80 MPH 21 hydro

[lohring]

Our gas sport hydro is very similar to our gas rigger except that it has a front wing rather than sponson tubes. It required a reduction in lift to allow the boat to go faster. The 12 pound boat blew off easily at 75 mph. It now runs nearly as fast as the rigger with the same engine and propeller. Many experiments on flying the rigger resulted in finally blowing it off without increasing the speed. It surprised me at how insensitive the speed of the boats were to aerodynamic changes as long as the boats were stable. The sport hydro was somewhat sensitive to hull angle of attack changes, but the rigger is completely insensitive. We ran the rigger (it has an airfoil shaped tub) at around 3 degrees positive angle of attack with no difference from a zero degree angle of attack.

Lohring Miller

 

[Bob Howard]

Maybe the addition of airfoils to the boom tubes could be done so they self center in the air flow, using heatshrink or something that would let them rotate on the shaft a little.
Would that keep them flat in the air flow when the attitude of the hull changes?

MikeP

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This is how they do the airfoil over the schocks on a full size Piper Cub

Bob

 

[MikeP]

What causes flutter?

MikeP

 

[Grimracer]

What causes flutter?

MikeP

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Mike its an air imballance of some type but i dont know what causes it..

However i know what fixes it.. A blunt trailing edge...Hummmmm J

Mike Z

 

[Preston_Hall]

OK, nobody said it, I don't think. But why have two boom tubes? Make a single, aero-shaped between the tub and sponson, large enough to get results similar to those previously posted, mount it at the rear of the sponson so it is closest to the CG, and use a boom mount inside the tub similar to the Crapshooter's to handle all the torsion a single tube will experience and allow for adjustment.

 

[Grimracer]

OK, nobody said it, I don't think. But why have two boom tubes? Make a single, aero-shaped between the tub and sponson, large enough to get results similar to those previously posted, mount it at the rear of the sponson so it is closest to the CG, and use a boom mount inside the tub similar to the Crapshooter's to handle all the torsion a single tube will experience and allow for adjustment.

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Preston

I have some sketches i should show you someday...

grim

 

[Joe_Knesek]

OK, nobody said it, I don't think. But why have two boom tubes? Make a single, aero-shaped between the tub and sponson, large enough to get results similar to those previously posted, mount it at the rear of the sponson so it is closest to the CG, and use a boom mount inside the tub similar to the Crapshooter's to handle all the torsion a single tube will experience and allow for adjustment.

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I remember seeing this on a boat in Virginia over 13 years ago. It was a production boat but I can't remember the name. The boat was a slug but I wouldn't relate it to the boat's design. It was who held the radio.

 

[Preston_Hall]

OK, nobody said it, I don't think. But why have two boom tubes? Make a single, aero-shaped between the tub and sponson, large enough to get results similar to those previously posted, mount it at the rear of the sponson so it is closest to the CG, and use a boom mount inside the tub similar to the Crapshooter's to handle all the torsion a single tube will experience and allow for adjustment.

69460[/snapback]

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Preston

I have some sketches i should show you someday...

grim

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I'd like to see them. I imagine a composite boat with the foils "mounted" at the CG and the incidence fixed to the proper attitude of the hull. A round tube would insert into the sponson with a clamping/adustment system built into the sponson.