Alternative take on hull design.

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orion

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No - the design discussed in the referenced PDF document is a cavity hull. They are very good but require relatively calm water to work well. There have been several companies world wide that have done quite a bit of work with this design, including build some sizable craft. The last paper I read on these was a Russian project circa around 1995 or thereabouts - the data therein clearly demonstrated the decrease in performance as the sea state got more agitated.
 

hogheadv2

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My thought lead to a less tall / aggressive hydofoil. A plane does not need to ride feet over the waves all of the time. Cut into the water at landing and help lift and cut out at take off. A few inches to a foot depending on the plane size and surf intended. What is lost due to the drag of the protruding and aerodynamic hydrofoils can be reclaimed in a slicker hull.

http://www.hanleyinnovations.com/multisurface/msa_hydrofoil.html
 

Aircar

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I just discovered this thread --which now makes sense of a question about seaplane rotation asked of me on another -- (also just read several of the links posted by Autoreply of Orion's writings and designs on the 'affordable airplane' and 'hulls' --the link to here ;-- very much agree with the summarising of the present backward state of the GA technology --we should have a thread to ***** about that in technical terms .

Amphibians have a special quality that nothing else in aviation quite matches --namely you can really get back to nature . gliders occasionally make an unintended visit to some piece of real estate somewhat off the beaten track but always in relatively 'civilized' and most probably amongst cultivation at least (or grazing country ) --and the recreational value of hot flat tar or concrete is very small. (What's that I hear? -your'e saying 'MAKE IT ROADABLE ?--and get off that bloody miserable airport and find somewhere that is actually nice to be -- drive it up into the mountains or to the seaside or?' ....... look this thread is about amphibians so stick to that rather than why you want to get onto the water in the first place. Oh, you can have a roadable amphibian ? Hmmmm.

I worked for a gentleman named Dick Schreder who was a second world war Martin Mariner captain (and in fact the first American to sink a submarine from the air off Bermuda --got the DFC for it , He was also assigned to test the huge Blohm and Voss eight engined flying boat taken by the allies in Norway . I went flying him with him in his Lake Amphibian and decided that an amphibiam made the most sense as a recreational aircraft and that THIS area of design was the most backward and had the most to gain from applying 'modern' design concepts and materials to --in the mid 70s . that was the start of the Opal which was designed to be amphibious and avoid the terrible drag,noise and handling drawbacks of the standard "motor on a stick" type small amphibian ( a far worse embodiment of the same layout now featured in self launching gliders less the retraction feature ) -- I wrote to molt taylor about his amphibian work plus shaft drive plus --less then - the Aerocar concept and in a way ended up combining all three .

The heyday of seaplane and amphibian research was the fifties when the aircraft like the Convair Tradewind and the Jet powered sweptwing Coronado ( might not be the right name -need to check ) the Ryan Seadart jet ski and all of the basic ideas were tested before being all dropped (like the VTOL wave in the same time period) and we have been mining the same pool of data ever since . --the configuration I settled on for the Opal was for a fin mounted rear pusher with a "beavertail" (platypus perhaps) rear fuselage and fold down spray suppressing panels --that is why the rear fuse was straight lines but had been 'coke bottled' as a glider . I came to the conclusion that a very much lower wingloading and higher CL were the neccesary major innovations required to make a viable amphibian (not yet then incorporated into the Opal which used large fowler flaps,spoilerons and a mid wing with mid wing outrigger wheels/float and centreline undercarriage (see photos posted earlier ) -- and for the hull In think that a multifluted -fore and aftwise hull that is a sort of tension field can get the lowest weight and softest impact

better end before losing this --cont
 

Aircar

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Among the first things I made (while at school) , bigger than small model gliders, from fiberglass, were canoes and the first one was made from a "half" boat (as if 'cut' in half crosswise in the middle --giving two 'ends' )that acted as a plug to make two identical molds from that bolted together in the middle for the lay up of hull and gave the neccesary part release .

Only the shaping of one half of the boat had to be done this way and I had made that from steel sheet spot welded and roughly formed before filling and finishing and taking off the molds -- as a result I had a watertight "half canoe" and decided to enter it in the end of school year 'anything that floats' race across the Murray river and back .
With many 44gallon drum rafts and the like as competition --lots of flour bombs and dunking etc but I thought 'this will be easy'..., as soon as I started to row a problem appeared --the bloody thing would NOT proceed "pointy end" first since it acted like a 'fin' up front ahead of the centre of bouyancy and wanted to swap ends (lacking the rear half of the boat to keep the centre of bouyancy and CG close ) --it would only work if I reversed the set up and rowed it blunt end first .

