Prop Diameter

[AviomaniaTexas]

I have been getting lots of advice from several of you on this including Scott Essex, Jon Carleton, David McCutcheon, Jeff Tipton, Kurt Carlsen, Tom Milton, Greg Mills, Gary Weaver and Kevin Koehler. It is appreciated!!!

Here is the problem we are trying to overcome before a test flight. I have a 60 HP MZ 202 on my CLT Air Commad gyro with a 3.11:1 gear box and a 62" 3 Blade Warp Drive Prop. It is apparrent that the Prop and gear box are not a good combination based on the static thrust numbers we saw last fall of only 270 lbs out of the 60 hp engine at 15 degrees pitch and 5950 max rpms and addtional research on prop diameter, horse power, reduction ratios and number of prop blades support the problem. I either need to change the gear ratio or get a longer prop to truly fix the thrust issue.

For now I am looking for the least expensive and least labor intensive method to find a solution.

After talking with Leon Massa at Compact Radial Engines, I can take some pitch out of the prop and go up to 6200 RPMs static. His redline is 6250 as posted with the engine manual, but, he says going over a bit for short periods of time in flight wont be a problem.

So before exchanging the prop with the factory, we will check the static thrust at 6200 RPMs. I need to get around 330 lbs of static thrust or more with a current gross weight of 640-650 lbs. If this test is not close, then I will look at changing to a larger prop by raising the engine just 1".

Currently there is 2 inches of clearance between the Prop and Keel. By raising the engine 1 inch, I believe that I can change to a 66" Prop.

Here is the math. Currently it has 31" blades with 33" between the Keel and the center of the Prop for the 2" clearance. Raising the engine just 1" provides 34" between the Keel and the center of the Prop. A 33" blade would still have 1" of clearance.

My new mast is 4 inches taller than the original, so going 3 inches higher with the prop should not be a problem.

I considered tilting to 3 degrees, but, that could require multiple modifications to the mount that can wait until next winter.

Photos are posted on my blog of the project. https://texassportpilot.blogspot.com/

 

[phantom]

A 66 inch is still a very small prop, if I was setting the smallest prop I would try is a 72 inch, a 76 would be better if you could swing it, it's not a matter of will it fly but how much reserve power you have at cruise, if you need to run near max power to fly you will burn a lot of fuel and engine life will be short.
Norm.

 

[ultracruiser41]

What's the all up weight of the gyro?

 

[AviomaniaTexas]

72" Prop

72" Prop

A 66 inch is still a very small prop, if I was setting the smallest prop I would try is a 72 inch, a 76 would be better if you could swing it, it's not a matter of will it fly but how much reserve power you have at cruise, if you need to run near max power to fly you will burn a lot of fuel and engine life will be short.
Norm.

Thanks Norm, I agree with the possibly of not having enough power to stay at Cruise.

The issue is clearance for the Keel and Rotor Blades. To increase the prop radius 5 inches for the 72 inch prop, I would need to raise the engine 4 inches, that would raise the prop radius 9 inches closer to the rotor blades. That would require raising the rotor head by changing to longer cheek plates, and that would require new control rods, perhaps pre-rotator cable, etc.

All that can be a project next winter, if I am not happy at 62" or 66", depending on the outcome of our test this week and future flights. Or as a final course of action, I could just save the dollars and labor and get a bigger motor with the correct gear box.

Right now I just want to get it flying.

 

[AviomaniaTexas]

Weight

Weight

What's the all up weight of the gyro?

Gyro Dry 370 lbs (24 DW Cruiser Blades)

5 Gallons Fuel minimum 31 lbs (Seat Tank capacity is 7 gallons, the two pods/brackets etc. could be removed to save additional weight)

Pilot 240 lbs (I need to lose 20 lbs)

Gross Weight 641 lbs

 

[scottessex]

From doing numerous thrust tests a long time ago.......the rotax 582 2.58, or so with a 60" prop seemed to be capable of 340-360, we tested about 6 machines all the same day at Wrens one year.

 

[Abid]

66 inch prop would be ok IMO for the 60 HP engine. We use a 70 inch prop for 100 and 115 HP 912 and 914
Good luck with that engine.

