wfield0455

My Feedback: (7)

This isn't jet related but I figured there would be plenty of people here that have experience with retracts so I thought I would go ahead and ask anyways. I recently completed an Aeroworks P-51 (told you it wasn't jet related) and I wasn't too keen on the air valves, servos and restrictors that were supplied with the kit so I removed the restrictors and replaced the servos and valves with two JetTronics dual action air valves. I was able to get everything set up so that the gear doors cycle properly and the gear extends and retracts in a positive fashion without slamming. The problem is that cycling the gear just once, nearly empties the air tank. I had expected to be able to cycle the gear at least 3 or maybe even 4 times. At 8" long and 2" in diameter I assume the supplied tank would be classified as medium sized? I have pressurized the system and let it sit for several hours without noticing any loss of pressure so I don't think I have any major air leaks. This is the first time I've used pneumatic retracts so I'm just wondering if someone has any suggestions about what may be wrong or if perhaps I just have unreasonable expectations for the size of the air tank installed. If there was more room, I would simply install a larger air tank but I don't think I could get anything larger in there. Any suggestions would be greatly appreciated.

Thanks
Wayne

FILE IFR

How big is your airtank? You're working gear doors and landing gear (tail wheel too?).... a fair amount of volume is needed.

Ruizmilton

My Feedback: (29)

Wayne:

Assuming you do not have any leaks, sounds like you just do not have enough volume of air, yet that will depend on the size of the retract cylinders and the weight of the gear, changing the mechanical valves for the jettronics valves and eliminating the restrictors would have had no impact on the cycles the system can do. I would check for excess air loss during the retraction cycles, some cylinders may leak air during the plunger movement and not on the up/down stops, yet it would be difficult to detect, what I do is retract the gear and stop it/hold it at the middle of it's movement and check the pressure gauge for air loss. Another thing to check is for resistance to movement or friction on the retract trunions.

I would put an additional 2 tanks in line with the one you now have, I'm under the assumption your gear requires a lot of air volume and the gear is very heavy.

highhorse

My Feedback: (2)

Air tanks weigh next to nothing, get dimensions for Robarts' tanks and get the biggest one (or two) you can fit into your airplane. The tank u have, at 2x8, sounds pretty small. Remember: while the volume increase is linear with length (a 1" increase in length would + only 12.5%) it's squared with the radius (a 1" increase over you current tank diameter would double the volume). Also, 100 psi is fairly standard, but 150 psi is do-able.

PaulD

My Feedback: (39)

Hate to ask a dumb question but are you sure the air tank is actually filling? I ask this as I helped a guy troubleshoot teh same problem with a jet and it turned out he had an air tank with a valve on the top. The valve was closed and all he was doing was filling his air lines which had enough volume in them to just make the gear move. Your description doesn't sound like this but strange things happen....

PaulD

FILE IFR

Good thought!

I had a 'sticky' shrader valve once. I had to pump air from the pump that had a PSI gauge.... the pump's gauge had to read about 170 PSI while the plane's on-board gauge would read around 80 PSI. I got rid of that filler valve.

wfield0455

My Feedback: (7)

Thanks for the replies. I hadn't considered that the cylinders may be leaking at mid travel. I'll try stopping the gear at partial travel and see if that shows any signs of leaking. I also do hear air continue to flow for a while whenever the gear is cycled but I haven't been able to figure out if this is something leaking or just the air being cycled out of the cylinders.. It seems to continue for 2 or 3 seconds after the gear has transitioned..

I did initially have a kink in the air line that was preventing the tank from filling but before I fixed that, the pressure gauge would indicate the tank was full immediately and the gear would only cycle while my air pump was operating. In any event I had replaced the kinked line and the air tank is filling properly... As this is a 20 something pound warbird it does have fairly substantial gear legs, gear doors and a tail wheel retract so perhaps it is just using a lot more air than I suspected. Between the existing air tank and the electronics, the main compartment over the wing is pretty well filled up... I may need to find a creative way to add another, larger air tank....

Thanks
Wayne

highhorse

My Feedback: (2)

If there's no room for a larger tank, you can always add additional small ones...........