Proposed: Pet Porpoise for Lady Anne

[larry cottrill]

Here's an attempt at a fast boat design - one of the most fun applications I can think of for a valveless pulsejet. This is very preliminary, as I have no experience in boat design at all, and mods will almost certainly be needed as cooler heads try to bring me back to reality. The idea here is that instead of planing on the hull, the water will mostly be separated from the hull by the jet blast (and entrained air) from the intake. Does anyone know a good reason why this shouldn't work? This design is pretty crude - the hull is flat-bottomed, with a fair size cutwater at the center point to act as an anti-skid surface in the turns.

The Lady Anne for this application would be a special mod, Rev 08, for this application. Both the intake and tail cone are re-designed so the outlet is a wide, flat oval instead of a circle, spreading the gas flow out to cover as much water as possible. This flow (the outflow, that is) is presented to the water through a three-sided "tunnel", which also acts as an eductor to entrain air into the stream. Liquid fuel setup is a tank and sump combo, to avoid air bubble engine-outs.

The engine CANNOT be made by simply flattening the intake and tail cone on one of the Lady Annes already built, because flattening will greatly alter the outlet area. Instead, the outlets here have to be carefully designed to equal the present circular outlet areas - then, a new cone needs to be designed for each of the two pieces, welded up and squashed to the final shape to get that area. This way, the intake still has essentially constant cross-sectional area over its length, while the tail cone area still progresses front the 32mm ID choke cone outlet to the tail end area in almost exactly the same way as in the Lady Anne Rev 07. The new engine will be called the Lady Anne Boleyn Rev08 'Marine', since the revision is especially for this use.

Comments?

L Cottrill

[Rossco]

Hey Larry,
Very nice layout!
Might get a bit hot in the wrong places saddling the engine, but... i suppose this one just cant be to ride on. RC planes have there purpose, although boats.... im of the oppinion that you should go for the fun with them.

OK... Hull design.
Yes, your engine does a lot of the work getting up on plane... BUT.
You will have to rethink your bow and sponsons a little.
Your design is triangle/wedged at the front... get monohull design out of your head. She is not going to look like a cigar, it has to look like a hydro to be a hydro.

The sponsens need to be inline with the direction of movement. The inner side walls are generaly straight, and the outer, up high, turns in to slim to a point at the front. The wedge shape in yours will plough, and "stick" to the water like a magnet.

On the same modification, widen her out! A mono, desplacement hull hangs on to a lot of water for stability, a flat bottom smashes all the peaks off to make itself a smothe surface, although a 3 point hydro... it just bumps, bangs, jolts itself allong, peak to peak!
Infact, you are suggesting a 2 point hydro here... even worse!
If you get it up to any speed whatsoever you will find it in a superfast barrel roll, and out of altitude!

What next... sorry, i dont mean to be all critique, just... you seem to have a great looking idea, although hanging onto a couple of illplaced concepts.

AH, tail plane... Widen it out with the hull, you need a good surface here! I would suggest taking the sweep out of the horizontal stabilizer too. This needs to be very fast responce to small angular changes in attack.
The virtical looks ok, although keep it as big as you possibly can. She's gonna be twitchy, and i can garentee that bottom portion of the rudder wont always be in the water.

Well, theres a start... ill leave you to it for now.
I probably should mention that i did start a similar project a while ago, although the Sabre took over. I have both RC and full scale hulls mostly compleated. (ok, maybe half) Ill see if i can dig out a pic of my hull for you.

Rossco

EDIT, ill grab i pic... and sorry, ive got some more suggestions for you!

[Rossco]

Found a pic.
This is a shot of the rough cutout of the mould for the model, sitting on the full size hull framework.

And, the other suggestions that have come to mind after looking again at your drawing.

The "cutwateter" NO! This is not a yaught!
Get rid of it, you will crash before you know what happened.

Again, turning is all down to the sponsens. The inside edge of the inside of turn sponson hangs on, and the outer slides.
You do need a bit of slide, and then power out of the turn. There is no tilt in a hydro, your turning flat. The whole design is aimed at keeping it flat, even in a turn.

The other is CG... mmmm, hard one. You may have problems with were you have your tanks.
CG needs to be, for high thrust line powered, at the back of the sponsons or aft. When widened, maybe you could have two main tanks either side? This is fairly critical.