The lesson is perhaps pertinent to some of these high finess ratio and high deadrise hulls with enormous projections forward (just a few posts back) -imagine such a hull encountering a wave at speed --it may well be that the trough is under the main hull while the nose is entering a wave at an angle and hence be unstable in yaw . Not a good situation and in the air the same directional destabilizing applies .

The best thing that any amphibian can do ( to lower the take off power needed ) is reduce the step speed -- and that requires a really low flying speed (the rho being 800 times higher PLUS the drag as the SQUARE of speed adds up to batter flying boat hulls like buggery) once again I find a commonality of the desiradata for flying cars (and ATOL,) soarability and water flying - a "morphing" or highly variable geometry wing.

On water the aircraft is also supported on a 'compliant surface' not on wheels (as is the case for ATOL by suspended cable arrays ) and much the same configurational constraints apply . The very low wing loading and speeds possible by VG also suit the soaring aircraft and ATOL/roadable mission --for a single seater all three are acheivable in the one package --two seats with only a little less efficacy and two out of three for a few more seats ) - a recipe for a desirable flying machine perhaps?

IF we are ever going to have affordable aircraft and therefore to sell them in large numbers then they have to be appealing to the general public and in that respect the boat and being on the water already captures the imagination of a wide segment of the population (on a hot day people head for water almost instinctively or even just to be near it --all cities need a source of water nearby )

After the cacaphony of a barely muffled high powered amphibian in flight (blunt engine nacelle and mostly pusher props) then in "landing", the pummelling of the waves on the hull and the deceleration and splashing,spray etc it is almost surreal to turn off the motor and have almost silence or just a bit of gentle lapping of waves on the hull and then to have ducks return to their business ... that is what it is all about....

(oh and somebody 'knocked' the flying submarine idea a while back --the DARPA call for solicitations revealed that as a wet submarine this is more than just a novelty and perfectly do able --might even lead to the breakthrough personal vehicle by default )
 
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orion

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My thought lead to a less tall / aggressive hydofoil. A plane does not need to ride feet over the waves all of the time. Cut into the water at landing and help lift and cut out at take off. A few inches to a foot depending on the plane size and surf intended. What is lost due to the drag of the protruding and aerodynamic hydrofoils can be reclaimed in a slicker hull.
Hydrofoils have been tested numerous times, usually with less benefit than imagined or with simply catastrophic results. Issues including increased draft, inadvertent contact with the water and contact with floating obstacles, all seem to work against any hydrofoil configuration's successful integration into a marine aircraft. Furthermore, scenarios like even minor obstacle impact generally result in catastrophic damage to the hull from either the support structure tearing a hole or a broken foil impacting and penetrating some portion of the hull bottom. Virtually all seaplane programs have pretty much concluded that hydrofoils will not be accepted by pretty much any seaplane operator.
 

orion

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.... the Ryan Seadart jet ski
The SeaDart was Convair's. Knowing what we know today, the SeaDart was a great example of how not to design a ski-based seaplane.

And BTW, probably the best authority I know on hydro-skis is located in your (Aircar) part of the world. As I'm writing this his name blanked in my head but last I heard he was in Christchurch, NZ.
 

hjs

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Have glanced trough the website information and of some reason I start to think about the "dromedille" design by Bror With.

After reading the text "Båt med midskeps interceptor", is the basic physics behind this the same as the stepped hull physics?

Himat

I found nothing that showed me how Dromdille works. I would be grateful for more information. Send directly to my e-mail.

Midship interceptor, cambered step, common step and common planing boats works completely different. They are therefore calculated in a totally different ways.

A common seaplane bottom shall be calculated as a normal planing boat, even if it at first glance looks like a boat with a step. The big difference is that the boat has constant weight while the weight of the aircraft is taken over by the wing lift as the airboat picks up speed.

This must be included in the calculation of lift, buoyancy, resistance, angle of attack, pressure point and moment. In addition, one must take into account that the angle of attack and the stability can be controlled by the aircraft's stabilizer and wings.


js
 

autoreply

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The lesson is perhaps pertinent to some of these high finess ratio and high deadrise hulls with enormous projections forward (just a few posts back) -imagine such a hull encountering a wave at speed --it may well be that the trough is under the main hull while the nose is entering a wave at an angle and hence be unstable in yaw . Not a good situation and in the air the same directional destabilizing applies.
Wouldn't you solve most of that problem if your floats/pontoons are wave-piercing?

If you remove the "negative V-fairing" of the pontoon you have a pontoon that's close to round in it's cross-section, with low (sideways) projected area and low sideways lift if it's not aligned with the waves or you have a drift angle on landing.


