A superior German fighter

[Shortround6]

Are you using suck through or blow though carb set ups?

Did you measure the the temp with and without fuel flowing though the supercharger but the supercharger supplying air at the desired pressures/volumes.

A Merlin XX at full power is going though over 2 gallons a minute of fuel. Granted it is also going through a LOT of air.

Big difference between cars and aircraft is that the Merlin XX was supplying a Manifold pressure of 9lbs (about 48in absolute) at 18,000ft or so and compressing the ambient air just over 3 times. This would be like a car at sea level having a supercharger supplying 30lbs of boost or 90in absolute. There was a lot more heat in the intake charge than most car engines ever see. Just supplying sea level pressure air at 20,000ft with a supercharger that was 65% efficient would see a temperature rise of about 175 degrees F above the ambiant air. Now compress it another 50% or so?

 

[GregP]

I can't find any reference that says the Fw 187 V5 was ever equipped with other than Jumo 210 engines. Maybe the paper follow-on planes were calculated with DB 601, DB 603 or DB 605 engines, but can anyone post a reference that shows an actualy flying Fw 187 was so equipped? I can find only the Fw 187 V6 that had DB's and it had the carbureted DB 600A's, not DB 601's. It also had a surface evaporative cooling system that gave a lot of trouble.

I believe the three 2-seat Fw 187's were used as factory test beds, but have never found out the details of the tests or the changes made to them before they were taken out of service, other than that in the winter of 42/43 they were used to study the potential use of the Fw 187 as a night fighter. That does not imply engine changes.

The subject hasn't exactly been completely documented in the books I have read, so maybe there are some data out there showing such. The planes LOOK good and seemed to perform at a good level, but seem to have been killed both by politics and by lack of defensive armament in being selected for the Destroyer role.

 

[davebender]

Jumo 210 engine ended production during 1938.

If Fw-187 enters mass production it will be during 1939 or 1940.

Common sense suggests Fw-187 was never intended for Jumo 210 engine. If Fw-187 prototypes were forced to use an engine that was out of production it was RLMs way of telling Focke Wulf their aircraft program was dead on arrival. He-112 program received similar treatment.

 

[DonL]

I can't find any reference that says the Fw 187 V5 was ever equipped with other than Jumo 210 engines. Maybe the paper follow-on planes were calculated with DB 601, DB 603 or DB 605 engines, but can anyone post a reference that shows an actualy flying Fw 187 was so equipped? I can find only the Fw 187 V6 that had DB's and it had the carbureted DB 600A's, not DB 601's. It also had a surface evaporative cooling system that gave a lot of trouble.

I believe the three 2-seat Fw 187's were used as factory test beds, but have never found out the details of the tests or the changes made to them before they were taken out of service, other than that in the winter of 42/43 they were used to study the potential use of the Fw 187 as a night fighter. That does not imply engine changes.

The subject hasn't exactly been completely documented in the books I have read, so maybe there are some data out there showing such. The planes LOOK good and seemed to perform at a good level, but seem to have been killed both by politics and by lack of defensive armament in being selected for the Destroyer role.

The complete history of this a/c is in this book:
Focke-Wulf FW 187: An Illustrated History: Amazon.de: Dietmar Harmann: Englische Bücher

The book is basing on original documents from Focker Wulf.
Please read my Post 37 and the PM I have send you.
At this book are official original specifications from Focker Wulf engineers with layout drawings for the FW 187 V4/A0 and the FW 187 as nightfighter/destroyer (1942) and as high altitude single seater fighter (1942). Also there are many photos at this book, also from the FW 187 V5 with DB 601 engines, that showed the small radiators of the FW 187 V5, which was not flying with a surface evaporative cooling system.

Here are several members at this forum with this book and I hope they will confirm my informations.

 

[altsym]

@ shortround6;

Used both centrifugal (blow through) and roots (draw through) and I can say without a doubt draw through heats the air/fuel mix like crazy.
This is determined by measuring exhaust gas temperatures, fuel flow, a/f ratio. Using the same engine, and changing to a blow through
blower, I can run 3-4 degrees more timing at the same boost pressure, and measuring exhaust gas temps , etc., overall, much better.

 

[GregP]

Thanks for the reference, DonL!

Hey DonL ... is that title available in English to your knowledge?

 

[bobbysocks]

i am sorry DonL...i cant buy the 109G being meat on the table. it's abilities were respected by us airmen and i know of accounts where the LW pilots (in G-10s) gave the airmen one hell of a fight....and took down its share of allied planes. i dont know any who thought it was a piece of junk or were relieved when they found that it was what they were dogfighting with. i will agree that it was an airframe that had little room left to expand on...especially trying to fit the duel role of fighter and bomber interceptor.....and that another SE fighter airframe should have been in the works as early as 41/42. but a lot of that was dependant on the german industry, economy, and politics. the 109 gave a damn good account of itself up to the end of the war. i always wondered how the models would have progressed if the LW had been able to keep it purely as a fighter and had something else to engage the bombers....

