Constant Speed Prop vs Variable Engine Timing

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...

"Kevin Horton" wrote in message
news
On Tue, 02 Mar 2004 07:32:33 -0700, Bill Daniels wrote:


The gear shifted prop was the last gasp of piston engine development
before the turbine age. Look at the Lycoming XR7755, Napier Nomad or
the
Rolls Royce Crecy. These were 5000 HP+ monsters that needed every trick
in the engineers bag. Piston engines produce more HP at high RPM at the
cost of fuel consumption but deliver low fuel consumption at low RPMS.
Props produce more thrust at low RPM and most efficiency with the blades
at a single best AOA. That AOA must be maintained over a wide range of
airspeeds. Just too many variables for a CS prop to deal with alone.

The two speed gearbox isn't perfect but it does buy the engineer a
bigger
range of options.

Bill Daniels


Bill,

Thanks for pointing out these fascinating engines. I had heard of all of
them, but had never really looked into the details before.

The Lycoming XR-7755 certainly was a huge, complicated monster.

http://www.aviation-history.com/engines/xr-7755.html
http://www.people.virginia.edu/~rjr/engines/

The Napier Nomad was a bizarre combination of two-stroke diesel and gas
turbine. It managed a very impressive specific fuel consumption of 0.345
lb/ehp/hr. The only reference I can find to a gear box was a variable
ratio gearbox between the gas turbine and the piston crankshaft of the
Nomad 2. Not exactly what the original poster was referring too, but
interesting non-the-less.

http://www.home.aone.net.au/shack_one/nomad.htm
http://www.yourencyclopedia.net/Napier_Nomad

The Rolls-Royce Crecy was a highly supercharged diesel, that supposedly
produced about 5,000 on the test stand. I can't find any reference to a
two-speed gear box between the engine and the prop either on-line, or in
Aero Engines, Bill Gunston, but neither have I found a detailed technical
description of the engine. So perhaps that detail was left out.


http://www.stobbe.dk/technical_liter...rolls-royce/Ro
lls-aircraft.html

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com


I keep dreaming that someone sifted through all the old engineering test
reports to find the gems of wisdom developed by the slide-rule engineers who
built these fantastic engines. I'd bet there are ideas that might not have
worked then that could be used today given the advances in materials and
fabrication techniques.

Imagine a Nomad or Crecy with ceramic bearings and piston crowns and thermal
barrier coatings - or with a FADEC system. I've read that all three
companies were certain that their engines could have been developed to
10,000 HP. Imagine a C-130 with one third the fuel consumption.

Bill Daniels

Kevin Horton wrote snip

Well, the AOA limiter an the Airbus's is set very close to the stall. It
is well beyond where a stick shaker would be. The curve of lift vs AOA
tends to have a fairly flat top with modern swept wing jets, so once you
get up on top of that curve there isn't any benefit to pulling more AOA,
as you don't get any more lift. I wish there was some way to get in a FBW
Airbus sim with you. We could do two windshear recoveries - one using
full aft stick riding on the AOA limiter, and one in Direct Law, with no
AOA limiter. I'm convinced you would do better just using the AOA limiter.


I would enjoy that. You could be right.

For the record I think FADEC is great. Do you want it in your GA airplane?

Well, I'm a suspicious type, and I want to see some more service history
first to assure myself that they've sorted all the bugs out. So not on
my RV-8 project, but maybe on the next one.

Sounds very wise indeed. Great shots of your RV-8 by the way.

pac

On Tue, 02 Mar 2004 20:25:48 -0700, Bill Daniels wrote:


"Kevin Horton" wrote in message
news
On Tue, 02 Mar 2004 07:32:33 -0700, Bill Daniels wrote:


The gear shifted prop was the last gasp of piston engine development
before the turbine age. Look at the Lycoming XR7755, Napier Nomad or
the
Rolls Royce Crecy. These were 5000 HP+ monsters that needed every
trick in the engineers bag. Piston engines produce more HP at high
RPM at the cost of fuel consumption but deliver low fuel consumption
at low RPMS. Props produce more thrust at low RPM and most efficiency
with the blades at a single best AOA. That AOA must be maintained
over a wide range of airspeeds. Just too many variables for a CS
prop to deal with alone.

The two speed gearbox isn't perfect but it does buy the engineer a
bigger
range of options.

Bill Daniels


Bill,

Thanks for pointing out these fascinating engines. I had heard of all
of them, but had never really looked into the details before.

The Lycoming XR-7755 certainly was a huge, complicated monster.

http://www.aviation-history.com/engines/xr-7755.html
http://www.people.virginia.edu/~rjr/engines/

The Napier Nomad was a bizarre combination of two-stroke diesel and gas
turbine. It managed a very impressive specific fuel consumption of
0.345 lb/ehp/hr. The only reference I can find to a gear box was a
variable ratio gearbox between the gas turbine and the piston
crankshaft of the Nomad 2. Not exactly what the original poster was
referring too, but interesting non-the-less.

http://www.home.aone.net.au/shack_one/nomad.htm
http://www.yourencyclopedia.net/Napier_Nomad

The Rolls-Royce Crecy was a highly supercharged diesel, that supposedly
produced about 5,000 on the test stand. I can't find any reference to
a two-speed gear box between the engine and the prop either on-line, or
in Aero Engines, Bill Gunston, but neither have I found a detailed
technical description of the engine. So perhaps that detail was left
out.


http://www.stobbe.dk/technical_liter...rolls-royce/Ro
lls-aircraft.html

--
Kevin Horton RV-8 (finishing kit) Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/ e-mail:
khorton02(_at_)rogers(_dot_)com


I keep dreaming that someone sifted through all the old engineering test
reports to find the gems of wisdom developed by the slide-rule engineers
who built these fantastic engines. I'd bet there are ideas that might
not have worked then that could be used today given the advances in
materials and fabrication techniques.

Imagine a Nomad or Crecy with ceramic bearings and piston crowns and
thermal barrier coatings - or with a FADEC system. I've read that all
three companies were certain that their engines could have been
developed to 10,000 HP. Imagine a C-130 with one third the fuel
consumption.

Bill Daniels

They were very complicated engines though, with a lot of moving parts. It
is hard to imagine that their reliability could have approached that of a
modern turbine engine.

The SFC of modern turbo props isn't all that bad. I couldn't find specs
quickly for the engine in the C-130J, but the 5,000 hp PW-150 supposedly
has an SFC of 0.433 at take-off power. I imagine the cruise SFC should be
slightly better, as that would be the design point. The engine supposedly
weighs 1521 lb. So I don't see how a development of those last great
piston engines would have one third the fuel consumption.

http://roger.ecn.purdue.edu/~propuls...ops/pw100.html

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

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?