Wingboat Design

[Dim]

Design process should be stimulated, TimB.
Cheers, Dim.

[Tim B]

Ok, at last I've got to a computer and I've drawn a pretty boat. Well, actually, this should have some sound physics behind it. I'm not too interested in the central hull at present, since I feel that the proper way to approach this project is to design a wing that will fly in ground effect. If anyone has access to a CFD package, I'd be very interested to know what would happen to the vortices (assuming a flat sea surface) down the wing. especially at the maximum curvature.

[Dim]

TimB,

It seems, that without a rudder of a direction with your idea it will be difficult to be controlled.

Cheers,
Dim.

[Dim]

Cheers,
Dim.

I was thinking abouot your diehedral on your delta wings and remembered the american navy had a delta jet sea plane and they stuck with positive dihedral, saw the thing in San Diego I haven't got to far down this road but a planing hull banks inward to turn , negative dihedral also loads your wing tips (WAVE ACTION) which will quickly increase the weight of your wing structure. What do you think?

Dear Guest,

I know about nuances of constructions a little, which I have demonstrated. All devices, introduced on illustration - construction of the prominent Russian engineer Alekseev. I understand, that in military fleets of other countries there should be similar constructions. I very much like enthusiasm and tendency TimB to learn something new and, probably, to use it in the his job. I want just to show him already existing devices (even at a level of the prototypes). I was engaged in problems that floats under a surface of the sea, instead of flies above its surface at university.

Dim.

[Dim]

I have written the message and has forgotten to make Login, excuse.

Dim.

[Dim]

By all it is a cruiser mode. I, to tell the truth, do not see interaction of a water surface and construction of a wing. But I not the large expert. Look above.

[SailDesign]

For a WIG vessel, positive dihedral just plain doesn't make sense. You are trying to hold the pressure field under the wing, not allow it to release. The SeaDart mentioned earlier was not a WIG, just a regular plane that landed on water (OK, not very regular for a fighter-style jet....)
Banking in the turn for a WIG also should be eliminated if possible. Wings have ailerons, and these can be used to negate most bank. If you bank inwards, the the pressure increases on the inside of the turn, which could cause the thing to wobble the other way, sticking the wingtip in on the outside of the turn. This is known as an "instant flat-spin initiation" ;-))
When the FlareCraft folks were testin on Narragansett bay, they routinely went into "hop" mode to turn, allowing them to use the limited free-flight capabilities to get sufficient height to turn like a normal plane, and then drop back into ground effect.
Dang! My brain hurts now - time for another coffee....
Steve

[Dim]

I with the large transactions have translated. But it is very interesting.
Thank you, Steve.

Dim.

[foxxaero]

Hi MasterBlaster, I love the design you originally posted. It looks beautiful, however I am somewhat skeptical of the operational abilities of such a design in ground-effect. I'm no expert, but have done a fair bit of research into WIG vessels. An excellent resource material regarding the parameters of WIG design was written by Bill Husa of Orion Technologies. You might be interested in downloading his document called 'WIG Matrix' which can be found here>

http://www.oriontechnologies.net/papers.html

Based upon my limited knowledge, I'd say your 'lateral stabilizers' should be located at the fwd extremities of the reverse delta wing, not only for better control, but also to dissapate wingtip vortices. Also, as others have pointed out the addition of a T-tail would assist with pitch control which is very important in WIG craft. I'll try to add a photo below of a Lippish configuration model I built in 1984-86 which exibits the above mentioned control surfaces.

Also, there is a Yahoo message board called the WIG Group which has many helpful discussions related to WIG design.

Changing topics, the first design you posted looks more like a World Water Speed Contender rather than a WIG to me. Look up American Challenge WSR.

Hope that helps. Please keep me informed of the progress of your design - foxxaero@shaw.ca

Many thanks

Russ

[foxxaero]

I had to go back to locate the URL about the WWSR url at the Worlds Most Radical Boat Designs. Will add a photo of the American concept below.

Ps - as someone already mentioned you need to keep the wingtips parallel to the centreline of the boat.

More info on speed design here...

http://foxxaero.homestead.com/indhydro_008.html

Cheers

Russ

[Dim]

Dear Foxxaero,

I do not want you to offend in any form, but construction WIG at first pictures I saw 20 - 25 years back in one yacht journal. He was a little small size. The designer - Lippish. He the german, which after WWII worked in States.
Once again thanks Steve. I have found in www a material on a theme him post.

Yours faithfully
Dim.

[Dangerous Doug]

The thing to keep in mind here is that you're designing what must become a low-flying aircraft, and the aerodynamics of your design require the following considerations be taken into account:

Pitch stability: There must be some way to offset the changeing lift vectors created by the wing as a result of velocity, wind gusts, and blanking of underwing airflow by wave action. This, it would seem, could be handled by a gyro-stabilized canard. You might increase it's effectiveness by computer-coupling these with rear mounted stabilators, which would also be gyro-stabilized in the Roll axis.

Roll control: Stabilators work as both elevators and/or ailerons, allowing the gyro to cross-control with the rudder to keep the wings level in a turn, reducing the chance of a wing dipping into the water causing a water loop.

