RR Peregrine on 100 Octane fuel

[Nick Sumner]

Did a search but couldn't find a direct answer and none of my reference books have it. Does anyone have the hp data for the RR Peregrine on 100 Octane fuel? All the data I've seen is for 87 Octane. Thanks!

 

[wells]

880 hp @ 3000 rpm @ +9 psi boost for takeoff. That's all I have, from Lumsden's British Piston Aero Engines

 

[tomo pauk]

Did a search but couldn't find a direct answer and none of my reference books have it. Does anyone have the hp data for the RR Peregrine on 100 Octane fuel? All the data I've seen is for 87 Octane. Thanks!

Not me, but we can extrapolate. This is for 87 oct (max = 885 HP at +6.75 psi @ 15000 ft; chart courtesy of Neil Striling):



Considering what the 'FS' (fully supercharged) Mercury engines gained when run on 100 oct fuel - making almost 1000 HP at ~9200 ft vs. 840 HP at 14000 ft;, +5 psi vs. +9) - methinks that expecting around 1000+ HP at 11000-12000 ft is reasonable. Per manual for the Whrilwind, max boost for Peregrine on 100 oct was +9 psi.
Chart for FS Mercury engines, again courtesy Neil Stirling:

 

[fastmongrel]

The Peregrine could be run at +12psi and iirc 1100hp

 

[tomo pauk]

The Peregrine could be run at +12psi and iirc 1100hp

At +12 psi?

 

[Nick Sumner]

Thanks for the replies all. Found something going through Bingham's book on the Whirlwind. Theres a data sheet on page 36 stating that the total power for an 87 octane Peregrine Whirlwind was 1770 (2 X 885) at 15,000 ft but on 100 octane would be 2030 (2 X 1015) @ 20,000 feet. I guess that's the answer...

 

[Nick Sumner]

...Or perhaps not 885 hp was the takeoff power it seems unlikely that a single speed supercharger would be able to maintain that out put at 15,000 feet so I cant help think its max hp and altitude for best speed not hp @ altitude.

 

[tomo pauk]

Thanks for the replies all. Found something going through Bingham's book on the Whirlwind. Theres a data sheet on page 36 stating that the total power for an 87 octane Peregrine Whirlwind was 1770 (2 X 885) at 15,000 ft but on 100 octane would be 2030 (2 X 1015) @ 20,000 feet. I guess that's the answer...

The 1st figure is right (2 x 885 @ 15000 ft).
The 2nd figure is not - high octane fuel is not a replacement for improvements of a supercharger. The 2 x 1015 @ 10000 ft is much more likely. Please note that all power figures are without ram effect; installation on the Whirly was lousy anyway to take much if any advantage of the ram effect.
Note at the chart for FS Mercury engines how 100 oct fuel improves only the power under the rated altitude, since there the supercharger can provide far more boost than at higher altitudes, while presence of hi-oct fuel prevents the pre-ignition and detonation that will happen if the 'low-oct' fuel is used. More boost = more power.

This chart is also good to clarify the things with regard to benefits and limitations of 100 oct fuel in everyday service use. People at RR (and other companies) were not designing better superchargers for nothing.

...Or perhaps not 885 hp was the takeoff power it seems unlikely that a single speed supercharger would be able to maintain that out put at 15,000 feet so I cant help think its max hp and altitude for best speed not hp @ altitude.

Please, take a look at chart I've posted. On 87 oct fuel, take off power was 765 HP; 885 HP was the power at rated altitude.
The Merlin III on 87 oct fuel was good for 880 HP for take off, and 1030 HP at 16250 ft, a single-speed supercharged engine.

 

[Nick Sumner]

The 1st figure is right (2 x 885 @ 15000 ft).
The 2nd figure is not - high octane fuel is not a replacement for improvements of a supercharger. The 2 x 1015 @ 10000 ft is much more likely. Please note that all power figures are without ram effect; installation on the Whirly was lousy anyway to take much if any advantage of the ram effect.

Certainly fair points Tomo, but in at least two places I've read of RR promising a 15% increase in Peregrine power with 100 Octane fuel which roughly co-responds to the 1015 figure. Its also not out of the ball park with Merlin improvements. Lumsden has the 880 hp figure at +9 lbs boost as being the 100 Octane rating (Lumsden Brit aero engines data tables at the end of the book). He gives a + 6.75 lb boost figure for the 87 Octane Peregrine but, unfortunately, no power figure!

