ljsoarinson

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I’m looking for ideas on using carbon retract mounting rails on a Yellow Aircraft Spitfire (25 lbs). Between my flying and previous owners, the retracts have been pulled out of this plane at least five times. Typical failure is the spruce rails breaking mid span, then one or more of the plywood sub ribs being pulled out of the foam. My latest fix replaces the ¼” ply ribs and extends them to tie in to existing spars at the leading edge and 40% back.

I do know the ½” x ½” wood rails are meant to fail rather than destroy the wing. The carbon should also break if forces are high enough. My hope is for the carbon to flex to minimize chances of breaking other things. I don’t think the gear will get pushed through the top of the wing since the two spars contact the wing top sheeting and transfer loads to the wing saddle of the fuselage.

Please reserve comments about landing skill. My intent is to make the gear robust enough to survive enough landings to get good enough not to need robust gear…

Using carbon flex plates to mount landing gear on jets seems to be commonplace. Has anyone tried carbon rails for warbird retracts?

Dash7ATP

having built two Yellow Aircraft models, I can understand your problem. My first was their F-4 Phantom, and my most recent build was the P-47. I can't speak for all of their models, but my experience suggests that the gear mounting pads are way too small. The wing at the gear mounts on the F-4 is only about a inch thick, and of course is foam. The 1/4" plywood mounting gear pad was maybe an inch or so wider than the opening for the gear. Not much support. On my P-47, I was concerned about this, so I did a little checking on the size of the mounting pad. Again , way too undersize for my liking. You can see what I did and my fix on my build thread at the following link.http://www.rcuniverse.com/forum/m_8836329/tm.htm Good Luck,Dash

Tommy_Gun

Make them too strong and your wing will have to "give" in other areas.
Use caution.

All Day Dan

My Feedback: (5)

Here's how I install my retracts in a foam wing. They survive a hard landing. A bad landing will bend the Robart struts and leave everything else intact. A terrible landing will rip out the maple mounts and leave the plywood box alone. A little rework will get it repaired in a day. I haven't ripped one out yet or ruined a wing. Dan.

LA7flier

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Hmmm....well I won't comment on your landing skills cause we have all been there with landings and gear. I have personally thought about and discarded the idea of stronger metal/carbon rails. As one post suggested, it is all about energy management. A poor landing absorbs a lot of energy and the long lever-arm of the gear leg provides tremendous leverage for that energy.....guess where it all goes? Yep, the mounting plate. If engineered correctly, the loads should be adequately dissipated throughout the wing structure but there is a limit as to how much energy the structure can handle. A carbon mounting plate/rails will not absorb very much energy and will pass it along to the ribs/spar to dissipate.....the point is, too much energy, no matter what the material is too much energy.....I constantly try to get better with my landings rather than keep building stronger ( and heavier)......I currently have two warbirds awaiting repairs for...you guessed it....gears torn out because of my poor landings.....Nuff said

ljsoarinson

My Feedback: (45)

Interesting ideas, thanks guys for the feedback so far. Dan, your mount method looks easy and straightforward. Nice photos. At first look I would guess the ply box would not have enough structure to prevent it from being torn out of the wing (unless the top skin has a extra glass reinforcement). But if the gear bends and the maple rails break first that's just fine.

LA7flier, my hope is to get the carbon sized right so it breaks before anything in the wing. If I have the right thickness the carbon will flex more than wood before it breaks. This should allow the carbon to absorb energy from a hard landing without anything breaking. If the carbon does break it could be a bolt-in replacement part. I know BVM came out with a stronger carbon flex plate for one of their jets but later recalled it because the gear could get pushed through the top of the wing before the flex plate broke. They went back to the smaller, thinner flex plate.

Dash, thanks for sharing your thread. I like the jigs. How did the landing gear mod hold up? I know the YA Spitfire was originally designed for a glow engine much smaller than the 38-70cc engines some are flying with. Makes sense that they would need more structure than what's shown on the plan.

Most of my landings are actually pretty good, it's just the occasional one that causes damage. Ideally the damage would be confined to a part I could easily get and replace like a strut. Or a replaceable mount rail. Other ideas are welcome!

Dash7ATP

I have not put many flights on my P-47, but so far, I have seen no problems. I was really concerned with the long gear legs and the small mounting pad in the wing. I have little doubt that a less than perfect landing would have torn the gear out. I also beefed it up with fiber glass around the gear n both sides of the wing.Joe