Catamarans High Speed Blow Over - Causes & Solutions

The canard or any airfoil will not stall in water (almost) because of the difference in density. A little forward motion in water equates to lift.

 

Wiki is, as often, right and wrong.

Both AA and Stall Speed are related. Not getting into this too deeply, you don't need that.

1. Horizontal Stabilization is what you need - with a true WIG as well. But, you want the true depth, altitude control done as much in the water as possible.

A forward inverted "y" and a rear inverted "y" is the best start - the Russians found the inverted "y" form, or an angled "u" form to do best in the 1960's. As your vessel lifts, less and less of the foil is in the thick medium, water, so it quickly adjusts appropriate lift for the current speed.

As the vessel slows, more foil, wing, buries into the water, going for minimal lift to maximum - what a dream .... that is where you get your soft landing. You want more lift 'capability' in front, and more drag in the rear .... always overcoming the stern's drag will keep you straight. Especially if you go to 3.

2. To understand the aeronautical side of your design, you only need to understand one thing.

a. Why do wing surfaces move? The wing is what gives lift and you want lift, so why would they move at all?

b. To vary lift. Everything is about varying lift, not about stall. You do not want to be in stall condition, you want to be out of it (faster than it). Canards, and Horizontal stabilizers are doing the same thing in reverse. Canards stall before main wing/body stall, and horizontal stabilizers stall after.

3. If you can move from a pusher to a puller configuration, much, most, if not all of your problems lessen. If your power source is pulling and pulls too much and you get too much lift, maybe a bounce off of a wake, the tail will pull you back down.

If you push, you have overcome the drag, and now it becomes unstable.

Look at the Russian WIGS and the Russian Ekranoplans, they were doing this well in the 1980's, way ahead of western 'technology' in this regard. Ekranolplans are an engineers DREAM, they are so ugly, but they WORK.

4. Many Russian WIGS and Ekranoplans pulled with the tail in the water, or almost in the water. Creating a very stable platform, but the "Black Sea Monster" still crashed when one of the pilots pulled up too hard and too quickly, and she still nose dived ..... what a loss.

You want your aeronautical controls to provide assisted lift - in WIG stall speed would be too narrow. Do you really want a vessel that works at 200 mph, but stalls at 190?



Well maybe a controlled crash, nice and soft, but that is not terribly common on water landings.

Wayne

PS The guy to ask about all of this would be the owner of Vans Aircraft and Bikes (Don't ask me, I don't know the connection other than the Wrights). He is very good at explaining the real "why's" you want to do x rather than y.

Things like Vne - and my gut tells me you are going to have to figure this out for your craft .... Yours won't be an altitude induced Vne, but the two media, water and air, working together must have some of that. There must be a true never exceed velocity if you are still in the water and the air - that is a gut feel, but it is a strong gut feel.

PSS - you really need to start working with aeronautical engineers (real ones) or Russians. Neither will steer you wrong. They will be brutally honest, this will not work - engineering, or this might work .... let me think about this - again engineering.

 

PS
Buzzi put the wing on Gancia dei Gancia as a joke

 

You do NOT want a 'canard design' unless you are talking part in the water and part out. Inverted "v", or "y". When the canard stalls, it will DROP your bow into the water.

Look to the ekranoplans, they have HUGE horizontal stabilizers, because that is what you need to control (induced drag on the tail end (stern) is part of the control).

 

can we separate out hydros as they are different beasts than tunnel boats
Hydros typically regarded as stable compared to tunnel boats and are faster

 

Nope. He had such a tight weight schedule for the Cesa 1882 (after he underestimated the design weight of the previous Nitro project by 25%) that anything that didn't have a practical function on board just couldn't be there.

The wing is there to dampen the roll which was "truly intolerable" (Buzzi's own words), and to prevent the chine walk.

