AOA Pitot Head Location

[cskelt]

I'm retrofitting a heated AOA pitot to replace a standard AN5812 on a Lancair 320. The designer's original location for the pitot head is just aft of the  wing leading edge, so with the extra 2 1/4 inches length of the Dynon unit, the AOA pitot head would be about an inch forward of the leading edge. The Dynon installation instructions recommend that the pitot head be 2 to 12 inches aft of the wing leading edge which would turn a simple replacement task into major surgery.

I'm curious as to the reason for this recommendation, and if I were to use the original AN5812 mounting, should I still expect a functioning AOA indication and pitot?

I'm sure I'm not the first one to do this retrofit, and the forward location of the pitot head is common on many GA aircraft.

Thanks in advance for your comments, and experiences.

Regards, Chris.

 

[dynonsupport]

The recommendations are based on the typical pressure fields around a typical wing, and represent where we'd expect there to be both good pitot and AOA performance. The general requirement there, by the way, is that the air look like free stream air. For example, if the pitot snout is too close to the wing surface, you can get into the boundary layer flow, where the flow is more attached to the wing and AOA may not be as sensable (since the air travels in the same direction), and the pitot may become less reliable (since air near the surface of the wing maybe faster or slower than the surrounding airmass).

But, those are just guidelines. I'd do the easiest drop-in install first, do an AOA calibration, and see how it goes. You'll probably be okay.