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Jan 16, 2015, 09:40 PM
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Captain Dunsel's Avatar
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Build Log

Xp-59


Poor Bell Aircraft Company. They designed several radically different airplanes in the 30’s and 40’s, but kept getting bitten. For example, they designed the YFM Aircuda to fit a requirement for a multi-seat escort fighter. They built what was requested, but (fortunately), higher-ups in the US Air Corps realized that whilst their execution of the concept was good, the concept itself was (think of the Boulton Paul Defiant), poor.
Likewise, their P-39 design. At a time when two to six .30 caliber machine guns were common, it stocked not only those pea-shooters, but also a 37mm cannon. Plus, it had tricycle landing gear to ease ground handling and a mid-fuselage engine placement to enhance maneuverability. Sadly, the turbo-superchargers that would’ve given it a chance to fight above nose-bleed altitudes were deleted (not needed for Army support, ya know). Net result was another failure for Bell.
Then came a call for radical designs, to be based around some new, equally radical engines (such as the Continental X-1400). Answering that call, Bell came up with a pair of twin-boom, pusher designs, the XP-52 and the XP-59 (the former to use the X-1400 and the latter to use the famed Pratt and Whitney R-2800).
Several other companies also responded to the RFP, amongst them Curtiss’s XP-55 “Ascender”, Vultee’s XP-54, and Northrup’s XP-56. Those, at least, made it to flyable (loosely speaking) prototypes. Bell’s XP-52 and 59 were cancelled when the X-1400 ran into developmental snags and got cancelled. At least, the Air Corps staff recognized Bell’s ingenuity, so when the first jet engines were provided by Great Britain, Bell was given the opportunity to build the first US jet aircraft.
Problem was, hard info on the engines wasn’t provided, so Bell wound up building an overly conservative airframe to use them. To keep secrecy, though, Bell was told to use the cancelled XP-59 designation for the new blow-torch-powered aircraft, calling it an XP-59a. The resulting aircraft, the Airacomet, is actually a pretty nice looking aircraft, with a very visible P-39 heritage. Sadly for Bell, though, it turned out to be too conservative (!), so only a handful were built. Lockheed was given the British engines and told to build something with them. Lockheed, in turn, gave the engines to Kelly Johnson’s team, and they produced the long-lived F-80/F-94/T-33 series with them.
Oh well, at least Bell got to carve its name in aviation history with their rocket-propelled aircraft, the X-1 (which Chuck Yeager took past Mach 1) and the X-2. Then, Bell went to helicopters and carved out the very successful niche they still hold.
Like many of us, I’m fond of rooting for the underdog. So, when I stumbled onto a book of US fighter designs that included both successes and purely paper projects, I got interested in several of the latter. After all, there’s been a strong interest in the designs dreamed up for the Luftwaffe, had the war gone past 1945. There were plenty of other “what if” designs dreamed up for other air forces around the world, including the US, Japan, and the UK. If folks can build models of “Luft 46” airplanes, why can’t I build a model of a similar, never-built, US design? So, I hit the Internet and started researching the XP-59.
The first problem I ran into was the severe lack of information on the plane. Repeated Internet searches turned up a handful of shots of the wind-tunnel model and the plywood mockup, plus a three-view from a defunct book. Interestingly enough, the drawings and mockup photos all disagree. So, I decided to go with the three-view for most details, then try to rationalize deviations as the result of a full-scale airframe’s development.
Interestingly enough, I even found a photo of a navalised version of the XP-59. That could provide a cheerful color scheme, but it made me think. Where did Bell plan to put the arresting gear? Couldn’t have something that might blow back into the contra-props!
Speaking of contra (or counter-rotating) props brought up another issue. We fly on a gravelly runway, so pusher props run a severe risk of foreign object damage (FOD). Bad enough with conventional props, it could be expensive with custom contra-props. So, I decided to go with a single, pusher prop for the first XP-59, then switch to contra-props after the plane (hopefully!) proved successful.
So, after many hours of designing, drawing, face-palm slapping and re-designing, I finally began cutting wood this morning. Tomorrow, I sand parts to shape, and, hopefully, commence building.

Since the model will be a twin-boomed pusher, I'm planning to build the model in one piece. The first sub-assemblies will be the booms (with two different sides) and the horizontal stab. Once those are done, I plan to build them into the wing (built upside-down), over big sheet of ceiling tile. The fuse bottom will follow. Once the bottom is done, the assembly comes off the jig and the fuse top is added, followed by foam to fill out the fuselage shape.

My target is to make the landing gear removable, so I can catapult-launch the model once I get it trimmed out.

This is the most complex model I've built in many years, with the most radical construction methodology I've used in a long, long time, so I expect some more hair pulling. But, I'm tired of simple sport ships, so, here we go!
Last edited by Captain Dunsel; Jan 16, 2015 at 09:55 PM.
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Jan 16, 2015, 10:48 PM
AndyKunz's Avatar
Looking forward to the build thread. Subscribed!

