I was hoping that you'd get the hint.If you mount your carb after the SC you get almost no mass charge increase due to fuel evaporation.
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I was hoping that you'd get the hint.If you mount your carb after the SC you get almost no mass charge increase due to fuel evaporation.
The removal of the chokes increases the supercharger compression ratio by about the same amount the fuel evaporation does under typical circumstances.If you integrate the effect of increasing mass charge over altitude, you can see that its contribution allows you to reach 30,000 feet in less time. Moreover:
Cited from "The Performance of a Supercharged Aero Engine" by S.Hooker, H.Reed and A.Yarker, March 1941
Although the late Wright R-3350 already used direct injection, the P&W R-4360 was fitted with an injected carburetor, which led to icing problems (mainly due to the engine being installed backwards, not fuel evaporation). Noticed while visiting the New England Air Museum. I assume, if you have a good pressured (injecting) carburetor and high quality fuel the need of direct injection is questionable.
P.S. I suspect that the Soviet VK-4 carburetor on the Ash-73 engine was actually a copy or further development of the Bendix Model PR58P3 injection carburetors fitted to the R-3350. I would be very grateful if someone could share a link to information about the VK-4.
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!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"
View attachment 745036
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.
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 itView attachment 745061
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.
Yeah, should've warned you guys about the watch ad.Yes. No true technical datas, and wrong chronology. But very good for selling watches....
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 -If you integrate the effect of increasing mass charge over altitude, you can see that its contribution allows you to reach 30,000 feet in less time. Moreover:
Cited from "The Performance of a Supercharged Aero Engine" by S.Hooker, H.Reed and A.Yarker, March 1941
Although the late Wright R-3350 already used direct injection, the P&W R-4360 was fitted with an injected carburetor, which led to icing problems (mainly due to the engine being installed backwards, not fuel evaporation). Noticed while visiting the New England Air Museum. I assume, if you have a good pressured (injecting) carburetor and high quality fuel the need of direct injection is questionable.
P.S. I suspect that the Soviet VK-4 carburetor on the Ash-73 engine was actually a copy or further development of the Bendix Model PR58P3 injection carburetors fitted to the R-3350. I would be very grateful if someone could share a link to information about the VK-4.
I found a photo that could be considered as proof that the K-4 (not VK-4) carburetor on the Ash-73 is a copy of the Chandler-Evans carburetor from the R-3350, and not the later Bendix-Stromberg injection carburetor.
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.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.
View attachment 745235
There are pics of the RAE Restrictor(s).Are there any pictures of Miss Schilling's orifice?
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....Are there any pictures of Miss Schilling's orifice?
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.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....
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.
View attachment 745235
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.
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.
View attachment 745636
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.
One of the book previews on ebay shows a drawing: Negative Gravity Life of Beatrice Shilling Book by Matthew Freudenberg | eBayAre there any pictures of Miss Schilling's orifice?
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.That is the smallest. Your water pressure is higher than early Merlin fuel pressure.
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