Huge Flying-Boat BWB Idea

[jcf]

Though you are correct that the B-747, A-380, and such are larger.  If I recall correctly though the B-747-400ER was 925,000 lbs (at least there was a proposed variant of that weight)

Yeah but the centerbody of the plane would be sitting flat in the water which would be a lot of surface area that would be in the water, though not too deeply below the waterline truthfully...

Honestly I don't know how the drag dynamics of all this would work out.

I worked on the 747-400ER, interiors electrical design (the oxygen mask-box latch system is my work, based on the similar system in the 777 but with a completely different control setup), and along with the 910K design there were 925K, 935 ~ 950K, 975K(-8 weight BTW) and 1,002K concepts.

The belly of the central hull of your aquatic BWB could have longitudinal strakes, which are typical on high-performance powerboats.




I've not seen any discussion of it, but, I'd think the BWB design would generate a huge ground-effect, which can be good and bad.

Jon

[tinlail]

I understand that water drag, and surface tension on the hull is a very important force on the ability for a flying boat to take off. That is why the hull has one or more steps to reduce wetted area on the hull at speed. A flying wing would seem to have this problem even more so since so much of the hull area in contact will be side to side.

A plan form shape like the Horton 229 with a hull/keel might help.

Another mode of attack on the problem might be a M hull like the M80 Stiletto along the area of the wing that touch the water allow are to get air and wake energy up under the hull and break surface contact. Not sure if in that case the rest of the wing to change shape along with the bottom or if you could just graft ridges on to the bottom of the wing.

[jcf]

I understand that water drag, and surface tension on the hull is a very important force on the ability for a flying boat to take off. That is why the hull has one or more steps to reduce wetted area on the hull at speed. A flying wing would seem to have this problem even more so since so much of the hull area in contact will be side to side.

A plan form shape like the Horton 229 with a hull/keel might help.

Another mode of attack on the problem might be a M hull like the M80 Stiletto along the area of the wing that touch the water allow are to get air and wake energy up under the hull and break surface contact. Not sure if in that case the rest of the wing to change shape along with the bottom or if you could just graft ridges on to the bottom of the wing.

BWB are not flat-bottomed like a flying wing, they have a definite 'fuselage' area, and if correctly designed,
in its at rest position the wing would not be in contact with the water.

Hard steps began to be eliminated on flying boat designs by the early 1940s, the majority of later designs
feature blended-steps. The longitudinal strakes of a high-performance deep-v hull perform much the same
function as a step, and do a better job of breaking up surface tension. The highest performance power-boats
combine multiple strakes and, in a return to very old power-boat design (first suggested in the 1870s, first built
prior to 1910), multiple small steps, however, using this directly as a pattern for an airplane is pointless as the single-hull
powerboat relies totally on engine power and hull design to get it out of "the hole", it doesn't have the aerodynamic
aid of a huge wing. Twin-hull racing powerboats also have little bearing on the problem, the old Hickman Sea Sled
form would be more logical, but unnecessary.

Anyhow the critical drag aspects of the boat hull and boat-hull form 'flying boat' are different from those of the BWB
by virtue of the massively increased wing area of the BWB.

Ekranoplans and WIGS are a better model for how to make a hydro-BWB work than standard flying boats.
Put a couple of fans at the leading edge blowing back under the wing and unsticking would not be a
concern.

Jon

[Mossie]

1.)  Is it possible to design some kind of telescoping hydrofoil in which essentially three panels can retract out of one and could substantially increase lift. 
2.)  To exploit super-cavitation is it possible to use some kind of mechanism to blow exhaust or some kind of air over the hydrofoil to help improve acceleration?  I remember there was a Russian torpedo design which used super-cavitation, was rocket powered and used some of the exhaust from the rocket and directed it over the skin of the torpedo to help get it up to supercavitation speed (where it could do it on it's own).


KJ Lesnick 

1)  You could, but you're getting into the age old engineering problem of adding weight for a small amount of benefit.  It's a vicious circle, you'd increase the lift, but the weight goes up, which means you have to increase the lift again & so on.
2)  Possibly.  It's adding a lot of complexity.  You could bleed some of the jet exhaust, but how do you channel it into the hull or hydroskis?  Not impossible, but you've got to determine if the effect is worth the extra engineering?  A hull would be easier, but with skis there becomes there's moving parts to think about.

Jons pretty much nailed it on the head with WIG craft/Ekranoplans.  That Be-2500P I posted earlier is a good soloution to the problem & seems to be just what you're after.  As it's name suggests, it's MTO would be 2,500 tonnes which is a monster as far as current aircraft go. The Ekranoplan approach is probably the easiest soloution with current technology.

