Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Catto on a Rocket?
- Thread starter GR8 8
- Start date
rv6rick
Well Known Member
My guess is that you'll find no one that has put a fixed pitch prop on their Rocket.....we will soon find out if I'm correct 
.
.At the risk of scorn and ridicule,
rocketbob
Well Known Member
I had some conversations with Paul Lipps about this very same subject and there are a few pro's and cons of running a fixed pitch prop on a Rocket. In a nutshell there is no reason why one couldn't do it however you would lose quite a bit of efficiency if you ran the engine at a RPM where the fuel burn isn't much more than a RV which is around 21-2200 RPM, where it doesn't hurt your wallet too bad.
Last edited:
fixed pitch Rocket
Rocket Bob, as I see it:
The "pro's": Lighter by 30-60 Lbs, less complexity, less cost, and can be just as fast, or climb just as well as a C/S (but probably not both), probably smoother than all likely C/S options I would otherwise choose.
The "con's": If tuned to best speed, it won't climb or take off as well as C/S, odd and unusual, pitch and diameter as well as airfoil are all needing to be tested and determined for best results.
Not sure about your comments on being less efficient at lower power settings... a slower turning prop is typically more efficient than a fast turning one, and at lower MP, my Light Speed ignition system should advance timing and maximize engine efficiency too. Maybe I'm missing something.
Are you thinking that it would be slower than an RV at an equal fuel burn?
Thanks for the comments, JR
Rocket Bob, as I see it:
The "pro's": Lighter by 30-60 Lbs, less complexity, less cost, and can be just as fast, or climb just as well as a C/S (but probably not both), probably smoother than all likely C/S options I would otherwise choose.
The "con's": If tuned to best speed, it won't climb or take off as well as C/S, odd and unusual, pitch and diameter as well as airfoil are all needing to be tested and determined for best results.
Not sure about your comments on being less efficient at lower power settings... a slower turning prop is typically more efficient than a fast turning one, and at lower MP, my Light Speed ignition system should advance timing and maximize engine efficiency too. Maybe I'm missing something.
Are you thinking that it would be slower than an RV at an equal fuel burn?
Thanks for the comments, JR
rocketbob
Well Known Member
FP props use airfoils designed for a coefficient of lift at an angle of attack at a given RPM, which is max RPM. They lose efficiency as the power is brought back. In a rocket the power is brought back a lot more than a typical RV to get fuel burn to something more reasonable. That and induction system losses from reducing manifold pressure to get reduced RPM as opposed to running a constant speed prop at a low RPM but with a wide open throttle also contribute. A RV with a fixed pitch prop is typically ran at 25-2600 so the losses aren't nearly as bad. In a Rocket at that RPM you're going to be burning 18-20 GPH. Fixed pitch would work well on a Rocket if one were racing.
vfrazier
Well Known Member
Don't forget this point also: a fixed pitch prop set up for cruise is not going to want to slow down in the landing pattern. You can end up with a long, flat approach in a short winged bird with not-so-good gliding capabilities.
This also means that your idle speed needs to be low so you don't float past your runway. Couple this with the lower inertia of the FP (wood?) prop and you've got a combination that may be close to dying on you in the pattern.
This was how my first RV-4 behaved and it wasn't a comfortable feeling.
The CS prop will slow you down when you want it to, like having a speed brake, and is a hands down winner for its performance in the pattern.
Spend the money and get the RIGHT prop the first time!
YMMV!
This also means that your idle speed needs to be low so you don't float past your runway. Couple this with the lower inertia of the FP (wood?) prop and you've got a combination that may be close to dying on you in the pattern.
This was how my first RV-4 behaved and it wasn't a comfortable feeling.
The CS prop will slow you down when you want it to, like having a speed brake, and is a hands down winner for its performance in the pattern.
Spend the money and get the RIGHT prop the first time!
YMMV!
smokyray
Well Known Member
No weapon too short for a brave man...
JR,
Mission: Two years ago I commissioned my good friend Craig Catto to build a 2 blade Rocket prop. Why? Improve my HR2's handling and reduce weight, especially out front. Also, my Catto props are quick revving and much less flywheel effect than the Hartzell, another goal for the HR2. Having tested Craig's first 2 blade RV prop on my RV4, testing the first HR2 prop would have been an honor....