Rossco

[Rossco]

ah.... i see, no sponsons.

You need sponsons.
I dont know how your flat bottomed font end would go... but i wouldnt say well. You need as little wetted surface as possible. Water is very sticky stuff, especialy in this size craft.

Even with sponsons, my boats need "air traps" off the end, to extend the tunnel and lift cusion a little further aft.

Now you have me confused!
Ill just shutup for a bit!

Rossco

[larry cottrill]

Hey Larry,
Very nice layout!

Well, thanks, Rossco, you started off very positive!

Then, you discovered the truth in what I said: I am no boat designer ;-)

OK... Hull design.
Yes, your engine does a lot of the work getting up on plane... BUT.
You will have to rethink your bow and sponsons a little.

Of course, you discovered later on that I'm not picturing sponsons at all. Yes, I should have provided a few sections or at least a front view of the boat. But, I was in a hurry to get the idea out there.

... get monohull design out of your head. She is not going to look like a cigar, it has to look like a hydro to be a hydro.
. . .
On the same modification, widen her out! A mono, desplacement hull hangs on to a lot of water for stability, a flat bottom smashes all the peaks off to make itself a smooth surface, although a 3 point hydro... it just bumps, bangs, jolts itself allong, peak to peak!
Infact, you are suggesting a 2 point hydro here... even worse!
If you get it up to any speed whatsoever you will find it in a superfast barrel roll, and out of altitude!.

All right, now we're where we can really start to talk theory. Why is the fairly broad beam of a hydro racer so important? Is it just to maximize stability in the turns - sort of a "wide stance is better" theory? Obviously, I can understand that there is an advantage to having some "footprint" as far from the centerline (lateral CG) as seems practical.

The main reason this hull is so narrow is that I think I can only get so much "spread" out of the intake outblast, and I want that (and the associated entrained air) to take up practically all of the planing zone of the hull at speed. If I make the hull wide, then I'm not really testing the theory of doing that (i.e. of replacing hull planing with ejected gas cushioning). Obviously, I could provide small "outrigger" planes to widen the stance, but again, that would be defeating what I'm trying to prove. Another way to widen it would be to use side-by-side engines feeding into a common "plenum" under the hull, but that complicates things more than I wanted for a "first try".

What next... sorry, I don't mean to be all critique, just... you seem to have a great looking idea, although hanging onto a couple of ill-placed concepts.

Yeah, apparently ...

AH, tail plane... Widen it out with the hull, you need a good surface here! I would suggest taking the sweep out of the horizontal stabilizer too. This needs to be very fast response to small angular changes in attack.

I wondered about that. It's a pretty small surface in relation to the overall plan, but I have no experience to tell me what's really adequate. It might be better to have a "flying tail", i.e. the whole surface rotating in lieu of a hinged "elevator".

The vertical looks ok, although keep it as big as you possibly can. She's gonna be twitchy, and I can garentee that bottom portion of the rudder wont always be in the water.

Hmmm ... that last bit seems like a potential problem.

And, the other suggestions that have come to mind after looking again at your drawing:

The "cutwater" NO! This is not a yacht!
Get rid of it, you will crash before you know what happened.

Why is that the case? True, it is a concentrated drag source. But remember, I'm trying to ALMOST eliminate physical contact between the hull bottom and the water in the planing region at speed. If we're going to turn the boat at all, total absence of contact just won't do. We need something to create side loads in the turns, and that something MUST be low to prevent the boat rolling out from the G force of the skidding turn. To me, the little cutwater "keel" simply takes the place of your straight inner sponson surfaces. Do you basically disagree with this? Either way, you are creating a "point to turn around" by providing the lateral load needed to counter the G force of the turn.

EDIT:
OOPS! I think I suddenly see your point on this one. The lateral load on the cutwater will be INWARD in the turn while the G Force is OUTWARD BUT HIGHER (acting on the boat's centre of mass). Even though the two forces are equal by definition, they form a couple that work to rotate the mass of the boat OUTWARD around the drag point of the submerged fin. Yes, bad news. What would you think of two little "outriggers" that are just thin blades to take the place of this? They would not substantially provide either flotation or planing, but would move the point of contact far out from the lateral mass centreline, which I would think would be a huge improvement (in essence, VERY MUCH like the inner surfaces of your sponsons). Not only that, but if the craft tries to roll out, the outer blade would dig in more so that any planing it provides will tend to counteract the roll. Does this strike you as reasonable?

