To illustrate the type of results that can be captured during a wind tunnel campaign, we next give a series of results for the Decode-1 airframe as measured in the Mitchell tunnel. In all cases, averaging has been applied to the raw results where possible but some slight variations from the expected trends are noted at some points in the plots.
Figure 16.5 shows the effect of flight speed (Reynold’s number (Re)) on the aerodynamic
coefficients when the control surfaces are in the neutral position. Several comments can be
- • The lift force is not affected by Re, only the stall, as would be expected, while stall occurs at higher AoA for higher Re, (some data for higher speeds are not available, because the loads and vibrations were too high to carry on the experiments safely).
- • The side force is generally low, and arises only because of slight manufacturing asymmetry, except during the onset of stall which occurs on one wing slightly before the other.
- • The pitch moment decreases with the AoA, because the lift on the elevator increases, but this effect seems to be evident mainly at low Re, when the wing wake has less affect on the tail.
- • The roll moment is generally almost zero, except during the onset of stall as for the side force.
- • The slight aircraft asymmetry, particularly at low Re, generates small yaw coefficients.