Goals: Every HR2 I have flown (5) and most C/S RV's I have flown (215 at last count) were nose-heavy. Many people like that trait, I don't. Additionally, I didn't want to add weight anywhere to improve handling, I wanted to reduce weight. Craig wasn't going to pitch the prop for top speed, but optimized for midrange aerobatics which is 90% of my flying. (2500 RPM) With a lighter nose you have to be more cognizant of aft loading, but aerobatics and high AOA maneuvering are much improved. My HR2 flew perfect with a 100LB passenger,which is cool, but solo aerobatics required much higher stick forces per G.
End game: I sold my HR2 before I could test the prop. As mentioned above, FP props are optimized for higher RPM and efficiency. However, experience has shown me otherwise. 2000 hours in my RV4 and RVX have yielded good midrange and lower cruise numbers alongside C/S equipped RV's. Additionally, I have never had any problems getting in and out of my STOL home strip with a FP Catto prop, (the secret is to make sure your engine idle is set below 700). Craig applied all this data into his formula for my HR2. Rick is correct, I've never seen a FP Rocket, mine would have been the first to go "Crazy Ivan".
However comma, my next one will have a Catto...
V/R
Smokey
PS: With proper technique you can operate out of short strips, glide further, fly formation and enjoy a much lighter nose, less moving parts and lower cost. A very good friend of mine and former F-18 Hornet driver removed the HH (Heavy Hartzell) from his very quick Lancair 360 in lieu of a Catto 2 blade. He gained 17 Knots at top end and still flies out of his 1800' strip!That's why I love Experimental airplanes...
JR,
Mission: Two years ago I commissioned my good friend Craig Catto to build a 2 blade Rocket prop. Why? Improve my HR2's handling and reduce weight, especially out front. Also, my Catto props are quick revving and much less flywheel effect than the Hartzell, another goal for the HR2. Having tested Craig's first 2 blade RV prop on my RV4, testing the first HR2 prop would have been an honor....
Goals: Every HR2 I have flown (5) and most C/S RV's I have flown (215 at last count) were nose-heavy. Many people like that trait, I don't. Additionally, I didn't want to add weight anywhere to improve handling, I wanted to reduce weight. Craig wasn't going to pitch the prop for top speed, but optimized for midrange aerobatics which is 90% of my flying. (2500 RPM) With a lighter nose you have to be more cognizant of aft loading, but aerobatics and high AOA maneuvering are much improved. My HR2 flew perfect with a 100LB passenger,which is cool, but solo aerobatics required much higher stick forces per G.
End game: I sold my HR2 before I could test the prop. As mentioned above, FP props are optimized for higher RPM and efficiency. However, experience has shown me otherwise. 2000 hours in my RV4 and RVX have yielded good midrange and lower cruise numbers alongside C/S equipped RV's. Additionally, I have never had any problems getting in and out of my STOL home strip with a FP Catto prop, (the secret is to make sure your engine idle is set below 700). Craig applied all this data into his formula for my HR2. Rick is correct, I've never seen a FP Rocket, mine would have been the first to go "Crazy Ivan".
However comma, my next one will have a Catto...
V/R
Smokey
PS: With proper technique you can operate out of short strips, glide further, fly formation and enjoy a much lighter nose, less moving parts and lower cost. A very good friend of mine and former F-18 Hornet driver removed the HH (Heavy Hartzell) from his very quick Lancair 360 in lieu of a Catto 2 blade. He gained 17 Knots at top end and still flies out of his 1800' strip!That's why I love Experimental airplanes...
Last edited:
Smoke'n my brand!
Smokyray, You're sing'n my song!
I am just now deciding on how the engine will go together, and I get to decide if I should save another 5 Lbs by eliminating the internal guts to drive the prop governor... In other words, "take the plunge"... no back door if this doesn't work out as planned.
Do you still have that prop laying around? Did anyone get to fly behind it?
Great help here thanks to all. JR
Smokyray, You're sing'n my song!
I am just now deciding on how the engine will go together, and I get to decide if I should save another 5 Lbs by eliminating the internal guts to drive the prop governor... In other words, "take the plunge"... no back door if this doesn't work out as planned.
Do you still have that prop laying around? Did anyone get to fly behind it?
Great help here thanks to all. JR
