Wardo

Wardo

Active Member
ok guys, new rv-8 builder here, and a&p mech. the question of fixed pitch or constant speed is one that has many pros and cons. from a mechanics point of view a constant speed prop is obviously more cost, more weight and most importantly, more maintenance. you have all the inner workings of the prop and prop governor and not to mention the extra lines available for fatigue and leakage.

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.
 
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Prop

You won't lose anything on top end speed if you choose the right fixed pitch prop. You'll lose a little on take-off, but RV's powerful enough that take-off roll and climb doesn't suffer a great deal compared to other (factory) airplanes.

On the other hand the added oomph on take off and the flexibility of the constant speed prop make it worthwhile to me.
 
Props

Probably the biggest difference is in your ability to slow down...RVs with fixed pitch props don't slow down like a Cessna when you reduce power.

Mike
 
Transporter said:
Probably the biggest difference is in your ability to slow down...RVs with fixed pitch props don't slow down like a Cessna when you reduce power.
Click to expand...

And that's a big, big difference.............isn't it! :D

I like being able to enter a pattern area without having to slow down miles ahead of time. You can just use the C/S to fit the circumstance. Besides, constant speeds are quieter in cruise, and offer improved takeoff performace at higher altitude airports. However, most RV's can takeoff rather well with F/P's too! But, FWIW, I'd never give my C/S up.

L.Adamson --- RV6A
 
Ask Van. All he would say is more money, more weight and more maintenance don't equal enough performance improvement. I have never ran out of runway even where I live at 2600 ft and 110 degrees with my wood cruise pitched prop. If you want to slow down just pull the nose up.
 
TBO:

* Sensenich: 2000 hours and no calendar! 20 cents an hour!
* Hartzell: 2000 hours or 6 years whichever comes first! That's 333 hours a year and if you fly that much it costs $1.00 per hour. If you fly 100 hours per year it will cost you $3.33 per hour.
 
agough277 said:
Ask Van. All he would say is more money, more weight and more maintenance don't equal enough performance improvement. I have never ran out of runway even where I live at 2600 ft and 110 degrees with my wood cruise pitched prop. If you want to slow down just pull the nose up.
Click to expand...

Ever noticed, that many of Van's demonstrators have somehow "morphed" to constant speed props... :D

L.Adamson
 
agough277 said:
Ask Van. All he would say is more money, more weight and more maintenance don't equal enough performance improvement. I have never ran out of runway even where I live at 2600 ft and 110 degrees with my wood cruise pitched prop. If you want to slow down just pull the nose up.
Click to expand...

Living on 2200' of grass, the fixed pitch Catto is not at all intimidated, getting off in about 1000'. With the MT CS and Subby, it was a shorter run but once the Catto is up to 100 knots, it is hauling butt. Climb rate is noticeably better but of course the airplane weighs 180 pounds less than it did a year ago. Like everyone living in this economy, it has slimmed down or is in the process of doing so. :)

Going down and slowing down doesn't work anymore. It takes more being ahead of the airplane than with CS, or perhaps a little less behind. No big deal, going around can be fun, an excuse to pull up and roll into the down wind, this time more on speed.

I definitely prefer the lighter airplane with FP. The NG weight has come down from 364 to 244 and that do make a difference.


 
Transporter said:
Probably the biggest difference is in your ability to slow down...RVs with fixed pitch props don't slow down like a Cessna when you reduce power.

Mike
Click to expand...


I plan to do a lot of formation, so a C/S is a must for me. Otherwise, I would probably consider a fixed pitch prop. Anyone getting a fixed pitch prop I would highly recommend you get a hollow crank so you could upgrade someday.
My 2 cents.
 
I am going with CS, just because I want to.