[PR19_Kit]

Has anyone ever used hydroFOILS for an aircraft before, apart from the American guy who flew a monster plane off the roof of a houseboat around the Wright Bros. time frame? Was that Langley?

The Sea Dart's hydroskis were different kettles of fish in that they ran fore and aft and watching vids of the Dart take-off they had almost none of their area in the water by the time it became airborne. Presumably the wing started lifting almost right away, even though it was awash when the aircraft was static. As I read it, the Dart's hydroski was mainly to soften the take-off and landing runs as it dampened out the 'crashing' if the aircraft ran into a wave etc.

Having had the pleasure of riding the Boeing Jetfoil from London to Ostend and back in the '70s, I was most impressed with the way it 'took off'. I managed to talk my way onto 'the bridge' (or 'the cockpit'......) on the return trip and apparently they could adjust the angle of incidence of the bow foil to nudge the ship into the air once it had reached a suitable speed. That seemed to be remarkably low, around 20 kts perhaps. We 'flew' up the Thames on the foils, which amazed me, but apparently they left almost no wash, much less than if the ship had been hull-borne.

Perhaps similar active control of the foils might help your monster 'boat?

[jcf]

Has anyone ever used hydroFOILS for an aircraft before, apart from the American guy who flew a monster plane off the roof of a houseboat around the Wright Bros. time frame? Was that Langley?

The Sea Dart's hydroskis were different kettles of fish in that they ran fore and aft and watching vids of the Dart take-off they had almost none of their area in the water by the time it became airborne. Presumably the wing started lifting almost right away, even though it was awash when the aircraft was static. As I read it, the Dart's hydroski was mainly to soften the take-off and landing runs as it dampened out the 'crashing' if the aircraft ran into a wave etc.

Having had the pleasure of riding the Boeing Jetfoil from London to Ostend and back in the '70s, I was most impressed with the way it 'took off'. I managed to talk my way onto 'the bridge' (or 'the cockpit'......) on the return trip and apparently they could adjust the angle of incidence of the bow foil to nudge the ship into the air once it had reached a suitable speed. That seemed to be remarkably low, around 20 kts perhaps. We 'flew' up the Thames on the foils, which amazed me, but apparently they left almost no wash, much less than if the ship had been hull-borne.

Perhaps similar active control of the foils might help your monster 'boat?

Langley didn't use hydrofoils, he didn't even really have any way of landing the machine after its catapult launch.
The floats that Curtiss added when he rebuilt/redesigned the Aerodrome so it would actually fly, or sort of fly,
were fairly typical pontoon design.

The float borne versions of the Ansaldo SV aircraft used tubular floats equipped with small hydrofoils and the Piaggio-Pegna PC7 racer design used hydrofoils.

The first attempt at a hydro-foil equipped aircraft was the pre-WWI Bristol-Burney X series flying boats that used Lt. Burney's 'hydro-ped' landing
gear. Trials ended just before the beginning of the war.
http://www.flightglobal.com/pdfarchive/view/1952/1952%20-%200405.html

The KISS principle argues against hydro-foils.

Jon

[KJ_Lesnick]

I've looked into WIG's a bit and one design that's interested me is the Boeing Pelican.  What has me quite fascinated about it is that it has a flat bottom, no ridges on the hull or any of that stuff.

KJ Lesnick

[tinlail]

I understand that water drag, and surface tension on the hull is a very important force on the ability for a flying boat to take off. That is why the hull has one or more steps to reduce wetted area on the hull at speed. A flying wing would seem to have this problem even more so since so much of the hull area in contact will be side to side.

A plan form shape like the Horton 229 with a hull/keel might help.

Another mode of attack on the problem might be a M hull like the M80 Stiletto along the area of the wing that touch the water allow are to get air and wake energy up under the hull and break surface contact. Not sure if in that case the rest of the wing to change shape along with the bottom or if you could just graft ridges on to the bottom of the wing.

BWB are not flat-bottomed like a flying wing, they have a definite 'fuselage' area, and if correctly designed,
in its at rest position the wing would not be in contact with the water.

Hard steps began to be eliminated on flying boat designs by the early 1940s, the majority of later designs
feature blended-steps. The longitudinal strakes of a high-performance deep-v hull perform much the same
function as a step, and do a better job of breaking up surface tension. The highest performance power-boats
combine multiple strakes and, in a return to very old power-boat design (first suggested in the 1870s, first built
prior to 1910), multiple small steps, however, using this directly as a pattern for an airplane is pointless as the single-hull
powerboat relies totally on engine power and hull design to get it out of "the hole", it doesn't have the aerodynamic
aid of a huge wing. Twin-hull racing powerboats also have little bearing on the problem, the old Hickman Sea Sled
form would be more logical, but unnecessary.

