donaziza

donaziza

Well Known Member
On a takeoff, today ( RV 8), the gear started to vibrate, kind of like the gear struts had a harmonic vibration, but out of sync with each other. (Had the tail up). Went away at lift off. Subsequent landing OK, as were another takeoff and landing. Didn't bother me at the time, but now it's bugging me. Anybody know what happened?
 
I would do a visual check for flat spots (pilot induced or just sitting in the cold induced) and even check the air pressures.
 
If they didn't do it previously, have you flown in temps like you've been having? The nylon cord tires really take a set when cold, and if you didn't taxi a long way before takeoff, the flat spots could definitely do that. I can feel a "whump, whump" when taxiing for the first 1/2 mile or so when it has sat in the cold.
 
RV 8 takeoff vibration-author's reply

To gnuse, Scott Chastain, and Alex Peterson. Thanks for your answers. No flat spots ( keep them at 35 psi), or cold Wx. I fly a couple of times per week, the Wx was 65*, and I had just done 3 takeoffs and landings that afternoon. It was takeoff 4 that did the vibration, landing 4 was OK, and so were takeoff and landing 5 right after that. The wheel balence that was mentioned might be something to check, but you'd think all takeoffs and landings after the initial incident would "also" vibtate--yes/no? Anymore thoughts out there?
 
G'day Don,

Sounds like an out of balance condition in one of the tyres.

Could be a flat spot/s on one of the mains caused by:-
1. temperature,
2. wear,
3. inflation pressure,
4. alignment,
5. uneven brake wear causing one brake to bind slightly,or
6. it could be from the tailwheel (and its assembly) and the cessation of the vibration at rotate being a pure coincidence.

Hope you sort it out.

Best Wishes,
 
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donaziza said:
kind of like the gear struts had a harmonic vibration, but out of sync with each other...... Went away at lift off.
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One other possibility just came to my mind-----if you hit a rock or other object, or a rut-----anything to get the entire gear leg vibrating-----it would stop when you got off the ground.

If it happens again, try tapping the brakes a bit right after take off----if it is a wheel balance/bearing problem, hitting the brakes will make it stop.

Good luck in figuring this one out.
 
I've seen this before, you need to re-torque your landing gear attach bolts inside the gear towers. Van's advises to do it at around 50 hours and most -8s will show some looseness by then.
 
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RV 8 takeoff vibration

randylervold said:
I've seen this before, you need to re-torque your landing gear attach bolts inside the gear towers. Van's advises to do it at around 50 hours and most -8s will show some looseness by then.
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Hi Randy,

You said "re-torque" my landing gear attach bolts. Re-torque means torque wrench to me. Could you tell me to how many Ft. Lbs. I would have the Mech re-torque to?

Don
 
takeoff vibration

I had a vibration some time ago, more on landing than takeoff. After checking the possibilities, it came down to the right brake pedal hanging up and not releasing the brakes completely. As they heat the rotors, the vibration starts. Make sure the pedals are not binding. There are different fixes for this problem as discussed on these forums in the past, including the longer bolts for the pedals, and installing springs on each master cylinder. They need to unload completely to release all pressure on the brake pads.:confused:
 
Hi again Randy,

When I wrote about how many Ft. Lbs. to torque to, I forgot to ask what the gear towers are. Are you talking down by the axle of the wheel, or up where the gear strut goes into the fuselage?

Don
 
donaziza said:
Hi Randy,

You said "re-torque" my landing gear attach bolts. Re-torque means torque wrench to me. Could you tell me to how many Ft. Lbs. I would have the Mech re-torque to?

Don
Click to expand...
Don,

It is in the plans. Simple enough though to verify the bolt size (AN6?) and look in any aviation reference. You'll find though that it's very difficult to get a torque wrench in there. Most builders that I'm aware of just go by the "that feels about right" method. Based on your description I suspect they are loose and once you go to tighten them it will be quite apparent. BTW, this is a two man job, one inside and one under the plane. You can put the torque wrench on the bolt heads on the bottom no problem but then you need to add some factor for the friction.
 
donaziza said:
Hi again Randy,
When I wrote about how many Ft. Lbs. to torque to, I forgot to ask what the gear towers are. Are you talking down by the axle of the wheel, or up where the gear strut goes into the fuselage?
Don
Click to expand...
The gear towers are the structures in the cockpit that the gear legs bolt to. They have large holes in them through which you must reach with your wrench.
From your question I'll assume you did not build the plane. Hopefully you got the plans and manual with it however and can look up things like the bolt specs.
 
randylervold said:
I've seen this before, you need to re-torque your landing gear attach bolts inside the gear towers. Van's advises to do it at around 50 hours and most -8s will show some looseness by then.
Click to expand...

Hi again Randy,

I forgot to ask, when you say "gear towers", are you talking about down by the gear axle, or up where the gear struts go into the fuselage?
 
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