14-13 gear struts

There is an empty space above the oil. The volume of this space varies depending whether the leg is extended or compressed. When you are landing, it is extended and contains a larger volume of air. Landing compresses the leg and the space as the leg is about 7 inches shorter when compressed. This volume change is better than 25 cubic inches. That air has to escape somewhere.

If the top is completely sealed, the air has to go past the bottom seal. This drags along the oil that has been laying on the side of the strut and is trapped between the top bushing and the bottom threaded bushing during flight. Every landing cycle pumps another quality of oil out making a mess. If the bottom seal did make a perfect seal and the bottom gear leg was complete smooth and ding free, the oil and the air would not leak out. If the struts were mounted like the tail strut then the oil would drain away from the seal so that when the air escapes, it wouldn't force out the oil.

The above mentioned drawing SK 468 reduced the amount of oil between the top bushing and the bottom threaded bushing by packing the space with a "hard" grease. By permitting the air to vent at the piston mounting top stud reduces the over all air pressure which has to vent some where. A grease fitting would ease the job of packing this quarter inch space between the bushings

A seal at the top bushing would also prevent this problem but I have a feeling that they wanted some oil leakage to lubricate the bottom threaded bushing .
 
Cy, I'm not disagreeing with what you see in that drawing. However, after talking this over with a couple owners and a DAR, I think the modifications proposed by the drawing - and I haven't seen it yet, are flawed. A loose stud could eventually break after working long enough. How did they propose to mount that 1/2" stud on the top of the piston? The original was welded on the inside of the piston, prior to assembly of that piston. The new securing nut is close to an interference fit with the adjoining filler port. If air can flow around this new stud, so can oil. Additionally, the OD. of the piston is a close fit to the ID of the lower gear tube. This small gap and the metering hole in the center of the piston are a calculated leak that cause the damping action of the gear. Yes, an 'O' ring could be installed in the OD. of the piston that would stiffen up the damping action of the shock strut - if you wanted that. I 'measured' the amount of air volume above the oil level with the strut extended and it's about as much as a 12 oz. beer [soda] can. this includes the air in the piston. Now, when the strut compresses, oil goes into the piston, air escapes the piston and flows into the upper part of the strut. This air does get compressed a small amount; but not enough to blow past chevron packings and a decent shaft. Chevron packings are still used in hydraulic equipment and the 2-3 PSI. bump aren't going to have an effect. If it did, you'd have a pool of oil under each gear leg every landing and no oil in the strut after a dozen or so landings. My point is, that if you have a decent set of packings, bushings and a true, proper size lower gear leg, you won't have much a problem of oil loss. Don't be offended. Bellanca had some good ideas and some, not so good. In 1949, the date of that print, he basically turned the whole operation of the shock strut upside down for the -3 Cruisair and the following Cruismasters. Dan
 
One side of my cruisemaster gear had a nut that would bottom out before it tightened up. It looked like a good place to break so I washered it up and have had no problems. If oil is allowed to get above the o-ring on the later gear the oil will just leak out, I had a conversation with one of the guys at Miller's and he agreed too much oil just ruins the o-ring when it is forced out. My 14-13-3 has the same gear my 14-19-2 has....Greg
 
I sure hope we are talking about the earlier system found in the 14-9, 14-12F3, 14-13 and 14-13-2! The -3 Cruisair and later had a different setup. Greg...call Russ Williams about maintaining the later system. Also, Alexandria Aircraft should have service details. Dan
 
I think the principle of 14-13 and 14-19-2 gear struts are the same. the nut on top of my gear leg has play, I left it that way.
 
I have to agree with Dan on this. If Bellanca made a note on a drawing to leave the nut loose back in 1949 I feel it was not a very well though out decision. Leaving the piston loose is only inviting trouble in the long run. The strut was not designed to be vented.
 
Glenn, The only similarity in the -3 Cruisair/Cruisemaster gear vs. the earlier system is that a fluid, flowing through a metering orifice provides the damping action of the landing gear. The later system - yours - incorporates the following parts, from top to bottom: spring, spring retainer, upper piston with O ring seal, lower piston [damper]. The earlier system incorporates the following in the same order: piston, taxi spring, and spacer. I believe the springs are the same, as the new springs Russ Williams received from Alexandria measure the same as my Cruisair springs. Dan
 
I defer to your experience Dan - I'm was only guessing the design philosophy was similar by posts thus far.
 
