I was hoping that you'd get the hint.
Beatrice Schilling's innovation...
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Deleted member 68059
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The removal of the chokes increases the supercharger compression ratio by about the same amount the fuel evaporation does under typical circumstances.
RR didnt have an artifical altiude test cell, which was the entire point of the Yaker/Hooker paper, because they were trying to find out why the Merlin projected performance at high altitude didnt match the real flight performance. Without knowing what they meant by "high" altiude (I dont have my copy of the book at the desk now), its impossible to say, but the fact is that the fuel in a Merlin 46 steadily decreases in evaporation percentage from sea level all the way up.
Under most conditions the benefit of the fuel evaporating was about 0.2 of a PR "point", up to a maximum of 0.4 (which you never get as the N SQRT T you get on the engine characteristic means the intersections to the SC characteristic lines dont let you reach those point) this is basically identical to the gain in PR caused be simply removing the chokes. In other words an engine with a proper chokeless pressure carburettor (not all were) will be the same power even if you negated the gain of the fuel through the supercharger. Or to put it another way, a port or direct injected engine will be basically even with the a carburettor passing fuel through the supercharger under the conditions most amenable to high evaportation through the supercharger (sea level, 20 Deg C), except of course the fuel economy will be about 10% better, and it wont cut out, or freeze up.
The chokes cost you about 50hp in a Merlin 46 at sea level.
In other words, a choke based fuel system feeding fuel through the blower, is more or less just "robbing Peter to pay Paul"
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Yes, and this is the closest that we will get as a reason from RR that they were wrong to stick with Venturi type carburettors. They only really had their arms bent to use the Bendix PD carb at a very late stage, partly because it had less Venturi restriction. RR was so over-a barrel to get better performance from the Merlin 100 series (other than 150 Octane fuel and good detail improvements) that they virtually had to copy/design their "own" FI system. All too late!
Eng
Similar graph for the Merlin III tested on the High Altitude Test Plant at R.A.E. - the difference between the calculated and measured BHP looks rather insignificant.
I am not sure, but it is probable that the use of pressured carburettors resulted in more appropriate droplet size distribution with a smaller droplet mean size. Thus, the effect of fuel evaporation at a higher altitude could be more signifincant for Merlin 66 and later.
Deleted member 68059
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Yes it will be more effective (which is to say retain more of the gain, since the fuel max flow doesnt go up with the 2stg SC, it just means you retain it
to a higher altitude, so the total maximum possible cooling effect will be the same) as the CR of the 2stg SC is about 6:1 peak compared to about... 3.7 or so
for the best single stage (40 series) so the charge air will be a lot hotter at the exit of the final stage. Since however supercharger losses in multiple stage setups multiply the losses of the first stage (which is why the first stage in a 2stg setup is the most important to develop), any inlet losses like chokes, will have an even more serious overall impact on performance
than they will on a 1stg SC. Or if you prefer, the RR 2stg SC would probably exhibit very significant gains without chokes, I dont "think" I have a compressor map for the 100 series to verify that, but I`ll look again I might have one hiding somewhere to see...(as it has no chokes)
Your graph may show insignificant differences, it depends what you`re comparing them TO, (it appears to be a Merlin X not a Merlin III test) At the time the issue was comparing RR and Air Ministry methods,
not comparing them to Wright-Field test plant, we also have no idea what the test plant setup was, and who knows if either of those result are actually correct !
Does it include ram effect ? Probably not, most graphs never include them as its so heavily dependant on the inlet system design which is almost entirely
dependant on the specific aircraft (totally different pressure drops, filter types, diffusion, boundary layer ingestion, propwash...etc etc etc).
If you re-read Hookers pamphlet you`ll see they thought it was a very significant problem, as I say its why that paper was actually written in the first place,
and made quite strenous attempts at including ram effect and exhaust ejector effect too, since they were trying everything to work out why the
Spitfire and Hurricane were measured to be flying considerably slower than expected at high altitude in the Battle of Britain.
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Elvis
Chief Master Sergeant
Yeah, should've warned you guys about the watch ad.
Sorry about that.
Beatrice Shilling was an enthusiastic motorcycle and motor car racer, involved in various motorsports including F1 until I started watching it. A remarkable person.
From Wiki
In the 1930s, Shilling raced motorbikes. After winning a race at the Brooklands racetrack on a motorcycle she modified herself, in a job interview she encountered the sexist comment of "I suppose the men let you win" from the interviewer.[3] On 24 August 1934 she lapped the Brooklands circuit at over 100 miles per hour, with an average speed of 101.85 mph (163.91 km/h) on her Norton M30. She was only the second woman to achieve this, the first being Florence Blenkiron earlier the same year. Both were awarded the British Motorcycle Racing Club's Gold Star award.[12]
After the Second World War Beatrice and husband George turned to racing cars, which were tuned and modified extensively in their home workshop - starting off their exploits with a much-lightened 1934 Lagonda Rapier registered KG 5363. Between 1959 and 1962 they raced an Austin-Healey Sebring Sprite 888 HPA, most frequently at Goodwood Members' Meetings, scoring a number of third places and even one race win.
