Comparing Merlin versus Hercules Engined Lancaster Performance

[Jim Campbell]

I have heard several reports about the comparitive merits of the radial
engined Lancs verus the more common Merlin powered ones. Most of them
are to the effect that the radial variant had more power down low while
the Merlins had a higher operational ceiling.

Based on http://www.lancaster-archive.com/Lanc-Eng-Props.htm:

Mark I used Rolls-Royce Merlin XX or 22; Mark III Packard Rolls-Royce
Merlin 28 or 38 and the Mark X Packard Rolls-Royce Merlin 224 all rated
at about 1,460 hp at 6,250 ft.

The Mark II used Four (4) Bristol Hercules VI or XVI. 14 cylinder
sleeve-valve, air cooled radial engines with two speed centrifugal
supercharger with 1,735 hp (altitude not reported).

I am guessing that the Bristol Hercules had relatively more
displacement while the Merlin had better supercharging. However I would
like to compare the data for myself. Is anybody aware of any online
power versus altitude tables or graphs for these two engines?

Thanks

Jim Campbell

[Maury Markowitz]

No, and not for a lack of looking. Even in my various printed
references, this data seems basically impossible to find. Once in a
while you get lucky and see something for a specific engine that was
posted to solve some debate -- for instance, about the performance of
the FW 190D's. I've also seen some HP comparisons for the various marks
of Merlins. But beyond that there's little of consistant quality.

Maury

[Peter Stickney]

Post by Jim Campbell
I have heard several reports about the comparitive merits of the
radial engined Lancs verus the more common Merlin powered ones. Most
of them are to the effect that the radial variant had more power
down low while the Merlins had a higher operational ceiling.

This is something I've been puzzling over for a long time myself,
actually. There's a lot of bum data out there, and a bunch of
hearsay, but very little facts.

Post by Jim Campbell
Mark I used Rolls-Royce Merlin XX or 22; Mark III Packard
Rolls-Royce Merlin 28 or 38 and the Mark X Packard Rolls-Royce
Merlin 224 all rated at about 1,460 hp at 6,250 ft.

Note that those ratings are for Emergency Power for the Low (MS) gear
of the supercharger.
A more full list for the Merline XX series looks like this:
A Hercules VI or XVI had the pollowing ratings:

It's odd that some references claim that the Lanc II's service Ceiling
was as low as 12,000'(!) when that's the point where the airplane is
developing its peak power at Climb Power, and is more than 5,000'
below the Economical Cruise Full Throttle Height. Thar doesn't add
up.

The contemporary Merlins were the XX, 22, and 24 series. From our
point of view, the only difference with these engines was in the
Takeoff and Emervency Ratings. The Climb and Cruise Ratings were the
same.

Merlin XX Takeoff Rating: 1280 HP / 3000R/+12/Sea Level
Merlin 22 Takeoff Rating 1390 HP / 3000R/+14/Sea Level
Merlin 24 Takeoff Rating 1620 HP / 3000R/+18/Sea Level

Combat Power for the Merlin XX and 22 was"
High Blower 1435 HP/ 3000R/+16/11,500'
Low Blower 1460 HP/ 3000R/+14/ 6,250'

The Merlin 24 was:
High Blower 1500 HP/ 3000R/+18/ 9,500'
Low Blower 1640 HP/ 3000R/+18/ 2,000'

Climb Power was the same for all at:
High 1175 HP/ 2850R/+9/ 17,500'
Low 1240 HP/ 2850R/+9/ 10,000'

Normal Power, Which was also Max Weak(Lean Mixture) for the 22 & 24
High 970 / 2650R/+7/ 16,000
Low 1000 / 2650R/+7/ 9,250

Just for fun, I'll throuw in the Merlin XX Max Lean Cruise numbers:
High 836 / 2650R / 19,650 / +4
Low 860 / 2650R / 13,050 / +4

Post by Jim Campbell
The Mark II used Four (4) Bristol Hercules VI or XVI. 14 cylinder
sleeve-valve, air cooled radial engines with two speed centrifugal
supercharger with 1,735 hp (altitude not reported).

The difference between the VI and XVI is that the XVI has a different
carburetor. The Carb used on the XVI had no manual controls, and
automatically set lean (weak) mixture at manifold pressures (boost)
below +2 psi.

