Armstrong Whitworth AW.681 / HS.681

alertken said:
Tks Jem: my approach to History, and especially to Why did they do that?, is to assume sanity - it seemed a good idea at the time - and to try to put myself in the boots of the mover and shaker. So, for example: why did USSR put IRBMs in Cuba, 1962? Well, take a globe and turn it so that Siberia is at the top. Now mark US/NATO nuke sites, such as Jupiter/Turkey. All then becomes clear. We, here (Euro-centric) can fall into the trap of believing the earth spins on a DC/London axis.
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Yes!
The whole Cuban Missile Crisis actually started a year or two earlier when the USAF forward-positioned nuclear missiles in Spain and Turkey. After the CMC was over, the USAF quietly withdrew some of their missiles from Europe.
 
And don't forget that at the very beginning of all this (1954-55) USAF literally outsourced IRBM to Great Britain (Blue Streak) to concentrate on Atlas+Titan ICBMs. Only to reverse that decision and create Thor, Jupiter...
 
For cargo aircraft and helicopters in general, when did the beaver/duck tail become preferable to clamshell doors?
 
From the minute you want to airdrop stuff? (other than men-paras)
In clamshell planes like Noratlas and Arava, you need to remove the doors before take off to be able to airdrop stuff.

With a tail like the herk, stuff can just roll down the ramp.
 
CJGibson said:
Not sure what you mean.

Chris
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A lot of the earlier freighter designs used clamshell doors, then they seem to disappear from designs to be replaced by beaver/duck tails.
 
An openable ramp door that formed the lower fuselage in other words.
The Arado 232 from 1941 had a ramp, but I think (not sure) also had clamshell doors, as did the C82 Packet of 1944.
One of the Ju-90 prototypes flew earlier with a hydraulic ramp, openable in flight.

The Budd Conestoga also had one in 1944, and was very influential design wise, like the earlier Arado.

I guess once the C-130 and Antonov An-8 and An-12 came about from the mid 1950's onwards and showed the superiority of it on a wide scale, that was that.
 
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Please define clamshell and beavertail.

To me clamshell and beavertail are the same thing - a horizontally-split upwards/downwards opening set of doors as in the Argosy.

I have seen the vertically-split doors on the StarLifter and Galaxy called clamshells but are they?

Hercules uses an integral ramp/door, horizontally-split, but work differently.

All are means to provide a pressure seal for a very large opening and on the Belfast lead to major drag problems.

What do the various manufacturers call them?

Chris
 
Just as an aside, as the Arava was mentioned.
The Arava, apart from its other problems, had an obsolete rear swinging door/rear fuselage.
Contempories such as the Skyvan and C-212 had a ramp door, and were thus more advanced conceptually.
I'm not surprised the Arava was not a success.
 
He is asking when rear loading ramps that form part of the lower fuselage, as opposed to large, swing-open doors/rear fuselage, became the norm.
From the mid to late 1950's.
 
"Clam shell" doors are made in 2 pieces with vertical hinges on the outer fuselage walls (Arado 232, Arava, Armstrong-Whitworth Argosy, Blackburn Beverely, Fairchild C-82 and 119, Nordatlas, etc. ... even the Bristol Freighter had clam shell doors on its nose). Since clam shell doors cannot be opened in flight, they need to be removed before they can drop heavy cargo (e.g. bulldozer), which limits speed and range.

"Duck tail" or "beaver tail" are non-standard designations. I prefer to call them cargo ramps. The principle difference is that cargo ramps have horizontal hinges and can be opened in flight. While Junkers may have built the first few narrow ramps (e.g. 252 and 352 tri-motors), the Budd Conestoga was the first serious production example of a rear cargo ramp. Some ramps are hinged at the rear (Shorts Skyvan's is purely an aerodynamic fairing and they fly quite well without their rear door) and some are hinged at the front, but most military transports combine both types for a long, easy entryway to load cargo.
A few of the faster jet transports (e.g C-141) have additional clam-shell doors that work only as aerodynamic fairings. Since their hinges are close to horizontal, they can be opened in flight, exposing the horizontally-hinged ramp.

Both types of tails can be used to para-drop (above AAA) or Low Altitude Parachute Extraction System heavy cargo.
 
The Arado 232A/B estalished the overall layout and the ramp/door came to the fore with the Fairchild C-123, after that it became the norm. Swing noses and tails were a solution to pressurisation trouble.

So, mid-late 40s.

Chris
 
Isn't the fairing between the jetpipes of an F-14 a beavertail?

