WEP on the C205

[Angus]

For Scholzie
"Why is using MW50 bad for the engine? Some allied late war planes used water injection. In AH the F4U4 for instance. The Merlin does not produce more power/torque for the same weight, the two engines weigh almost exactly the same."

The MW is Methan-Water right. Well, as far as I know, it's the Methan that really eats up the engine. The piston heads were the initial problem, but the thing really eats up everything, such as sleeves and valves. Using the MW would lead to either problems/inreliability, or very much maintainance, which in the late war could be a very hard task on the German side, being short of spares, engineers and facilities, - hence engines getting "old" mighty quickly.

About the Power and torque of the Merlin vs the DB, I had a close look at that actually. It was of course related to a Spit vs 109 debate, where I was trying to figure a path through so much biased data.
It is hard to figure really, - Speed, acceleration and climb do not absolutely rely on the same factor.
I picked climb as a basis for a torque measurment, calculating torque in NM/time for a given altitude. One can also have a look at the total newtons for a mass at a given speed through airflow, but it is harder to balance absolutely, for it has more curves to put in.
Anyway, a Spitfire with a similar propeller as a 109, with almost exactly the same power output, will definately pull more Newtons to altitude. It is quite more than a margin. If one levels that margin out with a different propeller for higher speed, the Spitty will in return be faster at the same power output.
(based on Spit I vs 109E3/4, both with 87 octane fuel)

Anyway, again,looking at the engines....
The Merlin is actually slightly lighter for a given power output, more or less. It is however a very marginal difference,- rating not much more at times than a fat pilot vs a thinner one. You are right, the engines do weight almost exactly the same, however, the favour tends to be a wee bit in the Merlins favour.
Torque is another issue, - as I define it, it is very much related with the boost. Remember that boost does not help so much with top speed, however drastically with climb. Why so? Torque curve maybe?

I have no Idea about the P&W. Did they use Methane as well? If they did, I am pretty sure that the US had a lot better alloys than the Germans, and bear in mind that that has nothing to do with engineering quality, just access to the alloys.

Anyway, if you have the Weight, power and climb capacity of a typical say 1942/43 109 model handy I'll gladly put it up in my algorythm and give you the climb torque as well as a co-time Merlin thingie.

Getting back to the topic, - if the 205 did not use MW, was there no other available overboost, and secondly, what about mixtures like the C-3????

[MiloMorai]

The Americans called it ADI (anti detination injection). The methanol was used as an anti-freeze while the water was the anti-detination fluid. The injected substance was a fluid not a gas which methane is. Are you thinking of nitrous oxide(GM1 by the Germans)? This is very corrosive.

Some Merlins in bombers used NOX.

The P-47 had ADI late war as did some P-51s.

[Batz]

Angus check Blogs link....

[GRUNHERZ]

If one levels that margin out with a different propeller for higher speed, the Spitty will in return be faster at the same power output.
(based on Spit I vs 109E3/4, both with 87 octane fuel)

Thats basically the ONLY time that was true.

Bf109F4
Bf109G2

All faster for less power.

G6 is slower.

G6AS isfaster than spit 9.

G10/K4 all faster for less power than griffon spits.

[Angus]

"If one levels that margin out with a different propeller for higher speed, the Spitty will in return be faster at the same power output.
(based on Spit I vs 109E3/4, both with 87 octane fuel)

Thats basically the ONLY time that was true. "

That is basically the last time a speed optimized propeller was used, - later props were more or less CS for improved climb and acceleration

Anyway, the G2 is the queen of the line....

[joeblogs]

I believe that P&W engines - late war - used water injection with alcohol to prevent freezing. In otherwords - methanol. Pretty common by that point.

I had thought the issue about engine damage from WEP had to do with very high heat and bearing loads. The result - (time between overhauls) TBO falls dramatically.

P&W and Curtiss Wright had one advantage over German engine makers and all the British (except Bristol) - years of engineering experience derived from serving the largest market for high powered civilian transports. US engines had a distinct advantage in TBO and sometimes in specific fuel consumption.

-Blogs

Originally posted by Angus
For Scholzie
 
I have no Idea about the P&W. Did they use Methane as well? If they did, I am pretty sure that the US had a lot better alloys than the Germans, and bear in mind that that has nothing to do with engineering quality, just access to the alloys.

 

[Angus]

Lol, noticed my typo, always calling methanol methane.
Must be all that cow work

[gripen]

joeblogs,
IIRC Bristol Hercules sleeve valve engine had clearly longest TBO of the WWII military engines.Can't remeber the numbers but something like 50% longer TBO than PW engines.

gripen

[joeblogs]

Gripen

That's why I excepted Bristol from my characterization.

Bristol had a great reputation with their poppet valve engines too, but they were a bit small in terms of displacement by WWII.

P&W tried, but never mastered a sleeve valve engine.

The other exception to make would be diesel aircraft engines, where the Germans had some of the best.

-Blogs

Originally posted by gripen
joeblogs,
IIRC Bristol Hercules sleeve valve engine had clearly longest TBO of the WWII military engines.Can't remeber the numbers but something like 50% longer TBO than PW engines.

gripen

[joeblogs]

I am always amazed when I see these charts for German engines. To me the fuel consumption numbers looks like some kind of average over power ranges even though the organization of the table would suggest otherwise.