Takeoff Power: 1615 HP at 2900 RPM, Sea Level
Maximum Power (5 minutes) 1445 HP/ 2900 RPM /+8 1/4 12,000' (FS)
(Later Rating) 1675 HP/ 2900 RPM/+8 1/4 4,500' (MS)

Climb Power (1 Hr) 1240 HP/ 2400 RPM/+6 12,000' High Blower (FS)
1355 HP/ 2400 RPM/+6 4,750' Low (MS)

Max Weak Cruise (Lean) 955 HP/ 2400 RPM/+2 1/2 17.750' High

Post by Jim Campbell
I am guessing that the Bristol Hercules had relatively more
displacement while the Merlin had better supercharging. However I
would like to compare the data for myself. Is anybody aware of any
online power versus altitude tables or graphs for these two engines?

As you can see, the Hercules Takeoff and Emergency ratings exceed
those of the Merlins by quite a fair bit. The cruise ratings are also
very close in power and Critical Altitude, with the slightly higher
power of the Hercules offsetting the slightly higher installed drag.
The drag figures are closer than you might think - the Hercules has a
larger diameter, but it also doesn't have the coolant radiators, and
it has a NACA cowling, which essentially "lifts in a forward
direction", and thus counters the drag of the engine.
Given similar carburetor ram recovery, and using the Hercules powered
Halifaxes and Wellingtons as a basis (Compared to their Merlin
versions), the performance between the 2 should be very similar. both
in speed and altitude.

[Jim Campbell]

Thanks Peter for your very detailed reply. Where did you get your
engine performance? data.

http://www.spitfireperformance.com/ has excerpts of "Aeroplane and
Armament Experimental Establishment-Boscombe Down" performance test
reports for various marks of Spitfires, e.g.
Loading Image... for climb performance
of a Mark V. I wonder if Boscombe Down would have done similiar tests
on Lancasters?

Jim

[Peter Stickney]

Post by Jim Campbell
Thanks Peter for your very detailed reply. Where did you get your
engine performance? data.

From a variety of sources - the 1942-43 Jane's All the World's
Aircraft, the 1945-46 Jane's, "Aircraft Engines of the World", Paul
H. Wilkenson, Pub. Paul H. Wilkenson, NY, 1943, and 1945, and the
Wellington III/X/XI/XII/XIII/XIV Pilot's Notes, the Beaufighter VI
Pilot's Notes, and the Lancaster I/III Pilot's notes.

Post by Jim Campbell
http://www.spitfireperformance.com/ has excerpts of "Aeroplane and
Armament Experimental Establishment-Boscombe Down" performance test
reports for various marks of Spitfires, e.g.
http://www.spitfireperformance.com/x4922climb.gif for climb
performance of a Mark V. I wonder if Boscombe Down would have done
similiar tests on Lancasters?

Yeah - Mike Williams has done some amazing work putting all that
together.
I'm certain they have reports on pretty much everything they've flown.
But - as I understand it, it takes some in-person digging to find
them.

[Maury Markowitz]

and it has a NACA cowling, which essentially "lifts in a forward
direction", and thus counters the drag of the engine.

Can you explain this a bit more? I see lots of references to the NACA
cowl, but no descriptions of how it actually worked.

Maury

[weasel]

Ignore the business about "lifting in a fwd direction"...!

A NACA (= National Advisory Comittee on Aeronautics; your tax dollars
at work in the 1920s and 30s...) cowling works by regulating the flow
of air through the engine cooling fins, and smoothing the flow of air
that goes around the cowling.

By slowing down the air passing through the cooling fins, the drag is
reduced. The slowing takes place because the opening in the front of
the cowl is smaller in area than the cross section of the airflow
passages between and amongst the fins. The amount of air allowed
thrugh the engine is regulated by "cowl flaps" on the trailing edge of
the cowl, which regulate the area through which the air exits. More
air allows more cooling , but more drag, and vice versa. Obviously,
the hole in front has to be big enough to let enough air through to
cool the engine at its hottest, slowest flight condition (numerous
attempts were made to violate this rule, with notable lack of success).

Some designs (like the Fw 190- not sure about the Herc Lancaster) put
the engine exhaust pipe ends at the exit opening to help suck air
through.

