Wingboat Design

[Dim]

I should be accumulated by time and to be going with spirit closely to study your answer. I am glad that you liked the document, Tspeer.

Dim.

[Tim B]

Oh dear, I seem to be getting behind with this thread. Let me try to explain my thinking. I am coming at this from an aerodynamic perspective, simply because I think that this is the hardest part to get right. Anhedral is obviously a necessity, since otherwise we'd end up with a straight wing with a vertical, downwards winglet. Many years flying Tailess aircaft has suggested that a vertical rudder is a prime reason for 'flat spins' (or 'divergent yaw situations' more correctly). Therefore, you can afford to let the inner wing sink slightly through the turn, rather than tring to fly it flat around the turn. I take the point about C.G. and this is largely down to where the centre of lift is. Assuming that the Cm is small enough to be ignored, then one puts the C.G. ahead of the centre of lift, then trim it with elevons (correct delta/tailess terminology for combined ailerons and elevators). Therefore, once the wing is designed, the rest of the boat can be designed around it.

Cheers,

Tim B.

[Dangerous Doug]

Tim B, a stabilator is an all-flying surface, used on aircraft like the F-14 to combine aileron and elevator effect. A tab type surface (elevon) is not likely to have sufficient authority to maintain adequate pitch and roll control in the velocity envelope of this type of craft. Gyro stabilization will be necessary because of the constant and instantaneous need for stabilization at the low altitude, which would be beyond the ability of the pilot to react to and keep up with. Like the F-16, I doubt if it could function without it.

[Tim B]

I am aware of the all-flying surface method, I use on on a model aircraft. In that case it is on a well-balanced straight tail-plane pivoted at the quarter chord. I have to admit, that there is little difference between the pitch control of that aircraft, and any of the normal (elevator controlled) planes I fly. My father has found the same thing with his aircraft.

So, If there's that little difference in control, then what's the problem. Three words, Flutter, Delta and Forces. All-moving surfaces are very prone to flutter. If there is any slack in the control system, it will flutter (if flutter is divergent it will break thus you lose the whole lifting surface. If an elevon flutters, you may be able to rescue the rest of the boat). The fact that it's a Delta would mean that we're looking at balancing somewhere around the aerodynamic centre. And that's going to induce a hell of a trim force. Therefore I would suggest the use of elevons.

Cheers,

Tim B.

[tspeer]

Originally posted by Tim B
...Anhedral is obviously a necessity, since otherwise we'd end up with a straight wing with a vertical, downwards winglet.

And why not a winglet? Especially if it connects to the planing hulls.

Many years flying Tailess aircaft has suggested that a vertical rudder is a prime reason for 'flat spins' (or 'divergent yaw situations' more correctly).

Spins and divergent yaw are two completely different things. Spins are not an issue for the craft under consideration, because a spin occurs at an angle of attack above stall - and this craft will never get near stall.

Divergent directional stability is a matter of balancing the vertical area to provide a statically stable configuration, just like on a boat. It has to do with how the yawing moments change due to a change in aerodynamic sideslip angle.

Therefore, you can afford to let the inner wing sink slightly through the turn, rather than tring to fly it flat around the turn.

Not for the craft as drawn. It is a boat, partially supported by wings, not an airplane. It is apparently powered by a water prop. As pointed out in the Kornev paper, you have to pivot about the inboard wing tip when doing a banked turn, which means the c.g. has to rise. This would take the boat completely out of contact with the water. The concept shown has to skid to turn.

I take the point about C.G. and this is largely down to where the centre of lift is. Assuming that the Cm is small enough to be ignored, then one puts the C.G. ahead of the centre of lift, then trim it with elevons (correct delta/tailess terminology for combined ailerons and elevators). Therefore, once the wing is designed, the rest of the boat can be designed around it.

No, no - controlling the pitching moment (Cm) is the whole point. It's not clear what you mean by center of lift - the two concepts people usually talk about are center of pressure (the reference point about which the instantaneous moment is zero) or the aerodynamic center (the reference point where the change in moment with a change in angle of attack is zero). Center of pressure is a very outdated (pre WWI) approach and not very useful because the center of pressure changes with angle of attack (and height for a WIG), and at low angles of attack isn't necessarily even close to being on the vehicle!

Aerodynamic center (for an airfoil), or the "stick-fixed neutral point" when talking about a whole vehicle, is the same as the point Kornev calls the center of pitch. What's missing from this discussion is Kornev's center of height, which is the reference point about which the change in pitching moment with a change in height is zero. You have to arrange both points to be located properly with regard to the center of gravity or you can get the kind of unstable pitch-heave coupling I described.

