Double Trouble: or how I learned to stop worrying and love the joke

So what follows started out as a complete joke.

I was doing some work in MITERS when I caught wind that the two trainer plane fuselages that had just been sitting in there for ages were up for grabs. Of course my mind wandered to one of my favorite planes: The Stratolauncher. I mean who doesn’t love making some unholy abomination of aircraft parts by simply joining two planes into one to create an aerial launch platform. Also in the vein of the parasite fighter experiments of the 50’s and 60’s, there was an obvious idea. I could create one beautiful wing, just one wing, and I could create an amazing monstrosity, capable of carrying any test design into the air and dropping it for a glide test.

This concept has been living in my head rent free for so long right now.

I even photoshopped in a wing to the picture I took, just for the laughs.

I really saved this as “puregenius.jpg” on my computer

At some point the laugher turned into more of the evil villain laughter, and now here I am working out a detailed design of this monstrosity.

The best part of all of this is that there is not much to do for it, I already spent a day cleaning the bodies, now I just need to design a wing with a structural hard point in the center for mounting some detachable pylon, mount that wing to the bodies, wire in new motors and props, et voila, un bel avion.

Design Design Design Design

Typically one would want to establish an exact estimate of weights and aircraft charateristics before doing a detailed wing design, which one should, which is why I am waiting to be back on campus for that, and in the mean time will be working on planning out design features I want here first, to be incorporated into the wing design.

Design (around constraints)

Constraint based designing is a beautiful thing. We can so easily prune our design space with constraints, and shape our creations around them. This wing has 2 main constraints. 1: it needs to have an effective mounting patch for each of the *two* fuselages. 2: it needs a hard point right in the center to mount a mechanism that can mount and release another rc aircraft.

In order to save weight I am going to try a new (to me) technique. Use a foam leading edge with a spar behind it and balsa or plywood ribs to create the majority of the wing. The foam will provide a very clean leading edge, while the spar provides strength, and the ribs behind provide shape without contributing to weight.

pink=foam, dark brown=spar, light brown=balsa

After drawing this out I found two immediate issues, with just one spar down the quarter chord (a typical location as the center of lift is usually here) there won’t be that much torsional strength, and additionally there will be some issue with creating hard points off of just one spar.

My solution to this is two different configurations; one for the center section, one for the outer sections. With a second main spar and a strip on the trailing edge, we should have plenty of strength for creating the hard points for the fuselages and mounting point. We don’t need that second spar for the outer wing sections, as they won’t expect as much loading, so we can cut down on some weight.

So, how to mount to the fuselage? Well, the fuselages were designed for elastic mounting. As you can see in the first image those little pegs coming out of each fuselage would have one side of a large rubber band on it, with the two bands forming an x over the wing. The idea behind this is deliberate failure points. Basically in the event of a crash,we want components like the main wing to survive, and the best way to do that is to make other parts that can be easily replaced, like nylon bolts, or rubber bands, break first. Typically we use nylon bolts to mount landing gear on aircraft, so that way if the landing is hard, the bolts shear and spare the fuselage from getting broken as the landing gear tear off.

I, for one am a huge fan of using nylon bolts for mounting aircraft wings, I have done it twice now for large scale rc aircraft, and that should translate well to this massive thing. Now all we need is a sheer plane on both the fuselages and wing. If I was a rich person I would jump to saying carbon fiber on wood or foam would make a great sheer plane, but given this is a mostly scrappy build made from spare and old parts, lets go with some scrap plywood for now. We an use some extra pieces of wood, and with some clever use of scrap composites, we can possibly get away with that.

With more detailed measurements and calculations out of the way I should be able o create a good wing layout, and work on cadding it out. I’d also like to leverage 3d printing and composites more in this design, so I might have some big revisions for the next update.


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