Some designs put carburator intakes and oil coolers and turbo
intercoolers inside the lip, too.

The lip of the cowl is nice and rounded to let the air which does NOT
go through the engine to flow smoothly around the front without
"separating" and causing lotsa drag.

Hope this helps

Wes

[Peter Stickney]

Post by weasel
Ignore the business about "lifting in a fwd direction"...!

I may be oversimplifying, but that's hardly the case - Find yourself a
good cross section of a NACA cowl and detrmine the lift vector off
the leading edge of the cowl from the relative airflow.

Post by weasel
A NACA (= National Advisory Comittee on Aeronautics; your tax
dollars at work in the 1920s and 30s...) cowling works by regulating
the flow of air through the engine cooling fins, and smoothing the
flow of air that goes around the cowling.

O.K.

Post by weasel
By slowing down the air passing through the cooling fins, the drag is
reduced. The slowing takes place because the opening in the front
of the cowl is smaller in area than the cross section of the airflow
passages between and amongst the fins. The amount of air allowed
thrugh the engine is regulated by "cowl flaps" on the trailing edge of
the cowl, which regulate the area through which the air exits. More
air allows more cooling , but more drag, and vice versa. Obviously,
the hole in front has to be big enough to let enough air through to
cool the engine at its hottest, slowest flight condition (numerous
attempts were made to violate this rule, with notable lack of
success).

You've messed a few steps there - first, not all NACA cowls have or
had cowl flaps - check out, for example, the B-17C, or the Republic
R-12 Rainbow. There was no cowl adjustment on the B-17C. The
Rainbow used translating slots to regulate airflow without creating
Parasite Drag. What is most important is the gap between the tail of
the cowling and the front of the fuselage. (Most aircraft, btw, had
much too large of a gap. NACA tests on prodiction airplanes in the
Full Scale Tunnel (As described in, say, NACA Wartime Report
NACA-WR-L-108, showed that significant drag reduction with no loss in
cooling air flow was achieved by reducing this gap. (The best
solution, from a drag and airflow point of view is a sliding aft
cowling section (translating fore & aft) that controlled the size of
teh cowling fuselage gap without sticking anything into the wind.

Post by weasel
Some designs (like the Fw 190- not sure about the Herc Lancaster)
put the engine exhaust pipe ends at the exit opening to help suck
air through.

True in the case of later airplanes - the Convair 440 comes to mind -
but not the radial engined FW 190s. They had individual ejector
exhausts directed backwards in order to gain some jet thrust from the
exhaust. (Roughly 10% of available Shaft Horsepower at 375 mph)
Cooling air for the Fw 190s was provided by a geared fan at the front
of the cowling.

The Hercules powered Lancasters had a rather interesting exhaust
system - The exhaust ports on the cylinders faced forward, and the
front of the cowling was used as a collector ring. (They had a
tendency to glow red-hot at night. At least it kept the cowlings
ice-free.) The exhaust was then directsd aft through a "Pine Cone"
diffuser (Looks sort of like a carrot, with a lot of small ports to
let the exhaust gas out) that effectively eliminated any visible
exhaust flame.

Post by weasel
Some designs put carburator intakes and oil coolers and turbo
intercoolers inside the lip, too.

In the lip leading edge, yes, in an attempt to take advantage of ran
compression - They didn't work all that well, though, because the
airflow wasn't perpendicular to the cowling (That airfoil-shaped
front again) If you look at later aircraft, like the AD Skyraider,
F2G Corsair, B-50, KC-97, or the various Convair airliners, you'll
see that the various inlets and scoops were moved aft, where they'd
be in relatively straight air away from the nose of the nacelle.

Post by weasel
The lip of the cowl is nice and rounded to let the air which does
NOT go through the engine to flow smoothly around the front without
"separating" and causing lotsa drag.
Hope this helps

Pretty good, Wes, thanks.

[Peter Stickney]

Post by Maury Markowitz

and it has a NACA cowling, which essentially "lifts in a forward
direction", and thus counters the drag of the engine.

