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T-Tails on 50 and 70 cm masts

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T-Tails on 50 and 70 cm masts

Postby lightandfrost » Tue May 01, 2018 9:00 am

Light and Frost, a non profit kite board research group, has been attempting to increase the stall resistance of a hydrofoil when operating 50 and 70 cm masts in heavy chop and wave during onshore wave riding.

When beating out thru multiple wave lines we began experimenting with small vertical tails the size of fins on twin-tip boards to help stabilize the foil. When hit with wave sheer usually cross wave similar to cross winds in airplanes, these small fins increased the directional stability so we enlarged the vertical tail size and mounted the rear stabilizer in a T Tail configuration. This configuration significantly decreased the foil stall when operating in the high wave sheer environment close to the surface where hydrofoils on short 50 and 70 cm masts operate. We tested this configuration on four different wing fuselage combinations on two different boards all with exactly the same result.

When beating out thru a wave line and hit with a wave or swell usually from the right/left forward area of the wing, the hydrofoil was barely affected. Prior to mounting the rear stabilizer on a T-Tail, the hydrofoil stalled easily unless the wing was loaded thru pumping or the fuselage was buried deeper into the water. With the T-Tail we could rest only our rear foot on the balance point and ride out through the advancing swell as the tail fin maintained the upwind angle.

The T-tail was mounted between the fuselage and the board to allow operating in shallower areas. We have not tested the T-Tail when mounted on the opposite side of the fuselage.

The board/mast.hydrofoil shown was the original test vehicle. Later we made the T-Tail more permanent as seen in the enclosed pics.

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Re: T-Tails on 50 and 70 cm masts

Postby evan » Tue May 01, 2018 9:58 am

Funny how you talk like a multimillion dollar research organisation while my gut feeling tells me that I am dealing with a few students that just learnded to foil on their home built hydrofoil, please correct me if I am wrong.

Almost all foils have some kite of vertical stabilizer and even the T-tail is done on multiple off-the-shelf foils. Good to know that is does indeed what it should: stabilize your foil ;)

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Re: T-Tails on 50 and 70 cm masts

Postby tahoedirk » Tue May 01, 2018 4:00 pm

Thanks for sharing your findings Lightandfrost

Those are some very specific, legitimate observations. It is so hard to find people sharing these hard won findings.

Usually there is some second year know it all to shoot you down from the comfort of their laptop

Keep up the good work and please keep sharing!
thanks, Dirk

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Re: T-Tails on 50 and 70 cm masts

Postby BWD » Tue May 01, 2018 6:10 pm

Interesting, your surf fin vertical tail rudder appears to give more area than most anything I can think of in kite foil tails.
Looks like with the big "rudder" you also can/must shorten the fuselage to get the turning you want. To me this seems like a decent idea as the tail of the foil is the most commonly kicked part, the most fragile part, and often runs aground first, leading to bent screws or fuselage.

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Re: T-Tails on 50 and 70 cm masts

Postby opie » Tue May 01, 2018 10:19 pm

Thanks for posting your results. :thumb:

Do you think the vertical surface area is making all of the difference, or does raising the stab out of the front wing turbulence have something to do with it?

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Re: T-Tails on 50 and 70 cm masts

Postby lightandfrost » Wed May 02, 2018 3:12 pm

When approaching this work keep in mind that our main interest here is to ride out thru a breaking wave line on 50 to 70 cm masts, turn around and ride
back in. We have no interest in racing or riding flat water or using longer masts.

We noticed that when hit with wave or swell when beating out, there would be a lateral yaw which sometimes resulted in a stall. As we have ATP rated pilots
testing these variants the logical aviation correction was to install a vertical tail above the stabilizer. We tried larger and larger vertical fins and got better and better results as the lateral yaw disappeared, was dampened and self corrected. But the real overall improvement was mounting the stabilizer on the T-Tail.

Our view is that all design comments by BWD and opie are valid. Placing the T -Tail above the fuselage protects the T-Tail/Stabilizer from damage. Better and better results were obtained as the size of the vertical tail was increased. And placing the stabilizer out of the front wing turbulence smooth’s the ride.

We have tested five different front wings on three different fuselages on three different boards and masts all with exactly the same results in that in rough turbulent water, stability improved.

We will probably install some vortex generators on the outer 1/3 wing sections' leading edge and see what occurs. You can find our vortex generator comments in this forum

In closing and in reference to BWD's comment "often runs aground first, leading to bent screws or fuselage." Our fuselage is a Stainless Steel square or rectangular rod filled with epoxy resin and silica powder. It is then covered with rubber cement and layers of shrink tubing. If the shrink tubing gets damaged we just strip off the outer layer and apply another outer skin replacement. We have never had to replace the outer cover on any of our various test fuselage variants. The stainless steel fuselage can sustain high impact as it does not crack or shatter due to impact resonance like carbon fiber.

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