such Bad Shiimmy the ELT went off

marcoseddi

marcoseddi

Cleared for Takeoff
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marc
so heading off for my first cross country.. had some issues with the radios but got it all fixed. Im all planned got everything going. Im heading off pushed throttle slowly and then put full power, i glanced at my airspeed indicator and notioced i didnt gain much speed.. All of sudden boom shakking shaking rattling .. real quick i pulled the power applied some breaks and right rudder as i was going off to the left i didnt want to fly off the runway.. it was pretty scary thought something seriously wrong with the plane. my cfi then took it up said its all good i went with him and he thinks maybe i held the yoke all the way down or something jut never ever did that i always have very smooth take offs this really threw me off im like totally out of it. we went around the pattern a few times and i just wasnt feeling anything after that. but still wanted to go after to make sure im still me and can fly but he said i should take off the rest of the day because went for about an hour right after that incident and it was hot.. but i dont know very odd that this happened making me think i dont really know where to put the yoke now and i feel like im giong ot have it back too much now its going to be those slow off the runway take offs where its like almost touching the rear on the runway.. i dont like that or wheelie sort of down the runway..

any advice comments whatever welcome.. or even bashing
 
Most of the planes I rent have problems with the shimmy damper. I get used to writing it up and doing a lot of soft field takeoffs and landings.
 
Other than a really short field, you can't have the yoke too far aft on the takeoff roll as long as you don't let the tail bang on the ground (and you should have learned about that already doing soft-field takeoffs). OTOH, too far forward can result in a number of difficulties, including the one you experienced.
 
You need to figure out specifically what happened, along with your instructor. It's the suddenness I don't like. Shimmies happen, but they shouldn't be sudden unless you hit something or slammed the nosegear or somesuch. I'd also want to rule out a prop strike.
 
it was pretty scary i kept my cool and got it stopped but yes i agree it was something else he says it was me though.
 
MAKG1 said:
You need to figure out specifically what happened, along with your instructor. It's the suddenness I don't like. Shimmies happen, but they shouldn't be sudden unless you hit something or slammed the nosegear or somesuch. I'd also want to rule out a prop strike.
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Shimmy is one of those things that, once started, can accelerate to violent levels in an instant. It's the result of a dynamic instability.

Many mechanics will fool with the shimmy dampener to try to stop it, but they're wasting their time. The dampener is at the other end of a bunch of linkage that develops a lot of slop, and that slop is due to too many hours between nosegear overhauls, or unaddressed shimmy, and the nosewheel fork can move left or right quite a bit before the shimmy dampener even starts to move.

Cessna sent out a Service Bulletin way back in 1984 to address the problem, but few folks know about it. The Cessna Pilot Club highlighted it in a newsletter some time back, which is where I saw it. Cessna says that the Number One problem is a dynamically imbalanced wheel and tire assembly, and they are absolutely right. We had shimmy problems on all our 150s and 172s in the training fleet until I started dynamically balancing those wheels. Most aircraft shops that have balancing equipment use a static balancer, which doesn't fix the problem at all. The wheel has to be actually spinning to determine what's up (and if you've been in a tire shop you've seen that) and so I used to hold the axle and spin the tire using a wire wheel, then experiment with placing weights in various places until it ran smooth. Then I modified an old automotive dynamic balancer and got scientific about it. The nosewheel shimmies all went away and never returned.

Imagine installing new tires on your $25,000 car and not balancing them first. It would be dumb, yet we do it on $300,000 light airplanes. Go figure.

Shimmy destroys all the instruments and radios by shaking them to pieces, and loosens structural connections. I have found loose nosegear mounting hardware. Shimmy is no joke and shouldn't be tolerated. We had a shimmying tailwheel in a Citabria that broke the steel tailpost. That was due to the instructors tolerating it and not telling me that it was shimmying. The airplane was down for weeks, and could have hurt someone if that busted post hadn't been spotted.

Dan
 
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MAKG1 said:
You need to figure out specifically what happened, along with your instructor. It's the suddenness I don't like. Shimmies happen, but they shouldn't be sudden unless you hit something or slammed the nosegear or somesuch. I'd also want to rule out a prop strike.
Click to expand...

I had a shimmy damper retire on me in a C172R - on deceleration after a very smooth landing, on rollout, going 25-30 knots (probably about time I let down the nose wheel). It was very sudden and hard enough that it shook the headset off of my head.
 
Did you accelerate through the turn onto the runway? Sometimes if the nosewheel isn't straight and full power is applied, the plane will never truly recover from the instability that it started with.
 
When I was student, I went out to the practice area solo and came back and landed. I decided to taxi back and make a lap around the pattern to get another landing in. I had a real bad shimmy during that takeoff and I decided to abort, thinking it might be an unbalanced prop or something. The shimmy damper was replaced the next day. I actually had a camera running and got it on video.

 
marcoseddi said:
it was pretty scary i kept my cool and got it stopped but yes i agree it was something else he says it was me though.
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Tell him there is some brown stuff squirting out his ears.

Your plane needs maintenance. Don't fly junk.

-Skip

ps: Congrats on handling the situation safely.
 
It's not fair for him to blame you- obviously the airplane needs repair.
But the short-term solution is to use the normal soft-field method- hold the yoke all the way back until it takes off, then ease off the back pressure as you get into ground effect. Unless you have the plane loaded WAY aft, you won't ding the tail doing that. Once the plane is rolling fast enough for the nosewheel to come up, you should have enough rudder authority to keep the nose pointed where you want it (assuming we are talking about a Cessna single, I speak from about 200 hrs' experience).
If you are uncomfortable doing that, shimmy or no shimmy, you could have a problem if you ever have to do a soft-field takeoff for real.
 
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