Propeller to jet engine

Even if the jets developed enough power to lift a useful load,and as pogno said,could carry enough fuel!!If the wing section was unchanged one would soon get into the situation where the stalling speed was about the same as the critical mach number.
From memory the U2 suffered that problem and I seem to remember reading that if you tried to turn too tight at very high alttude you could have the situation where the inside wing might be in stall buffet and the outside wing might be in mach buffet!! Hard work without an autopilot on the early ones.
Also from memory on the early U2 at very high altitude the difference between stall and Mcrit was in the region of 7 knots!!

As much as that? I heard it was more like 5mph. With regard to the problem of the wings in a tight turn, they should not have expected them to behave any other way when they stuck a jet engine in what was little more than an all metal glider. You could have produced the same problem by putting an Allison C-250 in a Blanik 😀 (anyone remember them?)

German “Fighter Command” (Jägerleitstelle) directed the aircraft so that the fighters normally closed in from frontal positions. When the fighters and bombers merged there were lots of opportunities from rearward attacks. But rarely fighters flew prolonged time to pass the bombers.
So I think a faster bomber would deny repeated attacks as the fighters have no speed advantage any more. But the more interesting effect of a jet engine is the higher altitude.

That method of attack would have been used for daylight bombers!!Head on attack at night was virtually impossible,at night the radar equipped night fighters would normally chase from behind or on the beam and those equipped with upward firing guns would remain slightly below the target aircraft.
The non radar ‘wild sau’ single seaters would work in conjunction with searchlight teams and ground ‘shroud’ lighting effect over the target areas and try to sillhouette the target a/c from above or high beam etc.

There seems to be a lot of gun camera footage from your countrymen that dispute that!😀

German “Fighter Command” (Jägerleitstelle) directed the aircraft so that the fighters normally closed in from frontal positions. When the fighters and bombers merged there were lots of opportunities from rearward attacks. But rarely fighters flew prolonged time to pass the bombers.
So I think a faster bomber would deny repeated attacks as the fighters have no speed advantage any more. But the more interesting effect of a jet engine is the higher altitude.

Yes, that’s the one. N1340N, converted 1969 and then destroyed August 1970 when she stalled pulling up from a water drop run. The NTSB summary http://www.ntsb.gov/ntsb/brief.asp?ev_id=1592&key=0 points the finger at pilot error, although I have seen suggestions that the thick smoke caused a power loss. There’s a picture here: http://www.warbirdregistry.org/b17registry/b17-426107.html

The Wellington was a test bed of late 40s vintage. I’ve just tried to find a web image withpout any luck, but there’s one in Bill Gunston’s history of Rolls-Royce engines.

There were Dart-powered Wellingtons and B-17s, for completely different reasons…

In the 60s a fire-fighting B-17 was converted to Darts in an attempt to improve performance. It may have also been an attempt to reduce maintenance costs.

The engines were cheap, having come from a retired UAL Viscount. Unfortunately, the plane soon met its end, and without checking sources, I believe it was not engine related.

A four-Nene Lancaster would present some interesting problems concerning the inner nacelles. Incorporating jet engines into nacelles along with the undercarraige would require some particularly creative design (putting it politely…) while the twin fins would sit in the middle of the jet efflux. Then there’s also the fact that the Lancaster is a tail-sitter, which doesn’t go at all wel with jet engines.
All in all, the necessary redesign would be so drastic you may as well start with a clean sheet of paper (and then call it Vulcan?)
Turboprops are rather more interestting. There were Dart-powered Wellingtons and B-17s, for completely different reasons, and I wonder whether the Shackleton MR3 shouldn’t have been a turboprop. As the Argosy wing was a Lincoln/Shackleton derivative it would have been a relatively low-cost project, I would imagine. I recall somewhere seeing an impression of a Mark 4 Shackleton with single fin and turboprops – at the least it would have save the hearing of many Shackleton crew. Does anyone have more concrete information?

Edit: I should have mentuioned the Douglas XB-42/XB-43 – piston and jet versions of effectively the same 1944-vintage bomber that perhaps answer the questions posed in the first post.

Fighters rarely attacked bombers from behind.

There seems to be a lot of gun camera footage from your countrymen that dispute that!😀

According to Bill Gunston, ‘Roy Chadwick wanted to put four Nenes in a Lancaster which would have been almost immune to intercption or flak’.

Fighters rarely attacked bombers from behind. A faster bomber would still be attacked, but it becomes more tricky for the fighter. The speed advantage for a pure retrofit is limited. Critical Mach number would be somewhere close to M0.65. Even the Me262 enjoyed only a small speed advantage.

