Re: Long EZ Shudder. Out of ideas...


jack hohner
 

This may or may not apply.  The RV-4 had shudder problems with it's spring steel gear.  It was a round tapered bar.  Some pilots would fly without the addition of the wood - (which was called for in the plans) - and glued to the steel gear legs.  The guys without the wood would get the shudder.  When the wood was added the shudder would disappear.  It seems the wood worked as a shock absorber.  Shock absorbers are wonderful for dampening out shudder in all kinds of applications.  The wood also worked as a stream line for the gear, but doubled as a shock absorber.  The reports by several in this thread indicate that shudder happens in general around 30 kts.  This indicates a harmonics that appears at a certain velocity and induces shudder.  The trick would be coming up with a dampening material that could be formed and bonded to the interior face of the gear.  It would need to be somewhat flexible and fairly stiff, but not springy like spring steel or fiberglass.  A laminated wood bow might do the trick, but it would also need to form to the chord curvature of the gear.  That sounds like a lot of work.  Laminating 1/8" wood strips in the bow shape is easy.  Matching the chord shape would be the tricky part.  One could flatten the inside face of the gear legs with flox and then add the laminated wood bows.  I would guess at it with a 1/2" x 3" cross section laminated from 1/8" birch plywood strips ... primary grain lengthwise.  It could also be tapered toward each end.  And it would not have to be the full length of the leg.  The bows might need to be thicker than 1/2".  Less might work too but I would hope the first effort would do the trick.  If that size didn't eliminate shudder, more strips could be added to the gear leg wood bow with lots of "C" clamps and glue.  If it worked, then the avid EZ owner could revisit the gear legs later and add streamlining.  Good luck.

Jack Hohner
Spokane, WA
LongEZ

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