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TB20 landing gear operation

Here is another video



The tiny judder at the very end of the last sequence might indicate that the landing gear hydraulic pump might need some attention in a few years’ time. It’s done 12 years…

Administrator
Shoreham EGKA, United Kingdom

Wow your TB20 is like a Furby it listens to you…

Interesting Video btw…are all three gears mechanically linked to the same actuator, motor..?

Last Edited by Vref at 06 Jan 16:30
EBST

It’s interesting that the left MLG hardly moves until the right MLG is fully up. I would pull the emergency release and manually push the gear legs up and down to see if there is any stiction causing this. The nose gear would behave differently in flight due to air flow pushing the gear up. All three release their latches at the same time – you can see the initial twitch. Whilst I wouldn’t expect all three to go up at the same time I also wouldn’t expect them to go up one at a time like this.

I would guess you have downsprings to assist emergency extension? If so I would have thought that the increasing resistance of the right MLG downspring would get the left MLG moving as the pressure builds up.

Having watched a friend (not Peter) take off in his TB20 a number of times, this sequence is, AFAIK, normal for a TB 20. What I find a bit strange (disclaimer – I am NO mechanic!) is that at 00:49 the right MLG seems to ‘hesitate’ before going into the fully ‘up’ position. Is that normal?

That looks pretty normal to me. My old TB20 developed a real shudder on the mains. It was thought to be the pump but it turned out to be internally corroded actuators. I got mine refurbished by a company in the US who made a tool to do it. Trouble is I cannot recall the company name but could dig it out if it helps. This is all 5 year old knowledge so things may have changed.
I recall new actuators being available but at stupid prices.
Judging by the video I’d do nothing.
Ian

EGNS/Garey Airstrip, Isle of Man

Concur. Based on the experience with my TB20 that looks pretty normal to me.

RXH
EDML - Landshut, Munich / Bavaria

The system is very simple. It has only one hydraulic pump whose pressure or flow are unregulated, so the fluid flows wherever it finds the least resistance, and it will flow preferentially into a path where the resistance is perhaps just 1% lower than elsewhere.

Anything else substantially complicates the system. You would need a constant volume flow rate to be driven concurrently into each of the three landing gear sections. I have no idea how say a 747 does it but it does move up/down evenly. I guess they either have multiple pumps, or a single pump with multiple chambers. Or they feed a regulated flow rate (not sure what sort of device would give you that – pressure regulation is easy, but flow rate regulation?) into each section.

It is a very good suggestion to manually waggle the main wheels, but it will have to wait for another year because of availability of a hangar where I can do maintenance and where we can jack the plane up. The hangar where this Annual was done is closing on 11th Jan.

However my gear has always behaved like this. You feel it during flight, with a lot of yaw for a second or two while the gear is operating.

It was thought to be the pump but it turned out to be internally corroded actuators

Interesting; my recollection from you was that it was the pump, but I could not see how that could cause it. Did you have any actuator leaks? How can one get internal corrosion when the actuator is full of hydraulic fluid? Was the fluid perhaps not changed often? I do know from my local maintenance scene that many planes don’t have fluid changed for 10-20 years.

Last Edited by Peter at 08 Jan 22:22
Administrator
Shoreham EGKA, United Kingdom

Looks much smoother on a Mooney! :)



YPJT, United Arab Emirates
…… and quite different with a purely pneumatic heavy gear :



cheers Vic
vic
EDME

On reflection I think one can achieve more or less simultaneous operation of the two main gear portions, simply by rigging the geometry such that the pressure required is very nonlinear versus the angle the gear has travelled through – if that makes sense. Then adding a spring to each half of the gear, which the pump works against, would finish it off.

Unfortunately that would give you a system which is spring-loaded into the UP position, which is no good if you want a gravity-assisted emergency release mechanism like Socata have.

Administrator
Shoreham EGKA, United Kingdom
24 Posts
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