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fixed pitch vs. constant speed

R

rockit

Active Member
I am look at purchasing a RV-7 and it has a fixed pitch prop. I have low tail wheel time in a champ but lots of time in a RV-9A. Someone mentioned a CS prop is better because it will help you slow down the airplane and better for low TW time pilots.
I was wondering if anyone has an opinion on this.
Thanks.
 
You will get lots of opinions...

I have a -8 with a fixed pitch catto and slowing down to land is no problem.

My previous a/c was constant speed so the thing I find I have to watch is over-speeding on descent...

By the time you do some transition training for the t/wheel you will be used to it...

Also one less conrol to worry about...
 
rockit said:
I am look at purchasing a RV-7 and it has a fixed pitch prop. I have low tail wheel time in a champ but lots of time in a RV-9A. Someone mentioned a CS prop is better because it will help you slow down the airplane and better for low TW time pilots.
I was wondering if anyone has an opinion on this.
Thanks.
Click to expand...

Yes, the membership has opinions about your question.....hundreds of them. ;)

Not trying to blow off your inquiry, but the Search function of the forum will reward you with hours of reading about the various aspects of fixed and CS props.
 
Sam Buchanan said:
Yes, the membership has opinions about your question.....hundreds of them. ;)

Not trying to blow off your inquiry, but the Search function of the forum will reward you with hours of reading about the various aspects of fixed and CS props.
Click to expand...

OK, here is one. :)

I didn't want the complexity, costs and weight associated with a constant speed prop. One caveat is that I live in Florida, fly over somewhat-lower-than-out-West mountains back and forth to Ohio, Georgia, etc.

I got 400'/minute in my Taylorcraft on a good day and found that fixed pitch RV-6 prop gave me 2000'/minute. If I lived in an area where big mountains were the predominate landscape I probably would have a different opinion.

I find no issue with slowing down. Just plan ahead.
 
GLPalinkas said:
OK, here is one. :)

I didn't want the complexity, costs and weight associated with a constant speed prop. One caveat is that I live in Florida, fly over somewhat-lower-than-out-West mountains back and forth to Ohio, Georgia, etc.

I got 400'/minute in my Taylorcraft on a good day and found that fixed pitch RV-6 prop gave me 2000'/minute. If I lived in an area where big mountains were the predominate landscape I probably would have a different opinion.

I find no issue with slowing down. Just plan ahead.
Click to expand...

What he said. He nailed it for me, except replace Florida with Louisiana
 
I live near lots of mountains with a -9 and fixed pitch. Was low time tailwheel when I finished it. Works just fine for flying or landing.
 
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The best

For an RV, a fixed pitch is the best lowest cost solution. Highly recommend a Catto. I had several of his props and they were great. Even have a new one on the wall. Can't bring myself to bolt this wonderful piece of art on my project.

However, My latest deal has a CS cause I like shifting gears rather than leaving it in first all the time, and my discresssionary income is not a hindering factor at this point in my life. Otherwise it would be a Catto.

Good luck on your search for the best prop!

Cj
 
No issues with FP

I had a similar dilemma when shopping for my RV, but as Ron said, by the time you do your transition training and get some time in the plane, you'll learn to slow it down. I can approach the field at 160 knts and easily slow down to 90-100 on the 45 and 80 (or slower if necessary) on downwind. You'll adjust quickly. I had 1 hr of TW time before doing my transition training with Mike Seager.

I've also had no issues with climb out, even when I had to go around at a field near Mt. Rainier in a narrow valley with a full load. Sure, a CS prop will give you better climb, but the FP climb is so good compared to most anything else, you still be very happy with it. In most circumstances, I rarely climb at Vx or Vy. A cruise climb at 140 knots is still better than most certified birds.
 
rockit said:
I am look at purchasing a RV-7 and it has a fixed pitch prop. I have low tail wheel time in a champ but lots of time in a RV-9A. Someone mentioned a CS prop is better because it will help you slow down the airplane and better for low TW time pilots.
I was wondering if anyone has an opinion on this.
Thanks.
Click to expand...

I would not own an RV with a fixed pitch prop.

IF the price was right, yes I would buy one that is fixed pitch that could be changed to Constant Speed and would change over as soon as I got it in my hangar.

Over 20-years ago, Allen Tolle changed over his RV-4 from fixed to CS. He reported at many EAA meetings that he saved 1.5 Gallons per hour changing over. The prop paid for itself in fuel savings.
 
A couple of thoughts for you:

Can a CS prop be added to the -7 you are looking at?