I put the new Buna n seals in and the new springs from Dan in. I only used 4 seals per strut as opposed to 5 of the V seals because they don't fit inside each other and the four were the same height. They do seem to seal better and I have not seen any oil leak past them yet. I do have a couple questions though. I did not see any shims in my right strut but there must be something in there because it does not compress as much as the left. With the airplane on jacks, when you push up on the wheel by hand to compress the stut, how much stut should remain exposed? On my left I have 2 1/2 inches but on my right I have 3 inches. Also when the gear is retracted should the small cable that compresses the stut only compress it up to where it hits the spring or is it OK for it to also compress the spring some?

Thanks,
Kevin
 
I can't think of any shims inside the gear tubes. Are your lower bushings threaded in the same amount? Usually, the strut will be compressed just enough that the tire just barely touches the front of the rear spar as it comes up..........and you do have the rub plates installed.....right! I don't think the cable compresses the spring to do this. It's only 1/16th inch and would break in short order if it had to. Dan
 
There must be something in there that is making it 1/2 inches longer. I will have to take it apart and see what is going on. The lower bushing is screwed in the same as the other but I don't see how that would change the height. It only changes how much the seals are compressed. I don't have any rub strips. I wish the cable did break but instead it pulled the cable out of the rib so now I need to repair the wood. I did not have the cable too tight with the strut extended so it must have tried to compress the spring too much.

Kevin
 
Well, I'm trying to figure how and what you are measuring for this 1/2" difference. The upper end of that gear cable is attached to a beefed up rib inside the leading edge. The rub plates were either a SB or AD back in '46 to protect the front of the rear spar from 'tire rub.' If you don't have them, I'll tell you how to build them. Dan
 
I am measuring the length of the exposed strut to the bottom of the outer strut (not the screw in bushing) when compressed. The lowers bushings are both screwed in about flush so it is about the same as measuring there anyway. What should the measurement be? The only way I can think that they would be different would be if there was a shim under the tower piece the spring sits on or is there some adjustment in the upper part of the strut that could cause this? I see that it goes up against a part in the upper part of the strut. Is the height of that part adjustable? I haven't taken the top part apart yet to see what is in there.

I see where the cable is attached to the rib and it has pulled out of the rib. The rib doesn't look any beefer then the rest of them.

I remember reading about the rub strips and I see long abandoned screw holes where they should be but had not gotten around to figuring out what to do about putting them back in. I suppose now is the time.

Thanks,
Kevin
 
Kevin, Did you replace both springs? Disconnect both retract cables at the gear leg. Have a friend crank the gear up to the point that the tire is about to touch the rear spar. Now, compress the gear by hand. Both of them. You should feel the piston contact the spring as the tire appears to barely touch the rear spar. Make sure your gear is symmetrical. You can now measure the length of your new cable. You can make it in one piece, though, I've seen some with a turnbuckle. The new springs are about 1/4" longer than the 60 year old originals, that have collapsed over the years. While your airplane is supported, now is the time to lube the 'U' joints and clean and grease the retract screw and trunion nuts. Clean the area where the rub plates go. Sand, varnish and paint as necessary. Give me your address and I'll send a pair to you. It'll take ten minutes to make them. An empty airplane, on the ground, will show approximately 1-11/4" of the machined area of the lower gear leg. Dan
 
OK, Dan, I will need to find what is holding these up. My address is Kevin Gassert 2328 South Road, Cincinnati, ohio 45233.
Thanks,
Kevin
 
Guys,
Enjoying this discussion, my gear legs are quite worn where they slide through the large bushing, which holds the seals in place. Has anyone else got this problem? I was intending to have them hard chromed and then machined back to correct size. What do you old hands think?
regards
Bernie
 
Kevin:

Just a thought, but, make sure you are not capping off the fluid service port with the gear extended and then trying to retract the gear. You may be fighting ( compressing ) the air in the strut. With new seals and smooth struts it will hold the air real good. The aircraft must be sitting on the gear when you install the caps , or the gear must be compresed to be sitting on the taxi spring.

M2c

joe:
 
Joe,
The seals and bushings are doing great on the Cruisair. There have been no leaks to date. It seems like the way you had them machined was perfect. Thanks so much!
Cheyne
14-13-2 N74398
 
Joe,

Thanks for the idea but I am sure it is on the spring and not compressing air. I took the right side back apart hoping to find a shim in the bottom but could not find anything loose. There is a washer in the bottom but it appears to be attached to be the bottom of the strut to give it a flat bottom. I did not take the left side apart to compare. At this time I have a new spring in the left side and the old spring in the right side and when I have the plane on jacks and I pull up on the well to compress up to the spring they are both at 2 1/2 inches and they both just fit in the wells without pushing the springs.

Kevin
 
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