Micro Amp (oz12413)

About this Plan

Micro Amp. Radio control electric powered powered glider, for Speed 400 motor.

Quote: "Build our 64-1/2 inch span electric powered glider, designed by Peter Holland for Speed 400 motors with 600 type cells and light, three function radio.

Quiet, carefree flying? Low building cost? Uncomplicated installation? All three are yours with your full-size plan this issue. 'Micro Amp' can be built for geared or direct drive motors and only needs two little servos and a BEC with its receiver. The wings plug in, and the tailplane has a single screw fixing, so it fits in the smallest car. Take a field charger and a spare battery pack, and you are set for the afternoon!

Micro Amp may not, at first sight, seem very different from other small electric gliders, but I set out to combine all those little improvements that I have found helpful in a series of electric powered gliders. Readily available and popular small light motors and NiCads really opened up the field for efficient flying. We have seen ultra light models, and faster versions which can make use of direct drive.

The airframe of this model has been lightened within the bounds of practicability, and with a flying weight of about sixteen or seventeen ounces, an efficient climb does not put a high load on the motor.

Remember that a high wing loading, whilst resulting in a higher flying speed, causes more drag, so that increasing the angle of attack to maintain climb, loads the motor more, which drains the battery faster.

You can content yourself on each flight, with a series of gentle altitude gaining, lift searching motor runs, interspersed with battery conserving glide spells. It is not a model for blustery, windy weather, because there is a limit to penetration consistent with climb, yet, at the same time, you need not restrict it to calm days.

By having plug-in wings, some of the overall depth at the centre is included in the fuselage, saving drag, and most helpful for the radio installation. Although the piano wire wing joiner weighs more than I would have liked, wire has been proven over the years on my other versions to be a wing saver - by bending, when escaping strong thermals.

Timber: Well, not much here. Choose it carefully - there is light, somewhat springy balsa and there is light, soft balsa. Use the former, because local damage will be more drastic with the latter. One mm thick sheet is much in evidence to make the wings warp resistant and flutter free. It covers top
and bottom of the Warren braced rear fuselage to resist crushing in handling. Only a small amount of 0.8 mm plywood is needed at the wing roots and under the nose. Use hard, but not heavy, sheet stripped for the spars and TE. Choose light 1/16 sheet for the wing ribs, which are strengthened at the thin TE with long gussets - lighter than cap strips.

Clear the board: If you are like me (perish the thought!) you will build the tail surfaces first. This not only commits you to getting started, but if you finish and cover them you can arrange the clearances in the fuselage while you are making it. This is because the tail surfaces, all that way, back, are a key item for getting the balance point right while you are finalising the positions of motor, gear and flight pack. Even the wings, heaviest part of the airframe as such, will not change the balance all that much.

Make up the tailplane outline complete with gussets, then cut and fit each lower set of bracing strip flat on the board. Follow up with a second set flush with the top, glued to the others where they cross. This is more warp resistant than one set of close spaced full depth bracing, even on so thin a tailplane.

Add the 0.8 mm ply patch at the bolt position and top of the LE where it may hit the fin if it stews round to resist damage. The elevator has proved to be quite powerful, quick to correct. Use soft but not floppy 1/8 sheet and round off the TE rather than making a sharp taper. Chamfer the hinge edge and hinge with Litespan. Make the horn from 0.8 mm ply soaked, and installed, in cyano.

The fin is no more than a piece of stiff 1/8 sheet. Use 1/8 square for the rudder bracing in an outline like the tailplane. Chamfer and hinge on the port edge. with the horn on the starboard side.

Wings: You can make both main panels, one at a time, over the same part of the plan; the starboard one faces towards you, so that the rib positions are common to both.

Lay the bottom piece of 1 mm LE sheet on the board and pack the front edge up 1 mm. Glue on the false LE. Pins will hold it and the packing in place. Follow with the bottom spar, and ribs, which you also pack up 1 mm. at their trailing edges. Remember that the two pairs of W1 are slightly slimmer at the spar to allow for root sheeting, which goes over the finished TE.