Andy
Jan 17, 2015, 02:01 PM
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Very neat.
Jan 17, 2015, 04:14 PM
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Captain Dunsel's Avatar
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Hi, guys!

Spent yesterday cutting out the parts on my ancient Dremel Motoshop, then today I sanded them.

Had a bit of a problem (as usual), getting the paper templates to stick to the poplar/lite ply. So, two more parts, the upper fuse 'backbones', won't get cut out until the glue dries.

My plan is to build the two booms tomorrow/Monday, followed by the horizontal stab.

CD
Last edited by Captain Dunsel; Jan 17, 2015 at 04:19 PM. Reason: Getting image right-side up.
Jan 19, 2015, 05:06 PM
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Captain Dunsel's Avatar
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Framed up the booms today. To make it harder for me to screw up, I made both the right and left booms at the same time. Since each boom has a shorter and longer side (due to the wing sweep), both booms are different.

One trick I tried to get the 1/8" sq. balsa to curve around the forward bottom of the booms was by scraping it along my workbench, to create a curl in the wood. Some of it still cracked, but most curved okay.

BTW, the red and black discs are pin clamps; the black ones came from Rocket City around 1988/89. The red ones were punched out from a raisin carton lid a year or two ago.

I use aliphatic glue (Titebond) for several reasons. It's cheap, it's easy to clean up, and it forces me to stop after a while -- which is good, as that gives me time to think about what I'm doing.

CD
Jan 19, 2015, 05:14 PM
AndyKunz's Avatar
I like your note to self in the bottom right corner. Do that myself sometimes...

Andy
Jan 19, 2015, 07:14 PM
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Captain Dunsel's Avatar
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Yes, I put all sorts of notes on my plans and on the print-outs. If you can do it wrong on a build, I've done it. So, I try to think ahead.

CD
Jan 20, 2015, 04:27 PM
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Captain Dunsel's Avatar
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Joined the boom sides together today, making a right and a left boom.

An old gel cell helps keep things straight in the middle whilst triangles keep the bottoms straight.

Next step is to join the booms at the rudder posts (whilst leaving room for the rudder posts) and sheeting the boom tops. I plan to leave the boom bottoms and fronts open for now, to allow installing the servos and pushrods.

No matter how many times I've drawn up plans, always find places I've goofed. For example, whilst adding the boom bulkheads, I found I'd cut slots in the second boom bulkhead for the servo tray 1/8" too low. So, I had to carefully cut out new slots. Fortunately, I was able to move the bits cut out for the new slots to fill in the old ones.

I just know I'll find more oopsies...

CD
Jan 22, 2015, 09:04 AM
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Captain Dunsel's Avatar
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Joined the booms at their rears, wrapping a bit of scrap 1/4 X 1/8" with sandwich wrap so it won't get glued into the spots the rudder posts will go (no pictures, yet -- should have them this afternoon). The 1/8" sq. side-to-side bits are in along the boom bottoms; I should be able to add them to the tops today, although building time will be limited as today's our day for volunteering at the county Dog Shelter.

I realized I should've installed the servo trays BEFORE gluing the sides together, so I squeezed them in...then repaired the broken side. Space will be tight in the front of the booms. There's more space behind the planned servo tray, but that puts the servos behind the CG. Since this is a pusher, I'm very wary of putting weight behind the CG. Problem is, I don't have any of the right-sized servos on hand, so I'll have to wait for them to come in before I can finish off the servo mounts.

My plan is to run the servo arms for the ailerons through the boom sides, and run the pushrods for the rudders and elevator 'down' the booms.

CD
Last edited by Captain Dunsel; Jan 22, 2015 at 09:16 AM.
Jan 23, 2015, 02:12 PM
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builderdude's Avatar
The best way I know of to get your 1/8" square balsa sticks to curve is to soak them for 15 minutes in water and then CA glue them in place. The water acts as an accelerant for the CA and it will set WHILE you hold it in place. Within 10 seconds, done.

By the way, there was the Bell King Cobra, the P-63, designed to use the upgraded Packard V1650 engine (the US version of the Rolls Royce Merlin). It was intended to cure the high altitude performance problem of the P-39. It was capable of 421 mph, still inferior to the faster P-51. That might have been the reason for the cancellation. With the brilliant North American P-51, why have a slower P-63? The Russians, however, who got the P-39 through the lend-lease program, really loved those planes and they made great ground attack tank busters on the Eastern Front against the Germans.

The Curtiss XP-55 was also crippled in top speed tests by being forced to use the weak Allison engine rather than the intended Pratt & Whitney X-1800, resulting in a top speed of 390 mph rather than the intended speeds of over 500 mph. Considering it managed to beat the P-40 by about 50 mph using the same engine, I think it showed its speed potential. But being basically a flying wing design (nose stabilizer was too small to really be considered a canard), it had dangerous handling qualities at the stall limit. Instead of cancelling it, they should have enlarged the nose stabilizer into a real canard and put a real engine in the back, and things might have turned out different.