Can you explain this a bit more? I see lots of references to the
NACA cowl, but no descriptions of how it actually worked.
Maury

Sure. In addition to directing air for cooling around the engine's
cylinders, and streamlining things in general, the forward section of
the cowl is airfoil shaped. With air flowing past it, it generates
lift in a direction basically perpendicular to the from of the
engine. Having the smoothly curved, fairly large radius section in
from also smooths out the airflow considerably. (Most high bypass
turbofan nacelles are set up the same way)

There's also a gain of a couple of percent, more or less, in propeller
efficiency, because of reduced flow past the draggy/low thrust blade
shanks down near the hub.

[Robert Sveinson]

Post by Jim Campbell
I have heard several reports about the comparitive merits of the radial
engined Lancs verus the more common Merlin powered ones. Most of them
are to the effect that the radial variant had more power down low while
the Merlins had a higher operational ceiling.
Mark I used Rolls-Royce Merlin XX or 22; Mark III Packard Rolls-Royce
Merlin 28 or 38 and the Mark X Packard Rolls-Royce Merlin 224 all rated
at about 1,460 hp at 6,250 ft.
The Mark II used Four (4) Bristol Hercules VI or XVI. 14 cylinder
sleeve-valve, air cooled radial engines with two speed centrifugal
supercharger with 1,735 hp (altitude not reported).
I am guessing that the Bristol Hercules had relatively more
displacement while the Merlin had better supercharging. However I would
like to compare the data for myself. Is anybody aware of any online
power versus altitude tables or graphs for these two engines?

Here is what I have at the moment hope it helps:

Date............Jan. 1942.........Sept. 1942..........Nov. 1942........May
1944.............Early1945
Type...........Prod. MkI.......Prod. MkII..........Prod.
MkI........MksI&II..............MksI&II
Structure....17,064lbs......
17,064lbs.............17,776lbs.........18,033lbs.............17,633lbs
Engine........10,720lbs........12,335lbs.............11,304lbs.........11610lbs...............11,610lbs
Fuel/oil.........1,796lbs..........1,796lbs..............1,990lbs...........1,999lbs................1,999lbs
Empty
wt....29,580lbs........31,195lbs............31,070lbs..........31,642lbs..............31,242lbs

Fixed Mil
Load.............4,120lbs..........4,120lbs..............4,334lbs...........5,169lbs................4,589lbs
Tare
wt.......33,700lbs........35,315lbs............35,404lbs..........36,811lbs..............35,831lbs

Crew,oil
fuel,mil.
load,bombs
&carriers...26,300lbs..........24,685lbs...........27,596lbs..........28,189lbs..............36,169lbs
Gr.
wt........60,000lbs.........60,000lbs............63,000lbs.........65,000lbs...............72,000lbs

T/off
Power..........5,120bhp.........6,2000bhp..........5,120bhp...........6,440bhp..............6,440bhp
Loading.....11.72lb/hp..........9.68lb/hp........12.30lb/hp.........10.09lb/hp.............11.18lb/hp

Sadly no info. on performance at altitudes. IIRC the MkII could not
climb as high as the Merlin powered Lancs. Same for the radial
Halifaxes.

Robert

[Robert Sveinson]

Gawd this is worse than useless
Maybe this is better!

Post by Robert Sveinson
Date............Jan. 1942.........Sept. 1942..........Nov. 1942........May
1944.............Early1945
Type...........Prod. MkI.......Prod.
MkII..........Prod.MkI........MksI&II..............MksI&II
Structure....17,064lbs......
17,064lbs.............17,776lbs.........18,033lbs.............17,633lbs
Engine........10,720lbs........12,335lbs.............11,304lbs.........11610lbs...............11,610lbs
Fuel/oil.........1,796lbs..........1,796lbs..............1,990lbs...........1,999lbs................1,999lbs
Empty
wt..............29,580lbs........31,195lbs............31,070lbs..........31,642lbs..............31,242lbs
Fixed Mil
Load.............4,120lbs..........4,120lbs..............4,334lbs...........5,169lbs................4,589lbs
Tare
wt..............33,700lbs........35,315lbs............35,404lbs..........36,811lbs..............35,831lbs
Crew,oil
fuel,mil.
load,bombs
&carriers...26,300lbs..........24,685lbs...........27,596lbs..........28,189lbs..............36,169lbs
Gr.
wt..............60,000lbs.........60,000lbs............63,000lbs.........65,000lbs...............72,000lbs
T/off
Power..........5,120bhp.........6,2000bhp..........5,120bhp...........6,440bhp..............6,440bhp
Loading.....11.72lb/hp..........9.68lb/hp........12.30lb/hp.........10.09lb/hp.............11.18lb/hp
Sadly no info. on performance at altitudes. IIRC the MkII could not
climb as high as the Merlin powered Lancs. Same for the radial
Halifaxes.
Robert

[Robert Sveinson]

Post by Robert Sveinson
Gawd this is worse than useless
Maybe this is better!

