Constant speed prop on a gyro, anyone care to share the experience?

I had a WarpDrive in flight adjustable and I found it almost completely useless below 2500 feet. Rotax recommends all day cruise setting to be 35 inches of manifold pressure at 5500 RPM. If I set the prop for 5700 RPM on full power takeoff which is only 100 RPM less than the 5800 max that Rotax recommends (for a climb setting ) for under 5 min. At that setting I can just get about 33.8 Inches of manifold pressure at 5500RPM in straight and level flight. I have a 914 So as I go to 3-5 thousand feet and higher is when I would wish for the option of an in flight adjustable prop especially because of the 914 is still making full power at high altitude. I have found that since I switched to gyros that scenario happens very little now so I got rid of it
The next time I go over New York at 9,500 ft. I will look at my manifold pressure gauge and see how high it will go at 5500 RPM. I am guessing it will be around 32 Inches of manifold pressure.
I would think a 912 would benefit far less than a 914.
 
Since gyros generally fly close to the ground (minimal difference between take-off and cruise altitude and minimal time spent climbing) and usually take-off from runways far longer than needed, for many there is often not a lot to be gained by being able to switch from fine to coarse pitch. But as others indicated in the West there might be other considerations. My home airport in Colorado is 7,500' and the passes on all sides of me require me to fly at up to 11,500' or more which in summer is a DA of 14,000'+. If I go to the plains east of me only 70 miles away near Denver I will be at 5,000'. Repitching is almost a necessity.

A few years ago when I flew to Oshkosh I had to stop and repitch my ground adjustable prop going each way because there just was no way I could use the same pitch at 1,000' as I had used at my home elevations.
 
To give you guys more concrete details, I will do some cruise comparisons this weekend. I can fly with the propeller pitch fixed at the ground take-off value (same as it would be in a ground-adjustable prop) and check my cruise speed, then compare that in the same conditions and altitude with cruise speed with CS mode turned back on.
 
Apologies for bumping a 5-month-old thread but I disagree with Abid on this one. He is in Florida so he only flies at really low altitudes (probably never even gets to 1000'), but the thinner the air gets, the more critical a CS prop becomes. I initially had a ground-adjustable prop and replacing it with a DUC (French) CS prop and it made an enormous difference. (I only have a Rotax 912.)
Agreed.

If the area to be flown from is fairly flat, whether at sea level or 7000’ feet a ground adjustable prop, if set correctly for the commonly used home airfield alt, will cope with the variation in altitude commonly flown in gyros for a reasonable range from that field.

If however there will be quite large variations in terrain alt and density alt around the home airfield, that is when an inflight variable pitch prop comes into its own...or if on a long flight with a fixed pitch, then be prepared to fine tune along the way.
 
Speaking from a little experience...I put an Ivo Magnum variable pitch prop on my SparrowHawk. That thing really made a difference on take off....
cruise...and top end. Its in one of my SparrowHawk threads in the archives here...but I recall gaining 8-10 mph.

I did have trouble with losing the electical connection once in awhile, an it was stuck at the pitch it was at. .

So when its working...I grade it an A. Overall a grade C with the fiddling I had to do with it.
 
I am not a fan of the ivo prop in that the prop blades are held to the hub by friction between the inner and outer prop hub plates, with a knurled surface. If the prop ever gets loose in the hub it will get very loose very quickly, and can eject a blade, which obviously can have deadly consequences

But saying that, I had a Ivo prop with electric adjust on a plane I used to own, a titan Tornado II with a 80hp Rotax 912. It did allow a slightly better cruise speed than the warp drive fixed pitch prop I ended up putting on the plane. It really didn't make much difference on take off and climbout, but in cruise you could add in pitch and load the engine up and pick up a few mph.

The electric adust pitch on the ivo makes it illegal for sport pilots. BUT........ It is very simple to remove the electric adjust portion of the prop and just make the prop fixed pitch if you ever needed to make it Legal for SP. Another option would be to move the switch for adjustment to some area that would be considered not accessible in flight, and it could still be adjustable and be legal.
 
Has anyone got any first-hand knowledge of a hydraulic adj prop used on a Rotax?
 
Yes, the DUC prop I'm using is hydraulic, driven by an electric pump. So you never need to rebrush motors like you do with Ivo and others, and it's been 100% reliable in the nearly 3 years that I've had it, unlike the Ivo which I flew with once in Florida and which failed immediately (due to a loose wire preventing pitch adjustment).
 
