Westland Welkin: Basis for a Whirlwind II?

[Bretoal2]

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.

Two points :

- As shown below, increasing the maximum boost on Merlin III gave better performance ONLY at low altitudes - see this graph: max speed at 18,500 feet is the same at 6.25 - 12 - 16 psi boost. Why ? Simply because these three numbers are just three different limiter setting, in all cases the supercharger is the same and gives its maximum at 18,500 feet.
Achieving 1010 hp at 21,000 feet with a displacement of 21 liters would have required a two-stage supercharger which was not available (for the Merlin) until the end of 1941. At that time, development of the Peregrine was abandoned.

- Do not forget either that the main problem of the Whirlwind was its small size which made it unable to receive large diameter propellers, essential to really absorb greater power. Correcting this drawback would have required redesigning the entire wing and engine installation, i.e. 80% of the plane.

 

[ThomasP]

re
"- Do not forget either that the main problem of the Whirlwind was its small size which made it unable to receive large diameter propellers, essential to really absorb greater power. Correcting this drawback would have required redesigning the entire wing and engine installation, i.e. 80% of the plane."

Or they could fit 4-blade props.

 

[Bretoal2]

re
"- Do not forget either that the main problem of the Whirlwind was its small size which made it unable to receive large diameter propellers, essential to really absorb greater power. Correcting this drawback would have required redesigning the entire wing and engine installation, i.e. 80% of the plane."

Or they could fit 4-blade props.

Yes, but losing some efficiency - or waisting some extra power.

The best propeller is always the largest.

 

[ThomasP]

True, but just like the Spitfires when they went from 2-blade to 3-bade to 4-blade props - or when the Corsair went from 3-blade to 4-blade props - it worked just fine for absorbing the additional HP. Each additional blade was slightly less efficient, but the overall total effect of the additional blades allowed increases in performance. Of course, it also helped that they were learning how to design more efficient blades.

 

[Geoffrey Sinclair]

Performance Tables of British Service Aircraft, Air Publication 1746, dated August 1939 but data includes 1940/41 aircraft

Maker	Westland
Name	Whirlwind
Type		1 Seat Ftr
Engine	Number	2​
Engine	Make	Peregrine
Engine	Cooling	Liquid
Power	Horse Power	885​
Power	At Height (feet)	15,000​
Size	Span (feet, inches)	45'
Size	Length (feet, inches)	32'
Size	Height (feet, inches)	9' 6"
Size	Wing Area (square feet)	231​
Men	Crew	1​
Armament	Forward Fuselage	4x20mm
Armament	Rounds Per Cannon	60​
Weight	Tare (pounds)	8,040​
Normal	Weight (pounds)	9,980​
Normal	Take Off (Over 50 ft) (Yards)	630​
Normal	Landing (Over 50 ft) (Yards)	750​
Normal	Climb to Height (feet)	15,000​
Normal	Climb to Height Time (Mins)	5.6​
Normal	Service Ceiling (Feet)	30,500​
Normal	Maximum Speed (m.p.h)	356​
Normal	Max Speed Height (Feet)	15,000​
Normal	Endurance (Max Power, hrs)	0.59​
Normal	Cruising Speed (m.p.h)	306​
Normal	Cruise Speed Height	15,000​
Normal	15 Minutes allowance Range (miles)	340​
Normal	15 Minutes allowance Endurance Hours	1.11​
Normal	Fuel (for range, pounds)	645​
Normal	Fuel (for allowance, pounds)	240​
Normal	Fuel (Total, pounds)	885​
Normal	Fuel (Total, Gallons)	118​
Normal	Miles per 100 pounds fuel	52.7​
Extended	Maximum Fuel Capacity (Gallons)	136​
Extended	Overload Weight (pounds) (Max Fuel)	10,115​
Extended	Take Off (Over 50 ft) (Yards)	580​
Extended	Speed (m.p.h)	306​
Extended	Height (feet)	15,000​
Extended	Range (15 mins allowance) (miles)	410​
Extended	Endurance (15 mins allowance) Hrs	1.34​
Extended	Fuel (for range, pounds)	780​
Extended	Fuel (for allowance, pounds)	240​
Extended	Fuel (Total, pounds)	1,020​
Extended	Fuel (Total, Gallons)	136​
Extended	Miles per 100 pounds of fuel	52.7​
Extended2	Speed (m.p.h)	190​
Extended2	Height (feet)	15,000​
Extended2	Range (15 mins allowance) (miles)	590​
Extended2	Endurance (15 mins allowance) Hrs	3.1​
Extended2	Fuel (for range, pounds)	780​
Extended2	Fuel (for allowance, pounds)	240​
Extended2	Fuel (Total, pounds)	1,020​
Extended2	Fuel (Total, Gallons)	136​
Extended2	Miles per 100 pounds of fuel	75.7​

