WAllied jet aircraft timetable improvement

[Tkdog]

I really think that what they would have had to decide in 1938 was "we want to lose this war" and then they might have had jets earlier.

Jet planes remained expensive, promising and fraught with issues for a long time. It does not seem at all clear that anyone was going to be able to make war winning numbers of jets by the early, or even mid, 40s. The allies not going for broke making jets should not be seen as a sign they couldn't have done it. It should be seen as a sign they were smart enough not to try. Overwhelming numbers of good, mature technology was going to win the war, and did.

Sure, they funded R&D. That was the smart back up plan and it was going to be needed post war. But logistics and organization was key and could beat "wunderweapons" tossed out by an increasingly frantic overwhelmed enemy.

 

[Shortround6]

well, there is a certainly downward spiral that you are in, if instead of needed replacement planes in several months and replacement engines every month, you need replacement planes every month and if you start flying on Monday you need replacement engines on Thursday.

German or Allied, neither side had engines that would be able to sustain widespread, constant activity in 1945.

You had a potential of the British doing a repeat of the ABC Dragonfly Engine fiasco of 1919. Fortunately the Germans surrendered in 1918 before hundreds of RAF pilots died trying to fly planes powered by Dragonfly engines.

 

[Zipper730]

By the way, here's the article that seems to cover the L-1000/J37's development.

The Lockheed L-133's development was inspired by compressibility problems expected to take hold in the XP-38. While most people generally assume that these issues were totally unexpected and caught everybody in the United States off-guard, the fact is that there was some research already in existence regarding trans-sonic (and even supersonic) flight owing to bullets/artillery shells, propeller design (possibly the first area in airplane design where compressibility effects were identified as a potential problem), and some supersonic wind-tunnel design that, while crude, provided some basic information, despite common misconceptions. Even as the P-38 was being designed, Kelly Johnson had already suspected the possibility (according to Warren G. Bodie's "The Lockheed P-38 Lighting: THE Definitive Story of Lockheed's P-38 Fighter") that the aircraft would run up on "Mach's number", as he called it, in dives. During the period leading up to the start of World War II in Europe, Ezra Kotcher, who was the head of the Air Corps Engineering School, had relayed the possibility of compressibility being a likely problem which would face the XP-38 (which was now flying for several months, but had not run into compressibility effects in high-speed dives yet) and suggested the development of a high-speed wind-tunnel as well as a jet-powered aircraft to work through this problem.

Whether they knew of Kotcher's proposals: They already were working on an aircraft with this capability in mind. It wouldn't just be a proof-of-concept jet aircraft, nor would it be a proof-of concept transonic aircraft either: It was to be a fully-workable fighter with some form of jet-powered propulsion system (jet-engines in those days didn't just mean turbojets/turbofans, ramjets, and pulse-jets, but any engine which used its exhaust gases to provide thrust -- depending on how you use this definition, even rockets sometimes fit), by 1940 this project developed further with the aircraft apparently being designed around being able to fly at 50000' at 600 mph (0.91 mach) in level flight. While the link above claims that Nathan C. Price came on as a consultant 1941 in order to help with the XP-49 turbocharger selection, but the (XP-49's) engines were already selected in 1940 (given that Price seemed to be the kind of guy who promoted ideas to those who'd listen, it seems that he probably ran the idea past Lockheed by 1940, considering that he'd been working on a gas-turbines for sometime).

Lockheed appeared to be aware of the effects of swept wings in one way or another (possibly as a result of data that came from the 1935 Volta symposium) though, according to Willis Hawkins, it was ruled out in favor of a straight-winged design for one reason or another (potentially low-speed handling), which would carry two of Price's engines: Initially, the design had a tail-configuration similar to the Westland Whirlwind, with a flush/glazed canopy that looked like it was inspired by the glazed-noses seen on bombers (or the later X-1), with engines fed by intakes on either side of the fuselage which were heavily blended-in with the wings via a fillet-like structure ahead of and behind of the wing; later the design gave way to an the design most people (who are familiar with the L-133) are familiar with: A canarded aircraft with a single-intake at the front feeding the two engines that exhausted behind the wings, which were heavily blended with the fuselage, a fairly ordinary looking canopy with razorback connecting to a large tailfin. The overall aircraft would have been considered fairly large by the standards of the time, with a length of 48'4", a wingspan of 46'8", a wing-area of 325 ft^2 with an expected weight of 18000 lb. (this later grew to around 20000 lb.) with an expected endurance of 3 hours. Armament was to be 4 x 20mm cannon

The initial engine design seemed to be built around the idea of maximizing fuel economy, to make it as close as possible to being competitive with piston driven engines (I'm not sure if this was dictated by Lockheed, Price, or both in agreement), and what the typical endurance expectations existed for a piston-driven fighter of the time period, but it might have played a role in the design.

