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Lightning Vertically Stacked Engines

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Lightning Vertically Stacked Engines

Old 19th Feb 2017, 00:17
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Lightning Vertically Stacked Engines

Lightning seems to be only fast jet designed with vertical stack arrangement of its 2 engines.
What was the disadvantage that meant it was not continued with any subsequent fast jets?
Also, any particular advantage for vertical stack?
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Old 19th Feb 2017, 05:36
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From https://www.flightglobal.com/pdfarch...0-%201766.html
Inspired design led to the unique Lightning staggered-engine configuration—both engines being installed on the aircraft centre line, viewed from above, but with the upper engine to the rear of the lower engine, thereby giving an effective powerplant frontal area only 1.5 times that of a single powerplant. This configuration not only minimises drag but also eliminates asymmetric engine-cut effects and allows the possibility of low-altitude cruising on one engine, as well as providing the only chance of getting home to base after an engine failure. It also simplifies the duplication of essential services, allowing increased reliability.
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Old 19th Feb 2017, 12:21
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Lousy accessibility for the upper engine. Two engines side by side gives a nice flat bottom with loads of room to hang things.
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Old 19th Feb 2017, 12:59
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Liked the 'increased reliability' bit. Not many of us who worked on Lightnings (the early ones at least) would agree with that statement.
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Old 19th Feb 2017, 15:37
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The advantage was reduced frontal area with the resultant reduction in drag. However it came at a huge price - no fuselage fuel. So the Lightning was very quick but not for long. Another downside was poor accessibility for engine ancillary components. Virtually all replacements required an ECU removal.
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Old 19th Feb 2017, 20:43
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I know it barely counts as a 'fast' jet, but the stacked Avons on the Shorts Sperrin were arranged thusly to enable the wing spars to run uninterrupted from root to tip, passing aft of and between the engines, whereas on the other V-bombers a double-banjo or holes in the spars were required.
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Old 20th Feb 2017, 08:05
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The SR53 had its engines stacked vertically, and by all accounts it was fast.
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Old 20th Feb 2017, 09:26
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Here's another jet-stacker, and for different reasons yet again. The F+W Arbalètte had four Turboméca Piméné turbojets disposed in vertical pairs; it was a 60% scale test-bed for the N-20 fighter and didn't have enough internal volume for buried engines.
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Old 20th Feb 2017, 10:09
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as well as providing the only chance of getting home to base after an engine failure.
What does this mean? Most aircraft with two engines can get down with one failed.
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Old 20th Feb 2017, 10:34
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I'd say it is actually a requirement for a twin engined aeroplane. For some older designs there certainly are examples that cannot maintain altitude on a single engine in certain weight/density altitude combinations, but not for anything designed in the past 40 years or so.

(actually, all aircraft will get down... but whether you can use the aircraft again afterwards...)
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Old 21st Feb 2017, 09:16
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ISTR (and I was not a Lightning jock) that closing down one engine for endurance was not always an overwhelming success
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Old 21st Feb 2017, 09:33
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Originally Posted by Herod View Post
What does this mean? Most aircraft with two engines can get down with one failed.
SOP for Farnborough based Lightnings was when returning on minimum fuel [300lb was it?](which they invariably did after a 'shoot' over Cardigan Bay) and unable to land at the first attempt in IMC, shut down one engine and divert to Brize. They would normally try to return with enough fuel to divert to Boscombe but this would mean they were marginally overweight to land straight away so would burn off in the visual circuit in a way that only a Lightning could!!.
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Old 21st Feb 2017, 09:34
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These days they're aiming for stealth, which tends to benefit from a wide, flat fuselage (blended into the wings) rather than a tall, narrow one. Having the engines side-by-side also allows space for a weapons bay between them (or at least between the intakes) and that improves stealth too.
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Old 21st Feb 2017, 10:55
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Recovery fuel

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A couple of points on your post, firstly 'normal' minimum recovery fuel pre diversion was 800lbs/side as I recall and secondly the Lightning did not have any 'overweight' landing restriction except that the F6 could not land with fuel in the overwing ferry tanks (if carried) and I doubt very much that they would have been for any activity in Aberporth Range.
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Old 21st Feb 2017, 13:16
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Originally Posted by nipva View Post
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A couple of points on your post, firstly 'normal' minimum recovery fuel pre diversion was 800lbs/side as I recall and secondly the Lightning did not have any 'overweight' landing restriction except that the F6 could not land with fuel in the overwing ferry tanks (if carried) and I doubt very much that they would have been for any activity in Aberporth Range.
I can't argue with what you say, but the Farnborough Lightning wasn't a 'normal' one; some of it's belly tank was occupied by a Mauser cannon so it was cleared to operate to lower fuel minimums.
As for being overweight for landing, maybe the pilots told us this because they enjoyed throwing it around when back in the circuit; I can remember it running if for a break just as a Buccaneer rolled; I warned the Bucc about the Lightning and the Lightning driver (Jack Frost if I recall) said 'do you have to give the game away' then there was the bang of reheat lighting he and promptly chased the Bucc as far as Basingstoke!

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Old 22nd Feb 2017, 12:02
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However it came at a huge price - no fuselage fuel. So the Lightning was very quick but not for long.
Remember an old friend telling me (no doubt an urban myth) that they never found the top speed of the F6 because it ran out of fuel first........
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Old 22nd Feb 2017, 13:00
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The final evolution of the Avro 730 supersonic bomber was intended to have 8 engines, arranged in a 2x2 stacked pair on each outboard wing section.

No doubt an engine failure on take-off would have involved more than one engine, so the pilot would have had a fine old time trying to keep straight on the bicycle undercarriage with only a periscope to view the outside wotld...
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Old 22nd Feb 2017, 14:41
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Pegasus,

Your friend was not far off the truth. However because the F6 was limited to M2.0 (directional stability) this could be achieved (just) without AAR. Indeed it was part of conversion to type when first joining an F6 squadron. In my case the sortie lasted 40' and as I recall was from abeam Wick to abeam Leuchars. It was the first and last time that I ever flew at M2.0 This was before the installation of the ventral gun pack with its associated reduction in fuel load and extra drag. Might have been a bit more knife-edge thereafter.

Last edited by nipva; 25th Feb 2017 at 09:11.
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