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Is it possible? A modern VC 10

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Is it possible? A modern VC 10

Old 3rd Dec 2020, 18:21
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Q: What was glamourous about the One-Eleven?

A: Philippine Airlines hosties.

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Old 3rd Dec 2020, 19:10
  #62 (permalink)  

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Hands up who would like to stand by the threshold of one of LHRs runways and see a ten depart again
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Old 3rd Dec 2020, 20:01
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Originally Posted by Chris Scott View Post
Looking forward to your ten cents' worth, Jelle!
Thanks Chris!

As a bit of context for power demands, the 777 has two 120kVA generators for a total generating capacity of 240kVA, the 787 uses four starter/generators of 250kVA each, for a total of 1000kVA. Compared to that, four times 48kVA is not a lot, but it was more than what the 707 needed...

I realised that fail safe/safe life are dated terms, but they were in vogue when the VC10 was designed. I don't know the specifics of all the modern airframes but on the 737 family, Boeing managed to increase the available life on a fuselage from 60,000 to 75,000 cycles when they went from the Classic Generation (-300,400,500) to the Next Generation (-600 and on) models. Long range airframes can take a longer time to reach such a cycle limit. A 747 was originally designed for 20,000 cycles, 60,000 hours or 20 years. On that airframe it is not an absolute limit (a 747-100 surpassed 100,000 hours in 1996) but it takes expensive repairs and modifications to make sure you can keep it in the air. There is an old FlightGlobal article here that includes a list of several types including design life numbers. The 787 was designed for 44,000 cycles (don't know the hours) but a test airframe went through a simulated 160,000 cycles without any cracking. While that validates the use of composites to counter fatigue related structural issues, the big question is whether other influences are going to age the airframe in any way as it clocks up the hours. Anyway, the point I was trying to make is that you better have a good thought about a realistic design life for the airframe from the start as it may help in keeping the weight down as well as the testing costs.

Things have gone a bit quiet on the plans to get the Dunsfold VC10 back in the air again. While I would not recommend restarting production on the VC10, putting one in the air again to provide AAR for a while may well be a worthwhile effort. And if it does work out, we may well get to listen to the roar of four Conways again...

Great photo of ZD241 there Tony
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Old 3rd Dec 2020, 22:17
  #64 (permalink)  
 
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Originally Posted by tdracer View Post
I think you'll find there are very good reasons why no clean sheet design in the last three decades has put the engines on the tail.
tdracer. This is an interesting point. Beyond considerations of compression and polar moments of inertia, I'm wondering what the principal disadvantages might be?

pax britanica. I have both arms raised!
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Old 4th Dec 2020, 01:35
  #65 (permalink)  
 
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Originally Posted by Gipsy Queen View Post
tdracer. This is an interesting point. Beyond considerations of compression and polar moments of inertia, I'm wondering what the principal disadvantages might be?
There are several big ones. First off, tail mounted engines are relatively high off the ground, making servicing and maintenance more difficult and time consuming. Not a big difference, but over a ~25 -30 year service life of an aircraft, it mounts up. Second, during the early design phases of a new aircraft, the engine weight is little more than an educated guess. Worse, the engines seldom get lighter - they are usually heavier, often a lot heavier. Now, if the engine is mounted on the wing - it's located near the aircraft CG, so a heavier engine is generally not a big concern to the overall design. Tail mounted engines - by definition - are way behind the aircraft CG. So when the engine gets heavier, the wing is suddenly in the wrong place. The only solution (short of starting over with a new wing position) is to add ballast to the nose - effectively doubling the weight penalty. According to people I worked with that worked on the MD-90, this hurt the MD-90 massively. After the basic design was frozen, the FAA required much better blade out and uncontained failure protection - resulting in a massive increase in the engine weight. Between that and the associated required nose ballast, the resultant aircraft was so heavy that it lost most of it's fuel burn advantage from the new engines (relative to the MD-80).
Structurally, putting the engines on the wing has significant advantages relative to the tail. I've been told there are some aerodynamic advantages as well although I admit it's not obvious to me what those might be.
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Old 4th Dec 2020, 11:54
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The story goes, that the DC-9 wing was a barely modified DC-8 wing. The DC-8 had excellent stall properties, so the DC-9 was expected to show the same good qualities, but it did not. Eventually, it was discovered, that the pylons of the DC-8 were part of the good characteriscs, so what they did was to build a mock mini pylon on the DC-9 wing, and presto, there were the good stall properties again. The little 5 days stubble under a DC-9 wing therefore, is just a deteriorated DC-8 pylon. Or so the story goes...
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Old 4th Dec 2020, 12:25
  #67 (permalink)  
 
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"I'm wondering what the principal disadvantages might be?"

