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Repair after a crash

As a helicopter pilot, we have to accept the fact that crash is a way of life that could not totally prevent.  If you are a beginner, the chance of crashing your helicopter is far more than those with better experience.

With this page, I would like to show beginners some ways to repair a helicopter.  I am logging the things I did once when repairing my own Shuttle CCPM, which crashed at lost of control during flight, as an example.

The above are the remains of my Shuttle CCPM after crash.  The tail boom was completely destroyed, main blades damaged, and with all shafts bent.  I did some disassembly on the field to dump some of the tail parts and damaged blades, so you could not see them here.  Usually repair a crashed helicopter involved four phrases:- Disassembly, check, clean, re-assembly, and final setup.

Sometimes after a crash the tail boom would be bent out of shape badly, and would make taking the tail out of the main frame hard.  In this case, I would  use a pipe cutter to cut the damaged tail boom in several sections to ease disassembly.  You could get one of these in any hardware stores, and get one that could cut pipes from 19mm to 28mm diameter would cover all your helicopter needs.

Almost always the flybar is the first thing that gets damaged  in a crash, and a bent flybar is not tasily to take out.  If a flybar got bent badly, like mine, you have to cut out sections of the flybar in order to take it out.  You could either use a saw, or a Dremel with a cutting disc.  Anyway you choose, take enough safety precautions not to hurt yourself.

Take out the engine and check to see if pistons and cylinders are scratched by dust and sands that might get into the carburetor at the time of impact.  A quick way is to turn the engine by hand and look at the exhaust port to note for cracks and scratches.  I would almost always disassemble the engine for cleaning and checking.  While checking your engine, you could also note the condition of your engine and it could also tell you whether your mixture is right, or your fuel is good blend.  A healthy engine should not have any scratches and dents on the piston and cylinders, and by themselves they should be gleaming with a shade of gold color.  The shade of gold color is from the lubricant in the fuel you use, and if yours is dark color it either means you are running it too hot, or your fuel blend is not good. At a too lean mixture setting the lubricant would burn itself out inside the engine due to the heat.  A poor blend fuel would  have deposits and debris, and these would always left residue inside the cylinder and piston. 

I highly recommend use of original crash parts, especially all the shafts, flybar and tail boom.  While you might save a few bucks using knock off parts, the quality of these cheap knock off parts are usually substandard, and your helicopter might crash next time due to these knock off parts fail during flight.

While assembling your helicopter back to order, its also a good time to do some cleaning.  Some parts of the helicopter could not gain access without disassembly, and why not take the time to do so now?  As you can see from the photo above, I am cleaning the inner side of the fan shroud, which I could not reach without disassembling it.  A clean fan shroud would be good for your engine because prolong flight would make the inside of the shroud attract a lot of dust, and since your engine draws air from the shroud for combustion, dust accumulated inside the shroud might get sucked into the carburetor and lead to engine damage.

In heavy crashes that leads to bent main shafts, those bearing that support the main shaft might be damaged due to the force of impact transferred from the shaft.  Damaged bearing would not run smooth, give slop and most important of all these rough bearings (rough bearing is the terms we used to described damaged bearings) would emit interference that jams the receiver and lead to lost of control.  How to check whether a bearing is rough or not?  Take a look at the photo above, you could hold the inner side of the bearings with fingers from one hand, run the outer side of the bearings with the other hand.  Try to feel if there are any rough notches when you run your bearings with your hands.  Replace those that are rough running.  If you do not feel any notches when running the bearing with your hands, but felt that the inner side of the bearing is getting loose, replace the bearing too.

Another thing to check is the clutch lining.  Sometimes when the helicopter crash to the ground the clutch would still be engaged and if so the lining would get wore out.  Replace wore out clutch lining if yours is too thin.

Check the main gear for any blurs and dent, and replace it if necessary.

Setup

After reassembly, setup your helicopter the way you did like last time.  Take note of the things that you found during all the repair phrases and setup accordingly.