Wing Asymmetry

Racing models are all asymmetric in some way. The lines go out one wing, the elevator may be only on one side, and there may be weight added to one tip. There is, however, an argument for even greater asymmetry. Provided the takeoff and landing qualities are not degraded so much as to present a risk, moving the wing in toward the handle has a significant drag advantage. In the example case below a reduction of about 0.32 cm^2 drag area, close to a 1% improvement in aircraft race performance (e.g. flying time for 100 laps).

In order to estimate the change in drag a computer program has been written. It can be developed further to provide answers with a better representation of the wing platform and so-on, however the approximate results even at this stage are of sufficient interest to show.

The wing aerodynamics are modeled after those of a 6% thick symmetrical section. Because the angle of attack and lift coefficient in level flight are very low the only variation modeled is the drag coefficient with Reynolds number. See the chart hyperlinked above as "Drag Data".

The variation in airspeed across the span is accounted for, and the 'system' considered is the drag of the wing plus lines from the outboard wing tip to 1 meter inboard of the thrust line. Thus if the inboard wing span is 400 mm there are 600 mm of the tether lines included in the drag. 50 mm of the center of the wing is excluded.

The first results are for a simple wing planform that has a chord at the 'centerline', a distance to the outboard tip, an outboard tip chord, distance to the inboard tip, an inboard tip chord. A more realistic planform is one potential refinement.

Comparison of two wings

characteristic

Value

Outboard wingspan

300 mm

Outboard tip chord

100 mm

Inboard wingspan

400 mm

Inboard tip chord

100 mm

Root chord

250 mm

Exposed wing drag area

5.497 - cm^2

Exposed lines drag area

3.298 - cm^2

Drag area sum

8.786 - cm^2