Tuesday, September 25, 2007

Top Tips for Free Flight model making

Free Flight Aeromodelling is not new by any stretch of the imagination. One of the most celebrated models of the 19th Century was this rubber power job by the amazing Alphonse Penaud called the Planophore or Planaphore, c.a. 1871:
All the modern aspects are there. This was about 20 years before Otto Lilienthal's daring gliding exploits and those of Percy Pilcher. Both aviators died as a result of plane crashes. The Wright brothers began to solve the control problems in the first few years of the 20th Century.

With so much development over a great deal of time, you'd think we may have learned something by now!

Here are five things that may help you to improve your free flight aeromodelling skills:

1. Build light. This means that within the relevant rules, the model should be as light weight as possible. If a model is built so tough that it is crash resistant it will be too heavy to perform really well. Generally glue is heavy. Choose materials wisely. Balsa is amazing in terms of the strength to weight ratio, but there is a great variation between planks as well. I had a balsa board that was as dense as spruce. I've not been able to utilise it in a model plane.

2. Stability is really important. It's no use having the flattest glide ever, if the plane spiral dives to earth whenever it hits a bit of turbulence. Learn about stability. Try to adjust or re-design planes that are not stable.

3. Learn to "pick good air". Get a mylar streamer or a 10 ft piece of old audio tape and attach it to the top of a tall pole. Stand it upwind of your launch point. Watch it carefully and work out what it does as the air changes. It will move around to show the wind strength and direction. Importantly, you may be able to feel cool air when the streamer points downwards and warm air when it points upwards. Thermals are often marked by a rise in temperature, a drop in the wind strength and a change in wind direction. It takes a lot of practice to learn to launch your model into lift.

4. Do try to minimise drag of the plane. However do not increase weight to do so. Putting it simply, at low flying speeds, one type of drag dominates while at high speeds, another type of drag is more important. The low speed one is due to the disturbance created by the model, mainly the wing and is called induced drag or vortex drag. The high speed one is to do with the form or profile of the plane, and its skin friction. Read up on drag and design accordingly.

5. Keep excellent records, notes, plans and sketches. For example, your model's flying weights and "still air" times (taken for flights in the early morning or late evening on calm days) are invaluable resources later. Design ideas can come out of the blue, so it may be a good idea to have a pocket book to jot them down in.

To close this post, here is a photo and some info about a century old, patented, rubber powered canard, by T.W.K Clarke that I snapped from the London Science Museum. I guess it was around 50 inches in wing span. Those years would have been exciting times for aeroplane lovers...

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