Brodak F-82 Twin Mustang

George you have mentioned the hollow logs at times. I'm a hollow logger myself. The F-82 is on my to do list. Your spot on in terms of wing area. Walt is friends of several of my club members and he came to our field in 2004 I believe. Walt said that many of his designs were redesigned to maximize wood, (2 18" wings from a 36" sheet) and some other modifications to fit things into the box. With two engines, your really taxiing the wing and the suggestion on the plan is one. However, I'm thinking a Sure Start would be lighter not to mention it would pull the cylinder back vs a Bee. Keep the tanks internally over the CG and it should do fairly well when the power is on. This is true of many of those designs, a integral tanked Bee out there is going to offer power but kill maneuverability. I have a Atwood Shriek that might be destined for a log.

This Brodak Twin has 1/4" solid fuselages. They're light, as a matter of fact too light. I'm going to have to silkspan these for some strength. One of the guys the other day had one and he broke the nose off of it flipping it. I found humor in it but he didn't. C grain should be used or a medium density balsa at minimum. I taper the rear of the fuse to the same thickness as the rudders so it's pretty fragile in the rear. I could of left it and this would've helped with the CG but I like the look. I was equally concerned with the rudders as they were extremely flexible and while doping they started cupping. When dry, I applied a very diluted mix of thinner and dope to the opposing side and it straightened up. It's quite hot here and doping in this heat causes fast drying which shrinks. it did allow me to get 2 decent coats on it.

The wood was so soft that I had to swipe the paper opposed to going at it because it would just tear right into it. The dope stiffened up everything and it looks good now in two coats aside from the blushing. Brodak dope and high humidity don't play well. I'm progressing away from using dope. It stinks, it's highly flammable and I'm sure it's real good for you. The final finish on this plane is not going to be dope but Systems 3 water based polyurethane which looks stunning.

There's no spar in this wing. The leading edge is the backbone but the entire assembly is made up of 3 butt glued sections with a ply joiner across the mid section. The design calls for one over each joint. I figured it would be fine as designed and I should've used my better judgement. I should of sourced a new leading edge mid section of the hardest balsa I had or run a continuous ply jointer. It will be fine, but I know the wing is going to be subject to flexing . It appeared to me that somewhere this design possibly had internal wing gear that was going to be used due to cutouts in the ribs for ply platforms that were not used or called for in the plan. Or it was just a oversight mistake.

Looking good Ken, I've been wanting to build one and convert it to RC.

Really NICE Ken!! I'm curious about the bellcrank arrangement. Is it similar to the way Sterling recommends with the P-38?

It's pretty much the same. However, they designed it without enough room. The fuselages don't utilize a root cutout and slip over the wing. They put a rib on each side of the fuse and allow the fuse to insert the full depth of the rib. Neat idea, it's a lot of extra wood and work and if not done properly is a big headache. If those ribs aren't square to the leading edge ( Which they were not) you need some wiggle room to square both fuselages. With all this material inside the wing, you really need to overcut most of it to allow for leadout clearance and swing.

Ken Cook wrote:         It's pretty much the same. However, they designed it without enough room. The fuselages don't utilize a root cutout and slip over the wing. They put a rib on each side of the fuse and allow the fuse to insert the full depth of the rib. Neat idea, it's a lot of extra wood and work and if not done properly is a big headache. If those ribs aren't square to the leading edge ( Which they were not) you need some wiggle room to square both fuselages. With all this material inside the wing, you really need to overcut most of it to allow for leadout clearance and swing.

Thank you for explaining that lay-out Ken. As you know; my scratch-built 1/2-A U-control P-38 utilizes a 1/8" sheet-wing construction. I decided to set-up the control-linkage "outboard" of the model's center-line.. and route the lead-out cables through tubes in the central-pod and inboard-boom. I hope that the arrangement will work-out.

Your model looks to be very close to the same scale as mine.. and we're both planning for Cox .049 reed-valve "twin-engine" power. I'm psyched that you're building this model.. because it's giving me some incentive to get mine in the air.

The nice thing about this plane is the wing as it's pretty generous. The wingspan is 32 1/2". That's pretty decent size and with two Black Widows honkin away this plane did very well. It also has a fairly long tail moment that allows for tight turning. It's really cool in the overhead maneuvers and stays out there on the lines which is pretty impressive. I think the newer laser cut version would even be better especially with beam mounted engines. 2 Medallions would be very optimal to use and they would fly this plane beautifully. Even a pair of Babe Bees would fly this plane nice. If your ever looking for a home for anemic engines, put them both on a twin and you would be surprised how much power they offer combined.

Airplane looking Sharp Ken , I've got a printed wood kit that i am not looking forward to building don't recall with one right now but not a twin . I hope the wood is good though! You're right about one thing to hot to fly and good building weather - the humidity , with the twins being built and flown lately gets me thinking but have some 1/2 built planes on the table now that need attention and thinking RC is where i want to go next anyway good luck with it and i will be checking in on the progress .

A neat tip when you have print wood, photo copy the sheets on the printer and you can spray some "77" on the paper and attach it onto new wood. This allows intricate parts and shapes to be easily replicated. If you really thin some dope down and brush on one coat before cutting it also prevents crushing when cutting using a X-acto.

Ken Cook wrote:A neat tip when you have print wood, photo copy the sheets on the printer and you can spray some "77" on the paper and attach it onto new wood. This allows intricate parts and shapes to be easily replicated. If you really thin some dope down and brush on one coat before cutting it also prevents crushing when cutting using a X-acto.

