Do Over

[Paul Taylor]

I might refinish a plane. What are your experiences with removing a dope finish down to the wood without compromising glue joints?

[GallopingGhostler]

I might refinish a plane. What are your experiences with removing a dope finish down to the wood without compromising glue joints?

Careful and patient hand sanding. Using a sanding block helps.

[bill bischoff]

I have had some success with using a heat gun to peel off old silkspan and dope. I would avoid using chemicals and stick to mechanical removal methods.

[mccoy40]

Dope thinner might help - you should also be thinking about how to re-glue if you need it

[Bob Hunt]

When I refinished the 2010 Crossfire in 2012 I used Clean N' Strip paint remover to get the top finish off. I understand that the formulas on most if not all paint removers have been modified to take out some harmful chemicals, and that has rendered them less effective.

When the top finish was off the model all that was left was the .02 ounce per square yard carbon mat. I very carefully block sanded all the carbon off, leaving me with fresh balsa on which to apply a new finish. It worked out great, although it was a lot of work. I went through the entire process in my Model Aviation column that I was writing at that time. That model had been picked up by a dust devil at the 2011 Nats and was broken in half. There was a lot of other damage to the plane, but thanks to Brett Buck and a few other very helpful friends I was able to get the model glued back together and just missed making the Top-5 fly off that year, placing sixth. Actually. the plane flew maybe even a bit better after the repair at the motel! That's what prompted me to refinish the ship. I carefully removed the top fuselage shell, leaving the bottom shell in place to hold the alignment perfect. I fixed all the internal damage and then molded a new top shell and glued it in place. Then I repeated the same process for the bottom fuselage shell. I also removed the flaps and the elevators and made new ones. I was able to salvage the fin, and installed that, and the refinish began. The Crossfire Extreme (the "Extreme" is how I designate all my electric powered models...) came out weighing exactly the same as it did before the repairs and the refinish!

And, it was worth the effort; I placed third at the 2012 Nats with that model, and even won one of the Top-5 Fly-Off rounds!

Long story short (I know, it's too late for that...), it is reasonable to refinish a model that has proper alignment, turns equally in both directions and is not too heavy to start out with.

I’m attaching a few photos that show some of the rebuild and refinish of the Crossfire Extreme. It is still flying very well after all these years and it even helped be fly to a seventh place at the 2021 Nats, just four point from making the Top-5. I guess it doesn’t owe me a thing at this point…

Later - Bob Hunt

Photos below:

The first photo shows the model with the fuselage sanded. If you look closely you will be able to see where Brett Buck and I glued it back together. I decided that trying to just refinish the model without taking a look inside at the internal damage was probably a bad idea.

The second photo shows that the top shell has been removed to reveal the internal damage. Very glad I checked on this!

The third photo shows the damage to the fuse sides repaired and the formers rebuilt.

The fourth photo shows the new top shell prepared with lightened formers installed and ready to glue onto the fuselage.

The fifth and sixth photos show the bottom shell ready for installation and then installed.

[Bob Hunt]

Here are more photos of the Crossfire Extreme refinish:

Photo 1 below shows one half of the stabilizer sanded down to the carbon.

Photo 2 shows the model with almost all the carbon gone, but I opted to carefully block sand all traces of the carbon from the surfaces at this point.

Photo 3 shows all but the vertical fin and the stabilizer sanded down to raw balsa.

Photos 4 and 5 show the finished results.

Later - Bob

   

[Bob Hunt]

Here's what it looked like just minutes before the "incident" with the dust devil...

Bob

[Paul Taylor]

Great info Bob!!!
Thanks I’m motivated!!!

[Phil Spillman]

Hi Paul, In 1992 I stripped an old Ringmaster with Zip Strip and it worked great! Now I wonder if it would work as well today 30 years later! I'd give it a try though! if all else fails use acetone sparingly hopefully the model wasn't built with with Ambroid although mine was! it still is flying. I built it for my son in 1976 and it was an original Sterling kit with heavy wood! I did rehinge the elevator with Goldberg Nylon 1" tape t works quite well!

Phil Spillman 

[Paul Taylor]

Hi Paul, In 1992 I stripped an old Ringmaster with Zip Strip and it worked great! Now I wonder if it would work as well today 30 years later! I'd give it a try though! if all else fails use acetone sparingly hopefully the model wasn't built with with Ambroid although mine was! it still is flying. I built it for my son in 1976 and it was an original Sterling kit with heavy wood! I did rehinge the elevator with Goldberg Nylon 1" tape t works quite well!

Phil Spillman

Thanks for the tip ole friend.

I will keep y’all posted.

[Air Ministry .]

A/ youll make a big mess . So a sealed area or outdoors or something , helps . Like a vacume cleaner on standby alert ! .

B/ Throwing rags / paper towels rather damp with acetone , softens big areas , to peel off .

CHISELS even when oversharp tend to dig in . Gotta usem upsidedown .

A hacksaw Blade, NEW . Dragged across like a slicer , lostens the covering , then peel . Work sticky spots .

The more dope under the covering the better its stuck . Just Butrate peels easy .

80 Wt sandpaper new & sharp , often replenished , on decent blocks / forms , to cut through stuck parts , initially .

The glue seams , right angle corners need the most patiance & care . A paint scraper to fold the paper over , or a few steel straight edges ( dosnt do them a lot of good )
a selection of square , triangle , half round & flat files , B'std first , are good too . One flat with one plain edge is handy . Newish ones work best . DONT DROP THEM ON IT .


Yerinfer a few days work . Whacking off the control surfaces is a good idea . Slicing over & under hinges & stabing edges , the pull easy / o.k. , with a bit of a wriggle & the odd re cut .
Bob's trick was / is to re fit timber in the holes resulting, and re cut slots . In one of his artiles at least .

So , youll be in for new hinges , too . If Fitted .

[Bob Hunt]

Yeah, I forgot to mention the hinges. At first I just carefully removed the moving surfaces (elevators and flaps) and tried to scrape the glue and hard balsa from the tangs of the exposed end. Ugh! I decided to remove the hinges by making cuts above and below each hinge spanwise, and then making vertical cuts at the ends of each hinge.They came out in what can best be described as a rectangular "plug." I cleaned up the holes left after removing the hinges with a file.

I then made custom fit balsa plugs for each of the holes and glued the fresh plugs in place, letting about 1/16-inch of balsa stick out at the aft end of the hole. When the plugs had dried, I block sanded the rear edges flush with the trailing edges of the stabilizer and the wing, allowing me to then make new hinge slots. It was actually very simple.

Refinishing an airplane is just about as much work as building a fresh new model. The only reason I have refinished models in the past (and it's ironic that the only two that I did refinish were the original Crossfire and the newer Crossfire Extreme...) is the fact that they turned equally, were very rigid, and were accurately built. The refinish of the first Crossfire (pictured below in its first finish and in its second finish) was prompted by a desire to lighten the model. I actually took eight ounces out of that model with the refinish, and was rewarded with not only a much better flying model, but also one that sat on the front row in appearance at that year's Nats!

Happy sanding - Bob  Hunt


 

[Paul Taylor]

Thanks Bob
I was going to ask you how you got the hinges out.

I know for some it’s easier to just build a new plane but I hate giving up on a plane just cause I got heavy handed with a paint gun. 🤪
It looks straight and it did not do anything weird in flight. I will give it one more try.

[Serge_Krauss]

When I stripped my P-Force a few years ago, I first tried with acetone. For that Brodak finish, I found that "Dad's" paint stripper actually worked significantly better than acetone in removing the silkspan.