Rotor influence on the horizontal stabilizer

[Jean Claude]

The deflection due to the presence of the gyroplane rotor on a horizontal tail located, for example, 1.4 m behind the axis and 1.4 m below the plane of rotation, can be evaluated using the Naca report 1319 , figs 6b and 6c:
Since z/R = x/R = 1.4/ 3.22 = 0.43 we can see that when the wake angle is at 90° to the plane of rotation, then V = 0.6 Vi , with very little difference up to 105°.


At 25 m/s, if rotor induced speed (i.e. Vi) is Vi =1.1 m/s . So, in the tail area, it will be 0.6*1.1m/s = 0.66 m/s and the local angular deflection produced by the rotor on the tail will be : ATan(0.66 m/s / 25 m/s) = approximately 1.5 degrees.

 

[Chook]

Jean Claude, you present some really interesting and wonderful calculations!
In the near future I wish to build a small wind screen assembly on the front of my single seat gyro.
This wind screen addition can sometimes cause more danger than it is worth, but without a wind tunnel to predict
these surprises a calculation that you have presented here will be a good start.
Thank you.

Regards........Chook.

 

[Jean Claude]

Chook,
1.5° A.o.A on a 1 m2 tailplane gives an offset of 30 N, requiring the aircraft's centre of gravity to be moved forward by about one inch to maintain longitudinal balance.

In the case of your windscreen with an initial angle of attack greater than 30 degrees, the rotor deflection is not significant.

 

[Chook]

Jean Claude, what is the Vi of your 30 N figure above please?
And if the windscreen is curved around the vertical plane, what is the mathematical relationship of that curve?

 

[Jean Claude]

Chook,
Tail lift = ½ ρ S CL Vf² .
So, if Vforward = 25 m/s and dCL /di = 2/rd, then tail lift = 30 N (i,e 6.5 lbs)

And if the windscreen is curved around the vertical plane, what is the mathematical relationship of that curve?

Since a windscreen is completely open at the rear, the flow is detached from the inner wall, and you only get an idea of the drag by assuming Cd = .7 relative to the frontal area. The angle has no appreciable effect

 

[Gyro-nut]

Jean Claude, I love your posts.... just wish I understood 1/10th of what you are posting.

 

[Jean Claude]

Don't you understand that, as the rotor pushes the air down, this affects the angle of attack of the HS?

 

[Gyro-nut]

For sure... that's the 1/10th I'm talking about
That was an attempt at humor Jean Claude. I enjoy learning a lot of the equations you toss around, but without prior knowledge of the formula's, it takes me a while to figure out what the variables represent.

Keep 'em coming... you can never learn too much!

 

[Doug Riley]

I wonder if this analysis applies to the many gyro pilots who swear that a gyro rotor has no downwash... If you don't believe in a physical principle, does it not apply to you?

 

[j4flyer]

Jean Claude do you think this might explain why short coupled Gyros with large horizontal stabs exhibit a “cabin hop” feel ?

 

[Jean Claude]

I wonder if this analysis applies to the many gyro pilots who swear that a gyro rotor has no downwash... If you don't believe in a physical principle, does it not apply to you?

Yes, Doug
Some pilots think that a gyrocopter rotor is not governed by the same laws as a helicopter rotor, and that the above report is irrelevant.
It is, however, a theory dealing more generally with ‘lift rotors’, as its title makes clear

The particular case of autorotation is simply that of a wake angle greater than 90°, i.e. above the plane of the blade tip.
Page 856 of this report explicitly states:

 

[XXavier]

The figures mentioned by JC can also be found here: https://ntrs.nasa.gov/api/citations/19980228400/downloads/19980228400.pdf

 

[okikuma]

The figures mentioned by JC can also be found here: https://ntrs.nasa.gov/api/citations/19980228400/downloads/19980228400.pdf

An excellent find Xavier. Muchas gracias!

Wayne

 

[Jean Claude]

Jean Claude do you think this might explain why short coupled Gyros with large horizontal stabs exhibit a “cabin hop” feel ?

Sorry, Bob
I don't know the "feel" you're talking about.