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Old 15th Aug 2011, 20:43   #1 (permalink)

 
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Martin P6M Seamaster

From what I remember reading, this aircraft had afterburners. Being that (as far as I know) it was subsonic -- why did it need those?
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Old 15th Aug 2011, 21:02   #2 (permalink)
 
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Jane-Doh,

Sea planes always fascinated me as a child. The Seamaster was intended to deliver nuclear store. Polaris systems were used instead.

You are correct; the Seamaster did indeed have afterburners. They were intended to provide additional power on take off. Unfortunately a slight fault in the design was found; the engine nacelle design was such that when in afterburner mode had a tendency to burn the rear fuselage and induce sonic fatigue.

The two afterburning jet engines were located side by side in each of' two nacelles mounted on top of the wing immediately adjacent to either side of' the fuselage. (The afterburners, an unusual feature for a large subsonic aircraft, were for use oil takeoff.) Inlets swept back at nearly the same angle as the wing leading edge were found to be unsatisfactory and unswept inlets were finally adopted; exhaust nozzles were behind the trailing edge of the wing.The location of' the engines was, of course, strongly influenced by the necessity of minimizing spray ingestion during operation on the water.

I copied that last paragraph from P6M SeaMaster. Go have a read
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Old 15th Aug 2011, 21:04   #3 (permalink)
 
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Seamaster afterburners ?

Just a thought, maybe to help it unstick from the water when fully loaded ? was a big machine , Paul H.
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Old 15th Aug 2011, 21:32   #4 (permalink)
 
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Although not supersonic it was required to achieve M0.9 at low level, this, combined with a max t/o weight of about 160000lbs may go some way to explaining it. The nature of a flying boats landing medium does result in a built in headwind.
Turbojets were still pretty gutless in the early '50's - the original design was going to use turbo-ramjets, but after development issues these were replaced by afterburning Allison j71s in the prototype and pre production aircraft. As far as I know, the production series had non afterburning J75s that were rated at about 17000lbs. This seems to be the most authoritative detail on the web.
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Old 15th Aug 2011, 21:45   #5 (permalink)
 
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these explain a fair bit re the engines
Shame we don't have fleet of these.

Last edited by jamesdevice; 15th Aug 2011 at 21:56.
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Old 16th Aug 2011, 01:09   #6 (permalink)

 
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hval

Quote:
Sea planes always fascinated me as a child.
I found them fascinating too, though I'm not sure for the same reason: For an airliner they could be so much bigger as a 10,000 foot takeoff run wouldn't be a concern, and night-vision could allow you to gauge the height of the swells, which would even make nighttime operation safe.

Quote:
The Seamaster was intended to deliver nuclear store. Polaris systems were used instead.
Correct, it could also deliver conventional ordinance including bombs, and even mines.

Quote:
They were intended to provide additional power on take off.
That would give the plane a pretty good T/W ratio -- I'm surprised you'd need such a high T/W ratio to get a sea-plane out of the water.


Kitbag

Quote:
Although not supersonic it was required to achieve M0.9 at low level, this, combined with a max t/o weight of about 160000lbs may go some way to explaining it.
It needed burner to hold subsonic speed at sea-level? I thought it would be able to fly dry down-low....

Regardless, just the fact that it weighed less than a B47, could carry a greater load at a higher speed up high and down-low, was sturdier (I don't know what it's maximum g-load was, but that aircraft was built like a tank), had a greater thrust to weight ratio and a lighter wing-loading all sound like awesome advantages, though truthfully I don't know if it could fly as far.

Quote:
Turbojets were still pretty gutless in the early '50's - the original design was going to use turbo-ramjets
Why would they need turbo-ramjets? How fast were they originally planning to design this aircraft to fly? Are you confusing this design with a Mach 4 design Convair proposed -- a turbo-ramjet makes more sense for that design than a high subsonic aircraft...

Quote:
As far as I know, the production series had non afterburning J75s that were rated at about 17000lbs.
Considering the thrust figures of jet-engines almost always seems to be under-rated (either a fudge-factor is incorporated, or the thrust figures are based on conditions other than sea-level thrust) -- as I understand it J75's had thrust levels as low as 15,800 (as used on the B707-220), with most around 18,000 - 22,000 lbf dry (this is consistent with the statements that the J75 was 50% more powerful than the J57).


jamesdevice

Quote:
Shame we don't have fleet of these.
Seaplane aircraft have a fundamental advantage in the fact that more of the Earth's surface area is covered by water than by land. The only thing that could be better would be an amphibious aircraft.