 

[Shortround6]

I should point out that the 27 l Merlin did not have any problem making similar power to the 35 l DB engine.

Bad example.
The 35 liter DB engine ran at about 6.1lbs of boost, once they got a few niggling problems solved, like holes appearing in the piston tops. by the time the DB 605 appeared the Merlin was not only cleared for 12lbs of boost but 1942 saw boost cleared to 15lbs and later 18lbs with strengthened supercharger drive. Please note that 15lbs of boost is 2.02 Ata.
Amazing how an extra 42% of intake pressure (which in this case is mass air flow) can equal 30% extra displacement.

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.

You are confusing two different things. A Merlin XX running 12lbs of boost had a temperature rise in the supercharger of 148 degrees C. This was the rise over the temperature of the intake air. The radiators had nothing to do with the temperature of the air in the intake tract, unless there was some sort of intercooler. A Merlin running less pressure would have a lower temperature rise. A Merlin using a lower gear ratio on the supercharger would have less temperature rise but would not have the same pressure available at the same altitudes.
This was why the Merlin VIII engine in the early Fulmars was rated at 1275hp at 9lbs of boost using 87 octane fuel. The low geared supercharger could only hold 9lbs of of boost to a very low altitude. The much slower turning impeller didn't heat the air as much.
The detonation limit in supercharged aircraft engines has very little to do with the detonation limit on non-supercharged cars/motorcycles. In the supercharged engine the intake fuel/air mixture at full throttle is very close to it's ignition temperature. Sometimes the pilot gets a warning in the form of conventional "knocking", which is local (in the cylinder) pre-ignition. Sometimes the entire cylinder flashes at once, instead of a controlled burn taking 30-40 degrees of crankshaft rotation all the burn burns in 0-2 degrees the resulting pressure breaks the piston/s, con rods, etc, In the case of radials it may blow cylinders right off the engine.
This is why the engine makers (and airplane) used intercoolers or water/alcohol injection. To cool the intake charge. Worrying about the engine overheating in 2-5 minutes came after you could get the engine to survive making the high power for even a few seconds.

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.

For some reason the difference in speed between the DH and Rotol props was only a few MPH. There was a difference in performance. Performance covering all aspects, not just speed. The finer pitch end of the Rotol props gave better take-off performance and perhaps better climb. If you are trying to fly at 350mph you need the prop pitch to be correct for 350mph (or very close) otherwise the efficiency goes to pot real quick. All the engine and propeller people had figured that out (matching pitch to flight speed) in WW I with fixed pitch props.
The Speed Spitfire used a fixed pitch prop.

Getting the wrong pitch in 1940 that cost 20-30mph on a fighter was not impossible. what is close to impossible is that they never fixed it.
All two pitch or variable or constant speed props have the blades mounted in collars that allow the blades to changed in pitch. The hub may only allow a certain range of motion, like the already mentioned 20 or 34 degrees but the max or minimum pitch is adjustable on the ground and experiments would be very easy to do. easier than swapping a propeller (or carving a new wooden one). Now with the 20 degree props maybe you have to sacrifice something else but sacrificing 20-30mph of top speed for??????? shorter take off run? better climb at 120-140mph?
And when comparing different propellers we have the fact that they often used different shaped blades. The blades also were twisted as they went from the hub to the tip.
A prop tip has a shallower pitch angle than the mid part of the blade because the tip is moving much faster than the mid span of the blade in relation to the forward motion.
Different propeller companies may have had different ideas as what the change in blade shape could be.
Experimenting with different blade shapes/profiles is a lot harder than experimenting with different pitch angles.

