Whoopee (oz13874)

About this Plan

Whoopee. Free flight indoor sport model for CO2 power or electric. Wingspan 257 mm.

Quote: "Whoopee was designed as an indoor model to fly in a small hall. Many CO2 models fly too fast for a small hall, so I needed plenty of wing area to give a low flying speed and a small wingspan to permit tight turns. A typical CO2 powered indoor model weighs around 35 grams. Reducing the weight below 35 grams will give slower flying speeds but as the motor weighs 15 grams not much speed reduction can be obtained without resulting in a model which is too easily damaged. I decided therefore to build a compact model with more wing area, and to make it reasonably robust by not building it too light.

Question: how do you design a model with a very large wing area and a small wingspan? Answer: use plenty of wings.

So Whoopee was born. It flies better than it looks as if it should. Why not build one? The good news is that there is no covering or finishing to be done.

At first sight it might seem as if this model has no lateral stability as there is no dihedral, but in fact the combination of side area and low centre of gravity give very adequate pendulum stability.

Choice of motors: This model has been flown with both electric and CO2 power. The plan shows both versions - the electric version has a shorter nose to maintain the balance. As the Telco CO motor weighs less than the Knight and Pridham electric motor it should technically be better for flying in a small hall. The weight is about 40 grams with CO and 55 grams with electric. However in practice there does not seem to be much difference. The electric unit is more reliable, and both the power level and length of motor run can be set accurately and repeatably.

Materials: Much of this model is made of 2 mm polystyrene foam wall veneer. This is an excellent material for indoor models as it does not break on impact (unlike balsa), it is very light (being only half the weight of 0.8mm sheet balsa for the same area) and it is also very cheap: Also, it needs no sanding, covering or finishing. It is available from decorating shops (eg Fads): a roll of 30 feet costs a little over £1.

Adhesives: Balsa cement and cyanoacrylate (super glue) cannot be used as they dissolve the foam. Copydex can be used but has the disadvantage that eventually it falls apart, particularly when exposed to sunlight. White glue (PVA) is better, or, best of all, is so-called 'R/C modellers glue' which is available from Deluxe Materials. Both white glue and 'R/C modellers glue' are slow drying and require pins or thin strips of masking tape to hold the components in position while drying.

Assembly: Begin by cutting out the four struts and 19 ribs. Glue 5 ribs onto each outer strut over the plan, remembering to make one right hand and one left hand. While this is drying cut out the fuselage sides, longerons and formers, and 5 rectangles of foam for the wings. If you are using CO2 power put in ventilation holes in F1 (below the engine) and F2 (behind the bottom of the tank). If you are using electric power cut out the hole in F1 for the motor using the template supplied, and cut a hole in F2 to clear the battery holder..."

Direct submission to Outerzone.

Update 26/8/2024: Added article, thanks to ilgk48. This is an extract from his full magazine scan as posted on HPA at https://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=13294

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