Excellent suggestion Ken on both points, and advantageous too over printing the wood. One, when they cut through the paper has clean wood when they remove the paper. One thing I found somewhat annoying about kit wood is seeing all the labeling through translucent doped tissue covering and part outlines. Some, you could sand the ink off, but then weakened the wood by making it thinner.

Some time ago, may be 30 years ago, there were a few cottage industry kit makers of peanut and walnut scale rubber powered stick build aircraft, that would sell kits with the printed paper temporarily pasted over the wood sheets. This was during the hay day of Peck Polymers. They usually had the more obscure WW1 aircraft and some WW2 aircraft that other kit manufacturers never bothered with. Since, I've lost touch with who these manufacturers were.

To fix die crushing or cut crushed wood, I'd put a drop of water then hit it with a Monokote iron. The steam generated would swell the wood fibers and help restore the crushed edge. Of course, some kit parts were unsalvageable because of such poor quality wood, would use the bad parts as templates on new wood.

I like rubber power and I built a Pacific Ace last year. This was a Golden State model which was printwood. I know what you mean by seeing the ink through the covering. It was quite difficult to rid the model of the inking.It wasn't horrible, but in the nose area you could see it. Currently, I have a Scientific kit which I want to do next which is from the 50's. This pre-dates Musciano models and this kit is printwood. It's a B speed "Atomic". Not only is it printwood, but it also utilizes planked surfacing for the cowling and turtle deck.

I finalized the twin today up to the point of bolting on the engines. I put it on the scale which ended up as 10.89 ounces. Unfortunately, when I did a quick cg check, the plane almost flipped forward out of my hands. I wasn't very happy with this. I built this model way back and it needed 35 cents on the tail to balance. This thing was WAAYYY over the top needing 1 ounce. I just don't get it. I cut weight in every possible manner to the point of even stealing 3/8" off of the fuse length. Seeing the problems I had early on just getting it together took the wind out of my sails. I could've mocked all of this up and did some adjusting. I just thought I pretty much nailed this one in terms of the last build.

One thing I did recognize is that the Silver Bees are a couple of grams heavier than the Black Widows I used before. Between the two engines equals almost 3/8 of a ounce. Not that that would fix the problem, It certainly would help. I knew better than to taper the fuselages, I just couldn't resist though and I tapered them in both directions to the rear. This is a common practice on Sterling models however, your taking away material where you need it the most. It still looks like I'm putting a big chunk of tail weight in it though.

Ken,
How much you figure the CG will slide back if you use postage stamp engines and external tanks? My Scientific profile P-40 was pretty nose heavy with the Golden Bee. Parking the AP .061 on it with an external tank behind the firewall moved CG back a bit and made for a looser flying engine-out landing. It certainly lost the "lawn dart" effect! Direction changes are easier too.
My Mossie practically has the NorVel .074s in the leading edge (well, not quite so far back).

Brodak offers 3 types of nylon/plastic mounts. The larger mounts is what is on my model which only is drilled for integral tanked Bee engines. The other 2 mounts are identical with the exception of what they're made of. One is a harder beige colored plastic offering product backplate application or tanked Bees. The 3rd is a softer opaque nylon which is quite flexible used on the 1st gen 1/2A Baby Clown ARF. My initial plan was to use the tanked Bees and then switch to the product engines. Then I discovered that not only is the Goldberg mount identical to hole location, so is the placement of the cylinder off of the firewall. If I was to use a product engine , not only would it be lighter, it would also pull the cylinder back approx 3/8". Unfortunately, the mounts required to do this are considerably smaller and their bolt patterns aren't the same.

I can bury the lead in the tail, I just should've explored this rather than guess but time is not something I seem to have a lot of. I use lead lined drywall at work. The entire back of the sheet is covered in lead of various thickness depending on what were shielding. This is quite nice due to being able to get sheet lead in 3 different dimensions.

Thats sucks you're haven those same issues even knowing from past experience and trying to make changes to compensate while building . If you add weight will it bee split between the two tail booms ?

That's what I'll do. The bummer is that I already put the plane in clear. I knew that was not a good thing . I had to take the chance due to the humidity we were having.

PM sent...

Ken,
Did you still want the CG mount?

Jim, sorry I didn't get back to you. After my findings, I went in yet another direction. At this stage, I won't be needing them. I do appreciate the offer. On my next builds, there will be no question in terms of what direction to approach. My gut instinct was to just do my own thing. I could've just left things stock but I just wasn't happy with the end result. Thanks again, Ken

Hi Ken, Please keep us posted on your progress. This model is going to "eat-up the sky".

I'm looking forward to flying it. Looking over my pictures, the approx time that I built my first one was nearly 15 years ago. Time does fly by.

Two good Testor Macs stripped of starters (or maybe not) on plywood firewall with wedgetanks would probably solve all nose heavy issues.

I don't want to instigate a bickering battle, those engines would never be considered by me. There's no place for those engines in my airport. I sold all of that stuff a few years back and I don't miss it a bit. I currently have one left in a Testor's Fly Em Zero. When it does start, it's a gutless engine that barely flies a plane with a wingspan less than 12". I have owned all of the Testor's series engines and I had one pipe bomb that stood out from the rest that was until the crank broke in 2 places. The conrod pins on the crank are extremely small and this is another failure point where the crank pin and web fracture off. I did enjoy that pipe bomb until the crank took a dump. Nonetheless, the quality in my opinion was always lacking.

I'm talking about an FRV, not a pipe bomb.