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michael(at)wikstrom.cc
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 Posted: Sun Jul 28, 2024 1:48 pm Post subject: Yak-18T main LG shocks air/oil filling procedure |
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Hi Vic,
Thanks for your recent input on my shock issues.
I've checked the main gear pressure, both bottom and top.
The bottom part has 65 kg/cm2 and the top part has 18 kg/cm2
The front shock has bottom 70 Kg/cm2 and top has 20 K/cm2 - This shock works fine.
I've not checked for oil yet.
What I don't understand is, with the aircraft empty (60L+60L fuel) with no-one inside, the main gear shocks are half compressed, and she is sitting statically at quite an angle, to the rear.
If I measure the ''shiny'' part of the shock, which when on jacks, measure 290mm, goes down to about 200mm when the jacks are removed.
If I fill up fuel and put 2 persons inside, the shocks compress almost completely.
What I'm wondering is, that as my aircraft is an earlier model yak18t (1979), maybe I'm, using the wrong pressure settings? Maybe the top part should have higher than 18 Kg/cm2?
I got the readings from the only yak18t description manual that I have.
Vic, can you confirm that it is pressure in the top part that determine the static position of the aircraft?
Note that I have no visible oil leaks, and no pressure leaks either
Thanks for any input that might help
Michael Wikstrom
Yak18T – F-HMSS
On 2024-07-09 16:59, Vic wrote: | Quote: | --> Yak-List message posted by: "Vic" <vicmolnar(at)aol.com (vicmolnar(at)aol.com)> 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 Read this topic online here: http://forums.matronics.com/viewtopic.php?p=513682#513682 Attachments: http://forums.matronics.com//files/p1040077_352.jp= - The Yak-List Emhref="http://www.matronics.com/Navigator?Yak-List" target="_blank" rel="noopener noreferrer">http://www.matronics.com/Navigator?Yak-Listhttp://for========================http://wibsp; - Lissp; -Matt Dralle, List Admin. _-= --> https://matronics.com/contributio===============
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Vic
Joined: 12 Aug 2008
Posts: 115
Location: Southern Bavaria
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| Posted: Mon Jul 29, 2024 5:51 am Post subject: Re: Yak-18T main LG shocks air/oil filling procedure |
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Hi Michael,
the air pressure numbers look a bit low at below 20 bar, maybe from a Yak 18 two seat. We did fill up a 18 T two years ago, but just cared for stand height, no worry about numbers. You fill up more than required and only by testing and wiggle on wings and later reduce air in small amounts for some angle in linkage at the tele. You don´t want all straight up, too stiff on the ground, see my photo. The two pressures inside are separated by a piston in the chromed tube. The high pressure side is only acitve at high bumps from heavy carrier landings, when that piston moves down from the excessive pressure rise in the low pressure system that you fill up at the top valve way up the gear. So just fill up at the top valve for stand height, no matter what numbers say, for your aircraft conditions in use.
Take care for dirt on the chromed teles, there is only a felt "seal" , that does not seal much but instead collects loads of dirt that ruins bronce bushes inside and scratches the hard chrome. So only help is clean all the time once you see dirt collected. For having a real seal and dust wiper you have to disassemble the complete landing gear, a bigger job but no rocket science. Standard seals inside are common o-rings, not great. Today I´d go for hydraulic type PU seals when available at these sizes.
cheers
Vic
P.S.: In second photo below your Yak in Thannheim - with mag troubles ??
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michael(at)wikstrom.cc
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| Posted: Mon Jul 29, 2024 1:24 pm Post subject: Yak-18T main LG shocks air/oil filling procedure |
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Thanks Vic, I'll let you know how it goes
Thanks
Michael Wikstrom
Yak18T – F-HYMSS
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