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Author Topic: Early British gas turbine development  (Read 132447 times)

Offline tartle

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Re: Early British gas turbine development
« Reply #120 on: May 14, 2012, 11:24:08 am »
The Rolls-Royce Nene and Tay linked to Pratt and Whitney:
 
Pratt and Whitney were late getting into gas turbines as the US military did not want them distracted from piston engine manufacture during WW2.
In the meantime Rolls-Royce were looking for new post-war markets in order to maintain revenue streams. In January 1946 a Philip Taylor contacted Hives with a request for a licence to manufacture and sell RR turbine engines in the USA. As the potential for sales in the USA was very attractive negotiations ensued and Taylor, who was the ex-chief engineer at Curtiss-Wright. Hives was reluctant to talk to him at first ...but after some negotiation Taylor signed a contract granting him sales rights to the Nene and Derwent and their spares for two years with a one-year getout clause. Taylor began negotiations with Grumman to supply Nenes and also with Pratt and Whitney. In Jan 1947 Taylor contacted RR with the news that P&W wanted to manufacture Nenes for Grummans under a sub-licence deal. C. J McCarthy vice president of United Aircraft Corporation, owners of P&W, had been given open house by Hives when he visited the UK in the summer of 1946 and so Hives contacted him to say Taylor had been in touch re-P&W licencing. In March 1947 Hives thought the deal so important that he sailed on the 'Queen Elizabeth to the USA to finalise a deal with P&W who were being encouraged by the US Navy to licence the Nene engine as it was more powerful and reliable than US engines and with the cold war starting they needed all the engines that they could get. Taylor eventually drops out of the picture after threatening to sue but P&W reached an accommodation. In May 1947 the Navy announced the deal between P&W and RR for the F9F carrier fighter from Grumman.
 
 Hobbs, boss of P&W, was concerned that Hives was too keen on the axial AJ65 to keep developing the Nene series, but in fact the Tay engine was proposed as the next engine for P&W.
 P&W had a team of engineers at Derby to work on the American version of the Nene and then to help design the Tay, essentially an uprated Nene for later versions of the Panther, as the Grumman F9F had been christened. The F9F-2 Nene powered version first flew on 27th November 1947, Gwinn(of P&W) cabled Derby: "Grumman Nene was flown yesterday for one hour, 15 minutes.Everything O.K. Pilot very pleased and snap rolled machine."
 Jim Boales was one of the RR Derby engineers who had responsibility for making the relationship work and he spent time in East Hartford as well as working in Derby on both the Nene and Tay. The Tay he told me came about because the Navy kept hanging more things onto the aeroplane and so extra power was needed, initially by water-methanol injection on the Nene raising the power from 5,000 to 5,750 then 5,950 lbt, but eventually by enlarging the Nene itself. The challenge was to accommodate a 1.14 times linear scale of the Nene within the airframe of the Panther. The Overall diameter of the Nene is 49.5 in, so the scale-up would give a diameter of 56.43 in.- too big to fit in the hole! The largest diameter that could be accommodated was 50 in so the RR/P&W design and engineering team at Derby started to determine what needed to be done to bring the engine into line with that figure!

......continued in#124 below.
« Last Edit: May 16, 2012, 05:24:32 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline LowObservable

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Re: Early British gas turbine development
« Reply #121 on: May 15, 2012, 06:54:20 am »
The US back-story here (in part) is that the USN had bet most of the rent on Westinghouse, which believed in small engines used in large numbers, and thought that jet engines could be scaled easily, despite having no aviation experience. The outcome was two engines that were too small to be of much practical use except as boosters (J30 and J32), the unexciting J34 (two engines required for decidedly subsonic fighters) and the catastrophic J40.

Did centrifugals offer better throttle response at the time?

