Tips for Wrenching and Repairing after a Crash

[cbhelo]

Here are some tips I've learned either on the 'hard road' or from reading talking to other pilots about repairing your bird. It took me over a year to get what I consider and effective repair process that is accurate, mostly error free, and gets repairs done in the least amount of time possible.

Tips for the Repair:

#1) Mark the crash site and have someone else help you look over your Heli especially the head for missing parts. Sometimes it is easy to find a popped link on the ground, but if you walk back to pits you will have a hard time remembering where you went in at.. If you see someone crash remind them and help them look for parts on the ground. I always forget this tip as I'm trying to figure out what I crashed or hitting myself mentally for trying that new move.

#2) Do your repairs at home. Sometimes I'll throw the main blades away at the field if I'm at a club with trash cans. Once I had a stress fractured J bolt that holds the head on. It 'fell apart' when I started to unbolt it. There was nothing wrong with the spindle or main shaft. I would have missed it at the field in a 'rush' repair.

#3) The only way to get an accurate inventory of parts is to disassemble the damaged parts and find everything that is broken. Do this in on a nice light colored table with good lighting (the oil residue from a nitro bird will stain, so don't do it on a nice table). A flooring other than carpet is ideal or put a white sheet down under you. Something will get dropped and 99% of the time it will be small!

#4) Get 4 or 5 ziploc bags. Depending on how bad the crash... As you take apart the heli, start with the most damaged area. Let's say that is the tail. Put all the good parts in ziploc bags and put all the bad parts to the side. Mark the ziploc baggie 'Tail Parts', 'Head Parts', 'Engine Parts', you get the point. Check ALL electrical connections. A repair job is a great time to look for wires chaffing on the frame or other potential causes for future failure!

#5) As you find a broken part, have a printed copy of the manual. Jot down on a piece of paper or better yet in notepad on a PC nearby the part number. Use the schematics towards the end of the manual as they are easy to see part numbers. Often you can buy a single part or a 'group' of parts. If more than one component is damaged the group is often much cheaper.

#6) Put the bolts back in! Often bolts are only 1 or 3 mm difference in length. I can't tell you how many used Heli's I've wrenched on that had the wrong bolt or missing parts. Just spin 2 or 3 turns to put bolts back in their parts before you ziploc them. (For instance if you drop the engine maybe bolt the brace back on but leave the bolts obviously loose so you will see them when you reassemble!) Put the head bolts back in as they could be confused with other bolts but are a special hardened steel just for the job of holding the head block on.

#7) CHECK BEARINGS! With 2.4Ghz radios you can ignore bearings when they are bad, but this leads to autos that are sapped for power, noisy heli, and they can and will FAIL. I've had really bad bearings disintegrate on removal of a part. How do you tell a bad bearing? Just take the 'shaft' that went through it, insert it back into the bearing, apply a gently up or down leverage on the shaft and turn. A good bearing will be silky smooth. A bad bearing will feel notchy. ONE crash can kill main shaft bearings and tail bearings. Check them every time. Some folks put there fingers in and spin them. You can detect the really bad ones this way, but I've found this method is not as reliable for smaller bearings like the tail area or 50% bad bearings.

#8) CHECK Carbon Fiber parts -- frames, blades, etc. The best way I know is to gently 'twist' and 'bend' them. If they 'crack' or flex or bend, then you need to replace them! Every time I try to talk myself into flying a 'not perfect' set of blades, I ask myself how dumb I would feel if I lost a newly repaired bird to $30 tail fins or $80 mains. I've heard stories of that very thing happening. DO NOT glue them. The only thing I will consider gluing with epoxy or JB Weld are non-load bearing parts. (aka nothing in the head or tail sections except maybe a tail fin or horiz stab.)

#9) Okay now you have your parts list. Get online (even if you are buying from LHS!). Use a site like readyheli.com or helidirect.com or amainhobbies.com or your favorite site. Use the 'Search' feature in the top right or left of the screen. copy/paste or type from paper the part numbers you wrote down as you took your bird apart. Find the part, verify the picture, and 'add it to cart'. Now when you are all done do a 'view in cart' and PRINT out your cart with all the prices and part numbers. (Or order them if you are buying online.) Take the parts printout with you to your LHS and you can use it to get the parts. I've rarley ever missed a part doing it this way. Just use a pen and check off the 'parts'. This also avoids all sorts of nasty surprises like shaft size differences in 450SA versus V2 etc. Often time if you just write down 'feathering spindle for 450', then people at a LHS won't know the difference between a V1 and V2.

#10) Time to put it all back together. If you are like me and can't stop a repair job, then don't start at 10PM.. Experience here Your neighbors won't appreciate your hover test at 2am I promise! Give yourself at least 3-4 hours. Most repair jobs seem to take 4-8 hours for a quality job on a 50-90 size bird and about half that on a 450 -500 sized machine. If you have to replace frames it could take 10-18 hours. I've done simple 450 repairs in 30 minutes, so it just really varies. The key is you want a quality repair job, not a rushed one.

