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Post  Ken Cook Wed Apr 10, 2024 4:42 pm

When I was at our 1/2A day this past Sunday a fellow approached me with this B-25. He asked that I fix it and make it airworthy again. It's a beautifully built model and the paint work looks awesome. This isn't a kit. A lot of tears in the silkspan and I hope i can fix that . It appears as though someone used enamel over the dope which is a nightmare. I asked if I could just recover it and he was slightly opposed. Nonetheless, he asked for first flight. I like everything about the model with the exceptions of the controls which are terrible. Major surgery to fix it but I believe I'm up to the challenge. I'm looking forward to seeing this COOL!!!! plane back in the air.

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Post  Onelife Wed Apr 10, 2024 5:06 pm

You definitely got your work cut out for you.
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Post  rsv1cox Wed Apr 10, 2024 5:29 pm

So much to like here Ken. Scratch built -big points! I love the way he blended the cowls back into the profile nacelles. Profile makes things simple yet it is quite involved. Iove it. But concerns. Probably about a 30"+ W/S with twin Cox engines drag and weight issues? Have you weighed it? Tissue on the wings? Must be a lot of paint, looks planked and heavy.

Looking forward to hearing about your re-do.
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Post  944_Jim Wed Apr 10, 2024 6:04 pm

Beautiful rendition there, Ken.

Can I have some particular dimensions?
Wingspan
Fuselage length
Root rib length
Wingtip rib length
Firewall engine side to tail of nacelle length

I'm thinking this is a mildly modified AMA plan #508:
https://plans.modelaircraft.org/wp-content/uploads/pdf/MA00508MA1.pdf

If not that one, then this one scaled down a smidge:
https://outerzone.co.uk/plan_details.asp?ID=8115

Thanks in advance,
Twinsies power rules!

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Never enough time to build them all...always enough time to smash them all!
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Post  Ken Cook Wed Apr 10, 2024 7:48 pm

This model was copied from the Aurora B-25 and TLAR.
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Post  GallopingGhostler Wed Apr 10, 2024 8:08 pm

Original builder did a fantastic job of building and finishing, Ken. Sounds like the new owner wants it just repaired. If it has tears already, makes me wonder if the silkspan is ready to easily tear elsewhere. But, those are my first thoughts, and may be more pessimistic than it really is.

You have your work cut out, but looks like a fun project.

Outerzone has a profile 42 inch span B-25 profile CL plan by Vern Schroeder from April 1958 Model Airplane News:
https://outerzone.co.uk/plan_details.asp?ID=8115

Says for two .09 - .15 engines of the time. Could be a starting basis by rescaling for .049 power.

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Outerzone photo.

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Outerzone plan thumbnail.
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Post  rsv1cox Thu Apr 11, 2024 7:36 am

I just looked at that George. Looks the same only he built the full cowl then blended it back into profiles at the leading edge of the wing. Everything else looks the same, nose, machine gun blisters etc.

B-25 Mitchell Oz_b-210

My Aurora B-25 - 25 1/2" wing

B-25 Mitchell P1017419

This is going to be fun, I hope that when Ken gets though we get an inflight picture/video/report.
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Post  andrew Thu Apr 11, 2024 8:16 am

GallopingGhostler wrote:.............If it has tears already, makes me wonder if the silkspan is ready to easily tear elsewhere. But, those are my first thoughts, and may be more pessimistic than it really is.
...............
Unfortunately, I think you're dead on about the silkspan having become brittle over time.  If it has dope under the color coat, it will have continued to shrink and some of the tears, with curled edges, look more like aging and deterioration rather than hanger rash.  

It will be quite a restoration job, but should be a beauty when completed.
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Post  Onelife Thu Apr 11, 2024 8:31 am

Would that product Brodak has (Rejuvenator) work. I never used it and pr would just tear of the old and add new and be done with it
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Post  Ken Cook Sun May 12, 2024 10:06 am

I fixed the controls on the B-25. Builder used epoxy to keep the bellcrank screw from coming out. Epoxy was all over and needed to be removed. The music wire even though twisted and wound tightly on the terminations , the builder felt the need to solder. Totally unnecessary and the flux was never cleaned off properly making a hardened mess.

Another common mistake I see is when the bellcrank is tightened. Many times the bushing isn't protruding enough above the bellcrank and when tightened down, the bushing not only expands slightly, it causes drag on the bellcrank. It takes a little but sanding down the bellcrank and removing a little more material goes a long way in insuring smooth controls and that your tightening down the bushing and not the bellcrank. If a washer is used under the head of the screw, remember that washers are stamped. They have even though not always detectable, a concave shape. Orientate the washer to your benefit. I also like to use a small dab of Super Lube grease on the bushing which offers tremendous smoothness. Just don't touch ANYTHING that will be receiving paint prior to washing your hands.

I also discovered from handling that even though the silkspan splits is due to age, strongly feel it was expedited by handling. I could see just from holding it myself how someone could put their fingers and thumbs through this wing as my hands lined up on these problems.I elected to sheet these areas prior to silkspan. So now that it's repaired, I have silkspan on and it's paint ready.

I discovered the inboard engine is a Cox car engine as it has the extra heavy crankcase. I tached it the other evening at 14290 with the 3 bladed prop and 25% nitro.


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Post  rsv1cox Sun May 12, 2024 10:34 am

I'm enjoying this story Ken.

Nothing I like better than a restoration of an older model. Sounds like you are catching and repairing the original builders mistakes. Good hints for all regarding bell-crank bushings and washers.

I imagine that the owner wants it back. But I would be tempted to offer him a trade or something. Hope to hear a flight report.
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Post  Ken Cook Sun May 12, 2024 11:14 am

Bob, indeed the owner wants it back. He asked if he could be the first to fly it and I'm looking forward to that flight myself. This is going to require asphalt take off. We do have a spot but it's tight. There's rough asphalt and bollards all around. My son usually uses a shop rag on the ground as a reference so he doesn't wander. I wish they would let us paint a nice straight 4" radius circle on the lot.

Sadly Bob, out of all the guys I fly with very few build or even repair anymore. I won't say it's because they're older. Some of the older fellows build quite a bit. I just think it's just how it is anymore. He gave it to me and asked me to get it flight ready. Keep in mind these are the guys I used to ask how to build stuff.
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Post  roddie Sun May 12, 2024 3:09 pm

Ken Cook wrote:      This is going to require asphalt take off. We do have a spot but it's tight. There's rough asphalt and bollards all around. My son usually uses a shop rag on the ground as a reference so he doesn't wander. I wish they would let us paint a nice straight 4" radius circle on the lot.

Sidewalk chalk.. Stick a piece in a sandwich bag.. and keep it in your pit-box.
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Post  getback Mon May 13, 2024 7:02 am

Sounds like a lot to get it back with the builder problems , getting in there to the small places to fix bell crank issues is a PIA its so close , did you take the bell out to do the repairs or work around it ? Looks Good watching for the paint !
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Post  rdw777 Mon May 13, 2024 9:49 am

Nice job on the repair Ken, A little difficult area to access… Any control system needs to be free but precise….Then plane will appreciate it!

Regarding car engines, I put a #8 cylinder/piston (single bypass, No SPI) on a Bee lower end with a horseshoe backplate just to see….About 12K max on a Cox black 6-3, 15% nitro….Would be great for a sport free flight…. Super easy starter too….
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