Offline tartle

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Re: Early British gas turbine development
« Reply #122 on: May 15, 2012, 10:39:02 am »
My gut response is that in the 1940s a centrifugal is less sensitive to abuse than an axial both in terms of control and mechanical integrity... most axials of that time seem to have a long development period whilst surge was tamed or vibration related blade failures were tuned out. The flatter performance characteristics of the CF vs. axial compressor helps but does not eliminate surge problems.
The US government originally put all its eggs in the axial basket which is why Whittle's machine was grabbed so quickly when offered by Britain. P&W after the war had ended also realised that Allison/GE were not getting on with development of the centrifugal with enough urgency and so, as RR were activally looking for outlets in the US, they took a licence for the Nene and later the Tay, as we are exploring at present. Westinghouse did well to design two small  but good turbojets. They scaled up in ambition with the J34 which at least did what it was designed to do. The J40 was a disaster that ruined many aircraft programmes. Westinghouse had entered into a licence agreement with Rolls-Royce and managed to screw up the transfer of technolgy to the USA on both the Soar and the late-model Avons. Geoff Wilde got involved in sorting the J-40 engine problems, but it was cancelled before all the changes could be demonstrated to work... Geoff regarded the Westinghouse venture a total waste of RR engineering time but Pearson was able to point out that the royalty payments were very large and very welcome when lean times were upon the UK  market. David Huddie was told in September 1959 that Westinghouse were out of the aero engine business.
« Last Edit: May 15, 2012, 11:08:40 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline tartle

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Re: Early British gas turbine development
« Reply #123 on: May 16, 2012, 05:23:30 am »
As I intimated  above, Jim Boales made a major contribution to the successful development of the RB44 Tay and later the Hispano Suiza Verdon engines. Below is a retelling of those times from notes I made after conversations with him in the mid-60s!
Encouraged by the growth in demand for more powerful engines for use by yhre military P&W turned to RR for advice on how to uprate the Nene. The Tay was the resulting engine, designed in Derby by a joint team that decided to scale the Nene by 14% linear.
The Overall diameter was limited to 50 inches by installation considerations. The larger impeller was 2 inches greater in diameter than the existing Nene making it 32.8 in.  Tests with a larger impeller on the Nene had shown that the tip clearance could safely be reduced from the 1.025 in. to 0.67 in. which was also the figure for the Clyde. The Clyde also employed wrap around diffuser passages to the combustion chambers. This has the effect of reducing the flow area for the rear entry of the impeller but has been found not to penalise overall performance.  Adopting this enabled the diameter to shrink to the required 50 in. To improve airflow through the impeller it was decided to allocate the 14% extra axial width by changing the relative proportions of the rotating guide vanes and the impeller itself, reducing the latter dimension. This allows smoother entry for the air and achieves greater efficiency
In order to control the weight many large components cast in aluminium were cast in Magnesium which turned out to be very satisfactory. an experiment was tried out: casting the impeller in Magnesium but was a step too far.
The third picture shows a J42 and J48 side view roughly to the same scale! The afterburner was initiated early in the Tay programme...
The photo of the J48 should be compared with the Tay photo posted earlier.
Rolls-Royce and P&W agreed a delivery programme for prototype engines in June 1948 that would result in 4 engines being constructed:
1st engine for RR by Oct '48
1st engine to be despatched to P&W Nov '48
2nd engine for RR Dec '48
2nd engine P&W end Jan '49
3rd engine P&W end  Feb '49
3rd engine for RR end March '49
4th engine P&W end  April '49.

In the end RR built 34 Tay engines to support all the development activity:
8 prototype flight engines for P&W
6 RR development for Ministry of Supply (2 for Lancastrian)
4 for the Viscount
6 for English Electric
6 for the Avro Tudor
all 34 were delivered by end of 1949.

