tintrax

I have never posted a picture here before and thought I should try it.
Got everything done Ok except I missed putting in a subject title - & then it all got lost!
So here is another try. Picture ( a bit blurred) shows gyro in flight - note the downward angle of the rearmost rotor blade. Just about to become the advancing blade and it will then lift up, giving a downward component to the angle of attack, plus reducing incidence due to the delta hinging. All automatic so there is no tendency for the plane to tilt to one side.
Colin Duthie - webpages on my gyros http://www.geocities.com/tintrax/page6.html

mnowell129

Don't you mean no tendency to pitch up, rather than tilt.
The extra lift on the advancing blade wouldn't take effect until
90 degrees later.

tintrax

True, the maximum amount of upwards `flap` of the rotor blade is delayed and presumably is when the blade is in the 12 o`clock position, however the airflow there is not as great as in the 3 o`clock position (anti-clockwise rotation when viewed from top). Greatest speed of airflow is at the 3`clock position, and even though the blade has not fully lifted at that stage it must have the required effect on equalling lift. So pitch change is not the problem, (I have never noticed any), but roll to the left is - anyone tried a model with non flapping stiff blades?
The first Cierva autogyros did not have the flapping rotor blades and after taxying to gain speed the aircraft would roll over on its side.
Comments welcomed on this interesting subject!
Colin Duthie

mnowell129

Cierva's experiment and results are commonly reported. Even now
without sufficient rotor speed an autogyro will roll over without
sufficient rotor speed. However the effect of the advancing blade
in flight, once rotor speed is established, is to pitch the rotor up not roll
it over. But you wouldn't notice because the effect of flapping automatically
cancels the pitch up, a helpful benefit.
The lift on the blade is irrelevant with a hinged blade because the force
on the rotor hub is all centrifugal force. The blades' centrifugal force applied
through the coning angle is what lifts the gyro. Only when the blade flaps
up in the front, caused by the lift on the advancing blade, is any moment applied to
the rotor shaft. In this case pitch up. The two blades at the side are at the same
angle with the rotor shaft and are at the same RPM thus the centrifugal force on these
two opposing blades is equal and at the same angle with respect to the rotor shaft thus
generating no rolling moment. It doesn't matter if the retreating blade has zero lift as long
is at the same angle as the advancing blade at the same rpm.
Another way to look at it is that the rising blade on the advancing side is experiencing
negative cyclic pitch that is the greatest at 3 oclock. Negative cyclic pitch applied at 3 oclock
is manifested 90 degrees later as nose down moment. Thus the rising advancing blade is producing
a nose down correction, not a roll right correction.
Some apparent confusion may arise because when the rotor is rigid the phase angle is not 90 degrees,
but perhaps 45 to 75 degrees. Thus the effect of the advancing blade is to cause a roll over and pitch up
at the same time because the maximum blade flap is then at 1 or 2 oclock. (There are videos of
models doing just this, appearing to perform a very tidy snap roll just at takeoff. )Converting the rigid rotor
to a flapping hinge changes the phase angle to 90 degrees so that the force is changed to a pure pitch up.
However since the blade is free to flap, it cyclicly unloads itself and applies the correct nose down cyclic.
So the effect of the flapping hinge is more complicated than generally reported. It changes the phase angle
of the rotors reaction to 90 degrees while simultaneously applying the correct nose down cyclic to cancel
the nose up moment produced by the advancing blade. A very helpful outcome.

You can have a ridid rotor, but you have to apply the same cyclic unloading to prevent the pitch up. In the
absence of a flapping hinge to provide the cyclic unloading what is commonly done is to "feather" the blade by
allowing it to spin on a bearing and apply the cyclic mechanically with a swashplate. You can do both as well and
use a swashplate to feather blades with flapping hinges, this combined system provides the correct advancing blade correction, doesn't
require that the rotor flaps back and allows for the relief of blade root/hub stresses caused by the rigid blade, all at the
same time. The Pitcairn book describes this as the system that Cierva had developed before he died.
After his death his patents were licensed by his board of directors to Flettner thus contributing to Flettners inital sucess with
the helicopter. In the US the Cierva Patents (39 of them cross licensed with Harold Pitcairn) were
used successfully by Sikorsky to build his machines for WW2 usage.


The actual behavior of the flapping hinge has been widely mis-described in
many famous and popular books. Modern rotor books don't make this mistake.
I believe that this misinformation in the popular books has been
partly responsible for model gyrocopter development taking so long compared to other
types of models.

Scotth

Been doing some research?????
Wow! Where did you get those books. I would like to read them...

mnowell129

My library contains :
Plans and articles for Roto Ruta, Super Libelle, Flying Banana, Whistler,
Gyro Schtick, ECDC, FA61 Gyrocopter, Osprey Gyrocopter, Spin Doctor,
a few I can't remember.
a couple kites, several free flight gyrocopters.
Two or three articles published in Model Aviation about gyrocopters.
Two or three articles by John Burkham, A fellow in the American Helicopter Society
and designer of the Penni FF copter.
Several papers by Gordon Leishman, Professor of Aerospace Engineering at the
University of Maryland, Former aerodynamicist at Westland Helicopters.
Helicopter Aerodynamics (3 volumes) By Ray Prouty of Rotor&Wing magazine..
Radio Control Helicopter Models, John Drake
Model Aircraft Aerodynamics, Martin Simons
Rotary Wing Aerodynamics, Stepniewski and Keys
Schluter's Radio Controlled Helicopter Manual
Principles of Helicopter Aerodynamics, Leishman
Helicopters and Autogiros, Gablehouse (Has some significant errors BTW)
Legacy Of Wings, The Harold F. Pitcairn Story, Frank Smith
Autogiro, The Story of "the Windmill Plane", Townson
Flying Model Helicopters, Dave Day
A dream of Flight, Igor Bensen
Radio Control Model Helicopter Handbook, Don Lodge

The only two I haven't read cover to cover are
Stepniewski and Keys and Leishman, mostly because
they cover a lot of theory about blade design, etc. that
doesn't interest me.

I'm still looking for a paper referenced by Drake by one of the engineers at
Hiller helicopter regarding following rate calculations.

Lodge and Drake do a good job describing the governing math for
rotor control and dynamics. Simons is good for stuff like reynolds number
and L/D explanations. Igor Bensens book is very interesting because
he was a degreed engineer, designed helicopters for GE and later
became head of research at Kaman. His gyrocopter designs, while
able to be built by homebuilders, really had a lot of serious engineering
design behind them.

Almost everything is out of print but you can find most of these on www.abebooks.com

mickey

Scotth

Any chance of me borrowing this reading material? I would pay for shipping....
Scott