I think your next question should be nose wheel vs. tailwheel, you can really get people fired up with that one
 
It's true that a fixed pitch prop. is lighter than a constant speed but not by as much as you might expect. It is a big solid hunk of aluminum and it uses a steel prop extension and six long 1/2 bolts (assuming an O-360). I don't know the exact amount but I believe it is inside of 10 pounds. The other factors are no prop. gov., control cable, or gov. drive (if it has been removed). I think the weight difference between a fixed pitch and constant speed is no more than about 15 lbs total. Scott McDaniels
Click to expand...
I believe Scott, quoted here from a post of a few months ago is entirely reasonable in his ballpark guesstimate. My constant speed equipped RV-8 came in within a mere few pounds empty weight of my fixed pitch Sensenich equipped RV-6A. This is a real world comparison, not a guess.
L.Adamson said:
I like being able to enter a pattern area without having to slow down miles ahead of time. You can just use the C/S to fit the circumstance.
Click to expand...
This oft cited and common assumption is simply misleading and inaccurate. I can easily enter the traffic pattern environment at top speed in my Sensenich equipped -6A and without flying a wide pattern STILL slow down to Vfe in plenty of time to make a normal landing. My experience is far from unique. Whether you are looking through the backside of a constant speed or fixed pitch propeller...it is always important to know thy airplane.

Once we "makes our brags" it is quite natural to defend our personal choice with oft cited bromides that tend to support our decisions. I feel no particular need to defend one choice as superior to another. My advice is dispassionate and straightforward. Equip your RV for the mission you will fly. For economical operating costs and perhaps a slight top speed edge, go fixed. If you fly out of short field/high altitude environments, or you simply want to experience kick-butt takeoff acceleration, go constant speed. How simple is that?
 
My quote:

like being able to enter a pattern area without having to slow down miles ahead of time. You can just use the C/S to fit the circumstance. Besides, constant speeds are quieter in cruise, and offer improved takeoff performace at higher altitude airports. However, most RV's can takeoff rather well with F/P's too! But, FWIW, I'd never give my C/S up.
Click to expand...

[/I] This oft cited and common assumption is simply misleading and inaccurate. I can easily enter the traffic pattern environment at top speed in my Sensenich equipped -6A and without flying a wide pattern STILL slow down to Vfe in plenty of time to make a normal landing. My experience is far from unique. Whether you are looking through the backside of a constant speed or fixed pitch propeller...it is always important to know thy airplane.[/I]
Click to expand...

What's a polite way of saying............."Oh Bull".. :)

I've been around to many fixed pitched RV's, and well know the differences.
To say I'm being mis-leading is actually the inaccurate statement. No offense to those who figure they need to justify F/P.

L.Adamson --- RV6A Hartzell C/S
 
build what you want

I went with fixed pitch for economical reasons, but if I would have had the funding for a constant speed, I probably would have went that way FWIW.

Randy
8A Finishing, FWF
 
Please!

I had a RV-4 for 15 years with a solid prop, constant speed is the way to go. Faster climb, quit cruse, slows down faster and no constant fiddling with the power. If your on a budget than one has to do what one has to do, but trying to justify the cost and fingering what it costs per hour, is insane! Figure what it costs to live in your house per hour x 24x365 x30 years,, makes a prop seem cheep!
 
Fixed pitch

With some misgivings, I am going with a Catto 3-blade fixed pitch prop for reasons of cost. The good thing is that it appears to be considerably lighter than constant speed. How much, I don't know, but when I get the prop, extension and hardware, I'll let you all know the total weight for comparison purposes. Craig Catto also tells me that the pitch I'm getting should give me as high or higher a cruise speed than a constant speed prop. I'll also let everyone know my performance figures whenever I get them.

I very much wanted a constant speed prop, but I have been flying a friend's RV4 with a Sensenich, and the performance is so good, even with 150 hp, that I just can't justify the expense of a constant speed propeller. I have to be more ahead of the airplane to slow down properly than with a constant speed, but it just requires a little extra planning. if I had all the money in the world, I'd be getting constant speed, but then if I had all the money in the world I'd be getting a Columbia 400 or a Lancair.
 
Since when is flying about slowing down?

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.

I can plan my pattern work based on what my airplane does. However, I do not get to decide when or if my engine quits. I would say the FP is safer in an engine out emergency.

Last Saturday I flew my granddaughter into CVH for lunch. I easily made the first turn which is at 1000' from the start of rwy 31 pavement. On takeoff I was airborne before the same point.

