Post #19,022
11/20/01 6:08:26 PM
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Oh, so *that's* what it is!
Didn't look at the company link before... Then it's even less than half of my idea. Hey, what the heck, here it is -- if nothing else, y'all can be my witnesses to "prior art" when some dickwad tries to patent it in a few years:
A water motorbike.
That is, it should have TWO waterskis, and no hull.
Yeah, sure, some of us would like a bit of buoyancy -- wimps! -- but that can be arranged; kind of like a bike with training wheels. Just make those outrigger hulls (or pontons) fold up outta the way once you're planing. I've been thinking, manually -- or rather, pedally, since your legs are more powerful -- on the basic models; and power-assisted (electric, hydraulic, whatever) on the "Gold Wing" model... :-)
Those of us with (too much?) hair on their chests will of course forgo the pontons altogether -- I dunno how they'll start, maybe off some kind of ramp down into the water...? Just make sure not to fall over where it's too deep! :-) Yeah, I guess I'm partly kidding... But only partly! Hey, that's one way water skiers start, isn't it? And worse, people ride *snowmobiles* over water!
There are several possible propulsion alternatives: a water jet, why not powered by that popular Mazda Wankel engine; a Volvo "in-out" drive, with an inboard motor and an outboard -- steerable, that is -- propeller; and the simplest to build, I guess, with a regular outboard boat engine. In the last (or both the latter two?) case(s?), I suppose the simplest arrangement for the rear ski suspension would be to make a hole in it and have it slide up and down the vertical power shaft housing.
There, think that's specific enough to stop some possible future Jeff Bezos-wannabe cold?
Christian R. Conrad
The Man Who Knows Fucking Everything
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Post #19,023
11/20/01 6:38:58 PM
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prior art
[link|http://web.mit.edu/invent/www/Waterbike.html|This] is kinda short on details, but looks like what you're talking about.
Have fun,
Carl Forde
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Post #19,024
11/20/01 6:51:25 PM
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Naaah.... Where's the engine?!? :-)
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Post #19,072
11/20/01 10:46:16 PM
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Dunno about 'handling' though..
Rubber / asphalt - one of the most delicate sensibilities is the er *slide* (and for the real Pros who started at age 3 and never stopped) - the two-wheel slide, an actual drift. That ol inner ear just Knows when the rear wheel is starting to move a fraction of an inch. Usually with trepidation on pavement, then rules change for dirt: it's normal and a blast.
Now WATER ummm - WTF could you do to estimate an OK 'radius' vs one which is gonna sink you? (obliquely, as they say). Hmmm - maybe not a good idea to deconstruct it, since logic is Not the way we learn kinetics. So build one and see!
Just have someone on shore with telephoto, OK? so plans can be laid for the Mk II, if'n ya don't come outta the first turn :[
Red October MHD-drive on each pontoon? :-\ufffd
Also - I don't see what this girl's bike is about, how it works - from teeny pic.
Surf's Up!
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Post #19,073
11/20/01 11:03:34 PM
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One aspect of handling
no gyroscopic forces. A motorcycle's lean is at least partially mandated by the gyroscopic precession of the wheels.
There's no analogous force operating on the waterbike. The operator would have to specifically lean it -- and if he (or she) got it wrong, splat, err... splash. Without the stabilizing precession, the thing would be, er, interesting to operate. [I'd try it, if given a chance. Can I, Christian? Can I PLEEEZE (Calvin-eyes) drive your waterbike? PUUUHHLEEESE?]
JetSkis are boats. A stable boat tends to come upright if left to itself; in a turn, it may lean in or out, depending on CG location. Runabouts lean in, big ones (freighters, aircraft carriers) lean out, or "list", in the turns. Consequence of having the water surface be at an angle to the G-vector. Most JetSkis I've encountered have the sort of hull that tends to lean in.
Christian's waterbike would be, essentially, a planing coracle. Now ain't that an image to conjure with --
Regards,
Ric
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Post #19,077
11/20/01 11:55:57 PM
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Gyroscopes? Don't got to show no steenkin Gyroscopes!
What mean?
Rake and trail of forks is the geometry and those #s certainly affect the 'handling' or progressive feel as the angle is increased; CG and the balance of centripetal / centrifugal forces - depending on the sharpness of the turn and the \ufffd coeff. of the tires (tyres): sets the angle of lean.
Easily drawn with the outward --> being the CG (centrif.) force line. At ground, the <-- arrow is the (centrip.) force line of traction F~\ufffdN*. Raise/lower the mass til these are equal and opposite. (Else one falls off) No?
* yeah with modrin techno-mixtures, you *can* exceed 1.0 for \ufffd thru a 'gearing' contact/stickiness. N=normal force vector; gravity assumed.