 

[davebender]

Germany had two promising Me-109 replacements during 1942.
.....Fw-190C.
.....Me-309.
Both aircraft required the DB603 engine which RLM cancelled during 1937 to 1940 and then funded at only a low level.

This isn't an airframe issue. It's an engine issue. If RLM wants to replace Me-109 with a larger / heavier / better armed / longer range fighter aircraft they need the larger DB603 engine.

 

[Shortround6]

@ shortround6;

Used both centrifugal (blow through) and roots (draw through) .

They gave up on Roots superchargers for aircraft in the 1920s because of the inefficiency (heating of the intake charge). The NACA did do some testing with them and the reports should be on the NASA server.

NASA - Search Results

 

[altsym]

Links are dead. But I suspect even with a centrifugal supercharger used as a 'draw through' type ( carb on the inlet side of the supercharger), the A/F mix temps would be somewhat high (as compared to Direct Cylinder Injection), unless an intercooler was used. But even that's dangerous, IF fuel collects in the intercooler and the engine backfires, its all over rover.

Correct me if I'm wrong, but didn't those Bendix-Stromberg throttle bodies use some means to heat the fuel to prevent icing?

 

[wuzak]

Links are dead. But I suspect even with a centrifugal supercharger used as a 'draw through' type ( carb on the inlet side of the supercharger), the A/F mix temps would be somewhat high (as compared to Direct Cylinder Injection), unless an intercooler was used. But even that's dangerous, IF fuel collects in the intercooler and the engine backfires, its all over rover.

Correct me if I'm wrong, but didn't those Bendix-Stromberg throttle bodies use some means to heat the fuel to prevent icing?

Yes, the air fuel mixture would be high for the draw through system (like that used in the Merlin).

But, it won't be as high as the air in a system where no fuel is added (ie direct injection, like DB 6).

It also highlights the different philosophies of the two engine manufacturers - Daimler-Benz opted for capacity, high compression and low boost (relatively). Rolls-Royce followed the path of the R engine - high boost, low compression ratio.

For the high boost route the fuel into the eye of the supercharger was invaluable in lowering induction temperatures.

 

[Aozora]

Thanks for the reference, DonL!

Hey DonL ... is that title available in English to your knowledge?

See my post #47 which has excerpts from the book, including part of the weight table for an improved Fw 187 using DB 605s or BMW 801s. Schiffer Publishing Ltd (8 Sep 2004), English, ISBN 978-0764318719. Unfortunately Amazon list it as "Temporarily out of stock" Focke-Wulf Fw 187: Amazon.co.uk: Deitmar Hermann, Peter Petrick: Books

The British weren't the only ones to have reservations about direct fuel injection, because the United States Navy had also examined the concept:

The usual claim seems to be that Rolls-Royce and other British manufacturers were somehow "backward" or ignorant in not adopting DFI and this, in turn, shows how advanced the Germans were:

The Flight article is interesting, but IMHO its more of a PR article from RR. Beggars cant be choosers, RR had no D.F.I. technology available, hell they even had problems making carburetors working properly... neither did they have any working engine in the 30 liter class - though they were developing the Griffon. It wasn't really a choice for them but a necessity, and make their arguments sound a very cheap. RR was an extremely conservative company and not very open to innovation.Still, they did one hell of a job with the Merlin, a conventional engine in all aspects, despite its limits with displacement. Given the constraints with a war going on and no time to develop a new 30-litre class engine (a path everyone choose in the end, but took steps sooner than RR), and no time to adop DFI, they did the right thing and sticking to what was already working was justifiable on the grounds of practicability, but not on engineering grounds. They made the best out of what was available, despite the handicaps of smaller displacement and having to do with carburetors.

The problem with such a pet theory is that it doesn't allow for the fact that the technology of both DFI and aero engines capable of developing 1,000 hp and well over was still new, and that there were perfectly legitimate doubts about the efficacy of using DFI in such high powered, supercharged engines. That Daimler Benz - via Bosch - and Junkers developed reliable DFI systems was a great achievement, but to use that in an attempt to damm the Merlin (with some faint praise) and other engines which did not adopt DFI is just ill-informed nonsense.

Correct me if I'm wrong, but didn't those Bendix-Stromberg throttle bodies use some means to heat the fuel to prevent icing?

No because, as the Flight article here explains:

The Stromberg possesses the following qualities:
(I) Freedom from icing-up because no fuel whatsoever passes the throttles.

