Gyro Vs. Helicopter Cruise Efficiency

XXavier

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I'm sure it's entirely possible that you would find it hard to believe. It requires a good deal of experience to understand something as complex as a helicopter.

First, just because you could maintain a hover while only using 10 to 15 percent of anti torque power in a lightly loaded helicopter, does not mean that is all that needs to be available, or all you will use. The heaver you load the helicopter, the higher the percentage of power becomes to counteract the torque, like when another person comes aboard, or you fuel up, or both.

Another little thing we like to have available in a helicopter is called maneuverability. Like.... while in a hover we like to be able to turn the tail the opposite direction it is being torqued once in a while. This requires more of a percentage of power to offset the balance of anti torque. It can require 20% or more of used power to do a pedal turn opposite of torque.

We also like the ability to hover or turn the tail into strong cross winds, which again increases the amount on anti-torque required up to 25% or more.

These parameters must be calculated into the requirement and allocation of power used, and available.
Well, yes... I'm not saying that you're not the expert here. But I insist: your statement was too general.

By invoking all needs to be available, higher loadings and strong cross winds, you have already modulated that statement. It's clear now. While designing a helicopter, you may need to reserve a large fraction of its engine power for the tail rotor, but we weren't talking about helicopter design constraints. Just comparing normal rotorcraft power needs.

XXavier
 

DennisFetters

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Well, yes... I'm not saying that you're not the expert here. But I insist: your statement was too general.
<Cut>
Just comparing normal rotorcraft power needs.

XXavier
First you say I'm being too general, and in the same statement you agree that we were talking in general about "normal" rotorcraft power needs. I don't think any answer will do for you.

The requirements I stated are for "normal rotorcraft power needs", just as you said was the discussion.
 

XXavier

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The exceptional is... exceptional, and hence excludes the normal.

Exceptional needs have to be taken into account in any design, and not only of rotorcrafts. But exceptional needs, being so, aren't normal features. And you're trying to label exceptional needs as normal features...

XXavier
 

DennisFetters

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I appreciate your answer, Dennis. Thanks for sharing your fantastic experience.First of all I think that is not fair compare dissimilar machines, such an open frame gyro with a full enclosed and streamed line helicopter.
I'm sorry, you must not have read what I wrote;
"My 582 Commander Elite gyroplane with a pod weighted 560 pounds gross, and would fly 85 mph. My Mini-500 helicopter weighed 790 pounds gross and flew 111 mph. Both used the same engine. Even the streamlined Tervamaki JT-5 gyroplane would only do 102 mph."

I specifically even mentioned the JT-5 Gyroplane, which is one of the most streamlined gyro's in the world, and has more horsepower than a Rotax 582.

Secondly I know that adding some power to a gyro rotor system improves its performance, but its very low speed performance only. It is an interesting question, but gyro’s poorest performance it’s at very low speed. Once you start increasing speed its performance improves quickly. For speeds higher than maximum range speed the performance decays again, but at lower rate than helicopters.
That is not true. By adding power to the rotor system improves performance across the board, especially at higher speeds. Anytime you can reduce the frontal area of a vehicle will increase it's aerodynamic efficacy. A standard 23 foot diameter by 8 inch cord set of rotorblades flying through the air with 3 degrees of coning and at 9 degrees angle of attack, in forward flight presents 360 square inches, of frontal area of resistance to the air stream. By just reducing the rotors angle of attack down to 6 degrees will reduce the rotor systems frontal area down to 197 square inches!

By reducing the disks' angle of attack will also reduce the amount of reverse lift acting as drag. Out of the rotor systems total lift created, approximately 10 percent "acts as a drag" due to it's aft angle of attack. Let's use 75 pounds as that number of drag that needs to be overcome in forward flight. When the rotor disk is reduced to 6 degrees of angle of attack, that also reduces the aft lift acting as drag down to 50 pounds.

Do you really think that the Robinson is more efficient?
I never said I think a Robinson is efficient. As good as an aircraft a Robinson is, it is not the most efficient helicopter built, but there are many more much less efficient than the Robinson, by far.

