Re: [FootyUSA] Re: ideal footy displacement
- One thing we often forget to do is realize that the physics don't scale down 1:1 when you get as small as the footy. Things like Reynolds numbers work differently when you get as small as footys are. That said I like this type of work and I think it benefits our class a lot. Build one and see what imperical data you can get to add to your theory. Who knows, you could be on the cutting edge!Allan----- Original Message -----From: mudhenk27Sent: Monday, September 28, 2009 7:37 AMSubject: [FootyUSA] Re: ideal footy displacement
Your analysis is
LR, that's a good analysis. I hope you'll build one and keep us informed. I think you might find that a boat that light could have some trouble in choppy conditions.. .you can't scale down the wave factor. I could be wrong, though, since the lightest boat I have is 340 grams.
--- In FootyUSA@yahoogroup s.com, "LR" <lincolnr@.. .> wrote:
> For further comparison, a full scale Soling is probably around 140. I think the one meter model is around 165.
> --- In FootyUSA@yahoogroup s.com, "LR" <lincolnr@> wrote:
> > I may be missing something, but it seems to me that footies as they exist are very heavy. If I understand correctly, the battery restriction is now gone, so it ought to be possible, with care, to build a very light footie. There is a ratio generally called the DL ratio, even though D/Lcubed would be more accurate. There's a neat calculator here:
> > http://www.sailingu sa.info/cal_ _dl_ratio. htm
> > Seems like most footies are close to a pound, or even heavier. One of the neat properties is that, for a footy with a one foot waterline, this ratio is very close to the weight in grams. So a typical footy might be 450. Now, we'd like fast boats, right? A J24 is around 180. A light US1M might be around 130 or so, although I guess some heavier boats are somewhat competitive at 150 or higher. To get a footy in that range you need to get it less than a third the displacement of a typical footy.
> > I think this could be done if you used one of the new 2.4 gHz radios from an indoor flyer, and maybe an HS-55 (!) for the sheet, while using the built in linear servo for steering. It would be radically different, but I bet it could sail a LOT faster in many conditions.
> > Maybe it would be worth it to go even lighter. I dunno.
> > This probably wouldn't require any exotic materials, just thinking and care. At one foot I think the weight is probably going to be determined often by the lightest gauge materials available, rather than strength or even stiffness. (Ok, this is intuition as I haven't built one yet.) And those indoor planes are pretty cheap. The receiver is only $60 by itself, or you can get the whole thing with tx for $120 if you don't mind throwing the plane away. If you're really sneaky use the motor to make a hidden auxiliary, but don't tell anyone.
- I have upgraded from the futaba 3115 to the futaba 3102 as well. metal gears enough torque...it is also the rudder servo for my footy, s1m, victoria, and odom. and I run a 2 cell lipo with no regulator with no burnouts yet...
I run a sloop rig