Auto-Flight, a multihull flight solution

Hi,

Here's a proposal for a simple device for controlling the ride height of a flying hull. This may sound either trivial or impossible, but for $20 in parts, you should be able to fly the windward hull or hulls of any multihull for an indefinite period of time, asleep, in the dark, big winds or light: If there's a way to trim the boat and sails and get that hull up; this gadget will (maybe!) keep it there with minimal attendance, for a very long time. It doesn't use lifting foils, should be extremely tolerant of variable conditions and will work in both small boats and large. Oh, and it's never been tested.

I wrote this for Proafile so it's heavily slanted for proa application, you can see that whole thread with discussion here: http://proafile.com/forums/viewthread/427/ Again, the device isn't limited to proas; it will work with any multihull sailboat.

Auto-Flight
Dave Culp (daveculp@gmail.com)​

Proas are uber-cool. They offer the most bang for the buck, they have least material stress of all multihulls, they have a super-cool backstory—proas have been the fastest sailing craft on Earth for 500 years. Who wouldn’t want one?

Some of the first Europeans to witness proas saw a bit of the “secret sauce” that makes these boats so fast and so fun—“flying” proas. Let’s face it, flying a hull is a blast. The wetted surface drag is reduced by a third. The wracking stresses and wave drag associated with two hulls trying to react to out of sync waves; it all drops away in that surreal few moments—dare we dream minutes?—of flying. AOXOMOXOA dude!

The risk remains though. Flying a hull is flying without a safety net. There’s only a tiny addition in sailforce between flying and capsizing, and for most of us, that’s simply a leap too far. Flying a hull is a little like lap dancing; it looks exciting, it’s something you’d maybe like to experience one day…… but not today.

What if we could automatically limit the flying hull’s altitude to some set height above the water, and never higher—or lower? What if we had a magic box that monitored hull flight all the time, yet let’s us actively sail the boat, when, where and as hard as we like. Our box would automatically ease the main sheet when we fly too close to the edge, yet follow our lead, bringing that sheet right back in as the hull comes down. This box would be Ginger Rogers to our Fred Astaire; we guide and she makes us look fabulous. Slow, slow, quick quick quick.

Yeah, we’re talking about computer control, actively measuring ride height then reacting in split seconds to control sideforce from the rig to sustain and control flight. We’ll need wave followers, we’ll need sensors and CPUs. We’ll need actuators and power supplies. We’ll want both kinds of RAM—computer memory and hydraulics. The system will be expensive to prototype and always susceptible to salt water shorting, but boy oh boy, won’t it be fun?

OTOH, do we really need all this stuff?

Could there perhaps be a purely mechanical “computer” capable of getting this job done? Most autopilots today are electronic computing works of genius, but once upon a time—and for hundreds of years—sheets were lead to tillers and the feedback loop/programmer’s wishes couple which defines “computer” steered our boats across the world’s oceans. Can we maybe pull this off for flying the ama? Go here for the rest of the story

 

Jaja, übercool.
Germans have eben Vorsprung durch Technik, so you use more and more german Wörter vor genauso sein.

pogo

 

Judging by the way the rigging is arranged, it looks like the loads on the blade are expected to reduce as the heel increases, easing the sheet. That may not be the case until the blade is almost out of the water.

There's probably not very much side force generated by the hull, because the boat is light (small displacement) and the hull is rounded (to minimize wetted area). The side force on the rudder is limited because it is at the stern and a large force there will turn the boat. So most of the side force may be taken by the blade.

The total hydrodynamic side force is basically constant, because it has to oppose the side force from the sail rig. As the boat heels, the blade will start to emerge from the water. This doesn't reduce the side force on the blade, though because it still has to produce the same force as before. Instead, the leeway angle increases to maintain the same force. But the force does become more concentrated toward the tip of the blade because the top of the blade is out of the water. This means the moment about pivot will increase as the boat heels, tightening the sheet. Just the opposite of what was intended.

Once the boat heels enough for the tip of the blade to stall and lose its grip on the water, then it will slip sideways and ease the sheet. This will act like a safety valve to dump the sheet just as the boat starts to capsize. The ama will drop, the blade will catch, and sheet in again for an automatic recovery.