Presumably you meant the Cmo, the pitching moment at zero angle of attack out of ground effect, when you said the Cm could be neglected or trimmed out. The pitching moment from whatever source - whether it's the camber in the wing or the stabilizer or the fuselage or the planing surfaces on the water - will have to be trimmed out at the cruise configuration. And that's not necessarily trivial, either. It may take a significant amount of control authority to do it, which is were all-moving stabilizers come in.

But after that, the slopes of ALL the pitching moments, aerodynamic and hydrodynamic, due to both a change in attitude or a change in height, have to be factored in. As I see it, both the aerodynamics and the hydrodynamics have to be completely integrated for this concept to work.

The wheelbarrow strategy I mentioned is one such method, which substitutes the hull for the large T-tail stabilizer normally seen on WIG's. In effect, it's a hydrodynamic canard that works by moving the "center of height" way forward.

As for flutter, slop in the linkages is a problem. However, mass-balancing the surface so the center of gravity of the surface is at or in front of the hinge line will also eliminate flutter. With proper mass-balance, the surface can be stable up to some speed even with no linkage attached at all.

Active feedback control might be useful, but I don't think it would be essential for such a craft. The fact that it's always in contact with the water may actually be an asset in this case, compared to the full-flight WIG. The planing hull acts like a big sensor as it rides across the water surface.

[Tim B]

It would be worth reading Airfoil Design for Tailless Airplanes at:

http://beadec1.ea.bs.dlr.de/airfoils/nf_2.htm

And won't this wing stall? It will if we screw up the design. don't forget that alphastall is only 8 or 10 degrees maximum for a straight symmetcrical wing.

Cheers,

Tim B.

[yipster]

Tim, whats that adres again? cant get http://beadec1.ea.bs.dlr.de/airfoils/nf_2.htm to open here...

[Tim B]

It used to work, I have a hardcopy and that's the address. Further embarassment is that I can't get into the site either!!!
Check this out though:
http://autos.groups.yahoo.com/group/wig/

http://www.desktopaero.com/appliedae.../tailless.html

[foxxaero]

With all due respect, I think much of this discussion is getting 'lost' or 'confused' in aerodynamics (as related to a regular aircraft operating in Ground-Effect).

An IMO classification-Type 'A' WIG Boat operates on a dynamic cushion of air and much of the aerodynamics applicable to a normal aircraft in ground-effect do not apply to the same extent.

As I said earlier, the 'Wingboat' originally proposed by MasterBlaster has attributes more suited to WWSR craft (in which case all the discussion about turning or banking such a craft becomes irrelevant). The 'Wingboat' (as proposed) will NOT be able to operate as an efficient WIG, without the addition of an appropriate tail stabilizer and other modifications. I have never heard of such a thing as a 'tailless' WIG - it goes against the principles of a dynamic ram-foil operating in ground-effect.

Before getting further lost in the aerodynamics of regular aircraft, I think interested parties should familiarize themselves on HOW a dynamic ram-foil (WIG ... IMO classification - Type A ) operates. Again, I suggest reading Bill Husa's WIG Matrix (originally a study made for Boeing)

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

as well as studying the explanations by John Leslie (currently employed by Flightship of Australia (developers of the FS-8 originally designed by Hanno Fischer of Fischer Flugmechaniks) >

http://autos.groups.yahoo.com/group/wig/ .

In my opinion, this discussion is branching off into a comparison of apples and oranges when attempting to compare the operation of WIG with the operation of a regular aircraft in 'ground-effect'.

Just my opinion and .02 cents worth

Cheers

Russ

[Tim B]

Has anyone considered just using "a regular aircraft in 'ground-effect'". cos it would be faster,smoother, and easier!! Just kidding.

[yipster]

from what i know that is the major contributor by "take off"... as Tom said: "controlling the pitching moment (Cm) is the whole point" than again as Russ said, this is no high flyer but air cushion type... if i'm rite... still wondering about its power and propulsion here.
yipster

[Doug Carlson]

I may be all wet..., but how about a canard (set to stall at or before liftoff) to control pitch, a stall fence synched to the vertical stabilizer/rudder to kill lift on the outside (faster) wing, and an integrated keel/propulsion system to turn around.

I guess you would need a retracting, in water, rudder for slow speed work.

Perhaps a rudder like the surface drives use would be all that would be required for both high and low speeds. Something tells me a judicicious use of steering control would be required!

[tspeer]

Typically, stall occurs at angles of attack of 12 or more. If this craft ever sees so much as 10 degrees of pitch attitude, it's because it's starting to flip over. It has to operate within a very narrow range of attitudes, which implies high pitch stability. Stalling the canard before the main wing works for aircraft because they are not restricted in their heave motion. The aircraft not only drops its nose when the canard stalls, the whole aircraft descends. This allows it to pick up speed and fly at a lower angle of attack.

