RV-8 on Ice
Thanks for the interesting article with empirical data on ice effects on an RV [“RV-8 on Ice,” July 2018]. One question for Nigel Speedy: How does ice affect a modern AOA indicator? Will the AOA show impending stall at the increased stall speeds with ice, or will stall now occur before the AOA indicates approaching stall?
Nigel Speedy responds: It depends on what you mean by a “modern AOA indicator.” The traditional way of measuring AOA is by physically measuring the angle of a vane, which swivels and aligns with the relative airflow. These AOA vanes look like small delta wings and are typically mounted on the sides of the nose of the aircraft. A “modern” way of measuring AOA commonly used by experimental EFIS manufacturers is to measure differential pitot pressure. This is the type of combined pitot and AOA probe fitted to my RV-8.
The Dynon SkyView system I use requires in-flight calibration where the pilot flies at low AOA (a gentle push over) and high AOA (a stall) that allows the system to determine the minimum and maximum differential pitot pressure for that installation. The Dynon probe comes in heated and unheated models. Mine is heated, and I turn it on in IMC conditions. So if I was to get ice on the wing, the combined pitot/AOA sensor should remain free of ice, and the EFIS should remain blissfully unaware of any ice on the wing and the degradation in lift that it would cause.
I think that the result with real ice would be the same as I had with simulated ice—that is, the pilot would have a low performing wing, but the EFIS and stall warning would think that the wing is in its normal ice-free state. So the stall warning would come on with much less margin to the actual stall or may not come on at all before the wing actually stalls.
With regards to the incident with the Velocity XL that crashed in Georgia earlier this year [“Checkpoints,” July 2018], Vic Syracuse reported that the airplane was totaled. Not so. The airplane is actually repaired and is in the paint shop now. It’s just waiting for the engine to be returned from the engine shop after the tear-down inspection.
—Duane Swing, CEO Velocity Inc
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