Westland Welkin: Basis for a Whirlwind II?

[tomo pauk]

Of course
Air Mistry document AVIA 15-37
It is unclear how much was tested, how much estimated, certainly Morris radiators were ordered, and RR agreed the figures quoted.

Thank you for the tables.

Someone at RR seems to have made a typo when sending out the data on the Peregrine running at 100 oct fuel.
The way the high-octane fuel works is this:
- at lower altitudes, supercharger can supply much more air than the engine can take advantage of, so the engine is throttled, lest the engine will be unsafely over-boosted, and knocking will destroy the engine
- hi oct fuel improves the knocking threshold, so the engine can be safely (if shortly) over-boosted
- extra boost = more power

Note again that the advantages of the hi-oct fuel are mostly confined to the lower altitudes.
The typo I was talking above was that the 1015 (2030/2) HP per engine was realized at 10000-11000 ft, not at 20000-21000 ft, thus leading to the fine people at Westland to came out with the calculated performance figures as they did. As with Merlin and many/most of the other engines, the only way to improve high-altitude performance was to improve the supercharger - that never happened for the Peregrine.

If the 100 oct fuel was of any help well above the rated height for the 87 oct fuel, RAF would've been flying the 400 mph Spitfire Is and 350 mph Hurricane Is during the BoB, that was not the case. You can see here, for the Merlin III, that benefits of the 100 oct fuel (darker shade of blue) are not present above ~16000 ft. Also here is what Mercury engine gained via 100 oct fuel and the accompanying over-boosting (made a tad under 1000 HP at lower altitudes, but no change above ~14500 ft) - kindly provided by Neil Stirling; click on the thumbnail:



Perhaps S Shortround6 , W wuzak or E Engineman will want to correct me on this?

Also note that the expected speed figures for the Whirlwind I on April of 1940 start optimistically at 390 mph at 15000 ft - quite a difference vs. the 360 mph figure that seems to be standard for the series-produced examples

Strangely in view of past debate regarding Rotol or DH propellers, it was considered straightforward to increase the pitch angle of the DH propellers without any major problem. What might have been, but the beauracracy was tremendous!

How many aircraft gained more than 10 mph (or even 5 mph?) due to the increase of the pitch angle of their respective props?

 

[Dave Smith]

The rated altitude will be the altitude at which the supercharger can supply the specified boost pressure at full throttle, and 20,000 ft would seem a reasonable enough altitude and would be classed I think as medium altitude. These documents were reviewed and seen by so many people, including Petter, that I doubt any such howler as getting the rated altitude incorrect would not have been immediately challenged. Given that maximum boost pressure in the case of the Whirlwind was not supercharger limited, but engine heating / detonation threshold / strength related it would seem that the additional detonation protection given by 100 octane fuels would be available up to the rated altitude, where it would be under full throttle conditions, being controlled at lower altitudes by throttling as you say, but at a higher engine output than with the lower boost. Interestingly the Morris radiators had both lower drag (7% from memory), and a higher cooling capacity so may well have allowed higher boost and faster speeds.

 

[tomo pauk]

The rated altitude will be the altitude at which the supercharger can supply the specified boost pressure at full throttle, and 20,000 ft would seem a reasonable enough altitude and would be classed I think as medium altitude.

Since classification of altitudes involves time frame, abilities of different engines and sometimes a subjective look on the matter, I'll not comment on the notion that 20000 ft should be regarded as medium altitude in 1940.

Rated altitude for the Peregrine on 87 oct fuel and the boost of +6.75 psi, 3000 rpm was 15000 ft:



The lower you go, supercharger will be providing an ever greater boost, that can be used if fuel is of high octane (otherwise the engine will die a fast death). The higher you go, the S/C will be providing an ever lower boost, unless the S/C is improved (preferably much improved).

These documents were reviewed and seen by so many people, including Petter, that I doubt any such howler as getting the rated altitude incorrect would not have been immediately challenged

Hey, RR is telling us something - they are engine company after all - and we like what they are telling us, especially in the light of the possible cancellation of both aircraft and it's engines, so there is no cost for us to suggest the over-performing aircraft.

Given that maximum boost pressure in the case of the Whirlwind was not supercharger limited, but engine heating / detonation threshold / strength related it would seem that the additional detonation protection given by 100 octane fuels would be available up to the rated altitude, where it would be under full throttle conditions, being controlled at lower altitudes by throttling as you say, but at a higher engine output than with the lower boost.

'Up to the rated altitude' is the key.
Or, in other words, not above the rated altitude.