Guess I don't see much place for worrying too much about precession and such re wheel rotation - til well over the ton (though you Could notice the rocking-couple of a BMW opposed twin, on blipping the throttle hard in a turn, or at idle). Still, the wheels (or a vert. twin's rotating bits) have never seemed germane; can only imagine they would, if the rim were made of iron (definitely if Uranium ;-).
On WATER - what do with those opposing -->s ? What's \ufffd like for a pontoon? Still and all - it sounds doable once you'd unlearned all your road instincts (Hah!) And.. all you Ought to get is wet if -
OK CRC: make three :-\ufffd
Merlin Engine Works
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Post #19,081
11/21/01 12:27:40 AM
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Don't got to show no steenkin Gyroscopes!
Shoo, Ash. Did the experiment with a bicycle once [had been reading science fiction -- remember Commodore Grimes?] Clamp bike frame in vise with front wheel off the ground and free; spin wheel, then rotate handlebars. Bike leans!
Happens the precession couple is just right to help get the thing leaned over. Nifty, wot? -- hard to believe a two-wheeler [well, awright, a simulation] would work right without that force in the mix. And my son's Rice Rocket has a front wheel that's, well, heavy. Rubber tough enough for tires will do that. Plenty of gyro-thingies without needing RPMs in four digits.
But for Christian's machine -- front "ski" needs sortofakindofa complex shape, IMO -- relatively flat in front, descending to a deep V in back; good place for the intake of the water jet, if a good flexible coupling can be found. Back one a little bigger -- idea is, front ski is only partially touching; you want the area in water contact to have the same bike mass / square whatever on both skis. Rear needs a pretty deep skeg, I think. -- and steering won't be by the handlebars; this is gonna be a "lean-only" machine, more like a hang glider than a bike. Let the front ski move against a spring for turns, but it still needs handlebars for the coolness.
Not to hard I think to hide enough voids in the frame that it barely floats. With engine air intake well elevated ["swimming jeep" :-) ] it at least doesn't go full fathom five with each wipeout.
Three, at least, Christian. This is sounding like more fun all the time. Need to get details nailed down, PERT chart properly colored in for delivery next Memorial Day [traditional beginning of summer here in the Untied Snakes..]
Regards,
Ric
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Post #19,084
11/21/01 1:15:31 AM
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Still a gnat or two, but..
Umm - motorcycle mass (of relevant objects) vs those toy bicycles OK? And the angle of lean (however aided or abetted by pesky torque) is still: set by rider on a motorcycle (or bike) er 'commanding' the angle of lean via contrary force on handlebars, positioning body for correct CG height! Checkout Isle of Man -like positions and rapid body shifting, for illustration.
Good thoughts on the propulsion, though steering and powering simultaneously + above matters = time to consult the Cartercopter team for weekend duty? I can't see much way to do the usual prop drive w/o some paraplegic worries and other problems of keeping the sucker in water. Tractor treads a la Pelton water wheel?
But what I really want
Catch Rocketman?
Yeah... rocket backpack + asbestos pants and nice control via say embedded-Linux and my 'palm squeezing' control. Who needs a space-frame? Solid-fuel accessory for those long cruises (throttleable via \ufffd means natch). All the stuff's there - what are we, a buncha Wimps?
Ashton Mitty Tesla
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Post #19,109
11/21/01 11:18:17 AM
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Didn't know that. But, I assume we can do without it?
I mean, I've ridden bicycles; their wheels weigh, at a guess, less than a pound (racing bikes, half that?), so any gyroscopic forces would have to be pretty small compared to your (or especially, *my*! :-) body mass... And bicycles still keep their balance pretty well.
Therefore, it seems to me as if this gyroscopic effect, while apparently beneficial, is not strictly necessary for a "balancing" vehicle.
And yes, I *was* actually thinking handlebar steering.
Thing is, I've heard or read somewhere -- yeah, typical, but isn't that the way it is with a lot of what we claim to "know"? (can't even recall if it was in a bicycle or motorbike context) -- that handlebar-steering kind of *is* steering-by-leaning: If you turn the bars, and *don't* compensate the imbalance by leaning to the inside of the turn, you'll fall to the outside. Now, the claim went, we actually use this effect all the time -- the very *way* we start that inside-leaning, is by (sub-consciously) turning the handlebars the *wrong* way. This starts us "falling" toward the outside of this wrong-turn, which we then utilize as leaning toward the *in-*side of the *correct* turn -- we just follow up by turning the handlebars in the now-appropriate direction, the one we originally *intended* to turn to.
Weird, isn't it? I tried to confirm it a couple years ago, by paying close attention to how I actually rode my bicycle, and by trying to do it this way *consciously*. The results were inconclusive -- it's *damn* hard to consciously monitor or guide your ingrained reflexes! -- but I certainly couldn't *dis-*prove it, anyway.
