Teeny Aerobat (oz15771)

About this Plan

Teeny Aerobat. Radio control sport model. All-sheet design. Uses a flat plate solid balsa wing, made from 1/4 in sheet. Wingspan 37 in.

The Teeny Trainer (oz6689) was first published in RM Sept 1990. This here is a later version, fully aerobatic with four-channel RC.

Direct submission to Outerzone.

Quote: "As my Teeny Trainer (oz6689) design is still on your website I thought you may be interested in a little variation of it.

Having been aeromodelling for many years now I’ve no real need for a trainer BUT I found myself in need of something simple to test a variety of 1.5cc or thereabouts engines. Most of my models these days are bigger or designed around a specific engine (so not easily swapped) and out of idleness I thought I’d revisit my Teeny Trainer design but updated a bit to allow for a greater range of maneuvers than rudder/elevator control would allow.

The original Teeny was built around 'standard' size servos and only 2 channel (27mHz!) radio so it had no throttle. Nowadays servos can be much smaller and my Tx is much more capable so I used 5 x 5.6gm servos (together weighing less than a single 'standard' servo) to give rudder/elevator/throttle in the fuselage and a pair of aileron servos which could be individually set up for differential (not needed) and flapperons if I fancied it. They were all HV types meaning I could safely use a small 2s LiFe Rx pack but there are others around the same size of course.

Construction of the model is very similar to the original so I’m not going into a blow by blow account her, just how I modified it. I shortened the nose a little to allow for the weight of the bigger engine (the original was really intended for smaller engines of 1cc or less) and increased the proportion of the rudder and elevator for greater effect while moving them back a little so that the elevator hinge line is at the rear of the fuselage. This way only the rudder needs a small chamfer to clear elevators rather than both sides, top and bottom, of the fuselage.

I noticed some comments about the original rudder being too small but this was very deliberate in the original design to avoid a beginner over controlling the model in the days before rates were fitted to cheap Tx’s, the bigger rudder should keep those folk happier. I also eliminated the dihedral, but interestingly, the model still turns nicely on rudder only.

Ailerons are deliberately narrow as I’m conscious of the possibility of the servos being overcome by airspeed with unthrottled engines that only run flat out and I’ve a few of those to try. Running out of control at high speed isn’t pleasant, been there, done that. If a throttle is to be fitted then these could be more effective if slightly wider. The narrow ones still work but roll isn’t desperately quick.

I recessed the servos into the wings and glued them in place. A groove takes the wires to the centre line where short extension leads from the Rx connect things. I used a D shaped 3mm carbon rod on the wing LE for strength with ding resistance and a bit of bent tinplate at the centre of the TE to stop elastic bands damaging the wing.

Fuselage is a little wider than the original just to give a little more room, engines are on a plastic mount rather than on bearers, for interchangeability reasons and I didn’t bother with ply doublers as I finished the fuselage with GRP which adds strength as well as fuel proofing.

About the only other change of interest is that I used 1.5mm c/f pushrods in SLEC orange tubing to go from servos to horns. To avoid bends the elevator horn, on the starboard side, is driven by the servo arm on the port side. Rudder is on the port side and servo arm is on the starboard. The crossover point being in the middle of the fuselage somewhere. See pictures [004, 005] showing the arrangement. Ends use a thin piano wire with Z bend connected to the rods with heat shrink and thin cyano. It’s easiest to pre shrink the tube over the rod and wire then slip it in place when needed before securing with the cyano.

Throttle is via a thin wire, connected using an electrical connector to another thin wire on the output arm with a Z bend. If you are only going to use one particular engine you could make something less adjustable. I made a tin tank (48cc) as I wanted to use diesels as well as glows (wouldn’t ever fill the tank for a diesel!) but initial flights using an Enya 09 glow were with a 2oz clunk tank.

Flying is pretty much as you might expect. As mentioned, roll is alright without being terribly quick, though it gets faster with airspeed. Rudder and elevator are effective, to the point where I’d recommend care in the use of elevator when flat out as the wings visibly bend in a loop! It does a mean flick roll and is maneuverable enough to keep me interested while playing with little engines.

Glide is surprisingly good, considering the flat plate wing, but you’re not going to be thermal soaring.

Just realised I forgot to mark c of g but it's no different to TT and in any case is a bit variable depending on preference. John Rutter"

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