FWIW, see how the Merlin III was 'behaving' with greater boost levels, that were available at lower altitudes:

 

[Dave Smith]

Well the maximum boost level would have been available at all levels below the rated altitude being controlled by the Automatic Boost Control. The engine conditions will be the same all the way up to rated altitude, and so the rated horse power will remain constant, it will not be higher at lower altitude if the boost pressure is controlled. Of course below rated altitude the supercharger could left to itself deliver a much higher boost pressure but would likely destroy the engine.

 

[Shortround6]

Given that maximum boost pressure in the case of the Whirlwind was not supercharger limited, but engine heating / detonation threshold / strength related it would seem that the additional detonation protection given by 100 octane fuels would be available up to the rated altitude,

maximum boost pressure is limited by several things. Depending on what the parameters are. It you set a given boost limit, like 6.75lbs then the altitude limit is at what altitude the engine will still give 6.75lbs of boost. (21.45lb absolute). It seems that the Peregrine supercharger would give about a 2.58 pressure ratio (output pressure vs inlet pressure).
Doesn't matter what kind of fuel you use. The engine/supercharger combo will only flow so much air.
Most engines were rated at the desired pressure with the throttle wide open (max air flow for the desired pressure). Also called Full Throttle Hight (FTH). Above that height (not counting RAM) the intake is not taking in enough air. Below that altitude the there are a few minor things going on. More air means a bit more drag/friction loss and generating higher pressures does involve a bit more power (and power loss, both of which mean more heat in the intake charge).
But the basics is why the Merlin (Or other engines) could make power at lower attitudes. Making and surviving more power are two different things.
Now somehow we are to believe a 21.2 liter engine made about the same power as a 27liter engine did and made it about 4000ft higher? You need a better supercharger than the Merlin 45 or Merlin XX did to do that given the difference in the size of the engines. Perhaps a scaled down supercharger from a Merlin 46?
That is the problem with vague proposals. We don't know they they were thinking. But just pouring 100 octane into the fuel tanks was not going to give the performance claimed.

Interestingly the Morris radiators had both lower drag (7% from memory), and a higher cooling capacity so may well have allowed higher boost and faster speeds.

Unless you rig a Morris radiator intercooler changing the radiators does little or nothing for allowing higher boost. Two different problems. Making and surviving more power are two different things. More radiator capacity may help you survive making higher power (burning more fuel per minute) but it doesn't do much for controlling detonation. Detonation can wreck the engine in seconds or fractions of a second.
Higher octane prevents the onset of detonation.
Higher octane fuel does NOT contain any more BTUs per pound than 87 octane or other low grade gasolines (mostly, exact BTUs per pound is given in each nations specifications).

We simply don't know enough about the proposed upgraded Peregrine engine/s.

Now on the subject on propellers. I have been very critical of British propellers, however the British did manage to build propellers that gave high speed. Even the fixed pitch props gave very good speed, the problem were in taking off and climbing. A bit like having a car with one gear. You can set it up for the same top speed as a 4 speed car, assuming you can get it rolling in the first place (slip the clutch a lot).
There is an article that is critical of the Whirlwind props for high altitude work. But the chances of changing props and picking up 20-30mph using the existing engines seems way to good to be true.

 

[tomo pauk]

Well the maximum boost level would have been available at all levels below the rated altitude being controlled by the Automatic Boost Control.

(my bold)
Not the case.
Maximum boost (of +9 psi for the Peregrine using 100 oct) would've been available between the S/L and some 10000-11000 ft, with the throttle being opened ever wider between the S/L and that altitude. After that, the boost would've petered out to 6.75 at 15000 ft, and would've been further ever lower as altitude is increased.

The engine conditions will be the same all the way up to rated altitude, and so the rated horse power will remain constant, it will not be higher at lower altitude if the boost pressure is controlled.

Engine rpm and boost would've been the same up to 10-11 kft, while the throttle would've been opened fully above that altitude (to keep the boost under check at +9 psi), and partially closed under that altitude. Power would've been increasing from SL to that altitude (mostly due to the throttle being ever more opened, so the throttle losses are lower), and then decreasing with altitude. Please see the power charts for the Mercury that I've posted, as well as the data and charts for the 1-speed Merlins and the 1-stage V-1710s to complete the picture of how this worked.