So, what does this mean, in practical terms, for this particular project? I dunno; could be that I've just ass-u-me'd handlebar steering out of inertia... But maybe it means, at least, that it won't actually actively *hurt* to do it that way.
Apart from the little keel-fins I'm also assuming under each ski (like the ones on regular water-skis and surf-boards -- that is, in a couple of the propulsion scenarios, the rear one would consist of the one on the propeller housing), I've been thinking that by just shaping the skis appropriately, we'd automatically get a correlation between our lean angle, and the angle between the lines they each cut in the surface of the water:
They gotta be rather strongly tapered (or, in extermis, triangular) -- the front one with the thinner end (or the point) forward; the rear one, rearward. Just thinking about it, at first it seemed to me that nothing would stop such an edge from cutting down into the water... But then, that doesn't happen with water skis, does it? (Why not?) Anyway, *if* there is a danger of that, then we can always add vertical up-standing edges to the skis (turning them into something like "trays"), which would then automagically become the second leg of a 'V-shape' when the ski is leaned.
It'd be "a planing c-oracle", eh? Well colour me green and call me Bede, but maybe I can get it sponsored from work... :-)
Christian R. Conrad
The Man Who Knows Fucking Everything
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Post #19,130
11/21/01 12:27:27 PM
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It's called 'countersteering'
And yes, it is how you steer a motorcycle. As Ashton said, you don't learn kinetics intellectually, but this one can be proved. Just get up to about 25 mph on a motorcycle, take one hand off the handlebars, and push the other side with an open palm. (I'm assuming you can catch it before everything falls over.) You will definitely lean in the direction of the bar you just pushed.
Found a good link [link|http://ist-socrates.berkeley.edu/~fajans/Teaching/bicycles.html|here]. He says that the gyroscopic effect is negligible, although he is talking about a bicycle. Motorcycle wheels are quite a bit heavier.
And another link [link|http://www.survivalskills.clara.net/riding_skills_5.htm|here] focussing on motorcycles from an instructor who got tired of answering the question over and over.
I've also done the experiment with a bicycle tire. At the Science Museum in Cleveland and the Franklin Institure in Philly, they have an example of this. There's a rotating stool, like a bar stool, mounted to the floor. Nearby are several different-sized bike wheels with handles mounted on the axle, and a rotating drum you can use to get it spinning. The idea is to sit on the stool holding the spinning wheel upright, then turn it on its side. You start spinning surprisingly quickly. I can't imagine the force of a motocycle wheel/tire at any significant speed not making a difference.
We have to fight the terrorists as if there were no rules and preserve our open society as if there were no terrorists. -- [link|http://www.nytimes.com/2001/04/05/opinion/BIO-FRIEDMAN.html|Thomas Friedman]
PS: I want one of your water scooters, too. Oh, and the girl in the photo is on a rig that is towed behind a boat and allows a paraplegic to waterski. I've seen them used before.
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Post #19,176
11/21/01 5:57:25 PM
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Nice links - and.. so That's how the girl's rig works!
That's clever of her - clearly then, her contraption offers a bit more stability during the crucial phase of coming up out of the water: training wheels for a water ski.
One exception to all of the above: Sidecars!
Vincent in particular, featured an eccentric cam on the (parallelogram girder-fork) linkage, so that rake/ thus trail could be altered with a wrench. While I have little experience with a sidehack, and none with the racing kinda uni-morphs.. you 'steer', not countersteer. Tends to freak out the newbie, coming off of solo. (Also vice versa, when one learns on a hack)
I also saw the Gamaunt 'leaning sidecar' in my youth, driven by the designer. In that scheme, where a parallelogram flex-linkage allows the car's lean to follow the bike's lean: you'd be back to counter-steering. (Alas, never got to try it) Note that certain of the Brit monster singles like the Panther, maybe Norton ES-2? featured usual telescopic fixed rake/trail such that - fine for sidehack work; squirrely when ridden solo.. One size does not fit all.
How odd that, even riders.. had some objections to author's explanation vs. "how they thought they were riding!"
Lastly, I am sure (!) that "the moving center" in us (by whatever name) operates much faster than does / can intellect: if you ever try to control even your car: by methodically applying forces to feet, hands, according to your er physics knowledge - you are apt to lose control (especially at speed). Corrections are 'instantaneous' / simultaneous, once that brain has trained-itself. On a motorcycle at speed, it is indeed a ballet of nuanced muscle pressures all around the body. Musicians describe similar exhilaration after a good performance as do cyclists - after clearing Bray Hill at the ton.
