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Lightning inlet cone


Max89
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1 hour ago, KevinK said:

 Kevlar wasn't invented until 1965 and Wikipedia states the first commercial use as early 1970's. Given that the Lightning had entered service in 1960, it seems unlikely.

I stand corrected.....dunno where the kevlar came from...even coremans says its fibreglass.....😳

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On 11/2/2021 at 11:36 PM, stever219 said:

The Lightning as a whole was designed to wring maximum efficiency from the available engines, initially the Armstrong Siddeley Sapphire, in order to achieve a fully supersonic performance, ultimately Mach 2 plus.  To achieve this intake duct design was crucial and it was optimised for the top end of the performance envelope.  

 

As a moveable shock cone was impractical on the grounds of weight, complexity and/or cost the relationship between the tip of the radome and the lip of the intake ring was vital as these created the initial shock waves which begin slowing the supersonic air flow to a speed acceptable to the engine compressors.  Further shock waves were created by the nosewheel bay and radome support structures and by the convergent/divergent form of the intake duct.  A final shock wave was created by the leading edge of the wing centre section where the duct splits to serve each engine independently.  Immediately aft of the bottom trailing edge of the nosewheel bay are a set of vortex generators (not inlet guide vanes) to energise the airflow along the lower surface of the intake duct .

 

 

Thanks for your very informative post !

There are a few things however that are not too clear to me...

You mention a number of shock waves generated inside the intake duct, now designers generally try to avoid shock waves deep into a duct, as these can crete reflections that can bring troubles of various types... not saying it can't happen, afterall the Lightning is a type from an era when the design of supersonic aircraft was in its infancy and many choices of the era were later superseded. One aspect I find strange however is the presence of a shock wave after the convergent-divergent section: the role of this is generally to decelerate the flow from supersonic to subsonic and there should be no supersonic flow after the throat, with any other structure at the end of the divergent section only needed to "correct" and direct the flow into the engines. Are you sure another shock wave formed after the convergent divergent ?

Then I have a question: did the Lightning feature any wayn of estracting air from the intake to control the pressure and move the position of the shock waves before the intake ? This is a system that can be used in place of a moving cone and for example was used on the contemporary F-104.

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On many early Lightnings it was easy to see that the front of the shock cone was fibreglass. You could see the yellow-greenish colour and the weave.

Fibreglass to be as transparent as possible to radar. Is kevlar transparent to typical radar frequencies?  I have no idea.

Apart from the fact it was a much later development than the LIghtning, why use expensive kevlar when cheap fibreglass will do?

 

It is also worth saying that at the time the P1, then Lightning, was being developed, understanding of supersonic flow characteristics and jet engine inlet and requirements were still  fairly limited. Few good wind tunnels (if any in Britain) operating in the right speed ranges, little modelling. It is easy form here to assume all sorts of things, all sorts of knowledge which simply did not exist.  A good deal was 'best guess' engineering based on experience and gut feel, backed up by testing - 'suck it and see'. A lot was learned and there were many surprises along the way.  Keeping it as simple as possible reduced the number of variables and unknowns and the risk of failure.  Good engineering practice! 

 

So, no moving bodies. I suspect if more work had been needed, Giorgio's suggestion of bleed air extraction for shock wave control might have been tried. Simpler & lighter than moving bodies.  Mr Petter was involved in the early design, a great believer in simplicity and lightness.

Edited by John B (Sc)
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Hallo

The number of shock waves depends on the speed and the geometry.

If the geometry is cleverly designed, as in this case, then a sufficient number of shock waves will be created in the respective speed range.

The supersonic wind tunnel, which remained from the German research institutions, was awarded to France.

Whether Great Britain had one and when is beyond my knowledge.

 

You can also get an insight into the effectiveness of an intake duct with a constant geometry the other way around.

Check all aircraft accidents in detail.

I know some of the Lightning, but not enough to make a statement.

This also applies to the F-16 today.

Here it is the case that the flying envelope is constantly adapted over the course of the aircraft's operating life, or other devices are installed in order to prevent such dangerous flow conditions from occurring at all.

 

Happy modelling

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2 hours ago, John B (Sc) said:

On many early Lightnings it was easy to see that the front of the shock cone was fibreglass. You could see the yellow-greenish colour and the weave.

Fibreglass to be as transparent as possible to radar. Is kevlar transparent to typical radar frequencies?  I have no idea.

Apart from the fact it was a much later development than the LIghtning, why use expensive kevlar when cheap fibreglass will do?

 

It is also worth saying that at the time the P1, then Lightning, was being developed, understanding of supersonic flow characteristics and jet engine inlet and requirements were still  fairly limited. Few good wind tunnels (if any in Britain) operating in the right speed ranges, little modelling. It is easy form here to assume all sorts of things, all sorts of knowledge which simply did not exist.  A good deal was 'best guess' engineering based on experience and gut feel, backed up by testing - 'suck it and see'. A lot was learned and there were many surprises along the way.  Keeping it as simple as possible reduced the number of variables and unknowns and the risk of failure.  Good engineering practice! 

 

So, no moving bodies. I suspect if more work had been needed, Giorgio's suggestion of bleed air extraction for shock wave control might have been tried. Simpler & lighter than moving bodies.  Mr Petter was involved in the early design, a great believer in simplicity and lightness.

 

It should be said that moving cones were used on some types that proved to be very robust and capable to be operated in harsh conditions, like the Soviet Su-7 and MiG-21. Now the Su-7 was a pretty large and heavy type, but the MiG was overall quite in line with Petter's philosophy of light and simple, probably more than the Lightning. So yes, a moving cone adds complications weight and cost, but really it's not such a big problem.

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13 hours ago, Bozothenutter said:

Any ex maintenance fellows about?

Yeah me 5 years on type and undertaken many intake inspections dues to being an propulsion tradesman. Slid past many a bullet.

 

The intake in the "splitter" as you call it was for a heat exchanger for the cockpit climate control system. The air intake for the Cold Air Unit (CAU) can be seen to the left (round hole) it did have a grill in it, you used to use a long rod to poke through to se if the CAU had seized. 

 

Edited by tweeky
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EE had the first induced flow wind tunnel in the UK running by the end of 1949.  It only went to Mach 1.07 initially, which was enough.

Reading some of the development story, it is impressive how little was known, in so many areas including inlet design, how much was done on best principles and good reasoning. With a fair degree of luck ! 

 

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2 hours ago, JagRigger said:

Lightning intake cone......... to a generation of RAF engineers it just leads to an ingrained image of Miss Wayward Body doing the intake check

Too true...   ...just go onto Yooochoob and search for Dr Fod and Miss Wayward body.  Just be careful where you do this.

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23 hours ago, canberra kid said:

I've just read through this hoping it may shed some light but unfortunately not, other than stating the P.11 (T.4) is aerodynamically no worse than the P,1A and in some respects better.

  gtmKmn.jpg

John

 

Was this not similar to the case of the Hunter two seater?  Slightly better aerodynamics after much  tweaking resulted in lower drag rather than higher for the two seater. I believe EE were given the canopy & spine lofting information from the Hunter two seater and use that as their basis - any confirmation of that, can't recall where I read/heard that?

 

John B

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