 

[Dave Smith]

Well Shortround smaller engines are not the limiting factor on power levels. I should point out that the 27 l Merlin did not have any problem making similar power to the 35 l DB engine. The power at maximum available boost would have declined above rated altitude clearly .the supercharger is capable of supplying excess air below the rated altitude so there is no problem with maintaining the increased power at lower altitude, the increased octane rating allowing more air and hence more fuel to be burned before the detonation or strength limit of the engine is reached. The amount of air being controlled by the automatic boost control. The figures quoted are those from RR and can therefore be taken as a safe limit for the suggested boost and duration used. these quoted figures are of course with the standard air flow radiators, the Morris items greater cooling capacity would have allowed the engines to run cooler for any given and hence allow extra fuel/air to be burned before the engine temperature rose to the level where the detonation limit was reached. They had a 7% lower drag resistance as tested which would have improved speed to some small extent. I believe the article you refer to regarding the propellers is not factual and not based on any evidence, so of course has been accepted as fact. The statement in AVIA 15-317 suggests that increasing the pitch angle of the DH propellers to the same extent as for the ROTOL items would have similar effects, The pitch range of the DH propellers is quoted as 20 deg whilst the Rotol items are quoted at a pitch range of 34 deg which might be of more of a reason for the difference in performance . The prototype unit with the Rotol propellers was indeed faster, I suggest the increased pitch range is the reason.

The numbers quoted are from Rolls Royce/. Air Ministry / Westland so should be regarded as accurate as under estimating would have been challenged by Petter, and over estimating by the Air Ministry!

Tomo I think you are agreeing with me!

 

[tomo pauk]

Tomo I think you are agreeing with me!

Dunno, I've voiced a lot of disagreement during the last 48 hours

The figures quoted are those from RR and can therefore be taken as a safe limit for the suggested boost and duration used.

This is what I've disagreed with the most - Peregrine will not be making 1000+ HP at 20-21 kft ft just because it runs on 100 oct fuel, just like Merlin III (not even the Merlin XII, XX or 45) was not making 1300 HP at 20-21 kft just because 100 oct fuel is used.

 

[Dave Smith]

Its not just the 100 octane fuel, its he increased boost this allows, so more air, plus more fuel, makes more power, These are the Rolls Royce engineers figures, not plucked from the ether. I presume you had to be competent to be an engineer at Rolls Royce lol!

 

[tomo pauk]

Its not just the 100 octane fuel, its he increased boost this allows, so more air, plus more fuel, makes more power,

It does, on altitudes lower than 15000 ft (for Peregrine).

These are the Rolls Royce engineers figures, not plucked from the ether. I presume you had to be competent to be an engineer at Rolls Royce lol!

RR is not above common sense - many times a typo or two messed with documents made by different companies and institutions.
If you believe that Peregrine as-is will beat a heap of FS Merlin versions at 20000 ft just because hi oct fuel is used, there is nothing I can do about that.

 

[ThomasP]

re

The rated altitude will be the altitude at which the supercharger can supply the specified boost pressure at full throttle, and 20,000 ft would seem a reasonable enough altitude and would be classed I think as medium altitude. . .

and

. . . smaller engines are not the limiting factor on power levels. . .

If everything else is approximately equal, then a smaller engine will put out less power than a larger engine. There is no way that a Peregrine (even with 130 grade fuel and an improved 1-stage/1-speed supercharger such as fitted to the 45 series or a 1-stage/2-speed supercharger such as fitted to the Merlin XX) would allow the same BHP at 21,000 ft as the Merlin XX series.

And just so it is understood, 1010 BHP is the mid-war output for the Merlin XX series at 21,000 ft.

A Whirlwind Mk II with Merlin XXs could probably do about 422 mph at 25,000 ft (with RAM). The 4400 ft/min ROC at SL would also be possible with Merlin XXs.

 

[Dave Smith]

Supercharged or turbocharged engine power output is basically, ignoring charge heating and so forth, directly linked to the amount of air forced through the engine by the compressor, power is basically directly proportional to the amount of fuel burned which drives the amount of air required for combustion,, which explains the 1000hp plus performance of 1.5 l Formula 1 engines. The quoted Whirlwind figures are not something I have made up, but official air ministry ones in a formal document with input from Rolls Royce and Westland, and noted in an official air ministry document as referenced. Petter thought they should use higher boost it seems so I presume the capability was there. The document was marked secret, but probably not with the intention of avoiding controversy on forums. As far as I am aware it does not quote specific supercharger performance levels, but was clearly within the expectations of the Rolls Royce Engineers

 

[wuzak]

Supercharged or turbocharged engine power output is basically, ignoring charge heating and so forth, directly linked to the amount of air forced through the engine by the compressor,

Which is the point that Tomo and Shotround6 have trying to put to you.

The supercharger is the limiting factor if the engine is strong enough to withstand the extra boost.

The Peregrine supercharger could deliver +6.25psi boost @ 15,000ft with the throttle wide open and the engine at 3,000rpm.

