Strengthening The Main Landing Gear

[Britpilot]

For some time I have been thinking of strengthening the main landing gear on my SC LP. I did not like those flimsy plastic strut covers and their little rubber bands. The covers seem to be for appearance only as they are to flexible to add any strength to the landing gear. I liked Dillzio’s idea of adding a doubler to the covers to give them some strength:

supercubclub.proboards.com/index.cgi?board=whls&action=display&thread=2501.

Then I thought why not replace the strut covers with new ones made out of a stronger material. Looking around my garage I found the perfect material, a piece of white aluminium gutter (yes, for our American readers that is the correct spelling of “aluminium”). The gutter aluminium is very light, strong and ductile and has a great white paint finish baked on one side.



After cutting a flat piece of aluminium out of the gutter I used the stock plastic strut covers as templates. I added 6mm extra material to the leading edge to allow room for a different strut securing system using cable ties. Bye Bye rubber bands !



Now it was time for some sheet metalwork. If you have not worked with thin aluminium sheet before a few tips. It is sharp! watch your fingers. Tin snips tend to roll the one edge slightly on the cut, keep the piece of metal you want on your left with finished side up when cutting (assuming you are using right handed tin snips) this gives the finished edges a better look. Drill a 3/16 hole first in each internal corner to give a radius corner, this will avoid sharp corners where cracks may start. (See picture). A 6’’ steel rule is a great tool for de-burring the edges of the aluminium and is easier than a file.



Here are the finished aluminium covers with the stock plastic covers in the background. Note the two 1/8’’ holes near the bottom edge of the covers for the cable ties. The weight difference over the stock covers is negligible.



And here is the finished project installed on the Cub. It really strengthens the gear by triangulating the struts yet still has a lot of spring to cushion my none to perfect landings! And no more silly little rubber bands!

[flydiver]

I predict a rash of battery boxes torn out.
Crappy landing force has to go somewhere.
Looks good though.

[Britpilot]

With multiple load paths that may not happen. One of the problems with any mod that strengthens a component is that it that modified component will survive a lot more abuse. However when you prang it badly the damage will be more severe. Cest la Vie!

[Dillzio]

Nice looking mod. If you find that you're getting nose overs on landing you should trim the bottom of your struts, it looks like they might be able to rub the wheels.

I actually saw some aluminium struts like this on ebay a while ago for about $20 bucks.

Don't forget to reinforce your battery box area with popsicle sticks and epoxy! The mod is on NECubFlyer's youtube channel.

[ginginho]

Nov 30, 2009 4:54:21 GMT 1 Britpilot said:

[snipped]
Looking around my garage I found the perfect material, a piece of white aluminium gutter (yes, for our American readers that is the correct spelling of “aluminium”).

Teehee, I think it's spelt that way globally (in English). ;D

That is a tidy looking mod, I think it looks better than the stock plastic ones.
I'd agree with the point that Fly mentions (rash of battery boxes torn out) but you may be able to negate that effect to a degree if you elongate the rear holes in the spats, allowing them to rotate slightly around the front screw a small amount when the gear is forced backwards, as happens in a hard landing.

Just an idea but keep us posted on how they perform and whether you suffer BB problems.

[Britpilot]

Thanks for the comments guys. I'm probably lucky but as of yet I have not experienced a hard landing but I'm sure it will happen. I've found the cub to be a beautiful landing aeroplane especially when you fit bigger wheels all round. Just don't over flare and stall it out a few feet up though then it just drops out of the sky just like full size aeroplanes do. I've been flying for a living for almost 20 years and have done my share of early flares leading to an arrival rather than a landing! During my many years as a flight instructor Iv'e had some students give me some wild landings from time to time as well! Anyway I'll look into the battery box mod and do that as recommended so when the bad one happens my sweet little SC may survive.

[flydiver]

Sounds like you know how to land. The usual scenario for new fliers is 'I want to learn to fly'. Flying is easy, landing is hard (pun intended).
Landing gear is FREQUENTLY the crappy, weak, overlooked part of a plane. It gets ripped out. Reinforcement is done to the LG but not to the surrounding structure. New flier still can't land. Whole system now ripped out. More reinforcement > bigger carnage. The cycle escalates.

Unfortunately on the Cub EVERYTHING seems to be tied to the BB and frankly, it's not mounted very well at all. It's a real weak spot. Bending the wire gear keeps the BB from being ripped out. I reinforced my BB with epoxy and carbon fiber after it started getting loose.

