HYSWAS anyone?

Can't see how it would be negligent, perhaps you meant negligible.

I'm sure you're right but my concept is a mixture of many principles and will not have much buoyancy from the pod.

It seems combining ideas and pioneering one off's challenging for the experts and the layman.

Thanks for your response though.

-Tom

 

LOL..spell check strikes again.

And we've already built and flown pretty much what you propose. But not at a 'very small scale'..more like at manned scale and 9 tons displacement.

I've eked out a business and a career out of designing, building and controlling 'one offs' and various odd combinations of HPMV technologies. Have fun with it..I sure do.

 

BMcF,

So, you want money to help me then, is that it?

I don't think that's the point of this forum is it?

-Tom

 

Hardly. I signed off the last with "have fun with it, I sure do".

Say..who was it started this thread with an inquiry about HYSWAS? And who answered it with some direct knowledge of same?..no more and no less.

 

So very helpful in the morale department.

Many thanks.

-Tom

 

You are quite welcome.

It has been interesting to observe, in recent years, the miniaturization and cost reductions, in 'stabilization packages', driven largely by the RC model industry and market. A decade ago, it was virtually unthinkable that the active pitch/roll stabilization system required to operate a small model hydrofoil or HYSWAS was even feasible. Now, fully flying hydrofoil RC models are seen often.

 

It is true that the explosion of small, cheap, digital processers and sensors has made implementing an active control system easier, but there are still a lot of problems going digital in large sizes. You really need to do a good system analysis to get a total working package.

Right now we are struggling with a problem that is almost funny. In a new build, they converted an old tube and pot analog system to digital because the analog system was hard to tune, but you could make a self tuning digital system. This allowed the contractor to down size the hydraulic servos and force producers because the simulations showed better control. But within a few months all the hydraulic valves in the system started failing. After replacing a few of the valves twice we really got to looking at them and found that they failed in fatigue. A quick check of the control system showed that it was hitting the servo pilot valves at 25 Hz....on valves rated for 20,000,000 cycles.... So now they had to install gaining to keep the valves from failing within a deployment but the gaining means you need bigger hydraulics and force producers which can't be retrofitted at the moment. New system, poorer performance, more maintence.

 

Those (whatever they are) must not be an appropriate valve selection then; we've been using servo valves - single-stage and pilot-operated - for a good 30 years now that easily hold up to the high-frequency high duty-cycle environment that is ship ride control. Moog, Bosch, Parker, Atos, Atchley, Rexroth... all make suitable servo valves and many more options than the 'old days', thanks to the growth of industrial automation and high-speed robotics and CNC machines.

That said..a typically superimposed 'dither' frequency would be on the order of at least 100 Hz, usually more. In the modern direct-activated solenoid servo valves, the PWM chop frequency is around 300 Hz and suffices in and of itself to provide adequate spool dither.

But sorry to hear about your problems in any event. We would be aghast were one of our control system retrofit/upgrade projects to turn out to be anything but.


The stabilization and ride control system for the USN HYSWAS was, of course, a digital processor core, but still relied on analog servo control of the fins. It was not until around 2001 that the first all-digital ride control systems came out..and the experimental USN Sea Fighter (x-craft) received one of them in 2003-2004 time frame.

 

I have thoroughly investigated the R/C world of gyros and levelers and if I choose to go that route it is surprisingly economical and effective. My R/C helicopter uses one and it's performance is staggering considering it minuteness.

BMcF, I think where you and I fell off the tracks is in the component of thrust. My challenge in lift-off is in getting the surface hull to sufficient speed where the foils will become effective and provide sufficient lift to achieve flight. The test hull has only achieved 2.2 knots. This is not going to fly. However, introducing laddering foils may be the answer as they would be designed to provide greater lift at lower speeds providing the lift needed (at those speeds) to free the hull from the surface and increase velocity. The main foil would then provide more lift and the laddering wings would rise up out of the water as flight level would be achieved.

I believe in your work there was ample thrust that these details were not a problem especially (as you pointed out) HYSWAS lends itself to easy lift off with loads of positive buoyancy from the pod.

I apologize if my terminology doesn't match yours or that of your industry but I do hope you understand this time what I'm trying to articulate.

-Tom

 

I must confess I remain confused still. I'm not sure what kind of propulsion system would yield a speed-thrust characteristic that would not move the hull through the water sufficient to achieve adequate lift to raise it clear...but then would have sufficient thrust to go faster beyond that point. There is no unusual 'break', 'kink' or platueau in the drag curve for a HYSWAS...it just keeps on increasing as speeed increases, presence of foils accounted for.

I recall various of the foil-assisted catamarans (and one foil-assisted tri-hull) that we've worked on; universally, the presence of lifting foils always causes an increase in drag at lower-to-moderate speeds...there is a 'cross-over' point at some higher speed where the presence of the foils produces a drag reduction rather than a drag increase. Those concepts that were marginal (or even complete failures) were those where the cross-over point was never achieved..or only barely so.

On the other hand, the use of 'ladder foils' and, more commonly, the variable lift from tapered and twisted surface piercing foils (Rodriguez, for example) has benefitted some fully flying hydrofoil craft over the years.

As for the stability component; other than perhaps a foil system operated by 'balance stick(s)', what other options would one have to keep a HYWAS upright than a system directly analogous to that used on the original craft?

 

To be honest, your state of confusion bewilders me. One of us is missing something here.

If a foil is able to support a hull at it's (the foils) max velocity where thrust equals drag and if that same thrust is inadequate to move that hull from a stand still to that velocity due to hull drag, then it's never going to achieve lift off.

-Tom

 

One of us is indeed missing something..since the most significant portion of the 'hull drag' in a HYSWAS never goes away; it is only diminshed in its rate of increase with speed somewhat as the wetted area is reduce with lift. The upper hull contributes very little since it remains in contact with the water at only very low speeds. Once up and flying..the drag from the submerged hull and strut (and appendages of course) dominates everything.

And all that is why a HYSWAS drag curve really looks little different than a regular SWATH drag curve..the slope in the higher speed region simply not quite as extremely steep as it is witha SWATH. Approx half as steep, of course..but still steep.

Are you perhaps planning to build a 'HYSWAS' that really isn't one?; a hydrofoil, in effect, with the foils attached to a marginally bouyant 'cigar tube'? If that is the case, then indeed, you are operating pretty much entirely in the realm of a full flying hydrofoil craft and not a HYSWAS that is ony supporting roughly half of its total displacement on foils.

It should/could certainly work though. Look forward to seeing it fly.

 

As Bill points out, if you intend to use a hydrofoil to produce lift to "go faster", the hull form must be of a type that has a "lift off" point, ie when the resistance is significantly reduced, or yields a major benefit.

The HYSWAS does not. It does not plan, the purpose of these hull forms is reduced motions. That is achieved by a low waterplane area. The buoyancy is in a submerged tube. All this has a fixed, or near fixed WSA. The WSA wont change with hydrofoils, ergo drag remains the same, so all you're doing is lifting it a bit, thus slight improvement owing to a slightly lower resistance.

The whole raison d'etre of SWATHs and their variants is low motions, ie low waterplane area. Understand that, and it becomes clear...The HYSWAS uses fins for stability owing to its very low waterplane area....the fins provide the restoring force which is absent in the hull form naturally.

 

Mentioned a couple of times in this thread that it is a combination of principles and not just a HYSWAS.

It's a shame I can't get any helpful information out of guys with so much knowledge and experience.

You win, I give up.

-Tom

 

You give up too easily, per'aps. What information are you seeking...specifically?