HE-100 vs Bf-109

Discussions on all (non-biographical) aspects of the Luftwaffe air units and general discussions on the Luftwaffe.
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Topspeed
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#106

Post by Topspeed » 28 Nov 2005, 18:43

Okay advice taken.

Alistair B
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#107

Post by Alistair B » 29 Nov 2005, 22:03

I would like to question whether it is possible that the Messerschmitt Bf 109F-4 in frontline combat service could really attain a top speed of 416mph, even if only for a few minutes.

A 6-page article in the May 2005 issue of Aeroplane magazine looks at the efforts of Daimler-Benz to increase the power of the engines installed in the Bf-109. Though it is mainly about the DB605 it starts off with the DB601, and considers why there was a "flat spot" in power output for about two years in 1942-43.

Shortly after introduction there were found to be problems with both the DB601E, and later the 605A. The crown (top) of the pistons were burning through well before reaching the 200 hours service life requirement. Both were de-rated from 1.42 atm manifold pressure to 1.30 atm in the spring of 1942. The problem was solved in two ways. During later production and overhauls new pistons were fitted with increased thickness crowns, though the author Chris Starr is not clear about exactly when this took place. The other part of the solution was the development of new sparkplugs. The materials technology of the 1940's gave sparkplugs only a very narrow 'heat range' for the so-called 'self-cleaning temperature', if it was to work without fouling. The original sparkplug was the Bosch DW250ET 7 and this caused pre-ignition at 1.42ata MAP.

New sparkplugs were needed to the end of the war for each increase in manifold pressure.

1.42ata - Bosch DW250ET 7/1.
1.80ata - Bosch DW250ET 7/1A and 10/1.
1.98ata - Beru F280 E43.

Chris Starr dates the introduction of the 1.42ata capable Dw250ET 7/1 sparkplug to the summer of 1943. This implies that whatever genuine results were obtained in the tests of an F-4 at Rechlin, these were not a realistic measure of what a combat pilot could achieve during the heyday of the aircraft, which was 1942. By the time Luftwaffe allowed its engines to be pushed this hard the F-4 had already passed from frontline service.


gabriel pagliarani
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#108

Post by gabriel pagliarani » 30 Nov 2005, 11:22

Alistair B wrote:New sparkplugs were needed to the end of the war for each increase in manifold pressure.

1.42ata - Bosch DW250ET 7/1.
1.80ata - Bosch DW250ET 7/1A and 10/1.
1.98ata - Beru F280 E43.

Chris Starr dates the introduction of the 1.42ata capable Dw250ET 7/1 sparkplug to the summer of 1943. This implies that whatever genuine results were obtained in the tests of an F-4 at Rechlin, these were not a realistic measure of what a combat pilot could achieve during the heyday of the aircraft, which was 1942. By the time Luftwaffe allowed its engines to be pushed this hard the F-4 had already passed from frontline service.
Nice infos. Generally holes in the upper crown of the piston are caused by a too poor stechiometric ratio oxygen/fuel. This phoenomenon causes a "thermal lance" (oxydric flame) effect making a hole in the upper sky (the "crown" for Englishmen) of the piston. Thre are only 3 chances to reduce the effect
1-by enriching the mix by adding more fuel. Done.
2-by enriching the mix by reducing the relative pressure of air.Done.
3-by lowering temperature by using shortest electrodes on the sparking plug (highest Bosch-number) .Done.
Consequently the change of the upper crown of piston with harder ones could be considered a structural development not hardly linked to the well known problem.
Last edited by gabriel pagliarani on 30 Nov 2005, 11:26, edited 1 time in total.

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#109

Post by Topspeed » 30 Nov 2005, 11:25

Alistair B wrote:I would like to question whether it is possible that the Messerschmitt Bf 109F-4 in frontline combat service could really attain a top speed of 416mph, even if only for a few minutes.
Alistair,

Mr Rausch have sources that tell Me 109 F-4/Z actually flew 441 mph.
M.Rausch wrote: I took a look on the Bf 109 F-4/Z speed curves a collector sent to me. These curves show a topspeed of 635 km/h with combat power and about 705-710 km/h in about 8 km altitude with GM-1 use.
The engines had to be removed after very low number of flying hours..possibly 200 hours tops.

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#110

Post by Alistair B » 30 Nov 2005, 14:20

I am not suggesting that the performance figures given by M.Rausch are incorrect, but that the aircraft tested to produce them are effectively "special editions", produced to show what the aircraft was capable of in theory, if problems with engine reliability could be sorted out.

When JG27 pilots took to the air in the summer of 1942 they did not have such performance available to them.

As for the Bf 109F-4/Z, my reference books make no mention of it, and I have never come across a record of it in frontline service. This may just be a gap in my knowledge. If 441mph at 8000m could really be achieved, such an aircraft would have had little trouble in chasing down Mosquitos. There were special units formed for such a task - were any of these issued with the F4/Z ?

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#111

Post by Topspeed » 30 Nov 2005, 14:26

Me 109 F - 4/Z meant it had GM-1 boost installed.


http://www.lexikon-der-wehrmacht.de/Waffen/Me109-R.htm

http://www.panzerplatte.de/Me109.html

http://airwar.iatp.by/luftwaffe/dat_bf109.htm


No mention whether it was used in action in the front units.