That won't change unless something else changes - engine rpm, supercharger gear ratio, supercharger design and/or size.

power is basically directly proportional to the amount of fuel burned which drives the amount of air required for combustion,, which explains the 1000hp plus performance of 1.5 l Formula 1 engines.

It is the amount of air that can be put through th eengine that determines how much fuel the engine can use and therefore its power.

Turbo F1 engines of 1981/1982 were about 600hp.
Those of 1985/1986 were about 800-1,000hp in race trim.

But I doubt that the turbos used in 1981/1982 could have delivered the air necessary to produce 1,000hp. If they could, they would be right at the edge of their capability.

The quoted Whirlwind figures are not something I have made up, but official air ministry ones in a formal document with input from Rolls Royce and Westland, and noted in an official air ministry document as referenced. Petter thought they should use higher boost it seems so I presume the capability was there. The document was marked secret, but probably not with the intention of avoiding controversy on forums. As far as I am aware it does not quote specific supercharger performance levels, but was clearly within the expectations of the Rolls Royce Engineers

The Peregrine was no doubt capable of handling a small increase in boost.

But the supercharger could not provide that extra boost at higher altitude without being changed in some way.

Edit: Added bolded part.

 

[ThomasP]

Sorry Dave Smith,

But Physics (as a science) and the engine Mechanics of the time would not allow what you are saying the documents portray.

There is either something significant (like the use of Merlin XXs) not being said in the document, or it is not going to happen.

To get 1010 BHP at 21,000 ft the Peregrine would have to be running at a minimum of ~3250 rpm, and the supercharger would have to be a 2-speed and similar in efficiency to the Merlin XX in order to deliver enough charge to generate the 1010 HP (no RAM) at 21,000 ft. The resulting heat rise in the charge would be too great for any change in radiators to negate (even in combination with 130 grade fuel) while still allowing the reduction in drag needed for the Whirlwind airframe to make 422 mph.

The 'Standard' Whirlwind Mk I performance (380 mph) as listed in the 1st column of the May'40 page you posted could reasonably be considered achievable with a change in the propeller (assuming that was the main problem) and mods to reduce drag - although it should be noted that the best achieved by the real 'Standard' Mk I during tests was only about 360 mph on 87 octane - so whatever the document is using as the 'Standard' Mk I is not the 'Standard' Mk I that actually existed, and or the Peregrine I they are using is not the Peregrine I (885 BHP at 15,000 ft) that actually existed as fitted to the real 'Standard' Whirlwind Mk I.

The 'Standard' Mk I airframe ROC of 4160 ft/min at SL would also not be achievable using 87 octane - you would need a minimum of +12 lbs boost with the real Peregrine I to generate enough power to climb like that. Again the 'Standard' in the document is not the 'Standard' Mk I of reality.

Trying to use modern day or even post-war Formula 1 engine design & performance to provide reason to think that the 1940 RR team could achieve the results listed in the 2nd column of the document is not a valid argument.

Whoops! I see that wuzak posted some of the same stuff I just did.

 

[Greyman]

The idea was that a further development of the Peregrine would be used.

A letter from Petter to the Air Ministry, 15 Feb 1940:
Development work of the Peregrine engine on parallel lines to that now in hand of the Merlin, i.e. clearing it for 12 lb. boost and a rated altitude of 20,000 ft. It is understood from Messers. Rolls-Royce that a good deal of the ground work has already been carried out and that no serious difficulties are anticipated.

The Air Ministry thought the +40 mph increase was optimistic, and estimated +25 mph at 20,000 ft and +15 mph below that.

 

[wuzak]

The idea was that a further development of the Peregrine would be used.

In that case it would be possible.

But such an engine did not exist other than on paper.

 

[ThomasP]

If they planned on using a Merlin XX type 1-stage/2-speed supercharger the high gear would have to put ~25% more charge per minute to achieve 1010 BHP at 3000 rpm (no RAM) with the Peregrine II. That would require +12 lbs boost for the Peregrine. The Merlin XX only manages +6.5 lbs at 21,000 ft with a Ø10.25" impeller at 3000 rpm engine speed and a S/C gear ratio of 9.49:1 - but as I mentioned in my previous post increasing the engine and/or impeller rpm and/or impeller Ø to any significant degree would raise the charge temperature past the detonation limit.

Maybe if they were planning on a Merlin 60 pattern 2-stage/2-speed supercharger with an inter-cooler?

