Westland Welkin: Basis for a Whirlwind II? (2 Viewers)

[tomo pauk]

The standard Peregrin I using 130 grade fuel:
980 BHP with 3000 rpm at +9 lbs boost at 13,500 ft

Would you be so kind to post the source for these figures? Would it really be 130 grade fuel they used in, I assume, 1940?

In 1941 at least one improved 1-stage/2-speed Peregrin was looked at on paper, and a standard 1-stage/1-speed Peregrin was modified and tested with different S/C gear ratios (the ratios were unspecified in the memo) to simulate the effects of different high and low gears. On the test stand (with 130 grade fuel) the test data indicated the 1-stage/2-speed Peregrin would have an output of:
930 BHP with 3000 rpm at +9 lbs boost at 15,500 ft in high gear
1010 BHP with 3000 rpm at +9 lbs boost at 6,500 ft in low gear
1000 BHP at 3000 rpm at +12 lbs boost for TO

These figures look very believable, for a Peregrine with a better S/C.
From where is that data from?

 

[Dave Smith]

The modification to the Merlin III engines was pretty much change the adjustment settings for the boost limiter on the engine.
Boost limiter closes the the throttle as the boost reaches 12lbs instead of 6lbs. There may have been periods of time as they sorted out which spark plugs may or may not have been compatible with the higher boost (or differences in lead content.)

Now you say you are experienced with highly tuned motorcycle engines.
If they are not supercharged their detonation may be different than the supercharged airplane engines. On turbocharged engines it may be exactly the same.
One the aircraft engines running at 15lbs of boost (making it simple) you already have a 2 to 1 compression ratio before the piston starts up (valve timing ignored) You also have around 250 degree F boost in intake air temperature that the supercharger caused. Now as the piston rises the engine is dealing with an actual compression ratio of near 12 to 1 (there is a difference in in theoretical compression and actual compression on supercharged engines) and the heat of compression adds to the temperature of the fuel/air mix. In the highly tuned motorcycle engine with a 12 to 1 compression ratio you may very well hit detonation. But your fuel/air mix started around 250 degrees lower.


Confusing the time lines doesn't help anything.
The most unreliable Merlins were the Mk Is of 1937 and the Merlin IIs got better and the Merlin IIIs got even better.
By 1940 the Merlins were pretty reliable engines, unlike the Hercules, the Vulture and the Sabre. Time also changed the reliability of those engines.
In 14 years on this forum nobody has been able to tell me what the problems with the Peregrine engine were. There were problems with exactor engine controls but that it not a problem with the basic engine. There were problems with cooling, a lot of that went away by changing the way the plane was operated, like don't taxi for long periods of time with the flaps up. The flaps helped control the air flow exiting the radiators. Blaming the engines for taxing around with the radiator airflow partially blocked sounds like pointing fingers without solving the problem. Changing the radiators might not have solved the problem of needing to taxi with the flaps partially lowered for good airflow. A too clever airframe decision compounded by inadequate training.
The Peregrine itself (with the aid of hindsight) was probably more reliable than the Hercules, the Vulture and the Sabre of 1940-41. Not sure when the Hercules got to the reliable area.

Well they ran the mixture very rich in general at max take off boost and so on, hence the two different octane ratings for AVGAS, they were, like many racing two stroke engines in modern times effectively fuel cooling the engines. My point about more effective engine cooling with the Morris radiators allowing increased charge is valid as it would create greater cooling for the engine allowing a higher rate of fuel burning / boost to be used before the detonation limit was reached, although most likely fairly small and not what could have been achieved by an intercooler, which is however never mentioned at all.

 

[Admiral Beez]

Whirlwind was a good design. Just a bit too small. I would scale it up to accept RR Merlin engines and a larger fuel tank rather then tinker with the Welkin.

Agreed. If you've got the Mosquito F Mk.II, you don't need the Welkin. Upsize the Whirlwind to take Merlins, reconfigure the cooling so that the wings hold fuel rather than radiators. Increase the ammunition capacity. But really, by 1942 we need to carefully consider the use of any Merlin that's not going into a Spitfire, Mosquito or Lancaster. The Fulmar and Barracuda can grudgingly have one.

 

[yulzari]

Agreed. If you've got the Mosquito F Mk.II, you don't need the Welkin. Upsize the Whirlwind to take Merlins, reconfigure the cooling so that the wings hold fuel rather than radiators. Increase the ammunition capacity. But really, by 1942 we need to carefully consider the use of any Merlin that's not going into a Spitfire, Mosquito or Lancaster. The Fulmar and Barracuda can grudgingly have one.

Of course if we employed hindsight then Britain would only be making Merlin's and Cheetahs so the production resources that went into the Napier and Bristol motors would be used to make enough Merlin's for all.

The essence of the Whirlwind was to have as little aeroplane as possible chasing two engines so squeezing in Merlin's not to an upsized airframe but to the existing one (as was finally offered IOTL) would make more sense. A 1942 2,600 bhp Whirlwind, 1944 3,200 and 1945 4,000 one.

 

[Admiral Beez]

Of course if we employed hindsight then Britain would only be making Merlin's and Cheetahs so the production resources that went into the Napier and Bristol motors would be used to make enough Merlin's for all.

