wet liners have stiffening ribsJ.A.W. wrote: ↑Wed Mar 03, 2021 1:55 am.... some erroneous assumptions about the Napier Sabre engine, & sleeve valves in general.
.... the Sabre doubled its supercharger boost levels
in service between 1942 & 1945, without habitually punching sleeves through its ports.
(How do wet-sleeve engines cope?).
the Mustang III flew at 17 gph (AP 2025G Pilot's Notes)J.A.W. wrote: ↑Wed Mar 03, 2021 11:00 pmIn fact, the unencumbered combustion chamber, with ideally placed sparkplugs
allowed the sleeve valve engines to operate on a higher compression ratio for
any given grade of avgas, & thus burned it more efficiently, in cruise settings.
The Napier Sabre reached its highest in-service boost levels on 100/130 avgas,
whereas the poppet valve R/R V12s required 150 grade fuel to safely run at
highest pressures, & were limited to more modest supercharging by 100/130.
Further, the excessive TEL dosing of 150 grade avgas caused 'leading' issues
for the poorly located sparkplugs of OHC V12s & damage to poppet valve seats,
while sleeve valve engines were not so affected by such 'lead poisoning'.
As for your comments on the the Tempest, of course for the RAF - both the low-level
defensive ops against Nazi V1 cruise-missile attack, then post-invasion tactical ops
on the continent - were naturally going to require their best performing fighter at the
altitudes where combat was happening (whereby 'trade could be done', in RAF speak).
Tommy Cookers wrote: ↑Mon Mar 08, 2021 12:26 pm
being a smaller engine - at low powers the Merlin consumed much less fuel than the Sabre (at those powers)
no matter if at its best-efficiency power some Sabre is better than some Merlin (at it's best-efficiency power)
and Wilkinson shows that the Merlin (61/V-1650-3) and earlier give 0.45 lb/hp/hr
ok later 60s 0.5 lb - seemingly the effect of the (for GB ?) Mod 987 camshaft change that increased overlap to 70 deg
it's often said that the Mustang (and eg bombers) prioritised range over power (so kept on using 1650-3s)
ok sleeve-valvers had higher CR (so they should with their lower boost) and were slightly more efficient 'on the bench'
but the Sabre VII was a fiction ie it was never cleared at 20 lb boost for flight or for sale (as I wrote 3 years ago)
eg what plane would have used 20 lb boost 3500 hp at takeoff ? - and with what propeller ?
20 lb boost was not available from Napier or Bristol - but it was used every day by Merlins
(remember RM17SM spec Merlins were iirc cleared with ADI at 25 lb - ok none were sold but they were cleared)
and the Sabre VII weighed 2500-2540 lb - remember even the Centaurus knocked 350 lb of the Tempest's weight
and the (then) official hp figures ignored exhaust thrust - proportionately higher with Merlins due to their 'low' CR
exhaust thrust was also quite useful in the climb
150 grade had no more lead than 100/130
(150 was often 100/150 - proving there was no more lead)
(the 150 came from the 2.5% monomethyl aniline)
115/145 of course is the one with the high lead content
Mod 987 engines required a particular type of spark plugs
remember GB supplied millions of plugs to the USA - on those eastbound ships
a Spitfire or Mustang designed around the low level role would have had much less wing etc etc than they did
(remember the Spit 3 and so some 12 conversions eg DP845 had less wing than any later clipped wings)
then consider the Republic AP-4 & AP-10 which was initially the XP-47 (100-130 sq ft wing area with an Allison 1710)
of course the usual argument against this is that armament must be less
Ah no, T-C, these figures are not supported by the official ratings published in Wilkinson,