The nice thing about a CS prop is the Blue knob is all the way forward for both takeoff and landing. So just like your -9A, you only have to play with the throttle while you keep it straight on the runway.

Oh, the -7 is easier to handle on the ground than the Champ.
 
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I chose a CS because the RV7 is designed for more weight on the nose so if I had went FP, I would have had to ad a big ole heavy crush plate to bring my CG in line. My CG ended up farther aft than I would like, even with the CS! But, I was very tempted by the lower cost, simpler, very good looking Catto 3 blade prop! If I had built a 9, I would have gone with the Catto.
 
Ron RV8 is right. Find a prop with the maximum pitch you can find that suits your engine and bolt it on! Your flying a sport aircraft.
 
A1A2

N941WR said:
A couple of thoughts for you:

Can a CS prop be added to the -7 you are looking at?

The nice thing about a CS prop is the Blue knob is all the way forward for bot takeoff and landing. So just like your -9A, you only have to play with the throttle while you keep it straight on the runway.

Oh, the -7 is easier to handle on the ground than the Champ.
Click to expand...

The seller is saying the engine has a hollow crank and i can change over to a CS prop anytime. However the docs say it is a Superior O-360-A1A2, which according to Superior's site is a fixed pitch engine.

From all the responses it sounds like I will be fine with a FP prop. I live in NC and there are a few mountains but they top out at 4000 ft and most of my flying is up and down the east coast. The way my RV-9A climbs with exactly the same engine I think the RV7 will do fine.
 
I'm also of the opinion that almost every RV will benefit from a CS prop, but they do fly just fine with fixed. That said, if your only reason for wanting one is airspeed control on landing, then you don't need one.
 
I seem to recall that Van wrote about the FP vs CS decision some years back. I recall him saying that the RVs are basically designed around FP, this in keeping with the philosophy that simplest is best. He also mentioned that with the power to weight ratio of an RV, CS is unnecessary. I believe his overall opinion was that the performance benefit was offset by the added weight.

His article was probably in the RVator periodical.
 
Rupester said:
I seem to recall that Van wrote about the FP vs CS decision some years back. I recall him saying that the RVs are basically designed around FP, this in keeping with the philosophy that simplest is best. He also mentioned that with the power to weight ratio of an RV, CS is unnecessary. I believe his overall opinion was that the performance benefit was offset by the added weight.

His article was probably in the RVator periodical.
Click to expand...

Take a look at the Factory Demo airplanes. Almost all of them have CS props.
 
FP vs CS

Do a search ," converting my constant speed prop to a fixed pich "
You will not find anyone looking to reduce their performance .
 
Any RV will work well with a fixed pitch prop. Performance will be compromised depending on what the prop is aimed at. Many people operate their RVs for many years with fixed pitch props. There are no real problems that you will not get used to quickly, you will have to think ahead slowing down. Prop maintenance will not require much.

Any RV will work really very well with a c/s prop - it will be more fun to fly and will probably burn less fuel (for the same speeds). Take-off performance will be substantially better. But any aircraft with c/s prop will be heavier, will have a further forward cg, and will be more costly on the maintenance front.

Its all a compromise, depends what your priorities are.

Pete
 
A ground adjustable prop may be a good compromise as well. You can tweak it according to what your mission is, and so could any future owner.
 
Superior IO360 with a Catto 3 blade on my RV8. Cost was 1/3 of a constant speed and operating costs of a cs is probably at least $3.00 per hour with a cs vs. little or no hourly cost for fixed pitch. After about 120 knots, I can climb same as a cs. But cs definitely has the initial advantage in climb. Fixed pitch is as fast or faster than cs. Mine was designed to produce 178 knots tas at 2700 rpm's. If I want dash speed, I can get 15 knots more exceeding 2700 rpm's. Or I can get178 ktas at 16,000 density altitude burning less than 8 gph. I usually cruise at 162 ktas at 2450 rpm's. But if I had a constant speed, I could probably cruise 24/24 and produce a better cruise speed at the same fuel consumption of my 162 ktas typical cruise. Lighter RV's handle nicer than heavier. But if you want a cross country cruiser, you may not care as much about a heavier less sporty feel. So it depends on personal preference. Mine is an occasional crosscountry, but mostly up and around for an hour once or twice a week. If I wanted to do a lot of cross country, i might opt for a cs. You won't be disappointed either way.
 
