Gyro Vs. Helicopter Cruise Efficiency

Tina

Senior Member
Joined
Dec 16, 2005
Messages
976
Location
Temecula, California
Total Flight Time
400+ FW 100+ GYRO
Understood Ferran, I see your point and more to think about when it comes to helicopter verse auto gyro. I am still new to all this and learning more all the time.
 

GyroJoel

Junior Member
Joined
Apr 30, 2007
Messages
9
Location
Westlake Village, CA
As you tilt the rotor disc forward in a helicopter to produce thrust, you lose some lift. So you have to then increase the collective to gain back the lift, but this increases induced rotor drag and therefore required power.

In a gyro, producing more forward thrust does not reduce lift and therefore it can be more efficient in theory. The rotor can just produce lift and the prop can just produce thrust.

So I guess it boils down to how much power is going into producing lift (to overcome gravity) and how much is producing thrust (to overcome drag). Presumably at high speed much more power is going into thrust and that is why in theory a gyro could be more efficient at cruise. But just looking at the production aircraft it doesn't seem to the case...
 

Rotor Rooter

Dave Jackson
Joined
Feb 23, 2004
Messages
2,835
Location
Yes
Dennis,

I agree with your statement and reason for the helicopter being more efficient than the gyrocopter in cruise.

Ferran does bring up an interesting point, in that the drag of the vertical stabilizer, required to counteract the main rotor's torque, plus any power to the tail rotor, will detract somewhat from the efficiency of the helicopter. By the same token the gyrocopter must loose some efficiency by having to react to the propeller's torque.

IMHO, a partially powered rotor, plus pusher propeller, may be the most efficient for higher cruise speed.

And the very best will be a helicopter with twin bilateral main rotors countering each other's torque. :D


Dave
 

DennisFetters

Gold Supporter
Joined
Jul 18, 2005
Messages
3,182
Location
Changsha, China
Aircraft
582 Commander Elite
Total Flight Time
Stopped counting years ago after 5,000
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
That not what I asked "what" about.

You said "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."

The higher the helicopters airspeed, and the more the vertical stabilizer counteracts torque the less tail-rotor power is needed, so more power is available for the main rotors.

A helicopter is more efficient in forward flight than a gyroplane.
 

ferranrosello

Member
Joined
Nov 14, 2005
Messages
379
Location
Madrid
Aircraft
Ela 07
Total Flight Time
FW: 600, HELOS: 3550, GYROS: 3020
Dennis, we are comparing helicopter versus gyro performances. Obviously the rotor tail sucks more power hovering than at cruise speed (8% versus 4%). But it still sucks a 4% of the required power in cruise. And tail rotor’s drag is bigger (much bigger) than vertical fin’s one. And helicopters have vertical fins too. But this is only part of the story.

Have you ever heard about inherent side slip? The tail rotor is always producing a lateral thrust, in order to compensate main rotor torque over fuselage. But you cannot compensate a torque (what main rotor is doing) with a moment (what tail rotor is doing). The undesired result is sideways translating tendency that must be compensated by tilting the main rotor. In other words, all conventional helicopters are always flying whit a side slip. And this creates more drag and reduces overall efficiency.

Gyros are naturally compensated: they have no inherent side slip. I always say that a gyro is like a helicopter which flew well…

Additionally a gyro doesn’t need to carry the transmission systems and the tail rotor, and will be lighter than a helicopter able to carry the same payload.

Please, don’t judge the gyro efficiency by comparing a specific machine… The efforts dedicated to develop gyros have been much smaller than those used to develop helicopters.

Gyros must be more efficient than helicopters at cruise speed. And if they are not is because gyros are much worse engineered than helicopters, but the concept is inherently more efficient.

Ferràn
 
Last edited:

XXavier

Member
Joined
Nov 13, 2006
Messages
1,041
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
579 gyro (March 2020)
Some people around here, like DennisFetters, state that A helicopter is more efficient in forward flight than a gyroplane...
but there are others, like Ferranrosello, who disagree: Gyros must be more efficient than helicopters at cruise speed.

I know little about helicopters, but believe that choppers and gyros are not so different... Both fly with rotors, after all... Yes, one has directly-powered rotors, and the other uses a 'pneumatic transmission', but both hang from rotating wings.

And, concerning the vertical rotor, it isn't used by all helicopters. The German pioneers didn't use it at all, and Russian constructions have favored the coaxial configuration.

Xavier
 

brett s

Gold Supporter
Joined
May 29, 2004
Messages
2,386
Location
Ball Ground, GA
Aircraft
none currently
Total Flight Time
1300 helicopter
I think that even considering tail rotor losses a pure gyro is still going to be less efficient than a helicopter - mechanical losses in driving the main rotor via a transmission are far less than aerodynamically driving it via autorotation.