Metrovick either left the engine business on their own to concentrate on steam turbines, or were forced (out by MoS). Margaret Gowing’s Official History of the UK Nuclear Programme has MoS, with more Aero capacity than Peace needed, putting them into electricity-generation nuclear reactors, $-sparse. We were cold, winter 1947.

Read the following (a slightly biased history I got on-line, so believe at your own risk 😉 ):

Metrovick F.2
The Metrovick F.2 was one of the earliest jet engines, and the first British design to be based on an axial compressor. Based on design work by A.A. Griffith from ideas he had developed in 1926, serious development of the F.2 didn’t start until the late 1930s, by which point Frank Whittle’s designs were already running. In the end the F.2 proved to be everything Griffith promised it would be; smaller than Whittle’s designs, more powerful and considerably more fuel efficient. However in his drive for perfection he also ended up designing an engine that was far too complex, and it never entered production. Work did not go to waste, however, and eventually resulted in an engine design that was passed on to Armstrong Siddeley, the Sapphire.

Griffith published a seminal paper in 1926, An Aerodynamic Theory of Turbine Design, that for the first time clearly demonstrated that a gas turbine could be used as a practical, and even desirable, aircraft powerplant. The paper started by demonstrating that existing axial compressor designs were “flying stalled” due to their use of flat blades, and that dramatic improvements could be made by using airfoil designs instead, improvements that made a gas turbine practical. It went on to outline a complete compressor and turbine design, using the extra exhaust power to drive a second turbine that would power a propellor. In today’s terminology the design was a turboprop. In order to prove the design, Griffith and several other engineers at the Royal Aircraft Establishment built a testbed example of the compressor in 1928 known as Anne, the machinery being built for them by Fraser and Chalmers. After Anne’s successful testing they planned to follow this up with a complete engine known as Betty.

In 1929 Frank Whittle’s thesis on pure jet engines was published, and sent to Griffith for comment. After pointing out an error in Whittle’s mathematics, he went on to deride the entire concept, saying that the centrifugal compressor he used would be impractical for aircraft use due to its large frontal area, and that the use of the jet exhaust directly for power would be extremely inefficient. Whittle was distraught, but was convinced that he should patent the idea anyway. Five years later a group of investors persuaded him to start work on what would be England’s first working jet engine.

Griffith continued development of his own concepts, eventually developing an advanced compressor design using two contrarotating stages that improved efficiency. His partner, Hayne Constant, started discussions in 1937 with Manchester-based Metropolitan-Vickers, a maker of steam turbines, to produce the new machinery. Ironically Metrovick had recently merged with British Thomson-Houston, another turbine builder who was supporting Whittle’s efforts. A contract for development work was eventually given by the Air Ministry the next year, and work on Betty, also known as the B.10, started. In 1939 the team, including Metrovick engineers led by David Smith, started work on a flyable design, the F.1. Compared to the Whittle designs, the F.1 was extremely advanced, using a nine-stage compressor, annular combustion chamber, and a two-stage turbine (the second driving a propeller).

In April 1939 Whittle gave a startling demonstration of his experimental engine, the WU, running it for 20 minutes at high power. This led to a rash of contracts to build a production quality design suitable for aircraft use. Development had just started on the F.1 when Whittle started building his W.1 design, planning to install one for flight in the Gloster E.28/39 the next year. Smith decided to end development of the F.1 and move on to a pure-jet instead, starting work on the otherwise similar F.2 Freda in July 1940.

Development of the F.2 progressed rapidly, and the engine ran for the first time in November 1941. By this point there were a number of engines in development based on the Whittle concept, but the F.2 looked considerably more capable than any of them. Flyable versions, the F.2/1, received its test rating in 1942 and were flown on an Avro Lancaster test-bed on 29 June, 1943. Production quality versions were installed on the F.9/40 Gloster Meteor and flew in this form on 13 November, 1943. As expected, the engines were more powerful than the Whittle design, first delivering 1,800 lbf (8 kN) but soon scaling up to well over 2,000 lbf.
It would appear that Metrovick had a winner. Nevertheless the Air Ministry didn’t order the design into production. Although the engine was technically superior to its Power Jets counterparts, it was also incredibly complex and nowhere near as reliable. In aircraft design reliability trumps performance in almost all cases, and this was one of those cases. The Meteor would be powered by the original Whittle design, now built by Rolls-Royce as the Welland, and later the slightly improved Derwent.

