A common problem we are seeing in the San Diego based Buckers is collapsed or sagging main landing gear springs. We have tried several vendors over the years with less than satisfactory results. The exception has been Joe Krybus landing gear springs which have held up and work great! Joe’s landing gear are outstanding in quality, but his gear fabrication uses US size tubing/ metering rods and the springs, which have held up in one of our Jungmann for over 20 years, only fit his gear legs. It is not an option to use Joes’ springs in a stock set up. THE SPRINGS WON’T FIT! His setup uses a 7/8 inch metering rod and a stock rod is 25mm (about an inch).
The springs in my Spanish Jungmann with stock gear legs, started to really sag a few years ago so I started to investigate buying new springs. The collective wisdom on other springs built in the USA for stock gear legs, was they didn’t hold up and collapsed in a few months. So I figured, buy a set from Europe. I did that and installed a nice set of stock looking Spanish design springs.( One long spring, a spacer, and one short spring.)
The particulars
The extended cavity within the landing gear is about 21 inches. If you install stock springs and spacer you just fill this space. You can just thread the nut onto the gear strut with minimal preload. My old stock springs (original with many hours on them) had sagged to about a 20 inch stack up, a weaker spring rate, and thus had some free strut motion when bolting it all together and the plane sat very low. (On the gaiter, safety wire to safety wire, about 1 to 2 inches). I used spacers for a while to fill the gap, but a weak spring is a weak spring and this did not help with wing sag or mush and they would bottom out.
The new springs from Europe looked great. The stack up of one long spring, a spacer, and one short spring was 21 1/8”. I installed them and the airplane sat very nice on its gear. (On the gaiter, safety wire to safety wire, about 5 inches. So far, so good. I then went flying. 6 landings later the gear was flat on the axels! Took the landing gear apart and the large spring/spacer/small spring stack up had collapsed 2 inches in free length! Spring rate also suffered as the gear leg end now sat on the axels under a static load. They were worse than the originals!
What’s happening? Most of the available springs (well, the ones I bought) just aren’t holding up. . Joe Krybus has had success yet others have not.
The springs are obviously highly stressed during the landing phase and the tempered condition in the replacement springs was allowing permanent deformation under these deflections and loads.
The stock landing gear tube is 1.69 inches ID and the metering rod is .984 inches OD (25mm). Most US springs were using 5/16 rod (.312 inch) for the basic spring material for a comfortable fit of the wound spring within the tube/over the metering rod. We noticed Joe used a thicker rod diameter and he uses one spring 21 inches long. No spacer is installed with his spring. Makes sense as this minimizes the strain on each coil for a given load.
John Hickman, my Bucker buddy and hangar neighbor, just happens to have a brother (Gary) who runs a machine shop and is an avid race car builder. Went to him and we talked spring design. He is an awesome guy, with great capability. We came up with a spring design that uses maximum rod diameter, .334 inch (8.5mm) and can still be wound to fit the landing gear tube ID , the metering rod OD, and with the number of coils to produce a spring rate that compares to Joes (220 lbs/in).
Gary uses a high tech spring outfit for all his racing suspensions, and he talked to them about our problem. The result is a modern spring steel alloy spring (not piano wire!), wound, tempered, pre stressed, re tempered, and shot peened. This produces a finished spring properly tempered, stress relieved, and to our final size and coil count.
I have the prototype springs from this effort. I installed these new springs in my Jungmann. The general fit was great. They were 21 inches long and required just a slight preload as I installed the strut bottom gland nut.
I then went flying. With 6 landings the gear stance still looked great with about 4.5 inches on the gaiter measurement.
The true test came with my 4000 mile trip up to the National Bucker fly-in in Montana and then on to Blakesburg Iowa for the Antique Aircraft Association fly-in. 51 hours and 60 plus landings later I disassembled the landing gear and measured the spring lengths. I found the length remained at 21 inches and no signs of collapse. They feel and work great. No wing sag or mush. So I’m happy.
I was the tester, but Gary is the contact if other people are interested in these springs. He is having more produced and making them available to the Bucker community. They will cost $380/set. His contact info is:
Gary Hickman
10734 Kenney St.
Suite F
Santee, CA 92071
(619) 456-4564
Hope this helps
Dave