This craft is a very different animal because it operates not just in proximity to the surface, but in contact with the surface. This makes it different even from WIG's. Yes, there's ram effect on the wing. But there's also planing of the hull.

As for propulsion, I reread MasterBlaster's original post, and I see he was talking about jet propulsion - presumably a turbofan engine. So it looks like it will have air-driven propulsion rather than water-driven propulsion.

Here are some photos of the vehicle for which I worked out the coupled aero/ground dynamics: http://www.fas.org/irp/program/colle...000T-002_s.jpg, http://www.fas.org/irp/program/colle...-43303-7_s.jpg, http://www.fas.org/irp/program/colle...000T-001_s.jpg. The motto of we flight controls engineers was, "Keep the black side down!" Unfortunately, when ship1 made its second takeoff, it failed to do that and ended up in a fireball beside the runway.

As you can see, it's superficially similar in that it's tailless and has the wing at the rear. It's not as close to the ground in terms of height/chord ratio, but every bit as close in terms of height/span ratio. And it's jet powered.

I looked at all 4 possibilities: all wheels on the ground (three point attitude), nose and one main on & one main off, both mains on & nose off (two point attitude), and both mains off & nose on (wheelbarrrow). If you're going to be largely supported by aerodynamic lift, wheelbarrowing was definitely the way to go. It's also the way a conventional geared airplane operates.

When we redesigned ship2 after ship1 crashed due to the unstable ground dynamics in the two-point attitude driving a porpoising oscillation on takeoff, we went through 4 landing gear designs until we got the extension damping just right so that the main gear would break ground just before the nose gear, ensuring that it would be momentarily wheelbarrowing just before it left the ground completely. This resulted in it being in trim and taking off from a stable situation. Very counter-intuitive, but that's what the vehicle dynamics said it needed.

Another thing to consider is pitch control. Whether you use wing flaps or a tail for pitch control, if the stern of the craft is in contact with the water, it will resist the aerodynamic pitching moments and you won't have any pitch control at all. It's like putting the doorknob at the hinged side of the door. You can push and pull all you want, but it will be very ineffective at opening the door because the hinges will resist the force on the knob.

The same thing will happen if the stern of the craft is planing. DarkStar had the same problem - the main gear were right at the effective point of application of the elevons. So there was essentially no pitch control when it was on the ground. In fact, we had to use the nose gear as part of the control system to rotate the nose for takeoff. Only when the craft was wheelbarrowing did we have any aerodynamic pitch control on the ground, because then we could raise and lower the tail with the elevons as the vehicle pivoted about the nosegear.

This also causes difficulties with canard control. I learned this when I tried to control a rigid wing sail with a canard. When the canard stalled due to the wing pivoting to too high an angle of attack, the drag on the canard caused a moment that tended to increase the angle of attack. This caused the rig to rotate completely out of control when the wing stalled, because even at a negative angle of attack, the canard couldn't generate a net moment to oppose the rotation.

A similar thing can happen with with this craft as it rotates about the stern in contact with the water. I doubt that a canard would be able to recover it once it starts to go, and it'll flip backwards like a hydroplane.

One final item about DarkStar. It isn't apparent from the photo's, but it had very effective yaw control, due to split surfaces at the wing tips(http://www.fas.org/irp/program/collect/darkstar_03.jpg). The long wing gave them lots of leverage, and they were more effective than the nosewheel steering at a surprisingly low speed. That yaw control was the key to stabilizing the craft when wheelbarrowing. The combination of active feedback for yaw and roll, with the natural pitch stability of the wheelbarrow was an effective solution for high speed operation when the craft was not completely flying nor completely supported by the surface.

[Doug Carlson]

Tom,

Its my understanding that a canard provides pitch control by increasing and decreasing lift as opposed to the creating downforce (conventional horizontal stabilizer/elevator). Your example of catastrophic failure in a stall with a canard seems to me to be a description of a secondary stall induced by a cg aft of the envelope not necessarilly a flaw in pitch control inherent to canards.

I see that you are right about the proposed propulsion. I still wonder if some form of fin to turn around could be employed to reduce skid.

I notice that I used the term "stall fence" in my earlier post. I think "spoiler" may have been the correct term.

Is there a ratio of lift generated by compression versus conventional aerodynamic lift for flight in ground effect?

It would seem to me that reducing the planing surface of the hull and varying its placement relative to the aerodynamic effects of the wing could/would greatly influence the balance of hydrodynamics to aerodynamics.

Doug

[foxxaero]

Here is the FS-8. (Gallery seems to be down at the moment!) Where do you see a design flaw?