Anyway we are discussing the aircraft concept efficiency, not about real machines. Prouty, in chapter 6 of its “Even more helicopter aerodynamics” talking about autogyro efficiency states:

“….Its fuel economy should be better than the helicopter’s even after accounting for propeller efficiency. This is because the rotor in or near autorotation is significantly more efficient than in the “propulsive” helicopter mode since more of the blade elements are operating at or near the angle of attack for the airfoil’s maximum lift-to-drag ratio.”
Yes, he said that.
 
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DennisFetters

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The exceptional is... exceptional, and hence excludes the normal.

Exceptional needs have to be taken into account in any design, and not only of rotorcrafts. But exceptional needs, being so, aren't normal features. And you're trying to label exceptional needs as normal features...

XXavier
Whatever you think.

I just always felt that it was a normal feature to want to turn the direction you wanted to, when you wanted to.

You are being argumentative just to be argumentative, but in doing so you are making yourself look foolish.
 

XXavier

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When reason doesn't work, insult won't help, either...

Xavier
 

Rotor Rooter

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say hovering in a 20kt crosswind, in these scenarios, the main rotor becomes MORE efficient and net used (main and t/r) is the same or LESS.
In this example, would it not be fair to say that TWO main rotors become even more efficient?


The efficiency of the tail-rotor has a lot to do with it's spin.
Such as whether one believes Sikorsky's Western spin or Kamov's Eastern spin.


Nick has been a strong promoter of Igor's fan-on-tail rotor, and a strong denouncer of the tiltrotor. It will be interesting to see how he settles into his new job at Bell.
 

ferranrosello

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“That is not true. By adding power to the rotor system improves performance across the board, especially at higher speeds. Anytime you can reduce the frontal area of a vehicle will increase it's aerodynamic efficacy. A standard 23 foot diameter by 8 inch cord set of rotorblades flying through the air with 3 degrees of coning and at 9 degrees angle of attack, in forward flight presents 360 square inches, of frontal area of resistance to the air stream. By just reducing the rotors angle of attack down to 6 degrees will reduce the rotor systems frontal area down to 197 square inches!”

Excuse me Dennis, but the rotor disc frontal area of a gyro reduces with forward airspeed…

Ferràn
 

DennisFetters

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“That is not true. By adding power to the rotor system improves performance across the board, especially at higher speeds. Anytime you can reduce the frontal area of a vehicle will increase it's aerodynamic efficacy. A standard 23 foot diameter by 8 inch cord set of rotorblades flying through the air with 3 degrees of coning and at 9 degrees angle of attack, in forward flight presents 360 square inches, of frontal area of resistance to the air stream. By just reducing the rotors angle of attack down to 6 degrees will reduce the rotor systems frontal area down to 197 square inches!”

Ferràn wrote: Excuse me Dennis, but the rotor disc frontal area of a gyro reduces with forward airspeed…

Ferràn
Ferran,

I don't know why you are not fully comprehending what you read or write, or why you choose to quote only a part of what you or I said where it has lost the meaning, but it is irritating that you are doing so.

You said;
"Secondly I know that adding some power to a gyro rotor system improves its performance, but its very low speed performance only. It is an interesting question, but gyro’s poorest performance it’s at very low speed."

My answer to your statement is above, as you quoted.

You now wrote:
"Excuse me Dennis, but the rotor disc frontal area of a gyro reduces with forward airspeed…"

My answer to this statement is, of course it does, who said it didn't?. But as I said, it decreases it's frontal area even more if you add some power to the rotor-system.
 

ferranrosello

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What I mean is that the improvement in efficiency occurs in the low speed environment, not in the high speed one. The only explanation that you have given is the rotor disc frontal area, which is really big at low speeds, and much smaller at high speeds.

And I don't understand the reason because you get irritated for this answer, gentleman.

