J.A.W. wrote:Well, even Lovesey admits having an issue with them during wartime..
AFAIR, Packard -9s were the highest rated mil-spec Merlins at 2200+ hp on ADI/90"Hg
The V-1650-9 was rated RM.14SM.
The RM.17SM was a 100-series development that didn't go into service. It was rated at 2200hp in MS gear and 2100hp in FS gear - without ADI. It was tested in 1944 at 2640hp (corrected to 2620hp), +30psi boost, with ADI @ 3150rpm in a 15 minute sprint run. It also was accidentally run for 30 minutes at 2380hp @ 3300rpm.
US Merlin Mustangs were overboostable by holding down the spring-loaded switch intended for preflight checks of High Blower operation
someone wrote that in saving his life this way he saw 97" for 5 min
(for J.A.W - 450 ias in a B-25 with High Blower engaged at low altitude - bombardier wrote that the asi redline was 370 but he never saw it below 450 when exiting target area)
RAF Mustangs had this switch omitted
generally the USAAF/AAC didn't have automatic boost control, by WW2 British-built aircraft always did
but eg the T-6/Harvard gives about 800 hp if the throttle is fully opened on takeof because the boost will exceed 50"
the rulebook requires the throttle to be opened only as far as gives around 36" and about 600 hp
the 36" is because the engine was designed for 80/87 fuel, but normal fuel is 100/130 and 50" is ok
just watch the CHT gauge
(a few N/A planes had intentionally excess CR for efficiency and power at altitude, ie Fokker D7 and De H Comet
so were not allowed full throttle at low altitude)
(similarly the Robinson helicopter(22 not 44 says Trini), it's throttled to 25" or so ie full throttle only at suitable altitude
this gives flat rating of power wrt altitude and allows greater engine life)
with supercharging there is a further effect due to engine rpm, more rpm gives more delivery from the supercharger
this will occur with a fixed pitch prop
overboosted, over-rev takeoffs were quite acceptable and legitimate
early WW2 US combat flying was by throttling as required (limited only by detonation)
detonation is conspicuous when sitting 6' behind a 20 or 30 litre engine
IIRC Don ? McVicar got 504 ias at ground level from his (private) 3 speed Mosquito by fining the pitch to raise rpm and blower delivery
..... 'screwdriver tuning' or what !
certainly the RAF had certified rev-counters and procedures to prevent this
the RM.17SM passed the Type Tests but was rejected ? after engine no 90369 twice failed in trials in Mustang FX 858
similarly the high power R 2800/P-47Ns were pulled from service ?
but these engines were good according to due processes
btw Merlin 113 Corliss throttle had less pressure drop and lighter operation (relevant to Mosquitos)
btw Wright found that big-end fretting could be prevented by silver plating the mating faces of the rods
as required they told all US manufacturers
maybe this would have saved the Vulture ?
btw the fault in the BRM H-16 concept that the basic engine was deficient in combustion speed and consistency
as were most others eg Coventry Climax and Cosworth SCA
BRM found a cure by accident, in the reduced rod ratio resulting from the stroking of the V8 towards 2 litres
so making a viable V12