I agree that the XP-59a Airacomet was a very attractive airplane. In fact, I had theorized (my own pet theory), that the American Junior 404 Interceptor was patterned after the Bell Airacomet, because the similarity is striking. (And the AJ 74 Fighter seems to be patterned after the F-84 Thunderjet).

In my opinion, the twin boom XP-59 that you're building looks just like a prop-drive version of a DeHavilland Venom. It also resembles the Estes Stratoblaster RC plane (ultra rare).
Jan 23, 2015, 09:08 PM
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Yes, the P-63 was the plane the P-39 could've been. Part of why I think Bell got a series of raw deals.

Don't know if the XP-55 would've worked without a lot of aerodynamic changes (plus a better engine). As I understand it, the wind tunnel tests predicted it would be unrecoverably stable in an inverted stall, which the test pilot verified when he flubbed a loop and the airframe dug a flaming hole in the ground.

The XP-59's configuration wasn't that odd for the times. The Saab J-21 and the XP-54 were similar, only the Saab was a success (and that's why I also wonder if the XP-59 would've made a decent jet, had it been converted to one the way the Saab J-21's were).

I have a 5' PVC tube I use to soak balsa in for curving and laminating. I usually soak the wood in boiling water (carefully, to avoid the PVC from bursting) and tape it to cardboard forms. For this job, though, I just scraped the wood to curve it (the way you'd scrape ribbons to make them curl). Then I pin it and let it the glue (usually aliphatic) dry.

Yay, the LBAT (UPS) came by today with my servos, so I can finish the servo mounts tomorrow. Today, I got the tailplane/HS finished, sheeted the tops of the booms, then cut out and pinned down the jig strips and the top spars. Hopefully, tomorrow I'll get the booms finished and glued to the HS, then get the ribs glued to the top spar and (hopefully) the wing LE.

It always amazes me how quickly planes go together, even though I use aliphatic and not CA.

CD
Jan 23, 2015, 09:34 PM
AndyKunz's Avatar
Quote:
Originally Posted by Captain Dunsel
It always amazes me how quickly planes go together, even though I use aliphatic and not CA.
I was preaching that sermon to one of the guys at work yesterday who is just starting to show the symptoms of CA allergy. He said he can't live without it, but I aim to prove him wrong

Andy
Jan 24, 2015, 09:20 AM
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Captain Dunsel's Avatar
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One of the reasons I prefer aliphatic to CA is that it gives me time to think about what I'm doing. Not a lot of time, but some time.

By the way, I thought I'd developed an allergy to CA and started using the odorless 'flavors'. But, the congestion, etc., wouldn't stop. So I went to aliphatic...and kept getting congested. I finally experimented and discovered the real culprit was vinyl spackling/filler! Sanding that indoors will lock my head up immediately (Even sanding over a vacuum box didn't prevent it). So, now I do a lot of my sanding outdoors (meaning a rainy day may keep me from both flying AND building).

CD
Jan 24, 2015, 11:17 AM
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builderdude's Avatar
One thing I learned from being a jet engine mechanic for 22 years in the Air Force was that it takes a period of time and exposure to develop an allergy. It's almost like being exposed to the chemical is okay for a time, like dripping into an empty cup. But when the cup gets filled to the brim and begins to overflow, you can't be exposed to the chemical any more.
Automotive painters experience that too. You spend a lifetime painting cars and eventually develop a reaction to the chemicals used in the paint.

I don't take any precautions, personally, and so far, I'm okay with CA. But maybe I should.
I use a lot of cellulose glue (Ambroid was my favorite, but now I use Sigment). The main reason is because it sands about as easily as the balsa wood it's gluing. But I do use CA for some things that it works better for. I like CA for sheeting wet wood because of how quickly it sets up. Then I use 30 minute epoxy for structural items. Main reason is because I like how it gives me time to make critical alignment adjustments.

Isn't canopy glue an alphiatic?
That's some good stuff. I always use canopy glue on canopies, and in rare instances, will use it for other things too, because of its similarity to wood glue or Elmer's glue.

I've also recently discovered hot melt glue. I did attach one canopy using hot melt glue and it worked okay, but it doesn't do as neat a job on the canopy as canopy glue does. It is about my favorite for building depron airplanes, which for me at least, uses very similar build techniques as balsa wood. However, in small scale, balsa and depron seem to be so similar in weight that it doesn't matter too much. It's in the large scale planes that foam has the big weight advantage. There's a guy in our flying club (Gary Jones) that has a huge 12 foot C-47 and I think it only weighs about 3 pounds. Flies so slow that you can almost take it for a walk, with it flying next to you. And I have a quarter scale Citabria built with balsa and canvas, and with motor, it probably weighs around 15 or 16 pounds. Quite a bit of difference when you get larger in scale.
Last edited by builderdude; Jan 24, 2015 at 11:23 AM.


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