I'm not sure I fully grasp the "midship interceptor" idea. Wouldn't it have similar wetted area when planing as a properly designed planing float and thus also comparable drag?
 

hjs

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I'm not sure I fully grasp the "midship interceptor" idea. Wouldn't it have similar wetted area when planing as a properly designed planing float and thus also comparable drag?


The point of increasing the lifting force with an interceptor or a cambered surface is precisely that the wetted surface can be minimized. The lifting force can be about 80% higher and therefore corresponding less wetted area. In addition, there is also that the center of gravity of the boat can not be moved, thereby is a normal boat's performance optimal only at one precise speed and load.

A planing surface lifting force in the water depends on its size, shape and angle of attack. A water skier can move its center of gravity to suit the optimum angle of attack, then drag-lift ratio becomes about the same as a normal hydrofoil, ie around 1:10. This is about the same glide ratio I can get with the interceptor or the cambered surface. A boat with a normal V-bottom usually has a drag-lift ratio of 1:4 to 1:5, but mostly worse than that.


js
 

orion

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Wave piercing hulls are great but only for limited application. If you land a bit cross ways for instance, you could find yourself upside down real quick. Their optimum L/D also decreases with speed since the wetted area is relatively constant as the craft accelerates. There is a possibility that this could be designed to work well with a wing but that's only a guess. I think the practical considerations might make it an inoptimal choice.
 

Himat

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The heyday of seaplane and amphibian research was the fifties when the aircraft like the Convair Tradewind and the Jet powered sweptwing Coronado ( might not be the right name -need to check ) the Ryan Seadart jet ski and all of the basic ideas were tested before being all dropped (like the VTOL wave in the same time period) and we have been mining the same pool of data ever since .
Where you thinking about the Martin P6M Seamaster?
http://en.wikipedia.org/wiki/Martin_P6M_SeaMaster

Sweept wing, jet power seaplane. The only such plane made in the USA.
 

Himat

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Wave piercing hulls are great but only for limited application. If you land a bit cross ways for instance, you could find yourself upside down real quick. Their optimum L/D also decreases with speed since the wetted area is relatively constant as the craft accelerates. There is a possibility that this could be designed to work well with a wing but that's only a guess. I think the practical considerations might make it an inoptimal choice.
A traditional airplane float/ seaplane hull do have a quite high "hump" drag and a rather large variation in trim with speed if free to trim. At a certain speed the trim can be altered by aerodynamic force from the elevator, but that increase aerodynamic drag.

As I see it design goals for a new airplane float / seaplane hull would be:
-Less drag in displacement mode than traditional float hulls.
-Less drag and less pronounced "hump" when transitioning to plane.
-Free to trim angle closer to optimum trim angle at all speeds.
-Handle better than traditional designs. At least not worse than today.

Maybe one option is to raise the transition speed between displacement mode and planing mode. This if drag in high speed displacement mode can be decreased. The planing lift could be less in this case, as the wing is lifting more at this higher speed.
 

orion

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Thank you - that's exactly who I mean (talk about a brain fart). We worked together on a WIG project some years back, at which point he introduced me to some of the potential benefits of hydro-ski application. Pretty fascinating stuff. Last I heard he was involved in a seaplane project down there somewhere that used one of his ski designs - don't know what happened to it though. Since it hasn't been announced in any way, I'm assuming it never got to the hardware stage - too bad, it was an attractive design.
 

Himat

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I have one more question when it comes to seaplane design:

What planing speed is the aim when designing seaplane floats or seaplane hull's?
(I do then think of planing speed as a fraction of take off speed.)

Did try to search the net and this site, but did not find something on the first try.
 

Himat

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No fancy 3D scetch, but a 3D modell of what I am thinking about:

At rest the airplane floats on the front outriggers and the aircraft body (centre hull).
The outriggers provide stability in roll.
At speed the airplane plane on the outriggers.
No novell idea, more a development and combinations of several ideas and previous concepts. (Some early floatplanes where taildraggers with two floats at and one float under the tail.)
SkraaSide1_3D.jpg
 

Himat

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I could see a little extra wing and a fan fitted to one of these...
http://media.tri-cityherald.com/smedia/2011/07/31/21/38/v8Wkl.St.13.jpg

Rick

There was a craze in the RC world some years ago with several of this kind. Light weight and lot of power, but not that much more wing. Did fly, but everything with the power to prop hang and then acellerate can fly if it's controllable.

Graupner_Hydro_Plane.jpg

Search for RC Hydro Plane and there is lot of pictures and videos on the net.
Actually the hull layot was what inspired me.
 
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