Neither the landing nor takeoff were near maximum performance.

Operating out of APA & BJC (Denver area) on very hot days, I never got the "I wonder if I'm going to get off the ground" feeling during takeoff. By comparison, my last airplane, an M20J, was not happy at all taking off in thin air, even with its CS prop.

I've definitely fallen out of love with CS props. My view now is that if an airplane has plenty of horsepower for the job, FP is fine. For me, that includes all the RVs.
 
Not sure it matters?

panhandler1956 said:
I plan to do a lot of formation, so a C/S is a must for me.
Click to expand...

Although I do have C/S, I fly formation with fixed pitched folks, and they have no problems. As you know, it takes constant adjustments of power to hold position. Power changes on manifold pressure (C/S) or RPM(fixed) but the power is what it is in both cases. Slowing down after the break works the same, pull 2g's and power, fixed or C/S, you should still have chewed up your airspeed quickly and slowed to your target speed (100mph) and your C/S just became a fixed pitch. I cant think of any other examples that would be of concern.
Take this for what it is as I have never flown a fixed pitch in formation although I am sure there are plenty on this site who have done both and could offer more insight to this than I.
 
fuel burn

ok, i'm leaning CS, but this thread is interesting. I plan on IO so i can run lean of peak easier. If i cruise 6K - 11K will a CS allow me to burn less fuel?

I have never flown behind fixed pitch in something faster than a 172 or citabria. My rv6a had io320 and CS and my bonanza is CS.

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
 
We have a C/S... and run a Formation School with FP and C/S.

One aspect that has not been mentioned above is aerobatics... I'm doing some Formation Aerobatics and potentially Display stuff, and the carefree handling in these areas of the C/S, particularly approaching VNE, is a bonus ;)

I do not think it is easy to justify a C/S if you on a tight cost or weight budget. By going FP, you will save a lot of $ (? ;) ) and lbs... and the benefits of C/S are really subjective (see above posts), but not performance limiting.

Formation is not a problem, even mixing FP and C/S apart from Formation Takeoffs (C/S can follow FP but be aware the engine will be way back on power! - FP following C/S is not really practical) and tailchasing (not ideal, especially a the teaching stage).

Andy & Ellie Hill
RV-8 G-HILZ
 
Andy Hill said:
We have a C/S... and run a Formation School with FP and C/S.

One aspect that has not been mentioned above is aerobatics... I'm doing some Formation Aerobatics and potentially Display stuff, and the carefree handling in these areas of the C/S, particularly approaching VNE, is a bonus ;)

Andy & Ellie Hill
RV-8 G-HILZ
Click to expand...

Andy,

Could you elaborate on the above, for instance in loops., both up and downhill? What are the main differences?

Jerry
 
Jerry Cochran said:
Andy,

Could you elaborate on the above, for instance in loops., both up and downhill? What are the main differences?

Jerry
Click to expand...
The main difference is that with a fixed pitch prop, on the downside of a loop, it may be necessary to retard the throttle to prevent the engine from exceeding RPM redline.
 
Jerry... Larry's given the quick answer ;)

A FP will have an IAS at full power at Max RPM. For a "Cruise" Prop this will be quite a high speed (150K+?) especially at cruise altitudes... Doing gentle aerobatics at height (say 3000'+), with moderate entry/exit speeds (~140KIAS), it might not trouble you...

Increase the IAS to ~195KIAS, drop the altitude to not a lot, and now do your aeros on someone's wing, and keeping the RPM in your scan becomes a :eek: See this Link ;)

Andy & Ellie Hill
RV-8 G-HILZ
 
"You won't lose anything on top end speed if you choose the right fixed pitch prop."

Can you elaborate on the right fixed pitch prop?. I have always said I am going to put a CS prop up front, but dollar for dollar I may end up with an FP prop. Seems like it is about 7k to 8k$$$ less upfront too. I only know of the Sensenich f/p..what are others?.. other than wood.
 
eat beans......

