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Fixed vs CS prop

wbhammack

Member
I'm about to pull the trigger on my first RV. I'm military / airline guy so my GA experience is limited at best. If anyone has any advice on a CS prop vs a Fixed pitch I'd be interested to hear your opinions. I've narrowed my search to a 7 or 8 (14 if I could find one) because I will doing some acrobatics. Nothing crazy but I want to keep that option open.
 
My son and I (both ex-militery pilots) have owned two RV-8s, one with a Catto three blade fixed pitch prop and one with a Hartzell CS prop. Both fly well but the CS just performs better especially during takeoff. We've also owned a RV-7 with a Whirlwind CS and it was awesome also.
 
With a constant speed prop you will get full, or nearly full, power at takeoff and early in the first segment of climb. With a fixed pitch prop, you most likely won?t - unless you have a fixed climb prop, which will negatively affect cruise speed. A fixed pitch prop is like driving your car with only one gear. Most of us chose a cruise type pitch if using a fixed pitch prop for speed reasons, at the expense of takeoff/climb performance. That isn?t as great of a penalty in an RV as it is with some airplanes, because RV?s still have excellent takeoff performance with fixed pitch props - just not as good as their constant speed brothers. My fixed pitch RV4 still gets airborne in well under 1000? and by the time I?m at the end of the runway on climb out, I?m out climbing my constant speed buddies. I?ve owned 5 RV?s. The 3 I built had constant speed props. The 2 I?ve bought, including my current RV4 have fixed props. Which is better? The constant speed is better for performance reasons. My fixed pitch RV4?s are/were better in terms of cost, weight, and simplicity. If you are routinely flying out of hot/high, or short airports, the constant speed RV will be significantly better. I?m a flat lander using mostly long (3000?+) runways, and my fixed pitch prop is not that much of a detriment, but it is a detriment. Formation takes a little more ?finesse? than my constant speed RV?s, but that is easily learned. All things being equal in your search (build quality, cosmetics, condition, instrument equipment) the constant speed RV?s are more valuable than their fixed pitch clone, both in terms of your overall performance, and in resale value. To me, build quality and condition trumps the constant speed/fixed pitch question, but that?s my opinion based on the type flying I do. Your requirements are probably different.
 
Like others have said, depends on your flying. I did not see a benefit having constant speed prop as take off performance is already outstanding with fix pitch on my 180 hp RV6A. Flying almost exclusively in middle America at cruise speeds, a fixed pitch is perfect for my flying. I think a big swinger in prop decision is HP. With 160 HP I would have gone constant speed, with 180 HP I think a cruise fixed pitch is a good choice.
 
Final Approach and Landing

I've had the pleasure of flying my fixed pitch Catto and O-320 RV-4 at all altitudes from sea level to mountain airfields at over 9000 feet MSL.

Now I'm flying an RV-7 sporting an IO-360 and Hartzell constant speed prop and have landed at airfields from sea level to mountainous high altitude runways.

Without a doubt the biggest difference I notice between the two types of propellers is approach and landing. A fixed pitch prop is going to remain at the same pitch used for takeoff, which provided a static RPM significantly less than maximum RPM. A constant speed equipped aircraft produces rated horsepower on takeoff, so it is when the propeller control is at "high RPM" or "fine pitch."

With a constant speed prop I need to add a little power above idle on final approach to maintain desired speed as opposed to pulling the fixed pitch RV to idle on downwind and leaving it there, even slipping to keep approach speed with full flaps on final. RV-4s are more slippery than RV-7s by a little, yes. I've flown a little in a fixed pitch RV-7 and RV-7A, they both were at idle on short final to maintain a normal glide path.

Enjoy the search! Its a fun and challenging endeavor to find a flying aircraft that you like, has the equipment you like and is in a place where you can adequately look it over before buying. This is why many build their own. I found one flying that checked all my boxes, so I know it can be done!
 
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Obviously CS is best but if you do find a nicely built plane but it has Fixed pitch, I would certainly not turn my nose at it. I bought a beautiful RV7 exactly 5 years ago and over the past five years I have not only put the panel that I wanted, but I added a CS prop and WOW :eek: what a difference!!! I absolutely love it.
 
