How dissimetry of lift is managed in Bensen type gyroplanes?

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

oriol

Well-Known Member
Joined
Dec 31, 2009
Messages
770
Location
Barcelona, Spain.
I found this article on the net explaining the use of blade flapping to overcome dissimetry of lift.
http://www.dynamicflight.com/aerodynamics/flapping/


What still remains a mistery to me is how the pilot of the gyro-hang-glider deals with precession on the video link in post 9?

Although during the video the pilot does not seem to perform any turn, he just seem to be hanging like a dead weight while on tow, he does move the bar forward particularly during the landing. The landing is performed like if the gyro was a hanglider; when the pilot tilts the rotor the gyro does not seem to flip affected by precession.

Perhaps it is not easily seen in the video and the pilot is moving the bar forward while at the same time putting his weight on one of the sides of the bar.


This below is a vintage video of a gyro with the stick connected directly to the rotor. At aprox 0.54 the pilot moves the stick forward to take off without any noticeable precession effect like in the gyro-hanglider video.
https://www.youtube.com/watch?v=SgbV5sFIPgE


Oriol
 
Last edited:

Aviator168

Well-Known Member
Joined
Sep 21, 2012
Messages
2,214
Location
Brookville, NY. USA
The blades are not bolted onto the mask, rather loosely connected. When the pilot tilts the gimbal, he is not tilting the rotating disc --> no precession. Post 17 describes how the rotating disc gets tilted.
 

oriol

Well-Known Member
Joined
Dec 31, 2009
Messages
770
Location
Barcelona, Spain.
Aviator168


I do not know,

From what I understand, if a rotor is spining and you change its orientation the resulting force is affected by precession. You can see that by yourself by spinning a bike wheel.

From the videos one can see the pilots using a Bensen rotor arrangement clearly tilting the rotating disk for taking off and landing on the videos (post 22 and 9). Helis control their flight attitude by changing the pitch of the blades and those "weight and shift gyros" does it by altering the center of gravity, in either case the spining rotor ought to be affected by precession.

To avoid precession in helis each manufacturer put the controls at a different azimut: 45º (Bolkow), 80º (Ecureuil). However Bensen seems to do well without having to change the position of the controls.

I am doing some reading about gyros and stuff, if I am unable to understand how the Bensen arrangement works I will try to contact some experts in rotor design.


Thanks!


Oriol
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,274
Weight shift will be part of it. And as the pilot tilts the disc up, the AoA increases on the advancing blade and decreases on the retreating, so the lift on the advancing side and loss of lift on the retreating will cause precession that tilts the disc in the desired direction.

I think. Never flew one.
 

BBerson

Well-Known Member
HBA Supporter
Joined
Dec 16, 2007
Messages
13,081
Location
Port Townsend WA
All spinning masses precess.
I didn't understand how the whole Bensen blade angle can "tilt" on the pitch gimbal until Hillberg explained it.
My previous understanding was wrong, it isn't weight shift at all.
 

deskpilot

Well-Known Member
Joined
Jun 30, 2009
Messages
1,122
Location
Morphett Vale, South Australia. Just south of Adel
Excuse my ignorance but with respect to precession, you have been referring to a spinning wheel BUT, unlike a wheel, the gyro blades have no rim so the reactions should be entirely different, shouldn't they? Normal gyro and toys all have that weight some distance from the center of rotation hence the precession (that's my understanding) Take that weight away, do they(the blades alone) actually cause precession?
 

Aviator168

Well-Known Member
Joined
Sep 21, 2012
Messages
2,214
Location
Brookville, NY. USA
Take that weight away, do they(the blades alone) actually cause precession?
There is no way to take the weight away.

Oriol,

When the gimbal is tilted, the orientation of the rotating rotor is NOT changed (only the blade angles at certain position is). This is important, otherwise the gyro cannot be controlled due to precession.
 

BBerson

Well-Known Member
HBA Supporter
Joined
Dec 16, 2007
Messages
13,081
Location
Port Townsend WA
Precession means that when you push on the bicycle wheel or rotor it takes 90° (more or less) to fully move to the new track.
A rotor doesn't have a wheel rim with huge mass at perimeter, but still has significant mass.
Sikorsky didn't understand it either, and had to adjust his cyclic linkage 90°, after the first flight.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,274
All rotating masses will want to precess. An airplane's propeller will cause precession; you can feel it in a steep turn. It takes more elevator back pressure in a right steep turn than in a left, because the prop pulls the nose down in the right turn and pulls it up in the left. Turning right, you are pushing on the left side of the prop disc, which makes the prop want to angle down, not right. The opposite is true in the left turn. A taildragger pilot can feel it when raises the tail in the takeoff run; the nose will pull left a bit harder while the tail is coming up.

Gyroscopes have their mass concentrated in the rim. That makes it most efficient for the weight of it.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,046
Location
97FL, Florida, USA
All rotating masses will want to precess. An airplane's propeller will cause precession; you can feel it in a steep turn. It takes more elevator back pressure in a right steep turn than in a left, because the prop pulls the nose down in the right turn and pulls it up in the left. Turning right, you are pushing on the left side of the prop disc, which makes the prop want to angle down, not right. The opposite is true in the left turn. A taildragger pilot can feel it when raises the tail in the takeoff run; the nose will pull left a bit harder while the tail is coming up.

