Outrigger Aerodynamics

[TomMoorehouse]

I'm trying to get other peoples thoughts on outrigger aerodynamics. I don't want to say too much on my thoughts yet in an attempt to not influence what others might say.....

What i'm trying to understand, or get more knowledge of, is hull lift or downforce. When I look at an eagle sgx I see a hull that attempts to simply be low drag but without much lift or downforce. When I look at a 21 Ninja, 21 Hawk, or my 21 Firefighter I see hulls that are trying to achieve downforce. Then I see a lot of the electric riggers (and maybe roadrunners) that look like they are trying to get aerodynamic lift. The German electric SAW boat almost looks like it is trying to be a WIG (wing in ground effect).

So what makes one method/design better than another? Why was one idea choosen over another?

What are your thoughts?

 

[Ian Inverarity]

Tom,

As we were covering in the SAW electric thread, I think the JAG boat was a deliberate ground effect design. I am guessing this was done for high speed stability, the ground effect would try to maintain a steady height and in this case it would maintain the attitude of the boat at high speed.

I would be interested to see if such aerodynamics would work on a nitro oval racer. I have my doubts. I think the CG/layout of the JAG type design would make launching very hard. And ground effect would be destroyed by waves. But I could be wrong!

I would love to put a rigger hull into a moving ground plane wind tunnel. I am convinced significant gains in high speed stability could be made.

Since downforce always comes with a penalty of drag, I think designing in downforce to counteract excess hydro-dynamic lift is wastefull! Some wind tunnel work may be able to eliminate unwanted aero-lift...

Nitrocrazed racing: Wind tunnel free...

 

[lohring]

Mike Bontoft gave very careful thought to aerodynamics in his origional gas outrigger design. He felt some lift was desirable with heavy engines. I'm not sure this is true though the wide airfoil shape fits over the carb and pipe well. After seeing some very non lifting European electric and nitro designs, I think the reason for rigger's stability is that they are largely non lifting. In fact, wide heat racing style sponsons look like they cause stability problems at around 100 mph.

Both Mike's boat and the streamlined nitro rigger I saw at the last Legg Lake straight line trials would heat race well with suitable turn fins. The narrow sponson design was very stable. Air doesn't get under the front and lift the sponson tips.

Water drag, power, and props are still the main factors. Aerodynamics contribute more to rigger stability problems than speed. In very fast Sport 40 designs the wing effect is critical. These boats now "fly" at rigger speeds. However, it is much harder to design and trim them for stability. Sport 40s are now going 80 mph, but riggers are still faster.

Lohring Miller