The basic details can be summarized here

1. Compressor Design
   • 11-12 stage axial-flow compressor with the first stage using a variable-pitch blade.
     • The first-stage later featured a boundary-layer system to avoid compressor stalls during engine-starts (some early compressors had that problem).
   • 3-stage centrifugal flow compressor downstream of the axial-flow compressor.
     
     • The initial idea called for either a reciprocating compressor or a centrifugal-flow compressor, with the centrifugal-flow design being selected.
     • The centrifugal flow compressor was hooked up to a variable-speed fluid-coupling, with the idea being that the RPM would be increased as the aircraft climbed into thinner air at high altitude to recover some thrust loss.
   • Compressors were to be handed.
2. Intercooling
   • Liquid to air-types between the axial & centrifugal-flow compressors, and between each centrifugal-flow stage: The aim being to keep turbine inlet temperature low while achieving a high pressure-ratio.
   • Intercooling radiators to be mounted in the skin.
     • This eventually changed to a core-type located within the two aft-augmenters (unsure if this means the afterburners or just inside the suck-in doors above/below the fuselage, which were pumped by the jet-efflux).
3. Can-Annular Combustion Chamber
4. Five-Stage Axial-Flow Turbine
5. Machinery & Accessories
   • The engine center was a bevel-bull that drove several accessory drive-pinions and shafts for the following purposes.
     • Starters.
     • Generators.
     • Hydraulic & Fuel Pumps.
     • A driving system to spin the landing-gears in order to provide additional power for takeoff.
     • A pumping system for a flap-blowing for lift-augmentation for takeoff/landing, and a possible boundary-layer control system for drag-reduction.
6. Afterburner
   • Fixed-Convergent Divergent Nozzle (contrary to the article, I saw a patent drawing of the design).
   • Projected to increase thrust by 20-25%.
   • Might have been the first gas-turbine to use an axial-flow design.
7. Weights
   • Initial weight of 1620 lb.
   • Weight increased with time to approximately 1700 lb.
   • Intercooler cores to be approximately 140 lb.
8. Thrust
   • Non-Afterburning: 4000-4167 lbf.
   • Afterburning: 5000 lbf.

The USAAF objected to a number of things

1. The early intercooler design would be prone to battle damage (something which plagued the early P-38's): Lockheed's engineers asserted the redundancy would keep a total failure remote.
2. The number of intercooling stages was seen as excessive.
3. The combustion chambers were excessively short and didn't work right (While Nathan Price seemed quite knowledgeable about combustion chambers and boilers, there seems the possibility that he was trying to avoid excessive engine length).
4. The hydraulic couplings would have to use up to 1340 horsepower across the performance envelope.
5. The accessory systems were overly complicated.
6. The effort needed to build up this airplane could tie up effort on the P-38 design: Lockheed disagreed.

My personal thoughts?

1. The accessory configuration was ridiculous
   
   • Jet-engines don't generally need handed-engines: Propellers do owing to the large angular flow produced by the rotating blades, whereas gas-turbines have stators between each stage and a final guide-vane that negates all that. While gyroscopic forces are present, they aren't generally massive.
   • There is absolutely no need to spin the wheels on the ground to assist the takeoff run (Airbus did look into a similar idea, it wasn't to shorten the takeoff run, so much as to reduce fuel burn while taxiing).
   • While laminar-flow control is an awesome feature: It wasn't really necessary for the aircraft. The aircraft only seemed to have incorporated laminar flow in a very limited extent (the suck-in doors used the jet-efflux to pull away some turbulent airflow, reducing overall drag).
2. The idea of spinning the compressors faster at higher speed seem to not reflect a very good understanding of aerodynamics
   • Spinning slower at lower altitudes would mean less thrust would be produced over spinning it faster.
   • Spinning faster at high altitude can cause transonic effects: Though it's possible to design a compressor to achieve supersonic rotational velocities, they often have to be properly designed (and performance usually still falls off after Mach 1.4 is reached).

Later on the engine evolved into a more advanced design as of 1943

1. Compressor Design
   • Low Pressure Compressor
     • 16-stages indirectly driven off the turbine via a gearing system to lower RPM.
     • First 4-stages to use variable-speed hydraulic-coupling to improve high-altitude performance (I think I remember hearing it also helped with engine-starting).
   • High Pressure Compressor
     • 16 stages driven directly off the turbine.
2. Intercooling
   • Between the low-pressure and high-pressure spools only.
   • Overall degree of cooling was reduced from earlier design.
3. Annular-Type Combustion-Chamber
4. Turbine
   • 4-stage axial-type.
   • Provision for air-cooling or liquid-cooling.
5. Afterburner
   • Regeneratively-Cooled.
   • Eyelid-Type Variable-Area Nozzle.
6. Dimensions
   • Overall Length: 139".
   • Overall Diameter: 25".
7. Weight of 1235 lb.
8. Thrust Figures
   • Sea Level
     • Non-Afterburning: 4250 lbf. static; 5583 lbf. with ram-compression.
     • Afterburning: 5100 lbf. static; 6700 lbf. with ram-compression.
   • At 50000'
     • Non-Afterburning: 1520 lbf. static; 1833 lbf. with ram-compression.
     • Afterburning: 1830 lbf. static; 2200 lbf. with ram-compression.
9. Specific Fuel-Consumption
   • Non-Afterburning: 0.61.
   • Afterburning: 1.85.

