roger.alli

So, I was flying my Balsa Bobcat the other day when on landing I dumb thumbed it into the dirt. (Not usually that easy as these planes land them selves). Anyways, I speared the front in, and it snapped off about 100mm of the nose cone, with the nose itself becoming confetti.. Bugger!
There was some minor damage at the rear end as well, but the nose section was going to create the most problem to fix..

Here is how it looked immediately prior to the mishap.


And the damage.



In this day of ARFs, I’m sure a lot of people would just get on the phone and order up a new one but I’m a bit more old school than that.. Here is what I did..

roger.alli

The system I used to repair I have done before and is actually pretty simple. It involves stitching the broken skin back together as best as possible, and then lining it internally with epoxy resin and glass cloth to recreate the strength.. Most types of fibre glass damage can be fixed like this. It does add a little weight, but it’s way better than buying a new fuselage.

The first thing to do is use tape and cyno to stick all the little parts back together as best you can. I decided to make a nose section first, then attach the finished nose back to the fuse. Doing it all in one would be quite tricky due to limited internal access to the front of the nose.
You need to try and get the parts to fit pretty well, which means some surgery and sanding is required.. The idea to get as many parts into exactly the right place as possible. Cyno and kicker is great for this. Not every part will fit exactly and there will be a few lumps and cracks. Don’t worry too much.



At this stage I found out I must have left a whole chunk of nose skin parts out on the field somewhere. DOH!!! (I actually drove back out to the field in a vain attempt to find them.. No such luck.) This gap had to be filled, so I used a small sheet of waxed Polyply sheet taped on the outside of the skin to make a sort of moulding surface.


Now that this part one piece, it is still pretty flimsy and needs to be handled carefully. After prepping internally, some small pieces of glass cloth were cut and these were laid on the inside of the nose cone. West Systems epoxy is my choice.



I put at least 3 layers of this weight weave on. (I think it is 2 oz). After cure, the repaired cone is very strong.

rcpete347

My Feedback: (251)

HI, the best way to repair the nose is to CA the small pieces on the outside, all back together, ( do not worry about the outside mess). If any spots are missing, just tape it with brown utility tape, Once finished, use carbon or fiberglass cloth and West systems epoxy, use several layers. When fully cured, sand the crap out of the outside, even through the old glass and then body filler untill perfect.
Rcpete

roger.alli

Now it just needs to be attached to the Fuse.. This was done using the same method of tape and Cyno. Care is needed to get it straight and truly positioned. I used the centre line and old paint lines as guides, plus spent a bit of time on my knee with one eye closed before I was happy. Then Cyno and kicker was applied.



Glassing internally was a similar to that described above, but getting the glass bandage into the area was a bit tricky due to the distance from the cockpit opening. I made up some long brushes with extension handles.



Once cured, the repaired nose looks pretty rough, but is way stronger than the original.

roger.alli

Now I just have to make it look pretty.
The trick to any shaping/finishing like this is to use FLAT sanding surfaces or blocks. I use a cork block mostly, and a rubber block for final sanding. You should never use sand paper in your hand as it will create hollows.

Firstly, the nose was sanded with 120 grit to take off all the rough edges.. I put tape and paper in place on the undamaged section to avoid sanding further back than necessary.



Prior to applying filler, I roughened up the low spots with my dremel to give the fill a key. Some low spots still had paint in them and I thought the filler might not take.

The first layer of filler is an automotive 2 pack fine grade filler..



Once cured this is sanded back almost completely. Then the first coat of primer is applied.. This first coat of paint is really only to show just how bad the surface really is.



From now on the filler I use is a single pack fibreglass pin hole filler. It dries in 30 mins if put on thinly. It is sanded back using 240-300 grit, again removing most of the filler and primer.



After this filler has cured it is sanded back again removing almost all the primer that was just applied.




This process of filling, sanding, and prime painting, is continued in cycles until you have a perfect surface.. I think I put 5 layers of paint on. This doesn’t take as long as you might think as the filler and primer are quick drying..