#11) Start with one part of the heli like head, tail, engine and start the repair job. Open the manual and lay it out on the page with the parts you are repairing. Even if you have built the heli 50 times! I've still noticed washers that got lost during the crash or disassembly and I know to put back in only because I see the picture. (No photographic memory here!) You will find this avoids the you put it together and forgot a bolt and have to pull it apart again. I have repaired TREX 600's that someone forgot the rubber cover to the torque tube (TT) bearing and the bearing came loose and was shredding aluminum all in the tail. This contributed to the tail seizing up and coming loose in flight! (Always look out for slop a sure sign of a missed part.)

#12) Keep your cleaner and paper towels handy. Clean pieces as you put them back together looking for cracks or signs the part is worn out. If you find a broken part you missed in the initial inspection, replace it! I know how tempting it is to fly with the broken part or do an epoxy job, but you are putting the safety of your friends and your safety. (Plus your beautiful bird if she shreds in the air.) Put locktite on parts that need them.

#13) Look for bent bolts. I see this all the time. You need to replace these. It is handy to buy a bunch of assorted bolts for the rebuilt process. I'd say 2 out of 4 crashes will bend the bolts that hold the skids on the bottom of the heli and replacement bolts don't come with the skids for most helis!

#14) Make sure each part moves freely or is firm if static piece. If links are stiff, size them. Put the tail blade / hub assembly on a balancer. I've found simple tricks like swapping a washer from one side of the tail hub to the other fixed the balance problem. Make sure you put set screws into the hub assembly before balancing because they do affect balance.

#15) When you are done with the repairs, check EVERY bolt in sight for tightness. The other day I went into a hover and heard a weird noise. I landed immediately and I'm glad I did. On inspection in the pits I had forgotten to tighten my horiz stab on the tail and it was vibrating against the boom.

#16) NOW you can throw away old broken parts. Notice I didn't tell you to throw anything away in step #4. The reason is I find when doing the repair job you will often miss something that isn't included with the new part that you have to reuse. A great example are the set screws in the landing skids of a TREX 600Nitro. You have to re-use those set screws as they aren't included with the skids. If you threw them away and didn't know that you would have to halt the repair job until you could drive up and get the parts!

I've probably forgotten something, but these steps really help me. There is nothing more frustrating than to be in the repair for a Saturday fly on Friday and you missed a part! I'd also advise you to not take apart the heli until you are within 7 days of the funding for the parts. I find them harder to put back togther if you wait too long between taking them apart and the repairs. (You can do a visual inspection and normally get withing $50 of the total repair costs by estimates.)

Finally share your tips for repairs!

[jeffsw]

These are great tips! Thank you!

[nasukaren]

Excellent! Definitely a sticky!!!!

You did forget: While you're browsing Helidirect, etc. -- try not to buy an entirely new heli out of grief for your old one! :-)

Karen

[Pinecone]

Very nice.

But for some people, if they only repaired at home, they would fly once per week. Only, if you repair at the field, take a towel to work on to catch dropped parts. I use an Align repair towel.

Also, I don't use zip lock pags, I use the plastic boxes that Align stuff (and others) come in. Easier to sort through when rebuilding.

www.rtlfasteners.com and www.microfasteners.com for sources for bulk bolts, nuts, washers, set screws, etc.

And keeping a good stock in spare parts on hand means not waiting for parts to fly. When I order replacement parts, I always order two of something that broke, that I didn't have. One to use, and one to have for the NEXT crash. Easy way to slowly build up a stock. Some people buy a spare kit, that way they have EVERY part. Then buy two when they take something out of the kit.

[nasukaren]

Pinecone -

Thanks for the link to microfasteners.com -- they look great.

REALLY STUPID QUESTION: Which is stronger, the alloy steel bolts or the stainless steel ones? They are the same price, but which would be better for our birds?

Karen

[Ultraviolet]

Originally Posted by nasukaren

Pinecone -

Thanks for the link to microfasteners.com -- they look great.

REALLY STUPID QUESTION: Which is stronger, the alloy steel bolts or the stainless steel ones? They are the same price, but which would be better for our birds?

Karen

The typical black oxide socket head cap screw has a tensile strength of 180000 psi. The same stainless steel cap screw is down around 70000 , which is a wee bit soft. Stick with the alloy steel unless you think your heli will be spending a lot of time in water. Then the stainless would work like a champ.

[nasukaren]

Originally Posted by Ultraviolet

The typical black oxide socket head cap screw has a tensile strength of 180000 psi. The same stainless steel cap screw is down around 70000 , which is a wee bit soft. Stick with the alloy steel unless you think your heli will be spending a lot of time in water. Then the stainless would work like a champ.

Interesting, thanks!!! I was assuming that the stainless ones were stronger because they were available in much longer lengths (e.g., M3 came in lengths up to 35mm in stainless vs. 16mm in alloy) so I was surprised to see your reply!

(Or is this due to a strength vs. brittleness issue?)

Although given how I fly and my proximity to the Atlantic Ocean, perhaps I should get stainless anyway -- never know when my heli hobby becomes a submarine one!

Karen