Bristol Hercules: how many HP at altitude?

[tomo pauk]

Could someone please provide good data about the Hercules' power at altitude? The data I have is from the chart found at the AEHS site (cca 1390 Hp at 5100 ft, and 1220 HP at 13000ft, all while using +6 lbs/sq in at unknown RPM); at 20000 ft the chart gives 900 HP.
The entry at WIlliams' site mentions the +8 lbs/sq in at 2900 rpm, the full throttle height with ram effect being 8,500 ft (327,5 mph) and 15,600 (333,5 mph); at climb the boost was restricted to +6.

 

[Shortround6]

Which models (marks) are you interested in?

The better WW II Versions ( Marks under 100) seemed to top around around 1545hp at 15,500ft ( no ram?) but there was some variation between Marks

 

[tomo pauk]

Thanks. I'm interested in any war time marks.

 

[Shortround6]

The figures I gave were for the MK VI and XVI with 100/130 fuel (8.25lbs boost).

MK III on 87 octane was 1250hp at 16,750ft/4lbs ?
MK VI on 87 octane was 1265hp at 15,750ft/5lbs ?
MK X on 87 octane was 1280hp at 16,000ft/4lbs ?

Figures are from Lumsden's charts in the appendix and unfortunately seem to be another instance of faulty proof reading. HP/boost and altitudes do not track well from one version to another ( or same version with different fuel)

 

[tomo pauk]

Thanks for the data. Would you be so kind to look at the Wilkinson's book(s), those seem to be accurate? Even if only the latest models are listed.

 

[wuzak]

From Graham White, Allied Piston Aircraft Engines of WWII

Hercules XI:
1315hp @ 2800rpm @ sea level
1460hp, @2800rpm @9,500ft.

Hercules VI/XVI:
1675hp @ 2900rpm @ 4,500ft
1445 @ 2900rpm @ 12,000ft

Hercules VII/XVII:
1735hp @ 2900rpm @ 500ft - cropped impeller

Hercules VIII: Experimental turbocharged engine

Hercules XVIII: 1735hp @ 2900rpm @ 500ft

 

[wuzak]

Hercules VI: 100/130 grade fuel
Takeoff: 1615hp @ 2900rpm, +8.25psi
Normal: 1400hp @ 2400rpm, +6psi @ 4,750ft (MS)
1,300 @ 2400rpm, +6psi @ 13,500ft (FS)

Maximum: 1750hp @ 2800rpm, +8.25psi @ 6,500ft (MS)
1545hp @ 2800rpm, +8.25psi @ 15,500ft (FS)

Hercules XI: 100/130 grade fuel
Takeoff: 1505hp @ 2900rpm, +6.75psi
Normal: 1325hp @ 2500rpm, +3.5psi @ 2,500ft (MS)
1,200 @ 2500rpm, +3.5psi @ 14,000ft (FS)

Maximum: 1575hp @ 2900rpm, +6.75psi @ 500ft (MS)
1510hp @ 2800rpm, +6.75psi @ 11,250ft (FS)


Hercules XVII: 100/130 grade fuel
Takeoff: 1725hp @ 2900rpm, +8.25psi
Normal: 1395hp @ 2400rpm, +6psi @ 1,500ft (MS)
Maximum: 1735 @ 2900rpm, +8.25psi @ 500ft (FS)


Hercules 100: 100/130 grade fuel
Takeoff: 1675hp @ 2800rpm, +8.25psi
Normal: 1515hp @ 2400rpm, +6psi @ 7,750ft (MS)
1,415 @ 2400rpm, +6psi @ 16,500ft (FS)

Maximum: 1800hp @ 2800rpm, +8.25psi @ 9,000ft (MS)
1625hp @ 2800rpm, +8.25psi @ 19,500ft (FS)

Data from Lumsden.

 

[tomo pauk]

Many thanks, I'll try to assemble a meaningful table, or to draw some graph(s).

The Mk.100 is a post-war version?

 

[wuzak]

Many thanks, I'll try to assemble a meaningful table, or to draw some graph(s).

The Mk.100 is a post-war version?

Late war.

 

[tomo pauk]

Hi, wuzak,
According to Lumsden, The Mk.VI is head and shoulders above the competition at altitude (bar the Mk.100):

(Hercules VI: 100/130 grade fuel
...
1545hp @ 2800rpm, +8.25psi @ 15,500ft (FS)

Any thoughts?

 

[wuzak]

What about the VII/XVII ~ 1700hp @ 500ft?

I don't hink any of them could be classed as high altitude engines.

 

[tomo pauk]

That seem to be in the ball park, the VII/XVII.
I'm not thinking about the Hercules as a dedicated high altitude engines, just were curious about the high altitude capabilities. About those 1545 HP @ 15500 ft for the Mk.VI - a typo maybe?

BTW, people: what were the main modifications that turned the Mk.100 into a viable high altitude engine? Was it a two stage version? Was there any version with inter cooler?

 

[wuzak]

BTW, people: what were the main modifications that turned the Mk.100 into a viable high altitude engine? Was it a two stage version? Was there any version with inter cooler?

No, still a single stage, 2 speed.

 

[Shortround6]

Revised cylinder heads with more fins, a revised crankcase, bigger main bearings in addition to a new supercharger.

 

[fastmongrel]

Revised cylinder heads with more fins, a revised crankcase, bigger main bearings in addition to a new supercharger.

Apparently early Hercules engines had a very poorly designed supercharger inlet and/or outlet design which choked the airflow. When Sir Stanley Hooker joined Bristol after the war he felt that the Bristol engine design team still didnt understand airflow properly.