Why was the Barracuda so much slower than the Avenger?

[hobbes154]

Possibly obvious, but I find it puzzling that according to Wiki the Barracuda's maximum speed was 38mph slower than the Avenger's despite:

• only 60hp less
• inline vs radial engine
• smaller wings
• lighter

The Avenger can carry a torpedo internally, but I'm assuming max speed is without torpedo? I'm not an aerodynamicist but just eyeballing pictures I don't see any screaming red flags like fixed landing gear (which anyway might not hurt too much at those speeds) or the Skua's vertical windscreen. Would the struts on the tail make that much difference?

Other guesses:

1. Wiki is just wrong? (Neither plane makes wwiiaircraftperformance.org, if anything the other numbers out there are even worse for the Barracuda, not so much for the Avenger.)
2. The Fairey-Youngman flaps add drag out of proportion to the extra wing area (I assume they are counted as part of the wing area)?
3. Thicker wings (relative to chord/absolutely)? The Avenger was NACA 23015 which is 15% thickness at the root (which seems surprisingly thin?). I can't find the Barracuda's airfoil, eyeballing it may be a bit thicker?
4. Aerodynamics is just weird and it doesn't need to be anything big/obvious?

(I'm thinking of the immediate aerodynamic reasons, not any underlying doctrinal reasons e.g. the Barracuda's dive bomber requirement.)

Edit: I guess another possibility is if the Merlin had worse altitude performance than the R-2600? The Wiki speeds don't come with altitudes but 16k vs 22k service ceiling does seem significant...

Edit 2: Other numbers are all over the place but don't indicate it's just an altitude thing e.g. Barracuda Max speed: 228mph at 1,750ft or 210mph at 2,000ft
Avenger Maximum speed 271 mph (436 km/h) at 11,200 feet (3400 meters) 251 mph (404 km/h) at sea level

 

[Shortround6]

Part of it is altitude.
The Merlin 32 used a single speed supercharger and the 1640hp was at 2,000ft, you lost power as it went higher. That 1640hp was at 18lbs of boost.

The engine used in the Avenger had a two speed supercharger. It could hold 1700hp to 3000ft and in high gear it gave 1450hp (?) between 8-12,000ft.

 

[SaparotRob]

Before the folks who know what they're talking about show up, I'm going with a "cleaner" airframe. Less stuff sticking out in the airflow.

 

[SaparotRob]

Dang it! SR6 showed up first!

 

[fubar57]

Dang it! SR6 showed up first!

 

[hobbes154]

Part of it is altitude.
The Merlin 32 used a single speed supercharger and the 1640hp was at 2,000ft, you lost power as it went higher. That 1640hp was at 18lbs of boost.

The engine used in the Avenger had a two speed supercharger. It could hold 1700hp to 3000ft and in high gear it gave 1450hp (?) between 8-12,000ft.

Sorry we may have crossed paths with my edit. I agree altitude is part of it but unless the speed/altitude numbers I found are wrong it doesn't account for all or even most of the difference. In the big picture they are both low altitude engines - it's not like a 1-stage vs a 2-stage.

 

[hobbes154]

Before the folks who know what they're talking about show up, I'm going with a "cleaner" airframe. Less stuff sticking out in the airflow.

Yeah but what exactly? The flaps - I thought they're already counted in the wing area? The tail struts - too small surely? Both planes appear to have a lot of antenna wire out there. If anything the Avenger's canopy looks less aerodynamic because of the turret. They both have retractable undercarriages and however messy the Barracuda's looks when lowered, it looks clean enough when folded.

 

[SaparotRob]

For some reason I thought it had even more struts than it actually had. I guess I always have a mental image of it with those flaps down.

Edit: I had check with Wiki as to what it actually looked like again. Gawd, it's still as goofy as I remember it.

 

[RCAFson]

Possibly obvious, but I find it puzzling that according to Wiki the Barracuda's maximum speed was 38mph slower than the Avenger's despite:

• only 60hp less
• inline vs radial engine
• smaller wings
• lighter

The Avenger can carry a torpedo internally, but I'm assuming max speed is without torpedo? I'm not an aerodynamicist but just eyeballing pictures I don't see any screaming red flags like fixed landing gear (which anyway might not hurt too much at those speeds) or the Skua's vertical windscreen. Would the struts on the tail make that much difference?