Ferran
 

Passin' Thru

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Ferran, I agree with Dennis on this one. Adding power to the rotor improves performance thru out the speed range. True, it is more noticable at low speeds, but it is is there at top speed too, although not as much due to the increased airframe drag being near "up against the wall".
It is really quite noticable at nominal cruise speed due to reasons Dennis already stated, it requires less throttle to the prop to maintain normal cruise speed.
 

mceagle

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Adding power to the rotor improves performance thru out the speed range. it requires less throttle to the prop to maintain normal cruise speed.
Less "throttle" to the prop but more throttle to the rotors. Less induced rotor drag but power is required to drive the rotor. The difference in "efficiency" is subjective, depending on too many variables.
 

Passin' Thru

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Less "throttle" to the prop but more throttle to the rotors. Less induced rotor drag but power is required to drive the rotor. The difference in "efficiency" is subjective, depending on too many variables.
Tim, I'm not sure what you're getting at or why, but Dr. Bensen's old rule of thumb seems to hold true; "every 1hp applied to the rotor relieves 5hp from the prop." Of course, there is a point of diminishing returns.
 
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Fl90

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I don't check in much, anymore. But, I am interested in this thread.

The Mosquito Air is comparable in weight and drag to a Bensen. I was able to fly a Bensen with a 36hp motor and cruise with 27hp at 55kts and a 505lb AUW. The Mosquito advertises a 60min. flight time on 5 gallons of fuel and 4.5gph at cruise.

If....1hp at the rotor equals 5hp at the prop...Then...the Mosquito would be able to cruise with ~6hp. Not happening folks.

In my endeavors to fly with less and less hp., I've found blade efficiency and component placement to have large impacts on power requirements. I'm still not sure which is more efficient at CRUISE. I'm impressed with the Mosquito line, and feel the Mosquito Air and a Bensen with DW's and a modern 2 stroke would be great comparisons.

Now all we have to do is get Tim C. in the air with his Rotax and a Mosquito Air to fly around for a day. I'd be pretty convinced by the results.

Phil.
 

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Playing with figures

Playing with figures

Benson Gyrocopter:
Gross Weight: 505 lbs
Maximum Power: 36 hp
Blade Area: 12.25 sq-ft
Blade Loading: 41.2 lb/ft-sq
Disk Area 415 sq-ft
Disk Loading 1.2 lb / sq-ft

505 lbs / 36 hp = 14 lb/hp *#


Ultrasport 254:
Gross Weight: 575 lbs
Maximum Power: 55 hp
Blade Area: 11.72 sq-ft
Blade Loading: 49.0 lb/ft-sq
Disk Area 346 sq-ft
Disk Loading 1.7 lb / sq-ft

575 lbs / 55 hp = 10.5 lb/hp *


Flettner Fl282 Intermeshing Helicopter:
Gross Weight: 2205 lbs
Maximum Power: 140 hp
Blade Area: 75 sq-ft
Blade Loading: 22.4 lb/ft-sq
Disk Area 1380 sq-ft
Disk Loading 1.6 lb / sq-ft

2205 lbs / 140 hp = 15.7 lb/hp *#


Cessna 150:
Gross Weight: 1600 lbs
Maximum Power: 100 hp
Wing Area: 160 sq-ft
Wing Loading: 10 lb / sq-ft

1600 lbs / 100 hp = 16.0 lb/hp *


* All four will use less power at slow cruise.
# The Intermeshing helicopter is approximately 15% more efficient than the gyrocopter. This MIGHT be attributable to the 15% inefficiency of aerodynamic power transmission between the propeller and the autorotating rotors.


Dave
 
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Fl90

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OK Pete, explain your post

"every 1hp aplied to the rotor relieves 5hp at the prop"

the Mosquito doesn't have a prop....so...?

looks cut and dried to me....I just don't agree

I am quite curious to know which is more efficient at cruise. If anyone has a Mosquito air, please, look up Tim Chick.

Phil.
 

Fl90

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Dave, my disk area was 415. Also, I tend to get 6.25-6.5 lbs. of thrust for each hp, at max rpm. But, that has nothing to do with the statements made.

All I'm saying is, the gyro and the heli are close at cruise, and saying the gyro is 80% less efficient is a little far off. In fact, they are so close at cruise, I don't know which is more efficient. And, the 2 machines that are great comparables are common enough for a couple of people to have a great time finding out.....for real....in the physical world.

Phil
 
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