Yaw instability

[Cobra]

Placing enclosed cabins on gyros (Dominators) are supposed to increase yaw instability, with potentially dangerous results.

Im guessing the reason is because a crosswind will put a stronger moment on the larger cabin surface area in front than the smaller vertical stabilizer/rudder surface in back, which will swivel the aircraft around the CG. Is this assumption correct?

Is the solution to have approximately the same exposed vertical surface in front and back (bigger vertical stabilizer/rudder area)?

[Dean_Dolph]

Placing enclosed cabins on gyros (Dominators) are supposed to increase yaw instability, with potentially dangerous results.

Im guessing the reason is because a crosswind will put a stronger moment on the larger cabin surface area in front than the smaller vertical stabilizer/rudder surface in back, which will swivel the aircraft around the CG. Is this assumption correct?That is not only a fair assumption but it is also true!

Is the solution to have approximately the same exposed vertical surface in front and back (bigger vertical stabilizer/rudder area)? Not necessarily!

You mentioned 'a moment' and that is what we are looking for, a larger moment arm behind the longitudinal Cg than in front of it. Consequently even a small rudder area would work if it was far enough back of the Cg. If the area behind is the same as the area in front of the Cg and the moment arms are the same then the forces are balanced. While that is a better situation I'm not sure it is a good situation.

What we really want is for the moment arm to be larger (more powerful) behind the Cg than in front so that the gyro will weather vane into the wind that contacts it from the side. This assures yaw stability where the gyro never tries to swap ends.

The question I have for the 'experts' is, if the flat plate area is ignored, does the enclosure design effect the degree of how much the wind will affect the stability? This question applies to both yaw and pitch. My intuition tells me that the answer is yes but without any experience to back it up.

[LAWOLF]

Placing enclosed cabins on gyros (Dominators) are supposed to increase yaw instability, with potentially dangerous results.

Im guessing the reason is because a crosswind will put a stronger moment on the larger cabin surface area in front than the smaller vertical stabilizer/rudder surface in back, which will swivel the aircraft around the CG. Is this assumption correct?

Is the solution to have approximately the same exposed vertical surface in front and back (bigger vertical stabilizer/rudder area)?
Double tail out in the breeze since the cabin blocks the tail and with the prop dead you have no rudder to speek of. The prop is nt useful 35% area around the center hub only the balance of the prop pushes across the tail area. So if you have a cab and the motor and the engine infront of the single rudder how is the gyro going to get control with the air not going across the rudder and if engine down it gets worse. Taller tail will get above the blockage.
Don Law

[GyroRon]

A easy test is to hoist the gyro up by the teeter bolt - blades off of course - and let it dangle in the wind. See if the tail can keep the gyro pointed the right way. Some cabin gyro will swap ends in this test and are very dangerous and should not be flown.

[StanFoster]

Don: My RAF handles high winds easily. I have the Parham stab which has the vertical winglets. I fly with the doors on a lot as I fly 12 months out of the year up here in Illinois. I have yet to notice any lack of rudder authority.

Stan

[PW_Plack]

Marian Springer notes in her autobiography an incident in which her podded Bensen suffered an engine-out, and that was the first time she discovered the vertical stab lacked adequate authority to maintain yaw control. She crashed.

I'd bet there are lots of podded machines out there that behave fine when the engine's blowing, but become a real handful or worse when dead-stick.

[StanFoster]

Paul: Excellent point and further emphasizes dead stick landing practice.

If I shut my engine off...I will increase my aproach speed 10 mph.

Stan

[animal]

A easy test is to hoist the gyro up by the teeter bolt - blades off of course - and let it dangle in the wind. See if the tail can keep the gyro pointed the right way. Some cabin gyro will swap ends in this test and are very dangerous and should not be flown.

better yet ,Ron park your Rv in front and give it some real wind!
I bet that bird has one heck of a prop blast.

[animal]

Marian Springer notes in her autobiography an incident in which her podded Bensen suffered an engine-out, and that was the first time she discovered the vertical stab lacked adequate authority to maintain yaw control. She crashed.

I'd bet there are lots of podded machines out there that behave fine when the engine's blowing, but become a real handful or worse when dead-stick.

This is why I am looking for info on that RF-170,and why if I build one I would like to put one of the Parham long horn Stabs,on it out on a boom behind the vertical stab. just looking at that big body on it looks like it could get wild fast if the engine died.

Tim H.