Gyro Vs. Helicopter Cruise Efficiency

GyroJoel

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Does a gyro really have a cruise efficiency advantage over a comparable size/weight helicopter?

In theory, it seems like it would as the helicopter rotor should be less efficient at producing thrust than a gyro's prop.

But the evidence seems not to support this. For example, comparing a Sparrowhawk to an R22, which are both around the same weight, the R22 appears better in all categories of performance, incuding range. And the R22 has a 131 HP engine while the SH has a 165 HP.

Of course the gyro has all of the advantages of simplicity and cost. But I am just referring to efficiency (i.e. total engine HP required to travel at the same speed -- or if we assumed both machines had the same engine then GPH of fuel consumption).

Can one of you smart people out there (C. Beaty?) help to educate me on this?

Thanks!
 

iNuhBaD

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I'm interested in this information too, but I feel I have a sufficient understanding of physics to have an idea of why.
 

DennisFetters

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Pound for pound, a helicopter can be more efficient than a gyroplane. An aircraft depending on 100% of it's lift from the rotor system will always be more efficient being "pulled" through the air by that system, than an aircraft "pulling" it's rotor system through the air. A helicopters' lift pulls it forward, while a gyroplanes' lift drags if back.

The transmission of power to a rotor system is much more efficient being directly injected into the system through a gearbox then a rotor system being powered non-directly through the forward velocity achieved by a propeller (which looses efficiency) and then to the rotor system from the forward velocity of air (which looses efficiency again).
 

gyromike

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Does a gyro really have a cruise efficiency advantage over a comparable size/weight helicopter?

In theory, it seems like it would as the helicopter rotor should be less efficient at producing thrust than a gyro's prop.

But the evidence seems not to support this. For example, comparing a Sparrowhawk to an R22, which are both around the same weight, the R22 appears better in all categories of performance, incuding range. And the R22 has a 131 HP engine while the SH has a 165 HP.

Of course the gyro has all of the advantages of simplicity and cost. But I am just referring to efficiency (i.e. total engine HP required to travel at the same speed -- or if we assumed both machines had the same engine then GPH of fuel consumption).

Can one of you smart people out there (C. Beaty?) help to educate me on this?

Thanks!
The R22 is a fairly slick machine aerodynamically.
Most gyros aren't.

Not saying that's the answer, but drag reduction seems to be overlooked on most gyros.
The Xenon seems to do fairly well on 100 hp, so you can see how drag reduction can help.
 

ferranrosello

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I agree, Mike. Not only the body's drag. Helicopters had been developed for more than 70 years. Autogyros only were developed for 15 years. I believe there are a lot of things to improve in our rotor systems..

But a helicopter only can be more efficient than a gyro at very low airspeeds. The tail rotor drag penalty in forward flight is notable.

Ferran
 

DennisFetters

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I agree, Mike. Not only the body's drag. Helicopters had been developed for more than 70 years. Autogyros only were developed for 15 years. I believe there are a lot of things to improve in our rotor systems..
But a helicopter only can be more efficient than a gyro at very low airspeeds. The tail rotor drag penalty in forward flight is notable.
Ferran
................What?
 

Tina

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I agree, Mike. Not only the body's drag. Helicopters had been developed for more than 70 years. Autogyros only were developed for 15 years. I believe there are a lot of things to improve in our rotor systems..

Ferran
I thought it was the other way around? Gyros came first then helicopters.

Take a look at this helicopter and the drag it is about to encounter!
 

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PW_Plack

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In theory, it seems like it would as the helicopter rotor should be less efficient at producing thrust than a gyro's prop...

What theory is that? If a prop gets more efficient as diamater increases, why would not a powered 30-foot rotor be much more efficient than a relatively small prop?
 

Joe Pires

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I thought it was the other way around? Gyros came first then helicopters.
I think what he means is once the helicopter was invented all the developmental energy went into the new creation leaving Gyro's not much changed from that point.
 

Heron

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What about glide ratio? How they compare?
Also in gyros what is the max and min. glide ratio so far?
thanks
Heron
 

GyroDoug

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What about glide ratio? How they compare?
Also in gyros what is the max and min. glide ratio so far?
thanks
Heron
I'll take a guess at this one and you more intelligent types can correct me if I am wrong.