[Britpilot]

Anybody got any pictures of their modified and strengthened battery box?
I watched the video on You Tube but it didn't show things in enough detail for me.

[Britpilot]

First flight test of my the new strengthened main landing gear.

At last today the weather co-operated to allow a flight, it stopped raining!. It was rather windy and gusting 10mph + and at times my red ribbon "anemometer was straight out so it was not a day for heroics.

The only piece of land on my local school sports field that is suitable for a take-off is the baseball diamond. This is mainly sand with clumps of weeds. On the stock gear the SC would dance around left and right on the take-off roll as a main wheel hit a clump of weed. This required quick reflexes on the rudder control. I had to take-off down wind today as into the wind was straight into the 20' high fence behind the diamond. This meant a longer take-off roll than usual but she tracked dead straight and rode over the clumps of weeds with very little deviation. As it was a gusty day I carried power on all my landings and just aimed for a reasonable touch down on the grass. On the stock gear the roll out after touch down would often end up in a bit of a ground loop left or right but today the ground roll was straight ahead on all landings.

It would appear that the stock gear although nice and flexible to avoid damage from heavy landings causes other problems. The wire struts will flex back as a main wheel rolls into a patch of higher grass or similar tundra. If this happens to one wheel only it shortens the wheelbase on that side and the aeroplane turns.
By triangulating the wire struts with my new rigid strut covers rearward movement of the struts is all but eliminated. Of course this is wonderful on decent landings but now I had better beef up the battery box for the heavier arrivals! Overall I'm very pleased with the mod but would advise it only for more experienced pilots who can consistently land their SC well.

[Dillzio]

Here's a couple of pics of my batt. box reinforcement:



This is the video I got the idea from:
www.youtube.com/watch?v=sa9pXnEG7uw

Start by cutting two popsicle sticks into sticks that are almost as wide as the fuselage. You then cut out a channel in the foam for the popsicle sticks to sit in with a soldering iron. I would advise drilling the necessary holes in the popsicle sticks BEFORE you stick them in. There is every likelihood you will split the popsicle sticks while you're drilling them and need to start again with another popsicle stick. I advise drilling the holes by hand with a very sharp drillbit.

Instead of just using the stock screws to hold the battery box in and relying on the threads in the popsicle stick holding, I opted to use some tiny bolts instead. I say bolts instead of screws because they are threaded for nuts. I filled the channels in the fuselage with araldite, inserted the bolts so that the threads stuck through, and put the popsicle stick into the channel to glue it in. I also covered the top of the popsicle stick with a layer of epoxy too.

I then put on the battery box plate with the threads sticking through, and put on the threads a washer, a split washer, and a bolt. To tighten the bolt, grasp the threads with some little vice grips to hold them still and tighten the bolt with some plyers or a little spanner. I then put some dome nuts on the end to cover up the potentiall sharp threads sticking through.

[Britpilot]

OK, got the idea now. I'll have a good look at my SC today ad see what my grey matter can come up with.

[flydiver]

Good reinforcement.
Would going lengthwise be better than sideways? More surface area and generally the forces are that direction. I've never done it, just thinking.

[Dillzio]

Dec 2, 2009 17:16:02 GMT 1 flydiver said:

Good reinforcement.
Would going lengthwise be better than sideways? More surface area and generally the forces are that direction. I've never done it, just thinking.

Can't go lengthways, otherwise the popsicle sticks would get in the way of where the battery box attaches to the plate. Mine is still as solid as the day I put it in, I think it works so well because it makes all the forces get transferred through the flexy plate before they're transferred to the popsicle sticks in the fuselage. By attaching the plate at the top and bottom with the popsicle sticks, it allows the middle of the plate (where the battery box attaches) to flex and adsorb some of the force from rough landings.

[Dillzio]

what can I say, I just had to jump on the bandwagon.

I made some struts out of 1.6mm aluminium. Went for a flight today in fierce wind and had a couple of rough landings and the landing gear held up beautifully.

The pair of struts weigh 25g, but because it's so close to the centre of gravity it doesn't throw out the balance of the plane.

[Legot]

I did this too, from a random Idea and sign that my dd got me that reads

NO COMBUSTIBLE MATERIALS STORED ON THIS LEVEL