Nice you had a chance to find out for yourself Oh.. and survive that exhilaration-fix :-\ufffd
Ashton Geoff Duke
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Post #19,135
11/21/01 1:11:52 PM
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uh ahem
early jet ski's look like a motorcycle on ski's. You sat in the water, crankit up and tried to maintain equalibrium while going 40 knots or so. Not like these mini boats they call jet ski's today.
thanx,
bill
tshirt front "born to die before I get old"
thshirt back "fscked another one didnja?"
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Post #19,156
11/21/01 2:43:20 PM
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You thinking James Bond?
...Like I did? The oldest example of a "water-scooter" I can recall seeing was on film; Roger Moore, I think. (Possibly in _The Spy Who Loved Me_, 1976, with Barbara Bach, Curt Jürgens, and of course Richard "Jaws" Kiel?) There's this one scene where Bond (Moore in a beige suit, as I recall) comes riding out of the Baddie's (apparently maritime) lair after having filched the all-important Secret Plan, on a thing that looks a little like a Vespa (only ever so slightly boxier). My disappointment at never seeing anything like that again, and at the -- as you so correctly point out -- "mini boats they call jet ski's [sic; ski's what?] today", when I first saw those in the eighties... May well have been (heck, *was probably*!) why I started thinking about how one could build something "*really* motorcycle-like" to run on the water.
Thing is, though, when I later saw that Bond flick again (they had a Bond festival on one of the TV channels here a couple years ago; that's possibly when I saw it), I made a point of looking at that thingy as closely as possible... And it was actually one of those "mini boats" too. It only *looked* "like a motorcycle on ski's" [sic; ski's what?] -- but it actually *had* a hull behind that broad flat front ski! (Only one thing puzzles me: The rear hull was almost completely submerged, even at speed and obviously aquaplaning -- so how the heck did Bond get on it and up to speed, *with his suit _completely_ dry*?!? At least the cuffs of his trousers ought to have been wet!)
Christian R. Conrad
The Man Who Knows Fucking Everything
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Post #19,182
11/21/01 6:24:01 PM
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Heh.. have to dig out some Vincent lore.
I don't know if they were first (though I'd like to believe that - allegiance and all), but near the end of Vincent's run ~'55, they produced something called a 'Firefly'. That was ~ a moped-like thing and certainly not successful enough to stem the blood-flow from the expense of making the big singles, Vee-twins, and trying to compete with the Corps via clapped-out WW-II left-over machinery. {sigh} Of all sad words of tongue or pen, the saddest are these: it might have been.
But I also recall this engine being put into a water contraption, another possible venue for survival. Next I see I have to get the story straight. When I first heard it - I'm sure there was nothing like an industry (as for today's toy-affording mass). That's why I remember it as a 'first' or at least near-so. Prolly it had a hull too, as a dim pic swims into the fog.
Anyway, I'd like it if Phil Vincent did come up with a First, however a bit prematurely / simultaneously.. too late :[
Ashton
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Post #19,290
11/24/01 11:27:24 AM
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nope, thinking nancy lake.
My buds in Alaska have been using these extremely annoying craft for years. the older models look more like a scooter than a bycicle, the handle bars are on a pivot at the base for up and down motion, there are unstable and fast as hell. Even the best swimmers (like myself) wear a life jacket because it is easy to go ass over tea kettle and smack yer head on the hull at 40 knots. I google but could only find pics of the newer ones.
thanx,
bill
tshirt front "born to die before I get old"
thshirt back "fscked another one didnja?"
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Post #19,641
11/28/01 11:36:43 AM
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Ah... She any relation of Ricki's? But:
1) Those are definitely later than Bond's "Vespa"-style[*] one too; I saw the film in the mid-seventies, and the first commercial ones appeared in the early eighties or, at best, the *very* late seventies.
2) And they're boats too; they just have a low enough hull that you don't much notice it, but a hull is still what it is.
[*]: Oh, and just to fuck up your language centers a bit more, a "Vespa-style vehicle" _I_S_ "a scooter" in most languages; you were apparently referring to a "kick-board" or "stand-up-on-it-and-kick-off-the-ground-cycle"?
Christian R. Conrad
The Man Who Knows Fucking Everything
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Post #19,484
11/26/01 11:39:51 PM
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Bombardier
First JetSki (it's a brand name, but I don't recall if the brand is the one applying to this) I ever saw was from Bombardier, of snowmobile fame. It was much as you describe: a minimal hull with engine, etc., and a ski (Pair of skis? Been too long) in front, steered with handlebars. IOW a snowmobile with a boat hull instead of the track in back. They were, errr, interesting to operate -- "squirrel in heat" was how a friend characterized it. It was, in fact, thinking back on that gadget that got me wondering if the gyroscopic effect wasn't more important than you might think.
