Why is The Squirrel Squirrelly?

[FlyingSkip]

Just starting to get past the "wet behind the ears" stage with this TwinStar and for the life of me I can't figure out what it is aerodynamically that causes the a/c to "shimmy" just before touch-down and right after t/o? It's really nice and stable all the way down in a vertical landing from a high hover and then POOF! It wants to dance within 2 feet of the ground... Conversely, coming up it wants to REALLY jump with translational lift immediately after t/o and then gets super steady about 2-3 feet up coming into a hover. WTF over? There's gotta be something I'm missing here cuz I can't understand what about the ground effect is causing such a huge change right before/after ground contact. If someone with more knowledge and a better grasp of the aerodynamic principles can explain it I'd appreciate it! Thanks in advance! Avbug, you've GOTTA have something to say about this one and I want to learn!

 

[helimech]

The Astar/Twinstar doesn't have any compensation for translating tendency built into the aircraft, hence when you go to set down or pick up the helicopter, you have the cyclic all the way to the right. As soon as you are in ground effect, if you are not easy on the controls or "smooth" as our pilots like to call it, you will do the dance. I've always put my aircraft on a pad, so I don't always feel the ground effect unless there is absolutely no wind. If you have a lot of Bell experience, it takes a little bit of getting used to the Astar/Twinstar. Bell and most other manufacturers compensate for translating tendency by tilting the mast, usually by tilting the way the transmission mounts to the aircraft. As the French would say, "This is the pilot's problem, to compensate for this effect". Yeah Frenchy!!!! If you ever get a chance to look at a longranger from the front, you'll see a little bit of a tilt, about 3% if I remember correctly, now look at the Astar/Twinstar, you won't see anything, it will look normal, everything straight. If you get your hands on an older AS350B Flight manual, it gives a real good description about why the Astar is the way it is.

 

[FlyingSkip]

Wow!

Ya know, I stood in front of a Bell the other day, and the TwinStar tonight and you're absolutely right! The mast offset is discussed in the POH for the Bell as well, although I can't find anything in the TwinStar book, but that's gotta be it! That would DEFINITELY not have been my first thought, but it sure answers the question! Thanks, HM. I can sleep easy tonight LOL!

 

[Propnose]

Hey Skip...

"There's no such thing as a squirrely airplane, only squirrely pilots!" Quote by Curtis Pitts

How are things going for ya? Married yet? Give me a call sometime. Happy holidays & fly safe. - Prop