 

[scottessex]

Tom just for a gee wiz example here are some results I did years ago with a 503 with a 2.58 box.
The 2.58to1 box was obviously way wrong for the small" props, but at least it gives you an idea of how much prop diameter changes things.
https://www.rotaryforum.com/forum/showthread.php?t=14718&highlight=thrust+test

 

[AviomaniaTexas]

Tom just for a gee wiz example here are some results I did years ago with a 503 with a 2.58 box.
The 2.58to1 box was obviously way wrong for the small" props, but at least it gives you an idea of how much prop diameter changes things.
https://www.rotaryforum.com/forum/showthread.php?t=14718&highlight=thrust+test

Scott, take a look at it Saturday, I can go to a 64 without changing the engine height. 1 more inch gets it to 66. I don't think raising the engine 2 inches for a 68 inch prop will work.

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[AviomaniaTexas]

Tom just for a gee wiz example here are some results I did years ago with a 503 with a 2.58 box.
The 2.58to1 box was obviously way wrong for the small" props, but at least it gives you an idea of how much prop diameter changes things.
https://www.rotaryforum.com/forum/showthread.php?t=14718&highlight=thrust+test

Thanks for sharing the thread, good stuff!

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[richardkennedy]

Tom, I would call Warp Drive and ask their opinion about adding a 4th blade. You would have to buy one blade and a four blade hub but it might be worth looking into.

 

[phantom]

Prop diameter has nothing to do with horse power, I'v had 90 inch props on 12 hp engines to move a heavy craft at low speed and I'v had 52 inch props on 300 hp engines to do a different job, there are two ways to move a craft without wheels connected to an engine, one way is to accelerate a small volume of air to very high speed in the opposite direction that you want to move, a jet engine will do this, it's not very efficient but it will go fast, the other way is to accelerate a very large volume of air at a speed a little faster than you want to go, this is a lot more efficient.
Norm

 

[AviomaniaTexas]

Tom, I would call Warp Drive and ask their opinion about adding a 4th blade. You would have to buy one blade and a four blade hub but it might be worth looking into.

I have and Daryl says that I need a longer prop for the 3.11 drive and that an additional blade may also help. An extra blade would reduce the pitch and has been rumored to help on 582 powered Dominators with 60 or 62 inch props with 2.55 drives. My drive simply turns a short prop too slow.

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[GyroRon]

You also need to come to grips with the fact that the MZ202 is almost certainly not a 60HP engine. In all the thrust testing results I have seen with that engine, it produces thrust much closer inline with what a Rotax 503DCDI produces and not close to what a 582 will make.

Adding a 4th blade is not exactly the best solution, because the extra blade will create additional drag. The additional drag may offset any gain in having the lower pitch in the blades.

Raising the engine a inch and going to the bigger diameter would help. Putting yourself and your machine on a diet would also help. Ask Ultracruiser how much of a difference it made when he put his first gyro on a diet....

Also is there not a different ratio you can put into the gearbox?

 

[j bird]

I would think Spinning a prop at 1930 rpm (6000 engine rpm with 3.11 gears) is way to slow. 2.18 gears would get you 2750 prop rpm, which is more like it for a 62" prop. I would think lowering the prop pitch would also help.

 

[Doug Riley]

Also, be careful about the mass of the prop. The smaller Rotax "B" gearboxes, at least, are limited to props of no more than a certain spinning mass (Something less than a 60" 3-blade Warp, IIR, never mind a 4-blader).

Warp Drive props are relatively massive, and certainly a 4-blade Warp will be quite a chunk of mass to mate to a chattering little 2-stroke. The gearbox will be stuck in the middle, getting chewed and pounded by the torque pulses. Make sure that the MZ box is rated for a spinning mass this large. The manufacturer should have the spec available.

 

[AviomaniaTexas]

Also, be careful about the mass of the prop. The smaller Rotax "B" gearboxes, at least, are limited to props of no more than a certain spinning mass (Something less than a 60" 3-blade Warp, IIR, never mind a 4-blader).

Warp Drive props are relatively massive, and certainly a 4-blade Warp will be quite a chunk of mass to mate to a chattering little 2-stroke. The gearbox will be stuck in the middle, getting chewed and pounded by the torque pulses. Make sure that the MZ box is rated for a spinning mass this large. The manufacturer should have the spec available.

Agreed, the 3.11 gear and this engine would work with a much longer 2 Blade prop.

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