Well, I'm back.  This time with some new information, though, so bear with me.  The last thread about my ES shake issues revolved around the nose gear strut and its role in the problem.  The latest tests do not support that position.

 

I have video taped the landing gear of my ES during slow speed taxi, high speed taxi, light braking, heavy braking, normal take off and normal landing.  I taped the nose wheel, LH main wheel and RH main wheel individually.  I now have a pretty good idea of what the "shake" looks like and where it is.  Of course, this is not the same as knowing what is causing it and how to fix it. 

 

The nose wheel is rock solid with no shimmy, shake or shudder at any speed.  This surprised me.  It also occurs to me that the "shake" that I have felt through the years has not changed.  That leads me to believe that the nose strut has probably not been a part of the problem on my airplane at all.

 

The video shows the main gear wheel pants exhibiting a light shudder, moderate shake or what appears to be a fairly violent shake at various speeds, conditions and brake application.

 

I did quite a number of tests and taped the following events (the left main exhibited somewhat more severe shake than the right main, but the events happened under the same conditions and speeds):

 

-Slight but definitely noticeable shake at steady taxi speed of 12 knots.  One or two knots either side of that number and the taxi is smooth.

 

-High speed taxi tests were conducted by accelerating to 50-60 knots, reducing power and braking as in a normal landing and rollout.   In every test the shake showed up at around 35 knots and went away at about 30 knots when decelerating.  The degree of the shake was directly related to brake force.  Harder braking, harder shake.  Light braking, light shake.  No braking, very little or no shake.  Shake lasts somewhere in the 2-3 second range.  It is felt in the seat somewhat but is more notably felt in the stick as a rapid, short stroke, front to rear movement.......think "rattle".  The impression is also there that the tail is jumping.  Don't know if it is, but plan on taping the tail during an event and see.

 

-Interestingly, the video showed that the mains shake moderately for a second or two during acceleration, somewhere around the 40-50 knot range.  I believe this has been present for quite some time and that I usually dismissed it, when I noticed it, as runway related.  The runway at my home airport was just resurfaced so I am now convinced that this shake is related to issues I am trying to address.

 

If this were a car and exhibited these symptoms I would suspect any or all of the following issues:

-Out of round tire, flat spotted or faulty ply.

-Severe out of balance tire/wheel assembly.

-Warped or wavy brake disc.

-Worn or defective suspension part.

 

At the present time, the condition of the wheel/tire/brake assembly is:  brand new discs, no visual defects or deformity in the tires, balanced on static fixture.

 

I do realize that tire balance can be relative to speeds and that a static balanced tire does not necessarily mean that the tire remains balanced at all speeds and forces.  The part of the puzzle that is most difficult for me is the consistent speed relation to the shake.  The current tires are Goodyear Customs, as were the previous set.
Before that, I had McCreary.  Before that was Michelin.  I don't remember what the original brand was that came with the kit. In all instances the tires were statically balanced.  In all instances, when the shake occurred,

it was at the about the same speeds.  As I write this, though, I seem to have the impression that when I installed new tires the shake would diminish somewhat.  The speeds would remain the same but the severity of the shake seemed to be less.  I don't really have any specific memories to support this.

 

The main gear has been aligned per factory specs.  I checked the alignment again during the recent annual inspection and found no problem.

 

I have run a variety of air pressures and can not really see any difference in how the airplane acts.  If there is an effect on the plane it is certainly small.  I currently run 60 in the mains and 45 in the nose.

 

The discs and wheels show about a .015" run out.  This was the same variance that I found with the old discs.  Evidently the wheels are slightly out of true.  The wheels and discs are the Cleveland numbers that were with the original kit.  However, it would  seem that if the disc were the problem that the shake would occur at all speeds when brakes were applied.

 

I am trying to draw conclusions from this exercise and am having trouble reaching the definitive answer.  It would seem on the surface to be a balance issue.  That is, until I throw in the braking and the fact that every set of tires has been balanced and every set has exhibited the shaking to various degrees at about the same speeds and under the same conditions as every other set.  This makes me think it might be an airframe related problem with harmonics and interaction of components, etc.  I wouldn't even begin to know how to chase that down.

 

If I were not so closely connected to the issue and were analyzing someone else's problem I would probably point to the tire assembly balance as being the problem and suggest that the tires and tubes be replaced and the assembly dynamically balanced rather than statically balanced.  I would suggest the wheels be replaced or rebuilt to true so the run out as a possible contributor would be eliminated.  I would assume that when the tire has a tendency to shake due to imbalance or tire deformity the application of brakes magnifies the problem and gets the violent shake going.  The person whose problem I was trying to solve would probably point out that I was being too simplistic and that the problem was much more complex than that.  Just thinking out loud............

 

I have been in touch with Lancair and they have been very interested in helping solve the problem.  They have asked some very specific questions and offered some suggestions.  I expect to continue that communication as well as posting this on the LML site for any additional input.  I would appreciate any input.  I apologize for the length of this post but there was just too much information.

 

If I can figure out how to upload the video I will do that, too. 

 

Thanks in advance for your comments, questions, solutions.................

 

Jim Scales