Lift distribution along rotor blade

[John.Roo]

Hello dear friends,
my main job is work on LSA-Glider Phoenix
Didier Givois.mp4 - YouTube
and electric version of PhoEnix
Elektra ultralight Phoenix Air - YouTube
but I really like gyroplanes.
Some time ago we had a long discussion with my friend and we decided to try to use our knowleadge from glider world to mae some development on gyroplane blades.
Goal is to decrease induced drag of blade = increasing L/D.
Of course we don´t expect to approach to normal airplanes.
But from our calculation seems that it is possible to improve blade characteristics using different depth of profile along radius.
Seems also that twisting of blade make a difference.
Can you please check the attached pictures to make a comment?
Maybe we are wrong in our expectations how is the lift discributed.
Threfore we are open to discuss the idea how to improve gyroplanes
Martin

 

[John.Roo]

Why?

Why?

Why we are interested to work on the improvement of something what is working well?
Honestly we would like to try make electric version of gyroplane - just for fun flying
Martin

 

[ckurz7000]

Why we are interested to work on the improvement of something what is working well?

Hi Martin, your research in this direction is certainly valuable. Precious little progress has been made in the design of autogyro rotorblades since the 60-ies. Compared to the helicopter rotor, which has benefited from a lot of research and big improvements, this is a rather poor showing. I strongly believe that there is still significant performance increases to be gained by optimizing the rotor.

Your graphs seem to be labeled in Czech or Slovak. Can you put them in English? That would make it easier for a lot of people to comment.

Thanks, -- Chris.

 

[John.Roo]

Translation

Translation

Yes, you are right - it is Czech language
I will change labels in Photoshop.

I am glad that you agree with idea that some improvement can be done.
In compare with helicopter construction of gyroplane is simple. Flying with gyroplane was very nice experience.
Ultraflight gyroplane.mpg - YouTube
I beleive that our knowledge from "motorglider" world can be usefull
Martin

 

[ckurz7000]

I beleive that our knowledge from "motorglider" world can be usefull

I am not so sure about that. The aerodynamics of a fixed wing versus a rotary wing are quite different. But you'll see for yourself...

Good luck, -- Chris.

 

[kolibri282]

Welcome to the forum, John! I think you are right in that the current constant chord, non twisted rotor blades are far from optimum for auto gyros. One little question regarding your calculations: it seems that you are using strip theory (and probably two dimensional profile data) to determine lift distribution. How do you calculate induced velocity of a blade section to get the effective angle of attack?

Cheers,

Juergen

 

[Rotor Rooter]

John, your objective is wonderfully but the hurdles are very high.

Power-to-lift is the major hurdle. And rotorcraft are, arguably, the most inefficient vehicle there is.


For interest, here is the most efficient rotorcraft ever built.

The total weight is 282 lbs [116.3 kg]
The total disk area is 13,700 sq-ft [1,276 sq-m]
For a disk loading of 0.0206 lb/sq-ft.

The horsepower required to climb was 1,100 watts
and to hover in ground effect it was slightly over 800 watts.​

A small electric gearmotor at each of the rotors would be interesting, but as you make the craft more and more practical the power-to-lift and the complexity will start significantly increasing.​

This page is a lead to much work that has been done in the pursuit of electric helicopters.


Enjoy the challenge.

Dave

 

[John.Roo]

Hello dear friends,
I fully agree that wing and rotor blade are different, but for example induced drag seems to be important issue in both cases. What is interesting for me is fact that standard rotor blade has the same depth along diameter. But air flow speed along rotor diameter is really different. And I would like to know effect of this "details" to rotor blade optimalization

Honestly... we like challenges
Therefore we already started and moulds are finished.
But as we go deep thru rotor blade aerodynamics, we can see that there is a lot of details maybe (or maybe not) affecting rotor performance. Like twisting of blade. To discover it we would like to precede that basic "assumptions" are wrong (like lift distribution of air flow thru rotor).

As I wrote above - our experience with gyroplanes is limited so therefore I really like possibility to discuss this issue here - between builders and gyroplane pilots.

Best regards!
Martin

 

[John.Roo]

Electric gyroplane

Electric gyroplane

I fully agree that electric gyroplane is real problem.
Example - our electric airplane has 40kW motor (weight 27,6 lb), controller (15,5 lb) and of course battery (capacity 8 kWh with weight 110 lb). Typical power required for our motorglider for horizontal flight is 8 kW.
In reality we achieved 45 min. flights.

Question...
Do you know what is power required for to keep horizontal flight in simple open frame one seat gyroplane?
Some info we have from GyroCalcWin software (author Mr. Tervamaki) and from discussion with Mr. Tervamaki (one of gyrobuilers legends), but your experience is interesting for comparizon.

Best regards!
Martin

 

[bryancobb]

I would be very interested in seeing data that confirms that a set of gyro blades with a <-7> to <-8> degree twist in the blades would perform worse than a set with some positive twist.

It has always seemed to me that having a higher angle of incidence nearer the tips, where velocities are greater and drag is much greater wastes a lot of energy just to overcome drag, where, if the blades had negative twist, that wasted energy could be used to spin the rotor faster and make more lift.

 

[C. Beaty]

I would be very interested in seeing data that confirms that a set of gyro blades with a <-7> to <-8> degree twist in the blades would perform worse than a set with some positive twist.

It has always seemed to me that having a higher angle of incidence nearer the tips, where velocities are greater and drag is much greater wastes a lot of energy just to overcome drag, where, if the blades had negative twist, that wasted energy could be used to spin the rotor faster and make more lift.

Why would you want your rotor tips to operate at negative lift?

