Swappable FoamCub(ish)

This is not an exact build of the Swappable FoamCub that Shawn Martin designed, but his design with some modifications.  My goal has been to build a platform for remote sensing, and Shawn's design was almost exactly what I wanted.

I had finished building the Storch not tool long before I found these plans, and told myself it would be my next build, either when I had the time or after one too many crashes of the Storch.  The other week my depth perceptions failed me, and on the final turn for my makeshift (street) runway I cartwheeled off of an overhead wire and snagged the tail on a lower wire.  I got the plane down, but in several pieces - time for more foamboard.

The first major difference is that since I still had a (slightly used) Storch wing, and since this wing is very similar to the Cub (same chord, but a flat bottom and 3 inches longer), I decided to save some time and recycle the Storch wing.  To make it fit with the flat bottom, I removed the slight rise on the top of the fuselage where the front of the wing sits.

Since I don't have a lazer cutter, I hand-cut straight lines for most of the fuselage parts, omitting the tabs and treating the side, top and bottom as separately pieces.  The only difference is the need to be a bit more careful when gluing.

I value function over looks, so skipped the poster board parts, and sheeted over the nose and front with foamboard.

I omitted the flaps (at this time), and set it up with dual airelons.  I may go back and make these into flaperons, or add flaps in the future.  For now I want to learn how to fly this plane as a simple trainer, before going on to more advanced flying.  I also skipped the tail wheel, and put on a simple skewer skid - another change that can be replaced in the future.

The biggest change is in the landing gear.  While I like wire landing gear for smaller planed, the wire landing gear of the Storch didn't take well to my hard landings (which were most of the time), and the wire for the FoamCub seemed to be even lighter.  What I built serves two purposes, it is both a stronger landing gear, as well as a mounting platform for about any type of sensor (or anything else) I want to mount to the plane's belly.  I cut a piece of hobby plywood to the demensions of the fusealage bottom plate, put put two holes in the front for the landing gear, and a series of holed down the center line for attachments.  1/4 inch nylon nuts are glued to the top of these holes.  I can now bolt on about anything, and the 1/4 size is the same as standard camera tripods.

The landing gear itself was a 14 inch piece of 1 inch wide alumunum (from the local hardware store).  At about the width of the fuselage I bent it on about a 45 degree angle, so the legs pointed out and forward. I tapered the ends by cutting off the corner (1/2 in and 2 inches up), and drilled a hole for the wheel wire. I considered just a straight wire between the ends of the legs, but got a bit fancier and turned it into a brace that extends back and is held in place by one of the bolts.  I really like this design, it doesn't add much additional weight, and holds up quite well.

The wire, in the final installation, is reinforced with an InstaMorph rectangular washer.  This holds the wire better, and reduces the pressure on the foamboard.

Series of bolts hot glued to the top of the board.

The wheel fits over the wire, with two 'pony beads' as bearings on either side.  The outer one is hot glued to hold it all in place.

This if the final install.  The two bolts hold on an InstaMorph clip for a cell phone (GPS tracking and HD video!).

The black line on the top of the wing is a piece of carbon-fiber.  I may be paranoid, but it does reinforce the wing.  As you can see, the wing tips are a bit worse for the wear from the wing's prior life.  This picture was taken after several flights.  This is the 'runway' I am using, the plane handles it quite well as long as I avoid the pot-holes.

Stats and Details:

Motor: HobbyKing 2830/1000kv , 30A ESC, throwing a 9x4.7 prop.  This is what I had on hand. The motor is only 210 watts, way below the 550 watts suggested for the FoamCub.  It doesn't have a lot of power for acrobatics, but is sufficient for a gentle trainer.  I tried pulling back on the elevator to see how it would stall, and got a back-flip loop.  I definitely feel that I am flying the wing, and not flying the motor.  I will likely try more power in the future (especially when I add cameras, etc), but this is sufficient for now.

Weight: full-up with a 3s 2200mA battery is 38 oz.  Adam's (Dollar Tree) foam board is obviously lighter than Shaun's Elmers (54 oz).  This weight difference is why I can get by with a smaller motor.

Set-up: I dialed back the controls to about 60%, and for what I am doing I could probably cut them back even more.  This gives me plenty of authority, and acts a bit more aerobatic that I am currently comfortable with.  It responds nicely with very little input.  I added an airelon mix with 50% rudder.  This helps with coordinated turns, though I may try upping the rudder a bit more in the future.  Flaperons are an option, but I haven't put them in yet.

Flight Characteristics: I am probably not the best judge of this, as my total experience is limited; but with the flying time I have had it seems to perform quite well, and I am quite pleased with it.  There was a light wind today (7-12 mph), and while it was affected a bit, it didn't stop me from getting in several laps and practice several landings.  It is balanced up on the CG and has a nice glide slope.  Take-off is short (10 - 15 feet), but without flaps it does float into the landing, and mine tend to have a few bounces.

I definitely want to give a big thank to Shaun for creating the plans and making them available.  This is a great plane and will likely be my standard work-horse.  The design is simple and clean, producing a great flyer.