Other guesses:

1. Wiki is just wrong? (Neither plane makes wwiiaircraftperformance.org, if anything the other numbers out there are even worse for the Barracuda, not so much for the Avenger.)
2. The Fairey-Youngman flaps add drag out of proportion to the extra wing area (I assume they are counted as part of the wing area)?
3. Thicker wings (relative to chord/absolutely)? The Avenger was NACA 23015 which is 15% thickness at the root (which seems surprisingly thin?). I can't find the Barracuda's airfoil, eyeballing it may be a bit thicker?
4. Aerodynamics is just weird and it doesn't need to be anything big/obvious?

(I'm thinking of the immediate aerodynamic reasons, not any underlying doctrinal reasons e.g. the Barracuda's dive bomber requirement.)

Edit: I guess another possibility is if the Merlin had worse altitude performance than the R-2600? The Wiki speeds don't come with altitudes but 16k vs 22k service ceiling does seem significant...

Edit 2: Other numbers are all over the place but don't indicate it's just an altitude thing e.g. Barracuda Max speed: 228mph at 1,750ft or 210mph at 2,000ft
Avenger Maximum speed 271 mph (436 km/h) at 11,200 feet (3400 meters) 251 mph (404 km/h) at sea level

The Barracuda 1 made 250mph at 12800lb (with a torpedo) at 10900ft with the Merlin 30 during Boscombe down testing.

The SAC data for a TBF1 and torpedo is 249 mph at SL and 257 at 12000ft (both with military power).

This is from Tirpitz: Hunting the Beast:

In his report, Lt Cdr V. Rance, wing leader of 52 TBR,
described the second wave action. Nineteen Barracudas
took off 0525-0535, formed up at a height of 50-200ft and
set off at 0537 (not the official 0538) on a course of 150
degrees magnetic. At such low level, aircraft had difficulty
in maintaining line astern, but this eased when they
adopted a Vic formation after crossing the coast. Three
smoke floats were initially dropped at intervals of one
minute to assist the following fighters in 'fine weather, sea
slight, swell nil'. Cloud in the target area was less than
1/10ths at 15,000ft, and the bombers closed Kaa Fjord at
10,000ft in a shallow double Vic. Over Norwegian territory,
they flew for 12mins at 165 knots true, then slowly reduced
height while increasing speed to 195 knots true. When no
fighters appeared, Rance ordered the wing into two
columns at 210 knots true to aid flak evasion. After Tirpitz
came into sight to port, the starboard column dropped back
'to keep the leader's column roughly between it and the
target'. The final dive commenced at about 7,500ft in the

Which was the 2nd attack on 3 April 1944.

 

[EwenS]

The first thing to remember about the comparison of the Barracuda & the Avenger is that although they served at the same time in WW2, they were a generation apart in development timescales at a time when, in the late 1930s, aircraft were developing at a rapid rate..

Barracuda development began in early 1938, with the contract for the prototypes issued in Jan 1939. By mid 1939 the RN expected production to run between April 1941 and April 1942, implying that there would have been a new design intended to come along to succeed it in service design of which should probably have begun about 1940 (the RN did issue a Spec E.28/40 in Feb 1941 for a research aircraft "for full scale investigation of the problems associated with increased weight of deck landing aircraft" which had all the characteristics of a new TBR design). Then came a host of delays with the result that production didn't start until April 1942 with squadron service from Jan 1943. And we then have to take account of the internal problems at Fairey under wartime conditions which frustrated the Admiralty and MAP.

Grumman received the contract for the prototype XTBF-1 on 8 April 1940 by which time there was a much greater urgency to progress its development, WW2 having started and the USN planning a major expension of its naval aviation arm and with the TBD Devastator long out of production. So its development was accelerated with production starting in Jan 1942 and the first aircraft seeing combat at Midway in June. But even its initial development did not prove trouble free. It just seems that greater urgency in a peacetime environment during 1941 allowed them to be sorted more quickly. And the Avenger did not meet the speed requirement that was initially sought by the USN (300mph).

Two years in the late 1930s meant a huge amount when aircraft development was racing ahead.

It also needs to be noted that the initial requirements called for in the Barracuda were fairly tightly drawn in terms of aircraft weight (10,500lb), free take off distances (British carriers generally had shorter flight decks than those of the USN) and speeds (76mph as generated by the catapults of the time in zero wind) and landing speeds (stalling speed 67mph). As I've noted in other threads that had an effect on the design of the Barracuda and its competitors. These limitations were set in part by the capabilities of carrier catapult and arrester gear of the period. Operationally Barracuda II/III in WW2 were flying at weights up to 14,250lb. And that without any increase in wing area. The RN only began to relax its landing and take off limitations in 1940 while at the same time beginning to uprate their shipboard equipment.

