Gweduck, evaluation of vertical tail airflow

Martin Seamaster through to the Canadair CL-215 & 415 and the Shinmaiwa US-1.

Gweduck, evaluation of vertical tail airflow

Postby Gweduck » Sun Apr 24, 2011 8:51 pm

Thought someone might be interested in some tests we just finished with vortex generators on the Gweduck's vertical tail. This project was done in cooperation with four engineering seniors at Washington State University, who needed a real world engineering project as part of their graduation requirements. We had identified a small null zone in the Gweduck's directional response to the rudder, that was a bit like riding a bike with 2 degrees of slop in the handle bars. The students laid out different configurations of vortex generator patterns which we flight tested, monitoring air flow by injecting liquid into the air stream just like the big guys (Boeing) do. The configuration shown in the below linked video met the goals of their project work statement, as well as substantially increasing the effectiveness of the trim tab. The trim tab, owing to its position in the wake of the elevator spar, had been very sluggish in biasing the rudder one way or the other.

http://www.youtube.com/watch?v=HHvA3XSQ9gI
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Re: Gweduck, evaluation of vertical tail airflow

Postby skimmerone » Sun Apr 24, 2011 9:02 pm

Very interesting. Skimmer One when first born had a huge fat pylon about 10 inches wide which blanked out the rudder. They claimed that every once in a while it would turn for no reason at all. They tried several ways to fix it, but the solution was to make the pylon narrower. Todays Lakes are very sensitive to any air disturbance like flapping gasket material or the holes to access the horizontal mounting bolts.
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Re: Gweduck, evaluation of vertical tail airflow

Postby Gweduck » Mon Apr 25, 2011 1:29 pm

Skimmerone,

We had a similar experience early on in Gweduck flight testing. There seemed to be a constant but subtitle buffet during cruise flight, that defied all efforts to identify. Finally a retired Boeing aerodynamics specialist stopped by for a visit and pointed to a small ski jump at the end of the cowl flap which was located on the top of each engine nacelle, as a possible cause. Five minutes with a pair of tin snips, and the buffet was gone.
.................... Ben
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