To assist with RRs workload P&W assumed design responsibility for the design of Tay jetpipe and afterburner for the North American P86, but will submit their designs to RR for comment. Initial design of jet pipe was based on reheat sizes but without reheat system or variable nozzle.
P&W will place an order, when RR is ready, for 2-3 afterburners but in the meantime they carried the workload themselves, using drawings of the RR design of clamshell nozzle.
The programme was very successful and a large number of J48s was produced by P&W. Production numbers at P&W were:
Nene: 1,137 and
Tay: 4,021.
Typical specs were:
                                     J42-P-6           J48-P-5
Dia (in.)                            49.5                50
Len (in.)                         103.2              236
Dry weight (lb.)             1729              2000
PR                                     4.3                4
Max thrust (lb) @          5750 (wi)      8,500 to 9,000 (7,000 with wi)
rpm                              12300           11,000
wi= water injection
« Last Edit: August 10, 2012, 06:36:59 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline tartle

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Re: Early British gas turbine development
« Reply #124 on: May 18, 2012, 02:43:31 am »
Immediately after the war there was a surge of interest in automotive applications for the gas turbine. Rover developed a 100 hp engine suitable for their production car, Centrax looked at the lorry market with a 160 hp designed by ex-employees of Power Jets, and Rolls-Royce looked at the feasibility of a small engine for automotive or small aircraft application.
Jim Boales was involved in this investigation and extracts from an undated report (late 46 or early 47) reads:
"  there are many uses foreseen for a 500 bhp engine, e.g. cars, light aircraft, where about 200 hp is needed or a trainer aircraft.
Advantages: lightness, simplicity, no gear changing or clutches. For traction purposes a free turbine is desirable, then engine power is not directly related to power turbine torque is obtained for starting. Also [the free turbine arrangement has] general uses for investigating different turbine arrangements, control systems, heat exchangers, etc.
For such an engine it was considered desirable to use an existing compressor that does not need development and a reasonably high pressure ratio, about 5:1. The free turbine enables the engine to be run as a pure jet. This greatly helps as the free turbine can be developed separately.
As a turbine power generator it is desirable to keep the leaving velocity from the turbine down to the minimum possible. Thus a low axial velocity turbine will have to be incorporated."

The RB60 engine was configured as:
"A Merlin 46 2-stage blower delivering via its own volute and single delivery pipe into a single reverse flow combustion chamber, from which the hot gas flows into an annular volute at entry to the high pressure turbine. This is a single stage turbine. The gas then flows through an annulus about 6 inches long to the low pressure turbine. This drives a gearbox at the rear.
The engine is fitted with an oil tank and pumps fitted to the h-p section wheelcase, and on the l-p section for the reduction gear and power turbine.
The cooling air for both turbine casings is an external supply. The wheelcase driven by the h-p unit carries the starter motor, fuel pump, oil pumps and tachometer. The fuel control systems apart from pump is mounted separately."

Jim Boales said that the turbojet ran at Barnoldswick but the power turbine was never built as there were other priorities.
The design performance was:
Press ratio 5:1
compressory efficiency 72.5%
Power output/lb/sec 64 bhp at a gearbox efficiency of 98%
so for 7lb/sec flow the output was 450 bhp at an sfc 0.845
Hp rpm 22,800
lp rpm 17,200
performance as a jet:
jet velocity 1025 ft/sec
total thrust 350 lb
sfc   1.08
« Last Edit: May 19, 2012, 05:40:31 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline Hobbes

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Re: Early British gas turbine development
« Reply #125 on: May 18, 2012, 05:46:28 am »
Immediately after the war there was a surge of interest in automotive applications for the gas turbine. Rover developed a 100 hp engine suitable for their production car, Centrax looked at the lorry market with a 160 hp designed by ex-employees of Power Jets, and Rolls-Royce looked at the feasibility of a small engine for automotive or small aircraft application.

Is this the work that led to the Leyland Turbine truck of 1968?


