Last & Best of the Piston Engine Fighter Aircraft.

[johnny comelately]

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]

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]

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]

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

[Tommy Cookers]

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

Calum Douglas gave a good talk at the Inst.Mech.E a year or so ago
including the vortex throttle (known in WW2 and now in F1) .... and how without it losses seemed big to German boffins
probably as quote not in reality - leaning & coarse pitch 60% revs a strong boost regulator rather eliminating throttling
also mentions a WW2 fuel '62% iso-octane' - maybe the start of physics teachers saying petrol/gasoline is iso-octane ?
(presumably real fuel constituents equivalent to 62% IO were for practicality treated as 62% IO)

btw 1 Ginger Lacey said he blanked off the 10 psi boost auto-throttle hole to get 12 psi - and had a new engine daily
France May 1940 (or later in Far East) I wonder

thinking about the V16 BRM and its VT that never materialised ....
it's less than clear how it would have been worked in racing (maybe that's why it never materialised)
IMO throttling (or waste-gating or diverter?) at full power might have been quite useful
or (the engine having said RR insufficient valve travel) ....
how is there a problem (for regulation at the top end) if there's some breathing restriction at the top end ?
(50 years ago the California spec Saab 99 turbo had throttling at full power)

btw 2 'they' were supposedly building 4 new 'anniversary' BRM V16 cars - but maybe Covid killed that ?
better luck with an H-16 anniversary !

btw 3 Kermit Weeks seems to have shipped his Tempests 2 and 5 to the UK for completion
iirc his Sabre is good - and similarly there's others eg a Typhoon in Canada ?