rotor size vs performance

K3vin

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Does anyone have any practical experience with different rotor lengths used on the same gyro in an ultralight setup? I'm in the process of having an ultralight gyro built for me starting with a Bensen gyro airframe. The below seat mounted gas tank is being replaced with a seat tank and a Kawasaki 440 (43 hp) with a 3 blade prop is proposed. The rotor would be 21.5 feet as proposed but I'm concerned as to whether this will produce acceptable performance. From what I've read I think I would get better overall performance with lighter blade loading and a resulting slow rotor speed from longer rotors. btw - I'm the mythical 150lb pilot!
 

down under

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Lower blade loading definitely requires less power at low airspeeds, -40knt. The blades I prefer for low speed work have a blade loading of approx 35lbft. These bigger blades are slower to respond to controls.
In hot thin air there is also a noticeble reduction in engine revs up to 50-60knt with the bigger blades.
With the open machine I have found no increase in drag up to 80knts.
 
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brett s

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Everything I've seen here says the Kawasaki 440 probably won't cut it even for a light guy like you - what it's rated at vs what power it really makes in the real world are apperently two different things.

I can't recall ever seeing one that was truly successful, and you're definitely not the first to try!

Rotax 447 or 503 is a much better choice & will definitely work.
 

Passin' Thru

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Everything I've seen here says the Kawasaki 440 probably won't cut it even for a light guy like you - what it's rated at vs what power it really makes in the real world are apperently two different things.

I can't recall ever seeing one that was truly successful, and you're definitely not the first to try!

Rotax 447 or 503 is a much better choice & will definitely work.

Hey Brett, I agree 100%, but didn't you hit the wrong thread? :lol:

Don't worry, it happens to all of us!:eek:
 

down under

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Some more info on my first post. The blades I used for a comparison whe 26ft and 28ft x 8" extruded rotors. 25ft DWs flew at a lower engine rpm at 30-35knt's than either of the larger blades. Below this speed the bigger blades were better, and no noticable power difference at higher speeds.
 

K3vin

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Thanks for the response guys. I'm skeptical of the Kawasaki myself and I've expressed it to the builder so we have an agreement that we will swap it out for a Rotax 447 (Gyrobee & Air Command) which have been demonstrated to be sufficient. I have found some articles saying the Kawasaki won't do the job but I can never find the details as to what prop was used to test with. Obviously the prop does need to match the rpm's being pulled and the torque characterstics of the engine. So using the same prop on both engines would not necessarily be an effective test. I have found several people (including my builder) who claim the Kawasaki has plenty power. The blades in question were listed as Bensens but they have a solid sheet of aluminum not sections so I'm not sure they are Bensens, based on what I have read here. Could they be Brocks?
 

scottessex

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I have a fresh rotax 532 with 2:00 to 1 gearbox, that puppy would scream!
I'll even throw in a 52" prop, and a radiator,for $2K!
take that kawasaki back. :)
 

MikeBoyette

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Most likely Rotordyne or Rotor Hawk blades. Bensen and Brock blades are basically the same with segmented top skins.
 

Friendly

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I have a fresh rotax 532 with 2:00 to 1 gearbox, that puppy would scream!
I'll even throw in a 52" prop, and a radiator,for $2K!
take that kawasaki back. :)

Scott,
He would be better with the 532 probably, but I dont think he will make ultralight with it. The muffler that Jbyrd sells with the K engine must weight 30 lbs by itself.
I have a friend with a K engine, he is starting to taxi his gyro. I am very interested in what it will do. I think the static thrust test was 245lbs. He had some belt slip issues, I think that is resolved.
 

Friendly

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Kevin,
I am that 250 lb pilot, I flew 22 ft Dragon wings up until about a week ago. The dragon wings are within a pound of the Bensens but the difference in lift is most noticeable. I don't think you will make the 63 mph limit with the smaller rotors , but you might with that k engine. I recorded about 50lbs difference in thrust between the 503 and the K engine. The K engine was not running properly at the time so it is not a fair comparison. Both engines had Ivo 60 in prop. I should be able to get some new test in the near future as I have the 503 at my place again and the K engine is local. Making the 254 lbs is much harder than it looks. Good luck in your endeavor and hope you reach your goal
 
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