I am not a fan of the ivo prop in that the prop blades are held to the hub by friction between the inner and outer prop hub plates, with a knurled surface. If the prop ever gets loose in the hub it will get very loose very quickly, and can eject a blade, which obviously can have deadly consequences

But saying that, I had a Ivo prop with electric adjust on a plane I used to own, a titan Tornado II with a 80hp Rotax 912. It did allow a slightly better cruise speed than the warp drive fixed pitch prop I ended up putting on the plane. It really didn't make much difference on take off and climbout, but in cruise you could add in pitch and load the engine up and pick up a few mph.

The electric adust pitch on the ivo makes it illegal for sport pilots. BUT........ It is very simple to remove the electric adjust portion of the prop and just make the prop fixed pitch if you ever needed to make it Legal for SP. Another option would be to move the switch for adjustment to some area that would be considered not accessible in flight, and it could still be adjustable and be legal.

Legally speaking once you install an in flight adjustable prop of any type on an aircraft it can never be again flown or sold to a Sport Pilot and fit under LSA definition. Personally I think that rule is downright stupid. One should be able to change the prop to a fixed pitch one and bring it back under LSA and fy it as a Sport Pilot
 
Yes, the DUC prop I'm using is hydraulic, driven by an electric pump. So you never need to rebrush motors like you do with Ivo and others, and it's been 100% reliable in the nearly 3 years that I've had it, unlike the Ivo which I flew with once in Florida and which failed immediately (due to a loose wire preventing pitch adjustment).

Well loose wire will fail any electric system including a fuel pump like in 914 or 915iS.
The trick with Ivo prop we found is to throw away the circuit breaker they give you and instead use a 5 amp Tyco circuit breaker. It pops before it allows your motor etc. to burn out. You can then simply reset the breaker and you are good to go
 
Wasn't there some talk about changing the LSA rules to allow 'pitch adjustable' props?
Yes, I know that they talk about lots of things (weight increase, adding gyros, etc.), but I wouldn't let this "you can't sell it to a Sport Pilot" be the top of the argument or dissuade someone from this optimization.
 
Legally speaking once you install an in flight adjustable prop of any type on an aircraft it can never be again flown or sold to a Sport Pilot and fit under LSA definition. Personally I think that rule is downright stupid. One should be able to change the prop to a fixed pitch one and bring it back under LSA and fy it as a Sport Pilot
I did not know you could not change it back.
 
Conventional wisdom has it that a low-speed aircraft such as a gyro will not gain much performance from a variable-pitch prop. I believed this until I by chance I had some "teachable moments" with MIS-PITCHED props.

1. I bought a used 1985 Air Command 447 way back, from Fred Gath of the original Sno-Bird. Fred had replaced the stock Ultra-Prop with a 3-blade, non-adjustable wooden Catto prop. The Catto apparently had more pitch than you'd normally want on a 40 hp gyro. It would climb at about 100 fpm on a hot humid day, but at 70-plus IAS, it took off and would do well over 80 on those 40 horses. Unfortunately, the original no-HS lowrider Air Command was so viciously unstable at those speeds that I never flew it that fast unless trying to keep up with some fast FW ultralight. In that case, I reluctantly hammered it, flew WAY nose-down, and just prayed that I would not get dumped forward into a PPO. Fun? Not. But the point here is that "cruise pitch" gave me an extended top end, though it ruined the climb performance.

2. Former student Dan LeCuyer asked me to try out his new 503DC Dominator. Ha had merely eyeballed the prop pitch. I later found out that the pitch was just about zero; the only "pitch" was created by the camber of the prop blades. Result? It would levitate off the ground at about 10 MPH IAS and wouldn't hold altitude at much more than 25 mph. I limped around the pattern, alternately diving to pick up airspeed and then using the speed to gain some altitude in a "scooping" sort of flight path. Lesson: a flat "climb pitch" prop can produce dramatic soft-field performance but won't allow you to cruise at a proper speed or even reach best rate-o'-climb speed.

A controllable-pitch prop that allowed you to toggle between the extreme cruise pitch in Scenario #1 and the extreme climb pitch in Scenario #2 would give you a very cool expanded flight envelope. The pitch range would probably be 0-14 deg. or more.

The mechanism MUST be simple, reliable and absolutely failsafe-and-bulletproof, though. Losing a prop blade in a pusher gyro is an excellent way to meet your maker. Even losing the pitch on ONE blade but not the others would produce a violent out-of-track vibration that could break things in flight.