Leyland Turbine by aecsouthall, on Flickr


Leyland Gas Turbine by gylesnikki, on Flickr

Offline JFC Fuller

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Re: Early British gas turbine development
« Reply #126 on: May 18, 2012, 06:11:20 am »
Not to mention similar work that was done on cars by Rover: http://www.rover.org.nz/pages/jet/jet5.htm

And trains by Metropolitan Vickers (BR18100) and English Electric with the GT3: http://www.enuii.org/vulcan_foundry/oddities/gt3.htm

Offline tartle

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Re: Early British gas turbine development
« Reply #127 on: May 18, 2012, 06:25:10 am »
Hobbes... the Leyland organisation acquired Rover in 1967  and its gas turbine research work which had continued all through the 50s and 60s was directed at powering a Leyland truck. There is a pic below from a brochure which can be read here
JFC Fuller ..and boats as we have already discussed.
« Last Edit: May 19, 2012, 05:31:38 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline tartle

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Re: Early British gas turbine development
« Reply #128 on: May 20, 2012, 05:05:27 am »
 I am intrigued by a review of the thesis The Development and Production of Turbojet Aero-engines in Britain, Germany and the United States by Hermione Giffard. Imperial College London, 2011. ... which leads me to think about how Rolls-Royce and Metrovick did not have the (gas turbine aero engine) field to themselves.

 George Bulman who was DEngRD for aero engines up until his retirement in 1943 relates how Tizard, head of R&D at the MAP (until Lindeman got him removed in 1942... an old feud.. was there a war on?) became increasingly concerned with Whittle's erratic responses to concerns about the speed of development.. decided to involve Frank Halford and de Havilland in the jet engine programme. Frank Halford, aided by Moult and Brodie had produced ranges of piston engines for de Havilland and Napier, of varying degrees of success (often constrained by those two organisations) and was asked to think of the sort of jet engine they could design for dH. Given their expertise in superchargers, such as the elegant Gipsy Twelve engine (see Flight article from which the supercharger drawing comes) and the Napier Sabre, it is not surprising this is where Halford started. With some, but limited access, to all the work then being sponsored the team went for an engine of 2,000 lbt and sized a supercharger impeller to suit. This was necessarily of larger diameter than Whittle's twin-sided design and alarmed the RAE who were aware of the failiures on Whittle's jets. However Halford's close relationship with Wallace Devereux at High Duty Alloys meant they were confident they could deliver a reliable impeller. Isaac Lubbock of Shell had been brought in to help Power Jets combustion challenges and this work was of great influence... Halford realised that two 180 degree bends in the Whittle reverse flow scheme increased the risk of uncertain combustion conditions as well as being a source of pressure loss so they opted for a straight through layout from day 1. They were not concerned about the shaft whirling issues as the single sided impeller design meant that no axial space was needed for the rear intake and so it was the diffuser elbow and combustion chamber length alone that determined the dimension from impeller to turbine, which could be linked by a simple shaft of appropriate (large) diameter.  Also the straight through layout enabled the adoption of a larger diameter turbine (not constrained by the reverse-flow combustion chambers). Progress on turbine disc materials also helped in this respect... so all this thinking without constraints imposed on Whittle a few years before resulted in the H.1, later known as the Goblin engine. A basic section highlighting the features is included below.
 As the various claims made by engine designers are not always as clear cut in practice as they are in theory I thought I would make an unfair comparison by putting a section of the 49.5 inch diameter Nene alongside the 49.85 inch diameter Goblin... see below... it is a really unfair comparison as the thrusts and therefore mass flows are not the same but we can see the Nene is a bit longer in shaft dimension than the Goblin... but the Goblin shaft diameter is relatively large... i. e. much stiffer. But the complexity that goes with a three bearing system on the Nene is certainly more complex than that needed on the Goblin two bearing system.
 
