Introduction: How to Get a Foam Ultra Micro Rc Back in the Air
Even the best of us crash but it seems the less experience we have the harder we crash. This was certainly the case when I let my buddy try flying my parkzone ultra micro p51, it is the resident learner plane among my friends and saw its fair share of the ground, trees, and roofs before my friend got his hands on it. But he certainly tested it to and past the limit, as he put it, "plane and earth tried to coexist in the same space, there was only one survivor." That is a painfully accurate description as you can see from the pictures, but I had faith that with the correct application of super glue and tape, she'd be back in the air in no time.
This is not a guide for how to professionally repair a plane, its simply a quick dirty way to get a destroyed plane back in the air. While it may not act quite the same and could require a little trimming I still enjoy the plane after the repair. This probably isnt the way youd want to do this if you have more money than time to spare but, being on a college budget it makes more sense to try get as much life out of this lump of foam before I pick up a new 12.99 body that's necessary to make the plane like new.
Step 1: Asses the Damage
First thing to do after a bad crash is to see how bad it really is. First give everything a visual inspection to see if any electronics could be damaged if you power the plane on. I got lucky here, the motor still spun freely and the board looked like it had only been knocked loose. Next step is to plug a battery in and check all functions (be careful spinning the prop up as it may be fully disconnected from the fues.) All my control surfaces moved fine and I didnt notice any binding as most of the damage was focused on the nose. If the control surfaces were messed up you should be able to strengthen them with tape or in bad cases (you can see on my elevator) small pieces of balsa wood or even fiberglass. Control surface hinges can usually be repaired with a little bit of tape, you want want to be stingy with the tape as too much will just cause binding.
Anyway you just want to look at the damage and see if its something you think you should fix or if youd be better off just getting replacement parts/new plane. For me part of the fun of flying is putting the planes back together after a bad crash so it takes quite a lot to deter me.
The main damage from this crash was the canopy spit towards the nose, the board lifted off from its mount, and the nose split from the rest of the body. While it might look terrible I was pretty confident that I would get it back in the air.
Step 2: Check Alignment
Theres no point putting a plane back together if when its together it wont fly in a straight line, so put the cracked pieces together and check that they form nice straight lines. You could also just look at the prop orientation but remember they have a small degree of right thrust to counteract the torque of the prop so I find it easier to just realign the body.
When putting it together I found the nose would be straight but there was some crumpling in the canopy, this is not a huge deal but for the purposes of the instructable Ill show how I dealt with this in the next step.
Step 3: Straighten If Necessary
If you find some pieces have foam have crumpled rather the cracked then you need to bring them back to their original shape, sometimes this is possible by hand but in this case it was so creased I could not coax it back into shape. So I used a method quite well known in the rc world, you need a bucket of very hot hot water, I used hot tap water but it would work better the hotter you get it. Simply submerge the foam in the hot water until the air inside each "bubble" of foam expands causing it to revert to its original molded shape. Obviously if the part that needs to be submerged has electronics on it you should remove them before doing this step.
Step 4: Glue
This is alot easier than it seems, most of the cracks on the plane were simple and mate up very well so no prep work is necessary and it looks almost seamless when you finish. The most important thing is that you use foam safe CA glue if you want to use CA glue. I learned this the hard way when I first tried to glue a foam spinner onto my prop, normal CA will eat right through it. You could probably use hot glue or epoxy but the CA works great for me so Ive never tried anything else.
You want to make sure you have good access to both joints to get good glue coverage and to better align, sometimes this means you need to do just a bit more damage. I had to pull the nose all the way off of the rest of the plane so I could repair it separately.
You just want to put a bead of glue along both of the surfaces that you want to join, get enough coverage but dont go crazy or it will take a long time to dry. Then press the pieces together and hold them in alignment until the glue dries, for CA and hot glue it should only be a few seconds, for epoxy you may need to devise some sort of jig.
For most joints this should be enough but as you can see on my plane the nose has taken so much damage from various learners Ive had to reinforce it with some balsa. This too is a fairly easy process, first glue the joint like you would any other, then cut a piece of balsa that will fit inside the fues. and provide the most strength, then just glue it in.
Step 5: Reinforce
Usually the glue will be strong enough but it can never hurt to make it a little stronger. I use regular scotch tape for this but clear packing tape would work even better. This might seem kind of silly but the tape is very good in tension so when it is on the outside of foam it works well to stop flexing. As you can see I put the branch of a tree through my left wing and its now held on with just tape but I have never had it flex or fold. It may not look pretty but after what the plane has been through the fact its back in one piece is all that really matters.
Step 6: Admire/fly
Check over your work and check movement of all the control surfaces again, you dont want to go out and after repair again on your first flight because you forgot to check something simple. Center the trims on your transmitter then try to mechanically trim all the control surfaces, on the these ultra micros that means bending the u-joints on the control rods in or out a little. This will give you the most throw in either direction if the plane still needs to be trimmed.
Now its time to fly, take it out to nice grassy field on a calm day and get it high quickly so you have room to trim it out. If all went well it should fly just about as well as before the crash.
Ill try to get a video of flying after the repairs up some time this week.