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Oct 25, 2011, 06:24 PM
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eastlondoner's Avatar
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Own-design boom/pod n' boom sport planes: .45-.62


Hi guys.
Relatively new to the forum, although I had registered quite some time ago.

Back in the late '80's, I was finally in a position to get into R/C planes. I was intrigued by a design called a 'Pipe Dream', a petrol-powered stick design with an aluminium tube for a fuselage, with a pod arrangement around the main wing area. It was produced by Byron Originals, if memory serves me correctly. It kinda stood out from their normal mainstay of big warbirds etc. The 'Duraplane' designs also intigued me a few years later. For some reason the sheer simplicity of the designs appealed, and the in-you-face detour from the conventional balsa/ply zealots also appealed.

I then discovered the SPAD designs and website some years ago. Again, while the simplicity of the concepts caught my attention, I still wanted to have a conventional R/C wing and conventional tail surfaces.

Due to various issues and studies, I had to shelve the hobby until a few years ago. Various other pursuits and interests have limited my flying somewhat, but the challenge to design and build my own super-simple design, which anyone could put together and also somehow bridge the gap between ARTF's and scratch-building, to some extent... How? Well the er.. fuselage is just a 20mm square aluminium tubing, 1 metre in length when bought but trimmed down 50mm once the design work was all done.
The wing is a conventional foam/veneer construction, constant chord and nice, relatively thick semi-symmetrical section.







6mm sheet balsa make up the tail feathers, with 6mm square anti-warp strips on the ends. Triangular balsa gusseting adds gluing surface area to the boom (with epoxy, after 'scoring' the aluminium and balsa to improve the bonds). The battery pack and receiver are housed in a thin-walled plastic electrical box, and a future design will have one for the tank as well to keep the design a bit neater in appearance.
The engine mount is a laminate of 2x 6mm birch ply sheets, bolted on and epoxied as well, and again supported by balsa gusseting.
Carbon fibre undercarriage and tail skid. The u/c is bolted onto a 6mm birch ply plate, which in turn is attached to the aluminium 'fuselage' with epoxy and 2 countersunk screws, and again supprted by balsa gusseting to spread the load and gluing surface area.

What took the most time, by far, was to make a simple enough way to attach the wing to the aluminium fuz, and I eventually settled for a simple cradle. This consists of an 80mm (lengh)piece of hardwood, which is 20mm square, thus the same thickness as the aluminium. I then cut 2 wider 6mm ply plates and glued these either side of the hardwood strip. These 'cover' the sides of the alumium tube, so that it can carry the 2x titanium bolts which hold the wing nto the fuz. I then drilled 2x 6mm holes for the titanium wing bolts. I also cut 2x 2mm aluminium sheet plates and glued these onto the sides of the 2 ply plates, to ensure that the titanium bolts' threads don't cause wear around the ply, after frequent removal and assembly. These were also then drilled for the titanium wing bolts, using the pre-drilled ply plate's holes as guides. I then inserted the 2 wing bolts, to ensure that the cradle is secure and square on the aluminium boom/ fuz. It was then ready to be glued ionto the wings.

This whole cradle was held in place by the 2x 3mm ply wing joiners (100mm in length), which had a recess cut into them to help hold the cradle. Part of the foam core was also removed to accommodate the cradle. I then spent time making sure that the cradle was sitting right in the wing before gluing, including 2 degrees of positive wing incidence and all square with the aluminium fuz. Once satisfied, it was epoxied into place. After that, a wing-joining kit was used to further secure both the cradle and wing join itself.

It came out OK, and the wings were covered with Profilm/ Oracover. As this was such a deviation from the usual Stick/ Stik fuz design, yet still similar in concept to the various electric Slo-Stik designs, I used some 'different' Maltese Crosses for the markings, care of stocks of my other interest, i.e. motorcycles.

I love 4-strokes, so settled for Saito's great .62a. I included 3 degrees of side-thrust when I cut the engine mount out of the ply. A small hole was drilled in the front of the plastic R/C gear housing, to feed the small throttle servo lead through and connect to the receiver. Similar slots were drilled at the back of this box for the other servos and to fit the switch harness and charging jack. The plastic container was bolted to the fuz with 3mm bolts.

