Aerotrike Cobra high speed roll instability

[Morph]

In a fixed wing it's called adverse jaw. The side of the body starts flying, especially at higher speeds, and especially if it has aerofoil shape. Whichever side gets more wind, causes the plane to rotate to the opposite side, you compensate using rudder, ailerons and the plane starts rotating the other way. You really have to be awake with your feet

The resolution is increasing the size of the vertical stab or adding a ventral fin underneath the body, Cheetahs, Challengers, CTsw all suffer from this

[LeighFly]

Thanks again for the interest and responses. This is a good way to learn about what really makes a trike tick. It's not as simple as it may first appear

For those of you that have Aerotrike Cobra's with 582 Rotax and full fairings, do you notice a distinct engine offset to the right and a thrust angle to the right. Mine does, and it looks very deliberately designed that way, but I'm just trying to cover all the bases.

There does not appear to be excessive wear on the hangblock or Pylon posts, as the wing resists any twisting movement quite strongly.

I've checked the battons too and found a noticable differece, left to right. One particular theory which has been mentioned to me a few times now, is that ,if there is more drag on the one side (RHS) due to increased Chamber and or reflex, then the wing will want to yaw (adverse yaw) towards the side with more drag, even though that side supposedly has more lift. It's almost like flying with crossed-controls in a fixed wing. Then what happens is that the wing may fly straight and level at one particular speed, but be out of tune at other speeds.

Does this sound plausible? My biggest fear about just setting all the battons back to the original profile is that the result may be quite dramatic on that subsequent test flight. Then the next issue will be how to tune the wing (aileron trim) while adding the least amont of drag to one side or the other.

My plan of action going forward is to get the batton profiles, have the trike test flown by an experienced test pilot (any suggestions? , have the discussion with the supplier or wing experts, set battons to factory profile, let test pilot fly the trike again, then using the best tuning methods, slowly set the wing to fly straight and level at all speeds. Then, for good measure, if there is still an instability, I may well put a set of large fin spats on.

Have I missed anything? The supplier has suggested that I trailor the trike back to the factory for inspection and testing/tuning etc. What's that likely to cost?

Thanks again
Leigh

[Tumbleweed]

Get an AP who flies trikes to check our your whole system.

[LeighFly]

Having now had some conversations with Jenya, who I have come to learn is one of the true experts in the flex wing industry, my faith has been restored. Jenya has been very helpful and his depth of knowledge, which he is willing to share, will surely win the day.

I will keep this thread up to date with the progress, as I'm sure others will take some benefit in future.

Thanks again
L

[LeighFly]

On inspection, we found that the brass bush at the top of the pylon tube is worn, such that the wing is forced to sit skew as described earlier. Thanks for the suggestion to check this too.

One email to Rainbow, had Walter and Mike sending me the correct replacement parts which I received a day later. This is great service guys. Thanks a million.

Thanks to Jenya, I also now have the correct batten profiles, so we can get the whole set-up back to factory spec.

Now we wait for some flyable weather

Thanks to this forum, and you guys who are willing to share your knowledge, I should soon have a great trike with great flying capabilities.

Will keep you posted

[Asterix]

Hi Leigh FLy - its been months - you said you will keep us updated - so - whats been happening?

(I have sudden interest in this - having bought a Cobra!)