Countersteering -- the half-motion you make before starting a turn on a motorcycle or bicycle -- did not work. You absolutely had to lean into the turn before starting same, or you wound up in a high-speed version of what happens when an unskilled skipper tries to weather ship instead of tacking in a sharp blow. As in, *splash*. It never quite happened to me, but then I was too timorous to get it up to full bore. My friend Tim did quite a good impression of a flat stone for a few moments there...
I don't have either the computer horsepower or the skill set to model it out, but seems to me you want Christian's triangular front ski, with the pivot set well in front of the center of pressure. Turning the handlebar puts the lift point outboard of the direction you want the turn to go, and it leans more or less automatically. The back one; hm. My first thought was point-forwards like the front one, but if you made it point-aft, and let it rotate along with the front, you'd double the forced-lean effect.
And no, I can no more tell you what I do to get a motorcycle to turn than I can fly without mechanical assistance. Over there gets filtered directly through the inner ear and medulla oblongata, without interference from that pesky low-MIPS gray stuff! Most any hand-eye-body coordination skill is about the same; if you have to think about it, you can't do it. ObSciFiRef: the boys in Heinlein's Rolling Stones, who couldn't believe their father (or anyone) could possibly solve the integrals fast enough to play baseball... when he maintained he could, they protested that, having been brought up living on Earth, he had a distorted notion of physics :-)
Regards,
ric
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Post #19,642
11/28/01 11:47:20 AM
11/28/01 11:52:24 AM
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Coupla points...
1) Kawasaki. I'm pretty sure of it, "Kawasaki JetSki" just sounds so right. (Not that it actually *has* any skis at all, AFAIK...)
2) I dunno if countersteering should work or not; I figured out the tapered/triangular shape just by trfying to visualize it in my head, what shape it would *have* to be for the inner edges of both skis to conform to a horizontal plane when the whole contraption is leaning to the inside of a turn... Might even mean that you'd have to steer *into* the turn directly, for all I know. Will think about that some more.
3) Why "pivot set *well* in front of the center of pressure"? I could understand a *little bit* in front, to stabilize things (and I was actually assuming that), but... Setting it "*well* in front" would only make it harder to get the damn thing to turn, no?
[Edit: Added point 4; forgot about that first. Previous #4 bumped down (up?) to #5.]
4) Yup, I was planning to have the rear ski *and* the front one pivot. Actually, at least in the propulsion-by-outboard-motor scenario, if you'd want only the one ski to pivot, it would probably be best to make it the rear one.
5) That reminds me, once again... I belong in outer space! Never could get the damn trajectory of a ball right in a gravity field.
Christian R. Conrad
The Man Who Knows Fucking Everything
Edited by CRConrad
Nov. 28, 2001, 11:52:24 AM EST
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Post #19,685
11/28/01 7:29:39 PM
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Pivots
Yeah, I think Kawasaki is right. Ah, well, Rice Rockets aren't precisely interchangeable, but they have a lot of common features. 3) Why "pivot set *well* in front of the center of pressure"? I could understand a *little bit* in front, to stabilize things (and I was actually assuming that), but... Setting it "*well* in front" would only make it harder to get the damn thing to turn, no? Depends on definitions. I was trying to combine your desire for handlebar steering with Ash's wish for lean steering. If the front ski is triangular, then as the thing gets up on step the center of pressure will move back, because the part that isn't in the water will only have airflow over it. You're going to want the pivot to be forward of the center of pressure in all circumstances. Then, when you lean, the CP provides a side force that turns the handlebars. OTOH, if you turn the handlebars, the CP moves to the outside of the turn, and applies a force that tends to make it lean. As I said, I haven't either the MIPS or the smarts to model it, which it needs before anybody starts laying fiberglass -- And I really think the outboard motor version is a nonstarter. It needs a jet pump, with the intake in the rear ski (which will carry most of the weight). Christian, would you be willing to compromise on a hydrofoil? The rear "ski" would instead be a pair of fins sticking out of a vertical strut. It would solve some problems [while introducing new ones, of course]. Among other things, differential trimming could provide forces in pretty much whatever direction you wanted, and I've been searching (and failing) for a righting force once the bike is leaned over, other than centrifugal; far as I can see, the best you can do with a two-ski gadget is metastability. Regards,
Ric
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Post #19,699
11/29/01 10:31:59 AM
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The Higher School of Aquatic Engineering. (Didn't go to it.)
