I have to replace my windshield anyway (it's starting to crack), so I thought it would be a good opportunity to try cleaning up the airflow a bit over the flat front/sharply rising windshield it had. I made this fiberglass piece, but am a little concerned that the added area ahead of the cg might cause problems with yaw. I think it's less than a cowled 440, but would like some second opinions before I start attaching it
Generally speaking a streamlined and rounded cowl is going to produce less drag than the engine just hanging out in the air no matter what direction you envision drag producing air flow coming from.
I'm afraid I don't have enough room between my ring gear and prop to safely wrap the cowl up to it and around my starter. The starter was creating rolling waves of very turbulent disturbed air that got extremely ugly when they got to the windshield (at least with the engine running an the ground, and a smoke maker in front of the prop). I played around with a lot of different foam plugs trying to make the best of the situation, and this is the result, it splits the air stream coming off the starter, and it stays quite smooth going back (again on the ground with smoke). My concern is more with it delaying recovery from an unintended spin since I'll still have the full exposed engine drag plus another square foot and half of "frontal" area on the wrong side of center in a spin situation, I'm probably over thinking it though.
if you've ever riden a motorcycle up behind a semi on the interstate, that point when it starts to buffet you from side to side, then you get just a bit closer and the air is smooth is what got me thinking. I'm projecting the lead in to the windscreen into the low pressure region of vortex drag behind the starter so it (in theory) is "drafting" from the starter, a stable low pressure region develops between the two parts and as far as the air is concerned they are one. Essentially creating a "fairing" out of the air itself.
It's cut case 45hp Hummel later refitted with a starter. 96 bore, 86 mm stroke, aluminum cylinders, Single mag ignition, zenith carb. Spinning a Tennessee 54 22 prop (4 3/4" wide). Put the bird on the scale today with crankcase full and pint or so of gas, small bag of tools on board, and a lot of axle grease etc that could be removed, it weighed 259lbs. Clean and empty it can make weight for UL, but JUST barely. That is with rib stitching, "light" tail, 2.9 oz cloth on the bottom, 1.6oz cloth everywhere else (finished in full polyfiber process with good poly spray layer on top, light poly spray on bottom). I'm in the process of reviving it, (previous owner deceased), after 1100 flight hours, and being 23 years old it had some condition issues (now resolved) so have not been able to get hard numbers on climb rate. I was concerned about the vw reputation for this and as the previous owner was very active in the local EAA chapter, I have talked to a good number of people who know this plane. Every one of them have stated that power and climb are more than adequate. I will be able to give solid data when the soybeans are out of the field and I can roll it for a grass strip
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