Landing Gear Issue
 

Posted for a friend at AirScan


Looking for any help at all on this gear issue.

Having a problem with gear extension on 932AS/SN 01879

Right gear locks down fine. Left occasionally is struck by downlock and prevented from full extension as the top of the strut is rising. The right gear gets fully retracted (observed on very slo-mo video) before the downlock engages. On the left side, as soon as the pin (chromed ball) on the overcenter arm is struck by the top end of the strut moving upward, and the downlock is released by the rotation of that arm, the downlock moves rearward, preventing the final movement of the gear to the full down position.
We have changed the downlocks. Left to right—same problem.
It is as though the right side remains passive until the gear is full up, while the left downlocks wants to engage immediately and forcefully once the arm rotates to release the small pin it’s been holding.
Both downlocks are hydraulically “T”’d together. Pressure SHOULD be the same in both. Snubber control was in earlier models (through 01671) on the respective main gear actuators. 01672 and after in the Pwr Pak, but there’s only a single hyd line to both gear actuators (T’d together) and both downlocks, (T’s together.)
Five of us working the problem are each struggling. There must be an Occam’s Razor simple solution. Help!!
Five us us have ben turning pages and scratching heads for over a week. Time and again we’ll get 20 perfect downlock sequences, then next day a series of failures. Hand pumping and Pwr Pak both.
Ideas?

Anyone have any thoughts on this issue?

Herb, has anyone tee'd in a pressure gauge to see if there's a dropoff in pressure?

I am really focusing hard on the words written to try and figure out what is going on. I have some confusion as some times he talks about "retraction" associated with downlocks and "full up". Is this just a mistype, or am I not understanding this post?

My understanding is that the sometimes the LEFT Main gear is not able to fully EXTEND (read DOWN AND LOCKED) as it is coming into contact with the downlock pin before it is fully seated in the saddle.

Jeff

Possible rigging
 

Unfortunately I only have schematics and a manual up to S/N 01462 so I can't provide any direction on the hydraulic pressure/power pack potential problems. However given my knowledge on the earlier models, the rigging is important to have sorted first. It sounds like the overcenter has not been rigged properly with regards to the downlock and associated linkage. The downlock should not overcenter until the gear contacts the overcenter release bolt on the downlock.

Potential causes in the rigging of your symptoms:

1. Is the downlock clevis shimmed properly? If it is over shimmed, then with pressure acting on the downlock during the gear extend sequence, it may move the down lock beyond overcenter once pressure is supplied.

3. is the Overcenter Stop bolt rigged correctly? If it is too far out, the downlock will overcenter before gear is up in the support.

2. Overcenter-arm button is too far out, allowing early release of the downlock. On the earlier models, during the gear extend sequence, the pressure is building up in the downlock during the extension. The overcente-arm with spring is also holding the downlock from overcenter (along with the proper rigging above). As the spring-gear comes up into the support, it will contact the overcenter button and now all the downlock needs is a little nudge from the gear on the overcenter release bolt and the downlock kicks over.

Again - by the description you provide, it sounds like the overcenter is not happening with the downlock.
Jeff

Here is the solution that fixed it
 

Thanks everyone for your comments but here is the solution I just received back from AirScan

It was finally determined that the “angle of repose” of the gear door uplock assy was slightly off. So very simple. AND that proper angle alignment is about the FIRST thing in the rigging.

Thanks Herb.

Sorry for being pedantic about the language used; "angle of repose" and "door uplock", but can you confirm that they are saying that the angle of actuator was not properly shimmed and therefore the downlock was not at the proper angle for the overcenter to work properly? I am kind of invested in what was wrong, but the description you provide is a little cryptic for me.

Thanks,
Jeff

an·gle of re·pose
noun
the steepest angle at which a sloping surface formed of a particular loose material is stable.

You said it right. Simply put, the actuator was at the wrong angle.

Thanks Herb!

If you have time Herb, a picture of the problem would be great.

Sorry, there were no photos that I could get