Oldtimers will recall the infamous "exploding prop" adventures with the Mac engine. Says I, no thank you.
 
Doug that would make a great chapter in a book about your flying/learning adventures at the same time. Add some math and it becomes a technical reference book at the same time.
 
I've found that "conventional wisdom" is frequently incorrect, based on emotion, and often lacking solid facts. ;)
 
I've found that "conventional wisdom" is frequently incorrect, based on emotion, and often lacking solid facts. ;)

It's true that the 'conventional wisdom' mentioned by Doug Riley in this thread may be –as he says– wrong, but the belief that gyros won't gain much from a variable-pitch prop is based on apparently valid reasons, if it's also true that the real workings of a prop are probably much more complicated than the usual picture: at any airspeed, the relative wind 'seen' by any blade station is the vector sum of the peripheral & aircraft speeds. The higher the aircraft speed is, the lower the effective AoA. Hence, and to compensate for that, you need a small pitch for maximum thrust at takeoff, and a larger pitch for maximum thrust at cruise airspeed.
Many FW planes have a cruise speed that is several times the airspeed at takeoff, and that's the reason of the usefulness of an in-flight variable pitch prop, either manual or automatic. In our gyros, the ratio between cruise and takeoff airspeeds is relatively small compared with a FW, and a variable-pitch prop should then have a limited efficacy...

In this case, fact may appear to diverge from theory, but that's probably due to an over-simplified theory...
 
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Hey I forgot to update this thread but I did my test a couple of weeks ago and I consistently got at least 15 kts faster (sometimes 17 kts) in CS mode vs fixed mode. Those speeds are calibrated, confirmed with GPS in both directions. For the fixed mode test, the blades were fixed at a pitch that lets it hit 5700 rpm on take-off, representing how ground-adjustable props are usually set. So it really does make a huge difference.

This was flying around 1500' in 80-degree weather.
 
Hey I forgot to update this thread but I did my test a couple of weeks ago and I consistently got at least 15 kts faster (sometimes 17 kts) in CS mode vs fixed mode. Those speeds are calibrated, confirmed with GPS in both directions. For the fixed mode test, the blades were fixed at a pitch that lets it hit 5700 rpm on take-off, representing how ground-adjustable props are usually set. So it really does make a huge difference.

This was flying around 1500' in 80-degree weather.

Setting the fixed mode to get 5700 RPM on initial climb speed is like a climb prop. For cruise prop, you would set it to 5400 RPM. Usually I aim for 5550 for a compromise between climb and cruise for fixed pitch props on climbout speed (60 mph). I don't think you'd see more than 8 knot difference if you do that. Of course I did not have access to a CS prop but just an in flight adjustable prop
 
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In addition to the performance benefits, an inflight adjustable-pitch prop allows you to cruise at a lower engine RPM. Again returning to my old 447 Air Command, I could loaf along at 5300 with that high-pitched Catto prop (though it wouldn't climb worth a damn). The reduced noise is most welcome (to pilot and groundlings alike). The gas consumption seemed pretty good (relatively speaking, for an inherently gas-hogging gyro; under 3 gph).

As far as engine wear is concerned, an engine has only so many revolutions built into it before it wears out. Few revs per minute equal longer life, as long as you don't "lug" it to death.

BTW, in commenting about "conventional wisdom," I am not challenging the math -- instead, I'm challenging one of those opinions that get repeated so often that they become accepted as fact.

The math actually bears out the enormous difference in prop blade blade AOA at a given RPM, between a gyro slow-flying at 25 mph and one doing, say, 100 mph. I imagine that the "variable-pitch props don't gain you anything in a gyro; they cruise too slow" meme may have arisen because people were thinking about FW planes with a stalling (i.e. minimum) airspeed of 60, not a gyro that could maintain altitude at 25 or less if pitched properly.

The AOA of a prop blade at a given engine RPM varies on the order of 8-10 degrees between slow gyro flight and fast, if no in-flight pitch adjustment is possible.
 
Abid, when I had the original ground-adjustable propeller, I typically set it for 5600 rpm but it climbed so slowly (especially on initial take-off where the engine is still fairly cold) that I was not willing to take passengers up like that, and would adjust it to 5700+ rpm before bringing a passenger. Which is a pain of course. At 5400 RPM you just can't take off here; that's way too low. Due to rising terrain you need to climb at a decent rate.
 
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