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F/P C/S

I had a C/S on my 4, and the more I flew it the more I liked it. Flew a 4 with the same horse power and a F/P prop for many hours. It was lighter on the controls and simpler in operation, and very much enjoyed flying it. It all depends on your mission, and personal preferences, for me I like being able to get the most H/P on take off and climb and yes an RV has a lot of performance with a F/P but at lower rpm the hp is lower also. I also like being able to put it in over drive in cruise, but again a F/P does extremely well with the right pitch, buy like Gary said, it will burn more fuel at the same air speed as a C/S. I like the breaking capability of the C/S but the F/P is easily handed, you just have to slow down a bit earlier. It's just like any other plane, just learn how to fly it, and it will be different than something else. Is it worth the expense? I know Gary has more than 2800 hours on his 6, if he saved 1 gallon per hour with the C/S prop, that would be $14,000 in fuel savings. Is it worth the complexity? And expense? That is up to you personally, flying a C/S prop only takes a minutes to learn how to use it, and you know we all have opinions.
The RV's are great with either configuration, build what makes you happy.

RT
 
not so fast

g zero said:
Do a search ," converting my constant speed prop to a fixed pich "
You will not find anyone looking to reduce their performance .
Click to expand...

Just a few days ago in the Classifieds someone was selling a Hartzell and a govenor.
Reason for selling " converting to fixed pitch.
 
g zero said:
Go Figure ! The only guy to ever do it is on this forum .
Click to expand...

Actually it's done more often than you think. They just don't post it on this forum because they know it will raise comments like this.
 
rockit said:
I am look at purchasing a RV-7 and it has a fixed pitch prop. I have low tail wheel time in a champ but lots of time in a RV-9A. Someone mentioned a CS prop is better because it will help you slow down the airplane and better for low TW time pilots.
I was wondering if anyone has an opinion on this.
Thanks.
Click to expand...

Ok, Ravi, have you decided yet whether or not anyone has opinions about their choice of prop? ;)

You have received some good advice, and some that is over the top. Be cautious when someone states that their choice of prop/primer/ landing gear/canopy/etc is the "only" way to go. :)

Best wishes for an enjoyable transition to your RV! You will love flying it regardless of what kind of fan it has.
 
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rockit said:
I live in NC and there are a few mountains but they top out at 4000 ft and most of my flying is up and down the east coast.
Click to expand...


Yeah, Kings Pinnacle is a puny 1700 feet as are Pilot and Sauratown.

Ever heard of Mt Mitchell (6684 ft) or Pisgah (5722) or the majority of Haywood County (noted as county with the highest number of high peaks on east coast)? The sectional chart shows VFR clearance altitudes of 6600, 6800 and 7000 in this area. The IFR OROCA altitude is 9000.
 
My tw instructor suggested that I put on a FP and learn the planes characteristics first. And if I ding the prop doing landing practice, its probably a so what moment - put on another prop because I (more than likely) saved my motor and my wallet. When I'm finally comfortable with the airplanes envelope, then spring for a CS - dinging one of them makes for a very bad day.

That said, all my TW instruction was in a CS.... I think in the end, its like buying tires for your car - performance tires or ultra performance tires. Yes theres a difference, but the drivers ability to get the most out of his equipment is more important.
 
maniago said:
My tw instructor suggested that I put on a FP and learn the planes characteristics first. And if I ding the prop doing landing practice, its probably a so what moment - put on another prop because I (more than likely) saved my motor and my wallet. When I'm finally comfortable with the airplanes envelope, then spring for a CS - dinging one of them makes for a very bad day.
Click to expand...

There is different prop strike engine inspection criteria FP vs. CS :confused: I imagine wood prop could be less, but can't imagine the end result of a metal prop strike CS or FP would be much different.
 
Prop strike=prop strike=prop strike=prop strike

60av8tor said:
There is different prop strike engine inspection criteria FP vs. CS :confused: I imagine wood prop could be less, but can't imagine the end result of a metal prop strike CS or FP would be much different.
Click to expand...

Any prop strike, no matter how minor, no matter what kind of prop, requires engine teardown and inspection.
 
Yes

10/4 on that Mel!
I've seen wood/composit props do no damage after tear down and other times seen everything from gears cracked to cranks that wouldn't pass inspection due to hairline crack. As much as it would burn my rear to teardown an engine after prop strike and not find any damage, the risk that there might be damage, especially now that we have learned more about wood/composite prop strikes, is too great.......At least for me it is, experimential or not.


Mel said:
Any prop strike, no matter how minor, no matter what kind of prop, requires engine teardown and inspection.
Click to expand...
 