But there was also a significant difference in wing area of the two types that would have further increased the Barracuda's wing loading. Avenger 490 sq ft. Barracuda 405 sq ft. The Avenger also had about 5ft greater span. The Fairey Youngman flaps fitted to the Barracuda were supposed to have the effect of adding to the wing area during normal flight so increasing its efficiency. But it seems to me that with shorter wings of less area and the requirement for a low stall speed the Barracuda wing must have been significantly thicker than that of the Avenger, which wouldn't help its drag despite the benefits of the flaps.

The USN did not set such restrictive limits in the first place although its flight deck equipment was not significantly more advanced that that of the RN. It is worth noting in this context that the Curtiss SB2C Helldiver ordered in May 1939 also suffered huge weight growth during its gestation period and also suffered great delays. Designed for a max weight of 10,189lb it entered service in SB2C-1 form with a max weight of 16,607lb, over 3,000lb of which increase came from the airframe.

The speeds more usually quoted for the various versions of the Barracuda are:-

Mk.I - Merlin 30 - 235mph at 11,000ft; economical cruising 138mph at 6,000ft
Mk.II - Merlin 32 - 228 mpph at 1,750ft; economical cruising 172mph at 5,000ft
Mk.III - Merlin 32 - 239mph1,750ft; economical cruising 170mph at 5,000ft

There were a number of features on the aircraft that would not have helped its drag. The whole folding mechanism was very efficient in reducing the folded width and the space it would take up on a carrier deck, but there were a lot of joints and edges and protruberences that could not have been sealed entirely and would undoutedly have added to the drag. Things like the brackets on the upper surface of the wings that locked into the tailplane when the wings were folded. Also the V shaped handling rails that folded into the underside of the wing to assist in the manual wing folding (this a product of the high wing, itself a product of the emphasis given in the design to the view from the observer's cabin). The various bits and pieces can be seen in this photo of the wing folding in progress.

The Avenger of course used Grumman's Sto-wing that was equally as efficient at reducing the aircraft folded width and had the advantage that it was powered, but did not have so many joints causing airframe imperfections.

And carrying its entire weapon load externally which required bomb carriers to be attached to the wings as a dive bomber, as in the preceding Swordfish & Albacore, was not so efficient. But with the requirement to carry no bomb larger than 500lb at the time of its design perhaps understandable. The bomb racks are visible in this photo.

Bombing up a Barracuda. Note all the panels and holes in the wing. How well could they be sealed?

The Barracuda's problems go much deeper than simply being underpowered. No better example is what happened when Fairey began to look at developing it further from June 1943 into what eventually became the Mk.V. Simply adding a single stage supercharged Griffon to a Mk.II airframe did not solve the Barracuda's problems (1,890hp Griffon VIII or 2,020hp Griffon 37 was eventually used in the Mk.V) . So began a series of other "improvements". It was put on a diet (despite the heavier engine weight growth of the airframe was limited to 1,300lb in the final version), the airframe was cleaned up by filling and fairing aerodynamic imperfections, the ASV.II radar aerials replaced with the pod of ASH radar, a modified tail fitted to improve dive qualities, a tail fillet was added to improve directional stability, an enlarged wing with square wingtips increased the wingspan by nearly 4 ft to reduce wing loading, new enlarged ailerons to increase maneuverability and last of all a pointed rudder. Despite all the changes the speed only increased by about 20mph!

In mid-1945, the Barracuda squadrons in 11ACS heading for the Pacific undertook a number of changes to their aircraft to reduce weight and improve aerodynamics. The TAG was deleted from the aircrew along with his guns and ammunition, the ASV.II set and its Yagi aerials was removed, and the bulged observers windows replaced with flush fitting perspex. I've not seen any figures for the effect that these changes had on the performance.

 

[SaparotRob]

The first thing to remember about the comparison of the Barracuda & the Avenger is that although they served at the same time in WW2, they were a generation apart in development timescales at a time when, in the late 1930s, aircraft were developing at a rapid rate..

