Wind dam on cats

[CraigP]

Formula 1 would still be in Jimmy Clarke style cars without the innovation of the aerodynamic engineer. I don’t let it bother me. I get my kicks out of the design, application and runtime evaluation which justifies the effort. The Cat hull is especially difficult, given the narrowness between the sponson tips that exists on many of the hulls. The effectiveness of the wing I applied to my cat was disappointing. I need to start with more cross section and place more discrimination between the upper and lower surfaces, in effect, make more of an old style DC-3 type wing. But the hydro wings work great! I have a couple of hydros known for getting too much air under them, and the wings corrected that problem very well...

[Krazykenny]

You are to be congratulated for your efforts Craig, heed not the whining of the doubting Thomases in life. I include myself as one who Can be resistant to new ideas,but realise without experiment there is no progression, doubtless automative engineers and aroedynamics technicians in the past experienced similar resustance (not just from the wind either) tontheir using spoilers on performance cars, yet look how far they have come and how well established they are now.

[CraigP]

Kenny, I design and construct reverse-lift, air diverting wings to put on the front of my hydros. These wings become more reactive as the angle of bow lift increases, created more down force and diverting this air stream up and over the top of the boat, instead of letting it flow under the boat. When I introduced it, it was ridiculed as bogus science. The dam under the boat will create non-laminar or buffet effects and gets less reactive as the bow lifts. The wings I design get up to 3.5lbs of down force. If you need more, then the cross section must be re-designed.

I think each guy should do their own science and just keep it on the down low. I don’t race and as such, I get a poor response to things I’ve done. But it is very exciting to see the wing in action, literally “flying” the boat gracefully back to the water surface! But I think you’re dead on. BTW, the math isn’t too bad, just takes iterations to get it just so...

[Krazykenny]

I would think that the faster model catamarans get, the more some RESEARCH into conduicive aerodynamics is gonna be required, what WOULD be advantageous is motivated minds with a fascination for aerodynamics, getting involved and possibly employed in hobbycraft design. Its got to be the way forward.

[dmitry100]

have any of you guys tried this on HPR type cats?

[tlandauer]

This was an old hull I bought and I trued the sponsons and kelp increasing the speed until I needed an air dam between the sponsons, it worked well for me.

https://www.youtube.com/watch?v=MJpmOgda8lE

https://www.youtube.com/watch?v=0EPjgmYRbZM

[rol243]

Its quite common for sport hydros to have this type of air dam built into the hull.

[Shooter]

It's all about balance. The air pressure below the hull is dependent on speed. Larry's comment was spot on. The faster you go, the more air you start packing (pressure under boat increases). Eventually, you reach a pressure that blows it off. You can compensate by moving the cg fwd, but then you start affecting turning performance (obviously not a big deal if you are just running saw). A lot of guys have had success either bleeding air off with air bleeds or running an air dam.

[peteatthebeach]

Thanks. I try that next week on hopefully its maiden voyage.


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[kfxguy]

Thanks for the reply. It looks like you’ve taped or fiberglassed the pipe in place?

Well there’s tape in that pic and it’s glued to the tape, for experimental reasons. But I did remove the tape and mounted it permanently.

[peteatthebeach]

Thanks for the reply. It looks like you’ve taped or fiberglassed the pipe in place?

[kfxguy]

I’m just getting back into RC boats and I’m new to fast cats and electrics. Does the tube in the picture disrupt the air enough to act as an air dam? Or am I missing something.


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I guess it does. That little 32” cat does 102-103 and hasn’t flipped yet.

[martin]

That's exactly what the tube is for.

[peteatthebeach]

I’m just getting back into RC boats and I’m new to fast cats and electrics. Does the tube in the picture disrupt the air enough to act as an air dam? Or am I missing something.


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[kfxguy]

I use them on my fast cats. It does help. I use a piece of carbon fiber tube