Last & Best of the Piston Engine Fighter Aircraft.

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johnny comelately
johnny comelately
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Joined: Thu Apr 09, 2015 11:55 pm
Location: Australia

Re: Last & Best of the Piston Engine Fighter Aircraft.

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Tommy Cookers wrote:
Wed Jan 25, 2023 10:04 am
johnny comelately wrote:
Tue Jan 24, 2023 10:49 pm
1.7?
now corrected
I meant to write 70% rich
ie 70% richer than stoichiometric

on the armouredcarriers site there's eyewitnesses saying their onboard RR tech rep proclaimed that....
there was per se no time limit on Seafire max boost - other than fuel consumption being literally a vital issue
About the same as the current nitro engines.
Big penalty with weight, but they had no choice at the time

Tommy Cookers
Tommy Cookers
594
Joined: Fri Feb 17, 2012 3:55 pm

Re: Last & Best of the Piston Engine Fighter Aircraft.

Post

johnny comelately wrote:
Wed Jan 25, 2023 11:36 am
Tommy Cookers wrote:
Wed Jan 25, 2023 10:04 am
ie 70% richer than stoichiometric
About the same as the current nitro engines.
Big penalty with weight, but they had no choice at the time
but nitromethane over stoichiometric isn't wasted - it combusts via the (available) oxygen that it carries

the GB view was presumably that WI was a weight penalty that might give no benefit to an operation
Sam Heron wrote that RR and Allison treated 115/145 as if it was 145/145 - ie they (mainly ?) used the fuel for cooling
I think he meant cooling the flame temperature - keeping the aromatics happy and the 145
and presumably unburnt fuel (or water in WI) would/could somewhat contribute to exhaust flow work ie jet propulsion

johnny comelately
johnny comelately
96
Joined: Thu Apr 09, 2015 11:55 pm
Location: Australia

Re: Last & Best of the Piston Engine Fighter Aircraft.

Post

Tommy Cookers wrote:
Wed Jan 25, 2023 1:34 pm
johnny comelately wrote:
Wed Jan 25, 2023 11:36 am
Tommy Cookers wrote:
Wed Jan 25, 2023 10:04 am
ie 70% richer than stoichiometric
About the same as the current nitro engines.
Big penalty with weight, but they had no choice at the time
but nitromethane over stoichiometric isn't wasted - it combusts via the (available) oxygen that it carries

the GB view was presumably that WI was a weight penalty that might give no benefit to an operation
Sam Heron wrote that RR and Allison treated 115/145 as if it was 145/145 - ie they (mainly ?) used the fuel for cooling
I think he meant cooling the flame temperature - keeping the aromatics happy and the 145
and presumably unburnt fuel (or water in WI) would/could somewhat contribute to exhaust flow work ie jet propulsion
Re: the excess weight. What I meant, if I am interpreting your figures right Tommy, is that with 70% excess over lambda 1 for every tonne of fuel carried 410kg would be necessary but a deficit for either range or armaments

Tommy Cookers
Tommy Cookers
594
Joined: Fri Feb 17, 2012 3:55 pm

Re: Last & Best of the Piston Engine Fighter Aircraft.

Post

johnny comelately wrote:
Thu Jan 26, 2023 11:07 am
Re: the excess weight. What I meant, if I am interpreting your figures right Tommy, is that with 70% excess over lambda 1 for every tonne of fuel carried 410kg would be necessary but a deficit for either range or armaments
eg by mid-WW2 the Merlin is automatically running lean most of the time ie except at high powers ie high boosts
but automatically eg running 60 or 70% rich at emergency powers ie power demand beyond the takeoff gate
(Bristol gave 60+% - maybe for the Pegasus ?)

reduction in demanded power increases prop pitch, reduces rpm and boost, and leans the fuelling
so actual throttling loss is zero or small
weak mixture at 20" manifold uses 17 imp gal/hr at low altitude
richening commenced above 46" manifold and 2700 rpm
Mustang 67" manifold/3000 rpm is WE power using 137 imp gal/hr - 61"/3000 rpm is takeoff using 112 imp gal/hr

WI is heavier/bulkier (its a very poor fuel) and less flexible
presumably less suited to British point-defensive type operations
WI users anyway surely ran ('wasteful') conventionally-rich at high power


btw the USAF P-51D flight handbook says eg
15 min power ratings don't limit to 15 min duration - they're only to help engine life conservation via low rpm & boost