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#112

Post by gabriel pagliarani » 30 Nov 2005, 15:49

Alistair B wrote:I am not suggesting that the performance figures given by M.Rausch are incorrect, but that the aircraft tested to produce them are effectively "special editions", produced to show what the aircraft was capable of in theory, if problems with engine reliability could be sorted out. ...
Not necessarily special editions in aircraft. The higher quality of fuel and lubricants respect with standard could change performances in a way you cannot believe at. I did it on my own motorcycle and now I know that "special"fuels could improve performances much more than an accurate tuning. For example there was an enormous differences between synthetic German fuels available in 1945, the Romanian fuel from Ploesti available till 1943 and the fuel coming from Middle East still available at the beginning of the war. Which one for tests? 8)
...No mention whether it was used in action in the front units....
It was a beautiful recce, too many times confused with the most common Gustav. The only report I have read about it was done by Pierre Clostermann who faced a couple of them over Scapa Flow while driving a rare Spitfire VIII at the highest ceiling.

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#113

Post by Topspeed » 01 Dec 2005, 11:25

Gabriel,


The MEREDITH effect produced 400 lbs of thrust in a Mustang.

http://www.airandspacemagazine.com/ASM/ ... stang.html


rgds,

juke

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#114

Post by gabriel pagliarani » 01 Dec 2005, 12:33

Topspeed wrote:Gabriel,


The MEREDITH effect produced 400 lbs of thrust in a Mustang.

http://www.airandspacemagazine.com/ASM/ ... stang.html


rgds,

juke
Ok! Now it works. :wink: Little less than 200kg pushing force. A little but not irrelevant help

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#115

Post by luigi » 01 Dec 2005, 13:43

After reading the interesting article, it's a pithy that no investigation was made on axis airplanes, I'm quite sure now, re-thinking the whole thing, that the Macchis incorporated this feature (albeit in no such refined way) in it's cooling system: I think to remember that the rear port was "endless" adjustable, not stepwise like the Spitfire and, also reading the tests of say, captured Bf109E against D520, you get the impression that pilots knew about the effect in that they tried to optimize the cooling setting in order to gain thrust (a research in older threads of the WarBirds forum will show a lot of references and original documents on the subject). They were aware that full open ports would bring a fatal loss of climb and full shut down only would rost the engine with poorer climb in comparaison to a mid-way solution even if at first wiew less efficient aerodinamically.

Maybe with today's tools one could calculate the meredith effect on these airframes.

Regards

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#116

Post by Topspeed » 01 Dec 2005, 13:47

I got the impression if the radiator totally was "bad" it would loose 240 hp:s compared to a Mustang.

Or how do you translate this:
Meredith wrote:As a result, the cooling drag was estimated at only 3 percent of the total and used only something like 40 horsepower for cooling purposes. While the comparable power used for cooling by the Spitfire is not available to me, the measurements made by Rolls-Royce show a total power required for the same speed (400 mph) as 200 horsepower more for the Spitfire than for the Mustang.
Somehow I get an idea of a false assumption here ! :)
Last edited by Topspeed on 01 Dec 2005, 16:39, edited 1 time in total.

luigi
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#117

Post by luigi » 01 Dec 2005, 15:05

I think he is mixing cooler system drag and total drag.
I believe to understand that he argues that the spitfire needed 200hp more than the mustang to maintain the same speed of 400mph.

If cooler drag = 3% of total drag, the drag at 400mph needed 40*100/3=1333,3 hp on the mustang while on the spitfire, being its vmaz 405mph, you needed already almost all of the engine power (1500hp more or less? that would make for the difference of 200hp) we don't know however, how much of the more drag of the Spit goes in account of the cooling system.

Regards

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#118

Post by Topspeed » 01 Dec 2005, 16:40

Mustang and Spit had totally different wingfoil.

luigi
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#119

Post by luigi » 01 Dec 2005, 16:50

of course Topspeed, I think he was making very gross comparaisons in a "chat", albeit held in front of a big audience.

try this, it's long but makes for a veryinteresting reading ;)

http://agw.bombs-away.net/showthread.ph ... ght=macchi

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#120

Post by gabriel pagliarani » 02 Dec 2005, 09:55

luigi wrote:I think he is mixing cooler system drag and total drag.
I believe to understand that he argues that the spitfire needed 200hp more than the mustang to maintain the same speed of 400mph.

If cooler drag = 3% of total drag, the drag at 400mph needed 40*100/3=1333,3 hp on the mustang while on the spitfire, being its vmaz 405mph, you needed already almost all of the engine power (1500hp more or less? that would make for the difference of 200hp) we don't know however, how much of the more drag of the Spit goes in account of the cooling system.

Regards
Spit as Me 109 were another stuff. they never had a single cooler in the belly but 2 smaller embedded in the wings hence using NACA profile of the wingfoil as air extractor. Far different computing and probable a far different effect from Meredith. Please don't add more variables to a too complex problem. In my umble opinion the key to solve the problem for both G55 and Mustang is in Energy count of "gain and losses" because the count of power losses requiress more unknown parameters to be added (as Cx, Cy and Cz drag forces)

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