Eventually a document dated 6/30/47 indicates an SFC of 0.87 on dry power and 1.71 on afterburning, as well as a pressure ratio of 25:1. There's other documents of interest here, here, here, here, and here, the last item includes (page 3) the following...

.....The government desires to continue a program which will evaluate the J-37​

engine design features and engine components for the following reasons:​

.....a. Cycle features. The design cycle features include intercooling, reheat​

afterburning and extremely high pressure ratios, which give small size, light​

weight and high efficiency as evidenced by approximately 20% lower cruising fuel​

consumption than any other jet-type engines now in existence. This engine​

similarly offers extreme advantages in the turbo-prop field. The engine is design-​

ed to improve altitude performance by a variable speed drive to a portion of the​

compressor, a feature not offered in any other engine. The mechanical features​

represented in this design are:​

..(1) Very light weight components.​

..(2) Accurate compressor blade construction.​

..(3) Possibilities of overcoming mass production difficulties now en-​

..countered in present construction methods for axial flow blading.​

..(4) A very fast method of attaching turbine and compressor blades to​

..rotor which reduces machining time to a minimum.​

..(5) A high load carrying type of bearing not used in present type​

..engines.​

..(6) Variable area nozzle design.​

..(7) A new type of fuel nozzle which flows both air and fuel.​

..(8) An open vortex type combustion chamber design for very high pressures.​

..(9) Air cooling of turbine blades.​

(10) An afterburner permitting temperatures up to 4000 F.​

(11) A liquid heat exchanger for applying intercooling in the compression​

..cycle​

(12) A constant speed engine offering safety advantages during wave-off or​

.......missed approach for landings.​

My personal thoughts?

1. Pressure Ratio: It seems a pressure ratio of 25:1 seems quite high. I'm not sure we reached these figures statically until the 1960's.
2. Compressor Layout
   • The configuration of the the LP compressor running off a gearing system is something I've never seen in an operational 20th century turbojet. While I'm pretty sure the intention was to reduce weight over a traditional twin-shafted design, I'm not sure if it would have either been possible or practical with the technology of the time-period for one reason or another ( drgondog , S Shortround6 , W wuzak , X XBe02Drvr you guys might have better qualifications to determine this).
   • I'm not really sure if the variable-speed hydraulic-coupling for the first 4 compressor stages was necessary at all: Unless it was absolutely needed to start the engine.
   • In principle, had they went with an all axial-layout from the outset instead of a mixed-flow design, they might have been able to produce something that would have reached static test (if not flight test) before the end of the war.
3. Combustion Chamber
   • Annular combustion chambers were used on a number of engines including the Westinghouse J30 & J34, possibly the Metropolitan-Vickers F.2/4, and the BMW 003: The BMW 003 had delays in development (which seems to be the reason the Me 262 ended up with the Jumo 004), the Westinghouse J34 wasn't running at all until around 1945, and the F.2/4 might not have been ready until after the war was over.
   • I'm not sure what an open-vortex is, but many combustion chambers use vortices to swirl up the fuel.
4. Turbine: The presence of air-cooled blades is an advanced feature, but the Jumo 004 seemed to make do with it (service life was short and FOD was more of a problem).
5. Afterburner: I'm not sure if there was any intrinsic problems with an afterburner, but they seemed to be seeking temperatures that were excessively high temperatures.
6. Nozzles: I don't see any issue in principle there.

Ultimately the L-133 was cancelled, the L-1000/XJ37 continued being developed for some time before it was finally cancelled with at least one attempt to develop it into a turboprop (some sources list the XT35 as the engine, but the turbomachinery was totally different, so the T37 or T39 might have been the design, but don't quote me on that) and, out of that came the P-80.

The P-80 used the wings of the L-133 along with a cruciform tail: While it wasn't going to be able to dive through the mach, it seems that the L-133 might not have been able to do so either. Whereas the L-133 was complex, with intercoolers and flap-blowing, the P-80 was simple with a fairly conventional engine, and flap-blowing system of any kind (far as I can tell). While I think they should have bit the bullet and put 4 x 20mm in the design over 6 x 0.50", it proved an effective fighter as it was (particularly when the wings were thinned a little bit, reshaped slightly, and strengthened).