Monday, January 20, 2020

Probe position is not responsible for IAS problem

Continuing our experimentation, I decided to mount the probe on the end of a 3/4" fiberglass pole securely fastened to the struts of N291DR. Here are a few pictures of the mounting:

The result is that, while our AoA numbers near stall decreased (expected since the probe is relatively free from upwash effects), our IAS readings remained consistent. This is a graph of the results:

Note that, at low IAS, we report numbers higher than the N291DR instrument. This is to be expected. We are compensating for AoA and yaw angle, whereas N291DR's instrument is just a simple tube sticking out into the wind. At high angles, N291DR's instrument will read low.

The mystery continues. The next thing is to do a proper calibration using a quadrangle course with ground speeds and record the results. At this point we're just knocking hypotheses off the list, and some may argue we should have done that before doing the probe on the long pole experiment, but this yielded interesting results in and of itself. It taught us that, while the AoA values change, the IAS numbers remain pretty consistent regardless of where we stick our probe.

We did capture a video of the approach to a stall, which you might find interesting. Check it out here.

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