So ...what was the most Seaworthy flying boat? (and a few stories)

Avimimus

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As the title says: What was the most Seaworthy flying boat every built or proposed?

The interwar Rohrbach Ro series with its pop-out sails for use once ditched?
Submersible aircraft?
Large flying boats with strong righting moments? There are a lot of candidates...


Given how light and fragile WWI aircraft were (and how prone to engine failure) it was quite the issue early on. I remember one story about how an FBA flying boat had an engine failure over the Mediterranean - her crew survived for more than a week awaiting rescue because one of the crew members used tubing from one of the only instruments on board to build a primitive desalinator.

Here is another story:

Testimony to the ruggedness of the type is to be found in the experiences of FF49c No. 1874, which, early on 10th May 1918, was swung out from the seaplane carrier Santa Helena for a reconnaissance patrol over English coastal waters. With an N.C.O. crew - Hans Sommermann (pilot) and Georg Patzoldt (observer) - the Friedrichshafen took off in company with another 49c and commenced to map a new minefield they discovered when they eventually reached their patrol zone. This they continued to do until the fuel gauges indicated time for return; Patzoldt signalled the crew of the accompanying seaplane, whereupon they turned in the direction of Germany.
By 11.00 hours, after some six hours in the air, fuel was exhausted, the parent carrier ship nowhere in sight; both aircraft alighted on the water, radioing SOS calls as they glided down. On touching down, the sea anchors were streamed to avoid drifting, as surface rescue vessels from either Borkum or Norderney were expected to reach them before dark. However, night fell with no sign of rescue, and with it came a freshening of the wind. The pangs of hunger and thirst became manifest to the crews, but there was no water other than that in the radiators, which, having been mixed with glycerine, was barely palatable. Soon after midnight a strong sea came up and No. 1874 broke away from her sea anchor and rapidly started to drift.
The drift continued, all through a stormy and overcast Sunday and again through another anxious night. Every second hour the crew of No. 1874 fired Very lights in the hope of attracting the attention of some vessel. With the break of another day came the hope that as the drift had been towards the English coast, perhaps they might be picked up by the Royal Navy, but no vessels materialised, and so their ordeal continued. The wind now backed to the south-west, and the seaplane began to drift away from British waters out into the North Sea again.
On the fifth day a list developed which they sought to correct by hacking away part of a wing panel but were too weak to wield the axe. Fog obscured the view on the sixth day, but when eventually it lifted fishing vessels were sighted, but these ignored all signals. Eventually, well after midday, Patzoldt somehow managed to tear out a piece of rib to which he fastened his handkerchief, and at last a vessel moved in to pick them up. This was the Swedish fishing smack Argo II, whose master later explained that he had interpreted the red Very lights they had fired as warnings to keep away - had white lights been fired he would have immediately come alongside, but by then they had none left.
Sommermann and Patzoldt were rescued some 27 miles from the Norwegian coast, and, exactly a week after their ordeal began, were landed at the Swedish port of Marstrand. Here they learned that their companion FF 49c had been rescued on the fourth day by a Dutch boat whose attention had been ingeniously attracted by SOS bursts from the aircraft's machine-gun.
It was finally reckoned, when Sommermann and Patzoldt returned to Germany, that the FF 49c No. 1874 had drifted almost twice across the North Sea in a period of some 140 hours.
 

Jemiba

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I would throw in the Dornier Do 24, especially, as I think, that stub wings aren't the
best aerodynamic solution, but the most rugged one.

https://www.youtube.com/watch?v=nU8JMbe9ljU
 

Abraham Gubler

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My grandfather had lots of stories of WWII flying boats. For seaworthiness the Catalina was rated far above the Short Sunderland. Which was generally considered a very bad boat for landing on rough seas or uncharted waters. The Sunderland’s hull wasn’t strong enough for war use and would rip up after any hard hits against the waves or anything solid in the water. He rated the Kwanisihi H8K “Emily” as the best four engine flying boat of WWII. Better than the Martin and much better than the Sunderland. But still thought the Catalina was a better combat boat because it was more manoeuvrable than the H8K. They once defeated a Jap fighter in the Catalina by flying hard high banking turns at sea level and the fighter stayed on their tail until it ran out of airspeed and went into the water.

