DESIGNING INDOOR MODEL AIRCRAFT
Whilst almost any model aircraft can be made to fly outdoors, the same isn’t true indoors, whether in the confines of a small sports hall or even the relatively spacious Velodrome at Calshot. To do so a model needs a wing loading of 4 oz/sq ft or less. But where do you start?
I learned to fly indoors with the Indoor Stick by Pico, but the best indoor trainer and general sport model I have seen is the Butterfly, availablele for the grand sum of about £35. This is the 34” span version that uses GWS gear, not the tiny Plantcro one! No article would be complete without mentioning Shock Fliers, brushless motors and 3-D aerobatics. There, I’ve mentioned them. Back to real model aeroplanes.
DO I NEED SPECIAL GEAR?
By far the most popular hardware is that supplied by GWS. The geared 150 “A”, a 10 x 4.7” prop, their indoor RX and speed controller, 2 Pico servos and a 350 mAh LiPoly 2-cell pack weighs less than 100 grams (4 oz) complete and will set you back about £100. They seem to last forever and will migrate into bigger models destined for the great outdoors. So no, you don’t need special gear, but if you want to fly more slowly, Falcon Models make unbelievably light flight packs, tiny motors and batteries that can bring model weights down to 40 grams, just 1.25 oz ready to fly, for roughly the same cost.
The GWS gear will let you fly a biplane of about 32” span or a monoplane of about 36” span, with a ready to fly weight of no more than 8 oz. These figures are only a guide, but the lighter you can build, the better it will fly. Falcon gear will let you fly much smaller and lighter models, and they have a large range of motors for different sized models. 24” span biplanes or 30” span monoplanes are possible providing that you build lightly.
4 models from this website illustrate the ends of the spectrum:
- The Supermarine Walrus. This is an 8-oz all-Depron model of exactly 30” span and 2 sq ft wing area, giving a wing loading of 4 oz/sq ft, at the top of the acceptable limits. I find it difficult to fly smoothly until I’ve had a few minutes on the sticks, as it needs very small control inputs! The original design was by Trevor Hewson and we collaborated on the plan, which was published in Flying Scale Models. It uses standard GWS gear.
- The Hurricane. This 35” span model is made from sliced pink foam (lighter but more fragile – did you notice? - than Depron) and only weighs 6 oz with standard GWS gear, giving a wing loading of a fraction over 4 oz/sq ft. Broke the rule this time! It flies very well indeed outdoors in calm conditions and a bit too fast for my reflexes indoors!
- The Lancaster. This was really just a bit of fun, grafting the motors from a couple of X-Twin toys onto some Falcon RC gear. And it flies! But it only weighs 2.25 oz and with 0.9 sq ft of wing area has a loading of 2.5 oz/sq ft, so there really is no reason why it shouldn’t. The fuselage and nacelles are 5mm Depron, the wing is 3mm and the tail 2mm. Lots of decoration makes it hard to tell (when you are flying it) that it is just a poshed-up profile model.
- The Auster. I class this as the easiest indoor model I’ve ever built or flown! It weighs just 1.25 oz for Falcon RC gear, with a PU05 motor and one LiPoly cell. The building process can be seen at www.cdmfc.org and look for projects. The wing loading is an amazing 1.3 oz/sq ft. I would recommend this size of model and method of construction to any competent modeller looking for an introduction to indoor flight.
- WWI single-bay biplanes are easy to make from Depron and at 30-32” span can be made to weigh 7 oz with a loading of 3 oz/sq ft. The standard GWS gear described above is perfect. It’s important to use thread bracing on these models to give some strength to the structure.
- The same type of aircraft, but to 24” span, can be flown with Falcon gear, their PU02 motor and a 150 mAh LiPoly 2-cell battery. The hardware weighs 1 oz and a lightly built all-balsa model can fly at 2 oz all-up, with a wing loading of 1.5 oz/sq ft. I have a 3 oz 24” biplane that also flies very well at a slightly higher loading.
- It should now be obvious that despite what I said at the beginning, any aircraft can be made to fly indoors, providing that it is light enough. A 2 oz B17 at 30” span for 4 little motors (or 2 PU05s), a 7 oz Dunne Tailless of 40” span for GWS, a 3 oz 24” Spitfire for Falcon gear – the only limit is in the imagination. I expect that a 35” span B52 for 4 little pusher motors would be fine.
DEPRON OR BALSA?
All I can say is that I’ve had great success with both materials. Depron is very easy to work with and you can accurately predict the overall weight of your model. Decoration is much easier. Traditional balsa structures seem to last longer and may be slightly lighter but are harder to finish really well.
CAN I GET A PLAN?
I can provide plans of lots of suitable models listed here, ,most of them with articles explaining the build and including a set of plain paper markings (transfers extra!). Some of the Sopwith plans have full data sheets. Nearly all the models require moderate building skills, except as shown.