>. they did it because the airflow over the tail >was so disturbed by just straight dive brakes without holes that the >plane was hard to stabilize in the dive so they could aim their >torpedoes. >Another reason holes are drilled in belly boards and wing-mounted speed >brakes is to lighten them. > >So I'll continue to keep my holes covered. > >Mike > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I read the test conclusions (copied below ) to say: At a deflection angle of greater than 50 degrees, uniform holes in the flat plate that cover 40 percent of the flat plate area can reduce buffeting by 66 percent while reducing drag by only 20 percent. They go on to suggest that the best arrangement is to have holes that amount to 25 percent of the board area and confine them to the central area of the board. This yields similar reduction in buffeting while creating a bit more drag. This would indicate that holes in the board, of correct size and spacing, are advantageous. My board, http://mysite.verizon.net/flesner/19.jpg , with holes deflects to near 90 degrees and works very well. I think I'll keep my holes. Larry Flesner ++++++===================++++++++=============+++++++++++============= For the isolated square plates tested, uniform perforations give substantial reductions in the level of velocity fluctuations, at the expense of comparatively small reductions in drag coefficient. The reductions in fluctuations are more marked at the low-frequency end of the spectrum, this being the more important range of frequencies from the point of view of buffeting in the wake when using these plates as air brakes. A free area ratio of 0.40 (with uniform perforations) gives a reduction in the low-frequency component of velocity fluctuations to about one-third of that for an un perforated plate, with a loss in drag coefficient of less than 2qi. It is suggested that this value of 0.40 should be a minimum for design purposes. With free area ratios larger than 0.40, the gain in fluctuation level becomes less but the loss in drag greater. A somewhat better arrangement is to perforate only the central portion, leaving an unperforated rim. In the arrangement tested, such a plate with a free area ratio of 0.25 gave as low velocity fluctuations as a uniformly perforated plate with a ratio 0.40, with higher drag coefficient. Perforating near the edges only is less effective than uniform perforations from the point of view of both drag and velocity fluctuations. A single test to determine the effect of size of individual holes gave negligible scale effect. -
