Brodak Mustang Build

JPvelo Mon Aug 17, 2015 4:05 pm

I just cracked open the box to my Brodak F-51. As usual I'm going to do enough mods I should probably have scratch built from plans by the time I'm done.

I'm building this for a year long points series we came up with at Central Arizona Control Line Club. Power will be Fox .35, it may get also get my Thunder Tiger .36 for a shot at 100mph at the club bracket race in October if it's done by then.

Shot of the finished model on the instruction book:
Brodak Mustang Build C6fLFOZ

I made new 3/32 ply doublers. Much stiffer than what came with the kit, also going further back on the wing. They angle up at 45 degrees to make the eventual paint scheme easier to pull off. Inboard is one inch longer to distribute the Fox shake over a wider area so the stress isn't concentrated in one spot. I also lengthened the bottom to cradle the wing a little more.
Brodak Mustang Build NOs9Dpf

The engine bearers had a little slop so they're shimmed with 1/32 ply. Empty space behind the engine is filled with 1/4" hard balsa with the grain running vertical to tie the bearers together and hopefully eliminate some vibration.
Brodak Mustang Build ObKmGcs

She's all epoxied up now and resting for 24hrs under a 1/2" oak board with 60lbs of barbells on top.

I want to use hard aluminum mounts for the Fox, any suggestions where I might find those?

Thanks,
Jim

**Cribbs74** Mon Aug 17, 2015 4:19 pm

Roddie did up a bunch of aluminum mounts a while back. He may still have some.

I like the mods, especiallly the extended mount on the engine side.

Ron

getback Mon Aug 17, 2015 4:47 pm

Looking Good Jim ! That layered mount is Neat and should suck up some vibration for sure , where did you get the Mods. ideas from ? Sounds like your club is keeping ya busy Smile

JPvelo Mon Aug 17, 2015 6:03 pm

getback wrote:Looking Good Jim ! That layered mount is Neat and should suck up some vibration for sure , where did you get the Mods. ideas from ? Sounds like your club is keeping ya busy

Thanks Eric,

I got the staggered doublers idea from Paul Gibeault, he does it on his Fox racers. The horizontal grain between the doublers came from somewhere on Stunthanger. As long as I was making extra work for myself I should have replaced all the material between the mounts with vertical grain. lol!

Jim

JPvelo Mon Aug 17, 2015 6:05 pm

Cribbs74 wrote:Roddie did up a bunch of aluminum mounts a while back. He may still have some.

I like the mods, especiallly the extended mount on the engine side.

Ron

Thanks Ron, I'll contact Roddie.

JPvelo Mon Aug 17, 2015 8:36 pm

I found these on Stunthanger Hobby when I was ordering the pushrod for this build and ordered two sets in 1 and 2 degrees.

http://stunthanger.com/hobby/product_info.php?products_id=343

If you're not ordering carbon pushrods from Stunthanger you're missing out, $6.95 and it's at your house in about three days.

http://stunthanger.com/hobby/index.php?cPath=24_48_80

JPvelo Tue Aug 18, 2015 6:51 pm

I found the included horizontal stab a little flimsy for my taste so I'm gluing up a blank to cut a new one from.

Brodak Mustang Build DhnOBKe

batjac Wed Aug 19, 2015 4:00 pm

JPvelo wrote: As long as I was making extra work for myself I should have replaced all the material between the mounts with vertical grain.

Jim

I don't think that I'd do that myself. Replacing all the horizontal wood with vertical wood between the engine bearers seems like it would create a natural stress riser at the point where the engine bearers and the vertical grain start. You'd only have the narrow upper and lower sections of balsa resisting the tensile stress. Seems like it would increase the chances of breaking the nose off right behind the engine, even with the ply doublers.

But, that's just me.

The Stressed Mark

**RknRusty** Wed Aug 19, 2015 4:19 pm

I'm inclined to agree with Mark on that. I think what you initially did with the vertical grain at the rear of the opening between bearers is the best. After some initial hairlines, my Yak isn't suffering from Fox vibes. I do think the laminated fuselage arrested some of them before they got deeper.
Rusty

JPvelo Wed Aug 19, 2015 8:06 pm

Mark and Rusty I think you guys are probably right.

Made some progress today, got the threaded inserts for the engine and tank installed as well as the new stab cut out
Brodak Mustang Build H134jtU

The stock profile didn't look much like a mustang:
Brodak Mustang Build T4vBVSE

So I broke out the expanded 3-view and cut till it looked like a P-51, I had to make a new canopy.
Brodak Mustang Build 4vomuyW

The bottom air scoop will need some trimming as well but I'm not doing that until the wing is built and I can make sure it's placed to cradle the wing nice and snug.

The Re-Sculpting Jim

**RknRusty** Wed Aug 19, 2015 10:28 pm

You're right about that, Jim. Yours looks much more like a Mustang should. I wish I'd brought the bottom front support of the Yak's wing farther back like that. I ended up adding a Bass strip to help secure the wing bottom. And I did an extreme re-carving of my scoop. It looked nothing like a real Yak-9 scoop.

For those that may wonder why I'm comparing the F-51 Mustang to my Yak, it's because Sterling produced them as sister planes to go head to head in Slow Combat. They are almost identical, just the curves are different. I am going to have a Mustang to keep my Yak company one of these days.

In fact, I think I'll take the Yak out tomorrow. I'm inspired, thanks, JP.
Rusty

Here's the Mustang's twin sister. It has a red spinner now, really makes it stand out.

JPvelo Wed Aug 19, 2015 10:32 pm

Rusty,

How do you reinforce your threaded hinges? I've been adding a strip of 1/32 ply to the bottom of my control surfaces so the string doesn't pull through.

