Jabberwocky
Staff Sergeant
The Tempest's drop in performance over 25,000 feet was tied to the barebones, almost elementary, centrifugal type supercharging of the Sabre engine.
Unlike the Merlin, the Sabre never recieved a two stage, two speed supercharger. Instead it stuck with a single stage, two speed supercharger, which lost efficiency as altitude increased and the air got thinner. The Sabre was tested with an advanced 3 speed, two stage supercharger in early 1942, but it was just seen as an added and unwanted complexity to what was a very unreliable engine at the time.
Later engines like the Centarus and Sabre V on the Tempest II and VI actually had even lower full throttle heights , so obviously the lack of high altitude performance didn't particulary worry the RAF.
The medium altitude restriction actually worked in the Tempests and Typhoons favour to some extent, ensuring their place as the premier low altitude fighter and fighter-bomber, respectively, of the RAF.
The wing radiators were initially dismissed for a few reasons:
1. The percieved vulnerability of wing radiators/oil coolers. During 1941 and 1942 both the Whirlwind and Mosquito suffered combat damage after sucking debris into their wing mounted radiators. The chin radiator was seen as more robust at the time, perhaps incorrectly.
2. The expense of manufacture. Although more efficient aerodynamically, the wing radiators were more complex and expensive.
3. Space for fuel. Getting rid of the wing radiators was supposed to allow room for more fuel tanks in the wings. However, i'm unsure if this capacity was used or not. The Mk II, with wing radiators, actually ended up being the longest ranged Tempest variant.
Unlike the Merlin, the Sabre never recieved a two stage, two speed supercharger. Instead it stuck with a single stage, two speed supercharger, which lost efficiency as altitude increased and the air got thinner. The Sabre was tested with an advanced 3 speed, two stage supercharger in early 1942, but it was just seen as an added and unwanted complexity to what was a very unreliable engine at the time.
Later engines like the Centarus and Sabre V on the Tempest II and VI actually had even lower full throttle heights , so obviously the lack of high altitude performance didn't particulary worry the RAF.
The medium altitude restriction actually worked in the Tempests and Typhoons favour to some extent, ensuring their place as the premier low altitude fighter and fighter-bomber, respectively, of the RAF.
The wing radiators were initially dismissed for a few reasons:
1. The percieved vulnerability of wing radiators/oil coolers. During 1941 and 1942 both the Whirlwind and Mosquito suffered combat damage after sucking debris into their wing mounted radiators. The chin radiator was seen as more robust at the time, perhaps incorrectly.
2. The expense of manufacture. Although more efficient aerodynamically, the wing radiators were more complex and expensive.
3. Space for fuel. Getting rid of the wing radiators was supposed to allow room for more fuel tanks in the wings. However, i'm unsure if this capacity was used or not. The Mk II, with wing radiators, actually ended up being the longest ranged Tempest variant.