I don't think either Gyros or Helicopters have anything to brag about with glide ratio. They both come down pretty steeply (at least compared to their fixed winged cousins). However I believe a Gyro will typically have longer rotors for the same weight aircraft and therefore a larger rotor disk area and since they are both in auto rotation when they are gliding the aircraft with the bigger disk area will have a better glide ratio. Am I thinking correct on this?

Gyro Doug
 

brett s

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Yep, disk loading is usually much higher in helicopters.

The R22 is only using about 100 hp in a 90 kt cruise when heavy...
 

Heron

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I am with you on this line GyroDoug . . .also the collectve operation (I think) will rob some altitude in order to load a smaller disc.
If a gyro with 26 foot disc and 7 inch chord can do 4 to 1 ratio, what happens with a 8 inch chord same dsize disc?
thanks
Heron
 

gyromike

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Also, helicopter rotors are twisted with more pitch at the roots than at the tips for hovering efficiency. The tradeoff is that they are less efficient at autorotation than a set of blades with no twist, or twisted like a set of DW's.

That's why the Florida boys would use Hughes blades, but mounted upside down and spun backwards.
 

WaspAir

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glide ratios vs. sink rate

glide ratios vs. sink rate

However I believe a Gyro will typically have longer rotors for the same weight aircraft and therefore a larger rotor disk area and since they are both in auto rotation when they are gliding the aircraft with the bigger disk area will have a better glide ratio. Am I thinking correct on this?

Gyro Doug
I'm still thinking on this one, but your conclusion isn't yet obvious to me. There's a difference between reducing your sink rate on the one hand, and increasing your best glide ratio on the other. A change that might produce a lower rate of descent only gives a higher glide ratio if you can simultaneously maintain or increase forward speed. If you slow the forward speed as well, you may not improve the ratio at all (you might just follow the same path at slower speed). The analogy may be flawed, but in the fixed wing glider world, low loading doesn't help. We commonly fill up tanks in the wings with water ballast, make a huge change in wing loading, and get absolutely no change in best glide ratio (we do it to shift our best glide to a higher speed). A lightly loaded glider can do very well in terms of gliding endurance (height loss vs. time) but poorly in terms of range (height loss vs. ground covered). It's an issue of lift to drag ratio, that I don't think is purely determined by loading.
 

ckurz7000

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I don't know, but it seems to me that a heli ought to be more efficient because it doesn't use airflow to spin the rotor in normal cruise. I seem to remember a statement by Mr. Bensen to the effect that 1 hp spent in driving the rotor is as good as 5 hp spent in driving the prop.

-- Chris.
 

Jtravis1

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Just for reference, the max glide ratio of a r22 is 4:1. It is much better in a R44, 4.8:1. You plummet like a rock in a Hughes 500, somewhere under 4:1. It must be noted that max rate of glide is not the single measure of autorotation performance.

As Waspair said, there is a difference between glide ratio and min rate of decent. The min ROD for most any rotorcraft, should be at the lowest point on the power required curve. This will not give the best glide ratio, but rather the most time before ground contact.

For a R22 this is 53kts. This will yield about a 1100fpm decent. Max glide on the other hand is at about 80kts and 90% rotorrpm. Much higher ROD +/- 1600-1800, but you will go much farther.

People must remember that the R22 was built for speed. Using it as a baseline to compare efficiency might not give accurate results. Both the 22 and 44 are the fastest helicopters in class with the 22 being far faster then any 2 seat piston, and the 44 will outpace most jetrangers even with only 205 hp max continuous.

Here are some other examples, the Hughes 269c has a 180hp engine and only cruises about 70-75kts. An enstrom F28 is about 220 hp and only cruises about 75-80kts.

I think helos achieve better speed because they are more streamlined. The rotor of a gyro is like a big parachute. I think efficiency could be gained in a gyro if you had a collective. This would allow you to keep RPM down as speed was increased. This would waste less energy in drag.
 
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ferranrosello

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Dennis and Tina, the autogyro is older (first flight in 1923) than helicopter (first real flight in 1936). But once the helicopter was a fact, just at the end of WWII, all the investigation efforts were directed to helicopters and the gyro was entirely forgotten. Mr. Bensen found a new application to an existing technology; by really he didn’t created anything.

Our gyro blades are not innovations, in fact the airfoil (everybody uses the same one) was developed a lot of years ago and there are not investigation and development programs in benefit of autogyros. This is a very different history from helicopters. Isn't it?

Ferràn
 
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