If you really want to reduce induced drag, the tip shape is not the place to look.
I have to disagree. You want the maximum span of the wing at the trailing edge.
In a Q-500 pylon race the wing is at 90 degrees in turn one and 45 degrees the rest of the time. Only time straight is on take off. Race has 30 turns and 20 straight of 600 feet. Ten laps is 2 1/2 miles
I just not going to agree with any of this either. All the tight turns (making the turn at 2/3 as one turn) approach 90 degrees if one maintains altitude through the turn.
The so called "straight flight" which ties together the turns at both ends is also a turn (at a 45 degree bank) where the airplane would be doing roughly 1.4g to hold altitude. Since a 45 degree bank results in a turn with a radius of about 1950 at 170 mph. Depending on turn radius at pylon 1, the "straights" distance is only about 530 feet. However the bank of 45 degrees results in too short of distance by about 50 feet. So the bank needs to be slightly less (assuming calm conditions), about 42 degrees. On windy days (wind from pylon one) the bank from turn three to one is even less, while from one to two is greater due to variations in ground speed.
OK, nobody can fly that course perfectly and the difference in bank of a few degrees is very minor. But the reason you want to fly a course with 39 turns is that you can lower the amount of time spent in the high g turns at Pylon 1 and Pylons 2/3 by about 8%, which results in faster overall times.