I can't win
Robert

Post by Robert Sveinson

Post by Robert Sveinson
Date............Jan. 1942.........Sept. 1942..........Nov.
1942........May 1944.............Early1945
Type...........Prod. MkI.......Prod.
MkII..........Prod.MkI........MksI&II..............MksI&II
Structure....17,064lbs......
17,064lbs.............17,776lbs.........18,033lbs.............17,633lbs
Engine........10,720lbs........12,335lbs.............11,304lbs.........11610lbs...............11,610lbs
Fuel/oil.........1,796lbs..........1,796lbs..............1,990lbs...........1,999lbs................1,999lbs
Empty
wt..............29,580lbs........31,195lbs............31,070lbs..........31,642lbs..............31,242lbs
Fixed Mil
Load.............4,120lbs..........4,120lbs..............4,334lbs...........5,169lbs................4,589lbs
Tare
wt..............33,700lbs........35,315lbs............35,404lbs..........36,811lbs..............35,831lbs
Crew,oil
fuel,mil.
load,bombs
&carriers...26,300lbs..........24,685lbs...........27,596lbs..........28,189lbs..............36,169lbs
Gr.
wt..............60,000lbs.........60,000lbs............63,000lbs.........65,000lbs...............72,000lbs
T/off
Power..........5,120bhp.........6,2000bhp..........5,120bhp...........6,440bhp..............6,440bhp
Loading.....11.72lb/hp..........9.68lb/hp........12.30lb/hp.........10.09lb/hp.............11.18lb/hp
Sadly no info. on performance at altitudes. IIRC the MkII could not
climb as high as the Merlin powered Lancs. Same for the radial
Halifaxes.
Robert

[Robert Sveinson]

Post by Robert Sveinson

Post by Robert Sveinson
Gawd this is worse than useless
Maybe this is better!

I can't win
Robert

The table is in the book Avro Lancaster The Definitive Record
2nd Edition
By Harry Holmes page 43.

Robert

Post by Robert Sveinson

Post by Robert Sveinson

Post by Robert Sveinson
Date............Jan. 1942.........Sept. 1942..........Nov.
1942........May 1944.............Early1945
Type...........Prod. MkI.......Prod.
MkII..........Prod.MkI........MksI&II..............MksI&II
Structure....17,064lbs......
17,064lbs.............17,776lbs.........18,033lbs.............17,633lbs
Engine........10,720lbs........12,335lbs.............11,304lbs.........11610lbs...............11,610lbs
Fuel/oil.........1,796lbs..........1,796lbs..............1,990lbs...........1,999lbs................1,999lbs
Empty
wt..............29,580lbs........31,195lbs............31,070lbs..........31,642lbs..............31,242lbs
Fixed Mil
Load.............4,120lbs..........4,120lbs..............4,334lbs...........5,169lbs................4,589lbs
Tare
wt..............33,700lbs........35,315lbs............35,404lbs..........36,811lbs..............35,831lbs
Crew,oil
fuel,mil.
load,bombs
&carriers...26,300lbs..........24,685lbs...........27,596lbs..........28,189lbs..............36,169lbs
Gr.
wt..............60,000lbs.........60,000lbs............63,000lbs.........65,000lbs...............72,000lbs
T/off
Power..........5,120bhp.........6,2000bhp..........5,120bhp...........6,440bhp..............6,440bhp
Loading.....11.72lb/hp..........9.68lb/hp........12.30lb/hp.........10.09lb/hp.............11.18lb/hp
Sadly no info. on performance at altitudes. IIRC the MkII could not
climb as high as the Merlin powered Lancs. Same for the radial
Halifaxes.
Robert