Ric ochet: [Quoting me]3) Why "pivot set *well* in front of the center of pressure"? I could understand a *little bit* in front, to stabilize things (and I was actually assuming that), but... Setting it "*well* in front" would only make it harder to get the damn thing to turn, no? Depends on definitions. I was trying to combine your desire for handlebar steering with Ash's wish for lean steering. Ah, OK. If the front ski is triangular, then as the thing gets up on step the center of pressure will move back, because the part that isn't in the water will only have airflow over it. What do you mean, "on step", in this context? I was envisaging pretty much flat skis, not "stepped" like some mid-twentieth-century racing boat hull. If you mean, "up and aquaplaning", then it'd actually be the other way around, since you obviously want the skis spring-loaded to have the forward tip up and possibly out of the water when you're not planing -- so when the weight goes onto the skis, this spring-load is eliminated, the front tip (well, the front *part*, if not the very *tip*, which is probably curved up) settles down onto the surface and moves the center of pressure *forward* compared to where it was with the tip out of the water. If you mean, "leaning into a turn", then AFAICS, the answer is: "Probably not -- rather, quite the opposite". In fact, what would happen if you *didn't* taper off most of the front end of the ski, and widen the rear of it... is that the rear end of it would rise out of he water as you lean into the turn, the front end would cut down under the surface, and you'd get an almighty fuck-up because the center of pressure moved entirely to much *forward*. Exaggerated example -- say we're turning left: Front end of ski goes left and rear goes right, we lean left into the turn, left becomes (to some degree) down and right up -- so rear end of ski is poking up outta the water and front end pointing sea-bottom-wards. To keep the direction of the edge of the ski we're now riding on -- the left half of it, more or less -- parallell to the surface, we *have to* slice off most of the left-front part, and add material to the left of the left rear. That will (in the ideal case, at the correct combinations of turn-in and lean) keep the center of pressure -- exactly in place. In pure-geometry terms, the proportion of a triangle that is to one or the other side of a point at X percent of the *height* of the triangle stays the same if we slice the triangle vertically *or slantwise a little off-vertical* if we slice through the *top point* of the triangle. Draw some (upward-pointing, approximately horizontal-base and vertically-symmetrical) triangles for yourself and see. An extension of this concept would be, as I think I alluded to elsewhere, be to have raised edges to the ski, which aren't in contact with the suface. As an extreme, say we have a 90-degree surface standing vertically, straight up, on each side: |______| ... (At the thinner end, the front, it's |_|) ... Going straight forward, not leaning, only the flat ______ surface is in contact with the water. Now say, still extreme-example, we lean 45 degrees in a turn to the left. The "L-shape" of the left edge *now becomes a V-shape*, as the upright left edge comes into play. Generalize that, and we see that a couple more "kinks" (the "step" you were talking about? Naah, hardly...), of something less than 90 degrees, would probably be better. Continue generalizing, and the bottom of the skis becomes curved cross-wise; go all the way, and our whole skis probably become conical segments, or something... You're going to want the pivot to be forward of the center of pressure in all circumstances. Yeah... For the front ski. How does this work for the rear one -- do we want the same thing there, or just the opposite? Anyway, as I've hopefully (but not probably) shown above, a tapered (or in extremis triangular) shape would accomplish that "automagically". Then, when you lean, the CP provides a side force that turns the handlebars. OTOH, if you turn the handlebars, the CP moves to the outside of the turn, and applies a force that tends to make it lean. Yup, think so... As I said, I haven't either the MIPS or the smarts to model it, which it needs before anybody starts laying fiberglass -- Fiberglass??? What's wrong with steel, or if you want to be fancy, aluminium? Remember, we are *_N_O_T_* building a boat hull here! (Or maybe *you* are, but *I* sure wasn't... :-) And I really think the outboard motor version is a nonstarter. Why??? Remember, I wasn't going to hang the engine off the rear ski, but the other way around... The prop wouldn't be at the end of the ski, but somewhere under the middle of it. What's wrong with that? It needs a jet pump, with the intake in the rear ski How is that different from a propeller, in principle? My very first idea was based on a water-jet pump, yes... But I was thinking, hang it under the *middle* of the contraption, poking down into the water (powered from above) on its own, quite separately from *both* skis. Can't remember why -- probably just the first thing that came to mind, perhaps because of some naive desire for symmetry. (which will carry most of the weight). Possibly, but not necessarily. Depending on how far forward you sit on the contraption, and the distance between the skis, you could get a weight distribution pretty close to fifty-fifty. Would that be a bad thing? If so, why? In the inboard-motor scenarios (like the mid-mounted water-jet, above), we could probably even get most of the weight on the *front* ski, if we wanted to -- not that I can see why we would want to... Christian, would you be willing to compromise on a hydrofoil? The rear "ski" would instead be a pair of fins sticking out of a vertical strut. It would solve some problems [while introducing new ones, of course]. Yes and no: Yeah, sure, that would be fun! But no, that would be *another* thing, that I'd like to *also* try -- a complement, not a replacement. Among other things, differential trimming could provide forces in pretty much whatever direction you wanted, and I've been searching (and failing) for a righting force once the bike is leaned over, other than centrifugal; Why -- isn't that enough? What more do you have on a motorcycle? far as I can see, the best you can do with a two-ski gadget is metastability. Uhh... What's "metastability"? Sounds kind of like what you have on a bicycle or motorbike, or for that matter, on a single waterski. And if that's what you mean, then it's *exactly*... What I *want* to achieve! Christian R. Conrad
The Man Who Knows Fucking Everything
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Post #19,730
11/29/01 3:42:38 PM
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A land-based conundrum..
