Short Plank (oz16806)

About this Plan

Short Plank. Radio control tailless slope soarer model. Wingspan 48 in, wing area 360 sq in.

Quote: "It wasn't a spiral dive, it was a vertical roll! Holding in a touch of down elevator and only a small amount of aileron produced a slow roll but a very fast dive! Centralising the sticks and applying up elevator to convert all this energy into a big loop was the intention and then it happened; it went wild, completely unstable and hardly controllable! The cause... the fin had come off! This was designed to be removable, but unplugging itself in the air was not in the plan! A heavy down wind landing caused the wing to depart the fuselage ripping out the dowel in the leading edge. The elevon servos in the wing merely unplugged themselves from the receiver in the fuselage - luckily damage was minimal.

It proves one thing, this 'plank' won't fly without a fin! The fin on this model is quite small but has sufficient area and leverage, mounted as it is, to provide stability in most of the flight envelope except maybe when flying slowly in turbulence, as when coming into land in the curl-over on the ridge. I find that landing a 'plank' is a bit more difficult than a conventional aircraft. Don't slow it down too much and try to flare out the touch-down. Make your approach dead into wind and plonk it down firmly with as little height and speed as possible.

Family Tradtion: Previous 'planks' I've built of 100 and 72 inch' wing span are good thermallers with plenty of wing area and controlled by rudder and elevator. At 48 in span the Short Plank is the smallest of the series and control is by elevons, more suitable for fast aerobatic flight from the slope in good lift conditions. Even with an all-up weight of only 17oz and a wing loading of about 7 oz/sq ft it isn't a floater; wind speeds above 10 mph are best.

Pitch (elevator) movement of the control surfaces is only about ±1/8 in to produce the tightest of loops. You won't pull the wings off this model! You could go to a smaller deflection for high altitude thermal flying. The roll (aileron) movement of the control surfaces is at least double at ±1/4 in, electronic mixing at the transmitter is required to achieve this. Short Plank aerial gyrations (aerobatics) can be as close to conventional manoeuvres as your skill and ingenuity can make them.

This is a real fun model, in good lift on the slope you can have a ball with some serious 'stick stirring'. Loops can be made really tight, rolls are easy but usually not very axial. Bunts can be executed, just! Stalls are a non event, slowed right down with gradual application of up elevator results in 'kiting' and flying backwards; just release the up elevator, the nose drops and forward flight recommences.

Minimal Modelling: The main benefits of this model are its small size, light weight, low cost of materials (there's not much of it!) and ease of building. The fuselage is minimal, it contains only the receiver NiCad pack plus, I'm sorry to say, about 3oz of lead in the nose to get the C of G forward to its correct position (15% to 18% of wing chord, critical on a plank).

A very important part of the fuselage is the block balsa on the top at the rear, it stops the wing moving backwards and disengaging the dowel in the leading edge from the location hole in F2 - catastrophic stuff!

Fuselage construction starts by cutting out the three formers; F1 and F2 are from 1/8 ply, F3 from balsa. Cut the fuselage sides from 1/16 balsa, add the 1/8 square bottom longeron and the 1/16 wing seat doubler. Glue together the sides at the back and to F2. When dry pull the sides in at the nose and glue F1 in place. The rear fuselage will now have bowed out slightly to form a fair curve. Now you can fit F3..."

Short Plank from RCM&E March 1999.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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