 The MAP and the Air Ministry noted the lack of paranoia as the aero firm just got on with the job... just a touch more challenging than a Gipsy Twelve but may be not as bad as a Napier Sabre?
 de Havilland had their challenges but this was to develop the rated power and sufficient longevity to make it a Serviceable engine for the military. The engine design started in April 1941 and as there was a closeness with the aircraft side of the business, the Spider Crab aeroplane design carried on in parallel... resulting in the engine featuring a bifurcated intake so that the ducting from the wing root air inlets was minimised. The first drawings were issued to the experimental shop on 8th August 1941 and a mere 248 days later the H1 made its first test run on 13th April 1942. Two days later the team were confident enough to carry out a half hour acceptance test at half design speed. On the 5th May the engine suddenly stopped- on investigation it was found that the intake had been sucked flat starving the engine of air and stalling the compressor. after stripping the engine little damage was found and soon it was rebuilt. Initial troubles involved difficulties in starting the engine, overcome by fitting two starter motors, and combustion issues leading to continuous improvements as the hours built up, as well as improving welding quality for longevity. The tailpipe was also liable to buckle so it was reinforced. Fuel supply difficulties were also experienced as the pump capacity was inadequate, so was increased. There were one or two impeller failures but the issues were diagnosed and fixed.. to be discussed later.
 After the strip and rebuild after the incident of May 5th the engine was taken up to full speed on 2nd June reaching the design thrust of 3,000 lb. By the end of July the board of de Havilland were investigating how they were to put the engine into production. On 10th September they received an official Ministry request for a detailed manufacturing plan which was submitted on 18th. On 26th September the engine completed a 25 hour flight approval test; a total of around 120 hours had been achieved in the overall test programme. Two years after the engine programme began the Goblin was ready to fly. However its designated Spider Crab or Vampire as it was to become, was not. The Mosquito and Hornet had been the focus  of DH's attention and so the programme slipped. Meanwhile the other British jet fighter was suffering just the opposite problem... the E1/44 (Meteor) was virtually ready but the Power Jets  engine was not. It seemed a good idea to look at the feasibility of 'Goblining' the Meteor.
 George Carter realised that if the Goblin intake was spun through 90 degrees the air inlet to the engine could be above and below the wing spar making the installation fairly straight forward. The Goblins were installed and cleared for flight at 2,300 lbt, 300 lb more than previously cleared by the simple expedient of increasing max rpm to 9,300 an increase of 300 rpm.So the Meteor and Goblin made their maiden flight on 20th Sept 1943.
 The British and Americans had been discussing the Goblin and the US Military decided to go ahead with Lockheed on an aircraft with one of these engines. The Lockheed XP-80 was the first product of Kelly Johnson's Skunkworks. June 23rd 1943 was the official start date and it was intended to fly 150 days later. he contract called for the aircraft to be completed in 180 days so the pressure was on! A crude mockup of the Goblin arrived on July 10th and it was the lack of engine which was the critical item for delivering the contractual timespan. August 24th saw the British Air Commission informing the Americans that a non-flyable engine was about to ship. A month later the engine was still in Britain as 'a part change necessitated by overheating the engine during a test run'. The engine was finslly delivered Nov 2nd 1943 and arrived on the Skunk Works shop floor on the 3rd. Everything was assembled and finally the aircraft headed off on a truck to Muroc arriving 14th Nov 1943.
 
On Nov 17th the Goblin was powered up for the first time. The installed, non-flyable Goblin delivered 2,460 lbt at 9,500 rpm.
....moved XP-80 stuff to #131.
« Last Edit: May 26, 2012, 02:53:13 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline alertken

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Re: Early British gas turbine development
« Reply #129 on: May 22, 2012, 05:58:51 am »
Who invented what, when?
 
In Spring,’41 DH Engines, repairer of Merlin and supplier of Gipsy for ragwings, was funded by Bulman, MAP into reaction; their design consultant F.Halford, onlie begetter of Sabre, designed H.1(Goblin) “from first principles,entirely independently of the Whittle concept” G.P.Bulman,An Account of Partnership,RRHT,2001,P.324 (pace: H.1 “would not have been designed but for the stimulus and information provided by (W.1” 2/10/47,Royal Commission on Awards to Inventors).
 