Gyroscopes have their mass concentrated in the rim. That makes it most efficient for the weight of it.
Yup, to go straight ahead in my airplane takes left rudder when pulling and right rudder when pushing. Flat spins are either stick back left rudder full power, or stick forward right rudder full power. That big aluminum propeller generated lots of gyroscopic forces.


BJC
 

oriol

Well-Known Member
Joined
Dec 31, 2009
Messages
770
Location
Barcelona, Spain.
When the gimbal is tilted, the orientation of the rotating rotor is NOT changed (only the blade angles at certain position is). This is important, otherwise the gyro cannot be controlled due to precession.
Most today gyro head rotors are similar to those find in helicopters with swashplates etc. In those machines your theory applies.

My point is that some earlier very light gyros (Bensen overhead stick, Haffner Rotachute) tilted the rotor or what is the same changed the weight position (action reaction) to alter the flight attitude. What strikes me of that system is that it seems to perform without being affected by precession

You can see the system I am refering clearly at the begining of this video:
https://www.youtube.com/watch?v=k8TBf032SwE

helicopter rotor.jpgshumeyko gyro glider.jpg

The two pictures above show the obvious differences between both control systems. One is that of a conventional helicopter in wich the rotor does not tilt and control is achieved by pitching the blades ciclycally, the other one is that of the Russian Shumeyko gyro glider in wich control is achieved by tilting the rotor/weight shift.


Thanks,


Oriol
 
Last edited:

cptcliffhanger

Well-Known Member
Joined
Jul 20, 2017
Messages
51
Location
san diego
it's tough to describe but it's worth understanding because it's is quite clever and elegant in its simplicity, so I will try to take a stab at it..

the rotor is a teetering rotor.. this means that it is attached to the mast with essentially 1/2 of a gymbal, or a simple hinge.

Imagine you are sitting in the pilots seat of the contraption depicted in the video you shared and the rotor blades are at 9 and 3 O'clock. if you were to move the controls for and aft (nose up/down) you would increase the AOA of the advancing blade, and decrease he AOA of the retreating blade for nose up input, and vise versa for nose down input...

Keeping the blades at 9-3 O'clock and ask a friend to hold one of the blade tips steady. if you give left and right inputs, the teeter hing allows the blades to teeter so that they do not move but your stick input is allowed to go left and right freely without imparting any force onto the blades.




now if you think about precession, you realize that in order to tilt the rotor disc left and right, you would need to effect the AOA of the blades when they reach the 12 and6 O'clock positions..

When you want to tilt the rotor disc fore and aft, you need to effect the blades AOA when the blades are at the 9 and 3 O'clock position..

so; now lets imagine the rotor is spinning and has the behavior of a gyroscope.. it wants to stay on plane until it is upset by forces, then it tilts 90 degrees from where the force was input.. you have your simple teetering rotor control that has no affect on the rotor when moved towards the tips of the rotor blades, but it does affect the AOA of blades when moved parallel to the chord-line of the blades.. with a little imagination, you can see that the rotor disc will always follow the angle of the control input. because when you move the control stick fore and aft it changes the aoa of the blades when they are to your left and right, 90 degrees from where you want to tilt the disc.

This can be confusing even if you have a teetering rotor in your hands.. you can make a simple teetering rotor with a paint stick from home depot, a small hinge and a shaft.. if you spin the contraption with a hand drill you can see that you feel no precession when you move the mast around (except for any precession you may feel from the drill motor). the aerodynamics of a paint stick are good enough to make the rotor always fly the disk to be square to the mast.

dirty quick sketch of a pait stick teetering rotor.teeter.jpg
 

cptcliffhanger

Well-Known Member
Joined
Jul 20, 2017
Messages
51
Location
san diego
in hindsight, I shouldve made the sketch first.. in essence the guy in the video has control of the mast in the sketch.. whatever angle you move the mast to, the rotor disk will fly until it has reached a new plane that is square to the mast.. the rotor disk adjusts it's plane via cyclic pitch of the rotor blades and precession, but the one holding the mast is isolated from the gyroscopic forces via the hinge. the only force you feel in the mast is the force it takes to change the aoa of the blades.


Hope this helps.
 

oriol

Well-Known Member
Joined
Dec 31, 2009
Messages
770
Location
Barcelona, Spain.
In essence the guy in the video has control of the mast in the sketch.. whatever angle you move the mast to, the rotor disk will fly until it has reached a new plane that is square to the mast.. the rotor disk adjusts it's plane via cyclic pitch of the rotor blades and precession, but the one holding the mast is isolated from the gyroscopic forces via the hinge. the only force you feel in the mast is the force it takes to change the aoa of the blades.

Thanks a lot cptcliffhanger!


At first I did not understood how precession forces were dissociated through the hinge to avoid the pilot having to fight them through the rotor control stick. Now it is clear, as you say, the pilot input only changes the AOA and precession does the rest.

Thanks for unveiling the mistery again cptcliffhanger you just made my day.

Thanks to the other members as well for their inputs, it was a great learning from all.


Oriol
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,346
Location
Fresno, California
OK guys, are you ready for a really stupid question?

Does the Earth’s Coriolis Effect have any bearing or effect on the choice of rotor spin direction? It affects hurricanes, tornadoes and bathtub drains (large to small), so does it favor a direction for rotor spin? All of the effects seem to relate to vertical flow along the axis of rotation, and a rotorcraft also has flow in the axial direction.
 
2
Top