Famous poor propeller is the early P-47. The speed didn't change much. The climb did, do the shape of the blades. More blade area.

 

[tomo pauk]

- As shown below, increasing the maximum boost on Merlin III gave better performance ONLY at low altitudes - see this graph: max speed at 18,500 feet is the same at 6.25 - 12 - 16 psi boost. Why ? Simply because these three numbers are just three different limiter setting, in all cases the supercharger is the same and gives its maximum at 18,500 feet.

Max speed a ~18000 ft was achieved with the +6.25 psi boost. Go ever lower from that altitude, and you can take advantage of the increased boost, provided the fuel of required octane/grade value is in use.
The +16 psi boost was available between SL and ~7000 ft, but not above that altitude.

(all values are with ram, as per chart; non-ram values are some 2000 ft lower)

Achieving 1010 hp at 21,000 feet with a displacement of 21 liters would have required a two-stage supercharger which was not available (for the Merlin) until the end of 1941. At that time, development of the Peregrine was abandoned.

Agreed.

This was why the Merlin VIII engine in the early Fulmars was rated at 1275hp at 9lbs of boost using 87 octane fuel. The low geared supercharger could only hold 9lbs of of boost to a very low altitude. The much slower turning impeller didn't heat the air as much.

+9 psi boost was on 100 oct fuel for the Merlin VIII (max power of 1275 HP).
Max boost on 87 oct fuel was +5.75 psi; for take off, that meant 1080 HP - 200 HP more than the Merlin III, despite a bit lower boost on same fuel and (low) altitude.
Shows how much power the superchargers were sucking up, and how much the throttle losses were a thing.

Getting the wrong pitch in 1940 that cost 20-30mph on a fighter was not impossible. what is close to impossible is that they never fixed it.

Was there a ww2 fighter that suffered 20-30 mph due to a wrong pitch, that we know for sure that was the case?

 

[Shortround6]

Was there a ww2 fighter that suffered 20-30 mph due to a wrong pitch, that we know for sure that was the case?

Actually I know of no such case, there may have been.
However if we believe that the Whirlwind MK 1 actually did 390mph at 15,000ft but production versions only did 358mph we are supposed to believe that the different props were worth 32mph? We do know a bunch of WW II era aircraft missed their projected speeds by nearly 10%. We even know a few that had production versions miss prototype speeds by that much or a bit more (Curtiss P-46). But they never blame the pitch of the propellers.

This is a Boeing P-26 fighter with a ground adjustable prop.

Loosen the bolt/s on the clamps and adjust the pitch to amount you want to try, tighten the bolts and test fly. Pilot has no control in flight.
There was no reason for plane to reach production status with a prop that was hurting the max speed by any measurable amount unless they wanted to trade a bit of speed for take-off performance. Once initial testing was done a customer could order fixed pitch props if they wanted to save money. The ground adjustable props offered more flexibility for operating in weather (temperature) or elevations (5000ft air field).
Both the Americans and British used metal fixed pitch props.

The Americans generally used metal fixed pitch on lower powered engines. It is almost impossible to make a wooden fixed pitch 3 blade prop, at least with technology of the time(glues/adhesives). You can use wooden blades in a metal hub. It is possible to unbend a metal fixed pitched prop (prop strike), you can't fix wooden props that have contacted the ground except for very minor strikes (may involve cutting the prop diameter a bit).

