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byronmfox(at)gmail.com
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 Posted: Sat Oct 31, 2009 7:10 am Post subject: Nanchang Air Gremlins |
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Happy Halloween!
Recently, partner Brian and I heard a hissing sound coming from our front seat gear handle/valve. Oh well, order a new from Doug Sapp. It arrived and we installed it on Thursday. We recharged the system, and damn, the same hissing was escaping the valve! What the devil was going on? Well, Brian quickly discovered that the air was coming from the two small ports on the bottom of the valve. You know, those ones through which air erupts when you raise or lower the gear.
Hmmm. What's the likelihood of having two bad gear valves? Not very likely. So, we called Doug. He pondered for a moment and then suggested that we check each of our gear actuators to determine if downside air was bleeding by one of the actuator rams and migrating along the upside air line back to the valve. Good idea. Did that by successively capping off each actuator. And guess what? All three were sound, and that bloody air poltergeist was still hissing merrily away. Notice how the amateur mechanic will tend to animate troublesome inanimate objects.
OK, after I had regained my equanimity, I sat down to study our enlarged, plastic laminated, CJ pneumatic system diagram. (A thoughtful gift from Dave King) Soon, it became clear that the front seat gear valve gets its air from the controlling back seat valve, where the instructor would sit. Makes sense. It was time to experiment. Up on jacks, I put the front seat gear handle in the neutral position and the back seat handle down. Same hissing but now from the back gear valve. Gear up, the hissing all but disappears.
One more bit of information - the back seat gear handle was extraordinarily stiff and hard to move most likely because it gets cycled once a year during the annual inspection.
My conclusion is that the gremlin lives in the back seat gear valve. For all I know, it's probably been in the airplane since 1968 and has corroded accounting for its stiffness. So, a new one is on its way, and we'll see if I'm right.
In the mean time, do any of you vastly more experience folks have any other ideas?
Many thanks,
Blitz
Byron M. Fox
80 Milland Drive
Mill Valley, CA 94941
415-307-2405
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dsavarese0812(at)bellsout
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| Posted: Sun Nov 01, 2009 5:10 pm Post subject: Nanchang Air Gremlins |
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Byron,
This is a very common problem with both the CJ and Yak 52. Rear gear selectors very rarely get used or even cycled during the annual condition inspection. I make it a point to cycle the gear from both the front and the rear gear selectors. I've seen rust and corrosion so bad in a rear gear selector that the tension spring was totally disintegrated and the two metal surfaces that mate inside the unit had pit marks so deep they could never be resurfaced.
Everyone should make it a point to cycle the gear from the rear cockpit at least once a year. The alternative is fabricate a by-pass around the rear gear selector which as everyone knows, passes the air pressure from and through the rear gear selector to the front gear selector.
Dennis
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