Which ever way you choose you will have a great airplane. But IMHO the C/S makes a great airplane even better. For me the ability to turn max rpm
at takeoff at airports in the west where the Density Altitude in the summer is
7k+ is real nice.... Rosie should chime in here...he has had both. A wise
man once told me...."eat beans for a year if you have to....but buy a C/S prop!"
 
Had both, FP from now on.

I have had a CS on a Lancair, a Mooney and a RV. I have owned a FP on a Mooney and part owner of another. On every CS(Hartzell and WW), ADs, SBs, governor issues and most recently major issues with the prop company have soured me on the benefits of a CS prop in the future. A FP cruise prop will not cost me enough takeoff or climb out performance to justify repeating my past CS experiences. Simplicity, cost and maintenance are the primary reasons my nearly complete RV-6A will have a FP prop. Future project like a RV-10, HRII and Ercoupe, all already in house, will have FP props. A guy like Craig Catto is the reason all of them but the Ercoupe will have a Catto prop.
 
CS better on Fuel in Theory

lsu-rv said:
ok, i'm leaning CS, but this thread is interesting. I plan on IO so i can run lean of peak easier. If i cruise 6K - 11K will a CS allow me to burn less fuel?

I have never flown behind fixed pitch in something faster than a 172 or citabria. My rv6a had io320 and CS and my bonanza is CS.

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
Click to expand...

I fly FP only. However, at lower power settings, the ability to reduce RPM's and thus fully open the throttle plate (yes, FI engines have them, too) and reduce pumping losses should mean that the CS can operate more economically. However, if you want to cruise at 75% at 8,000' then the CS has run out of advantage because even the FP is wide open up there. Same goes for higher, of course. I have no idea how big the advantage is at, say, 65%, but in theory it is there.
 
Climb rate and take-off acceleration only...

I thought that having a CS prop would allow one to bring the engine speed right back to save some fuel in the cruise.

Taking at look at the data in the Superior O-360 installation manual it appears in reality a 60% cruise at 5000', if you're going to run LOP, demands at least 2300rpm - probably much closer to 2400 if you really lean it properly. At this point, you're already on the fixed-pitch prop load curve in the manual. I don't see where you could go with a CS prop that would improve fuel burn significantly.

Actually, I can begin to see why an O-390 could produce a significant improvement in fuel burn over an O-320 if you were to run a CS, especially if you could re-tune it to lower the peak torque speed allowing you to run higher power levels at lower engine speeds. You'd have to sacrifice some maximum power to do it though.
 
We were hanging a unit heater at a large hangar today. I brought up this subject, since I knew that all RV pilots present, wouldn't dream of being stuck with a "half baked" fixed pitch. Of course I was still correct in my assessment. No one had any desire for an F/P. :D

L.Adamson --- Just telling it... like it is...
 
Define your mission

You need to decide what your needs are.......ie: Define your mission.

Both have advantages and disadvantages. Cost, performance, fuel economy, do you fly IFR, acrobatics, and the list goes on.

I recommend you close your eyes to cost and look at how you will use your plane. VFR pleasure flying would suggest FP since 95% of your time is spent in cruise. Gonna fly into heavy IFR, then a CS is a much better choice.

Make your list and then decide. Good luck.....
 
Webb said:
You need to decide what your needs are.......ie: I recommend you close your eyes to cost and look at how you will use your plane. VFR pleasure flying would suggest FP since 95% of your time is spent in cruise. Gonna fly into heavy IFR, then a CS is a much better choice.
Click to expand...

Actually, cruise is where a C/S is excellent. The RV is like a car, where you're begging for just one more gear ratio to lower the rpm's and noise while cruising down the freeway. My motorcycle certainly has that problem! With a C/S, you have that option, and I use it all the time. The difference in sound, is VERY noticeable.

L.Adamson --- RV6A, Hartzell C/S
 
L.Adamson said:
Actually, cruise is where a C/S is excellent. The RV is like a car, where you're begging for just one more gear ratio to lower the rpm's and noise while cruising down the freeway. My motorcycle certainly has that problem! With a C/S, you have that option, and I use it all the time. The difference in sound, is VERY noticeable.

