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Old Jan 09, 2011, 09:13 AM
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Fairplay, South Park, CO
Joined Sep 2005
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Optimizing the depth & contours of the shallow KF3P discontinuities


I continue to brain-storm on how to build a foamie wing that shows the benefits of implementing stepped discontinuities in the aft 50% of the airfoil's top surface, while minimizing or eliminating the 'drag penalties' associated with deep squared step contours.

On 9-27-2010, I designed the MH32/KF3P airfoil build which uses shallower depth steps and uses a (~flat) panel running from the primary step at 48% of chord back to a shallower secondary stepped discontinuity at 70% to 75% of chord. (The relative positions of these discontinuities are tapered forward towards the wings leading edge as the wing tapers towards the wing tips.)

On 12-24-2010, I drew up the wing structure profile below, changing the contour of the front surface of the stepped discontinuity 'pocket' to a rounded profile which should allow for smoother airflow in the recirculating flow behind that rounded step. Dick Kline converted the structure drawing into the black silhouette, & I then did a bit of modifying from there to have this version show my optimized concept. (I've actually also added an aileron hinge line gap cover on the wing's lower surface to further minimize drag in that area.)

Do these shallow discontinuity structures actually trap a continuous recirculating vortex? Or are they simply very effective turbulating structures which achieve the purpose of minimizing massive boundary layer airflow separations, while also minimizing drag?

With only a ~2mm to 3mm depth to the primary step, and only 2mm max height of the secondary step structure, the recirculating vortexes themselves which are theorized to occur may not be very extensive, chord-wise, yet they may be keeping the airflow behind that shallow structure turbulated and thereby they may be effectively preventing massive airflow (lift) separations.

In the case of the second shallower discontinuity which is located within 1/2" of the aileron hinge line, the shallower depth of this step in this location seems to *improve* the aircraft's response to aileron deflection at all airspeeds... again, possibly by producing a turbulated surface layer airflow that does not easily separate from the aileron's surface. (The thin clean trailing edges of the ailerons also contribute their part to the wing's precise response to aileron deflection.)

I'll be adding these rounded contours to the stepped discontinuities on the 62" MH32/KF3P wing this morning, and hopefully get in some test flying with this wing mounted on the DANCER III sleek EPP fuselage before the next snow storm moves in later today. It's more challenging to evaluate a wing's performance during cold weather with irregular air.... it would be nice to have some good thermal or slope conditions to really do the test flying... But I'll see what I can observe today.

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Last edited by viking60; Jan 09, 2011 at 09:19 AM.
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