In the data here, specific fuel consumption varies from .43 lbs/hp/hr to 0.49 lbs/hp/hr. A comparable range for an American radial over the power spectrum would run from 0.42 to 1.0 or even higher.  Most of the increase is explained by the switch from lean fuel mixtures to rich mixtures to prevent detontation under higher manifold pressure.

I don't see how the German engines can escape the physics here. Can it really be explained by direct fuel injection? Are the calculations done differently?

Paul Wilkinson (1945) estimated the best SFC for the DB605 A1 was 0.44 using 92 octane avgas.

-Blogs

Originally posted by VO101_Isegrim
As in fact they did even a bit earlier on :



British report of Bf 109G-2/trop dated 8th February, 1943.

Another point of interest is the very economical fuel consumption even when high powers are involved (Merlin 66 consumed 150 gal/hour at WEP).

[GScholz]

Those are Imperial gallons. Converted to US gallons the 1.42ata 2800 rpm fuel consumption reads as 123 gal/h. That would be consistent with the German documentation on the DB605A.


Here's page three of the DB605A Motoren-Karte. It says approximately (ungefär) 480 L/h (126 gal/h) on 1.42ata 2800 rpm and 400 L/h (105 gal/h) on 1.3ata 2600 rpm.








The Motorenmuster is more accurate and I get 473 L/h (124 gal/h) on 1.42ata and 393 L/h (103 gal/h) on 1.3ata.

[joeblogs]

Yes I was worried about that, but that just changes the scale a bit, about 20 percent.

The odd factor that remains is that charts of American engines show a 70-100 percent increase in specific fuel consumption moving along the power curve from max cruise to take-off. When you look at tables of german or russian engines (the one's I've seen are compiled from British or German sources), you see a variation in specific fuel consumption on the order of 20-50%.

For example, using your second chart, and converting to American units, we have SFC ranging from 0.53 to 0.74, a variation of only 40 percent.

I just don't understand what explains the discrepancy unless the calculations are made under different assumptions. For example, suppose the take-off and climb numbers assume you throttle back when you hit the 10 minute or whatever limitation is specified in the pilot's manual?

-Blogs

Originally posted by GScholz
Those are Imperial gallons. Converted to US gallons the 1.42ata 2800 rpm fuel consumption reads as 123 gal/h. That would be consistent with the German documentation on the DB605A.


Here's page three of the DB605A Motoren-Karte. It says approximately (ungefär) 480 L/h (126 gal/h) on 1.42ata 2800 rpm and 400 L/h (105 gal/h) on 1.3ata 2600 rpm.




The Motorenmuster is more accurate and I get 473 L/h (124 gal/h) on 1.42ata and 393 L/h (103 gal/h) on 1.3ata.


 

[GScholz]

No they are actual fuel consumption at that power setting per hour, even if the engine couldn't be run at that setting for a whole hour. The inline engines were a lot more fuel efficient at high power than the big radials, even the Merlin with its carburettors were a lot more efficient.

Exactly why this is I don't know, but I have a hunch it is because of cooling. The air-cooled radials must have used a very rich mixture at high power setting just for cooling purposes. I know this is so for the F4U4 which has awful fuel consumption at MIL power, but because of the water injection its WEP consumes much less fuel. The liquid cooled engines were not so vulnerable to overheating parts of the engine (cylinder tops, piston heads, valves etc.).

[Angus]

Scratching my head here....
Well, in princip, an inline engine has a systematic cooling pattern for the price of a more vulnerable design perhaps? The Radial cooling is simple and brutal.
How about the BMW radial then? or the russian engines?

Oh, BTW, which engines had sleeves and which not?

[joeblogs]

I have done a similar caclulation for the Allison v12. It's still the case that above 65% rated power fuel consumption increases dramatically.

In other words the levels at different power settings may vary, but the steepness of the consumption curve really shouldn't. I don't know why we don't see that in the European charts.

My numbers also say that water cooled engines are not always as fuel efficient and the reason is quite simple - they are typically run at higher RPM. The benefit of a water cooling is really seen in the smaller displacement, higher compression ratio (sometimes) and lower dry weight rather than in the fuel economy.

The most fuel efficient engines are models of the cyclone, twin wasp, and Bristol Hercules - all air cooled.

It is still true that that the P&W R2800 engine was more thirsty for gas than Wright's at high power settings. There is some evidence this was due to the carburetor and not the engine. Very late war models corrected this problem.

-Blogs

Originally posted by GScholz
No they are actual fuel consumption at that power setting per hour, even if the engine couldn't be run at that setting for a whole hour. The inline engines were a lot more fuel efficient at high power than the big radials, even the Merlin with its carburettors were a lot more efficient.

Exactly why this is I don't know, but I have a hunch it is because of cooling. The air-cooled radials must have used a very rich mixture at high power setting just for cooling purposes. I know this is so for the F4U4 which has awful fuel consumption at MIL power, but because of the water injection its WEP consumes much less fuel. The liquid cooled engines were not so vulnerable to overheating parts of the engine (cylinder tops, piston heads, valves etc.).