 

[Shortround6]

Links are dead. But I suspect even with a centrifugal supercharger used as a 'draw through' type ( carb on the inlet side of the supercharger), the A/F mix temps would be somewhat high (as compared to Direct Cylinder Injection), unless an intercooler was used. But even that's dangerous, IF fuel collects in the intercooler and the engine backfires, its all over rover.

Correct me if I'm wrong, but didn't those Bendix-Stromberg throttle bodies use some means to heat the fuel to prevent icing?

Some links are , some are not. They have changed the front pages since the last time I visited.

Only one aircraft engine in WW II used an intercooler (or after cooler ?) with a single stage supercharger, a certain model of the Jumo 211. The other engines with inter-coolers (or after coolers) had two stage superchargers. The supercharger heats the air, the fuel evaporating in the supercharger can lower the temperature, The direct injection system cannot. The Germans injected the fuel directly into the cylinder between the spark plugs, not into intake ports or above the intake valves.

I shouldn't think that heating the fuel will help the Bendix-Stromberg much. The Fuel was being injected into the eye of the supercharger, a number of inches away from the throttle body, in some models or from the base of the throttle body or adapter. In any case several inches below (after) the throttle plates.

 

[altsym]

The supercharger heats the air, the fuel evaporating in the supercharger can lower the temperature, The direct injection system cannot.

Isn't that was this was for (along with the 'Ram' effect) to cool the intake charge?

Thanks for the info/links for the Bendix-Stromberg throttle body..

 

[wuzak]

Isn't that was this was for (along with the 'Ram' effect) to cool the intake charge?

Thanks for the info/links for the Bendix-Stromberg throttle body..

No. That was for intake air and ram effect. It does nothing to cool the air after the supercharger. Of course having cooler air to start with helps, but Rolls-Royce engines also had such intakes.

 

[Aozora]

No. That was for intake air and ram effect. It does nothing to cool the air after the supercharger. Of course having cooler air to start with helps, but Rolls-Royce engines also had such intakes.

For interest here's an article which explains the working of carburettor air intakes AEHS Article - carby air scoops. pdf

When Stanley Hooker was recruited by Rolls-Royce one of his first jobs was to redesign the carburettor air intake for the Merlin after he had discovered that it was badly designed. In 1941 Hooker wrote a report for R-R analysing the performance of the Merlin in particular, and which had a great deal of bearing on later developments: an analysis of this report can be found here: AEHS article. pdf.

 

[Shortround6]

I fail to understand how that cools the intake charge.

On a car you have a choice, hot under hood air or cool outside air.

On an airplane you have the same choice, sort of, the provision of thousands of cubic feet of air per minute needs a bit more thought than just trying to suck it from inside the cowl. A forward facing airscoop does provide "ram" air, it also WILL heat the air slightly, If the air reaching the carburetor (or engine inlet as opposed to airframe inlet) is at higher air pressure than the ambient air then the air was compressed in the intake duct and if it was compressed it was heated (or it's temperature raised).

We are now getting into technical hair splitting. A couple of degrees more or less is not a big deal, 20-30 degrees C is.

RR (Hooker) said the Fuel evaporation was worth 25 degrees C, they had the test instruments, the test stands and test houses ( they could supply air at controlled temperature, pressure and humidity to the engine intake) they had flight tests, both their own and from users like Hawker. What reason did they have to lie? To cover up their NOT adopting direct fuel injection?

The figure was given in this booklet.

Performance of a Supercharged Aero Engine by Stanley Hooker. It is available from Amazon.

By the way, the booklet has a good chapter on exhaust thrust.

 

[altsym]

Well 2 degrees could be the difference between max power and catastrophic detonation. Lets say for example, if a supercharged engine is pushing 10 psi of boost at sea level (ambient pressure of 14.7 psi, ambient temperature of 24°C @ sea level, the temperature of the air after the supercharger will be 71.4 °C. At 22°C air after the supercharger is 64°C. Now if the detonation point was 69°C air after the supercharger, that 2°C just made the difference. All well in good on just the engine/supercharger, right? Now you have the 50%/50% water-methanol to throw into the equation.

 

[wuzak]

Well 2 degrees could be the difference between max power and catastrophic detonation. Lets say for example, if a supercharged engine is pushing 10 psi of boost at sea level (ambient pressure of 14.7 psi, ambient temperature of 24°C @ sea level, the temperature of the air after the supercharger will be 71.4 °C. At 22°C air after the supercharger is 64°C. Now if the detonation point was 69°C air after the supercharger, that 2°C just made the difference. All well in good on just the engine/supercharger, right? Now you have the 50%/50% water-methanol to throw into the equation.

Where/how did you calculate those temperatures, using what assumptions.

2°C difference at intake does not make 7°C at the discharge.

 

[wuzak]

Double post