The essence of the Whirlwind was to have as little aeroplane as possible chasing two engines so squeezing in Merlin's not to an upsized airframe but to the existing one (as was finally offered IOTL) would make more sense. A 1942 2,600 bhp Whirlwind, 1944 3,200 and 1945 4,000 one.

Hindsight is not needed to make an improved Whirlwind as I describe above. But by the time the prototype is flying by late 1941, its Merlins will be in high demand for Spits, Lancs and Mossies. So, I don't see the Whirlwind making it into production.

Unless................... we're not improving the Whirlwind with a larger follow-up, but are instead substituting Petter's original pre-war idea using early Merlins. Now, that will take some foresight and faith in what the Merlin will become.

 

[ThomasP]

Hey tomo pauk,
re

Would it really be 130 grade fuel they used in, I assume, 1940?

The UK Air Ministry began using the single-cylinder CFR test method as standard in 1935orB4. The British Air Ministry subsequently developed a standard single cylinder RMR (Rich Mixture Rating) procedure based on a Pegasus engine 8:1 CR cylinder (which was representative of the 'most severe service engine' in use at the time) in which fuel batches were checked against the various reference fuels. The new CFR test method was designated the British Air Ministry modified Motor Method. The Pegasus type cylinder used by the test engine was later changed to a Hercules cylinder (I have no idea why). Note that the abbreviation B.A.M. stands for British Air Ministry.

The designation B.A.M.100 (or BAM.100) that we often see used to reference pre- and early-war UK '100 octane' was actually the testing procedure designation that was to be used for proofing the fuel material batches, rather than the designation for the actual '100 octane' fuel material. The UK started using the term BAM.100 in January 1937 as a provisional designation for the new '100 octane' fuel.

Approximately 1000 tons of '100 octane' Avgas was trialed at RAF Sqn level beginning in June 1937, with the tests ending in September 1938. These tests gave the Air Ministry important information as to what appeared practical to achieve with the new fuel and what possible fuel blends allowed the desired improvements in engine performance.

The lean and rich mixture 100/130 PNs were set in September 1938 and remained the same for the rest of the war. (I believe Snowygrouch referenced this as well in one of his posts but I could not find it using Snowygrouch, as the search term is no longer usable due to his leaving the forum.) The BAM.100 testing procedure, which defined what method was to be used (in this case the British Air Ministry modified Motor Method for '100 octane') defined the PN (Performance Numbers) that had to be met by the actual fuel material. 72,000 tons of BAM.100 fuel were ordered in November 1938. First delivery of BAM.100 to England was in June 1939 (I think).

As to what fuel they actually used when testing the engines, all war-time engines were required by the Air Ministry DED/DERD to be tested using what they called a 'reference fuel' - ie a fuel that met the minimum standards set out in the test specification. There were different reference fuels for different grades - ie 73, 80, 87, 100, etc. The reference fuel used for testing BAM.100 had to result in PNs that matched or exceeded those of 100% iso-octane plus 4cc TEL per Impgal. So in theory at least, RR and the other UK engine manufacturers used the specified 100/130 PN reference fuels when they rated their engines.

After 1938 the fuel material blends were allowed to change, but they all had to achieve the 100/130 PN using the BAM.100 testing procedure. Before 1940, due to the fact that they had not settled on the specific blends achievable and allowed, there was no formal DED number assigned to the '100 octane' fuel material. (The designator DED.2475 may have been assigned to the '100 octane' fuel material sometime during the war but I am not sure.) In early-1940 responsibility for the fuel material specification was transferred from DED to RDE, and British '100 octane' fuel material meeting the BAM.100 test requirements became RDE/F/100.

When I was researching the pre- and war-time fuels I found it interesting that when the UK was paying cash for the fuel purchases (prior to the US entry into the war and Lend-Lease) the US refineries and government agencies often referred to British orders for '100 octane' by variations of the BAM100 designation - due to the British purchasing agencies requiring the US refineries to use the same testing procedures as the UK refineries (or testing procedures that gave the same results, subject to approval by the UK). There were a fair number of memos passed back and forth between the US government agencies involved and the refineries complaining about the difficulties in meeting the requirement. Part of the problem was the rapid expansion in production and the learning curves, and part of it was due the attempts to use less aromatics and reduce the expense.

Incidentally, when the tankers arrived in England (and overseas) they were met by specialists who tested the fuel. The Air Ministry also ordered various amounts of aromatics and TEL and had them shipped with the fuel material if necessary - the intent being to add aromatics and/or TEL if so needed to bring the fuel material upto standard. One or more of the refineries in England was also tasked with producing the aromatics specifically for this purpose.

 

[Daggerr]

...................
(I believe Snowygrouch referenced this as well in one of his posts but I could not find it using Snowygrouch, as the search term is no longer usable due to his leaving the forum.)...............................

His posts can still be found be searching member name: Deleted member 68059

 

[ThomasP]

Hey Daggerr,

Thank you. I thought I had tried that but it did not work at the time - maybe I spelled something wrong.

It worked when I tried it just now.

 

[spicmart]

His posts can still be found be searching member name: Deleted member 68059

That is really a loss. Why would he leave/be deleted?