Slow gear cycle?

[n86121]

Being a nerd, years ago I actually studied the hydraulic schematics in the service manual. BTW, it is NOT a great topic of discussion with fiends.

Anyway, my pre takeoff procedure is to taxi the gear handle DOWN while taxiing (or during runup).

This pressurizes and cycles the whole system.

How long the handle takes to pop back up from 'gear cycle down' to 'gear is down and locked' position indicates fluid level.

In the summer its about 4-5 secs. In winter a bit longer.

If it takes longer, it tells you the system low.

AND, if there is a leak and it doesn't pop back up because it can't hold 1200-1500 PSI (as I recall), or takes really too long, then you find out BEFORE you takeoff (Which is much better than AFTER).

[n86121]

I do think the system will self purge, but can take a lot of full cycles to do so.

So even after 'topping' the tank, it will continue to burble air up, and need to be re-topped a few more times before it stays full and happy.

[Jhogan0101]

Thanks David, where does air usually get introduced?

Also, is there a way to force the system to purge the air?

Sounds to me from what you were saying earlier maybe holding down the gear handle?

[JAG]

I think the system can generally handle a bit of air and would eventually purge through the tank...over time. However, as I highlighted below, air above the reservoir - specifically the suction line to the pump, is not self purging. I learnt this the hard way. Cessna even recognized this and highlights this in the Service Manual. Ensuring you have no air between the reservoir and the pump is essential, and it is simple to remove. It may take a little time to prime that line, but only needs to be rarely.

Jeff

[mshac]

Here's a thought - What about manually cycling the gear doors several times on the ground, with the hand pump? Would that help purge any air in the system?

[wslade2]

I suspect it would purge air from gear door actuators but not the actual landing gear actuators. So that would be some. Of course the big concern is getting your landing gear legs to push into lock position.

Just got finished doing the front actuators, jacking it up and cycle gear thing.

BTW, reminder, don't have to have a mule. Power drill and splined socket from harbor freight will power the pump after removal from the engine to cycle your gear.

[mshac]

Originally Posted by wslade2

BTW, reminder, don't have to have a mule. Power drill and splined socket from harbor freight will power the pump after removal from the engine to cycle your gear.

Unless you have a late-model Skymaster that doesn't use engine-driven pumps.