Add the unshaped TE tilted on the rib packing. Follow with the gussets and top spar, then webs, dihedral braces and tubes for the joiner, doublers and wire hooks and incidence pins. Then add the top LE sheeting. Remove from the board and sand the TE to section before finishing the root sheeting top and bottom. Cut and drill four identical 0.8 mm ply root facings and glue one pair to the wings.

Make the tip panels in a similar manner, but incorporate 3/16 in washout before sheeting. Thread them onto the braces. prop up, glue and gusset well.

Sand any sheeting vertical if it projects beyond the false LE, glue on the LE cap and sand it to section, blending in with the sheeting. Cap the tips and round off.

Fuselage: Cut out the forward sides from stiff 2 mm. sheet and laminate with diagonal 1 mm sheet on the inner faces. If you use PVA glue, clamp them together until set or they will twist. Meanwhile, build the rear fuselage sides over the drawing. Make sure that they do not try to distort, by pinning each side of the longerons until set. Check that the forward sides align when you fix them to the rear. You can cut the notches in situ.

Set up the sides, when set around Fl. F2, F3 and F4, pull the tail ends in and sheet across top and bottom. Measure carefully, the position of the wing root facings and drill through from the holes therein. Add the servo bearers, but ensure that the incidence pegs will clear the servos when in place. The front bearer support also takes the compression load at the incidence peg, should the wing get pushed back. The plan shows two nose options. For the direct drive, omit F1 and mount the motor in a rolled paper tube, then fill the corners with scrap sheet, prior to rounding off outside. The exact nose detail will depend on whether you elect to use a direct drive or gearbox and shaft.. The simple extension shaft has been used on many of my models for 540 motors direct, as well as geared 380 motors. Incorporate an access hatch below, in case the rubber '0' rings need to be replaced The test prototype started with a geared set-up and I also tried an Astro 02 with a home-made gearbox as one of the geared options, then cut back the nose for direct drive, to make a comparison. You too, can have versatility.

Finishing off: Use Litespan throughout, applied with Balsaloc. Check that you have not introduced any warps. then make up the pushrods from bamboo barbecue skewers and wire ends, which should be thin enough to fit the servo arms without drilling them out. I make one piece wire devises and bind them in place with thin copper wire, then solder to the wire ends when setting up the neutrals. They can be bent slightly to get the trim spot on, or if you have a 12 volt soldering iron, re-solder on the field.

You can use six or seven cells in the flight pack, but seven is best for direct drive. Adjust the position of the pack to obtain the correct balance. This will show where to fix F1A which has to be notched for the wiring. Add pairs of wire hooks with cyano to the sides for rubber bands which will retain the pack. Side hinge a ply cover over the radio compartment aft and secure it with a piece of masking tape or tiny screws. You will only need to get at the radio for crystal changes.

Bung it time: Try a few gentle, level hand launched free flight test glides in smooth air, to see if any initial trim adjustment is needed. The prototype just floated on, although the first power-on flight showed that I had the CG a bit further aft than intended. A battery shift cured this and resulted in a steady climb. The elevator has lots of authority, and most of the rudder can be taken off after a good nudge. Maintain plenty of speed, but keep climbing. Gaining height is not about climb angle - in fact a steep angle will shorten the motor run and slow the climb rate. The more air you use up, the better chance of finding lift.

The wing has a fairly sharp leading edge, in common with other examples with this efficient type of aerofoil. This helps penetration, although there is a chance that you might stall it, by hypnotising yourself into thinking that it will go just that bit slower on finals, or pinch that extra bit of altitude. As you progress with your 'Micro Amp', you should find that duration goes up, because you would be exploiting its efficiency to the full. Happy Amping!"

Direct submission to Outerzone.

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