Gyrocopters / AutoGyros
Discussion
Ayahuasca said:
I still cannot fathom how an autogyro generates lift - for autorotation to occur the rotor's angle of attack needs to be negative, but if it is negative it cannot generate positive lift.
No it doesn't. You are confusing autorotative lift in a Helo with autorotative lift in an Autogyro.
While lift is proportional to Alpha (AoA) it is also proportional to the square of the speed of the airflow over the aerofoil. As long as the blade pitch is not too coarse for the TAS, then it will rotate, and in so doing, produce lift.
For a rotor to produce autorotative lift there must be a thrust component to spin the rotor.
Now, in a Helo, for autorotation to occur, ie post engine failure, this forward component is a factor of the descent vector due to Gravity, ie as the a/c descends there is both a vertical as well as horizontal component, the later providing the thrust vector to spin the rotor (in fact it is the upwash through the rotor). Given that this is occurring in an unpowered descent (where your forward speed is courtesy of Mr Newton) it follows that you must reduce the AoA of the rotor blades else they will slow and stall (with predictable results), ie you 'dump' the 'Collective'.
In an autogyro the propellor provides the forward thrust vector, thus, once you have the rotor spinning, it will continue to spin and produce lift, even at positive Alpha. Indeed if the rotor was at negative Alpha the autogyro wouldn't get airborne.
AnotherClarkey said:
T
Apparently the main thing to watch for is the position of the thrust line relative to the C of G. Many recreational gyros can be prone to unrecoverable 'push over' if too much power is applied suddenly and the rotor control speed is low.
It can also be a problem at relatively high IASs.Apparently the main thing to watch for is the position of the thrust line relative to the C of G. Many recreational gyros can be prone to unrecoverable 'push over' if too much power is applied suddenly and the rotor control speed is low.
Which is why, if you get too nose high you do not bunt. If you do, you will case 'blade sail' which will chop the tail of and kill you (which is what happened at the demo at Farnborough in 1968).
What you do is put it into a wing-over. Rotary pilots do this because they know the the problems of blade sail (which fixed wing pilots have probably never considered). Try watching the RAF SAR Helo display and note how the a/c is recovered from fairly extreme pitch angles.
Ginetta G15 Girl said:
Ayahuasca said:
I still cannot fathom how an autogyro generates lift - for autorotation to occur the rotor's angle of attack needs to be negative, but if it is negative it cannot generate positive lift.
No it doesn't. You are confusing autorotative lift in a Helo with autorotative lift in an Autogyro.
While lift is proportional to Alpha (AoA) it is also proportional to the square of the speed of the airflow over the aerofoil. As long as the blade pitch is not too coarse for the TAS, then it will rotate, and in so doing, produce lift.
For a rotor to produce autorotative lift there must be a thrust component to spin the rotor.
Now, in a Helo, for autorotation to occur, ie post engine failure, this forward component is a factor of the descent vector due to Gravity, ie as the a/c descends there is both a vertical as well as horizontal component, the later providing the thrust vector to spin the rotor (in fact it is the upwash through the rotor). Given that this is occurring in an unpowered descent (where your forward speed is courtesy of Mr Newton) it follows that you must reduce the AoA of the rotor blades else they will slow and stall (with predictable results), ie you 'dump' the 'Collective'.
In an autogyro the propellor provides the forward thrust vector, thus, once you have the rotor spinning, it will continue to spin and produce lift, even at positive Alpha. Indeed if the rotor was at negative Alpha the autogyro wouldn't get airborne.
This proposal is half auto-gyro and half helicopter, the VTOL works because the two coaxial rotors spin in opposite directions, once in the air the rear fans give thrust, and the drive to rotors is cut and they auto rotate.
an adaption of an idea for a helicopter by AVX which claim increased performance
If I am flying along in my C130 at, say, 25000ft and I suffer an engine failure with a blade hang up, then, as I descend the TAS vs Alpha relationship of the blades is such that they will slow down as I descend (because they are too coarse for the reducing TAS) even if the hang up is on the Fine Pitch Stop. They might stop in extremis (dependent upon blade angle) but they don't rotate the other way (for that to happen they'd have to be at reverse pitch with a decoupled prop).
The point is the TAS / Blade Angle relationship.
In an autogyro you have a forward TAS of 'whatever' which helps to spin the rotor, given the blades Alpha, but remember, aside from blade angle, you have, what effectively is disc angle, which means, even in forward flight, you get an upwash through the rotor disc which keeps it turning.
The point is the TAS / Blade Angle relationship.
In an autogyro you have a forward TAS of 'whatever' which helps to spin the rotor, given the blades Alpha, but remember, aside from blade angle, you have, what effectively is disc angle, which means, even in forward flight, you get an upwash through the rotor disc which keeps it turning.
ben10 said:
My dad has just sold his for quite a tidy profit:
[pic]
|http://thumbsnap.com/KtsFsfCI[/pic]
And has just swapped it for the upgrade:
They are awesome fun, can take off in about 100-200m and land in about 50m if that.
In regards to the rotor turning whilst on the ground, they have what is called a pre-rotator which is to aid faster/shorter take off. It is just driven by the engine and only until take off is completed.
He regularly buggers off to the other side of the country for breakfast or a coffee.
Where is the gyro based?[pic]
|http://thumbsnap.com/KtsFsfCI[/pic]And has just swapped it for the upgrade:
They are awesome fun, can take off in about 100-200m and land in about 50m if that.