Its possible the 1015 figure is assuming a higher boost on a Mk II engine.

 

[tomo pauk]

Certainly fair points Tomo, but in at least two places I've read of RR promising a 15% increase in Peregrine power with 100 Octane fuel which roughly co-responds to the 1015 figure. Its also not out of the ball park with Merlin improvements. Lumsden has the 880 hp figure at +9 lbs boost as being the 100 Octane rating (Lumsden Brit aero engines data tables at the end of the book). He gives a + 6.75 lb boost figure for the 87 Octane Peregrine but, unfortunately, no power figure!

Its possible the 1015 figure is assuming a higher boost on a Mk II engine.

I have no problem with 1015 HP figure, but at 10000-11000 ft, not at 20000 ft. Peregrine will be certainly doing the 880 HP at +9 psi for take off.
Is there something wrong with primary sources?

 

[Nick Sumner]

Is there something wrong with primary sources?

Certainly not. The figure in Bingham is allegedly from a note from Westland to the Air ministry. It also gives the figure of '20,000 feet' as being the altitude at which the Whirlwind would attain its best speed powered by a 100 Octane fuelled Peregrine. The engine data on page 144 gives the maximum power of the 87 Octane Peregrine I engine as being 885 bhp at + 6.75 lb boost at 15,000 ft. Taken with the figures in Lumsden this implies (but doesn't prove) that the 100 Octane Peregrine delivered 1015 hp at + 9 lb boost at 20,000 feet.

 

[Nick Sumner]

Oh! the data on page 144 also proves your point about take off power Tomo. It gives it as 765 bhp at 6.75 lb boost.

 

[tomo pauk]

Certainly not. The figure in Bingham is allegedly from a note from Westland to the Air ministry. It also gives the figure of '20,000 feet' as being the altitude at which the Whirlwind would attain its best speed powered by a 100 Octane fuelled Peregrine. The engine data on page 144 gives the maximum power of the 87 Octane Peregrine I engine as being 885 bhp at + 6.75 lb boost at 15,000 ft. Taken with the figures in Lumsden this implies (but doesn't prove) that the 100 Octane Peregrine delivered 1015 hp at + 9 lb boost at 20,000 feet.

The +9 psi boost ain't gonna happen above ~12000 ft even on a high speed aircraft (= maximum ram effect) powered by Peregrine. Supercharger was providing +9 psi at perhaps 10-11 thousand feet, lowering to +6.75 psi at 15000 ft, and lowering further down as the altitude increases. At 20000 ft, the supercharger of the Peregrine will be providing perhaps +4 psi boost even with ram effect.

The only way for Peregrine to make +9 psi boost at 20000 ft is that RR/Hooker does the clean-up job of the air intake(s) between carb and impeller like it was done on for the Merlin XX - and that didn't happen historically for Peregrine. As before: hi-oct fuel is no substitution for a better supercharger, whether we talk about Peregrine, Merlin, V-1710, BMW 801 or whatever piston engine.

 

[Nick Sumner]

The only way for Peregrine to make +9 psi boost at 20000 ft is that RR/Hooker does the clean-up job of the air intake(s) between carb and impeller like it was done on for the Merlin XX - and that didn't happen historically for Peregrine. As before: hi-oct fuel is no substitution for a better supercharger, whether we talk about Peregrine, Merlin, V-1710, BMW 801 or whatever piston engine.

Absolutely, so I can only assume that Rolls Royce planned to do exactly what they did with the Merlin XX with a developed Peregrine, had the decision to curtail Whirlwind production not happened. Obviously, the plan wasn't put into effect.

 

[tomo pauk]

Absolutely, so I can only assume that Rolls Royce planned to do exactly what they did with the Merlin XX with a developed Peregrine, had the decision to curtail Whirlwind production not happened. Obviously, the plan wasn't put into effect.

For better or worse, the decision to curtail the Whirlwind production was a direct result of cancellation of Peregrine development & production. The Air Ministry agreed with Rolls Royce that Merlin will offer far more while costing far less, not just since Merlin was in volume production by several sources in the UK (while the deal was in process for US production, 1st with Ford there, then with Packard). That was also a reason Westland made a sales pitch with a 'gown up' version of Whirlwind powered by Merlins (not to be confused with the Welkin).