Barracuda development began in early 1938, with the contract for the prototypes issued in Jan 1939. By mid 1939 the RN expected production to run between April 1941 and April 1942, implying that there would have been a new design intended to come along to succeed it in service design of which should probably have begun about 1940 (the RN did issue a Spec E.28/40 in Feb 1941 for a research aircraft "for full scale investigation of the problems associated with increased weight of deck landing aircraft" which had all the characteristics of a new TBR design). Then came a host of delays with the result that production didn't start until April 1942 with squadron service from Jan 1943. And we then have to take account of the internal problems at Fairey under wartime conditions which frustrated the Admiralty and MAP.

Grumman received the contract for the prototype XTBF-1 on 8 April 1940 by which time there was a much greater urgency to progress its development, WW2 having started and the USN planning a major expension of its naval aviation arm and with the TBD Devastator long out of production. So its development was accelerated with production starting in Jan 1942 and the first aircraft seeing combat at Midway in June. But even its initial development did not prove trouble free. It just seems that greater urgency in a peacetime environment during 1941 allowed them to be sorted more quickly. And the Avenger did not meet the speed requirement that was initially sought by the USN (300mph).

Two years in the late 1930s meant a huge amount when aircraft development was racing ahead.

It also needs to be noted that the initial requirements called for in the Barracuda were fairly tightly drawn in terms of aircraft weight (10,500lb), free take off distances (British carriers generally had shorter flight decks than those of the USN) and speeds (76mph as generated by the catapults of the time in zero wind) and landing speeds (stalling speed 67mph). As I've noted in other threads that had an effect on the design of the Barracuda and its competitors. These limitations were set in part by the capabilities of carrier catapult and arrester gear of the period. Operationally Barracuda II/III in WW2 were flying at weights up to 14,250lb. And that without any increase in wing area. The RN only began to relax its landing and take off limitations in 1940 while at the same time beginning to uprate their shipboard equipment.

But there was also a significant difference in wing area of the two types that would have further increased the Barracuda's wing loading. Avenger 490 sq ft. Barracuda 405 sq ft. The Avenger also had about 5ft greater span. The Fairey Youngman flaps fitted to the Barracuda were supposed to have the effect of adding to the wing area during normal flight so increasing its efficiency. But it seems to me that with shorter wings of less area and the requirement for a low stall speed the Barracuda wing must have been significantly thicker than that of the Avenger, which wouldn't help its drag despite the benefits of the flaps.

The USN did not set such restrictive limits in the first place although its flight deck equipment was not significantly more advanced that that of the RN. It is worth noting in this context that the Curtiss SB2C Helldiver ordered in May 1939 also suffered huge weight growth during its gestation period and also suffered great delays. Designed for a max weight of 10,189lb it entered service in SB2C-1 form with a max weight of 16,607lb, over 3,000lb of which increase came from the airframe.

The speeds more usually quoted for the various versions of the Barracuda are:-

Mk.I - Merlin 30 - 235mph at 11,000ft; economical cruising 138mph at 6,000ft
Mk.II - Merlin 32 - 228 mpph at 1,750ft; economical cruising 172mph at 5,000ft
Mk.III - Merlin 32 - 239mph1,750ft; economical cruising 170mph at 5,000ft

There were a number of features on the aircraft that would not have helped its drag. The whole folding mechanism was very efficient in reducing the folded width and the space it would take up on a carrier deck, but there were a lot of joints and edges and protruberences that could not have been sealed entirely and would undoutedly have added to the drag. Things like the brackets on the upper surface of the wings that locked into the tailplane when the wings were folded. Also the V shaped handling rails that folded into the underside of the wing to assist in the manual wing folding (this a product of the high wing, itself a product of the emphasis given in the design to the view from the observer's cabin). The various bits and pieces can be seen in this photo of the wing folding in progress.

View attachment 729775

The Avenger of course used Grumman's Sto-wing that was equally as efficient at reducing the aircraft folded width and had the advantage that it was powered, but did not have so many joints causing airframe imperfections.