In regards to the rotor turning whilst on the ground, they have what is called a pre-rotator which is to aid faster/shorter take off. It is just driven by the engine and only until take off is completed.
He regularly buggers off to the other side of the country for breakfast or a coffee.
I've had the pleasure of being shown around Ken Wallis' home and workshops by the man himself. He's mad keen on old vehicles, and being quite local the vintage motorcycle club goes to see him quite regularly.
The last time I was there we were casually looking around his collection when he asked whether we'd like to see him fly one. Of course we said yes, so he clambered into the closest one, fired it up and went taxying down his gravel drive. There was dust and stones flying everywhere, then he turned left (whilst holding the top rotor to stop it turning) and went stright through a hedge, cutting a nice hole in it! The other side of the hedge there was a field, so he let go of the top rotor, upped the rev's and he was away!
He did several low level passes, sitting side-saddle with no hands for one.
He really is one of my hero's. A true quirky Brit that has done so much in his lifetime. He's built his own cars, bikes and even a set of tiny revolver guns. He's written a book, which I'd thoroughly recommend. He signed mine, and put "(007)" in brackets after his name as he did all of the stunt flying in Little Nelly.
A real gent and as mad as a fish on a bike
The last time I was there we were casually looking around his collection when he asked whether we'd like to see him fly one. Of course we said yes, so he clambered into the closest one, fired it up and went taxying down his gravel drive. There was dust and stones flying everywhere, then he turned left (whilst holding the top rotor to stop it turning) and went stright through a hedge, cutting a nice hole in it! The other side of the hedge there was a field, so he let go of the top rotor, upped the rev's and he was away!
He did several low level passes, sitting side-saddle with no hands for one.
He really is one of my hero's. A true quirky Brit that has done so much in his lifetime. He's built his own cars, bikes and even a set of tiny revolver guns. He's written a book, which I'd thoroughly recommend. He signed mine, and put "(007)" in brackets after his name as he did all of the stunt flying in Little Nelly.
A real gent and as mad as a fish on a bike
eharding said:
erdnase said:
I thought PH would be all over the autogyro ethos! To me, they're like flying TVRs.. raw, minimalist and for the dedicated.
Anyway - Yaks are the TVRs of the sky - ferocious appetite for fuel and maintenance, sound fantastic, handling that can get vicious when provoked, but are sociable beasts which like to congregate and move as a herd.Our old RO always used to refer to maneuvering a group of TVR owners as "like herding cats".
Friend of a Friend took me up in his 2 weeks ago at an airfield outside York. This is it here and a link to the company who make them -
http://www.rotorsport.org/
http://www.rotorsport.org/
ATM said:
Friend of a Friend took me up in his 2 weeks ago at an airfield outside York. This is it here and a link to the company who make them -
http://www.rotorsport.org/
An MT03 by any chance?http://www.rotorsport.org/
Same as my Dad's old one
NoelWatson said:
ben10 said:
My dad has just sold his for quite a tidy profit:
[pic]|http://thumbsnap.com/KtsFsfCI[/pic]
And has just swapped it for the upgrade:
They are awesome fun, can take off in about 100-200m and land in about 50m if that.
In regards to the rotor turning whilst on the ground, they have what is called a pre-rotator which is to aid faster/shorter take off. It is just driven by the engine and only until take off is completed.
He regularly buggers off to the other side of the country for breakfast or a coffee.
Where is the gyro based?[pic]
|http://thumbsnap.com/KtsFsfCI[/pic]And has just swapped it for the upgrade:
They are awesome fun, can take off in about 100-200m and land in about 50m if that.
In regards to the rotor turning whilst on the ground, they have what is called a pre-rotator which is to aid faster/shorter take off. It is just driven by the engine and only until take off is completed.
He regularly buggers off to the other side of the country for breakfast or a coffee.
erdnase said:
I had no idea the main rotor is unpowered! Apparently the lift is created by autorotation? In that respect, they're more than just mini helicopters - which is what I thought they were.
Haha 
Somewhat less than a mini-helicopter in fact, in comparison helicopters are fantastically complex and sophisticated - which is why there are so few mini-helicopters..
Autogyros are awesome however, bascially a rotary wing plane.
v8will said:
Mr Dave said:
v8will said:
Ayahuasca said:
v8will said:
I built a RC one years ago with my father, does that count?
It was a pig to fly and after I binned it for the 4th or 5th time we gave up. Electric Helicopters came down in price and the battery performance improved so I started flying those instead.
We used to have some old video in the house that my dad shot at an airshow, It was Ken Wallis having a crash in the Little Nellie Autogyro, I think it was built for a James Bond movie. I can't remember where it was but I'm sure it was before I was born.
Is this it?It was a pig to fly and after I binned it for the 4th or 5th time we gave up. Electric Helicopters came down in price and the battery performance improved so I started flying those instead.
We used to have some old video in the house that my dad shot at an airshow, It was Ken Wallis having a crash in the Little Nellie Autogyro, I think it was built for a James Bond movie. I can't remember where it was but I'm sure it was before I was born.
http://www.youtube.com/watch?v=E2YOFcZr2tM&fea...
Autogyros are for the insane or "eccentrics" if they are a bit posh as well as insane. They will kill you and everything you hold dear and destroy all that is around you.
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