Directional control: I would think that a wet rudder as well as a central turn fin will be necessary for directional control, as the small size of the craft will necessitate a correspondingly small air fin. The resulting rudder will have little authority to turn such a craft in much other than airboat-like slides.

Balance: Since you're developing lift with those wings, the craft must be balanced much like an aircraft. Have you computed the center of mean aerodynamic chord? Have you computed the center of gravity? The inverted delta wing shape will present it's own lift vector problems, but will likely resemble a forward swept wing behaviorwise. You will also have to develop a way to move balast or components in such a manner to verify balance before each 'flight', because the cockpit, being forward of the CG, will mean that if the driver has lunch, or visits the bathroom between runs, there could be CG changes ranging from minor to disasterous.

Such a small craft has less room to 'fudge' things, and the wing loading ft/sq will be very high, requiring higher speed than a larger, lower loaded wing. Good luck. Perhaps you might bring these questions to the aerodynamics thread at www.rcuniverse.com for comment. Those guys deal with small (relatively speaking) aerodynamic platforms every day.

Dangerous

[tspeer]

Excellent article, Dim! Mateev's stuff is good, but can be hard to understand because he doesn't use the standard symbols used in the US. BTW, his stability criteria for height and pitch stability are also applicable to hydrofoils, although the variation in stability derivatives with height will be different.

Note that the region close to the surface, where he says static stability criteria are not sufficient to ensure dynamic stability, is exactly where Tim B's craft is supposed to operate. It's really tough to design something that's not really flying and not really supported by the surface. I was once on the accident investigation board of an unmanned aircraft that crashed on takeoff due to unstable dynamics in this netherworld.

Given the low altitude of the craft, several flying characteristics of WIG aircraft aren't applicable. For example, most WIG's bank to turn, as Kornev and Mateev point out. But this craft as drawn will have to skid to turn, which means it has to generate side force instead of tilting the lift vector like bank-to-turn aircraft do. Since the hull is fairly blended into the wing, there needs to be a vertical fin near the center as well as vertical stabilizers positioned aft. The side force could come from a fin in the water, of course, but it's entirely possible the fin could skip out of the water in waves, which would result in a loss of directional control.

Another contributor to the dynamics for such a craft is unstable pitch-heave coupling due to the interaction between the planing lift on the hull and the aerodynamic lift on the wings. What you want is for the craft to wheel-barrow, lifting the stern by the wings while planing on the bow. As hydroplane drivers know, if you lift the bow while planing on the stern, the craft flips up end-over-end.

Here's what's happening. If the craft is supported by the water behind the c.g. and it starts to rise, the support from the water drops off. Since the water was supporting the stern, this makes the craft pitch up. The increased angle of attack increases the aerodynamic lift, raising it further. The water support drops off more, and the craft pitches up even more. In the terms of the Kornev/Mateev paper, the heave stiffness of the planing hull moved the center of altitude way behind the center of gravity.

But if it's wheelbarrowing, this pitch-heave coupling is stable. As the craft rises, the planing support at the bow drops off, causing it to pitch down. This reduces the aerodynamic lift and counters the rise. The craft will tend to pivot about the bow, seeking a stable aerodynamic angle, and rising higher (more bow-down) with speed. The planing bow has moved the center of altitude forward of the center of gravity.

But wheelbarrowing is difficult to handle directionally. Sideforce on the bow makes the craft directionally unstable unless it has lots of aerodynamic stability, so big fins are a must. A single hull forward, as drawn, would allow the craft to both wheelbarrow and bank to turn somewhat, using both the aerodynamic lift and the planing lift at the bow to generate the side force for the turn.

However, rolling about the bow creates a pendulum motion that the pilot is likely to find objectionable. In order to start the turn, the stern has to swing to the outside as the craft banks into the turn, moving in a coning action about the bow. Since the cockpit is behind the center of rotation, the initial sideways acceleration is in the opposite direction compared to what it will be in the turn. If the craft has positive dihedral effect (a characteristic of both high wings and swept back wings, even with some geometric anhedral), it will tend to roll more and possibly generate over-steer. So when the pilot turns the wheel, the seat-of-the-pants feel says the boat is going the wrong way at first, possibly causing the pilot to turn the wheel more. Then the boat catches up and overshoots, so the pilot has to compensate the other way. If the pilot gets out of phase with the boat, this can lead to a wild pilot-in-the-loop oscillation.

The pendulum motion can be stopped by going to a pickle-fork configuration that wheelbarrows on two points and resists rolling. But the aerodynamic lift still has to be in the stern to get it to wheelbarrow. So the pickle-fork bows should be cantilevered quite a ways forward with the wing well aft.

And of course, if the craft is going to wheelbarrow in waves, there has to be enough freeboard and reserve buoyancy to keep from nosediving. The bow(s) should have significant sheer so that when it is in the bow-down flying attitude the deck at the bow is at least level. Better would be enough sheer that in the flying attitude the deck is parallel to the steepest wave it is to meet. 30 degrees is the steepest a non-breaking wave can be, so that sets an upper limit for the sheer and level-at-the-flight-attitude sets the lower limit. Somewhere in between is the right value, depending on how aggressively you plan to drive the boat.