily slow down to that 115 mph in just a few seconds; before joining the pattern...........with a C/S.

L.Adamson

 

[wickedsprint]

I'm still torn myself, I like the idea of more takeoff power and not overspeeding the engine as easy during acro, not to mention the speed brake...but the weight and cost is something that puts me off.

 

[L.Adamson]

Get the C/S!

I'm still torn myself, I like the idea of more takeoff power and not overspeeding the engine as easy during acro, not to mention the speed brake...but the weight and cost is something that puts me off.

Today, while returning from a cross-country; I had to tuck in between an Arrow, Cessna, and two helicopters. With the constant speed, managing this was a precision act of excellence! There is no way you could do this with a fixed prop with out having to slow down dramatically before the 45 to downwind, or extending the downwind for spacing, etc. RV's are just much too slippery compared to those spam cans. Or at least they should be!

I was able to precisely maneuver where I wanted to be, at the perfect time, and easily slow down down on the base to final, with an exit at the first taxiway.

If a fixed pitch pilot tells you they can do the same...............then they have far to many antenna's for drag, or perhaps exposed wires to hold the plane together! If that's not the case, then they are kidding themselves. It's like having a bike on a hill with brakes, or just using your tennis shoes.
Both might be manageable, and the tennis shoe dude may be proud. But is he as precise? I don't think so...

L.Adamson --- RV6A/ 0360/ Hartzell CS

 

[N941WR]

...If a fixed pitch pilot tells you they can do the same...............then they have far to many antenna's for drag, or perhaps exposed wires to hold the plane together! If that's not the case, then they are kidding themselves. It's like having a bike on a hill with brakes, or just using your tennis shoes.
Both might be manageable, and the tennis shoe dude may be proud. But is he as precise? I don't think so...

L.Adamson --- RV6A/ 0360/ Hartzell CS

Easy, it is called a slip. Stick the tail out and the plane will slow down. You can do the same by managing the flaps. How about S-turns? Load up the plane and it will slow down. All safe stuff and none have to lose altitude.

There are many tricks such as these that any pilot should know in order to manage airspeed and altitude.

Sorry LA, I?m still not buying the need for a CS prop. Besides, there is always one other option; fly off, let the hoards land and then get back in the pattern. If fitting is such a delicate balance such as you describe, then maybe taking a pass would be the better option.

One other thing, funny how all the fast FP prop equipped airplanes don?t have problems landing at the big air shows such as SnF and OSH.

 

[N941WR]

I'm still torn myself, I like the idea of more takeoff power and not overspeeding the engine as easy during acro, not to mention the speed brake...but the weight and cost is something that puts me off.

Tony,

There is no problem flying an RV with a FP prop. The CS prop does give you some more options but there are a bunch of RV’s flying with FP props w/o any problem.

Check out Dan C's W&B page, http://rvproject.com/wab/.

Look at the empty weight vs gross weight and add that to your decision making tree. I also suggest you do a search for fixed pitch prop threads. There is a lot of good info out there (once you get past all the “You must have a CS prop” comments) on speeds, ROC, etc.

 

[pierre smith]

What Bill R. said........

.....is true. Y'know, if cost is no object and there's plenty of money, go for it, but I can assure you, the lighter airplanes seem to be the most nimble as well.
That matters to me....maybe not to you.

Regards,

 

[RV8iator]

Why would you BLAST into the pattern at 160 mph when 90% of the aircraft that might be in that pattern are flying at about 115 mph or less???

And, yes......... if you cut the power at flap speed abeam the numbers with a FP prop, you can make a tight steep approch and land with ease in 600 feet. 6A............

It's called situational awareness, efficiency, and just plain fun. My question would be , why would you not do it.

I'll probably get blasted for this too, but if I'm in a pattern on downwind past where I usually turn base and I'm following some Cessna B-52, I'll turn base, call him in sight and always be off the runway before he touches down.

That too goes under the situational awareness column.
Just so I don't get too off thread, a constant speed prop helps, but by no means is required to fly a nice tight pattern. I've had both on my 8 and loved them both.

 

[Rick6a]

.....The F/P is always stuck somewhere in the middle; or at worse, towards one end or the other......less airspeed on the top end.......I'm only stating the facts and advantages of a C/S. L.Adamson --- RV6A, Hartzell C/S

The "facts" according to whom? As I stated in a previous post, I can easily cross midfield at 180 MPH in my FP equipped fast, slippery steed and easily slow down to Vfe before base leg...and rarely need to slip either. You did not believe when I stated it then and I doubt you believe it now. No matter to me. So believe what you will Larry, and let us just stick with...the "facts." Less airspeed on top end you assert? Horseradish.

One only has to review the fifth 2003 edition of the RVator to put yet another oft-repeated bit of misinformation to rest. The article was written by Van himself, subtitled "How Much Difference Is There Really? " after flight testing a variety of propellers ON THE SAME 160 HP RV-6 AIRFRAME. Sorry Larry, it seems according to Van's own research, my FP Sensenich (at top speed) outperformed most other pretenders....including your CS Hartzell. Should we believe Van....or you?

 

[Radomir]

These numbers for Sensenich make no sense to me.. 3 mph difference between 2500 and 2730 RPM? I don't think so... at least, not on mine.. the difference is a lot more than 3 mph..

Also, this wasn't tested on 160hp.. but that's less important... Was this a 200hp engine by any chance -- it's kinda hard to spin up a 90" pitch sensenich to 2730 on 180hp..


Either way, it's all ONLY about money.. nothing else... it's that simple.

 

[L.Adamson]

Easy, it is called a slip. Stick the tail out and the plane will slow down. You can do the same by managing the flaps. How about S-turns? Load up the plane and it will slow down. All safe stuff and none have to lose altitude.

You'd think that after 40 years, I'd have never heard of those "secret" tricks.

C/S rules....

L.Adamson --- RV6A/ Lyc 0360/ Hartzell CS