And carrying its entire weapon load externally which required bomb carriers to be attached to the wings as a dive bomber, as in the preceding Swordfish & Albacore, was not so efficient. But with the requirement to carry no bomb larger than 500lb at the time of its design perhaps understandable. The bomb racks are visible in this photo.
View attachment 729776

Bombing up a Barracuda. Note all the panels and holes in the wing. How well could they be sealed?
View attachment 729779


The Barracuda's problems go much deeper than simply being underpowered. No better example is what happened when Fairey began to look at developing it further from June 1943 into what eventually became the Mk.V. Simply adding a single stage supercharged Griffon to a Mk.II airframe did not solve the Barracuda's problems (1,890hp Griffon VIII or 2,020hp Griffon 37 was eventually used in the Mk.V) . So began a series of other "improvements". It was put on a diet (despite the heavier engine weight growth of the airframe was limited to 1,300lb in the final version), the airframe was cleaned up by filling and fairing aerodynamic imperfections, the ASV.II radar aerials replaced with the pod of ASH radar, a modified tail fitted to improve dive qualities, a tail fillet was added to improve directional stability, an enlarged wing with square wingtips increased the wingspan by nearly 4 ft to reduce wing loading, new enlarged ailerons to increase maneuverability and last of all a pointed rudder. Despite all the changes the speed only increased by about 20mph!

In mid-1945, the Barracuda squadrons in 11ACS heading for the Pacific undertook a number of changes to their aircraft to reduce weight and improve aerodynamics. The TAG was deleted from the aircrew along with his guns and ammunition, the ASV.II set and its Yagi aerials was removed, and the bulged observers windows replaced with flush fitting perspex. I've not seen any figures for the effect that these changes had on the performance.

I was right?

 

[RCAFson]

The first thing to remember about the comparison of the Barracuda & the Avenger is that although they served at the same time in WW2, they were a generation apart in development timescales at a time when, in the late 1930s, aircraft were developing at a rapid rate..

The Barracuda was designed as a torpedo-divebomber and was stressed for vertical divebombing. The TBF was not stressed for divebombing and was unable to safely perform hi-G manoeuvres, so the TBF is not a comparable aircraft to the Barracuda, and the nearest USN equivalent was the SB2C. What really hurt the Barracuda was the high wing design (which was forced upon Fairey by the Admiralty who wanted better visibility for recon) and this forced the use of extended length LG, whose drag hurt TO performance. The Barracuda, once airborne had other faults (which were overcome) but then so did the TBF which were inherent in the design:

This was published in the USN's Naval Aviation News in 1947, IIRC:

Attention TBM Pilots

The pilot of a TBM had completed
four glide bombing runs in which his
pull-outs appeared normal and during
which he apparently experienced. no
unusual circumstances. He was experi-
enced in this type of attack in the TBM
and familiar with its operating. restric-
tions.

On his fifth run part of the star-
board wing and tail section left the
plane at the pull-out altitude of ap-
proximately 2500 feet. The plane dove
into the water out of control and all
three occupants were killed.

The accident board is of the opinion
that the pilot became too steep in his
downwind approach and may have used
elevator tab during the pull-out.

Grampaw Pettibone says:

This is the FORTY-EIGHTH
accident of this nature in the Avenger
type aircraft in the past thirty months. In
almost every case there were no survivors
Surely this should indicate the necessity
for observing the operational limits on
this plane. As every Naval Aviator knows
the TBM was not designed as a dive.
bomber. It was designed to be used as a
torpedo and horizontal bomber. As a re-
sult the maximum permissible speeds and
"G" forces are considerably less than
those applicable to any other currently
operated carrier aircraft.

The safe limits for the operation of this
plane are explained in Technical Order
49-45. and in Flight Safety Bulletin 3-47.
If you intend to do anything other than
straight and level flight in the TBM, read
these limitations. - MEMORIZE THEM.
Then subtract a few knots from the top
limit and save a "G" or two for the wife
and kids, DON'T BE NUMBER 49!

 

[Greyman]

Figures I have from A&AEE testing:

Barracuda II (Merlin 32) +18 lb sq in boost, 3000 rpm (w/ torpedo 13,200 lb) w/ 'Lancaster' flame damping exhausts, no ASV
Barracuda II (Merlin 32) +18 lb sq in boost, 3000 rpm (clean 12,000 lb) w/ 'Lancaster' flame damping exhausts, no ASV
Avenger I (GR 2600-8) 42/41 inch boost, 2600 rpm (15,160 lb) w/ no exhausts extensions, one ASV aerial under each wing

For what it's worth, if added -- ASV aerials knock off 5 mph on the Barracuda.
The Avenger later had exhaust extensions added to bring CO2 levels down to a safe level and these resulted in a loss of 6 mph.