Anyhow the critical drag aspects of the boat hull and boat-hull form 'flying boat' are different from those of the BWB
by virtue of the massively increased wing area of the BWB.

Ekranoplans and WIGS are a better model for how to make a hydro-BWB work than standard flying boats.
Put a couple of fans at the leading edge blowing back under the wing and unsticking would not be a
concern.

Jon

I didn't realize that steps had go away as a design option. Thank you.
A blended wing under surface area is still wider than that a conventional boat hull. The M shaped hull design looks to me like it could be thought of strakes that got really big, as I understand it it purpose is to  create tunnels to trap air under the hull. It really depends the shape of the underside, as to what is the best option. Such a design might also be useful if you wanted to create the pressurized area as a series of tubes laid side by side.

[jcf]

A blended wing under surface area is still wider than that a conventional boat hull. The M shaped hull design looks to me like it could be thought of strakes that got really big, as I understand it it purpose is to  create tunnels to trap air under the hull. It really depends the shape of the underside, as to what is the best option. Such a design might also be useful if you wanted to create the pressurized area as a series of tubes laid side by side.

That width could actually work to your advantage, as the weight would be spread over a much greater area it
is possible that the hydro-BWB would end up with a very shallow draft, and a simple bubble-mat air-lubrication
system is probably all that would be required to come unstuck. Its an idea that hasn't worked too well in boats,
but would probably work on the BWB, again because of the ground effect from its large wing area.

Edit: the Air Cavity form of air lubrication may be the answer.
http://docs.hydrofoils.org/SAS03.pdf

Jon   

[KJ_Lesnick]

When you say air-lubrication you mean like the same principle behind air-hockey?

[tinlail]

Found this quote about the M-hull.

"In sea trials of a boat embodying such a hull, the act of increasing power to test the advantages of the air planing cushion at higher boat speeds led to the discovery of two new phenomena. First, the horsepower-to-speed ratio increased in an almost linear form indicating that increased air intake with increasing boat speed enhanced the air cushion planing efficiency so as to offset the exponential increase in wave-making drag with increasing boat speed. Second, the boat operated downwind more efficiently at lower boat speeds, but upwind into a 10-knot breeze the boat was propelled at almost 25% greater speed than when operating downwind. Such unexpected characteristics of an M-shaped boat hull promise significant benefits, and so a need exists for ways to develop and exploit those characteristics."

http://www.globalsecurity.org/military/systems/ship/m-hull.htm

[KJ_Lesnick]

The M-hull kind of looks a little bit like the hull underside of the BWB airship in Ace-Combat 6 actually I think...

This an M-hull? 
http://www.acecombat.jp/ace6/estovakia/aigaion01.jpg

[jcf]

Found this quote about the M-hull.

"In sea trials of a boat embodying such a hull, the act of increasing power to test the advantages of the air planing cushion at higher boat speeds led to the discovery of two new phenomena. First, the horsepower-to-speed ratio increased in an almost linear form indicating that increased air intake with increasing boat speed enhanced the air cushion planing efficiency so as to offset the exponential increase in wave-making drag with increasing boat speed. Second, the boat operated downwind more efficiently at lower boat speeds, but upwind into a 10-knot breeze the boat was propelled at almost 25% greater speed than when operating downwind. Such unexpected characteristics of an M-shaped boat hull promise significant benefits, and so a need exists for ways to develop and exploit those characteristics."

http://www.globalsecurity.org/military/systems/ship/m-hull.htm

All of which is pretty much irrelevant for a flying machine that only requires a 'hull' for takeoff and landing.
The same features that make the M-hull advantageous for a marine craft would be disadvantageous for a
flying machine for reasons of drag, and that form would be a major source of drag.

In the early days 'flying boats' were almost literally that and the concentration on
good hydrodynamic form led to compromises in aerodynamics. Towards the end
of the time of the big flying boats the formula was reversed and compromises in
hydrodynamic form and performance were accepted in exchange for improved
aerodynamics and the resulting higher flight performance.

I'll reiterate what Simon and I have said, forget about looking at classic flying boats
as a model for a water based BWB, WIGS and ekranoplans are a far more viable point
of reference.

jon

[tinlail]

The M-hull kind of looks a little bit like the hull underside of the BWB airship in Ace-Combat 6 actually I think...

This an M-hull? 
http://www.acecombat.jp/ace6/estovakia/aigaion01.jpg

Kind of, the Stiletto consists of two M-hulls side by side. As you can seel the M consist of a deep middle with shallower outer chimes that are also back further that catch the bow wake.

[KJ_Lesnick]

Did the Boeing Pelican take off from land, from sea, or both?