L.Adamson --- RV6A, Hartzell C/S
Click to expand...

Flying on trips in my RV-6 320 C/S turning 2300 RPM with an RV-6A 360 FP turning 2500, we burn the same fuel. What makes less noise, a 320 turning 2300 RPM or a 360 turning 2500 RPM?
 
RV6_flyer said:
...What makes less noise, a 320 turning 2300 RPM or a 360 turning 2500 RPM?
Click to expand...
Good question Gary. Does anyone know? I would like to see an RPM versus SPL graph. It might be surprising! I don't reject the notion that RPM and noise have a relationship, but I don't know what it is.
 
Nosie freq might be a factor as well

n5lp said:
Good question Gary. Does anyone know? I would like to see an RPM versus SPL graph. It might be surprising! I don't reject the notion that RPM and noise have a relationship, but I don't know what it is.
Click to expand...

I've always thought that lower RPM equated to more comfort, but I had an interesting experience this past weekend. I was flying formation with a slower aircraft and had my plane pulled back to 2200RPM. The low frequency energy was noticable and seemed to go through me. I broke off and increased RPM to 2500. The noise was much more tolerable and comfortable. I don't think there was less noise, but is was definitly higher in freq and less noticable. I was more comfortable as a result. Your mileage may vary, as I think my plane is on the loud side as far as RV's go.
 
Airspeed is the limiting factor for acro

n5lp said:
The main difference is that with a fixed pitch prop, on the downside of a loop, it may be necessary to retard the throttle to prevent the engine from exceeding RPM redline.
Click to expand...

For my Catto, controlling airspeed would be the reason I need to control the power. RPM overspeed is not the issue when flying acro. Generally I enter a loop at 150kts and don't need to touch the throttle during the maneuver. Care needs to be taken not to overspeed the airframe during acro in a FP or CS RV. FP is fine for acro in an RV. Don't make that the reason to spend money.

Light weight might be more of a factor for enjoyable acro. In that case, consider a carbon fiber prop rather than aluminum.

No doubt, CS is better than FP for cruise fuel economy and better short feild performance, though an FP RV is still a good short feild airplane.

CS definitly slows down when you pull the throttle, but I don't view this as an issue at all. Anyone with moderate piloting skills can fly an FP and get into short strips just fine. If slowing down is a major factor, get a J3!

CS is more stable for IFR, but not a big deal if you have an autopilot.

If at all possible, you should make arrangements to fly both and then choose for yourself. Otherwise you will go nuts making this decision.
 
Can happen

whifof100ll said:
I was flying formation with a slower aircraft and had my plane pulled back to 2200RPM. The low frequency energy was noticable and seemed to go through me. I broke off and increased RPM to 2500. The noise was much more tolerable and comfortable.
Click to expand...

In our installation, our Hartzell prop has an "Avoid continuous operation between 2000-2250 RPM" restriction. In that range, vibration actually can be unpleasant. So, like the SB says to, I avoid it!

--Paul
RV-6 O-360-A1A HC-C2YK-1BF
 
Catto

Garage Guy said:
In our installation, our Hartzell prop has an "Avoid continuous operation between 2000-2250 RPM" restriction. In that range, vibration actually can be unpleasant. So, like the SB says to, I avoid it! What engine/prop do you have?

--Paul
RV-6 O-360-A1A HC-C2YK-1BF
Click to expand...

Catto 3 blade. There was no vibration that could be felt by touching the panel. It was bothersome to my ears but with no perceptible vibration.
 
whifof100ll said:
CS definitly slows down when you pull the throttle, but I don't view this as an issue at all. Anyone with moderate piloting skills can fly an FP and get into short strips just fine. If slowing down is a major factor, get a J3!
Click to expand...
Couldn't have said it better myself. All it takes to slow down a FP is a longer lead time compared to a CS and even then there should be plenty of time. If incapable of thinking 30 seconds ahead of the airplane...get a Cub.

