Engine power for a ultralight

Aviator168

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Trying to build an ultralight gyro. What is the maximum engine power I can use for it to stay in the ultralight limit, like less than 62mph with MTOW less than 430lb?
 

BEN S

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Look up Federal Aviation Regulation (F.A.R.) part 103.
Last I checked it is 254 lbs. Total AUW. Unless you have some kind of safety features that are an exception, like floats.
Other reqs were (from memory) 5 gallons of fuel, single seat only....
But if you want to know for sure, thats where to google.
 

Aviator168

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430lb I indicated is total weight including fuel and payload. Empty weight is about 200lb. I am just asking the power required for such a gyroplane.
 

Jean Claude

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It depends on the diameter of the rotor and the diameter of the propeller.
With a 23 'x 7 "rotor and a 63" diameter propeller, more than 35 hp are required for a total weight of 430 lbs
 

Brian Jackson

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430lb I indicated is total weight including fuel and payload. Empty weight is about 200lb. I am just asking the power required for such a gyroplane.
A popular (and safe) design is the GyroBee by Ralph Taggart. The prototype was a true 103 ultralight with a Rotax 447 which, IIRC, clocks in at ~39 HP. I'm curious about the 200 lb. empty weight. It's very difficult to build under the 254 lb. legal limit with conventional materials and components. How was the 200 lbs. estimated?
 

WaspAir

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430lb I indicated is total weight including fuel and payload. Empty weight is about 200lb. I am just asking the power required for such a gyroplane.
If you have a max weight budget value in mind for the powerplant choice, you could state that, and people could tell you what powerplant installed weights for various combinations they know about from their experience.

Minimum required power to make it fly decently on warm days at your all-up weight might be a bigger practical concern than having too much power and busting the speed limit (as you asked in the first post). The 35hp mentioned by Jean Claude is a number I have seen mentioned many times as a floor value for a practical ultralight.
 

XXavier

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It depends on the diameter of the rotor and the diameter of the propeller.
With a 23 'x 7 "rotor and a 63" diameter propeller, more than 35 hp are required for a total weight of 430 lbs
Interesting...

Could you please write down the derivation...? I'm interested in the general case...
 

Jean Claude

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No simple formulas, Xavier. Just my many simulations with the best ratio power/weight of engine, the best ratio load/ weight of airframe and the best ratio weight / diameter of rotor.
I have never obtained a result lower than 35 hp to takeoff with a nose-up rotor of 18 degrees.
This angle gives a takeoff in a reasonably short distance. Takeoff with less angle is obviously possible but does not seem to me to be practical enough.
Here, I'm talking about the traditional layout, but of course more complex and expensive layouts could be better (bi-rotors side by side for example)
 

XXavier

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No simple formulas, Xavier. Just my many simulations with the best ratio power/weight of engine, the best ratio load/ weight of airframe and the best ratio weight / diameter of rotor.
I have never obtained a result lower than 35 hp to takeoff with a nose-up rotor of 18 degrees.
This angle gives a takeoff in a reasonably short distance. Takeoff with less angle is obviously possible but does not seem to me to be practical enough.
Here, I'm talking about the traditional layout, but of course more complex and expensive layouts could be better (bi-rotors side by side for example)

Thanks, I see...

I've done a (very rough) estimation of the power required by a gyro of 430 lb => 194 kg = 1900 N Assuming a L/D of 3 and a horizontal airspeed of 41 mph = 18 m/s, a glide would require a 'gravitational power' of 1900 x 18/3 = 11,4 kW = 15,3 HP, but if the prop has an efficiency of 50%, for a (barely) s/l flight the shaft power would have to be double, close to the 35 HP that you mentioned...

But I was intrigued by the (theoretical) influence of an oversized rotor and an oversized prop... Hence my query...
 

Aviator168

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To answer the question above about my ultralight. I was hoping an engine of 35hp to 40hp for a basic flying machine. I want to build it as light as possible. Other than the rotor head and the engine, the rest will be built with CF (I do have composite experience). So it is not inconceivable for it to be about 200lb.

XXavier,
Do you have a spreadsheet to do the power estimate?
 

XXavier

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To answer the question above about my ultralight. I was hoping an engine of 35hp to 40hp for a basic flying machine. I want to build it as light as possible. Other than the rotor head and the engine, the rest will be built with CF (I do have composite experience). So it is not inconceivable for it to be about 200lb.

XXavier,
Do you have a spreadsheet to do the power estimate?
No, I don't. It's Jean Claude who has designed his spreadsheet...
 

Aviator168

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Minimum required power to make it fly decently on warm days at your all-up weight might be a bigger practical concern than having too much power and busting the speed limit (as you asked in the first post). The 35hp mentioned by Jean Claude is a number I have seen mentioned many times as a floor value for a practical ultralight.
I thought so. 40+ hp is better. It all comes from the huge drag of the rotor. Does lamina blades help?
 

Jean Claude

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Xavier's calculation is correct, because the finesse he evaluates corresponds to that of the nose up angle of 18 degrees.
But he neglects add the weak parasitic drag of the airframe at this time.
On the other hand, his speed of 18 m/s is suitable for lifting the weight of 430 lbs at this angle of attack with a 23' rotor.
A larger rotor would theoretically allow a slower takeoff, and therefore less power. Unfortunately a larger rotor rotates more slowly, and requires heavier blades to limit coning. And a slower take-off decreases the efficiency of the propeller (unless a larger propeller)
Hence the low limit of 35 Hp

Laminar blades are a view of the mind. The working environment of a rotor does not allow the blade profiles to be laminar as in a wind tunnel with low turbulence
 

hismiths

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I've owned and rebuilt an EXPERIMENTAL fixed wing (Spezio TuHoler). I believe you can STATE the max airspeed in your aircraft operating manual. There is no requirement to demonstrate it. So, the entire issue may be moot.
 

scottessex

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I think the Rotax 447 weighed 87 lbs and made 40 hp, the pollini weighs <40lbs and makes 36.5 hp, so it does have much better power to weight ratio.
 

scottessex

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I think the rotax 447 weighed 87 lbs and made 40 hp, the Thor weighs <40 lbs and makes 36.5 hp, so it does have a much higher power to weight ratio.
Look through this thread here, some of the videos are not up any more, but it will give you an idea:
 

Aviator168

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I saw that video. At the time I did not know the power of the engine and that was the reason I asked the question here.
 

scottessex

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The original gyro did use a smaller engine, He later upgraded to the Thor engine.
 
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