For the Catalina the amphibians were worse than the regular flying boats because of the weight of the gear. Of course they had their advantages in being able to land on land. My grandfather flew from Darwin to Townsville overland in a flying boat once and half way along one of the engines blew up. So they spent a lot of time looking very closely at that remaining engine because outback scrub was not a good place to try and land a boat. But they used the flying boats for the Blackcat sea mining missions because it could fly much further than the amphibians which were used for rescue work.

The RAAF had a few Do 24s from the Dutch East Indes but only used them for transport. They were well liked as sea boats and the third engine was very popular as it gave them a survivable one engine out capability.
 

Artie Bob

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After WW II, one of the Boeing 314 boats, at that time owned by a small airline, had to make an emergency landing in the Atlantic during a storm. It took some time for the US Coast Guard to reach the flying boat and rescue all the passengers and crew. In the end the Coast Guard had to sink the Boeing (by gunfire IIRC) in order for it not to become a hazard to navigation. There was a first hand article on this event, in the US Coast Guard house magazine some years ago.

Best Regards,

Artie Bob
 

AeroFranz

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There is a very neat review of the D0.24 in Eric Brown's collection of flight reviews. He said he was shown the Do.24's capabilities by a German pilot at the end of WWII. The pilot never left the inner confines of a harbor and simply took off by accelerating on the water while banking aggressively on one of the sponsons, completing three quarters of a circle and hitting his own wake, and leaping into the air, if that makes sense.


The Japanese US-1, of much later make, can land in some of the roughest seas due to its large size and low speed capability. Depending on what metric you are using, that might be the most seaworthy seaplane.
 

Bill Walker

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The circling technique is regularly used by modern float plane pilots when space is at a premium. However, they need a fairly large circle. This works best if the pilot gets enough airspeed for the ailerons to have some effect before starting to circle.

Float planes in general, and many small modern flying boats, make terrible boats. We certified the Trigull for operation in 12 inch waves, which really isn't very rough. This was a conservative theoretical limit, based on expected hull strength. We unintentionally demonstrated operations in 18 inch waves shortly after this, and lived to tell the tale.

From what I have read, i suspect the US-1 family is very seaworthy (for an airplane). Still, the conventional wisdom in the flying boat design field is that the Japanese and the Russians persist with flying boats because they only operate in the relatively calm Pacific (or from fresh water in Russia). You don't see any more big flying boats in the North Atlantic.
 

Abraham Gubler

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AeroFranz said:
There is a very neat review of the D0.24 in Eric Brown's collection of flight reviews. He said he was shown the Do.24's capabilities by a German pilot at the end of WWII. The pilot never left the inner confines of a harbor and simply took off by accelerating on the water while banking aggressively on one of the sponsons, completing three quarters of a circle and hitting his own wake, and leaping into the air, if that makes sense.


For those who haven't seen this before here is a video of a Lake Renegade doing a circular confined takeoff. Once they are airborne the camera looks back at the wake and you can see what they were doing. But this is not the sort of thing you do in any kind of a seaway. With any sort of waves the last thing you want to be doing is changing your direction in relation to the waves! OK for lakes and harbours but not for out at sea. Of course out at sea you tend not to be limited in having a long straight takeoff run!


https://www.youtube.com/watch?v=71-i02xhqKY
 

Richard N

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The ShinMaywa US-2 may be the most seaworthy flying boat ever. The Japanese have a very good reason for persisting with flying boats: They live on relatively small pieces of dry land totally surrounded by lots of water. Flying boats are several orders of magnitude faster to the scene of an incident at sea than a ship or seaworthy speed boat. The ShinMaywa US-2 site: http://www.shinmaywa.co.jp/aircraft/english/us2/
 

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Bill Walker

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Very interesting video Abraham. As I said, this technique is still in use, to use available area or available calm area (inside a harbour or in the lee of land). A couple of points I noted on the video:

Notice the airplane banking in to the turn at higher speeds. Only aerodynamic forces can do this, centrifugal force wants to bank you out of the turn (because your c.g. is above the centroid of the water forces, which predominate at low speeds). The pilot has to judge the speed at which he starts to turn, based on available aileron authority.

Looking at the wake we see the turn radius increasing as airspeed increases. The pilot needs to be aware of this when deciding if the area is suitable for a circling take off.