I can't 'see' any further into the general problem than what's summarized above. Your more extensive analysis forced me to review what I (thought I) knew re cycle dynamics.
I haven't retained most of the elegeant essays in (old, UK) mags like The Motor Cycle and Motorcycling - dunno if these mags even survive there, today (?) I used to subscribe to both. In US - ___ Jennings-like authors (believe he's a car-type guy) probably refined the earlier notions a bit, but I don't recall *anything* which "made cycle design er Simple" to grasp.
Ex. Dick Mann, a notable track, scrambles all-around Ace some years back - was a friend of a cohort of mine. He was famous for pithy quips about such matters. One I recall re a Ceriani fancy fork assembly (with 28? different adjustments re rake, trail, fork damping etc. etc.) was in his style ~ Yeah and ya can get about (28!-1) screwed-up settings outta all that.. Let's go climb Snotty Hill and see..
Anyway, he designed frames, forks - raced them and sold them. Land stuff with the above er 'metastability' seems ~ about the inherent pseudo-balance of a cycle - esp. when sliding. Reminiscent of the cone as illustration of "degrees of freedom" in a geometry: Stable is on flat-end; conditional on side, where it can roll. And then we have the Famous Analogue of Windoze "stability":
-*-
{{\\______/}}
___\\____/
____\\__/
_____\\/____
//////////////
_*_ = a fly about to land
Cycles are of course more stable than Windoze or - we'd all be dead. So omit the fly effect: there is a 'conditional stability' even in sliding-friction mode - until \ufffd happens to change abruptly (oil, leaves, gravel). Always amazing is - how fast! is the 'instinctive brain', especially in the Aces (whose boots I am unfit to run over). But that is not instantaneous, even amongst the mutants.
What I cannot envision is - the 'way' that these behaviours can be translated to water! where "\ufffd" is as evanescent as.. integrity in a 100 mile radius of Redmond. What I mean is - *this* appears to be where the cycle model goes Nutzo.
My guess - the folks engineering the Carter Copter most likely had similar fits in envisioning dynamics in YAN fluid: more so than mere water - and that had to include the lo-speed passages from ground to airborne, controlling of yaw, pitch etc. at near 0 ground (not rotor) speeds.
I suspect that a lot of trial and error - mostly error would precede a rideable device (less'n one cheats and tosses in a gyro! with a Humongous MK\ufffd !)
But maybe you're getting some stuff I'm not ..
Happy sleuthing,
Ashton
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Post #19,751
11/29/01 8:32:00 PM
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Metastability
is when it doesn't particularly want to go anywhere on its own, but if an external force intervenes -- Ash's fly, or (in the case of Windows) either trying to do something with it, or the simple passage of time...
My version of the front ski was triangular from all directions -- long and skinny with the tip chopped off from the top, inverted isosceles from the front/back, and flat on top/deep aft from the side, for exactly the reasons Christian (who has plainly thought more deeply about it than I) gave. The back ski is roughly the same shape, but deeper to accommodate the water-jet's intake.
Yes, the engine goes in the middle -- it's supposed to be a motorcycle analog! I simply thought that the engine lower unit of an outboard would be too much of a keel. We don't want to restrict the thing from sliding sideways! If we do, it's going over toward the outside of the turn, like a fatass freighter in ballast taking a turn too quickly, or an inept sailor weathering ship in a blow that's just a little too strong --
Therefore a water jet; engine properly between the knees, pump just under the saddle, ejecting the drive jet from the back. From a black-chrome trumpet :-)
And Ashton, this thing is continually going to be in side-slide mode, more like a dirt-tracker busking dunes than anything on a highway. We need the crosswise flow to create a roll couple that holds it up when it leans. No winding in and out of cones here, especially at speed, and the turning radius will be ::ahem:: fairly large -- not that it matters. Motorcycles need a short turning radius so they can stay on the pavement, absent gravel patches (my elbows remember!) and spots of ice/grease/water. Our machine has the whole lake to skid in.
