Weird thought #5 - horizontal stabilizers

[serverlan]

Traditional wisdom -
If you put a horizontal stabiliser in the airstream from the prop,
then it will

be more effective because of the increased air velocity over it.

Problem:-
The stabilizer will then

respond more to the prop air stream than the relative flow of ambient air.
i.e. if you are in a PPPO

nose-dive situation, then the stabiliser will keep you pointing the way you are going, relative to the

prop.
i.e. it will keep you pointing down.

A bigger stabiliser out of the prop stream will react to

the ambient air, and tend to level your flight out again.

Am I making any sense here?

don

[le-wardy]

Don,
A PPO (Power Push Over) occurs when the

rotor goes into a sustained zero-gravity situation, meaning the rotor is not creating any lift from it. In

the meantime, the propellor at the rear is pushing the aircraft forward.

With no lift from the rotor

to hold the aircraft's nose up, the rear of the aircraft will try to overtake the front of itself. Hence the

term, power push over.

THrottle control is the key here. Knowing when to ease off the prop thrust at

the start of zero-g situation, and getting the g-loading back onto the rotor by bringing the cyclic stick

back to you. The actions required to do this does not mean sudden movements at the

controls.

Horizontal stabilisers play a role, but are not the total saving grace in respect to size.

Pilot reaction to the warnings beforehand of a sustained zero-g effect is the critical factor here.

In

the course of your training Don, your instuctor at the time will make you aware of zero-g situations in

theory and in flight, and show the correct and safe method of dealing with it.

[rehler]

Don,

Your post regarding the HS being within the prop wash ("then the stabiliser will keep you pointing the way you are going, relative to the
prop.") is a common misunderstanding. Actually the HS within the prop wash is more effective in responding to the gyro pitch than being outside it. This is difficult to understand, as it seems to go against the common belief that the prop thrust air comes off the prop perpendicular to the prop circle at all times. In reality, the prop thrust air changes as the relitive air hits it. For example, if the gyro turns (with rudder) to the right, then the relative wind hits the prop thrust air and makes it "bend" to the right, so when it hits the tail it is not straight.

The best place for a HS and vertical rudder is centered on the prop center, like the SparrowHawk or Dominator gyros.

An example often given to help explain this is to take two electric fans, one representing the gyro with strings tied to the fan face to show the air movement and direction, and the other representing the relative wind. It clearly illustrates that if the relative wind is coming at an angle from the side (say 45 degrees from front) that the prop thrust air of the gyro is no longer straight, but is at an angle between the two fan directions. The angle of the air is determined by the stregnth of the prop blast and the relative wind.

Also it is important to know that the effect of air on the control surface (rudder or HS) is greatly affected by the speed of the air. In fact, if the air speed it doubled the effect (push) on the HS is four times as much (the square of the speed increase). For example, if the gyro is traveling at 60 mph and the air coming off the prop is 120 mph then the HS is 4 times as effective within the prop blast than outside it but at perhaps half the angle. So, even though the angle of the air coming off the prop is less than the angle of the relative air alone it is about twice as effective since the air hitting it is moving faster, than it would be outside the prop blast area.

I hope I didn't just muddy the water. Chuck Beaty (the most knowledgable gyro expert I know) explains it much better.

[serverlan]

An excellent explanation. Thank you very much!

Don