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Initially intended as standard equipment for the Luftwaffe, in operational service it was found that GM-1 had some drawbacks. The additional weight of the equipment reduced performance on all missions, while the system was only used in the cases where the aircraft went to very high altitudes. GM-1 also became less attractive than originally imagined when in 1943, the previous trend towards ever increasing combat altitudes ended.
Mit einer Bf 109 G-1/R2 ließen sich mit GM-1-Anlage 100 km/h Geschwindigkeitsgewinn in 12.000 m Höhe und eine Gipfelhöhe von 13.800 m erzielen.
Beim Einsatz in Höhenaufklärern Ju 88T mit BMW-801-G-2-Motoren konnte die Leistung, die bei diesen Maschinen in 10.000 m Höhe von 1.730 auf 880 PS abfiel, durch GM-1 auf 1.430 PS gesteigert werden.
Yes, a bunch of Mossie nightfighters were converted. Rawnsley's book, Night Fighter (about him and John Cunningham) mentions it. Added 50mph.
Using GM-1 was an hassle, the product being highly volatile you could not fill the tank and just wait a few days before using it.
Moreover it lost most of it's interest when the engine being produced reached FTH in the 7-8km range, indeed GM-1 could not really be used below FTH+1500/2000m meaning that you had to fly at 9000-10000m to use it.
At such an altitude you most likely need a pressurised cockpit and it's very unlikely you'll encounter anyone except for some recce a/c.
G-5/U2 and G-5/U2/AS were kept with GM-1 just for such business, intercepting high flying mossies and the likes.
Most usefull was the MW-50 boost which permitted higher outputs for a long time at usual combat altitude.
Beginning in April 1944 the G-6/U2 were transformed on the production line for MW-50 use rather than GM-1 moreover 200 kits were issued to transform the existing GM-1 using G-6/U2.
THe aircraft transformed on the production line were issued the light tank similar to the later G-14, but the modified G-6/U2 kept their the heavy GM-1 tank.
Using GM-1 was an hassle, the product being highly volatile you could not fill the tank and just wait a few days before using it.
Moreover it lost most of it's interest when the engine being produced reached FTH in the 7-8km range, indeed GM-1 could not really be used below FTH+1500/2000m meaning that you had to fly at 9000-10000m to use it.
At such an altitude [9-10 km] you most likely need a pressurised cockpit and it's very unlikely you'll encounter anyone except for some recce a/c.
Most usefull was the MW-50 boost which permitted higher outputs for a long time at usual combat altitude.
From a practical standpoint GM-1 remained in use for aircraft operating at high altitudes and expected to remain there
Whatever altitudes many combats may have started at most continued at a lower altitude. Some finished at close to sea level. Without digging through dozens of references I would conjecture that the added performance at very high altitudes obtained by the use of GM-1 injection was considered not worth the trade off in weight and other problems for day fighters.
There are literally hundreds of combat/encounter reports available. How many of these include combat above 8000-9000 metres (26,000-30,000 feet)? I have been sifting the encounter reports of the P-47s 0f the 56th FG for someone recently. Generally combats (on escort missions) commenced between 18,000 and 22,000 feet (roughly 5,000 to 7,000 metres) and descended from there. At this altitude GM-1 was not going to be useful to a Luftwaffe fighter. MW 50 on the other hand would have been. I don't believe that it was an accident that many Luftwaffe fighters were MW 50 equipped.
On other mission types the combats took place much lower.
I thought you must be reading different reports to me so I checked the first ten on your link.
Only one mentions starting at above 25,000 feet stating 28,000 feet.
On three the initial altitude is unclear.
Five start at 25,000 feet or less. One states that they climbed to engage the enemy at 26,000 feet, which means six out of ten started from 25,000 feet or less.
Now, those ten are not representative of the whole body of data but they tend to confirm what I have seen in other reports.
25,000 feet is lower than 8,000 metres.
Looking from the other side I have seen many claims from Luftwaffe pilots for B-17s and B-24s. It is remarkable how often the figures 6,000 and 7,000 metres appear considering popular wisdom is that US bombers flew higher than this. 8,000 metres is less common, though not rare . The highest height given for a bomber "pulk" that I have seen with a quick look through my notes is 8,500 metres.
This would be a representative account, from Lt. Ekkehard Tichy of 9./JG 3.
"At 10.15 hour I took off in a Bf 109 G-6 with three MG 151/20s and two MG 131 as Staffelfuhrer in the Gruppe of Major Dahl against an enemy formation reported in the area of Mannheim. It contained 60-70 aircraft staggered from 6,000 to 7,000 metres."
I have one individual report where a Fw 190 pilot (Uffz. Gerd Wiegand, 8./JG 26) claimed to have dived on the bombers, through the escorting P-47s from 11,000 metres, but this is a rare exception. More often the Luftwaffe fighters attack from an altitude similar to that of the bombers.
Cheers
Steve