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How to withdraw jacks from the plane

As I just had an owner tell me the old story how a reputable shop did bend his wing I was wondering how this should be done. After releasing the plane from the jacks it will usually rest quite high with the struts partly extended. Then at some moment the struts will break loose and the plane will come lower to its normal height on the gear. I have seen shops withdraw the jacks fast in order to reduce the time they are below the wing but that is no good solution either. How should it be done? Best would be to lower the jacks all the way down before withdrawing them but many hydraulic jacks will not come down properly without any weight on them.

www.ing-golze.de
EDAZ

many hydraulic jacks will not come down properly without any weight on them.

I have never seen jacks like that, and would never use them if I saw them. The procedure I have always seen (and participated in myself) involved lowering the plane, one little bit at a time and with all 3 jacks moved concurrently, until the plane is fully resting on its landing gear, the jacks continue to come down and when they are all the way down they are withdrawn.

Anything else is risking having a jack going up through the wing, probably into the fuel tank, with massive damage and a massive fuel spillage inside a hangar.

But maybe I am misunderstanding what you describe.

Administrator
Shoreham EGKA, United Kingdom

It has to do with the weight of the actual aircraft. You won’t have this problem on most larger aircraft, on some other aircraft the jack won’t go down any further when their is weight on the wheels, but shocks still extend further than usual.

It is common practice to either support the wing and remove the jack, or force the jack further down by pulling down on the jack (always from the side part, never put hands between the top of jack and the aircraft) and remove the jack when down.

After the jack is removed rock the wing slightly so that the aircraft will get lower.

When the aircraft still has the jack under it but no real weight on them, it is dangerous to rock the wings, it would easily be pushed of the jack points.
Either the wing support and removing of the jack, or manually lower the jack is safer operation.

Peter I think you understand it correct. Maybe you have more weight onto the jacks (full tanks?) Actually I never seen jacks that retract without weight on them (apart jacks used for cars). Would you like to share which jacks you use?

JP-Avionics
EHMZ

I have used various jacks, borrowed from some maintenance company down the road

They all retract on their own if you let the pressure out, or it’s easy to pull them down manually.

However they have all been quite heavy – something like 20kg each, minimum.

I am looking to buy 3 jacks for myself (because the borrowing stuff is sometimes a problem) but haven’t yet found any which are light enough for me to carry – 15kg max.

Administrator
Shoreham EGKA, United Kingdom

Then at some moment the struts will break loose and the plane will come lower to its normal height on the gear.

Do you really think this is even remotely comparable to an average landing? Even dropping the aircraft from 1m high should be OK.

I think literally “dropping” from 1m might be a little excessive for a normal landing

Administrator
Shoreham EGKA, United Kingdom

Aircraft jacks are variable in the extreme when it comes to retracting, it’s all about the internal friction, there is no good way to get a sticky jack to retract but my advise it to keep your fingers clear at all times, don’t let anyone touch the aircraft, and get a ratchet strap to retract the jack to a point that if the aircraft drops it will not hit the jack when you are removing it………… All a lot easier to say than do!

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