Partially powering the gyro rotor changes the picture, as already pointed out.
 

XXavier

Member
Joined
Nov 13, 2006
Messages
1,041
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
579 gyro (March 2020)
[...] mechanical losses in driving the main rotor via a transmission are far less than aerodynamically driving it via autorotation.
It seems a good point, that. Autorotation may be simple and cheap, but seems a wasteful way of powering the rotors.

Xavier
 

StanFoster

Active Member
Joined
Nov 16, 2003
Messages
16,914
Location
Paxton, Il
Aircraft
Helicycle N360SF
Total Flight Time
1250
StanFoster

StanFoster

The Helicycle has its T-62 turbine exhaust pointed to the right. I would assume this sideways thrust would counter some of the translating tendency that the tail rotor and main rotor torque are applying to the fuselage. Can anyone confirm this and could add how many pounds of thrust the exhaust has? I ask because I noticeb the turbine exhaust on the Mosquito is split in a Y and equal thrust is exiting out to the left and right. I heard them say it was 60 pounds of thrust! Stan
 

DennisFetters

Gold Supporter
Joined
Jul 18, 2005
Messages
3,182
Location
Changsha, China
Aircraft
582 Commander Elite
Total Flight Time
Stopped counting years ago after 5,000
Ferran,

I am fortunate enough to be one of the few people to have ever designed, built, tested and manufactured both helicopters and gyroplanes. As a matter of fact, 7 different gyroplanes and 3 different helicopters with 11 variants, and manufacturing 1700 of those designs, so I feel confident that I have some authority in the matter. Not a brag, just a fact.......... as the Duke said.

Dennis, we are comparing helicopter versus gyro performances. Obviously the rotor tail sucks more power hovering than at cruise speed (8% versus 4%). But it still sucks a 4% of the required power in cruise. And tail rotor’s drag is bigger (much bigger) than vertical fin’s one. And helicopters have vertical fins too. But this is only part of the story.
Maybe this is where your misconception is derived. You see, depending on gross weight, a tail-rotor uses 20% to 25% or even more of the power needed to hover. Not 8%. We wish it were 8%!

This is why we can add the majority of that power to the main rotor for forward flight when the vertical tail is loaded enough to counteract most of the torque from the main rotors.

Have you ever heard about inherent side slip? The tail rotor is always producing a lateral thrust, in order to compensate main rotor torque over fuselage. But you cannot compensate a torque (what main rotor is doing) with a moment (what tail rotor is doing). The undesired result is sideways translating tendency that must be compensated by tilting the main rotor. In other words, all conventional helicopters are always flying whit a side slip. And this creates more drag and reduces overall efficiency.
Sure I have, that is why I design the mast to lean sideways 2.5 degrees, to compensate for tail-rotor thrust when the tail-rotor centerline of thrust is lower than the main-rotors disk. This also allows for the helicopter to take off and land level on both skids, while others have to lift off or set down on one skid then the other.

But for the case of our discussion, as the helicopter achieves higher speeds, and the vertical tail starts to take over the majority of the torque from the main-rotors, the thrust of the tail-rotor must be reduced to compensate. When this happens, the rotor disk does not need to compensate near as much for tail-rotor thrust, so the disk will level out. So now not only do you have your main-rotor disk thrust-line pointing forward and level, but you are now pumping a majority of that extra 25% of power, no longer needed for anti torque, to the main-rotor!

Note; older designed helicopters that did not have, or have too small of a vertical stabilizer did not benefit from the above. They behaved as you say.

As I said, I designed and flown both helicopters and gyroplanes. As a matter of fact, I designed both a helicopter and a gyroplane that both used the same engine.

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.

As much as I love the gyroplane over the helicopter, a helicopter is more efficient.
 

GyroJoel

Junior Member
Joined
Apr 30, 2007
Messages
9
Location
Westlake Village, CA
Dennis,

Thanks for sharing your experience.

How much power do you think would need to be applied directly to the gyro rotor (i.e. PPR) to achieve the same cruise efficieny as a helicopter? That is, assuming all other things being equal (weight, drag, etc.)
 

Rotor Rooter

Dave Jackson
Joined
Feb 23, 2004
Messages
2,835
Location
Yes
Stan here is a somewhat related situation.

The two angled rotors of the Kaman Huskie turn inside forward (breaststroke). Their combined torque wants to pitch the nose of the craft up. This stovepipe exhaust was used on one variant as an attempt to offset this torque.




