Design > Stunt design
Another odd question - Forward sept wing trailing edge and flap hinge line
Bill Schluckbier:
Hello,
I have another odd question regarding flaps. I have been reading Bob Hunt's Genesis book (highly recommended) and in it he mentioned that Bill Werwage's Juno with had the wing trailing edges swept forward significantly and that it seemed to handle the wind well. In the build article for the Juno it was mentioned that sweeping the trailing edge forward allowed to keep the wing's center of pressure (CP) roughly in the same location for the wing as a whole as the flaps moved up and down. Seemed like an interesting idea and explanation. I also noticed that Bill's follow on designs used a straight wing trailing edge so maybe there is my answer....
I understand that a straight trailing edge makes building the models simpler without the need for lucky boxes or separate horns for the flaps. Would sweeping the flap hinge line forward provide an aerodynamic benefit? In the real world, most airplanes with tapered wings sweep both the leading and trailing edges. Any insight?
Thank you,
Bill
Dave_Trible:
I don't know of anyone really testing this in a meaningful way for stunt airplanes. I have not used it as a design feature on any of my own designs but I have a couple classic airplanes that fly extremely well and have a small amount of forward sweep in the flap hinge line. I've read where some thought it created trim issues. Again I've not seen that. These I have are only about 3/4" forward sweep at the tips and don't require lucky boxes or separate horns. There is enough 'give' in everything that they work fine in the limited range they have to travel-maybe 35-40 degrees each way. I would think the 'tiny' benefit they might have is that the airflow boundary layer is ever rolling outwards towards the tips and facing the flaps more into that airflow could in theory add some lift though it would seem imperceptible . I'd think the reason most have done it is for cosmetic reasons, being able to taper the wing planform a little more that you can do with a straight trailing edge.
Dave
doug coursey:
https://youtu.be/xjjqtSO8Tds?si=kUW1b4knLzCaFkAh
JUST WATCHED THIS WINDY VIDEO ON HIS LAST SPITFIRE WHICH HAD FOWARD SWEPT TRAILING EDGE AND SAID IT WAS THE EASIEST TO FLY OF HIS SPITFIRES
Bill Schluckbier:
Thank you Dave and Doug for your replies; I will definitely watch the video. I have seen many of Windy's videos but somehow I missed this one.
Thank you,
Bill
Brett Buck:
I think the swept-forward hinge line is probably a mistake, if nothing else, I think it makes it much more prone to yaw instability with the controls deflected.
Brett
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