Perhaps this is what was intended, if the blade is up against a mechanical stop in normal operation, corresponding to the vertical position shown in the figures. In waves, the behavior could be unsettling, as the boat repeatedly lets go and then abruptly slams back into operation.

 

I write basic code for a small embedded computer called a Raspberry Pi (google it). They have GPIO pins to be able to interact with real world equipment, motors, sensors, logic controllers etc. The Pi costs about $35 and is very powerful while using very little power itself. I have seen projects using a Pi and ultrasonic sensors to check fuel levels in remote tanks by measuring the distance of the bounce back. seems flight adjustment couldn't be too much further away from that. Shame I don't have a "Rave" or something already foiling to test.

 

Tom is dead right; the device must not be the sole leeway preventer. The proa illustrated is a meant to be generic, the auto-flight device and its rigging to the main boom are the show. The specific geometry, with the aft rudderboard all the way down and the fwd one all the way up is not atypical of what actual proas with non-moveable masted unarigs have experienced, cf: Tiny Dancer.

Regardless, the auto-flight device relies on *not* creating all the side-force or it won't work.

Regarding leeway and waves; the device is essentially binary; the hull is either wet or it's dry; the sensor is operating either in water or in air. As initially conceived, the paddle axis was rotated 90 degrees and it was a simple moth-type surface follower--a sensor only, like the ones on moths. Later the axis was changed, increasing the power output a great deal (think horizontal axis windvane autopilots versus vertical axes) Next the size was increased, to perhaps 25% of total side-force generation, which repurposed the sensor as sensor-actuator together.

As with any binary system, there can be "shades" of zero and of one--greater than half-voltage = "1", less than half voltage = "0" in an electronic system for instance. So also in a mechanical binary system. Thus the extended taper to the plan shape of the blade. Now as the blade is withdrawn, force decreases gradually so that the delivered force is attenuated. We're now sensing where the water surface is approximately, rather than precisely.

Leeway doesn't increase (much) because the "main" board(s) are in another hull. As the blade is extracted by the ama's lifting, the center of lift of the blade is retreating from the pivot. This reduces the gadget's leverage and attenuates the actuator force as well.

I'm reasonably confident that the two effects can successfully stop the system slamming from lock to lock, and (perhaps) functionally ignore wave input, "contouring" to average ride height as a steady state. Experimentation is needed, but I believe a single combination of settings can successfully handle most/all conditions where hull flying is possible for a given boat. And the fundamental simplicity of the device is preserved. Experimentation will be inexpensive as well; there just isn't all that much there and tolerances are large.

Dave Culp

 

I get what you are trying to achieve, not sure I have my head around the mechanics though !

Would this device not have a brighter future if promoted/geared towards an anti capsize tool ?

 

Thanks for the post. This *is* an anti-capsize tool. The difference is that it does not "trip" when activated, therefore does not need to be reset. The constancy of the gadget's sensing and output allows us to use it to constantly control the angle of heel/altitude of flight, instead of having a single, one-time tripping event + reset. It is and remains, however, fundamentally a capsize-preventer.

As to brighter future, you may well be right, but over the past 30 years there's been a marked apathy towards capsize prevention--yet all sorts of interest in flying on fewer hulls. ;-)

Dave

 

So I guess the $64,000 question is.......when will it be built and tested ?

 

So, do you have a boat? Do you have access to a boat? Where would you like me to send the drawings? When can you start?

;-)

Dave Culp

 

I have a mirror dinghy at present.

;-)

 

I grant it takes a bit to get one’s head around just what this gadget actually does: It has nothing to do with controlling the course of the boat, and it contributes nothing to lifting the ama against gravity. It simply and only defines the upper edge of the performance window. The helm maintains complete control of all other aspects within that window at all times. It’s a bit like a self-braking car that slows itself if the road ahead is obstructed. The driver can do whatever he pleases at all times, except to direct the car to crash into something. Similarly, the auto-flight equipped helmsman can direct the boat to do anything at any time, except to capsize via over-powering the main.

Dave