No airline would buy it????

I seem to remember Bill Gunston discussed the advantages that Boeing discovered when they designed the B-47 - in addition to the points mentioned by tdracer they found less drag, much safer in case of an engine blowing up, much easier to upgrade to bigger engines later (also see the 737)

It's no coincidence that the Russians went for under wing engines after the Il-62.

jets at the back still have a place on business jets and small commuter aircraft but I can't see anyone designing a medium/large airliner with rear engines again
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Old 4th Dec 2020, 12:48
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VC10 looks like a DC9 mated with a 707
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Old 4th Dec 2020, 12:54
  #69 (permalink)  
 
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Pugilistic Animus, NEVER! it looked far better.
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Old 4th Dec 2020, 14:01
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Originally Posted by pax britanica View Post
Many lovely trips on tens and Supers among them LHr-Barbados-LHR LHR-Nicosia Khartoum Addis Seychelles , JFK-Antigua Barbados , SeychellesMauritus. A a lovely comfortable aeroplane -but that doesnt sell, witness the wonderful A 380 ,and re engining it would do nothing for the over heavy wings (no cantilevering balance from poddied engines, no huge tail for lack or moment arm and no Forth Bridge at the rear of the fuselage to hang the engines on.

As for the age demographics well to have been a pax on VC10 you have to be pretty old or flown on one as a small child, to have actually flown a civil one possibly older still.

Noise-unparalleled altho somehow a Caravelle with only two smaller engines sometimes seemed to rival them. The strange moaning noise as it taxied to the threshold and then the howl as it spooled up for full take off power remains a great memory from my childhood spotting days, pretty cool on approach too.

I lied the Trident as well, always seemed to zip along nicely much to the delight of the crews it seemed who more than once on trips I was on took great pleasure in pointing out a Scandi DC9 we were overtaking on the way to Stockholm and a VC10 we passed from Rome to LHR
Also very quiet inside but not outside , the 3 and a half engine version being the noisiest but I think the 1A version the fastest and trickiest.

Quiet planes , A 380 top of the league and biz class on an MD80 left you with the feeling there were no engines at all.

Interesting the relatively derided 1-11 which I didnt like much preferring the quieter and indeed better selling DC 9 - actually did sell pretty well and to airlines in all parts of the globe . But then thats us brits again always preferring the glamour to the practical

So there you go-the past is another country and they do things differently there.

(UK second biggest aersopace industry ? well USA of course but surely Airbus which has no British ownership anymore does it is huge and the French element probably bigger than ours . Whatever I do so hope RR sort out their problems and the Brexit calamity doesnt see the Airbus Industrie Uk elements which are critical gradually get moved to the rest of Europe . We dont do much in manufacturing hi tech engineering line and it would be a tragedy to lose even one of these enterprises . Not World Beaters to use that idiotic jingoistic phrase thats been the bane of so much of Britains recent history but genuinely highly regarded global enterprises of which we have very few that involve actually doing anything in terms of long term investment , employment and preservation of engineering and technology skills.

Hands up who would like to stand by the threshold of one of LHRs runways and see a ten depart again
pax britannica,

Yes, UK aerospace industry second largest in the world. Airbus is not French, despite the huge operation at Toulouse the company is actually registered in the Netherlands, and counts the UK as a 'home country.' Ownership of an industry is largely irrelevant in these globalised industry days. The Uk designs, manufactures and assembles each and every wing ever fitted to an Airbus airliner or military airlifter. In addition the UK designs the undercarriage, the fuel system and the hydraulic system, and manufactures a good percentage of these items too. Whilst the UK may only assemble complete aircraft in relatively small numbers in the shape of Typhoons, Hawks, Islanders, Merlins and microlights, it is present on almost every large scale platform such as A220 (wings), Martin Baker ejection seats, 15 to 20% of each and every F-35 built and so on and so on. Rolls-Royce of course is a huge international player and there are UK engines on platforms across the world, and a huge component industry.

