Someone mentioned the heating up of the oil and caused the damping to be less effective, and one of the ES guys did a test heating up the oil, and several other oils.  Yes, the damping is less when they're hot.  Most ES guys now block the nose gear fairing so the heat can't get down through the fairing and heat up the strut, which does help alot.  The IV obviously does not have the fairing, but indeed could very well get heated up, and if you lowered the gear say on short final, it would not have enough time to cool.  Since the ES also has a nose wheel fairing, the shimmy is much more pronounced.   Most ES's have a slight shimmy at about 40 kts.   I've flown more than 40 different ES's, and a vast majority of them have at least some shimmy when braking.  I've had the same shimmy in several IV's, but nothing out of the ordinary.  In the ES community it's referred to as "the big one".   This is the difference between a normal shimmy, and one that is teeth rattling, holy crap type thing.  I've also been in one of those which sounds like what Paul had.   In this case, the mount cracked and the engine rattled around so much that it also hit the cowling and cracked the paint.   One other ES had a severe shimmy and collapsed the nose gear, broke the mount and of course had a prop strike.   There was a mod just a few years ago that added a second O ring to the ESCO strut which helped, but you really must do the "grease plate test"  often, and inspect the strut for any sign of leakage.  If there is ANY oil at all leaking out of the strut, you need to fix it before you fly.  The new strut with the shrader valve at the bottom of the strut is completely different damping and just doesn't do "the big one".  This is basically the same strut as the Columbia.    There have been at least 7 ES mounts with cracks in them lately, and two of them were most likely caused by nose wheel shimmy.  As far as engine mounts cracking goes, there have been several IV's, and ES's with cracked mounts.  I would guess there are a LOT more mounts cracked out there that have gone undetected.  Everyone should have the mounts beefed up to at least what Lancair now does to the new mounts, but I'd rather see them with an additional bar across the front mounts.  In an ES it can just go straight across, and the the IV, it has to go out slightly.  There has been a great deal of discussion on the Lancair ES email list about shimmy and engine mount cracks.   To get in depth detail on all this, I'd suggest doing a search on the ES group list.  You can find lots of pictures of the modified mounts too.  You can find it at yahoo groups under Lancair_ES. 

The ES and IV have the same basic mount and nose strut. 

Here is a picture of a TSIO550 mount from a different certified airplane just to give you an idea of what can be done to beef up the mount.

Ron Galbraith

So--just how do you check fluid levels, internal leaks and dampening force on a ESCO strut with internal dampeners???  I know how to service the strut by compressing it until the fluid runs out and then airing it up to about 300psi, and that was done about 18 mos ago.  So it seems to me if the strut does not collapse and there are no visible leaks (other than the normal engine oil residue after every extended flight) then it is reasonable to assume all is ok with the innards--is there is more to the story, well please enlighten me.

paul, N94PT

 

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