The only drawback that the P6M had would be that it wasn't really designed to reliably land at night as the height of the swells could not be reliably gauged. Though as far as I know the plane could refuel in mid-air, so as long as there wasn't an imminent problem, they could just keep refuelling until the sun comes up, then land.
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Old 16th Aug 2011, 06:40   #7 (permalink)
 
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It was supersonic in a dive

It also had aerodynamic weaknesses - the first prototype had a tailplane problem which lead to both wings clapping hands and all where lost in the following crash

What killed it after a fair few were built , but not put in to service, was not only polaris but the supercarrier ( nimitz class ?) programme and the fact the bomb bay doors sealong system was not massively reliable.

Cool programme none the less
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Old 16th Aug 2011, 07:04   #8 (permalink)
 
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Wrong decade, dagenham.

Martin P6M Seamaster:
First flight 14 July 1955; program canceled August 1959.

the Supercarrier program:
CVA-59 Forrestal: Commissioned: 1 October 1955
CVA-60 Saratoga: Commissioned: 14 April 1956
CVA-61 Ranger: Commissioned: 10 August 1957
CVA-62 Independence: Commissioned: 10 January 1959
CVA-63 Kitty Hawk: Laid down: 27 December 1956, Commissioned: 29 April 1961
CVA-64 Constellation: Laid down: 14 September 1957, Commissioned: 27 October 1961
CVA(N)-65 Enterprise: Laid down: 4 February 1958, Commissioned: 25 November 1961
CVA-66 America: Ordered: 25 November 1960
CVA-67 Kennedy: Ordered: 30 April 1964

Note:
CVAN-68 Nimitz; Ordered: 31 March 1967
etc.

Note2: the "A" (attack) part of the supercarrier designation was dropped 30 June 1975.
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Old 16th Aug 2011, 07:46   #9 (permalink)
 
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Jane-Doh,

Seaplanes may be split into two groups; float planes and flying boats. Neither is able to take of in particularly rough weather, in fact the weather needs to be relatively calm. Flying boats are able to take off in rougher weather than sea planes. Sea state/ water state limits the number of days that sea planes may take off; more so than an aircraft taking off from a runway on land.

Floating objects are another hazard

A seaplane during take off has to overcome hydrodynamic forces (water drag is the major part of the forces resisting acceleration). This resistance reaches its peak at a speed of about 27 knots, and just before the floats or hull are placed into a planing attitude. Several factors greatly increase the water drag or resistance; heavy loading of the aircraft or glassy water conditions in which no air bubbles slide under the floats or hull, as they do during a choppy water condition. In extreme cases, the drag may exceed the available thrust and prevent the seaplanes from becoming airborne. This is particularly true when operating in areas with high density altitudes (high elevations/high temperatures) where the engine cannot develop full rated power

For seaplanes, the forces involved in take off are different to land planes. Sea planes have to overcome hydrodynamic forces which require additional power (I think of the water as being “sticky”). These forces increase until the float hull is out of the water or on the stepping plane. Did you know that float planes have two hull designs? One for when the aircraft is sitting in the water/ taxying around and one for when on the stepping plane and taking off.

I am now going to quote from a useful website (Flying Seaplanes): -

The seaplane takeoff may be divided into four distinct phases:
(1) The "displacement" phase (plane sitting there or taxying)
(2) the "hump" or "ploughing" phase, (accelerating for take off)
(3) the "planing" or "on the step" phase, (overcome most hydrodynamic forces, accelerating for take off)
and
(4) the "lift off." This is where the wings produce lift and start to raise the hull from the water.


Take a look at the web site I have linked to. It may answer many of your questions re sea planes.

Sea planes are great, but economically, as passenger aircraft, they were not viable in todays requirements for being on time. As stated above, not only do sea planes have to take in to account the same weather conditions as land planes, but also the added component of sea state.

Hval.
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Old 16th Aug 2011, 13:57   #10 (permalink)
 
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Similarity

Is it me or does this aircraft (or sea plane?) have more than a passing ressembance to a HP Victor?

