Originally Posted by N941WR
Yes Dan, but... if the cut only slants forward an inch, what is the speed loss? 2 knots, maybe 3? Well worth the tradeoff, if all else fails. Also, IL looks better than adding louvers or a lip and simpler than adding a cowl flap.
Bill R. asked an interesting question. Although it's hard to precisely quantify in terms of speed loss, it can be quantified in terms of exit area increase. Knowing how much you actually opened the exit is important, because it offers some realistic expectation about additional cooling.
For five angles of cut (see the diagram below) the multiples of original exit area are:
10 deg 1.0154
20 deg 1.0642
30 deg 1.1547
40 deg 1.3054
45 deg 1.4142
What this little trig exercise tells us is that you'll need some significant cut angle to actually increase area very much. For example, assume the existing RV-6 cowl exit is 6" high (I'm guessing, don't have one handy). Cutting it back 1" would be a cut angle a fuzz less than 10 degrees, so the area multiplier would be 1.0154, or only about 1.5% larger than stock...which would not make any
measurable difference in speed or cooling.
IF you elect to cut the exit for more area, you'll probably want to choose 30, 40, or 45 degree cuts. For an exit originally 6" high, those angles would mean cutting forward roughly 3.5", 5", or 6", for an area increase of 15%, 30%, or 41% respectively.