I joined this forum looking for advice on Citabria oleos, but come to find out, I now know more about them than most members, from what I saw in posts going back quite a few years. I was unable to get to this forum before I found out the answers for myself. That's good, because there's a lot of misinformation presented in the old forum notes, which I'd like to address.
I have a 1966 Citabria 7ECA with oleos. We (my A&P and I working together) just finished an annual that took four months, its first with me as owner. There were lots of issues. One of my biggest concerns was the landing gear. The aircraft used to sit as though someone had stepped on it. The camber of the wheels was negative, which means they're closer together at the top. The oleos had half an inch of travel. This was all wrong.
In the process of attempting to find out what was supposed to be inside the oleos I contacted several "experts," and got more misinformation. The only parts book I have is the reprint by Univair, which tells the WHOLE STORY, but omits the photo of the 2-1655 Belleville-washer taxi spring. What I'm about to write is based on very recent experience with getting my airplane set up correctly.
When my airplane is resting on the ground the piston sits on the taxi springs. That is why they are called taxi springs. The upper springs act to extend the oleos in the air, and partly cushion the landing as the oil does its work. My oleos used to have the short taxi springs, 2-953, which were 3.2" long and just under 7/16" wire diameter. These provided only half an inch of travel, and negative camber. The CORRECT springs, as the parts book specifies for my bird with its O-235 engine, which is 75 pounds heavier than the O-200, are the "high-energy taxi springs." These are the Belleville washers, 2-1655, which are more than an inch longer than the 2-953s.
One member posted a photo showing aluminum spacers that made up the length difference between the two types of taxi springs. Apparently the older, original Belleville washers (2-1655) had a tendency to work harden and break.
Replacement 2-1655 springs were not available for some time until Univair began making them again, for which I thank them profusely. But you could get the shorter (incorrect) taxi springs, and add a spacer to get the correct camber (and prop clearance) for the heavier engine.
With the Bellevilles in my airplane the camber is finally correct, and the oleo travel (on the ground) is slightly over an inch. The Bellevilles have a lower spring rate, so the ride on bumpy ground is a bit softer.
Another thing: You cannot simply open the little drain plug and change the oil. You won't get all the old stuff out. It gets trapped on top of the piston and you need to work the piston to get it all out. The POH tells how to properly fill it with new oil. It specifies a measurement from the end of the oleo to the top of the oil. Remove the entire oleo to do the job correctly and more easily. The big cap on the bottom of the oleo (as mounted) comes off easily by hand -- or it should. Take it off, drain the oil, find out what springs you have, and then rest the oleo on a rag and pump the thing to get all the old oil out of it. If you let it drain overnight it will NOT come out, or so I found. The required amount is 8.5 ounces, and you will have to pump the thing to get it all in. We could not do so by "tapping" it, as the book suggested.
Before you put the cap back on, DEBURR the end of the oleo to avoid damaging the new O-ring, which goes inside the cap.
If you have an after-market spacer, be sure to reduce the 8.5 ounces of oil by the volume of the spacer. These two-spring oleos requre both air and oil inside. However, if you have a spacer, I suggest you leave it out and put in the correct 2-1655 spring assembly (43 Belleville washers held together by an internal spring). Note that the Bellevilles are arranged in very specific order. Don't mess with that.
Next, the oleos do NOT make the wheels toe-in as they flex downward, as someone noted. This is an illusion. The plane of rotation of the axle and oleo assembly is perpendicular to the fuselage, so the toe-in does not change. Only the CAMBER changes. Old gear gets incredibly loose, which we found, but by clever work, spacers in the right place, and some luck you can tighten the gear so the toe-in remains slightly positive, and ground handling will improve.
Now, I don't claim to have all the answers, and still have some questions about the oleos in Citabrias, but the above is all 100 percent correct as I found it in my aircraft.
.........Ray
:twisted: :evil: 