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during take off and landing at 40-70 knot speed SHIMMY.....:(


thunderturk
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during take off and landing at 40-70 knot speed SHIMMY.....:(

Again shimmy , during take off, shimmy starts 40 knots continuing until 70 knot and at landing starts 70 knot stops at 40 knots.

upper and lower torgue arm are tight.tire pressure 60 psi and same level.tires condition good. nlg door rigged.steering control valf normal.fulcrum bearing replaced.steering cable tension checked.

there is no any fault at nlg .

PLEASE SEND ANY ANSWERS. PRIORTY 01.

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If the shimmy is only at certain speeds and stops after take off then maybe the tires are good. Change them anyway. After that, drop the steering collar and check there is no wear on the keyways and the key is fitted. Then change the steering control valve. If that fails then change the NLG.

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When our guys have that problem and can't find something wrong, they always change the Nose tires, even if they can't find anything wrong with them. I'm not a hydro troop or crew chief, but it seems to work for them.

While I was stationed at Naha & CCK, That was usually the cure!!! At Cam Rahn Bay, it was always the cure!!!

I have no idea if it really was, but somebody always signed it off in the books!!!

Then, my bird became O.R. , and I could get some rest!!!!

Ken

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Many times changing both front tires will cure the problem. It could be something else, but you don't want to overlook the easiest fix. I hope it isn't a steering control valve, since there are few to no spares out there.

Play in lower scissor, wheel nut loose, bad bearing?

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Check your MLG...

I agree if the nose has been checked, check the MLG wheel and tire assemblies and ensure the MLG axle nuts are torqued correctly especially the forward ones and do ensure the nose tires and bearings are changed, like it has been said always go for the easy fix first.

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  • 3 months later...

shimmy is only caused by the pressure in steering control valve.

Sorry to disagree with you but if you believe that your either new to the bird or ignorant of the systems.

Just like your family car, if you get a shimmy, shake, rattle and roll in a specific speed ranges then its either your tires or bearings 90% of the time.

Same with the aircraft, most nose wheel shimmy's are cured by simply changing out the NLG tires and bearings, NOT the control valve.

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Changing the tires is correct if somrthing else in the system is not bad. The reason for changing the tires, is that if they are retreaded nose tires they tend to shimmy. Use tires that are not retreads. Also ensure you have a matched tread set and rim set. If you are using spoked tires they are tubed tires even though the rubber on the outside says tubeless. If you are using solid rim tires they are tubless. Never the less ensure you have matching treads and rims.

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About a week ago we had the same problem, severe nosewheel shimmy on our Herc, after doing all the usual stuff, one off the guys touched the R/H steering actuator and found it to be very hot to the touch. When they took the actuator out, they found the piston rod broken clean off. After the actuator change our problem was solved. Feel the actuator temps after a flight, might indicate a bypassing actuator or something more serious like ours.

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Gentlemen, nobody has mentioned it yet, and it deserves to be acknowledged. When everything else works OK and you still have a shimmy, you should pay attention to the mechanical side of things. The shimmy dampeners are there to take the shimmy out of minor problems, but once the minor problems grow large enough; you can start experiencing them again. Everyone seems to have their own pet "fix" for shimmies, and I'm afraid that we spend a lot of money on needless tire changes because it is quick and visible. It can be something as simple and worn scissors bushings compounded by bad bearing or tire balance. It also can be that someone previously disconnected a hydraulic line in the nosewheel sterring systems and didn't bleed the air out, so now the shimmy dampeners are attempting to eliminate a shimmy with air in the system.

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dumb as it sounds, it may be your engines being slighty off on torque value. had this problem several times over the years and always just changed the tires and the problem went away. had a shimmy a few months back and changed every component in the nlg, then changed the strute itself and the problem still maintained. so we swapped a motor and it went away...dumb if you think about it...but it's no longer a problem.

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  • 1 month later...

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