4mm self-adhesive foam strips acts as a 'seat' for the tank and, importantly, absorbs the vibrations from the engine. Wing seat tape helps prevent the cable tie rubbing directly onto the fuel tank. A thin slot along the plastic container holding the R/C gear lets the cable tie 'loop' around. These slots were all made with the ever-handy Dremel.

The rudder and elevator servos were fitted to a 6mm birch ply cradle and slid up and down the boom with the short carbon pushrods, until the balance point was achieved. (usual third from the leading edge).

I got my good pal Paul to 'maiden' the plane for me, while I filmed the take-off and took pics of low fly-bys with my iffy digital camera. The plane flies well, much to my relief! :-)

Yes, this design is obviously not as light as a conventional fuz construction, but it's also not much heavier, much to my surprise. No covering, sealer, etc.. and hell yeah, it's damn quick and cheap to build that fuz! Yeah, it bridges that ARTF v/s scratchbuild gap in some emphatic way, LOL.

I'm really happy how well the plane performs and I'm keen to build one with a 2 metre wingspan with OS200 four-stroke up front, some kind of ode to that Pipe Dream from Byron Originals that originally inspired me all those years ago.

Previous pod n' boom sportplane designs:

Here's some of the other designs that I've built, with a pod and boom arrangement, also modular in concept and with the boom and tail feathers combo bolted on, so that if I do crash the plane, a whole new fuz won't need to be built.. hopefully! The booms are thin-wall aluminium (I battled to find thinner than 1.6mm, but this modular shower curtain set sold in the UK here has aluminium rectangular tubing with just 1mm wall thickness; great weight saving compared to the more usual aluminium wall thickness found in hardware stores.
All 4-strokes again, mainly OS. The fuselage pods of these are mainly 3mm Liteply or 3mm balsa with 1/16 ply doublers. 3 degrees side and down thrust, 2 degrees positive incidence on the main wing, 0 on the tail. I called the design 'SCRAP': (Shower Curtain Rail AirPlane!), obviously referring to the boom construction, and these are all slightly different in either wing design, fuselage consturction and other minor differences as the design evolved from one into the next:



















Regards,
Dave.
Last edited by eastlondoner; Oct 25, 2011 at 07:35 PM.
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Feb 01, 2012, 10:46 AM
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I'm starting a scratch build... dura plane design but w/electric motor and I was wondering what are the dimensions of your birds? wing span and chord, but most importantly the tail. I have a tail section froma Pz habu that I was going to use but, I'm not sure if it has enough surface area for the desired authority it will need on the tail
It measures 17" span and approx a 7" tall vertical stab. ???????
Feb 01, 2012, 11:28 AM
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Oh yes one more thing???? I understand the theory and reasons behind adding a few degrees of right and down to the motor, but what is the 2 degrees positive incidence on the main wing? I was planning on fashoining a flat bottom wing instead of a semi-symmetrical wing. So I guess my question is, what is +/- angle of incidence and would i need to use any on a flat bottom wing or could I mount it flat (square) onto my fuz? The fuse by the way is going to be a 2.5" square thin wall pvc downspout/rain gutter
May 13, 2012, 10:45 PM
Registered User
Got a pod and boom under construction right now with the motor mounted above the wing in tractor fashion. Using a 10mm carbon tube for the boom.

I wanted the pod to look fairly decent asthetically yet easy to build. So i used two pieces of 1 1/2 blue insulation board glued together. Cut with a bandsaw to what to me where pleasant contours. Took my router and rounded all the edges other than where the wing sits.

To clean out the centre of this I slabbed off both sides off of the block with the bandsaw. Then cut the internal space out of the centre core piece. Laminated 1/32 ply on the two side pieces and glued it back together.

But first to give good clean side window cutouts used a straight cutter bit in the router after making a template jig to follow. I could not think of a better way to get accurate well defined window cutouts in foam.

The 1/32 ply with adaquate lightening holes driled through it is enabling me to construct internal structure to adaquatly support the boom and various other requirements. I desire decent strength and fairly light weight in the pod. So far this is about as far as I have gotten on this one.

Other than the 55 inch wing and motor pod are built and covered at this time. I am using a little carbon fibre to strengthen up areas as I see the need.

Wing covered with motor and prop installed in the pod weigh 8.37 ounces. Pod and boom with tailfeathers I would like to see about four ounces empty of equipment. This plane is not going to be seriously stressed in flight. I am trying to keep it fairly light but yet strong enough for relaxing type flying.


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