This study investigates the effect on the principal aerodynamic forces caused by home-built under-wing attachments excluding possible consequences on the aircraft’s control and manoeuvrability. Many other types of wing attachment have already been used and investigated of time. However, none of these attachments match exactly the attachment under investigation in this study.
For aerial display purposes, one of the team members of the Whiskey Formation Team created an under-wing firework launch platform attached to the tie-down points of the aircraft. These tie-down points are fixed to the quarter chord wing spar at about 90% of the half wing span near the wingtip. The launch platforms themselves protrude about a quarter of their own length in front of the wing’s leading edge. The remaining part is attached flush with the wing’s lower skin.
After installing the attachments on the aircraft’s wing, the creator took it upon himself to do some trial high speed taxi runs followed by a standard take-off. A circuit around the field and a full stop landing completed his trial run during which no adverse effects on the aircraft handling or flight safety could be detected.
Next, on the first trial flight as a formation with the launch platforms attached, the team leader claimed he experienced a slight performance increase. Earlier lift-off and sharper turns were among the examples of this performance increase he gave. No claims on the aircraft’s fuel consumption, cruising speed or power-off gliding performance were made. This was not investigated and is deemed not to be relevant to the aerial display.
This report investigates these claims by modelling the aircraft for computational flow simulations, with and without the platforms attached, for both take-off and high G-load turns. For the take-off condition a runway surface is modelled at a wheels-height distance from the aircraft’s wing. Realistic speeds of 50 and 60 knots respectively are chosen together with 10 degrees of geometrical pitch.
The result of these simulations was then validated in real life circumstances to eliminate possible adverse results due to modelling error of the real life aircraft. A number of comparative test flights, 5 in total with 6 take-offs per flight, were performed registering weight and take-off speed for a trimmed stick-free configuration. The results obtained from these test flights are likely to confirm the results obtained from the simulations. For the simulations, a larger lift and lower drag force are noted for the configuration with the launch platform attached for The steep turn case. For the take-off case a drag increase was noted. In the real life test this could be confirmed by the almost identical take-off velocities even though this falls well within the error margin of the experimental setup. The gain in lift, most pronounced for the steep turn case, comes from the blocking of the spanwise flow by the launch platforms hereby likely reducing the lift-induced drag caused by the wing tip vortex. The total drag of the modelled wing is reduced for the steep turn case even though the launch platforms contribute to the friction drag. Moreover, the model’s lift-to-drag ratio, a common measure of aircraft’s performance, is increased.
It can therefore be concluded that for the investigated cases indeed a small effect of the launch platforms on the aircraft’s performance can be found though it is deemed unlikely that this difference is be noticeable. Real life tests only show little promise since the error margin occludes the effects on performance. For flight display purposes a different meaning of the word ’performance’ is meant. The lift force is considered much more important than the drag force, even though the drag force is reduced too. Therefore it can be concluded that the installation of the launch platforms does not adversely affect the aircraft’s performance parameters such as lift and drag. Moreover, it is plausible that they do improve the aircraft’s performance parameters and do improve the performance of the aircraft for aerial display purposes.