Posted: August 4th, 2013, 3:22 pm
Science Olympiad Student Center
This has come up in the past. This is not official, but I do not see a clear statement in the rules that would prohibit an air screw.Olympian_Cau2134 wrote:Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around
I don't know if it would help, but I was going to make a prototypechalker7 wrote:This has come up in the past. This is not official, but I do not see a clear statement in the rules that would prohibit an air screw.Olympian_Cau2134 wrote:Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around
More importantly, why do you want to make an air screw? If you look at all modern helicopters and vertical take-off aircraft, they follow very similar design strategies.
Hmmm...,coppersquirrel wrote:I'm new at ordering materials for science olympiad events and I've noticed that some in the past (on this forum) have recommended Roy White as a source for mylar for helicopters/egg drop in prev. years. Does anyone by any chance have his contact email/phone? I've had no luck trying to locate him on google data search. Thanks so much.
Start with usual comments about not offcial, this isn't a clarification, just one guys opinion, etc...Olympian_Cau2134 wrote:Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around
I asked someone in my science group, and he said it would be terrible toojander14indoor wrote:Start with usual comments about not offcial, this isn't a clarification, just one guys opinion, etc...
I assume you are doing this as a way to get the single blade bonus. As I read the rules, there are no restrictions on Chord (not what I recommended, but that's why I preface my messages about not official, my suggestions aren't always followed, nor should they be) so a diVinci airscrew should be legal.
BUT, as chalker7 said, there is a good reason you don't see daVinci air screws in real life. While propellors are often called airscrews that is REALLY misleading. The whole screw concept falls apart when you take it out of a solid. Propellors and rotors don't work like a screw at ALL in fluids. They act like a wing flying in a really tight circle. All validated models, theory, analysis, etc are based on that, NOT a screw.
Now, why do chalker7 and I suspect a daVinci screw won't work well. Take that screw surface and unwrap it from the axis. It becomes a very long, not very broad surface. Something called VERY low aspect ratio. This is a VERY bad thing in theory and practice for a lifting surface in a fluid. Their is a reason the wings on a man-rated glider are VERY long and skinny (high aspect ratio), this turns out to be the shape needed for an efficient wing. See, what happens on all real wings is that nice theoretical straight air flow isn't, straight that is. Some of the airflow spills over the tips of the wing and reduces the available lift. A wing with LONG tips in relation to their width (span) spills a LOT of air, those with short tips vs width (span) spill relatively less air. The wing that spills less air is more efficient. And an efficient airfoil is much of the game in these endurance events (the rest is LOW WEIGHT).
So, what happens with a daVinci screw? Instead of the air being driven down, creating a reaction force upwards called lift, most of it spills outward in all directions creating little net force.
Now, feel free to prove me wrong, science wouldn't advance otherwise. But you should understand where you are starting from when you set out to prove conventional wisdom wrong.