 

That. And given the speeds involved, I cannot imagine using an underwater control appendage; cavitation limits most of those, transom tabs and interceptors excepted, to speeds well less than 100 mph and, regardless, they are all useless once they leave the water.

So that's where the active aerodynamic devices enter in.

 

Let us do some quick analysis.

A tunnel hull works best with the CG at 25-30% of the length. The whole deck is shaped into one long airfoil. It is a wing with very low aspect ratio. This constant chord wing with no sweepback will have its aerodynamic center (AC) in the center and the required center of gravity (CG) slightly forward. Comparing the hydrodynamic part with the aerodynamic part, the required CG is too far apart. A headache in balancing.

With a canard wing configuration, there are two wings. The main wing at the back and the small wing in front called the canard. With two lifting surfaces, the coefficient of lift (CL) is increased. In the canard configuration with two lifting surfaces of different areas, the AC shifts towards the leading edge of the main wing and the required CG just slightly ahead. Since the main wing is placed at the aft end, the AC and CG is now nearer to the designed CG of the hull. With the mass moment of inertia closer together, it will now be easier to control.

While the coefficient of lift is increased, there is also a corresponding reduction in the lifting area because there is no increase in width. This can be viewed as a penalty but with a higher CL, it may not be so much. The canard, because of its location out front can have a max CL of 2 while the main wing can have only 1. In “flying” condition, the canard is lifting. With a rise in altitude, it increases the angle of incidence of the main wing increasing its lift. When the speed is slowed down or reaches stall speed, the canard loses its lift, the nose goes gently down, and the main wing angle of attack is reduced. This keeps the main wing from stalling. The canard has to stall first.

Unfortunately, the main wing area cannot be increased significantly to gain lift (with flaps) as any increase in wing area (or lift) will be detected by the canard. That is why its CL can only be 1 out of the theoretical 1.8 for a conventional wing arrangement.

Whether the canard configuration will improve the performance of the boat or enlarge its “flight envelope” depends on the amount of study that will be put into it. I look at the book on aircraft design and all preliminary calculations are there. It is just I am not up to it.

 

There you have it. Same device..same control objective...different platform.

 

I'd love to know how can the wing dampen roll as it creates the same lift in the same relative direction regardless of the vessel roll?
I would have thought a huge vertical fin would do that?

 

Drag.

 

Gentlemen, we have two options:

A. You understand a canard, and you know this is NOT the place to use a canard.

B. You understand a little about a canard and think this would be a great place to experiment.

Let me give you a couple aeronautical notes to clarify.

1. I asked this above, what is the purpose of parts of a wing, a wing surface moving? It is to increase or decrease lift (control).

2. Why are canards loved and hated - they stall before the 'main wing' In this case you are trying to use a boat body as a lifting device.

3. The boat hulls in these examples are not, NOT, READ THAT NOT, good lifting devices. They are NOT airfoils. They are deflectors. They deflect air and gain the equivalent of lift.

NOTE: an airfoil is designed well when it can produce lift with minimum interference from turbulence - separation of air from the foil.

In this example, you must have at least a single appendage in the water, for drive, and to call it a 'boat.'

Why not use that appendage as your true control point? Move that point forward so you are pulling rather than pushing.

In an aircraft, pushing is preferred (mostly) over pulling especially at high speed. But, in a boat, the opposite would be true - when at high speed.

4. MOST important, a canard will NOT avoid pitch going vertical. It cannot do that. If it has lift, it will always PULL up (vertical pitch). If it loses lift, it will bury the bow of the boat in the water. You can add fighter aircraft like computer controls, but unless you have access to that kind of $ it won't be easy. They use those controls because they designed the planes to NOT FLY. Then they use the controls to fly them anyway.

It is much safer unless you have a need to design for safe flight than it is to design around safe flight.

 

Quite correct. And if the center of mass of the hull and the main wing is close together, the control becomes very responsive. Might need special training or computer control.

 

so the wing needs to be about static water level then?

 

Not that close. Just vertically close.