 

[bryancobb]

I don't remember learning that a helicopter in autorotational descent has a negative lift area at the tips, when the blades are twisted <-8>. Seems to me...if that helicopter in autorotation could have a pusher engine magically appear on its tail with enough thrust to transition to straight and level, it would gyro-along just fine with those twisted blades?

 

[C. Beaty]

A gyro will certainly fly with the blades twisted the wrong way but with a sacrifice of efficiency.

It’s not a big thing, ~10% reduction of lift/drag ratio.

For those who can’t follow simple vectors, the direction of inflow combined with rotational velocity in a helicopter results in a higher angle of attack at the tip. An autorotating rotor has just the opposite lift distribution.

This misunderstanding was the cause of all the silliness abut retreating blade stall.

 

[Rotor Rooter]

Question...
Do you know what is power required for to keep horizontal flight in simple open frame one seat gyroplane?
Martin

This is information on the Gyrobee gyrocopter. [40 hp. minimum] Others on this forum are much more knowledgeable.

_______________________​

For a comparison, this is information on the original Mosquito helicopter.


IMO the helicopter is more efficient than the gyrocopter because the mechanical power transmission loss of 2-5% is less than the aerodynamic loss of 15% between propeller and rotor.
A plus for the electric drive in a helicopter is that this drive can be located at the rotor.
In addition, this configuration of Schoeffmann's coaxial, but with larger disks can be autorotated and be controlled by simple weight-shift.

Here is a little of the information on Pascal's electric helicopter. Much more is available.


This comparison page might give you some idea related to how the changes in helicopter rotors effect the power requirement.


Dave

 

[XXavier]

[...]
Question...
Do you know what is power required for to keep horizontal flight in simple open frame one seat gyroplane?

[...]
Martin

An estimation can be easily be done assuming that an open-frame single-seat gyro of about 3000 N weight has a L/D of 4,5 for v = 65 mph.

If I haven't got it wrong, simple calculations show that the vertical velocity in a glide of slope D/L = 0,22 = without power is 6,54 m/s, hence the 'gravitational power' of the gliding gyro is 19,62 kW = 26 hp approx.

Of course, the power needed for horizontal, unaccelerated flight at 65 mph is the same. Only that it's no longer 'gravitational', and thus you have to account for the prop losses. If the prop has an efficiency of 0,85, that means 31 hp engine output power, more or less...

 

[John.Roo]

Thank you - this means that to stay in the air is necessary to have continuous power approx 25 kW.
The idea we follow is to try to reduce induced drag (therefore composite blades - twisted and with different depth) = reduce also power requirements.
However - 25 kW is already acceptable.

Second problem is takeoff.
I have short experience only with Magni M-16 (Rotax 914) and Cavalon (Rotax 912S). Subjective opinion - the takeoff distance was the same or longer comparing with "normal" LSA airplanes. Yes, better with Magni M-16 due to lower weight and 914 used, but I don´t want to compare this two different beautifull products.
So how to "save" energy during takeoff? Seems to me that pre-rotation to near in flight rotor RPM could help. Actual possibilities of electric motors and controllers are allowing to achieve 8 kW power for pre-rotation. But on existing models producers are still prefering mechanical clutch and flexible/cardan shaft. Is there real reason (except price and simplicity) for that?

Maybe "price and simplicity" are also reasons for non twisted constant depth meteal blades and practically no development in rotor blade aerodynamics...

Martin

 

[XXavier]

Thank you - this means that to stay in the air is necessary to have continuous power approx 25 kW.
The idea we follow is to try to reduce induced drag (therefore composite blades - twisted and with different depth) = reduce also power requirements.
However - 25 kW is already acceptable.

Second problem is takeoff.
I have short experience only with Magni M-16 (Rotax 914) and Cavalon (Rotax 912S). Subjective opinion - the takeoff distance was the same or longer comparing with "normal" LSA airplanes. Yes, better with Magni M-16 due to lower weight and 914 used, but I don´t want to compare this two different beautifull products.
So how to "save" energy during takeoff? Seems to me that pre-rotation to near in flight rotor RPM could help. Actual possibilities of electric motors and controllers are allowing to achieve 8 kW power for pre-rotation. But on existing models producers are still prefering mechanical clutch and flexible/cardan shaft. Is there real reason (except price and simplicity) for that?

Maybe "price and simplicity" are also reasons for non twisted constant depth meteal blades and practically no development in rotor blade aerodynamics...

Martin

My personal experience is like yours. I once flew a Tecnam P-92 that needed a shorter run than an ELA gyro in order to 'get unstuck'. But the gyro fans can live with that, since gyro flying is far more fun than FW... There's no real need for a shorter takeoff run. Of course, it would be welcome, as a jump-start capability would also be...

Concerning pre-rotation, a stronger (and heavier) rotor hub would be needed to withstand the stress of a very high pre-rotation speed. And concerning power, I suppose that a mechanical transmission could be made strong enough for 8 kW (and more).

And, yes, price and simplicity are important reasons...

 

[kolibri282]

Hope that helps a bit:
http://www.rotaryforum.com/forum/showthread.php?p=545214#post545214

Good luck with your project!

Juergen

 

[SandL]

Please don't get put off by take off run
have a look around youtube , gyros love a bit of wind
take off in a fixed wing is of course shorter, but in a gyro much, much shorter, it's all about rotor speed
for example

Gyrocopter High Wind Takeoffs at El Mirage - YouTube

 

[WaspAir]

Concerning pre-rotation, a stronger (and heavier) rotor hub would be needed to withstand the stress of a very high pre-rotation speed.

Just wondering here . . . if a rotor hub can handle the stress of full flight rpm while in flight, is the stress any greater during pre-rotation to less than flight rpm?

[I assume "very high" here means approaching but not exceeding flight rpm; if you're going to flight rpm and beyond, you'll want adjustable collective pitch.]