This question comes up all the time and there are plenty of opinions. The reality is, it's not an opinion question, it's something that can be solved with simple analysis.

But it requires solid input data, starting with "what are your mission requirements". Many people choke right there.

I do long cross country work at max gross weight and that is the overiding consideration for me. I'm in and out of short strips, climb mountain ranges and run WOT, LOP for hours on end. Simply put, I "require" 2750 RPM for takeoff/climb as well as the ability to pull the prop back to 2300 in cruise with the throttle against the stop (WOT). That makes it a pretty simple choice for me.

What are your requirements?
 
Welcome to one of the never-ending debates!

As others have said...it is critical to define your mission first. The decision may be simpler after that.

CS is typically heavier. CS has better TO performance. Both have almost the same performance in cruise, as has been documented on the forum in the past. I fly a FP 7 and have confirmed this with other CS RVs on our field. One other benefit to the CS is in slowing the plane down. The CS is like having air brakes. With the FP you have to be more aware of your energy management. There is more complexity and maintenance with CS.

One thing not really discussed is the maintenance. There is more to inspect with the CS prop and controls. CS according to the manufacturer requires an overhaul at specified time or hourly intervals. Can be expensive. In Canada FP metal for Certified requires 5 yr corrosion inspections (not sure what the US requires). Costs much less in time and money. You can debate whether or not to do it on a homebuilt.
 
Really? Why? I thought the idea was to use the throttle the most, but I'm not a formation flyer.

-Marc

You still use the throttle but the speed of the airframe reacts quicker due to the governor adjusting blade pitch. This is generally a good thing but one should be aware of the limitations on counterweighted engines concerning the prop "driving" the engine. Using the prop as an "airbrake" is a bad thing on some engines.
 
Formation with a fixed pitch prop works out fine. You just need a little more ?talent?/anticipation. Energy management takes on a new level of importance.
 
If even remotely thinking about formation flying; CS.

Don`t tell this to Luca and Franz from the Formation Aerobatic Team CrewRV8.. They both have a 3 bladed fixed pitch Catto Prop?

(and this was the reason why I chose one too. Its simpler, lighter, cheaper and if they can fly formation aerobatics it is good enough for me... )
 
A Corvette will start in 4th gear, and can attain nearly its maximum velocity on level ground in 4th gear. Would you buy a Corvette stuck in 4th gear?

Many of us do exactly that. You don't "wear the clutch out" because the clutch is air, but you do pay a climb penalty and don't have as many power / rpm choices (your power gives you whatever rpm it gives you, you can't run full power / lower rpm).

Like any nice feature, the trade offs are complexity and cost. If money is no obstacle, a Cessna Caravan will do just about anything any RV will do and carry passengers too... ;)
 
You still use the throttle but the speed of the airframe reacts quicker due to the governor adjusting blade pitch. This is generally a good thing but one should be aware of the limitations on counterweighted engines concerning the prop "driving" the engine. Using the prop as an "airbrake" is a bad thing on some engines.

Only as far as the prop driving the engine, but that is true. Pulling the power back far enough to put the pitch on the fine stops but not yet driving the engine (9 or 10 inches MAP) results in really good drag to slow the airplane.
 
Only as far as the prop driving the engine, but that is true. Pulling the power back far enough to put the pitch on the fine stops but not yet driving the engine (9 or 10 inches MAP) results in really good drag to slow the airplane.

If only all pilots had that level of awareness and finesse. Based on what I hear in the pattern and from word of mouth, there are a lot of people chopping the power and "throwing out the boards".
 
If only all pilots had that level of awareness and finesse. Based on what I hear in the pattern and from word of mouth, there are a lot of people chopping the power and "throwing out the boards".

My method may be a little unorthodox, but I basically come in to the pattern the same whether I?m flying a F/P or a C/S.