Jim

**RknRusty** Wed Aug 19, 2015 11:08 pm

JPvelo wrote:Rusty,

How do you reinforce your threaded hinges? I've been adding a strip of 1/32 ply to the bottom of my control surfaces so the string doesn't pull through.

Jim

After drilling the holes with a pin vice, I soak the area surrounding the hinges with thin CA to harden it, using a pin making sure it gets into the holes. The stab on the Yak was already silkspanned and painted, and I should have hardened it while it was still bare, but I didn't. I did take a pin and get some CA into the holes. However the elevator was to be Monokoted with no silkspan, so I did harden it, and then cut strips of Monokote and ironed them down on its hinge lines, and punched pinholes through it. Then Monokoted the whole elevator.

I did it the same way on the Shoestring. On that one, I learned to pre-stretch the dacron line before stitching, because it does stretch a little, and then seems to stop. I have since sealed the hingeline on the SS, but I pre stretched it on the Yak. Tied it to a doorknob and walked off a good long piece and gave it the ol' tenderness test. Watching the Winter Olympics and sewing that cold night. The Yak's hinges are still nice and tight. I've flown hundreds of flights on the SS.
Hope that helps
Rusty

JPvelo Tue Aug 25, 2015 6:58 am

Here's a couple shots of my "Super Paranoid Bellcrank Mount". The bolt is captured top and bottom, the mounts are epoxied to the spar and tie into the center sheeting as well. I'm planning on putting my Thunder Tiger .36 on this and trying for 100mph so it will need to pass a heck of a pull test.
Brodak Mustang Build 3wJCdUg

Here's a couple shots of the mockup:
Brodak Mustang Build BFl9NTT

Ken Cook Tue Aug 25, 2015 12:02 pm

Jim, I'm curious to know why the big demand for such a strong pull test. Is this a rule for a certain event your having? The plane should only be required to be pull tested in regards to it's weight which will be actually quite light. The plane if properly trimmed is not going to pull very hard. I find it hard to believe that it would require a pull test above 45 lbs. 100 mph with the Thunder Tiger shouldn't be that difficult to achieve. Phil Cartier was pushing them harder but unfortunately, he kept breaking the crankpin. A common practice for a combat plane with a center rib as you displayed would be to cut a 1/8" dado into the center rib and have the platform plug into it with a 1/8" dowel going through the center. The load would be placed onto the center rib entirely . Your picture indicates to me at least that your now placing all the load onto the next rib outside the center rib and the platform just butts into it. Vertical shear webbing in that open bay just on the other side of the rib that the platform is touching would prevent that rib from separating off of the spar. Ken

JPvelo Tue Aug 25, 2015 5:20 pm

Ken,

It will be pull tested for a 100mph bracket race, probably to around 45lbs. That number scares me a little so I would rather overbuild than under build. I added 3/32 ply shear webbing to the next bay just to be safe.

Jim

JPvelo Wed Nov 11, 2015 6:30 pm

Well, Tucson 1/2a and Phoenix Carrier Plus are out of the way so I have some time to work on this one. It's been so long I forgot I had a thread going!

Got some good work done this week. Wing is pretty much done but for final sanding. I made adjustable leadouts and a weight box just for fun.

Brodak Mustang Build A7Z4dJ1

I hope to have it ready to finish when I get back from what looks to be a very cold backpacking trip next week.

roddie Wed Nov 11, 2015 7:31 pm

Geez..it looks great Jim! I'll have to see if Brodak stocks a wing-kit. I butchered my original Sterling S2's wing decades ago. It was my first built-up wing attempt... Embarassed

Still have all the parts.

Brodak Mustang Build Dsc01210

I really like your modified nose-doublers.. and their vibration isolation properties. I will think about that for when I run my Foxes!

JPvelo Wed Nov 11, 2015 8:33 pm

Here you go Roddie:

http://brodak.com/control-line-parts/rib-sets/sterling-f-51-mustang-rib-set.html

**RknRusty** Wed Nov 11, 2015 9:43 pm

Ken Cook wrote:...cut a 1/8" dado into the center rib and have the platform plug into it with a 1/8" dowel going through the center. The load would be placed onto the center rib entirely...

I like that. I don't always intuitively think of these structural advantages. Also, I am glad to see the crank in on the inboard side. My Yak has the controls on the outboard side where more oil and grime get into it, but the mount is naturally stronger. This dowel pin takes care of that for an inboard bellcrank.

I'm glad to see this thread active again.
Rusty

RK Flyer Wed Nov 11, 2015 10:31 pm

Jim, Does the Brodak kit come with any type of jig system for the wing?
I am just starting to build larger planes but I have trouble building the wing. I am learning a lot from you & all the other posting the how to builds, keep up the good work !!

Thanks RK Flyer Flying

fredvon4 Thu Nov 12, 2015 9:01 am

If you look at the Brodak Sterling F51 Mustang kit and scroll down to the extras you can bundle with the kit is the Brodak wing Jig...hard to find looking around in tools or building supplies

duke.johnson Thu Nov 12, 2015 12:48 pm

I didn't use a jig when I built mine, but looking at Jim's pictures on page one of this thread, there's jig holes in the ribs. I think mine had something in the kit to lift the TE and I built it on the drawings. Mine has been ready for paint for at least two years. I built mine for NW Sport .40 Carrier. Nice kit.

JPvelo Thu Nov 12, 2015 5:01 pm

I don't use a jig but will probably make one next build. I installed the center rib, tip ribs, and the the bottom spar. Fill in the remaining ribs from there then the top spar. Required a little steam persuading from the tea kettle when done but not to bad.

Jim

roddie Thu Nov 12, 2015 10:14 pm

JPvelo wrote:Here you go Roddie:

http://brodak.com/control-line-parts/rib-sets/sterling-f-51-mustang-rib-set.html

Thanks Jim, Good to know.

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