Power Mouse (oz2088)

About this Plan

Power Mouse. Free flight cabin model, a 1/4 scale version of the classic Powerhouse design. This was a full size free plan in Aeromodeller August 1987.

The original 84 inch Powerhouse (oz5644) by Sal Taibi first appeared in Nov 1939 MAN. This here is a 25% version at 21 in span, for CO2 power.

Quote: "Power Mouse. Just in time for our Vintage Weekend - build Bob Jones' CO2 miniature of a Stateside classic.

I BUILD quarter-scalers; no, not those mower-engined monsters scaled from full-sized aircraft, but quarter-size replicas of model aircraft.

My interest in miniature models came about during the Second World War when, having no access to full size plans, I tried building direct from the 'one-third' reproductions in Aeromodeller. These were mostly unsuccessful, and with the advent of a Beau-Glider (oz8497) kit via the ATC, miniatures were forgotten.

Some thirty years later I saw Doug McHard with an early Brown CO2, motor and my interest was renewed. First attempts were Indoor Scale models using Brown and Telco motors.

With the advent of SAM 35, thoughts turned to the old time 'gassies' I had always longed to build. Looking through an American magazine I came across a quarter-size reproduction of the Privateer (oz4922) used to advertise the full-size plan. When my CO2, motor was held over the Brown Junior 10cc engine thus shown, it was found to be almost exactly the same size. A rush for a pair of No.1 Trexler airwheels and yes; spot on! I then determined to make the model as near an exact quarter-scale replica as possible, using all the full-size construction and quarter-sized wood. Longerons came out nicely at 1/16 sq from 1/4 sq, and the original 1/8 wing ribs could be cut from 1/32 sheet. The wing spars, now 1/16 x 1/32 instead of 1/4 x 1/8 required care but took the flight loads OK. The only real deviation was a 1/16 motor mounting plate instead of engine bearers. The resulting model was one of the most consistent performers I have built, and it inspired a number of other modellers to think along similar lines.

Encouraged by this success I searched through all my old mags (no mean task) for other suitable drawings, but in most cases found the fuselage drawn on one page, and the wings to a different scale on another. I had been very lucky to find that first one! The only answer was to produce my own drawings and the Powermouse is the result.

Go for the wood: Balsa selection is important. You will need medium-hard 1/16 x 1/16 balsa for the fuselage and wing spars. Wing leading edge should be medium grade. Look for firm and light quarter-grain sheet - 1/32 for wing ribs, 1/16 for tips, trailing edges and so on. If you cannot find the right grades in your local model shop, contact a specialist balsa wood supplier.

The fuselage is straightforward. Incorporate the 1/16 sheet cowl pieces when you build the sides, remembering to mark the insides for motor plate alignment. Fit your CO2 motor before adding the upper and lower cowl blocks; when fitting the latter cut a small slot at the back to allow the filler tube to pass through. Mount the filler firmly on the outside of the block. Support the tank with scrap balsa. Wing and tail dowels should be check fitted but not fixed in place until the fuselage covering is complete.

Take care to cut accurate wing ribs. I use a thin ply template held on the wood with two pins and carefully cut around with a sharp balsa knife. Note that the trailing edge must be shaped before being fitted. The wing tips should be level with the top of the trailing edge and central at the leading edge. Remember to pack up the rear wing spar 1/16in to allow for the undercamber.

The tail surfaces take time but the result is a simple, rigid structure as per the full-sized model. Use light wood and sand carefully to aerofoil shape. The original undercarriage was made from 1/8 diameter wire so you will need some of 1/32 diameter for your quarter-size miniature. Bend the front and rear legs to the shapes on the plan and solder the front cross-bar in place. Bind both legs to the fuselage cross-members with cotton at the points shown. Bring the legs together, bind at the bottom with fine wire and solder. When you are satisfied that the model sits correctly run a small drop of cyanoacrylate along the cotton bindings.

All the dope: Before covering sand the whole structure to ensure a smooth, bump-free surface. This is best achieved by using a sanding bar. Cut a piece of 1/4 in ply or hard balsa to approx 12 x 2 inches. Fix fine sandpaper on both sides with double-sided carpet tape. The bar will help to avoid digging-in when sanding, and the sandpaper seems to last longer!

If you have covered models with tissue before you will no doubt have found a method that suits you - if so OK stick to it. However, if you are having trouble try the following scheme.

Give all parts of the model (where issue is to be attached) two coats of thinned sanding sealer. Sand each coat when dry using the sanding bar. Remember that the tissue must be stuck to the underside of the wing ribs. Now attach the tissue with a mixture of 75% thinners and 25% clear dope. Apply with a small brush and rub the edges down well. When covering the wings start with the underside, working first spanwise and applying the mix to about three rib bays at a time. If you have trouble getting the tissue to stick to the bottom of the ribs add a little cement to your dope mix - use an old tin lid as a 'palette'. Try to achieve an even covering rather than a super-tight one.

When the dope is dry check that all the tissue has stuck down. Any loose edges can be re-stuck using dope brushed on top and rubbed through. To shrink the tissue apply a light mist of water using a spray. Then give it two thin coats of thinned clear dope. Check for warps.

Plan your colour scheme using coloured tissue, keeping colour dope to a minimum. Add any transfers and your name and address label. A neat way to apply an address is to type it on a piece of tissue and stick it down on the finished model with thin dope. Do not brush over the typing or it will smudge.

The finished model should weigh about 1-1/2 oz. Check that the model balances near the centre of gravity position shown on the plan, then try a hand glide. The prototype needed a 1/32 shim under the front wing spar for a smooth descent. Do not expect a long, floating glide; this model has large wheels and a 'fixed' propeller. When you are satisfied with your hand glides, try a medium RPM setting and gas charge on your motor, checking to avoid a too-sharp turn under power. Mine seemed to prefer a 'right' pattern. Take care - the original flew right off the large site at Cocklebarrow Farm on its second flight! It has also flown successfully indoors. See you at Old Warden?"

Update 30/08/2019: Added article, thanks to algy2.

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