Just the overall layout but especially the tail section.
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Old 16th Aug 2011, 14:17   #11 (permalink)
 
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tail flutter test
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Old 16th Aug 2011, 15:15   #12 (permalink)
 
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Another similitary

"Victor-like" the Seamaster's tail certainly is, but I am also reminded of the Soviet Union's equivalent, by Myasishev (sp?) whose Soviet and NATO designations escape me*

Or was it Beriev? Aged grey cells oscillating ...
Over to the experts with more than memories to rely on ...
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Old 16th Aug 2011, 15:29   #13 (permalink)
 
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MYASISCHEV MYA-4 "Bison"
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Old 16th Aug 2011, 15:53   #14 (permalink)
 
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Jig Peter, the aircraft to which you refer was not the Myasishchev M4 "Bison", it was the Beriev Be-10 “Mallow”:

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Old 16th Aug 2011, 15:56   #15 (permalink)
 
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I assumed the meant the Soviets equivalent to the Victor - which was arguably the Bison However theres a striking similarity to all three - especially the Bison wing profile
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Old 16th Aug 2011, 15:58   #16 (permalink)
 
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Russian jet boats

Thanks Beagle (fount of much knowledge) for the photo - wasn't there also a 4-engined one with engines above the wing, like the Seamaster?
Lurking in my erratic memory is the thought that some were based in the Russian Far East, and also seem to appear in shots of "water bombing" operations.
Regards and respect,
JP
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Old 16th Aug 2011, 16:14   #17 (permalink)
 
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theres two you could be thinking of, both by Beriev. Both are much more recent though
Be-200 https://secure.wikimedia.org/wikiped.../Beriev_Be-200
A-40 https://secure.wikimedia.org/wikiped...ki/Beriev_A-40
A-40 might make a good Nimrod replacement...
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Old 16th Aug 2011, 16:16   #18 (permalink)
 
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re carriers etc - same funding discussion re what USAF, USN and USMC have from a deterent perspective.

the original great planes documentary, not the trashy discover remake gives a good overview of the projects going on publically and not publically and how the infighting panned out.

the seamaster was cancelled really before it flew....... really keeping martin in business

really interesting to compare the US approach with that of UK

see wiki " The major defense budget cuts of the Eisenhower administration were forcing the Navy to make choices. In August 1959 Martin was told to halt operations; the program was going to be canceled. Seaplanes were a small community in Naval Aviation, and the P6M, significantly over budget and behind schedule, was competing with aircraft carriers for funding. The Navy had an impending superior system for the nuclear strike role, the Fleet Ballistic Missile Submarine." ref Martin P6M SeaMaster - Wikipedia, the free encyclopedia
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Old 16th Aug 2011, 16:32   #19 (permalink)
 
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how much practical use would it have been in a non-nuclear role? e.g. as a maritime patrol aircraft? Or as a tactical bomber? Strangely enough as I type this I've got a you-tube video running about "the nuclear bomber" and it states that the USN actually intended powering the turbines with a nuclear reactor.
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Old 17th Aug 2011, 03:27   #20 (permalink)

 
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dagenham

Quote:
It was supersonic in a dive
Oh, I didn't know that

Quote:
It also had aerodynamic weaknesses - the first prototype had a tailplane problem which lead to both wings clapping hands and all where lost in the following crash
I thought that was a deep-stall related issue (happens to T-tailed planes). The airframe was subjected to 9g's.

Quote:
What killed it after a fair few were built , but not put in to service, was not only polaris but the supercarrier ( nimitz class ?) programme
The first super-carriers were the USS Forrestal. Part of me honestly thinks it would have been interesting to see fleet-carriers that were more like the Midway size but with elevators, arrestor cables, and catapults to operate heavier aircraft (albeit a lower number). Sounds counter-intuitive but even if each carrier had a little bit less fighter capacity; if you had a significantly greater number of carriers, you would technically have more carrier-based fighters and attack-planes in total.

If you had a large number of carriers and one goes to the bottom, you lose a smaller percentage of your overall carrier strike force; if you have a few super-carriers, a loss is far more catastrophic; furthermore it will take longer to replace it.

Quote:
and the fact the bomb bay doors sealong system was not massively reliable.
I'm surprised they couldn't fix it as Martin had built seaplanes before.


hval

Quote:
Seaplanes may be split into two groups; float planes and flying boats. Neither is able to take of in particularly rough weather, in fact the weather needs to be relatively calm. Flying boats are able to take off in rougher weather than sea planes. Sea state/ water state limits the number of days that sea planes may take off; more so than an aircraft taking off from a runway on land.
The P6M was a flying-boat technically right?

Last edited by Jane-DoH; 18th Aug 2011 at 21:03.
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