Make it "structural"
jimski9 said:
The plans describe bonding wooden gear leg dampeners to the main gear legs.
Is there any concern about this permanent bonding? I wondered if it may make it difficult to inspect the gear legs for cracking later on. I am considering drilling five or six holes in the wooden dampeners and attaching them to the gear leg with beefy zip ties.
Has anyone else done this and will this provide enough dampening effect?
Thanks Jim Talbot Tauranga New Zealand
Jim don't worry about inspection access for cracks. You should be worried about corrosion. Some materials like instant foam, which some have used on gear legs can hold mosture corroding the steel.
The gear legs don't crack; they might bend, but I would not worry too much about cracks. If there's a crack it'll happen down low where it bends for the axial. I say that with some knowledge of metals, crack growth and damage tolerance. Certainly a crack can occur, but it will "grow" fast. It's unlikely you will catch it in time unless you do gear inspections frequently. So you can cover up the leg with out too much worry.
To avoid corrosion a good finish is important. I am not a huge fan of the powder coating on the gear as they come now, but that's what we have. I would rather an epoxy primer for this part. We don't need a pretty gun metal gray, like the canopy frame. No one can see it. As long as the PC coating does not chip, flake or crack, allowing mosture to contact the steel. Corrosion is not likely even if you do cover it with fiberglass.
There was one case where instant foam was used to fill the fairing. The combo of chemical reaction and foam holding mosture on the steel gear leg, which was not properly primed (pre powder coat days), was a disaster. In a year or so period of time, the thing was a corroded mess.
kevinh's right, consider trying with out at first. However with you will have a firmer more solid ride and reduce the chance of shimmy significantly, but it comes at an expense.
The twist ties may add too much "thickness" as mentioned, and I doubt they would be "structural". If you are going to put them on you might as well make them work.
Extra thickness from attaching the stiffener increases the gear fairing frontal area. Fiberglass wrap is my method of choice to attach the stiffener. It adds min thickness and is very strong. It is semi permanent but it is not impossible to remove.
You could try some stainless steel bands, like the steel bands around freight, but I would worry about the metal bands making a nick in the gear leg. I said cracks are not a worry before. I lied. If you put a notch or nick in steel you will increase the chance of a crack by a huge margin. Don't allow any nicks or gouges in your gear legs.
If you do add the stiffener, use some sealant between the gear leg and stiffener to keep junk out. Pro seal would work. The adhesive is not meant to be structural but helps the parts work together, reduces abrading of he powder coat and keeps mosture out.
They way I attach a stiffener is wrap it with carbon fiber or "S" glass tape, at the top, mid and bottom, at minimum. You don't have to go crazy, but a couple of wraps around at each location, about 3-5" wide will do. Added thickness will be min.
On my RV-4, the difference noticeable. I could taxi fast and never get shimmy. It was just more solid. I made may own stiffener out of OAK. Actually a woodworking genius friend make them for me. The fit between the stiffener and leg was like a glove. Making a double tapered wood stiffener with a concave mating surface to match the gear leg is a trick. Van's method of gluing two pieces of wood molding together, with a "V" notch fit, works and is way easier, but if you have the skill to make a one piece solid stiffener that nests onto the gear, verse just sitting on top a V-notch with two contact points, the better.
Flying (taxing) without the stiffener, I did get a main gear shimmy when taxiing (way too) fast, but I would just check speed, slow down and it stopped. No big deal. The solution without the stiffener was taxi a little slower. I put the stiffener on because I thought I had to. In retrospect I could have left it off.
With the stiffener the feel was solid and could taxi straight, in a turn, go fast with out worry of wheel shimmy. Taxi at any speed over any surface felt solid like a car. I guess it helped a little on landing, but no shimmy taxi was the main advantage.
On my current project I am leaving them off for the simple reason of build, time, weight and keeping the fairing "skinny".
The stiffener needs to work as one with the steel leg. Just throwing it on so it can move and shift decreases effectiveness. The tie wraps I think will not cut it. If you are building a RV-7A, I think stiffeners on the mains and even the nose gear may have positive affect on the nose gear issue.
G
. Therefore my pieces of wood never got installed - saves weight, effort and servicabilty if you luck out.