Richard, thank you for those images. I would add to the last image that blowing the rudder and elevator not only increases low speed stability, but also increases low speed control authority. Control authority often limits the minimum safe speed on modern multi-engined aircraft. The ability to rotate or touch down at lower speeds is the main reason for the big difference we see in landing and take off distances for the US-2 compared to the Cl-415 or BE 200.
 

AeroFranz

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Bill, could you please describe how low alighting speeds help coping with high sea states? Is it a matter of avoiding high impact forces on the hull?
 

Bill Walker

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AeroFranz said:
Bill, could you please describe how low alighting speeds help coping with high sea states? Is it a matter of avoiding high impact forces on the hull?

The kinetic energy imparted to the hull by striking a wave is directly proportional to the square of your velocity relative to the wave. 90% touchdown speed gives you 82% of the energy. Half the speed gives you one-quarter the energy into the hull.

A secondary effect is the reduced time spent at higher speeds. Less time travelling at higher speeds reduces the probability of encountering a high wave at high speed. Another way to look at this is lower touch down speeds give you the ability to touch down and decelerate in between large waves. Then you can ride out the large waves at a low speed.

An interesting reversal of this is the effect of wave height on take off distance. Tests with the Walrus showed shorter take off runs as the wave height increased, up to the theoretical maximum wave height. The aircraft at some point was skipping from wave top to wave top even below rotation speed, and accelerating quicker during the brief periods the hull was out of the water. This only works if your hull doesn't break during all this, and if your flight crew can hold on to the controls during all this.

Structural loads on the hull are only part of the issue. A boat hull, compared to floats, will continue to give you greater buoyant forces as the hull submerges deeper due to an encounter with a wave or unfriendly aerodynamic and inertial forces (like a botched landing). A float, at some point, is completely submerged and driving it deeper into the water no longer creates greater upward forces. If the combination of inertial forces and wave forces continue to drive the aircraft down then other stuff contacts the water, like wings or props. Then you may have real problems.
 

Richard N

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ShinMaywa US-2 videos


https://www.youtube.com/watch?v=vV6NnVTOBjo https://www.youtube.com/watch?v=Fx4OE6cvOkI
 

Jemiba

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Impressive videos, thank you !
I've no statistics at hand, but thinking of reports and photos I've seen of flying boat mishaps and accidents,
torn off auxiliary floats seemed to have been quite a great part. Nevertheless in all current flying boats,
such wing mounted floats are used (US-2, Beriev A-40/100), instead of solutions like that, developed by Dornier
for the Do 214//216. Aerodynamic disadvantages only, or other reasons, maybe decreased stability on the
water ?
 

Abraham Gubler

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Jemiba said:
Aerodynamic disadvantages only, or other reasons, maybe decreased stability on the
water ?


Weight would be another saving. With those big turboprops I doubt the US-2 has any problems with thrust to drag ratios. But sticking a load of power operating retracting gears and doors on the wingtips would require a much stronger wing leading to a lot more weight.
 

AeroFranz

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Bill Walker said:
AeroFranz said:
Bill, could you please describe how low alighting speeds help coping with high sea states? Is it a matter of avoiding high impact forces on the hull?

The kinetic energy imparted to the hull by striking a wave is directly proportional to the square of your velocity relative to the wave. 90% touchdown speed gives you 82% of the energy. Half the speed gives you one-quarter the energy into the hull.

A secondary effect is the reduced time spent at higher speeds. Less time travelling at higher speeds reduces the probability of encountering a high wave at high speed. Another way to look at this is lower touch down speeds give you the ability to touch down and decelerate in between large waves. Then you can ride out the large waves at a low speed.

An interesting reversal of this is the effect of wave height on take off distance. Tests with the Walrus showed shorter take off runs as the wave height increased, up to the theoretical maximum wave height. The aircraft at some point was skipping from wave top to wave top even below rotation speed, and accelerating quicker during the brief periods the hull was out of the water. This only works if your hull doesn't break during all this, and if your flight crew can hold on to the controls during all this. [...]


Bill, thanks for the exhaustive explanation! That's precisely what I was hoping for.
 

Sundog

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What about the Marlin? Any idea on how it compares to most of the aircraft listed, in terms of it's ability to handle rough sea states?
 

Richard N

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Video of the development of the Shin Meiwa PX-S.


http://www.youtube.com/watch?v=oh8mn0DeKSs&list=UUXIr3Mqm_FS_gmqyKdHNSJQ
 

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