# Thrust Numbers

#### kmccormick

##### Newbie
I have been informed that in order to have a "fun" gyro, you need to have a static thrust number of around the weight of the empty aircraft (254 lbs). Has anybody found that they fly with much less thrust than this, and were still able to climb over the 25 ft tree that is 1000 ft from the end of the runway?

Kevin
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CL360

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#### gyroplanes

##### FAA DAR Gyropilot
Sorry to burst your bubble, but I believe it is the flying weight of the aircraft, with you and fuel onboard.

I do to Tom .

#### rfi

##### Senior Member
A good rule of thumb is that you need thrust equal to half the gross weight of the gyro to have respectable rate of climb.

#### kmccormick

##### Newbie
Sorry to burst your bubble, but I believe it is the flying weight of the aircraft, with you and fuel onboard.

That would mean that I would need over 500 lbs of thrust. Man....That would take 100 hp plus. Half gross would be roughly 250 lbs with fuel. I can handle that thrust. I think 1000fpm would be respectable, but with with a 1:1 thrust/weight ratio, that means I can hover:whoo: Maybe I need to power the rotor...ha
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XVZ1300

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#### gyromike

Staff member
That would mean that I would need over 500 lbs of thrust. Man....That would take 100 hp plus. Half gross would be roughly 250 lbs with fuel. I can handle that thrust. I think 1000fpm would be respectable, but with with a 1:1 thrust/weight ratio, that means I can hover:whoo: Maybe I need to power the rotor...ha

I think you misunderstand.
The rule of thumb is:
Thrust, in pounds, should equal ½ of your All Up Weight (AUW).

My AUW on my Bensen is 515 lbs. with me and a full tank of gas.
My thrust is ~ 300 lbs.

It performs okay.

#### GyroDoug

##### Active Member
HP rule of thumb

HP rule of thumb

The rule of thumb I was taught was that you need to have HP to Weight ratio of 1 HP per 10 lbs of Gross Weight or better. So a 600 lb. Gyro and Pilot would need at least 60 HP to be able to fly well.

My Gyros gross weight will be about 900 lbs so I should be able to fly reasonably well with 90 HP but since I want to be able to fly in the mountains and areas where better climb performance would be an added safety feature I am planning on having 100 HP. You also need to take into account the degradation of HP available with density altitude when you decide how much engine you will need to fly well. At least that's what I have been taught and believe.

Gyro Doug

#### Greg Mitchell

##### Senior Member
From the Propellors thread regarding thrust tests.

Confirmed with Larry Neal that he repeatedly got 280 lbs of thrust on the prototype Butterfly with 503 single carb. Tennessee wood prop 60" X 40 pitch.

Since I had the Butterfly Ultralight at less than 254 lbs, I have added
31lbs with extra blade weight...Bensens to Patroneys 21' 9" to 23' 6" (Glass Blades 76 lbs all up)
12.5 with extra tail weight (T Tail)
46 lbs with pre-rotator (MLS)
25 lbs of fuel (5 gallon tank not full to top)
220 lbs pilot weight (probably more fully dressed)

I am now looking at approx AUW 590lbs with the 4/5's tank of fuel.

Before installation of the MLS the Blue Emporer Butterfly on the larger disc flew about the same as when it had Bensen's. I expect to see a major change in performance this time around. I'll keep you posted.

I realise you want on avg half the thrust of your AUW, so I guess I will be marginal.

Question fellas if you please, can you throw some AUW's of your gyros at us when you are listing your thrust test numbers. The thrust test on it's own is only part of the story. I am curious to know how many pilots run at or on the border line off this marginality. (if that's a word)

Cheers,

Mitch.

#### kmccormick

##### Newbie
I think you misunderstand.
The rule of thumb is:
Thrust, in pounds, should equal ? of your All Up Weight (AUW).

My AUW on my Bensen is 515 lbs. with me and a full tank of gas.
My thrust is ~ 300 lbs.

It performs okay.

I understand Mike. I was just appeasing those who thought I needed 1 pound of thrust per lb of AUW. I should think that 250 lbs of thrust will get me into the air in the ultralight category.

Mike, Do you know any Lacour's around Mouton Cove? Will you make it to Gonzales this weekend?
________
Yamaha DT125

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#### gyromike

Staff member
Can't say that I know any Lacours.

I plan to be a Gonzales for Saturday if the weather is decent, but I probably won't bring my gyro.

#### Greg Mitchell

##### Senior Member
Above figures should read....after finding fault with my numbers and having them tweeked.

Since I had the Butterfly Ultralight at less than 254 lbs, I have added
34lbs with extra blade weight...Bensens to Patroneys 21' 9" to 23' 6" (Glass Blades 76 lbs all up)
3lbs with extra tail weight (T Tail)
38 lbs with pre-rotator (MLS)
15 lbs of fuel (5 gallon tank 1/2 full)
220 lbs pilot weight (probably more fully dressed)

So my AUW for testing the MLS will be 564 lbs

Estimated/expected thrust test values of 280 lbs

May disc loading will be less now, so with the very efficient composite Patroney Blades and my thrust test which I hope will afford 280 lbs, I feel the Butterfly will handle it. I should have it thrust tested within a couple of days.

Mitch.