Totally agree with you on the A380 by the way, simply the most comfortable and pleasant airliner I have ever flown on.
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Old 4th Dec 2020, 14:55
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Originally Posted by tdracer View Post
There are several big ones. First off, tail mounted engines are relatively high off the ground, making servicing and maintenance more difficult and time consuming. Not a big difference, but over a ~25 -30 year service life of an aircraft, it mounts up. Second, during the early design phases of a new aircraft, the engine weight is little more than an educated guess. Worse, the engines seldom get lighter - they are usually heavier, often a lot heavier. Now, if the engine is mounted on the wing - it's located near the aircraft CG, so a heavier engine is generally not a big concern to the overall design. Tail mounted engines - by definition - are way behind the aircraft CG. So when the engine gets heavier, the wing is suddenly in the wrong place. The only solution (short of starting over with a new wing position) is to add ballast to the nose - effectively doubling the weight penalty. According to people I worked with that worked on the MD-90, this hurt the MD-90 massively. After the basic design was frozen, the FAA required much better blade out and uncontained failure protection - resulting in a massive increase in the engine weight. Between that and the associated required nose ballast, the resultant aircraft was so heavy that it lost most of it's fuel burn advantage from the new engines (relative to the MD-80).
Structurally, putting the engines on the wing has significant advantages relative to the tail. I've been told there are some aerodynamic advantages as well although I admit it's not obvious to me what those might be.
Very interesting as always, tdracer. Your point on the aft CG is only too pertinent to the VC10, as it was to the One-Eleven. Empty ferries were always a problem. They usually happen after an unplanned diversion to an aerodrome where the airline has limited facilities, and typically involve a short flight to the original destination. Loading fuel into the VC10's centre tank as forward ballast could be a hostage to fortune, and ballast is not necessarily available. The usual expedient was to gather as much of the remaining catering and its canisters into the forward galley. A CG near aft limits played a part in the accident that caused the demise of the VC10 ex-prototype, G-ARTA, landing at Gatwick on a positioning flight from Heathrow..

In addition to the weight of the engines, sticking them on the rear fuselage pushes the tail-plane/horizontal-stabiliser (referred to on the VC10, oddly, as the TPI) upwards. On the Caravelle, it went about half way up the fin, but on most aeroplanes to the top. So, on the VC10 the "bullet" that housed the pivot point and the top of the screw jack was around 38 feet above the ground.

Am no expert on structures and aerodynamics, but there are further disadvantages for tail-mounted engines in both those areas. For the non-cognoscenti:
1) Aircraft have a maximum zero-fuel weight (MZFW) that is limited mainly by the strength of the wing root, and affects the maximum payload, So - in effect - every ton of equipment or structure added to the fuselage or empennage reduces the maximum payload weight. (That also applies to fuel in any belly-mounted tank, as in the VC10's centre tank.)

2) It follows from (1) that the engines being supported in flight via the wing root is less efficient than mounting them on the wing, because - everything else being equal - the wing root has to be thicker and creates more drag.

3) Less obvious to the lay person is the aspect of wing-bending relief, a subject on which, as a non-engineer, I'm going to have to tread carefully and stand to be corrected. Pilots of big jets know (and flight engineers take for granted) that even aircraft with wing-mounted engines like to keep the outboard wing tanks full of fuel as long as possible, particularly at high ZFWs. From a structural viewpoint, it's best to place weight as close as possible to where the necessary aerodynamic lift is being generated. Emptying the outboard tanks prematurely would result in the outer wing bending upwards. Although engines are of a fixed weight, distributing them at intervals across the wing enables a lighter wing structure, as well as a thinner wing root.

There's little doubt that, versus the B707, DC-8, CV-880 and CV990, the VC10 suffered cruise penalties from having rear-mounted engines. Crews will remember the so-called aileron-upset system. At high all-up weights, it was deployed after flap retraction. The ailerons were angled up slightly to move the wings' centres of lift slightly inboard - presumably to reduce the stress on the wing root and/or the bending up of the wing tips. Perhaps someone can remind me, however, why that was no longer necessary above 24,000 ft?

To stray off topic for a moment: based on the argument I've offered in (3), above, I'm also curious about the conflicting factors of two wing-mounted engines versus four on long haul.
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Old 4th Dec 2020, 15:32
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I seem to remember Maggie went out to the States on a VC10 and landed in a Trident, departed back to the UK in a Trident and landed in a BAC1-11, after that they stopped us gagging dead engines with pax on board if my memory hasn't failed me.
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Old 4th Dec 2020, 15:45
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Not only short ferries Chris. I remember getting on a VC-10 in the Seychelles to fly to Colombo and much to my surprise was invited up to Business or whatever it was called in those days, along with about 10 other passengers. Once in the cruise I was invited to retake my seat in steerage. The hostie was most apologetic but said "it's something to do with the trim". Is that why the Russkies always used to prop up the tail of the IL-62 when it was not loaded?
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Old 4th Dec 2020, 17:23
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Originally Posted by VictorGolf View Post
Not only short ferries Chris. I remember getting on a VC-10 in the Seychelles to fly to Colombo and much to my surprise was invited up to Business or whatever it was called in those days, along with about 10 other passengers. Once in the cruise I was invited to retake my seat in steerage. The hostie was most apologetic but said "it's something to do with the trim". Is that why the Russkies always used to prop up the tail of the IL-62 when it was not loaded?
Unless you were asked to return up front for the landing, VG, I can't explain that. Presumably it was a standard VC10 (Type 1101), as I remember from day stops in the Seychelles in the early 1970s. OTOH, if it was a Super, I suppose there might have been fuel stuck in the fin tank for the T/O that could have been burned later en-route. But that's a guess: I don't know the fuel system on the Super.

