Joe Nunley said, > " . . . and put holes in your belly board. ;)
We've talked about this subject some years back . . . it'll all be in those great archive resource we have. In my experience and in looking into the subject, the main plane we think of as having holes in their dive brakes was the SBD Dauntless. I think the Stuka had them too. My KR came with holes in the belly board so back when I first got it (ten years ago this July!) I was wondering if I could get better drag from it if I covered up the holes. So as an experiment, I did. I covered the board with duct tape thus creating a flat surface. Having the holes covered made a very, very slight improvement in the drag effectiveness of my belly board. It also did a better job of creating a bit of lift, thus reducing stalling speed. The difference was very slight. In researching the reason the Dauntless and other dive bombers had perforated flaps, I found out they did that for two reasons. One was reducing weight but the main reason was that having perforated flaps instead of solid flaps made the aircraft much more controllable in a high speed dive. The solid flaps created so much turbulance over the tail section that the aircraft was practically uncontrollable in a dive. Perforating the flaps disturbed the airflow sufficiently that the buffeting was either eliminated or mitigated enough that the aircraft was controllable. So those were the reason the Dauntless, and perhaps the Stuka, and whatever other aircraft of that era, had perforated flaps. The holes weren't introduced to increase drag. My duct tape covering my drag flap holes didn't hold up very well so when it got so ragged that the holes were no longer covered I removed the remaining duct tape and have flown the belly board with the holes ever since. It "seemed" my belly board gave me more drag and more lift when it was covered. Very subjective. With a hole saw I could have cut circles of correct thickness to fill the holes, but the difference between holes or no holes was so slight I just left it alone. For drag flap effectiveness the best thing to do is make it large and make it so it goes down at as much of an angle as ground clearance will allow. After flying Jim Morehead's KR with such a bellyboard I was extremely impressed at how much easier it was to slow down and to land at a higher angle of attack (his is a tri-gear which helps tremendously with that aspect of things. KR taildraggers hit the tail first when trying to touch down at full stall.) Jim's bellyboard had no holes. Just a big flat surface that came down at about a 70? and boy did it work great. Langford has mentioned that his belly board slightly reduces his stall speed when deployed. Bellyboards, being a type of flap, add a bit of lift. I've found this observation of Mark's to be true with my plane - moreso when my holes were covered. In my case, my flap only comes down about 30? so whatever additional drag and lift I get is pretty insignificant - but I always use it anyway since every little bit helps when trying to get these slick little things slowed down. Mine doesn't do all that much, holes or no holes, since my KR-1? is narrower than normal KR-2 bellyboards and it also doesn't come down at a steep enough angle (due to ground clearance) to really dig into the slipstream. They can be a great help though when done well, as in Morehead's plane. Mike KSEE ____________________________________________________________ Wall Street Daily Peter Schiff: China Just Armed its Financial Missile http://thirdpartyoffers.juno.com/TGL3141/570553a489b3e53a40e41st02vuc