#### gyroguy

##### Senior Member
More thrust with autogiros?

More thrust with autogiros?

In a Popular Rotorcraft Flying article by Chuck Beatty, published in October 1977, Beatty gave a formula to calculate thrust. He stated that if a propeller had no losses, static thrust would be calculated as:

Thrust = (Horsepower X Diameter)2/3 X 10.4

Beatty added that allowing for profile drag, tip vortices, and other losses, the 10.4 would become 6.5 (a propeller of 62.5 percent efficiency). Beatty noted that in an aircraft speed range, the 10.4 would become 7, because with a 5- 5.5-foot propeller the tip speed is slower.

In 1999, George Pate, a now-deceased autogiro designer, calculated thrust requirements for some of the old-time 1930s autogiros. In Pate's calculations, the 6.5 factor was used, because the classic autogiros in the examples have propeller diameters larger than 5.5 feet.

So, using the equation "Thrust = (Horsepower X Diameter)2/3 X 6.5," Pate compared classic tractor autogyros of the 1930s to the "1/2 pound thrust for 1 pound of gross weight" rule of thumb for modern pusher gyroplanes.

Autogyro.............Horse-..Propeller....Gross.....Thrust......Pusher.....Difference
Make and............power...Diameter...Weight...Produced...Thrust....(Pusher thrust
Model..............................(Feet).......(Lbs).......(Lbs).....Needed.....- Tractor ")
Cierva C.19 Mk 1...100.......6.75..........1,300.......498.........650......-152 (-23%)
Pitcairn PA-24.......160.......8.00..........1,800.......763.........900......-137 (-15%)
Kellett D-1............245......8.80...........2,400....1,079......1,200......-122 (-10%)
Pitcairn PA-19.......420.....10.00...........4,200....1,683......2,100......-417 (-20%)

Pate concluded that classic tractor autogyros were more efficient, because they had been flown with 10 percent to 23 percent less thrust than "1/2 pound thrust for 1 pound of weight" rule of thumb for pusher gyroplanes.

What do you think of that?

#### GyroDoug

##### Active Member
In a Popular Rotorcraft Flying article by Chuck Beatty, published in October 1977, Beatty gave a formula to calculate thrust. He stated that if a propeller had no losses, static thrust would be calculated as:

Thrust = (Horsepower X Diameter)2/3 X 10.4

Pate concluded that classic tractor autogyros were more efficient, because they had been flown with 10 percent to 23 percent less thrust than "1/2 pound thrust for 1 pound of weight" rule of thumb for pusher gyroplanes.

What do you think of that?

I wonder if a big part of that isn't due to the fact that a tractor gyro is more streamlined and faired with a lot less of the airframe sticking out in the wind causing drag. Most pusher gyro's, because of the typical speeds they are flown at, don't seem to be too worried about drag. I wonder if that draggy airframe soaks up the additional thrust required to fly well. It would be interesting to see if a pusher design that had been cleaned up aerodynamically, could fly well with thrust #s closer to what the tractors used. Anyway, that's a thought that came to my mind.

Gyro Doug

#### giro5

##### Senior Member
maybe cause the prop is out in clean air has a major effect to the benefit of a tractor style.

#### Udi

##### Platinum Member
There are a few reasons the old autogyros were more efficient than current pusher gyros:

- As Doug said, the airframe was more streamlined and has less parasite drag

- As giro5 said, the prop itself was more efficient both because it was larger and also because it operated in "clean" air. I would say prop efficiency with a large tractor configuration is at least 75%.

- The rotor itself was more efficient. Those large multi-blade rotors used to turn significantly slower than today's two-blade teetering rotors. This means less parasite drag.

- Because the airframe had less drag, the gyro could fly faster with the same power. A gyroplane rotor is more efficient (less induced drag) at higher airspeeds, so -- by reducing airframe drag you actually benefit twice - once from the lower airframe drag, and another time from a lower rotor induced drag at higher airspeeds.

Udi

#### Murray Barker

##### Junior Member
Seeing as you all are talking tractor gyros and thrust etc I will share my experience with tractor verses pusher.

This is a new gyro I have just finished building and have only got it to fly in ground effect so far.

Why??? because the fuselage,even with the small frontal area it has soaks up over 100 LBS of static thrust.

This I tested with three props,two tractor,one pusher.

With the tractor props the best was 250 LBS.

With the pusher prop 350 LBS at almost full power.

The engine in the gyro is a 532.

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#### ben

##### Gold Member
now thats cool murray

swwewweeeeeeeeeeeeeeeeeeeeeeeettttw

what that weight??????

#### Udi

##### Platinum Member
What size prop do you have there, Murray? You may want to try a larger 2-blade prop.

Your engine and radiator are located in the high-velocity area of the prop. Mounted as you have them is creating much more drag in a tractor configuration than a pusher configuration. Get the radiator out of there and build a cowling.

If a pusher configuration was inherently more efficient than a tractor configuration, most prop airplanes would be pushers. Making an efficient cowling, one that allows for enough air flow into the radiator without creating too much drag losses is an art.

Udi

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#### Friendly

##### Platinum Member
Murry,
Is that your own tail design? , do you have more pictures. You know you can't post something unique like that and only show one picture.

Nice gyro.

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