... The whole design is aimed at keeping it flat, even in a turn.

I think you can see that I understand that, though you probably disagree that I can implement it suitably.

The other is CG... mmmm, hard one. You may have problems with were you have your tanks.
CG needs to be, for high thrust line powered, at the back of the sponsons or aft.

In my case, you mean on or aft of the step. Is this just to counteract the pitching caused by the high thrust line? If so, have yet another look at the plan - in effect, the actual thrust lines (mid and aft) are only just barely higher than having a prop in the water! It seems to me that the static balance ought to be just in front of the step, trying to hit the center of the planing zone actually achieved. Of course, in this case, I have no idea what that planing zone will actually look like - it will vary with the actual speed achieved, of course ;-)

When widened, maybe you could have two main tanks either side? This is fairly critical.

Yes, that would be possible. We could have two tanks, much closer to the balance line, draining into the central sump for pickup by the engine (or fuel pump, if required).

What do you think at this point? Obviously, I am short on theory in this field, but it's fascinating to chew on with somebody who knows what they're doing.

L Cottrill

[larry cottrill]

All right, Rossco, you got your sponsons and no keel, plus larger control surface and sexier front end.

(Of course, they're just sort of mini-sponsons ;-)

What do you think now?

Mate, this is getting to be one nasty-looking watercraft!

L Cottrill

[Rossco]

OOOOh, NICE!
Wig, here we come!

I shall think on the details somewhat before running my fingers off this time. Give it a while to swim a good few laps around in my head.

Im wondering why you want to place so much load on your central rear edge? You have a theory here your not willing to let go... lets hear it.

Also, id like to hear your thoughts on pitch stability. If you look at most hydros, you see an area, the faster the smaller, that is basicaly linear to the water surface in "flight" attitute. You have a fair angle there on your running surface. Is that in conection with the intake cusion? I have a feeling that it could lilt on that edge, and become violent at speed. Id like to see just a little something to flatten that balance curve peak out, something for it to settle into. Which follows onto my next point, if not part of it.

I did like the idea of the side knife edges, there is potential there. Although, do not retreat from your mean outriggers, they are just too cool!
On my hydros, as mentioned, i have "air trap" extensions on the sponsons. I need to elaborate on these. mmm, picture will do better than me waffling, ill draw something up.

Keep thinking on these knife edges, as well as your sponsons. They only need be small, just enough to take a scrape of surface for grip, and give a little side wall to your cusion. Then, you can take the load of that big flat "trailing edge"! Swap the virtical distance of the outriggers to that much bellow the hull rather than above.

Just keep thinking of your aircraft flying with a stream of treakle (i think thats the term?... Golden Syrup) flying at its belly! The tinyest little things make a very big difference. More so that those ones that only fly in the air!

Mean looking craft indeed! Ha, something from a sci-fi flick, even space travel rather than water.

Just give me the word when your happy enough with it, and we shall see what it looks like in rendered, 3D glory! Maybe even some CFD... If im game.

Rossco

PS, i have a great vision of you spinning around on an island, in the middle of some lake! Im just waiting for the line control points to be fitted!

OK, i just cannot help but comment now on those wings... Very, very cool.....but..... they are dangerously far foward! WHEN you get airborn, your going to have two options in a hurry! flip nose up into a stall, and land on its lid, facing the wrong way still doing much speed. Or, your tail corrects and your wings "bite in" pitching you into... well, something a porpoise whould surely do right after its been in the air for a bit!

Just one more edit...

... the high thrust line? If so, have yet another look at the plan - in effect, the actual thrust lines (mid and aft) are only just barely higher than having a prop in the water!

mmm, this doesnt seem to hold true, although i dont have a good theory as yet. Something to do with the surface. Air driven thrust, into air (one i even had below the surface... some thing) seems to give a net upward vector of force to the hull (up into the transome, pitching the nose down) and water thrust... into water or air (hydro jet) seems to be oposite.
As far as i have tested, and can tell without any terribly accurate methods, this is moreso than taken into acount by the line of thrust through, above or below the CG rotation.

[Irvine.J]

Holy crap I want one!
I hope that explains everything!

[larry cottrill]

OOOOh, NICE!
Wig, here we come!

