Ralph White

Hi,

I'm installing a set of Robart air up/spring down retracts #514 nose gear and #510 main gears in a Saturn pattern ship I am re-storing.
The problem is the nose gear retract will not lock down. The spring appears to be too weak. I have checked to make sure it is not binding, even removed the unit from the mounting rails. I haven't tried the mains yet.
Is there an easy way to solve this problem? Possibly a stronger spring in the cylinder? I have read all the post I can find on this problem but none of them seem to give an answer.

Anyone that has solved this problem PLEASE let me know what you did. I don't want to send them back to Robart if I can fix them myself.

Thank you,
Ralph White, Neoga, IL

Crash Campbell

Hi Ralph,

Are the retract units old or new? I have had problems with corrosion on old retracts, (the aluminium had turned a battle ship grey), this was cured with 600 wet and dry followed by dry lube. Never had a problem with new units but I guess there could be a piece of swarf or a rough edge causing the retract not to seat properly.

Cheers,

Colin

Ralph White

Colin, They are brand new. What worries me is if they are so marginal at locking down now what is going to happen when the plane is flying and has air pressure pushing against the nose gear when I try to extend it.

Ralph

JohnBuckner

My Feedback: (1)

Are you testing them with the airplane upside down?

Ralph White

John,

Yes, I am testing them with the plane upside down. But it seems to me the headwind on the nose gear would be more force against the nose wheel locking down than the weight of the wheel and wire upside down. The nose gear extends fine up to the point of locking. At that point I would think the weight of the nose wheel would not be involved with the final movement of the piston into locking position.

Ralph

JohnBuckner

My Feedback: (1)

Extension has only gravity and the spring to extend and lock,
take the help from gravity away and the system won,t work properly.

I know nothing about the Robart copies but I have two sets of Springairs on my Wing P-38's and they are wonderful systems. But they cannot function properly inverted. Flip your airplane over so the gear can work as designed.


John

Ralph White

John,

I'll see how they work with the plane upright. But I'm still skeptical about the nose gear extending and locking with the head wind against it. I'm thinking I need a little stronger spring in them.

Ralph

Ralph White

I find it hard to believe that nobody has a fix for this problem with Robart spring down retracts. I know other people have had to have trouble with the nose gear locking down because mine only locks down about 2 out of 3 times. And that's with no head wind working against it. Guest I'll have to call Robart. I'm thinking of adding an external helper spring but hate to mikey mouse a unit that is suppose to work as advertised.

Thanks Colin and John for your replies. Both your comments helped, but still the authority that the retracts lock down with just is not there. Now I'm wishing I had rebuilt my old set of Rohm Air Retracts, but thought that something new would be better than something 30 years old.

Ralph White,
Neoga, IL

Edwin

My Feedback: (2)

My guess would be, its defective. We know the concept works. Must be a weak spring. You've done all I would, the only other thing I can think of is maybe a drop of 3 in 1 oil. I do that as maintenance on my air systems. Shouldnt need to on new ones though.
Edwin

Ralph White

Edwin, Thanks for the reply. I was thinking of taking the unit apart. Does the end cap on the cylinder simply screw off?

Ralph White

Edwin

My Feedback: (2)

Dont know. Never had to do that. Seriously, if its new I would send it back. I've only used spring-air. I've seen the robarts at the field but not up close.
Edwin

Ralph White

Edwin, I'm definately going to call Robart next week.
When the Spring Air extend, does it go into lock rapidly or slowly? Also will the gear extend into lock if you have the plane upside down? Seems to me the air resistance on the nose gear would be about the same as extending it with the plane upside down.

Ralph

Ralph White

Opps !! I edited the last post.

JohnBuckner

My Feedback: (1)

My Spring Airs in both airplanes will bang down with some authority but when upright the nose wheel will frequently not lock when operated inverted.