AA  Griffith had moved, 1/6/39,  from RAE to be newly designated Chief Scientist at RR, where engineers, not impractical boffins, reigned. His work on C.R.1/2 Internal Combustion Turbines did not move at the pace of Power Jets (nor, as we now know, of v.Ohain).
 
None of them "invented" reaction thrust. Each one applied mind to the "what if..:" the basic metals industry could "invent" discs and blades that would stay where they should, while spinning dementedly in a continuous explosion.
 
Quite sensibly Ministries tasked with putting weapons into young men's hands concentrated on reliability, longevity and power in pistons. Contemplate your day, Air Minister Lord Swinton, after Anschluss, when the writing was on the wall: there you are trying to kick reciprocating teams to cause enhanced Merlins to work well, "Hyper" Sabre, Centaurus, Deerhound...to work at all; you have just sequestered the entire auto industry to stop earning and start spending to build interim Mercury, Pegasus, onway to Hercules when/if that works. An eccentric, difficult engineer (oddly a serving RAF officer - how can that be?) claims his gyre will deliver sci-fi dash speed...if only it would stop exploding on the rig.
 
The wonder is not that UK, Germany, US took awhile before throwing vast sums into reaction, but that any of them ever did, at all.
 
Neither Griffith, nor Whittle, nor v.Ohain, nor RAE scientists, nor Gottingen academics "invented" jet propulsion...alone. They all did.. and all needed a Eureka from obscure grafters in metallurgy. Just as $100Bn. for nerds in Silicon Valley derived from some sandy fellow unsung by history.
« Last Edit: May 22, 2012, 06:05:11 am by alertken »

Offline tartle

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Re: Early British gas turbine development
« Reply #130 on: May 26, 2012, 02:50:36 am »
I thought I would split off the XP-80 story as post #129 was getting very long!
The British and Americans had been discussing the Goblin and the US Military decided to go ahead with Lockheed on an aircraft with one of these engines. The Lockheed XP-80 was the first product of Kelly Johnson's Skunkworks. June 23rd 1943 was the official start date and it was intended to fly 150 days later. he contract called for the aircraft to be completed in 180 days so the pressure was on! A crude mockup of the Goblin arrived on July 10th and it was the lack of engine which was the critical item for delivering the contractual timespan. August 24th saw the British Air Commission informing the Americans that a non-flyable engine was about to ship. A month later the engine was still in Britain as 'a part change necessitated by overheating the engine during a test run'. The engine was finally delivered Nov 2nd 1943 and arrived on the Skunk Works shop floor on the 3rd. Everything was assembled and finally the aircraft headed off on a truck to Muroc arriving 14th Nov 1943.
On Nov 17th the Goblin was powered up for the first time. The installed, non-flyable Goblin delivered 2,460 lbt at 9,500 rpm.
The engine ran up on the first attempt and the installed thrust measurements were taken. The non-flight Goblin gave 2,460 lbt at 9,500 rpm. No major problems were uncovered during this first run.
On the 18th they decided to have a second run with the aircraft restrained. A major incident occured when the engine suddenly stopped. On inspection in the intake ducts had collapsed and debris had entered the engine damaging the leading edge of the impeller. First thoughts were that the engine was ok and ducting had collapsed due to incorrect load distribution. It was stressed assuming there would be a 4psi pressure differential which was exceeded in practice... restressed for 12 psi, the duct was replaced with a heavier gauge one. On the 21st the night shift were shaken to discover a 3½  inch crack in the impeller. Close inspection determined that this was not as a result of the duct incident but was a failure due to a material defect.
De Havilland were working on a more robust impeller. The impellers were machined from great 'cheeses' weighing 500lb and at that time were the largest RR50 forgings to be made. The size meant that there were compromises on the material properties in the centre of the forging (shades of RB211 fan disc disintegration many years later) which were still there after the cheese was reduced to a 109 lb impeller. Wallace Devereux, the engineering brains behind High Duty Alloys, advocated controlling the silicon content of the alloy to less than 0.25%. This produced an impeller with acceptable properties throughout and, with the additional benefit of producing the alloy by continuous casting, a better cheese was produced.
Obviously with so few Goblins around there was no spare easily available, nor spare parts as every part being made went to build a new engine, or replace a broken part. But the DH team were keen to help Kelly and by 27th agreed that a new engine could be shipped on Dec 11th to be in the USA by 15th. The damaged engine was shipped back to England. On 9th December disaster struck when the eleventh Goblin engine, which had been allocated to Lockheed, disintegrated on test! It was decided that swapping out an engine intended for the second Vampire was the best course and this could be shipped out by 22nd December 1943. It arrived at Muroc on the 29th Dec and was immediately prepared for installation. The next day it was statically tested and apart from minor adjustments was running well. New Year's Eve saw the engine run up to 9,600 rpm, the max cleared speed for flight. A well deserved day off followed and on 2nd January 1944 the tail was reattached and the aircraft readied for taxi trials on the 3rd. A day for inspection and then first flight on 5th were pencilled in. Kelly also signed off on most of the XP-80A proposal on that day. Kelly also decided that letting Muroc's test field dry out a day or two longer would also enable them to get all Skunk Works personnel up to witness the take-off so on 8th Milo Burcham, Lockheed's chief test pilot took it into the air for 6 minutes and on landing noted the landing gear would not retract... A fix was found and a second flight of 20 minutes followed.
The final picture shows the XP-80 being readied for its first flight with the Skunk Works team on the hill behind.
...tbc
« Last Edit: May 28, 2012, 01:03:17 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline LowObservable

