This is kind of a mish mash for a number of posts to this thread.

1. The Merlin (In P-51) had a 2/1 reduction gear. At full throttle
engine turned 3000 rpm and the big prop only turned 1500 rpm.

2. Merlin had a two stage blower. Low blower was set so at 'gate' you
could pull 61 inches at sea level. There was a spring loaded switch
that you could check high blower prior to T/O. The high blower was
controlled by a aneroid and it automatically shifted to high blower
between 12-14K (not a precise altitude). If you were in formation and
the lead bird shifted to high blower and your bird hadn't yet, we had
a fix for that problem. The mech would take a length of safety wire
and loop it under the spring loaded switch and thread it up behind the
safety guard over switch. Then to manually switch to high blower to
stay in formation you would grab the ends of the safety wire and
manually lift the switch to shift to high blower and at the same time
just wrap the safety wire around the safety cover over switch. Of
course after your engine had shifted to high blower automatically, you
could unwind the wire and let switch go back to the automatic position
so you wouldn't inadvertently over boost the engine during descent.

3. I also on a number of missions, flew with the prop pitch pulled
full back (high pitch) and full throttle. (all within the allowable
BMEP). Airspeed was about 140-150 mph under 500 feet where we were
flying. About every 30 minutes Merlin would get rough with that power
setting and we would have to clean the engine out. First pull the
throttle back and then start the prop lever forward (toward flat
pitch). That 'old' Merlin would buck and spit and shake and blow
black balls of smoke out of stacks and cut out and you would have to
stop and let if clean itself out a little at which time you could push
the prop some more forward again. If would take a minute or two to get
the engine to take full throttle at max rpm and you then ran full
throttle for 2-3 minutes to clean things out and then you pulled back
to the low rpm again. At the low rpm the MP was self limiting and full
throttle only gave you 15 or so inches. In this mode the prop was
turning so slow that you could see the blades and count them as they
went by.

All this is just an aside on engine operation with the Merlin in a
time and land far away (sure beats a 65 Cont G).

Big John


On 26 Feb 2004 13:04:46 -0800, (Jay) wrote:

Seems to me that some of the benefits of the constant speed prop were
based on the limitiations of timing (ignition and valve) of the
Lyco/Conti engines. If your engine was designed to have a large
dynamic range of efficient operation, you won't need the articulated
prop as much.