dreamer

from nasa

aerodynamics

The science that deals with the motion of air and other gaseous fluids and the forces acting on objects as a result of the relative motion between the air and the object

Gary Anderson

While we're on the subject. I've always wondered why cat makers have not added an adjustable wing between the front of the sponsons. With speeds in excess of 100mph, it would seem to be an effective way to control trim.
Anyone know of any attempts at this?
Gary

dreamer

some use a tunnel tab at the rear

BROWNIE

Formula, Betty Cook and John Connor built a pretty advanced composite 38' cat in the 80's. It had a had a non-slotted nose flap that extended down and forward like a dc9. Didn't work. On a dc9, it modifies the wing shape, makes it larger and gives more lift and drag. On the boat, it only stopped up the tunnel and slowed it down.

GregP

Yep. A friend did some design consulting for the unlimited hydro boys on adjustable front wings between the sponsons to kill the lift at take-off and try to help prevent blow overs. I don't remember which team. Trick I think was no one could dedicate enough attention to how the boat was flying to be able to kick the wing fast enough if it started to get away.

-Greg

Sean H

you would spend all your time trying to adjust the angle of attack on that wing and unable to throttle or drive, the main problem with adj wings on boats is that boats never have the same attitude... they are always pitching and rolling, just like a tunnel tab that is used incorrectly, a front wing like that could be deadly in a high speed cat...

GregP

The water surface for a cat acts just like the ground on formula cars, and creates a much different set of aero than a wing in nice free space on an airplane (it's also a much more complicated analytic model). Rolling tires are even harder to model correctly.

The height/spacing is very critical, on formula cars a 1/4" or less change makes a big difference. On a cat running height over the waves is continuously varying, making it nearly impossible to optimize as a single solution. In "very" general terms the height of the gap as a function of the wing/tunnel length as a % is what drives the effects, so on a 40' cat the senestivity is less, but still a few inches matters.

-Greg

wcmarine

Randy Scism built a victoryTeam cat in the early nineties, with a big stabilizer wing on the back and also an adjustable front tunnel flap. I can't seem to find photos of it.
They called it the bat boat. was weird looking, but fast.
It had a huge wreck with Polli and Curtis, who were in the BILBOA boat, I think it was in St. Tropez.

GregP

Wings produce lift (more accurately a normal force) and drag (axial force). If the camber/angle-of-attack is "up" it make lift ala an airpalne. If it is down it creates downforce ala race cars. If you put it vertically it creates side force (like in direct sideforce generators for advanced fighter aircraft). It's the same wing, same physics. Just point the force the direction that you want it.

Oh, and if you rotate it "just right" it produces thrust for a propeller or lift again for a helicopter rotor.

"Streamlining" is the coloqial term for minimumizing drag or disturbance to the airflow. Now days it's just called drag reduction.

I won't get into boundary layers and viscous -vs- induced drag as it's time for lunch.

-Greg

dreamer

http://www.grc.nasa.gov/WWW/K-12/Foi...l/fsim001m.htm