It's also a legal requirement at least for a certified engine anyway! Not sure how experimental engines are affected legality wise...
 
Add up the inertia of the items geared to the crankshaft (magneto rotors, camshaft, even the occasional standby alternator) and you can see why engine builders find partially sheared crank gear bolts and dowel pins all the time on teardown. A lot of people feel if the prop flange dials out straight you are good to go. Not true.
 
jdmunzell said:
It's also a legal requirement at least for a certified engine anyway! Not sure how experimental engines are affected legality wise...
Click to expand...

The biggest problem would be when the inspector signs off the next condition inspection and states,
"This aircraft has been inspected............and found to be in a condition for safe operation."

Would you feel comfortable making this entry knowing a prop strike has occurred and the proper engine teardown has not been accomplished?
 
Back to the OP question, another feature of CS, is the increase in engine out glide distance when pulling the big blue back.
 
No oil pressure equals fine pitch unless it is an electric cs. So engine out glide will be with the brakes on, ie less glide ratio
 
brad walton said:
No oil pressure equals fine pitch unless it is an electric cs. So engine out glide will be with the brakes on, ie less glide ratio
Click to expand...

...Also an aerobatic C/S hub is the opposite, as no oil pressure will put the prop in course pitch. With a standard hub, and the engine windmilling, you usually will still have oil pressure. In this case you will have pitch control and can dial in course pitch for glide. My 9-A actually glides better windmilling, mixture pulled in course pitch than it does prop stopped in fine pitch. Thanks, Allan..:D
 
I'm a bit wary of wading into this never ending debate, but I have a couple of observations.

First, we're forgetting that there is big variation amongst both fixed pitch and constant speed props. A friend at KLVK bought a constant speed prop off of a wrecked plane and its performance was so bad he switched to a Catto fixed pitch and it dramatically improved the performance. The constant speed prop was designed for an airframe that didn't have the performance envelope of RVs.

I have another friend who is helping Catto test designs of his new props for Long EZs. He uses an old Catto prop as his normal prop. We fly formation regularly and we flew together with one of the first iterations of the new prop and he immediately had to go back to Catto because he couldn't keep up with me in his Long EZ and was extremely disturbed:D With the old Catto prop he is significantly faster than I am. So there is great variation even amongst fixed pitch props from the same manufacturer.

So switching from a bad version of one kind of prop to a good version of the other will be better, no matter which direction you're switching.

Now, going from props optimized for RVs, the fixed vs CS debate becomes much closer to religious arguments and I will bow out at this point;)
 
jjconstant said:
I'm a bit wary of wading into this never ending debate, but I have a couple of observations.

First, we're forgetting that there is big variation amongst both fixed pitch and constant speed props. A friend at KLVK bought a constant speed prop off of a wrecked plane and its performance was so bad he switched to a Catto fixed pitch and it dramatically improved the performance. The constant speed prop was designed for an airframe that didn't have the performance envelope of RVs.

I have another friend who is helping Catto test designs of his new props for Long EZs. He uses an old Catto prop as his normal prop. We fly formation regularly and we flew together with one of the first iterations of the new prop and he immediately had to go back to Catto because he couldn't keep up with me in his Long EZ and was extremely disturbed:D With the old Catto prop he is significantly faster than I am. So there is great variation even amongst fixed pitch props from the same manufacturer.

So switching from a bad version of one kind of prop to a good version of the other will be better, no matter which direction you're switching.

Now, going from props optimized for RVs, the fixed vs CS debate becomes much closer to religious arguments and I will bow out at this point;)
Click to expand...

Very good points. I flew a buddies RV3 converted to an electric CS prop. I think it qualifies as the slowest RV3 on the planet after the change. Sure flew nice though....
 
jjconstant said:
I have another friend who is helping Catto test designs of his new props for Long EZs. He uses an old Catto prop as his normal prop. We fly formation regularly and we flew together with one of the first iterations of the new prop and he immediately had to go back to Catto because he couldn't keep up with me in his Long EZ and was extremely disturbed:D With the old Catto prop he is significantly faster than I am. So there is great variation even amongst fixed pitch props from the same manufacturer.
Click to expand...

+1

Back in the day I help Bernie Warnke test his designs on a 180 hp RV-4. His original "club" (wide chord) generally performed better that his later "toothpick" design.
 
