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keithmckinley
Joined: 11 Aug 2008
Posts: 434
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 Posted: Tue Jan 19, 2010 8:31 pm Post subject: CJ Nose landing gear brace |
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Looking at the repair manual I'm not sure if I'm reading the tolerance correctly on the nose gear brace.
I've just replaced my NG actuator and with the actuator locked at full extension with no air pressure on the actuator I believe I saw that the brace should be 5mm from the fully locked position.
I'm sure this is so that the brace isn't over extended and bent.
Now I can't find that number specifically as it applies to adjusting the actuator length.
Have gone through the PT-6 repair manual several times. Still looking for more definitive number.
Attached the pages from the manual and the way I read this is that the brace should be 5mm short of max extension and has a plus 3mm tolerance...so min 5mm max 8mm??
Keith
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Noplugs
Joined: 27 Aug 2009
Posts: 35
Location: Houston, TX
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| Posted: Wed Jan 20, 2010 7:34 am Post subject: Re: CJ Nose landing gear brace |
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I have not got into my landing gear yet and reading my Manual and looking at the Parts manual, this how I interrupt the PT-6 Manual. On page 2-4 Fig 5 (for the Nose Gear Brace) Detail “B” it gives you 2 dimensions.
1: 5 (+3) is for the Eccentric (off center / out of round) limit for the bearing surface, I do not believe it is in “MM” either. Since I see no bushing in the upper and lower Brace I assume that the parent metal is the bearing surface so it’s a pass/fail inspection not an adjustable dimension.
Page 2-3 Par. 2.8 It allows the “Ball Bushing” (lower bearing attaches to strut) to rotate in the joint “not more than 686 N.cm. (X Axis) Also it allows it to “rotate Deflectively” Not real sure what they meant but I think it’s the side to side limit or tilt (Y Axis). Then the “Clearance” limit is for the bearing ball to the brace bearing surface.
2: The other clearance of 0.05 – 0.15 mm is the down and locked dimension which is adjustable by adjusting the rod end of the actuator. This dimension is taken between of the forks of the upper brace.
3: On page 5-6 Par 4.1 you can test you actuator for the proper stroke of 333 +/- 2mm as well as pressure/leak test.
I hope I helped and of course if I am wrong, I hope someone will help us both out with their lessons learned.
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keithmckinley
Joined: 11 Aug 2008
Posts: 434
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| Posted: Wed Jan 20, 2010 2:34 pm Post subject: Re: CJ Nose landing gear brace |
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Looking back over the info in chapter 2 I see the .05 -.15.A small feeler gage should tell the story. Measurement is done with no air pressure I believe.
K
Seems to me that there are three ways to hold the gear down in in order of priority
1. The locking pin/ball in the actuator
2. air on the system
3. NG brace over center
My guess is the reason for the small tolerance is to get the brace over center but not enough to close that gap and bend something when the air is on.
Keith
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wlannon(at)persona.ca
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| Posted: Wed Jan 20, 2010 9:17 pm Post subject: CJ Nose landing gear brace |
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I intended to get the book out and reply to this today but did not get
there. There appears to be some mis- conception on this subject.
There is only one function that positively locks the gear down. That is the
over center position of the drag link ( landing gear brace in Chinese
terminology).
The ball lock in the actuator is there for the sole purpose of maintaining
the drag link in the over center position. This serves the same pupose as
the over center latch on many US gear systems and, if I am not mistaken,
also on the Yak 52.
All of the gear up load applied through sideways motion or rough ground is
carried directly through the drag link not through the actuating cylinder or
the ball lock.
In fact, if the nose gear ball lock (in the CJ) were to fail, rough ground
and bouncing could move the drag link out of safety and collapse the gear.
The extended piston rod would end up looking like a pretzel even with full
down air pressure.
The over center measurement of 5 to 8 mm ( 7/32" to 5/16" ) and the contact
surface clearance of .05 to 1.5 mm (.002" to .006") are both established by
adjustment of the actuator piston rod fitting.
If all set up and working properly the gear should be safe with no air
pressure.
Walt
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