An early Helicycle (prototype?) had a separate single pusher propeller, with its own motor, located on one side of the craft. Apparently this was done to offset the torque of the main rotor.

Dave
 

DennisFetters

Gold Supporter
Joined
Jul 18, 2005
Messages
3,182
Location
Changsha, China
Aircraft
582 Commander Elite
Total Flight Time
Stopped counting years ago after 5,000
Dennis,

Thanks for sharing your experience.

How much power do you think would need to be applied directly to the gyro rotor (i.e. PPR) to achieve the same cruise efficieny as a helicopter? That is, assuming all other things being equal (weight, drag, etc.)
I'm working that out now on a new project. Looks like around 4 to 5hp.

By adding horse power to the rotor system allows you to decrees the disks angle of attack because you would need less V+V (Volume plus Velocity) to power the rotors, plus when the angle of attack is decreased, so is the reverse lift off the disk, decreasing drag from the rearward pointing lift vector. For each horse power you apply to the rotor system is like adding 5 horse power to the engines performance.
 

mceagle

Gold Member
Joined
Oct 31, 2003
Messages
1,239
Location
Sunshine Coast, Qld, Australia
Aircraft
Eagle Rotorcraft
Total Flight Time
600 hrs
Efficiency is a subjective thing - Too many variables.
When an solo R22 and a solo 2.2 Subaru powered gyroplane are mustering in the same paddock on the same day for the same period of time, the Gyroplane uses considerably less fuel. It should be even more so with a 912 powered gyroplane.
 

ferranrosello

Member
Joined
Nov 14, 2005
Messages
379
Location
Madrid
Aircraft
Ela 07
Total Flight Time
FW: 600, HELOS: 3550, GYROS: 3020
I appreciate your answer, Dennis. Thanks for sharing your fantastic experience.

I have my experiences too, not manufacturing gyros and helicopters but flying both. 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.

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.

I usually fly an ELA 07. I’ve performed a long trip to Canary Islands flying more than 5500 Km (3300 S. Miles) in 25 flights. My average take off weight was 530 kg (262 lb)(aircraft empty weigh is 125lb). My average cruise speed was 80-90 mph, and my fuel consumption of 20 litres per hour (5.2 gallons). These data can be comparable to a Robinson 22, which has a little bit more power (115hp-124hp) and a similar payload. Despite R-22 are an enclosed cabin and ELA an open frame this could be balanced because the gyro is a tandem configuration (less frontal area).

My engine is a Rotax 914 and I use a Duc fixed pitch propeller. The results would be better with an enclosed machine, using a variable pitch propeller and a variable collective pitch rotor.

Do you really think that the Robinson is more efficient?

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.”
 

XXavier

Member
Joined
Nov 13, 2006
Messages
1,041
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
579 gyro (March 2020)
I'm not questioning anyone's credentials, but this statement by Dennis Fetters on tail-rotor power needs is perhaps a bit too harsh:

depending on gross weight, a tail-rotor uses 20% to 25% or even more of the power needed to hover

Good performance in hovering flight is a key feature of rescue helicopters, and the fact is that the conventional 'Sikorsky', i. e. main + tail rotor configuration has been used for S&R helicopters, both light and heavy ones. I find it hard to believe that S&R helicopters may need such a big fraction of its power for the tail rotor while hovering.

Perhaps there are other factors here, apart from gross weight, like boom length and tail rotor diameter.

Rgds

XXavier
 
Last edited:

brett s

Gold Supporter
Joined
May 29, 2004
Messages
2,386
Location
Ball Ground, GA
Aircraft
none currently
Total Flight Time
1300 helicopter
Dennis is correct - worst case it's a pretty high number. Wind direction & speed make a large difference - in still air it won't be that much though.

Even given that, it's still a better compromise than the alternatives the vast majority of times - that's exactly why most helicopters still use the configuration.
 

DennisFetters

Gold Supporter
Joined
Jul 18, 2005
Messages
3,182
Location
Changsha, China
Aircraft
582 Commander Elite
Total Flight Time
Stopped counting years ago after 5,000
I'm not questioning anyone's credentials, but I find it hard to believe that Dennis Fetters' statement on tail rotor power needs:
depending on gross weight, a tail-rotor uses 20% to 25% or even more of the power needed to hover
is perhaps too general. Good performance in hovering flight is a key feature of rescue helicopters, and the fact is that the conventional 'Sikorsky', i. e. main + tail rotor configuration has been used for S&R helicopters, both light and heavy ones. I find it hard to believe that S&R helicopters may need such a big fraction of its power for the tail rotor while hovering.
Perhaps there are other factors here, apart from gross weight, like boom length and tail rotor diameter.
Rgds
XXavier
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.
 
Top