Chris
 
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I remember studies from the mid nineties on FLA (aka A400M) into rear door config. We looked at 2, 3, and 4 doors. All of these had been studied before from a structural perspective but not the systems impact. The baseline at this point was a 2 door (I’ve never heard of it called a beaver tail) with the upper going up and lower going down. The 4 door config was a nightmare for locking both open/closed, number of Actuators, ramp integration, unloading stability and rigging. The three door configuration, with the lower descending downwards to form a ramp was better but two was just simple hence a winner.

One of the problems with two outer opening upper doors was aero loads for the in flight para dropping…. required big heavy structure and powerful actuators.

I don’t think any of A400m predecessors, FLA, FIMA, FLAG, 681 (the one they were building) had more than two.

Another interesting study was the inclusion of an overhead crane, which was very useful for palletised cargo but alas never taken up.
 
Zoo Tycoon said:
I remember studies from the mid nineties on FLA (aka A400M) into rear door config. We looked at 2, 3, and 4 doors. All of these had been studied before from a structural perspective but not the systems impact. The baseline at this point was a 2 door (I’ve never heard of it called a beaver tail) with the upper going up and lower going down. The 4 door config was a nightmare for locking both open/closed, number of Actuators, ramp integration, unloading stability and rigging. The three door configuration, with the lower descending downwards to form a ramp was better but two was just simple hence a winner.

One of the problems with two outer opening upper doors was aero loads for the in flight para dropping…. required big heavy structure and powerful actuators.

I don’t think any of A400m predecessors, FLA, FIMA, FLAG, 681 (the one they were building) had more than two.

Another interesting study was the inclusion of an overhead crane, which was very useful for palletised cargo but alas never taken up.
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Heard the description beaver tail a long time ago in reference to the C130
 
CJGibson said:
The Arado 232A/B estalished the overall layout and the ramp/door came to the fore with the Fairchild C-123, after that it became the norm. Swing noses and tails were a solution to pressurisation trouble.

So, mid-late 40s.

Chris
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Chris, good call on the C-123...but I have to differ on the era.
The C-123 only flew in the 50's.
Whilst it was based on the earlier Chase XCG-20 from the 40's, this was an unpowered glider.
So, whilst the Chase XCG-20, along with the Budd Conestoga and Arado 232 from the 40's had shown the way, this loading ramp was established only really in the 50's as the norm, which is what PMN1 was asking.
For example, there were plenty of companies still designing and producing primarily loading swing doors/fuselages into the 50's.
The Beverley, Argosy, Noratlas...etc all first flew and entered service in the 1950's.

It really was once the C-130 and An-8 and An-12 flew and entered service from the mid to late 1950's, did we see the rapid demise of the other types, from a design and production point of view.
 
It's all covered in On Atlas' Shoulders. I don't have a copy at hand at the moment and don't recall how I described them.

PMN1 - I think your question should have been 'When did end-loading become the norm in military transports?'

Kaiserbill is correct about the development of the Chase and C-123, both end-loading, and also covered in Atlas. As far as I'm concerned the Arado Ar 232A/B is the original tactical transport. Rear ramp, end-loading, high floatation undercarriage, flap blowing and the only things missing are thrust reversers and ABS.

I've never heard of the door/ramp on a Herk or an Argosy referred to as a beaver tail but that part of the airframe aft of the Herk's empennage is a beaver tail, like the same item on the F-14. Feel free to point me at an example.

Chris
 
Late to this party but I have a vague recollection of reading about beavertails somewhere but haven't been able to recall exactly where.
I seem to remember the beavertail was a more aerodynamic solution to help the airflow. Horizontal clamshell doors of course can't be opened in flight (huge airbrakes) but vertical ones can and the flattened profile of the Argosy's (Argosies?) doors limits the turbulence hitting the horizontal tailplane. The doors themselves form the profile of the rear fuselage pod when closed.

The Argosy is the only example I can think of in having such a layout, most twin-boom transports had horizontal opening doors, though the Rotodyne Z was to have a similar arrangement.
Single-tail transports like the C-130 etc. are not beavertails, just ramps, thought the do feature boat tails (see comment below) to smooth the airflow in that area.

CJGibson said:
Isn't the fairing between the jetpipes of an F-14 a beavertail?
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I think that's a boat tail, or at least that's the terminology Ray Whitford used. Similar concept though I would imagine.
 