There is one item of note I have not seen discussed that may be at least mildly interesting to some builders. My FP Sensenich has the 2600 RPM limitation and is fitted to the 160 HP 0-320-DIA. The data plate affixed to the Lycoming engine notes the following: At 2600 RPM the engine develops 155 hp.
 
whifof100ll said:
No doubt, CS is better than FP for cruise fuel economy and better short feild performance, though an FP RV is still a good short feild airplane.

CS definitly slows down when you pull the throttle, but I don't view this as an issue at all. Anyone with moderate piloting skills can fly an FP and get into short strips just fine. If slowing down is a major factor, get a J3!
Click to expand...

I'm sensing a pattern in this thread. Those that don't have C/S seem to make excuses as to why a C/S isn't all that great. I see that now were down to pilot skills, and no issues, and marketing as an "excuse". That's really rubbish!

To the newcomer,and uninitiated, this might be believable. To all my C/S friends that I brought this subject up to yesterday.................it's laughable! Fact is, we've all flown F/P for many years, and now we all fly C/S. The differences are overwhelming.............in what can be accomplished! I'd never go back to a fixed pitch prop period...............unless I indeed had a Cub or Cub variant.

L.Adamson ---- RV6A
 
To somewhat reiterate, my, and other posts above...

IMHO you can never justify a C/S Prop on Cost / Economy / Performance grounds :eek: The benefits are marginal, and a FP RV will still way outperform the "competition" or the way "you flew before".

A C/S will be "more fun", "easier" and give you things to brag about ;) It will weigh more, take more time to fit, cost more to buy and maintain :( Your choice about C/S will be about cost/hassle/weight v fun... but then so is the rest of the RV ;)
 
Say it Brother!

Andy Hill said:
To somewhat reiterate, my, and other posts above...

IMHO you can never justify a C/S Prop on Cost / Economy / Performance grounds :eek: The benefits are marginal, and a FP RV will still way outperform the "competition" or the way "you flew before".

A C/S will be "more fun", "easier" and give you things to brag about ;) It will weigh more, take more time to fit, cost more to buy and maintain :( Your choice about C/S will be about cost/hassle/weight v fun... but then so is the rest of the RV ;)
Click to expand...

Can I get a AMEN for Andy?
 
L.Adamson said:
...To all my C/S friends that I brought this subject up to yesterday.................it's laughable! Fact is, we've all flown F/P for many years, and now we all fly C/S. The differences are overwhelming................
Click to expand...
Well all my F/P friends think the subject is laughable also:) The differences are overwhelming and all of us can't understand why some people add unneeded weight and complexity and expense to their airplanes for marginal gains.

I hereby propose that all my friends have a no-holds barred brawl with all of your friends at the next LOE to settle once and for all who has the smarter friends.

Me, I'll watch.
 
I looking forward to standing on my tail on take off and standing on my nose on landing. I love short approach landings. I hate taking the time to put on flaps, I hate having to slooow waaaay dowwwwn before I get to the airport. I hate people telling others what to have.

I basically think the normal way of flying is way boring. So that c/s will help with that. my take, take it or leave it.
 
OK Brother!

allbee said:
I looking forward to standing on my tail on take off and standing on my nose on landing. I love short approach landings. I hate taking the time to put on flaps, I hate having to slooow waaaay dowwwwn before I get to the airport. I hate people telling others what to have.

I basically think the normal way of flying is way boring. So that c/s will help with that. my take, take it or leave it.
Click to expand...

Steve, we will put you on the blue knob prayer list! Cold beer works wonders!
 
allbee said:
I looking forward to standing on my tail on take off and standing on my nose on landing. I love short approach landings. I hate taking the time to put on flaps, I hate having to slooow waaaay dowwwwn before I get to the airport. I hate people telling others what to have.

I basically think the normal way of flying is way boring. So that c/s will help with that. my take, take it or leave it.
Click to expand...

Great...someone else who's been watching the way I fly! :)

Cheers,
Stein
 
RV6_flyer said:
I would rather walk than fly an RV with a fixed pitched prop.
Click to expand...

Sorry, but I am going to have to call B.S. on this!

Any aviator worth his salt would rather fly a ratty ole C-150 with a fixed pitch than walk. Now once you are flying, then you can wish for a better ride.

Pat
 
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