Any air up/spring down system must operate rapidly to function any attempts to slow the extension down will result in failure to lock especially the nose wheel

Do check that your system when retracted is fully in the up position if it is not then the spring will not be at full advantage during attemps to extend agine resulting in locking failure

.John

Edwin

My Feedback: (2)

Mine dont exactly slam down but its pretty quick with no doubt about it being locked. You hear it click. They only time they didnt, was because the mount wasnt ture.
Edwin

Ralph White

Thanks John, I'll check that. I also just thought, maybe the air is not escaping the cylinder fast enough. Maybe the hole that the air escapes from is particuly stopped up.
Ralph

Edwin

My Feedback: (2)

I would think that eventually when all the air is gone the spring should still be strong enough to lock down.
Edwin

Ralph White

Edwin,
I agree. Rolling Thunder from FG (who had the same problems) told me he called Robart and they replaced the air up/spring down cylinders with air up/air down cylinders. Same retract unit, changed cylinders only. If I don't get this problem solved soon, I believe that is what I'm going to try. I assume I would have to get a different air valve.

Ralph

JohnBuckner

My Feedback: (1)

Interesting that is nothing short of a complete conversion back to a conventional system and a complete copout that their system is poorly designed if true.

I have no idea but Springairs have been around a long time, long before Robart copied the idea and I love them.

John

Ralph per chance did you ever compete in Grand Prix motorcycle road racing at Daytona in the sixties?

Ralph White

John,
They replaced the cylinders just on Rolling Thunders set. They still sell the air up/spring down units. I like the idea of the spring extending the retracts if you happen to loss air pressure. Seems to me they could combine the systems so they have air up/ spring assisted air down. Would be the same as air up/air down cylinder except with a spring in the cylinder that pushes on the actuator arm in the down direction in case air pressure becomes to low. Kind of had to explain. Seems to me it would be simple to put the right size spring in the cylinder on the side that pushes the actuator arm down.
Ralph White

Ralph White

John,
Nope, wasn't me. In the 60's I was in the army and then went to University of Illinois studying Aeronautical Engineering, then worked for Boeing aircraft for about 3 yrs. Started flying RC about 1966. Owned Fliteglas Models from about 1971 to 1981. I did win the 1978 Sport Scale AMA Nationals with my Fliteglas P-51D Mustang. Which I still have.
Ralph

Which kit are those P-38s? They look great and just the right size. Also what engines?
Ralph

airbusdrvr

I agree. When testing on the bench, sometimes when the plane is upsidedown, they don't lock. If they work right side up, I wouldn't worry about it.

JohnBuckner

My Feedback: (1)

Thanks Ralph just a long shot that you were a fellow competitor from long ago

The whole point in the spring systems is to eliminate near half of the air plumbing and the complex distributor air valve for just a simple dump valve. Any attempt at half way would be pointless you would still have to go back to the complex valve and all those extra lines every one of which is a additional potential failure point.

If you have an airleak it will be obvious in flight as the gear will hang down the procedure is simple do a high G turn and flip the gear switch to down to dump any remaining air the G will lock the gear.

Any time a gear lock is in doubt mearly do a steep turn and trigger the gear down when you are pulling up elvator. Unless there is a mechanical hangup it will lock every time.

Ralph I built both 38's from wing short kits as the are the best of the best flying 38's in that size (a Hal Parenti design) Built specifically for Warbird pylon racing and I raced them for two seasons, What great fun. Both have TT.46's The Red one was lost to a mid air late in the second season.

Congratulations on the Nats win.

John

Ralph White

John,
Thanks for all the info. I know the thrill of warbird racing. I raced in 3 warbird races in St Louis right before I stopped flying about 25 years ago. I few the same Mustang that I won the '78 Nats with. I managed to win 1st place the first 2 years flying against warbirds the guys from St Louis built just for racing. It was great to beat the specially built for racing planes. The third year I was again in first place until the last lap of the last heat when I cut the far pylon (according to the judge). It was a great time racing warbirds. Wish there was some more races in this area. Probably is but I don't know where since I just got back into flying 2 summers ago. Below is a picture of my Fliteglas P-51D.
Ralph

airega1

My Feedback: (204)

Ralph! DO NOT PUT OIL INSIDE THE AIR CYLINDER! , it will swell the o-rings and you will have bigger problems. Try removing the air cylinder and stretch the coil for more pressure. There probably will be enough lube of a safe nature already inside, a wax free oil type must be used, like refrigeration oil, but use very little.