Thanks! I think the second try really was much better.

Im wondering why you want to place so much load on your central rear edge? You have a theory here your not willing to let go... lets hear it.

Also, id like to hear your thoughts on pitch stability. If you look at most hydros, you see an area, the faster the smaller, that is basicaly linear to the water surface in "flight" attitute. You have a fair angle there on your running surface. Is that in conection with the intake cusion? I have a feeling that it could lilt [I think you mean 'lift'] on that edge, and become violent at speed. Id like to see just a little something to flatten that balance curve peak out, something for it to settle into.

Mostly ignorance on my part. In this revision, I flattened out the area just in front of the step, and the bottom region of the sponsons, too. This causes the front end of the sponsons to be significantly lowered.

Keep thinking on these knife edges, as well as your sponsons. They only need be small, just enough to take a scrape of surface for grip, and give a little side wall to your cusion. Then, you can take the load of that big flat "trailing edge"! Swap the virtical distance of the outriggers to that much bellow the hull rather than above.

I think you're saying that the sponsons needed to be lowered, so they plane almost constantly. I have done this, which lowers the nose of the sponson a little more to preserve a nice-looking contour.

Just keep thinking of your aircraft flying with a stream of treakle (i think thats the term?... Golden Syrup) flying at its belly! The tinyest little things make a very big difference. More so than those ones that only fly in the air!

I can just imagine!

Mean looking craft indeed! Ha, something from a sci-fi flick, even space travel rather than water.

Spacecraft only look like that in second-rate sci fi movies. There is no reason for a real spacecraft to have any aerodynamics at all. But, you know this.

Just give me the word when your happy enough with it, and we shall see what it looks like in rendered, 3D glory! Maybe even some CFD... If im game.

That would be fun to see!

PS, i have a great vision of you spinning around on an island, in the middle of some lake! Im just waiting for the line control points to be fitted!

I thought of exactly that, for an unthrottled proof of concept model - except that my "island" would be one of those little pontoon boats with an elevated flat deck, you know the little ones that are only 14-footers or some such. Get it out to the right spot, drop a couple of anchors, and you're all set with your "island foothold".

OK, i just cannot help but comment now on those wings... Very, very cool.....but..... they are dangerously far foward! WHEN you get airborn, your going to have two options in a hurry! flip nose up into a stall, and land on its lid, facing the wrong way still doing much speed. Or, your tail corrects and your wings "bite in" pitching you into... well, something a porpoise whould surely do right after its been in the air for a bit!

You're right, of course. The wings are only there as stressed-skin struts to keep the sponsons from wobbling around. I shifted them significantly rearward, then added top-surface spoilers to kill the smooth flow over the top. Spoilers are wonderful lift-breakers, and they induce only minimal drag. The effective lift surface they wipe out behind them is huge. I also refined the upper part of the fore intake into an anti-lift plane, making the intake a rounded rectangle rather than circular. This also gives more of a "spoiler" effect at the intake ring's rear edge, rather than creating smooth (possibly lifting) flow over the engine chamber.

Just one more edit...

... the high thrust line? If so, have yet another look at the plan - in effect, the actual thrust lines (mid and aft) are only just barely higher than having a prop in the water!

mmm, this doesnt seem to hold true, although i dont have a good theory as yet. Something to do with the surface. Air driven thrust, into air (one i even had below the surface... some thing) seems to give a net upward vector of force to the hull (up into the transome, pitching the nose down) and water thrust... into water or air (hydro jet) seems to be oposite.
As far as i have tested, and can tell without any terribly accurate methods, this is moreso than taken into acount by the line of thrust through, above or below the CG rotation.

Well, I just don't know. It seems to me that a prop at the transom must create a low pressure region in front of it, where this setup should create slightly high pressure at the two jet stream locations. If so, that would be very different, for sure. Some experimentation required.

Holy crap I want one!
I hope that explains everything!

Well ... most certainly.

Another effect of changing the angle of the planing zone is that the bow area was deepened slightly. This allows both the main tank and sump tank to be deepened, for significantly larger capacity. The mid eductor internal contour was also opened up slightly. The planing waterline was lowered just slightly (about 1 mm at scale).

Thanks for your suggestions and thoughtful insights, Rossco. I think this is starting to look like an awfully good boat.

L Cottrill