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Yak-18T main LG shocks air/oil filling procedure

 
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michael(at)wikstrom.cc
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PostPosted: Fri Jul 05, 2024 2:07 pm    Post subject: Yak-18T main LG shocks air/oil filling procedure Reply with quote

Hi
I’m trying to understand why my Yak18T main LG shock absorbers are very soft,  and when sitting on the ground with no-one inside and low fuel, chocks are half compressed and very soft when you try to move the wing tip up and down.
I measured the pressure in the left Main Gear to be close to the documented 65/18 kgcm2 in the lower / upper part.
Could a lack of oil make the shocks stay in a half-compressed state when on the ground?
What would be the effect if they were filled with air instead of nitrogen?

Does someone have a procedure for filling oil in the shock absorbers for a Yak18T, and what type of oil is needed.
My documentation says 755cm3 /  355cm3 of AMT-10 oil for main & front chocks – what is the western  equivalent of AMT-10 oil

Any ideas?


Thank You
Michael Wikstrom
La Colle sur Loup, France
Yak18T – F-HMSS


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Vic



Joined: 12 Aug 2008
Posts: 116
Location: Southern Bavaria

PostPosted: Tue Jul 09, 2024 12:59 pm    Post subject: Re: Yak-18T main LG shocks air/oil filling procedure Reply with quote

Hi Michael,
there are two places for pressurizing the lg struts: You checked the bottom filling valve but that is just for extra hard landings when a second piston gets active, which is sitting in the top of the hard chromed inner telescope. This filling does nothing for the standing height. Look way up at the painted outer section of the lg strut, there is another filling valve next to the brake hose, see photo below. There you can add oil or change it by fully compressing the strut to get old oil out. Don´t know about the amount of oil but you found some numbers. Anyway, at the top filling valve you can add some more air, nitrogen no real argument. But don´t do excessive pressure, it would give you a harsh ride. I´d want some angle in the brackets that align the wheels for parallel tracks.
In case you disassemble the whole landing gear I´d suggest to bin these old felt seals at bottom , they collect a mass of dirt and lead that into the strut and destroy bushes and hard chrome. Better have real dirt wiper seals there, like on motor bike teles, saves you precious hard chrome restoration costs.

cheers
Vic


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