Bistol Type 153 wins the F.37/35, no W. Whirlwind

From Beaufighter (F) Mk.VI Testing


".This aeroplane is the prototype Beaufighter VI. Externally it is similar to the Beaufighter I, the main difference being the installation of Hercules VI engines and larger oil coolers and oil cooler ducts.

...........Tapered shrouded slotted flame damping exhausts were fitted on both engines.

...........The aeroplane was painted with the normal green and brown camouflage, not night fighter black. It had undercarriage doors and not skirting pieces as on some previous Beaufighters. 4 x 20 m.m. guns were fitted in the nose and neither the gun tunnels nor the ejection chutes were sealed for these tests. The holes for the 6 x .303" guns in the wing were covered over, but the ejection chutes remained uncovered.

...........The aeroplane had a "straight" tailplane, not the 12 1/2 deg. dihedral version. There was no camera gun above the cabin roof. A W/T aerial was fitted between the aerial mast on top of the fuselage and the tail. Neither A.I. nor I.F.F. aerials were fitted."

After test were competed the engines were re-rated and some or all of the tests run again at the higher rating. Apparently there was a bit of a mismatch between the props and the power available at the higher ratings.

Top speed was 334-334mph at 15,600ft-16,500ft.

Something sure seems to be off, and it cannot be blamed on flat black paint or radar aerials or IFF aerials or????

Shortround6 said:

After test were competed the engines were re-rated and some or all of the tests run again at the higher rating. Apparently there was a bit of a mismatch between the props and the power available at the higher ratings.

Top speed was 334-334mph at 15,600ft-16,500ft.

Something sure seems to be off, and it cannot be blamed on flat black paint or radar aerials or IFF aerials or????

Click to expand...

The 'old limitations' for the Mk.VI are listed as 2800 rpm and +7 psi, while the new ones are 2900 rpm and +8 psi.
Bristol gives 1675 HP at 2900 rpm and +8.25 psi, S/C in low gear; I don't have the date. On 2400 rpm and +6 psi ('climb and max continuous'), low gear, the max power was 1355 HP. To me, 2800 rpm and +7 psi looks like 1500-1550 HP down low.

On 2900 rpm, +8.25 psi and S/C in high gear, Bristol gives 1455 HP at 12000 ft. On 2400 rpm and +6 psi, they give 1240 HP at 12000 ft. We'd be probably looking at 1360-1380 HP at 2800 rpm and +7 psi?

The Mk.XVI (difference vs. Mk.VI was a single-lever carb control, made possible due to the automated weakening of the mixture for cruise settings) on 2800 rpm and +7 psi made 1600 HP at 5000 ft, and ~1375 HP at 13000-13500 ft, so my math is not that bad for the Mk.VI on reduced settings.
(better power values were with 2900 rpm and +8.25 psi boost, obviously)

Again, note that data sheet gives very optimistic rated altitudes' values for the Hercules VI (they do the same with rated altitudes for the Merlin XX, BTW).

FWIW, BMW 801C did 1361 HP at 15090 ft (2550 rpm), plus better exhaust thrust value.

Hercules VI production, 5 in March and 1 in April 1941, the series production from August 1941, with 183 built August to December 1941, first Beaufighter VI production was 5 in November 1941 from Bristol Weston, 9 built by end 1941. As already noted 71 Hercules June to December 1939, and 636 Hercules in 1940. In January 1941 the Hercules X and XI were being made, but the X was ending production. The first XVI in September and the first XVII in October 1942, no exact date for XVIII, probably early/mid 1944, first Hercules 100 in February 1944.

According to Morgan and Shacklady in 1940 the Merlin III with 12 pounds boost using 100 octane at 3,000 RPM at ground level could produce 1,320 BHP for an engine lifetime of 10 hours, 20 with stronger blocks. The engine could be pushed to 2,150 BHP, lifetime 15 minutes at full throttle, with water injection, 25 pounds boost and SR24 fuel.

Geoffrey Sinclair said:

Hercules VI production, 5 in March and 1 in April 1941, the series production from August 1941, with 183 built August to December 1941, first Beaufighter VI production was 5 in November 1941 from Bristol Weston, 9 built by end 1941. As already noted 71 Hercules June to December 1939, and 636 Hercules in 1940. In January 1941 the Hercules X and XI were being made, but the X was ending production. The first XVI in September and the first XVII in October 1942, no exact date for XVIII, probably early/mid 1944, first Hercules 100 in February 1944.

Click to expand...

Thank you for the production figures.
This leaves us with Hercules XI for 1941. Data points of interest include:
- 1500 HP at SL (1600 for take off); 1320 HP at 5000 ft - all for S/C drive in low gear ('MS')
- 1460 HP at 9000 ft, 1360 HP at 12000 ft, 1210 HP at 15000 ft - all for S/C drive in high gear ('FS')

All of these are 5 min limits.
Per the document kindly posted at the 'Engines' sub forum here.

I know that this is about the Bristol 153, but I do find it odd that two of the other contenders for F37/35 ultimately got built. The Hawker design (based on the Hurricane) sort of was reincarnated as the Hurricane Mk IIC, and later Spitfires did eventually carry 4x20mm cannons. The Supermarine 312, from what I've been able to discern, was a modified Spitfire with a ventral radiator and 4x20mm cannons.

Ironically, Bristol became known for mostly making twin engine aircraft (such as the Beaufort and Beaufighter) and as an engine supplier. They would, maybe to make this come full circle, license build some Hawker Tempest Mk IIs very late in World War II and early post-war. Of course, the Tempest II used a Bristol engine (the Centaurus)

Initially all Tempest production was intended to be by Hawker and its sister company in the Hawker Siddeley Group, Gloster. In Sept 1942 Gloster was awarded a contract for 500 Tempest II, confirmed in Feb 1943. But because of delays in development, and the need to continue Typhoon production at Gloster, in Aug 1943 the contract was transferred to Bristol and increased to 600. Later another 30 were added to the contract.

Why Bristol? Because by the time that it was expected the Tempest would begin rolling off the production lines, Beaufighter production would be slowing down and they would have surplus capacity in their existing factories. It ensured best use of a trained workforce.

Bristol produced its first Tempest II in Oct 1944. It completed 30 and parts for another 20, which were assembled at Hawker's Langley factory, plus 30 fuselages used in ground tests. The rest of the contract was cancelled at the end of the war.

Some 900 Tempest II had also been ordered from Hawker to be produced at Langley. Eventually those orders were cut back by Feb 1946 to the 402 eventually produced there.