It is this final stages sanding that I start to use the foam rubber sanding block it allows a slight curvature, without putting a hollow in the surface.

When I was happy with the surface, the last prime coat is lightly sanded with 600-800 wet/dry, and the nose is finally ready for colour.

roger.alli

As I painted the model originally, this was relatively easy for me. Prime coat, followed by a white base coat and then the colours. I used some 800 grit wet and gry around the perimeter of the repaired section, in preparation for blending the old and new paints..

Getting the finished paint blended into the original paint is the hard part. I have never been able to make the blend completely, but the end result will be invisible to all but the closest inspection. Very few people will ever know it has been damaged.. I hope...


The whole job has taken me two weeks of evenings, and I am a slow worker..

roger.alli

So there it is..

This technique has no doubt been covered on RCU before, and I know that RCJI has done an article on it recently.. To the expert builders out there this kind of repair is childs play, but I hope that some of the newer entrants to the jet set will find this interesting.

Damaging a model is never fun, but working through the repair is very satisfying for me. It takes some thinking but it is really not that difficult.

It is also a good way to learn how to paint as you are only working on small area at a time so there is little chance of ruining a lot of preparation work like you would on a complete model.



Roger

roger.alli

Hi Pete,

you are the master at this stuff. I learned an awful lot on this following your FrankinBandit thread.. That was a way bigger mess than my Bobcat.

Jeremy_D

Nice job Roger! I was out there that day and saw it after the landing, your repair job is fantastic! It looks better than new!

Harley Condra

My Feedback: (4)

Nice repair job!!
Here's a tutorial from BVM regarding repair and paint matching, or blending. http://www.bvmjets.com/tips/Flying%2...%20Repairs.pdf

The use of a blending solvent will make the new paint blend into the original paint.
I have been using PPG PPG DX840, but it has now replaced with "One Choice" SX840. http://us.ppgrefinish.com/PPG-Refini...Finish-Blender
I am anxious to try the SX840, but BV has tried it and reports that it is even better than the older version.
The "One Choice" is in a spray can, and requires no mixing with the new paint to do the job, as did the original (DX840).
After polishing the repair with fine compound, you can't find the transition from new to old.

RCISFUN

My Feedback: (44)

Nice job Roger, people don't realize how easy fiberglass is to work with if you have the right tools!
Posting photos of repairs may give some the courage to give it a try!

cmjets

Hi, fantastic repair job, congrats. But you had another option... To buy me a new fuselage or only the nose for fit in your fuselage.
Regards from Spain.
Carlos.
_______________________
www.cmjets.blogspot.com

cmjets

vega406

My Feedback: (73)

Here is video of B-1 Bob at SpeedWorld this past year with my KingCat doing repair about the same you have and I have 30 more flights out of it now there is video the next day by noon of me flying it https://www.youtube.com/watch?featur...&v=ndatBvvIg0g

vega406

My Feedback: (73)

I did like RCPete said i super glued parts back on to hold it so Bob can repair..We had everybody there donating carbon fibercloth-resin-brush-sand paper and got ready to fly and noticed my boom was also damaged so an hour later it was carbon fibered and flying

smaze17

My Feedback: (60)

Beautiful work Roger. I repaired several Vipers and Mavericks this same way. Those were the good ol days

S

roger.alli

Thanks Harley,

Yes I have seen "blending solvent" at my local auto paint store.. It is sold in 1 Lt tins which is not friendly for our purposes.. To date my blending technique it to use very fine 2000 grit wet & dry, followed by rubbing compound and elbow grease. (I don't uses a buffer machine on my finished clear coats). This brings back some of the polish, but it still leaves a slightly dull area compared to the un-worked paint..

I try not to get too obsessive with it nowadays.. Trying to achieve, and then maintain a perfect paint finish can drive you nuts..

roger.alli

..

757Driver

My Feedback: (90)

Thanks for the lessons! Very good information.