I come screaming in to downwind at a fairly low altitude and fairly tight to the runway. When I?m abeam the numbers I pull power and pitch up. By the time I?ve climbed back up to a proper (normal) approach altitude I?ve bled off enough airspeed that I can then push the prop full forward without ever increasing the RPM?s. Then basically, all in one motion, I?ll kick her around and turn from downwind to base to final. The C/S will then act as my air break and I can almost point the nose straight down and still be going slow enough to deploy two notches of flaps all while keeping the RPM?s in a normal range.

If I?m flying a F.P. my procedure is exactly the same, other than not being able to point the nose straight dawn on final..... my final approach has to be a little bit flatter to keep the speeds where I want them.
 
The answer is there is no right answer!

As mentioned above, it probably depends on your personal preference. This is one of those never ending discussions. I have a fixed pitch 2 blade Catto RV-4 with an O-360. It is light (975 lb) and performs great in all aspects. I regularly fly formation, and if I am lead I always have to pull back the throttle to let my CS buddies catch up on take off. Most of them are heavy, and in my opinion a constant speed prop does not make up for a heavy airplane.

My prop is pitched a little fine for most folks. Since I race, I want to get the RPM's up to about 3000 RPM for more power at max level speed. Static RPM when sitting still is around 2100. Top speed with the FP prop for me is right at 200 knots TAS. Climb rate at gross weight (pilot, passenger, and bags) is about 1800 fpm at 120 knots depending on the temperature. I live in Idaho, so I deal with mountain ranges and shorter runways regularly, not a problem.

One interesting factiod is that I also own a 1999 BMW M3, 0-60 in 6.0 seconds. My RV-4 with only me in it is quicker based on the airspeed indicator and accounting for any wind down the runway. In 6 seconds I am doing about 75 knots. By the end of our 5400 ft runway, I am doing 130+ knots.

As far as landing distances go, if you do it right, you can match Van's numbers, about 425 ft. The problem is, most RV's weigh too much. They have heavy upholstery, 6 pack of steam gauges (heavy), fiberglass with way too much resin it, etc. A constant speed prop probably adds 50 lb or so to the airplane. This extends landing distance (and takeoff.)

My main point I guess is that if you find a well built, light airplane, you don't need CS.
 
...My main point I guess is that if you find a well built, light airplane, you don't need CS.

Again, there is little debate that a light, well built, fixed pitch RV is a strong performer. But the above statement discounts the requirements other people may have. And to that point, if one has a requirement for one airplane to produce redline RPM at minimum airspeed AND a significantly reduced RPM at near maximum cruise, then it doesn't matter how light or well built the airplane is - one equipped with a FP prop simply can't meet requirements.

A CS prop is simply a piece of equipment that allows more choices and capability - much like night lighting or a full suite of IFR Avionics. Not everyone needs the added capability, but if you DO need it, there's no work around - you aquire the equipment or go without the capability.
 
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I agree to a point

And to that point, if one has a requirement for one airplane to produce redline RPM at minimum airspeed AND a significantly reduced RPM at near maximum cruise...

I agree, true statement. That being said, I cruise at 170 knots at 7 gph at about 2600 RPM, so I do give up the 2300 rpm capability at a good cruise speed as you say. But, I have an AFS5000 EFIS, Garmin G5 backup EFIS, Avidyne GPS/NAV/COM, and an autopilot. I fly IFR regularly. So I don't think you give up much with a FP.

Also, I have to admit that I have done a lot of aerodynamic work on the plane to get it to go that fast, and that adventure is not for everyone. When I first finished the plane the speed at the same power setting was about 15 knots slower. Takeoff distance, landing distance and climb rate have not changed much however.
 
I have flown my 180 hp FP -9 for over 900 hours and have flown a number of other RV's, with and without CS props.

The initial acceleration with a CS prop, even with only 160 hp spinning it is just a kick in the pants!

Slowing down for landing with a FP prop means you have to creap up on the airport. If you try to enter the pattern at cruise speed, you will be in the next county before you slow down.

Is a CS prop required, even at GW? No, it is not. You can even fly formation with a FP prop, but it is a real challenge and if lead has a CS prop and chops the throttle, you are going to sail right by and there is nothing you can do.

