thunderturk Posted October 20, 2010 Share Posted October 20, 2010 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. Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted October 20, 2010 Share Posted October 20, 2010 Check your MLG... Quote Link to comment Share on other sites More sharing options...
Lkuest Posted October 21, 2010 Share Posted October 21, 2010 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. Quote Link to comment Share on other sites More sharing options...
trev130eng Posted October 21, 2010 Share Posted October 21, 2010 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. Quote Link to comment Share on other sites More sharing options...
Mt.crewchief Posted October 21, 2010 Share Posted October 21, 2010 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 Quote Link to comment Share on other sites More sharing options...
tinyclark Posted October 21, 2010 Share Posted October 21, 2010 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? Quote Link to comment Share on other sites More sharing options...
P3_Super_Bee Posted October 21, 2010 Share Posted October 21, 2010 The reason tires that "Look" good are changed, or "can't find" the problem is because they are changing them for the wheel bearings. Quote Link to comment Share on other sites More sharing options...
bischoffm Posted October 27, 2010 Share Posted October 27, 2010 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. Quote Link to comment Share on other sites More sharing options...
ali86 Posted February 25, 2011 Share Posted February 25, 2011 shimmy is only caused by the pressure in steering control valve. Valve is replaced. Quote Link to comment Share on other sites More sharing options...
gdmunro1 Posted February 26, 2011 Share Posted February 26, 2011 If the A/C is configured with static line cables on both side this can cause vibrations behind the dash or in the NLG area but only if the cables are to tight. Also the MLG tires and bearing should be checked and or replaced. Good luck! Quote Link to comment Share on other sites More sharing options...
Dan Wilson Posted March 2, 2011 Share Posted March 2, 2011 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. Quote Link to comment Share on other sites More sharing options...
Pitchlock42 Posted March 2, 2011 Share Posted March 2, 2011 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. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted March 2, 2011 Share Posted March 2, 2011 Spoked rims, what, are they putting double deuces on 'em now. Pretty soon, well have that set of 3 buick engine cooling vents under the flight deck windows... Quote Link to comment Share on other sites More sharing options...
larry myers Posted March 3, 2011 Share Posted March 3, 2011 Haven't seen a tubed aircraft tire since about 1970 Quote Link to comment Share on other sites More sharing options...
Zaherk Posted March 6, 2011 Share Posted March 6, 2011 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. Quote Link to comment Share on other sites More sharing options...
Steve1300 Posted March 8, 2011 Share Posted March 8, 2011 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. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted March 8, 2011 Share Posted March 8, 2011 (edited) Found one with spokes in the archives... I know, it's just plain wrong. *** Edited March 8, 2011 by tinyclark Quote Link to comment Share on other sites More sharing options...
larry myers Posted March 8, 2011 Share Posted March 8, 2011 Your right, Tiny, this is sooo wrong. It's apparent, you have way too much time on your hands. Quote Link to comment Share on other sites More sharing options...
thec130dude Posted March 8, 2011 Share Posted March 8, 2011 I'm with Tiny check you MLG tires for out of roundness..... AKA Egg shaped....... Like the spinners Tiny....... Quote Link to comment Share on other sites More sharing options...
jackjack Posted March 15, 2011 Share Posted March 15, 2011 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. Quote Link to comment Share on other sites More sharing options...
JohnWSKYeng Posted May 14, 2011 Share Posted May 14, 2011 There's always the very small chance you could have a tire with water in it, but that doesn't sound like it applies to 40-70KIAS. Also, has anyone noted steering control movement during the shimmy? Quote Link to comment Share on other sites More sharing options...
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