Although the Standards were tail-heavy for an empty ferry, they were on the nose-heavy side at the beginning of long sectors with a full pax load; partly because the centre tank would be full. As i wrote in a previous post, that was always noticeable after top of climb, when the TPI needed to provide a lot of nose-up trim; i.e., more negative lift than usual. (The more negative lift that is being produced by the tail-plane, of course, the more positive lift has to be generated by the wing, increasing total drag.) Once the centre tank was empty, the situation was a lot better.

Our Type 1103s were combis, and I think we also used a tail strut when loading main-deck cargo via the freight door, which was forward of the wing. If you think about it, the first few pallets always end up at the back of the cabin, so we probably used them when loading and unloading our B707-320Cs as well. I can't remember.
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Old 4th Dec 2020, 18:07
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"VC10 looks like a DC9 mated with a 707"

And it had a beautiful whale tail ..



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Old 4th Dec 2020, 19:48
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Originally Posted by VictorGolf View Post
Not only short ferries Chris. I remember getting on a VC-10 in the Seychelles to fly to Colombo and much to my surprise was invited up to Business or whatever it was called in those days, along with about 10 other passengers. Once in the cruise I was invited to retake my seat in steerage. The hostie was most apologetic but said "it's something to do with the trim". Is that why the Russkies always used to prop up the tail of the IL-62 when it was not loaded?
Its a long time since I flew the VC10, 40 years, but my understanding of the IL. 62 pogo stick relates to industrial espionage. The main landing gear of the VC 10 was just a little forward of the ideal position. When designing the 62, copying the 10, the Ruskies heard that the gear was in the wrong position
and decided to correct it. Sadly, for them, they corrected it in the wrong direction and moved THEIR MLG. Forward instead of aft, hence the need for a pogo stick. Or so I heard ! . Replacement for the VC 10 ? The Boeing 757 or 767 . Better payload/ range and lower cost per pax. Sad but true. and I have operated all three.
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Old 4th Dec 2020, 20:26
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The tail prop on the Ilyushin is more a design choice than a mistake, see here: The competition: Il-62
It allows the use of a smaller tailplane and manually powered elevators.
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Old 4th Dec 2020, 20:57
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Originally Posted by Jhieminga View Post
The tail prop on the Ilyushin is more a design choice than a mistake, see here: The competition: Il-62
It allows the use of a smaller tailplane and manually powered elevators.
That's presumably related to the fact that, as I seem to recall, the Il-62 had a huge amount of unused (and presumably unusable) space at the back end of the cabin.

I have fond memories of struggling up shaky steps on the ramp at LHR to fit the massive engine intake blanks on night-stopping Il-62s, and of the weird contraption that Aeroflot used when refuelling to allow them to add anti-freeze to the fuel from the bowser.
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Old 5th Dec 2020, 02:49
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I'm also curious about the conflicting factors of two wing-mounted engines versus four on long haul
Not sure of the conflicting factors to which you refer Chris. Both offer wing bending relief but at the expense of increased fin/rudder size to handle asymmetric conditions. Having two rather than four is just economics.
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Old 5th Dec 2020, 05:50
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Originally Posted by Asturias56 View Post
SNIP

I seem to remember Bill Gunston discussed the advantages that Boeing discovered when they designed the B-47 - in addition to the points mentioned by tdracer they found less drag, much safer in case of an engine blowing up, much easier to upgrade to bigger engines later (also see the 737)
I seem to remember long ago that there was also a rather subtle point about damping oscillations (or something in that kind of area of structural stability--I am manifestly out of my technical depth) that was the result of the engines being hung largely forward of the leading age.

Is this a false memory, or was there something like this that was a further, unexpected, benefit of podding?
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