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Re: Early British gas turbine development
« Reply #131 on: May 27, 2012, 08:16:47 am »
I have often wondered whether contact with de Havilland - which had built the first Mosquito using an integrated, isolated and secure design-build team - had an influence on the original Skunk Works approach.

Offline tartle

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Re: Early British gas turbine development
« Reply #132 on: May 27, 2012, 04:32:30 pm »
Good question... my gut feeling is that the two aircraft companies independently came up with a similar solution to a similar question... how do I keep a new project secret, away from people who might object to diversion of some of the best brains away from problems of war production?... both projects were not really accepted by the mainstream military decision makers. Although Lockheed had contact with DH engine personnel they [the DH engine people] may not have been aware of Mosquito activity.
In the end the [Lockheed] Skunk Works achieved a 143 day timespan for XP-80 airframe completion; only non-availability of engine prevented them achieving the 150 days to aircraft availability to fly. The beauty of Skunk Works is that they remove queuing, so contingency can be removed from the critical path...in a sense everything is critical! Dr Eli Goldratt in 1997 talked of the theory of constraints and the critical chain which roughly meant if you were an expert at 'x' and were required to give, say ten projects your attention, then you would be spread so thin that many would suffer as they waited for you to arrive. Health Services experience this!
So do aircraft project teams if they are in the main office.
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline tartle

