Building and Finishing
23rd March 2014
A tip for film covering from John Corkill
Here's a tip for Solarfilm (or similar) covering. It's not specifically mentioned in the website instructions for these covering materials but is essential to ensure a model flies accurately and predictably.
When you iron on Solarfilm, or similar, to your wing, do you firstly attach it securely round the edges, then pass the heatgun over the panel until the covering is smooth and taut. Now ask yourself the question, are you attaching the covering to the model, or the model to the covering? Sounds like a strange question, but consider ...
When a plane is flying, most of the lift comes from the reduced air pressure on the wing upper surface. So the airflow is actually lifting only the top covering, and the wing and all the rest of the plane is simply hanging on as well as it can, in many cases by only a thin band of adhesive around the edges of the wing.
If the covering is not secured to all the ribs, it will lift unpredictably due to the reduced air pressure above it, forming its own random aerofoil shape which will vary with flying conditions. Not only will the aerofoil efficiency be reduced but the effect is quite likely to be different from one wing to the other, with obvious results.
The answer is always to ensure that all covering is tightened and rubbed down when hot onto all the sheeting and ribs, both on the wing top and underside (especially on aerobatic models). If you are concerned about marking the covering if using an iron rather than a gun, use a sheet of tissue under the iron.