I once "raced" a 160 hp RV-9A With a CS prop from the runway to 3500'. My 180+ hp FP -9 was smoked through 2000'. Once we got to our cruise speed, it wasn't even a contest. The Catto cruise prop just walked the lower hp CS prop.

The only way I would put CS prop on my RV is if had Catto composite blades on a CS prop, which is coming.
 
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I agree, true statement. That being said, I cruise at 170 knots at 7 gph at about 2600 RPM, so I do give up the 2300 rpm capability at a good cruise speed as you say. But, I have an AFS5000 EFIS, Garmin G5 backup EFIS, Avidyne GPS/NAV/COM, and an autopilot. I fly IFR regularly. So I don't think you give up much with a FP...

I wasn't suggesting that you need a CS prop to fly IFR. I was only using the VFR/IFR mission as an example of hard mission requirements driving hard equipment requirements. If you must fly IFR, you need to be equipped for it or you don't get to participate. If you must fly at night, you need lighting or you don't participate. If you must have max takeoff RPM and a sedate cruise RPM at WOT, then you must have a CS prop... That's all.
 
Bill,

?Is a CS prop required, even at GW? No, it is not. You can even fly formation with a FP prop, but it is a real challenge and if lead has a CS prop and chops the throttle, you are going to sail right by and there is nothing you can do.?

If your lead chops the throttle in close formation (unbriefed), you need to find a new lead. If he briefed it, knowing he had a fixed pitch wingman, and still does it, you still need to find a new lead. That would be the opposite of ?wingman consideration?. I don?t think I?ve ever flown formation with a lead that ever tried that. There?s no question, a constant speed RV is EASIER to fly close formation with than the same airplane with a fixed pitch prop, but it?s what you?re used to. I have no problem keeping my station with my fixed pitch RV4, just like I did with my CS RV8?s - just some different techniques. There are plenty of RV?s that don?t have CS props. The OP wanted some guidance in selecting the right airplane. I think putting too much emphasis on the need for a CS prop if you want to fly formation is misleading. There?s no question that a CS prop provides a wider range of operational capability and efficiency, but I would hate it if he bypassed a perfectly good airplane because it didn?t have a CS prop, because he thinks he can?t successfully fly formation with a FP prop. That is absolutely not the case.
 
Is there a "theory of operation" for CS props for those that have never used one?

Obviously you can set the rpm, but what difference does it make in cruise to turn down the rpm, vs just going full blast all the time?

Some people advocate just going full throttle all the time with perhaps a little less rpm for less noise/vibration.

What are best practices for various rpm settings, assuming you want to go fast? Assuming best range?
 
Have you flow one?

Reading all these comments from a few of the folks so convinced their experience and knowledge applies to everyone, and is the only way, surprises me.

If an RV is set up and configured to perform the mission it?s owner has chosen, that position should not be downplayed by someone else trying to push their point of view.


CS and FP both have advantages and disadvantages over each other. If your happy with your configuration and it does the job, give others credit for their choice as well.
 
Then there are people like me. I would not own an RV (other than RV-12) that does not have a Constant Speed prop.

There is a reason that all the factory airplanes built in the last 10-years that are not LSA have had Constant Speed props on them.

The Constant Speed prop on the RV is the ULTIMATE Total Performance RV.
 
Observations

Is there a "theory of operation" for CS props for those that have never used one?

Obviously you can set the rpm, but what difference does it make in cruise to turn down the rpm, vs just going full blast all the time?

Some people advocate just going full throttle all the time with perhaps a little less rpm for less noise/vibration.

What are best practices for various rpm settings, assuming you want to go fast? Assuming best range?

Lots of good videos on YouTube out there explaining the theory and use of constant speed props.

For a fundamental approach to engine and propeller operation, listen to Mike Bush's "Leaning Basics" EAA webinar, also on YouTube to understand why running wide open throttle at a lower than red-line RPM is beneficial. Summary - less RPM means my engine is producing less power, the intake is most efficient at WOT and I can still lean when less than 75% power, so less RPM gives me a way to save fuel by leaning. The cost of saving 1 gallon per hour over the course of the life of my engine more than pays for a nice constant speed prop and many maintenance costs.