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Re: Early British gas turbine development
« Reply #133 on: May 30, 2012, 06:23:14 am »
Carrying on from #131:
As well as changing the material to low silicon RR50 aluminium alloy de Havilland also decided to test every impeller on an overspeed rig to check for soundness. The impellers were run at 15-20% over max rpm and then inspected for any evidence of faults. Also as the hours built up some impellers showed signs of fatigue cracking on the blades, which the team thought could be vibration-induced. Work started to investigate what excited the vibrations and what was the magnitude of any induced stresses. This involved working out how to attach strain gauges to the impeller, which had not been done before in such a highly loaded environment. It was soon established that the impeller had natural frequencies excited by the inlet arrangement:
The first was excited at 4x the engine speed, induced by the inlet arrangement, and
the second occured at 16times/rev. This was induced by upstream 'bow waves' from the shock of the air entering the 16 diffuser passages.
The first of these two 'exciters' was mitigated by moving the 4th order excitation (induced by the 4 intake radial vanes- see first picture) out of engine operating speed range- achieved by cutting back and chamfering the leading edge along its front entry part of the blade- raising the first flapping mode to higher frequency. A beneficial side effect was improved aerodynamic performance sufficient to allow a higher thrust and lower operating temperatures.
The bifurcated intake arrangement on both the XP-80 and the Vampire meant a circumferential temperature traverse of the jet exhaust exhibited wide temperature variations. By calibrating the fuel nozzles in each of the 16 cans, adjustments to fuel flow to each chamber could be made removing the hot spots around the traverse.By the end of January the flight tests had indicated flight handling mods necessary to improve the flyability of the XP-80. On 27th it was taken out of service and a whole list of mods incorporated. On the engine side the fuel flow modifications were incorporated.
Flight testing began again on 10th Feb 1944 when it made its 6th flight. The only glitch from an engine perspective happened during a ground run after flight 9- Feb 14th.- excessive heat was spotted on rear fuselage. Investigation revealed 2 stator blades had burned away. The burner in front of these blades had loosened, turned sideways and allowed excessive fuel into the can, generating excess heat. A locking device was devised and fitted on all burner nozzles, eliminating the problem.
A revised and improved engine cleared for 9,800 rpm was made available from Britain and fitted at the end of May. Unfortunately high tailpipe temperatures restricted running with the engine. On May 31st a restriction on rpm was placed on these engines, due to an explosion on test at DH. A few days later this was revised to a 9,500 rpm restriction. But the high jet pipe temperatures were still a nuisance as the hot summer approached.
By this time GE were promising production of the I-40 and so the XP-80A was designed around this engine.
Allis Chalmers never got really into licence-production with the Goblin.
« Last Edit: May 31, 2012, 02:32:43 am by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.

Offline tartle

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Re: Early British gas turbine development
« Reply #134 on: June 07, 2012, 12:34:24 pm »
Napier, Armstrong Siddeley and Bristol also got into the act a little later than RR and Metrovick. RAE had inspired an axial thread to the gas turbine development and being familiar with Metrovick had asked them to continue after the B10 rig. RR came in via a desire, partly altruistic, to get Whittle out of a pickle! Napier had its hands full with Sabre issues that had to be solved by throwing development and production expertise at it... namely Bristol and English Electric. Eventually the combination of taking over a DH project and using the experience from Nomad supercharging got them into the arena if not into the race. Bristol joined in the the 2nd GTCC meeting and realised the technology train was speeding out of the station so asked if they could get involved. Not wishing to duplicate work they decided their civil and bomber background should help in turboprop development so that is what they suggested to the Ministry. They got a contract to develop a turboprop and heat exchanger system. Armstrong Siddeley shook off the Griffith inspired route they were following and went for an axial turbojet, again trailing Metrovick. They could of picked up the F2 work at this stage but that meant collaborating with Metrovick which was culturally difficult so thay went for a trombone of a layout.
Although Griffith and Hayne Constant were axial advocates their scientific understanding had accelerated past their engineering capability to deliver and so even The small team at Power Jets showed a sound aero technology stretched hard could still win over a new one. Aero engines could not afford to let efficiency leak away like industrial applications, hence the hard time steam turbine firms had in the sky. Roxbee Cox and his backers were wiser souls with their technologies tempered in the heat of war so were more inclined to let firms that would regard the gas turbine as just another prime mover with a different set of problems to solve.
We'll follow their fortunes ............in the next few posts.
« Last Edit: June 09, 2012, 04:31:36 pm by tartle »
"... prototypes are a way of letting you think out loud. You want the right people to think aloud with you.” - Paul MacCready, aeronautical engineer.