No one wanted the work to go to waste, and development of the F.2 continued on a version using a ten-stage compressor for additional airflow. The new F.2/4 Beryl initially developed 3,250 lbf and was installed in the Saunders-Roe SR.A/1. Thrust had already improved to 3,850 lbf for the third prototype, and eventually settled at 4,000 lbf, making it one of the most powerful engines of the era. Development of the SR.A ended in 1947, ending development of the Beryl along with it. Nevertheless a Beryl was used by Donald Campbell in his famous 1955 Bluebird K7 hydroplane in which he set seven water speed records between 1955 and 1964. Meanwhile the F.3 was developed, adding a turbine-powered fan to the rear of the engine to improve airflow and thrust at low altitudes, producing the world’s first turbofan engine.

Metrovick eventually ended development of the F.2 in 1944. Development of the basic concept continued, however, eventually leading to the considerably larger F.9 Sapphire. However in 1947 the Air Ministry demanded that Metrovick get out of the jet engine business, and their design team was quickly snapped up by Armstrong Siddeley. Although Armstrong Siddeley already had a turbine development of their own, the ASX, they were primarily focused on turboprops and the Metrovick team was a welcome addition. The Sapphire became a successful design, besting its Rolls counterpart, the Avon, and design features of the Metrovick line were worked into Armstrong Siddeley’s own line of axial compressor turboprops.

* Depending on the sources, Metrovick either left the engine business on their own to concentrate on steam turbines, or were forced from the market by the Ministry of Supply.
Either way, Metrovick continued development of naval GTs, producing the G.6 for the RN’s County class DDGs, as well as the Italian San Goirgio (D 562/563 refitted) class Destroyers & Alpino (F 580/581) class Frigates.

What if the Men from the Ministry had allowed Whittle to continue with his LR1 Turbofan – about 50-80% complete when PowerJets were ordered to stop work on all engines.

Whittle was looking at around 6,000lb thrust.

The government didn’t even use its powers to give the idea to an established aero-engine company – talk about wasted years.

Also the almost forgotten Metropolitan Vickers series of Axial flow engines,one of which(F9) eventually became the Sapphire ,also bought by Armstrong Siddeley as Sapphire and licence built in the US as J65 for the B57 etc. Metrovic Beryl being used in Saro Flying Boat fighter.
This company I think had an axial flow engine running in 1941,but it would have still needed years of development to make it fit for series production.

That’s what happens with central governmental control of the economy & business.

What if the Men from the Ministry had allowed Whittle to continue with his LR1 Turbofan – about 50-80% complete when PowerJets were ordered to stop work on all engines.

Whittle was looking at around 6,000lb thrust.

The government didn’t even use its powers to give the idea to an established aero-engine company – talk about wasted years.

Even if the jets developed enough power to lift a useful load,and as pogno said,could carry enough fuel!!If the wing section was unchanged one would soon get into the situation where the stalling speed was about the same as the critical mach number.
From memory the U2 suffered that problem and I seem to remember reading that if you tried to turn too tight at very high alttude you could have the situation where the inside wing might be in stall buffet and the outside wing might be in mach buffet!! Hard work without an autopilot on the early ones.
Also from memory on the early U2 at very high altitude the difference between stall and Mcrit was in the region of 7 knots!!

Two Lancastrians VH737 and VH742 were fitted with Nenes in the outboard positions only, in 1946, Merlins remained inboard.
I suspect it was the high fuel burn of the jets that made this impractical, they would have gone like the clappers but only for a short while, an indication might be in the fuel carried, 740 galls for the Merlins and 2,385 galls of kerosene for the Nene,s.
The same was said of the Jet Viking, that had the range for a quick trip to Paris but not much more.

Richard

Any other WW2 bombers suggested for conversion to jet power?

The Chinese put turboprops on an Tu-4 or a local copy of one (either way it’s an unlicensed B-29 copy).

A Lanc was certainly used as a testbed for Nenes, I believe it demonstrated at SBAC with the Merlins in the inner nacelles shut down. But would enough Nenes have been able to be produced in useful time? Although a few a/c were flying with Nenes before the end of the war (prototype Gloster Ace, Supermarine Attacker etc.) none were in production.

There was a Nene-Viking I believe – just makes you think, a jet Wimpey! 😮

According to Bill Gunston, ‘Roy Chadwick wanted to put four Nenes in a Lancaster which would have been almost immune to intercption or flak’.

Anyone seen the expected performance for this?

Any other WW2 bombers suggested for conversion to jet power?

Well there is the little known experiment involving a HP 0/400 and 2 RR Speys – the engines took off but the rest of the aircraft was trucked down by road several days later 😀