 

[tomo pauk]

The 'Standard' Mk I airframe ROC of 4160 ft/min at SL would also not be achievable using 87 octane - you would need a minimum of +12 lbs boost with the real Peregrin I to generate enough power to climb like that. Again the 'Standard' in the document is not the 'Standard' Mk I of reality.
Trying to use modern day or even post-war Formula 1 engine design & performance to provide reason to think that the 1940 RR team could achieve the results listed in the 2nd column of the document is not a valid argument.

Agreed 200%.

The idea was that a further development of the Peregrine would be used.

A letter from Petter to the Air Ministry, 15 Feb 1940:
Development work of the Peregrine engine on parallel lines to that now in hand of the Merlin, i.e. clearing it for 12 lb. boost and a rated altitude of 20,000 ft. It is understood from Messers. Rolls-Royce that a good deal of the ground work has already been carried out and that no serious difficulties are anticipated.

The Air Ministry thought the +40 mph increase was optimistic, and estimated +25 mph at 20,000 ft and +15 mph below that.

The further developed Peregrine would've been indeed an interesting thing, but it never materialized. So it is a whole new ball game vs. the 'Peregrine on 100 oct'.
Granted, not that I'm saying anything new there.

The wording of clearing it for 12 lb. boost and a rated altitude of 20,000 ft should read IMO "max boost of +12 lb boost; full stop; rated altitude of 20000 ft" - ie. we'd be satisfied if +8 psi boost is obtained at 20000 ft (= equivalent boost as the best 1-stage Merlins) due to a much improved of the supercharger for the new Peregrine version.

 

[tomo pauk]

D Dave Smith raised the question of believing the official docs in a strict fashion.
We've had a discussion about this official document before, for example. The Mustang (Mk.I) is noted to be powered by Allison V-1710 F32 engine - not the case, since the engine on the MkI was F3R; the F32 (actually the F32R) was a 2-stage 3200 rpm engine with intercooler from 1945, for the XP-51J 'lightweight' Mustang.
Doc also states the power delivered at 19000 ft as being 1150 HP - again not true, engine on the MkI was making that kind of power at ~12000 ft; by 19000, it was much less, even with ram effect calculated in.

My point - reader's discretion is as advised as ever.

 

[Dave Smith]

Well the document is the official document that stated all involved parties positions at the time. Given the number of people involved with it in terms of submitting information and its circulation it does not appear to have been challenged except by Petter who thought the listed performances could be improved upon. Of course being a smaller capacity engine the Peregrine would need less airflow from the supercharger than a Merlin to reach any particular boost pressure but the flow required would be all things being equal be similar for any specific power level in terms of airflow and fuel burned,. As I have noted it does not mention any specific details about the supercharger per se, but clearly does not register any show stopping problem about achieving the extra boost pressure, or indeed a desired even higher boost pressure as Petter wanted. If similar levels could be achieved in a single speed, single stage Merlin Merlin 11 from 1030 to 1310 with the introduction of 100 octane fuel and increasing boost pressure (( From Wiki From late 1939, 100-octane fuel became available from the U.S., West Indies, Persia, and, in smaller quantities, domestically,[54] consequently, "... in the first half of 1940 the RAF transferred all Hurricane and Spitfire squadrons to 100 octane fuel."[55] Small modifications were made to Merlin II and III series engines, allowing an increased (emergency) boost pressure of +12 pounds per square inch (183 kPa; 1.85 atm). At this power setting these engines were able to produce 1,310 hp (980 kW) at 9,000 ft (2,700 m) while running at 3,000 revolutions per minute))" , they would likely be achievable in a Peregrine also which used a similar single stage single speed supercharger I believe. I have seen no reference to employing a twin speed supercharger drive but it would likely be entirely possible. The document also mentions the four cannon nose with increased ammunition capacity, which was built but not adopted, the extra weight of this would presumably needed extra power to maintain performance, let alone the increased performance postulated in the document ((see replica in the Kent BOB museum, which would have also carried the small 27 gallon extra fuel tank that contributed to the extra range postulated)) Clearly neither Rolls Royce or Westland had any major concerns regarding the increased performance they had postulated. The decision to discontinue the build of Peregrine engines and the Whirlwind itself does not appear to have been taken on technical grounds but on logistical ones and brought this line of development to an end. Increasing the Peregrines power to the suggested level was I would suggest no more difficult than what was achieved in the Merlin by means of use of 100 octane fuel and increased boost pressures and was of a similar percentage increase. I make no analysis of the figures presented as exactly how the increased boost pressure was to be achieved is not discussed, but was quite clearly thought achievable by Rolls Royce. What is indisputable is that this was an officially issued Air Ministry Document and was sensitive enough to be classified as secret and would have been agreed by all major contributors including Rolls Royce, and is not an after the event postulation.