Catamarans High Speed Blow Over - Causes & Solutions

ZERO-ZEROS .... best solution. Might break your back, but that is a different engineering request ....

 

You might be surprised how many very advanced active control systems have already been developed and fielded for advanced marine craft. Hydrofoils, SWATH and surface effect ships, in particular, really pushed the envelope of marine flight and ride control systems. The development of those dates back to the late 70s, using analog control technologies, and going fully digital in the early 80s.

There just have never been very many of them built....so "how" they fly as they do isn't necessarily widely understood.

 

I guess this would depend a lot on the "air time" any systems could be expected to control.

Jimboat touched briefly on this earlier. If a boat is traveling in a straight line at high speed when it leaves the water, and drag was equal, it wants to continue in that direction the drives were pushing it. This can be seen in videos from off shore races where boats catch serious air over waves and recover perfectly again and again. Long as any part of those drives or ruder is touching water, you have decent vertical axis "yaw"control.

However when making high speed turns, that rule goes out the window. All boats including Cat's can spin out fairly easy if trimmed too high in a turn. Excessive drag from engine or drive failure will also cause you to spin out on cats. Can be violent, but it's also uncommon. Here is what that looks like in a V-bottom.



My thoughts are a good starting point in any aerial stabilization systems must focus first on "pitch" along the lateral axis. If you can control pitch, you keep those drives and rudder submersed, and thus maintain yaw control. But as someone previously listed, this has to be crisp and exact so not to stuff the bow on landing creating a whole new problem.

That leaves us with "Roll" along the longitudinal axis. Here is where those gyroscopic forces pop up I mentioned above. There is some great gyro demonstration videos out there, gotta love the internet.. These rotational forces can be created by the spinning engines and drives, along with those caused by launching off waves. While in flight, guessing they would compare to forces exerted on a single engine prop plane.

So basically we need an elevator and some ailerons to keep our boat flying level and return it gently to the water. Could twin bow canards possibly accomplish this? We also have huge amounts of deck surface to that could be utilized as ailerons...

BMcF; Any good links to those hydrofoil designs using control surfaces?

 

Kidturbo, are you talking about retrofitting the existing cats or about a new design?

Because, if you look at the H1 unlimited class example in my post #33, you'll see that a design similar to what you propose already exists (no ailerons though, and the elevator is fixed in that case - but that's just a detail which can be modified), and the pic shows you what would a boat equipped with all these aerodynamic surfaces approximately look like.

Cheers

 

Check out the old Miss Geico turbine race boat in this video from 2009 Sarasota Grand Prix. Count how many times the hull leaves the water compared to the drives or rudder [by the lack of roost]. Great demonstration of how they are designed to fly by prop trim alone..

Also check out those small hatch panels flapping near the transom at like 2.48. They look like little ailerons don't they?

 

By the sheer numbers of cats out there presently, retrofitting options would be my first priority. Kinda where this discussion got going on another forum. Many of these boats get re-rigged a few times over their life and power levels along with the designers COG point get shifted. So any design that could be fitted to an existing boat would be well accepted. I'll test it...

Proven control surface designs are available to hull designers as you have listed. Guess it's just gonna take the buyers requesting these as safety "options" to get them motivated with the pen.

 

As long as it is flying the elevators and airleron will do its job but when it has reached its position/velocity, the point of no return, the airfoil becomes useless as it has "stalled". In fact, in canard design, it is the canard that stalls first, reducing lift in front, front dives, increasing velocity (as long as there is enough ground), permitting the main wing to recover.

At the stalled condition with little or no forward velocity, it becomes a flat plate at high angle of attack, like a kite.

 

Got ya. So while a canard might help increase bow lift, it's not going to do much for reversing it?

What we are actually looking to do then is detect the boat is lite "leaving the surface", then check it's speed and pitch. If speed is above X, and pitch is increasing quickly, we need to force a stall upon the tunnel airfoil surface long before it reaches it's natural "critical angle of attack" ?

From wikipedia

Above this critical angle of attack, the aircraft is said to be in a stall. A fixed-wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below a particular airspeed. The airspeed at which the aircraft stalls varies with the weight of the aircraft, the load factor, the center of gravity of the aircraft and other factors. However the aircraft always stalls at the same critical angle of attack. The critical or stalling angle of attack is typically around 15° for many airfoils.

So some sort of reversed "slat" on the leading edge / bow, or an elevator near the transom should do it? If fast enough acting, a slat could be retracted once stall is detected by an inertia sensor, and the airfoil is returned to providing lift before the sponsons landing back on the surface.

But if we use an elevator at the rear, we increase the risk of lifting the drives out, which opens us up to possible yaw and roll problems. All that sound correct?

I sure hope so cause I'm lost if not....

 

I don't have any links but I do have some published technical papers that are in pdf format. I'm out of the office for another week however (training a crew on how to use the active stabilization system on their new high-speed patrol craft). You can google "Navy PHM" and find some information that way..

 

But...if the angle-of-attack of the entire canard is actively controlled, the situation is quite different. Even just active control of a trailing edge flap on a fixed canard (maybe 20% of chord) is going to have an effective envelope large enough to actively prevent the onset of a blow-over.

We use both types of canards as active underwater appendages.

 

how does it work when its in the air but it was designed to be in the water?

 

??? I'm pretty sure I wouldn't be "stretching" the skills of any aerodynamicist to develop a canard that is intended to operate in air vice water. In fact...it would be much easier. Water imparts some big loads.

Too many people fail to grasp that some very advanced marine vehicles operate exactly like aircraft with wings and canards and fully active flight control systems...just operating in (much) denser medium.

 

Thank you very very much... I was reading about the different types of canards when you replied. :idea::idea:


http://en.wikipedia.org/wiki/Canard_(aeronautics)

Thus, a control-canard mostly operates only as a control surface and is usually at zero angle of attack, carrying no aircraft weight in normal flight. Modern combat aircraft of canard configuration typically have a control-canard. In modern combat aircraft, the canard is usually driven by a computerized flight control system.[12]

One benefit obtainable from a control-canard is the avoidance of pitch-up. An all-moving canard capable of a significant nose-down deflection will protect against pitch-up.

So.... Control Canard's, say a pair placed on a shaft between the sponsons slightly ahead of the tunnel leading edge, individually and artificially (fly-by-wire) actuated, could possibly act as elevators and ailerons for ride stability. Come with the benefit, "avoidance of pitch-up", which is the primary goal we are looking for in this situation.

Why didn't someone just say that 5 pages ago... lol
God it's late and I'm Slooooooow....
Sorry.

 

Yes I understand that either you have a wig vessel powered via the air or you have a vessel that stays in the water and the control surfaces are in the water not designed to ever leave the water.
I can see its easy to have flight control systems to keep each of these under control and they already exist.
Now lets move to the race boat, that between these two I would think?
We need to perform like a wig when its flying yet to might still have the props in the water

 

Someone did, 5 pages ago : http://www.boatdesign.net/forums/hy...over-causes-solutions-48276-3.html#post651316 :

Basically, you are looking into transforming your cat into an H1 racer. Add a computer-controlled actuation system (which is not allowed by the racing rules, otherwise they would already have it installed) to the existing aerodynamic surfaces of an H1, and you'll have what you need. And we've been continuously circling around it over the last 3 or 4 pages.

More about these boats here: http://www.h1unlimited.com/hydros-101/

Cheers