Constant Speed Prop vs Variable Engine Timing

So what did you do if your plane shifted to high blower but the lead didn't? Pull it back real quick I suppose...

I like that 15" and (maybe) 500 rpm - really lugging it...

--
Dan D.



..
"Big John" wrote in message ...
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.

Dan

Yep. Not a problem it you shifted first to high blower. You just
adjusted your power to stay in formation. You had more power than lead
and so just tucked it in and went on with mission.

Engine did not lug. We ran the figures on the BMEP and well within
acceptable range. Was not stressing the engine at all.

Big John

On Wed, 03 Mar 2004 01:17:54 GMT, "Blueskies" wrote:

So what did you do if your plane shifted to high blower but the lead didn't? Pull it back real quick I suppose...

I like that 15" and (maybe) 500 rpm - really lugging it...

I didn't mean stressing, it was really just ticking over, and still you were going 140-150 mph - what was the power
output at that setting?

--
Dan D.



..
"Big John" wrote in message news
Dan

Yep. Not a problem it you shifted first to high blower. You just
adjusted your power to stay in formation. You had more power than lead
and so just tucked it in and went on with mission.

Engine did not lug. We ran the figures on the BMEP and well within
acceptable range. Was not stressing the engine at all.

Big John

On Wed, 03 Mar 2004 01:17:54 GMT, "Blueskies" wrote:

So what did you do if your plane shifted to high blower but the lead didn't? Pull it back real quick I suppose...

I like that 15" and (maybe) 500 rpm - really lugging it...

Dan

We normally cruised about 240 mph IAS under 10K in low blower. When
escorting bombers we would cut back to 190-225 or such for duration
and range. Still had to 'S'.

As I remember:

3000 rpm and 61 in. HG for T/O. Only time I pulled 67 In. HG (War
Emergency) got detonation even with the 'purple' (115-145
octane) gas.
2700 rpm and 45 in. HG for climb.
2200-2400 and 30-35 in. HG for cruise.
100 mph landing speed.
Final was 115 mph +/- depending on weight and reducing over over run
to stick on end of R/W.

Been a long time ago and could have been 125-130 cruise?? but seem to
remember it was a little higher than that.

Remember it was not close to stall speed and comfortable to fly.

Dash one shows that 1400 rpm/24 in. = 140 CAS at sea level where we
were flying but am sure the power setting was lower than that.

The '51 was a pretty slick bird and both oil and coolant doors were
probably stream lined due to low power output so no extra drag there
and still got the heat boost/thrust.

Weren't many rules back then and you could do a lot of things
especially during the war.

One story about a P-47 jock in Italy after VE day. One of the things
they did was capsize sail boats by flying over at full throttle and
low altitude and pulling the nose up as they went over and the prop
blast in the sails would turn the boat over.

So, one day this guy was out screwing around and there was a big fancy
sail boat and he made the pass and capsized it. Next day the word came
down asking who was flying that day and was turning boats over? The CO
asked around and sent the jocks name up the line thinking it was some
Italian big wig complaining.

Seems that all the Generals were out for a Sunday sail and partying
and they got turned over. Next day this guy was on a boat for the
Pacific and stayed well after VJ day G They wouldn't let him come
home even though he had the points.

With nothing but time on his hands, he used to fly (P-51) up to the
British (BCOF) base at Bofu (Honshu) that had a hill in the center of
the field with the tower on it. He wouldn't call in but dive down to
deck off the field and as he got to field roll over inverted and fly
across the field going up and over and then down the hill at 20 FT
altitude or so. BCOF troops thought that was wonderful and asked our
base who was doing it so they could invite him up to meet the troops
and have a party. When the Base CO found out he sent the guy home to
be kicked out so guess he finally broke the chain and got his
discharge G

Big John

On Wed, 03 Mar 2004 02:03:45 GMT, "Blueskies" wrote:

I didn't mean stressing, it was really just ticking over, and still you were going 140-150 mph - what was the power
output at that setting?