As for fiberglass -- the frame should be made of *tadaa* welded tubing (Duh!), but the skis will be moderately complex shapes. Fiberglass (or carbon fiber composite) are the easiest way to do that, especially since it's possible to quick-and-dirty them on male armatures -- I strongly suspect there will be several iterations before the optimum shape emerges!
Regards,
Ric
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Post #19,766
11/29/01 11:29:17 PM
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LRPD's eval: IWETHEY's Terrible Horde of Epithetic Yammerers
(No doubt the Great Oracle approves of the Beastly refs.)
OK - 'dirt track' I'd guess too; none o' that IOM precision dicing. So: since the shape has to somehow accomplish that which human lore + feedback does on land, umm where shall the skill enter in? T'would seem that, overcooking a 'turn' would result in merely.. increasing the turn radius automagically / not elbow burns (splashes?)
But then.. I have little feel for What those folks do on water anyway - except with water skis it's apparent where the skill is needed, just to stay up. Played a bit with a speedboat at Tahoe once. Cute but tame, and seems to bring out the vandal-mind in most practitioners (and.. did I mention noisy?)
Hmmm .. guess my Interest would be more in the vein of a video clip ~ 3 years back, about a (local!) guy developing a personal submarine! Lie prone in a tube; imagine an optically kewl paraboloid front. Don't recall max depth he was aiming for, but it was in hundreds of feet. Maybe even deeper.
Alas, such a thing would be unlikely to reach prod. levels where anyone could afford it - but imagine an entire new world to explore, without the rigors of Tri-Mix and the usual SCUBA training and hazards. (Not to worry: exceed crush depth and.. no time to worry.)
He seemed to think he could make a commercial one, though obviously not into the plan for usual bizness reasons. Physics + new materials - under $20K? Don't think I heard his hoped-for price. 3-D: now That's what a watercraft *ought* to do !!
Ashton Beebe Verne
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Post #19,771
11/30/01 12:24:16 AM
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Thought that was "Pathetic Yammerers"
[link|http://www.aaxnet.com|AAx]
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Post #19,781
11/30/01 8:37:45 AM
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It is
But see, since we are an eCommunity, we are ePathetic. And ePedantic.
When I visit the aquarium, the same thought keeps running through my mind;
Leemmmooonnn, Buuttteerrr, MMMmmmmmm good!
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Post #19,816
11/30/01 4:28:57 PM
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LRPD be versatile as well as prescient..
empathic
epithelial
eclectic
ecdysiastic
ecoterroristic
euphemistic
eulogistic
eutectic
endo-European
enneagrammatic
eucharistic
euphonious
Euripidean
expropriating
extricating
edifying
excommunicating
exasperating
endodontic
effusive
ecStatic
erroneous
ectomorphic
efficacious
egregious
eigenfunctioning
extraterrestrial
ejaculative (hey! that's about words)
ejective
emending
ebullient
eponymous
and..
ecumenical
(But only on Fridays)
All Hail the Llanthropythical Elll Arrrrgh Pee Dee !!
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Post #19,838
11/30/01 8:19:33 PM
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Where's the skill?
OK - 'dirt track' I'd guess too; none o' that IOM precision dicing. So: since the shape has to somehow accomplish that which human lore + feedback does on land, umm where shall the skill enter in? T'would seem that, overcooking a 'turn' would result in merely.. increasing the turn radius automagically / not elbow burns (splashes?) Well, now, don't think even a Beowulf cluster (still current?) would be able to model the thing well enough to eliminate the skill. Too much lean? You get wet, with a strong flow up your nose (that is the direction it's going). Not enough, a-over-t -- call me skippy... And despite the utmost efforts of able engineers, the surface of the water is not a plane. Related story: A friend in high school once had a boat made of two pieces of marine plywood and a few sticks of 1x10. Build a wedge, 10" thick at the back, then cut the front out in a semicircle. Power was an old "seven-horse" Evinrude, from the days when outboard racing was by manufacturer's advertised horsepower. Change the reed and the jets, and it was more like fifteen. Directional "control" was the skeg of a broken slalom ski, screwed to the bottom in more or less the center... we were out on the lake one day, with plenty of fuel, and another friend was driving it. Probably thirty MPH across the water -- and a Chris-Craft passed across his bows at about ten knots. Have you ever seen the bow wave one of those puppies puts out? Boat climbed the wave, went airborne, then (against all expectation) began nosing over instead of flipping bow-up. Thin end of wedge entered the other bow wave, more or less perpendicular to the water surface. plurg!Hardly a splash. Tim had on a good life preserver, as evidenced by the fact that he did bob to the surface eventually, as did the boat (though quite a ways away from the, er, scene of the incident). Don't think the nabobs in the Love Boat ever noticed anything... The boat was retired to pontoon duty on our fishing trips. Ah, youth. Regards,
Ric
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