 

[RCAFson]

Figures I have from A&AEE testing:

View attachment 729873

Barracuda II (Merlin 32) +18 lb sq in boost, 3000 rpm (w/ torpedo 13,200 lb) w/ 'Lancaster' flame damping exhausts, no ASV
Barracuda II (Merlin 32) +18 lb sq in boost, 3000 rpm (clean 12,000 lb) w/ 'Lancaster' flame damping exhausts, no ASV
Avenger I (GR 2600-8) 42/41 inch boost, 2600 rpm (15,160 lb) w/ no exhausts extensions, one ASV aerial under each wing

For what it's worth, if added -- ASV aerials knock off 5 mph on the Barracuda.
The Avenger later had exhaust extensions added to bring CO2 levels down to a safe level and these resulted in a loss of 6 mph.

Thanks for that. Very interesting! However the Barracuda II didn't use the Lancaster type flame dampening exhausts against Tirpitz, and stub exhausts were used. I suspect the dampeners were removed for daylight ops.

 

[EwenS]

The exhaust system on the Barracuda caused a whole host of problems wiith a range of fixes being tested, eventually numbering 9! The original system with the recessed, angled downpipe to minimise drag while being an effective flame damper proved useless. It glowed red and was visible from 5 miles away! It also caused the pipes and gaskets to burn through.

The eventual solution (least worst option?) was use of individual Lancaster stubs with the downpipe recess faired over to reduce the drag.

 

[RCAFson]

The exhaust system on the Barracuda caused a whole host of problems wiith a range of fixes being tested, eventually numbering 9! The original system with the recessed, angled downpipe to minimise drag while being an effective flame damper proved useless. It glowed red and was visible from 5 miles away! It also caused the pipes and gaskets to burn through.

The eventual solution (least worst option?) was use of individual Lancaster stubs with the downpipe recess faired over to reduce the drag.

Mason's The Secret Years states:

Lancaster Mark I, III and X

On the Merlin powered versions, flame damping
requirements were soon achieved, in December 1941 on
DG3595 with an A& AEE designed box after earlier attempts
using fish tail ejectors had been unsuccessful on the first
prototype. The new 'cascade box' contributed largely to a
reduction of 14 mph (true) in top speed; attempts by the
Establishment, Rolls Royce and an RAF unit to alleviate
the speed penalty were ineffective.

 

[hobbes154]

Thanks all, so I'm writing this off as a combination of
1. published speed figures are all over the place*
2. the Barracuda had a lot of small aerodynamic imperfections relative to the Avenger that added up
3. altitude advantage to 2-speed R-2600

*I find the figure below especially puzzling as the Merlin 30 is still a 1-speed supercharger, though tuned for a slightly higher altitude (6000ft vs 2000ft), and with about 300hp less than the Merlin 32. Let alone the external torpedo (another site says max speed w/ torp @ sea level - 194mph)!

The Barracuda 1 made 250mph at 12800lb (with a torpedo) at 10900ft with the Merlin 30 during Boscombe down testing.

 

[hobbes154]

I was right?

Near enough, although to be pedantic some of it sounds like gaps letting the airflow in where it shouldn't rather than stuff sticking out

 

[Shortround6]

There may have been a few major aerodynamic imperfections.

Granted I have not spent a lot of time looing but I have not seen a photo of the Barracuda without the flaps hanging down.
The flaps will lower from horizontal for higher lift for landing.
The flaps will hinge upward for dive bombing.

Correction welcome but it seems like the rest of the time the flaps looked like (operated like) a mini biplane. Or something like a short Junkers flap.

Perforated flaps like the SBD also had drag.

 

[RCAFson]

Thanks all, so I'm writing this off as a combination of
1. published speed figures are all over the place*
2. the Barracuda had a lot of small aerodynamic imperfections relative to the Avenger that added up
3. altitude advantage to 2-speed R-2600

*I find the figure below especially puzzling as the Merlin 30 is still a 1-speed supercharger, though tuned for a slightly higher altitude (6000ft vs 2000ft), and with about 300hp less than the Merlin 32. Let alone the external torpedo (another site says max speed w/ torp @ sea level - 194mph)!

The Merlin 30 and 32 had the same gear ratios and rotor dimensions. There were internal mods on the 32 to allow for 18lb boost, otherwise I think the performance curve at 12.5lb boost was the same.

I suspect that some performance figures use 12.5lb boost or they are with max underwing ordnance (6x250lb B bombs). I suspect that the flame dampening exhaust cost ~10-12mph but it doesn't seem to be used in daylight service.