Beatrice's and George's driving ambitions became more serious with the 1961 acquisition of an Elva 200 Formula Junior single-seater, but there were accidents for both of them, and the Elva was converted into a Mk VI sports car.[13]
In 1967 Shilling was brought in to help Dan Gurney solve overheating problems with his Eagle Mk1 Formula 1 racing
From Wiki
In the 1930s, Shilling raced motorbikes. After winning a race at the Brooklands racetrack on a motorcycle she modified herself, in a job interview she encountered the sexist comment of "I suppose the men let you win" from the interviewer.[3] On 24 August 1934 she lapped the Brooklands circuit at over 100 miles per hour, with an average speed of 101.85 mph (163.91 km/h) on her Norton M30. She was only the second woman to achieve this, the first being Florence Blenkiron earlier the same year. Both were awarded the British Motorcycle Racing Club's Gold Star award.[12]
After the Second World War Beatrice and husband George turned to racing cars, which were tuned and modified extensively in their home workshop - starting off their exploits with a much-lightened 1934 Lagonda Rapier registered KG 5363. Between 1959 and 1962 they raced an Austin-Healey Sebring Sprite 888 HPA, most frequently at Goodwood Members' Meetings, scoring a number of third places and even one race win.
Beatrice's and George's driving ambitions became more serious with the 1961 acquisition of an Elva 200 Formula Junior single-seater, but there were accidents for both of them, and the Elva was converted into a Mk VI sports car.[13]
In 1967 Shilling was brought in to help Dan Gurney solve overheating problems with his Eagle Mk1 Formula 1 racing
Did I not read somewhere that an engineer visited Germany in 1937/38 and brought back a Bosch mechanical injection fuel pump? Apparently he showed it to his contact in the Air Ministry and told him that there wasn't a company in England that could make that to the necessary tolerances to make it work?
Deleted member 68059
Staff Sergeant
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- Dec 28, 2015
Yes Bulman did that, but his statement that it was a tricky bit of kit to make was dated 19th Dec 1928,
at the time his conclusions were probably fair, but this applies to any new technological advancement
and it was their job to put in motion development and works to make building such things a reality.
By 1935 Bristol were running injection tests using Bosch pumps they had bought commercially,
so all were very familiar with them.
at the time his conclusions were probably fair, but this applies to any new technological advancement
and it was their job to put in motion development and works to make building such things a reality.
By 1935 Bristol were running injection tests using Bosch pumps they had bought commercially,
so all were very familiar with them.
You kind of skipped over the Injection Impellers in the superchargers of many R3350s. In order to get more even mixture distribition, (Injection into the compressor diffuser wasn't quite cutting it) the NACA developed a method of discharging the fuel through the supercharger impeller itself -
Reverence - NACA-TR-821
I became familiar with this type of Bosch mechanical fuel injection pump when I raced a 1974 Porsche RSR in the 1980s. Years later, a mechanic, Neil Bainbridge, showed me a cutaway version that he had. I marvelled at the precision and tight tolerances of this, basically, little piston engine. Bosch were ahead of their time. I very much enjoyed your book, Calum. The story of Britain not developing fuel injection is a sad one.
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Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
Within four years of Bulman`s comment on the BOSCH direct petrol fuel injection pumps being inconceivable to manufacture in the UK, both Ricardo and the R.A.E. were making their own pumps which were basically identical in principle and method of control. Of course a few laboratory items is not the same as a mass produced item, but generally if you can make ONE you can transfer that knowledge to larger firms with experience and it is just a matter of time and funding to be in a position to be making as many as you like. This was a huge missed opportunity, probably the most serious British managerial aviation lapse of the 1930`s.*
* You can of course make a case for the turbojet being the biggest one, but the two are not quite in the same category of failure, the pump being something everyone knew
already worked and was in use elsewhere, the jet engine was still just a dream at that stage, which was not at all guaranteed to be a great future technology. It is at least therefore understandable why it was perhaps not given the full might of a national development effort until quite late.
* You can of course make a case for the turbojet being the biggest one, but the two are not quite in the same category of failure, the pump being something everyone knew
already worked and was in use elsewhere, the jet engine was still just a dream at that stage, which was not at all guaranteed to be a great future technology. It is at least therefore understandable why it was perhaps not given the full might of a national development effort until quite late.
Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
Its literally a 0.036" thick washer with a 0.2" bore and chamfer on one side. There is a basic drawing on page 127 of her Biography "Negative Gravity", which is sadly out of print. There was however rather a lot of work in finding out that it needed to be a 0.2" bore....
That is a big surprise, I always imagined the orifice to be small, 0.2" (5mm) is around the same as my garden hose on "jet" setting.
That is the smallest. Your water pressure is higher than early Merlin fuel pressure.
Eng
Daggerr
Airman
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Oh I know, I somehow thought it was smaller. But from my very limited knowledge of fluids flowing down pipelines, it is far more complicated than just the size of the hole.