On a slightly related note - in the book 'The Merlin in perspective' by A.H. Bailey, 4th edition from 1995, there is not a single word mentioning (Sir) Stanley Hooker. Grudge can go a long way?

 

[Deleted member 68059]

Sorry it took so long. Thats the trouble with not making things up, takes longer !

I would take careful note of the word "proposed". It appears to me from this, that because the Vulture and Peregrine share the same bore
and stroke, they have extrapolated the results from a single slice "4 cylinder X" of the Vulture onto the Peregrine V12 configuration
to obtain that.

So I do not think this is from an actual test of a Peregrine on 100 Octane.

 

[wuzak]

Do you have a date for that document Calum?

That is, was it early in the Vulture's development before all the problems came to light?

I have always wondered why the Peregrine was rated at 3,000rpm, while the Vulture, with the same bore and stroke, was rated at 3,200rpm (and 3,250rpm in that document). I'm guessing that's why the projected Peregrine power was not half of the Vulture's.

 

[Deleted member 68059]

Do you have a date for that document Calum?

That is, was it early in the Vulture's development before all the problems came to light?

I have always wondered why the Peregrine was rated at 3,000rpm, while the Vulture, with the same bore and stroke, was rated at 3,200rpm (and 3,250rpm in that document). I'm guessing that's why the projected Peregrine power was not half of the Vulture's.

have to check, but its pre-war

 

[wuzak]

Makes sense. Before all the derating occurred!

2,200hp is the most I have seen for the Vulture.

Was the 50h test just an intermediate test, to allow the engine to be used in flight testing?

 

[Daggerr]

Thanks for the replies all. Found something going through Bingham's book on the Whirlwind. Theres a data sheet on page 36 stating that the total power for an 87 octane Peregrine Whirlwind was 1770 (2 X 885) at 15,000 ft but on 100 octane would be 2030 (2 X 1015) @ 20,000 feet. I guess that's the answer...

Note that Bingham page 36 shows a table, not really a datasheet.
Unfortunately it does not mention boost, and moreover the second column with 100 octane data is for the Whirlwind Mk 2 which was only a plan.

Bingham page 38 states: "In presenting the performance data for the Mk 2 Whirlwind, Petter was more than a little premature, and certainly a little optimistic, about a Peregrene development using 100 octane fuel. .................................................................... In fact, on 5 May the DEP (G.P. Bulman) stated that the estimated engine output at 20,000 ft compared with the present approved rating at 15,000 ft was a tentative one only, and had not been endorsed by Mr Elliott (Chief Designer at Rolls-Royce)."

Bingham page 37 states: "Development work on the Peregrene engine was continuing in parallel with that on the Merlin, clearing it for 12 lb boost and a rated altitude of 20,000 feet, but it was not at that time envisaged for the Whirlwind."

Note also the table on Bingham page 32, which shows performance data of the Whirlwind F1 based on A&AEE Boscombe Down Test Reports.
It shows 1,530 bhp total power at take-off, or 765 bhp per engine, and a max speed of 354 mph at 15,800 ft.

Niall Corduroy, in his Whirlwind book, quotes the same test data and mentions that the tests were done using the second prototype L6845 in april 1940. The max speed of 354 mph was less than the 370 - 390 mph expected by both the Air Ministry and Petter, according to Corduroy.
Corduroy also mentions that "the Peregrine was rated at a maximum of 6.75 psi boost on 87 octane leaded fuel to give a take-off power of 765 hp at 3,000 rpm. After testing at higher boost pressures during the summer of 1940, Rolls-Royce rerated the engine for short term use at 9 psi boost with 100 octane fuel. Small modifications were made to the priming system, boost control and other ancillaries during the Peregrines life, but otherwise the engines in use at the end of the Whirlwind's career were identical to those with which it entered service over three years earlier."

Note also that running an engine, that can mechanically deliver only +9 lb boost at rated altitude, on 100 octane instead of 87 octane will not result in more power at that or higher altitude. More power requires a higher manifold pressure (more boost), but if the engine is mechanically not capable of delivering that then the power won't increase no matter how high the fuel octane number.
To take advantage of the higher fuel octane number would require modifying the supercharger to deliver +12 i/o +9 lb boost (for example by increasing its impeller diameter, and/or its speed, and/or ......) but that never happened.