I have a friend with a 7A and CS, O360. My neck hurts when we takeoff. I have never felt acceleration like that in a light airplane. You will get better performance no doubt. But the OP was about slowing down and it being easier for a new TW pilot. I don't foresee any difference once you've had some training. I would put CS in my 4 if I had the dough, but I don't so I know a FP will still be a great airplane compared to anything out there that is non RV.
 
sblack said:
I have a friend with a 7A and CS, O360. My neck hurts when we takeoff. I have never felt acceleration like that in a light airplane. You will get better performance no doubt. But the OP was about slowing down and it being easier for a new TW pilot. I don't foresee any difference once you've had some training. I would put CS in my 4 if I had the dough, but I don't so I know a FP will still be a great airplane compared to anything out there that is non RV.
Click to expand...

I totally relate, Scott. I did my transition training in a 7A set up just as you describe. On my first takeoff roll, it jumped so hard that I failed to push the throttle in all the way (which my instructor quickly corrected). Crazy acceleration!

That said, I'm very happy with my FP Catto. It climbs very well, and I just like the lightness and simplicity of the setup...less to go wrong and maintain.
 
CS performs better on take off and climb, costs more, weighs more and is most satisfactory to anyone going that route.

FP performs better than most span cans, costs less, weighs less, and is most satisfactory to anyone going that route.

Been there with both and liked both. It is a matter of personal choice and circumstances when deciding.

You can't go wrong either way with a RV.
 
Robb said:
Constant speed is the only way to go unless cost is an issue.
Click to expand...

Well...I guess that means the thousands of RVers with fixed-pitch props are financial sub-standard members of the community who can't afford the best...... ;)

That's the problem with making absolute, blanket statements.... :)
 
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Given a certain dollar and weight budget, Is it better to have a heavier, more powerful engine with a fixed pitch, or a lighter, less powerful engine with a heavier CS Prop?

I think it is a top speed vs climb rate tradeoff.
 
Robb said:
Constant speed is the only way to go unless cost is an issue.
Click to expand...

Boy do I ever feel the fool. The enjoyment of the last 17 years of flying an elegantly simple and efficient design was just an illusion.

Maybe with a heavier, more expensive and more complicated propeller that wouldn't let me fly any faster but would accelerate better during the takeoff roll, I would actually be having fun.
 
vlittle said:
Given a certain dollar and weight budget, Is it better to have a heavier, more powerful engine with a fixed pitch, or a lighter, less powerful engine with a heavier CS Prop?

I think it is a top speed vs climb rate tradeoff.
Click to expand...

The thumb rule a few years ago was a O-320 with CS prop was better compromise for an RV than an O-360 with FP prop.

The idea was the CS prop made up for the loss of power on takeoff (the smaller engine could produce full power while the larger FP engine could not get full power RPM), and the smaller engine still had a boat load more power than the majority of us use in cruise.

If the majority of your flying is max power, 2700 RPM cruise then just pick a FP prop that does that with whatever engine your wallet can support. I suspect few fly like this.

Carl (had a FP RV-8A and changed to a CS prop after 300 hours - and was very happy with the upgrade).
 
Like everything else in this world, it depends.

I have an RV-9 with a Catto FP "Ubercruiser" prop, spun by a "stock" ECI O-360.

A year ago I led a five ship formation flight out of a 5,000' county airport and was the only FP plane of the lot.

All the other planes had IO-360's or better so during our briefing we discussed what speed I should use for the climbing left turn. All four wingmen were experienced card holding formation pilots and all four said to climb at 120 knots and make the turn as they would catch me.

What none of us took into consideration was how well the 9's wing works and at 120 knots they kept asking me to "give 'em some" until I was down below 100 knots and they could join up.

With 700+ hours on my plane, the only time I wish I had a CS prop was when flying formation with someone who forgets and cobs the throttle and when landing with a bunch of CS prop'ed airplanes. It would be nice to have that big speed brake up front. However, for normal flight operations, I am very content with the FP Catto up front.
 
Carl Froehlich said:
The thumb rule a few years ago was a O-320 with CS prop was better compromise for an RV than an O-360 with FP prop.

The idea was the CS prop made up for the loss of power on takeoff (the smaller engine could produce full power while the larger FP engine could not get full power RPM), and the smaller engine still had a boat load more power than the majority of us use in cruise.

If the majority of your flying is max power, 2700 RPM cruise then just pick a FP prop that does that with whatever engine your wallet can support. I suspect few fly like this.

Carl (had a FP RV-8A and changed to a CS prop after 300 hours - and was very happy with the upgrade).
Click to expand...

There is not much cost difference between a 320 and 360, maybe $1500. The difference from FP to CS is $5k and up.
 
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