Far from me to disagree with Ray Whitford, but i always thought the term 'Beaver tail' referred to a flattened fuselage end when viewed in plan view. I've also heard the term 'platypus tail' (but don't quote me on that!). I submit exhibit 'A", and actual beaver tail, i think it does evoke an F-14 or C-130 fuselage end :D
1657117765861.png
 
JFC Fuller said:
I found this interesting piece in a 1962 Flight Global article:

'The AW.681 over-comes the difficulty by being powered by four Bristol Siddeley BS.100 lift/thrust engines with rotating nozzles, hung in nacelles under the swept wing. The total thrust of some 120,000lb, swivelled suddenly down at the unstick point, should enable the 681 to take off at maximum weight in some hundred yards, and the aircraft might rise vertically at reduced weight. Cruising at some 500 mph should be possible on two engines.'


Certainly an interesting solution, I wonder why the BS.100 idea was dropped?
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Maby the medway had better fuel efficiency?
 
Cjc said:
JFC Fuller said:
I found this interesting piece in a 1962 Flight Global article:

'The AW.681 over-comes the difficulty by being powered by four Bristol Siddeley BS.100 lift/thrust engines with rotating nozzles, hung in nacelles under the swept wing. The total thrust of some 120,000lb, swivelled suddenly down at the unstick point, should enable the 681 to take off at maximum weight in some hundred yards, and the aircraft might rise vertically at reduced weight. Cruising at some 500 mph should be possible on two engines.'


Certainly an interesting solution, I wonder why the BS.100 idea was dropped?
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Maby the medway had better fuel efficiency?
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I remember someone mentioning Rolls was in trouble some time in the 60s - could they have been “throwing the dog a bone”?

Additionally, certifying the aircraft with the totally new BS100 could have been longer and more expensive - the angles of thrust deflection required and to be avoided, the effect of PCB on ground infrastructure and aircraft structure, and delays (Medway had been, or was near bench-running).
 
Some of the earlier Argosies;as operated by Zantop Air Transport, had vertically hinged
“ swing-away” doors fore and aft.
They flew the LOGAIR ( Logistics Air Command) contract for USAF. With rollers on the floor the load/ unload time was extremely short with both doors open.
 
JFC Fuller said:
I found this interesting piece in a 1962 Flight Global article:

'The AW.681 over-comes the difficulty by being powered by four Bristol Siddeley BS.100 lift/thrust engines with rotating nozzles, hung in nacelles under the swept wing. The total thrust of some 120,000lb, swivelled suddenly down at the unstick point, should enable the 681 to take off at maximum weight in some hundred yards, and the aircraft might rise vertically at reduced weight.

Certainly an interesting solution, I wonder why the BS.100 idea was dropped?
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OMG - 16 afterburners kicking in simultaneously pointing downwards, the noise, the shear volume , the molten runway, the dust/hot air/chunks of runway kicked up….. oh don’t get me wrong, I’d love to have seen it.
 
Strictly from a horsepower perspective, using 4x Pegasus engines would have been much better than 4x Medways. The Medways only made 13.7klbs, while a Pegasus 5 made 15k and the Pegasus 6 made 19klbs. Nevermind the straight-through version that made 28klbs of thrust...

Also, I would have been a sneaky bugger and added an augmentor hoop around each vectored nozzle, to pull some extra air through the hoops and make a bit more thrust that way. See also Ducted Rocket.
 
The Flight 1962 reference to BS.100 was wrong. A Pegasus variant was funded by MoA for schemed HS681. That was funded into prototype build 5/3/63, engine to be confirmed; Medway funded 9/63. BS.100 was funded into full R&D for P.1154 25/3/63. MoA resurrected Medway for industrial balance to preserve 2 UK engine sources: RR 8/63 had Speys in civil and Bucc 2 berths, little long term.
 
In a world where TSR2 and 1154RAF go into service I think 681 and the DH/HS 129 (a smaller airlifter like the Do31) have to survive too. Not easy I know but the rationale of the mobile RAF needs them.
 
uk 75 said:
In a world where TSR2 and 1154RAF go into service I think 681 and the DH/HS 129 (a smaller airlifter like the Do31) have to survive too. Not easy I know but the rationale of the mobile RAF needs them.
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HS129 basically a twin engine version of the 681?

With the 1154RAF needing BS100 engines, I could definitely see the VSTOL transports also getting BS100s for commonality.

Do we have any idea what the non-PCB thrust would have been? For those times that you didn't want to try to light off 8x or 16x afterburners more or less simultaneously and crater the runway?
 

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