PDA

View Full Version : Definition of an autogyro


CBLong
11th Oct 2005, 14:18
I was just reading this definition of an autogyro (http://en.wikipedia.org/wiki/Aircraft) in the Wikipedia... it sounds wrong to me but I thought I'd check with the massed wisdom of Pprune before wading in and telling them.

The line in question is:Helicopters and autogyros use a spinning rotor (a rotary wing) to provide both lift and thrust.

Unless I'm very much mistaken (which is entirely possible), autogyros always have a normal engine-propellor for thrust, the rotor being freewheeling and producing lift only (abnormal flight conditions excepting).

For those that may not be aware, the Wikipedia (and Wikis in general) is a slightly hippy-esque "power to the people" website in which anyone may make corrections or additions to the pages, thus, in theory, tapping into the collective knowledge of the entire planet. Or at least, that part of the entire planet which has internet access.

Would someone like to redraft that paragraph, or shall I have a bash?

:)

PAXboy
11th Oct 2005, 15:17
Uumm, I think that they have it correct. I followed the link you gave (I use Wikipedia often) which went to a definition of Aircraft. I then followed their link to Autogyro and found the following definition the empahsis in bold is mine:An autogyro (only an autogiro when produced by the Cierva Autogiro Company or one of its licensees (see below), sometimes called a gyroplane or Gyrocopter™) is an aircraft supported in flight by an unpowered rotary wing, or rotor.

Though the autogyro resembles a helicopter, it is driven in flight by an engine-powered propeller similar to that of an airplane. Though often mistakenly characterized as a hybrid between an airplane and helicopter, the autogyro is a distinct type of aircraft that made its first successful flight in 1923 at Cuatro Vientos Airfield in Madrid, Spain, predating the first successful helicopter by 13 years. All helicopters utilize rotor technology first developed for the autogiro: the helicopter owes its existence to the brilliant work conducted by Juan de la Cierva and his associates.
Found at this location: Wikipedia (http://en.wikipedia.org/wiki/Autogyro) they have a lengthy and (to the amateur reader) cogent explanation of how an autogyro works, it's strengths and limitations.

barit1
11th Oct 2005, 15:20
CBLong - You are correct.

Incidentally, in cruise, compound helicopters (such as the Lockheed AH-56A Cheyenne of the late 60s) put most or all of their onboard power into thrust, and the main rotor thus freewheels. Thus it transitions to autogyro mode.

Check around with Google - you might find a ready-made writeup.

CBLong
12th Oct 2005, 13:01
Thanks for the replies. PAXBOY - the definition you quote, from the autogyro page, agrees with what I thought... it's the single line that I quoted, from the main "airplane" page, that's wrong, and indeed is inconsistent with the definition on the autogyro page that you've quoted.

I'll submit a revision...

I\'ve changed the sentence to read:Helicopters and autogyros use a spinning rotor (a rotary wing) to provide lift; helicopters also use the rotor to provide thrust.

The change is already visible here (http://en.wikipedia.org/wiki/Aircraft), which will cause no end of confusion to people reading my first post from now on...

:)

cwatters
16th Oct 2005, 19:24
I think you are wrong... How would an autogyro glider work if it can't produce forward thrust? I know they were originally designed to be towed up but they can glide if the rope is cut.

http://home.wanadoo.nl/jackjanssen/gyroglid.htm
Quote: It seems like flying a thermal with the gyroglider is somewhat smoother than with a hang glider, probably due to the higher air speed, that makes turbulences of less impact. Of course at lot remains to be learnt. Presently I'm investigating the planes limits in steep turns and spiral dives and I have to think really hard of a way to throw the emergency chute.

http://www.nasm.si.edu/research/aero/aircraft/benson_b6.htm
Benson B-6 Gyroglider
http://www.nasm.si.edu/research/aero/aircraft/images/benson_b-6.t.jpg

http://avia.russian.ee/vertigo/hafner_rotachute-r.html
Hafner "Rotachute"
http://avia.russian.ee/vertigo/foto/hafner_rotachute.jpg

CBLong
18th Oct 2005, 18:19
Hmmm... well, my immediate response would be that no glider of any kind produces forward thrust, by definition. The Gyroglider must, like all gliders, tilt its lift vector forwards to generate 'thrust'. However, that's exactly what helicopters do, too, so perhaps you're right...

I admit I'm no aerodynamicist, but it seems that a key difference between any helicopter and any autogyro is that the net flow of air is down through the helicopter's rotor disk but up through the autogyro's rotor disk. In both cases, there must be a downward acceleration of the air, to produce an upward force. This requires the gyroglider to be descending through the air, just like a fixed-wing glider.

I'm convincing myself that the gyroglider is actually more similar to a helicopter that a powered autogyro. My understanding is that a powered autogyro in straight-and-level flight gets all its thrust from its propellor, and the lift vector from the rotor must actually be tilted back slightly, in order to get the required airflow through the disk to keep it spinning...

WHBM
18th Oct 2005, 18:59
For those that may not be aware, the Wikipedia (and Wikis in general) is a slightly hippy-esque "power to the people" website in which anyone may make corrections or additions to the pages, thus, in theory, tapping into the collective knowledge of the entire planet. Or at least, that part of the entire planet which has internet access.
Sort of defines PPRuNe, yes ..... ?

BTW never quite thought of us all as "hippy-esque" :)

Dan Winterland
19th Oct 2005, 02:09
My definition of an autogyro is 'A triumph of engineering over common sense'.