Best practices you'll hear all the time from RV drivers for economy and speed, winds aloft aside, are that flying wide open throttle between 8500 and 9500 feet. Arrive a couple minutes later by running lean of peak to maximize economy while only losing a couple knots.

What a constant speed prop allows an RV pilot to do is fly at the best altitude for winds aloft and be wide open throttle, reduce the RPM to remain below 75% power and enable running lean of peak to maximize efficiency while still only losing a few knots below best power mixture.

You're sure to get a lot of techniques and opinions here. Definitely check out the videos by an EAA recognized A&P and pilot with lots of recognized experience.
 
Formation Techniques

Bill,
There?s no question, a constant speed RV is EASIER to fly close formation with than the same airplane with a fixed pitch prop, but it?s what you?re used to. I have no problem keeping my station with my fixed pitch RV4, just like I did with my CS RV8?s - just some different techniques.

We are interested in the other techniques you've used with a fixed pitch RV in formation.

I've flown my RV-4 with a fixed pitch Catto 3-blade prop on an O-320 in formation and used several techniques to hang with the constant speed RVs no matter what...often with wingmen learning to lead, after all, so many mistakes were being made while I hung on and stayed safe.

Yaw. Not only do we have throttle to control a fixed pitch aircraft's speed, but instantaneous rudder control can yaw the aircraft and use the fuselage for aerodynamic braking. Leaving the power up and using momentary yaw pulses can provide slowing and then almost instant acceleration to maintain position with a constant speed prop equipped RV doing the same thing.

A lighter, more maneuverable RV-4 on the wing of a heavier aircraft also gives the fixed pitch wingman more options. Light weight fixed pitch planes will change speed more quickly, even just a little bit, which makes a difference when only a few feet away.

Another technique, choose a lead pilot that flies a fixed pitch RV. Then it doesn't matter if the wingmen are flying fixed pitch or constant speed aircraft.

These two techniques make the biggest difference when landing on the wing, especially when lead may pull the power near idle in the pattern and at or near touchdown.

I'd like to hear about other techniques that fixed pitch prop pilots use, and it might help the OP see what is possible.
 
Is there a "theory of operation" for CS props for those that have never used one?

Obviously you can set the rpm, but what difference does it make in cruise to turn down the rpm, vs just going full blast all the time?

Some people advocate just going full throttle all the time with perhaps a little less rpm for less noise/vibration.

What are best practices for various rpm settings, assuming you want to go fast? Assuming best range?
Lycoming engines are designed to make TBO at 75% powered while spinning on the redline.

With a fixed pitched prop, that is the only way you are going to make 75%.

We are interested in the other techniques you've used with a fixed pitch RV in formation.

I've flown my RV-4 with a fixed pitch Catto 3-blade prop on an O-320 in formation and used several techniques to hang with the constant speed RVs no matter what...often with wingmen learning to lead, after all, so many mistakes were being made while I hung on and stayed safe.

Yaw. Not only do we have throttle to control a fixed pitch aircraft's speed, but instantaneous rudder control can yaw the aircraft and use the fuselage for aerodynamic braking. Leaving the power up and using momentary yaw pulses can provide slowing and then almost instant acceleration to maintain position with a constant speed prop equipped RV doing the same thing.

A lighter, more maneuverable RV-4 on the wing of a heavier aircraft also gives the fixed pitch wingman more options. Light weight fixed pitch planes will change speed more quickly, even just a little bit, which makes a difference when only a few feet away.

Another technique, choose a lead pilot that flies a fixed pitch RV. Then it doesn't matter if the wingmen are flying fixed pitch or constant speed aircraft.

These two techniques make the biggest difference when landing on the wing, especially when lead may pull the power near idle in the pattern and at or near touchdown.

I'd like to hear about other techniques that fixed pitch prop pilots use, and it might help the OP see what is possible.
Great explanation! I have tried all those and drop 10? of flaps, when slow, to try to stay in position.

Briefing beforehand is key and even then I have had experienced leads chop and drop, because that is what they are used to.
 
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