I keep saying that propeller design is close to witch craft. The best speed prop is not even the same diameter as the best climb prop. The best size/diameter prop for 1000ft is not the best best size/diameter prop for 20,000ft and so on. The CS props made some things easier but did not solve all the problems.


Now the far as the "uprated" Peregrine goes. How much was talk and how much was actually done or how much was just figuring that what was being done on the Merlin could probably be done on the Peregrine I don't know. We do know that the Merlin XX was well in hand in early 1940, We know that the Merlin XII for the Spitfire II was entering production and the higher gear ratio allowed for about 2,000ft higher altitude than the Merlin III engine, this is counting RAM using a Spitfire. What I don't know is where the Merlin 45 was at this point, ( I am assuming it was well into the planning stage as it is basically a Merlin XX with one gear left out as far as function goes, production was another story).
The next possibility is where the Merlin 46/47 was in timing. Production didn't start until late in 1941 but where was it in planning? The Merlin 46/47 is a number of months ahead of the two stage engines.
The problem is not just getting the Peregrine performance at 15,000ft up to 20,000ft, it is also adding abut 14.5% in prop shaft power at the higher altitude. General rule of thumb is that you loose about 2-2 1/2 % per 1,000ft of altitude.

Now I can and have, looked at several other aspects of the Whirlwind engine set up that may have been less that optimal (state of the art for the time) that hurt altitude performance.
Like questionable intake configuration and questionable exhaust thrust.

I like the Whirlwind and think it got a raw deal. But the idea of taking plane that was between a Spitfire and Hurricane and converting it to twin Merlins takes a lot belief (Unicorn level) unless a lot of modifications are done.

The letter never says what would be needed, just says it might be possible.

 

[Dave Smith]

Two points :

- As shown below, increasing the maximum boost on Merlin III gave better performance ONLY at low altitudes - see this graph: max speed at 18,500 feet is the same at 6.25 - 12 - 16 psi boost. Why ? Simply because these three numbers are just three different limiter setting, in all cases the supercharger is the same and gives its maximum at 18,500 feet.
Achieving 1010 hp at 21,000 feet with a displacement of 21 liters would have required a two-stage supercharger which was not available (for the Merlin) until the end of 1941. At that time, development of the Peregrine was abandoned.

- Do not forget either that the main problem of the Whirlwind was its small size which made it unable to receive large diameter propellers, essential to really absorb greater power. Correcting this drawback would have required redesigning the entire wing and engine installation, i.e. 80% of the plane.

I presume this is why the increased pitch angle capability (34 deg) of the Rotol propeller on the prototype provided better performance, and one of the suggestions in the document is increasing the pitch angle capability of the DH propeller to a similar level from their standard 20 deg. I presume pitch angle increase can absorb higher power until the blade stalls. Since the beast took off OK on its standard sized props, It should be able to do so OK with more horsepower, and gain improved performance in the air from improved pitch angle capability from the propellers

 

[tomo pauk]

However if we believe that the Whirlwind MK 1 actually did 390mph at 15,000ft but production versions only did 358mph we are supposed to believe that the different props were worth 32mph?

That's the kicker - I don't believe that a Whilrwind Mk1 did 390 mph. Especially with full weapon set-up, aerials, cammo paint etc.
Note that Westland stated 380 mph at 15000 ft the next month (May vs. April).

We do know a bunch of WW II era aircraft missed their projected speeds by nearly 10%. We even know a few that had production versions miss prototype speeds by that much or a bit more (Curtiss P-46). But they never blame the pitch of the propellers.

Bingo.

Now the far as the "uprated" Peregrine goes.

I'm not sure that uprated Peregrine, that mimics the boost levels of the Merlin XX, if not these of Merlin 46/47 at high altitudes due to the much improved S/C, ever flew. Or that it even made a bench run.

Now I can and have, looked at several other aspects of the Whirlwind engine set up that may have been less that optimal (state of the art for the time) that hurt altitude performance.
Like questionable intake configuration and questionable exhaust thrust.

Yes, both of these - low-hanging fruits - seem to be done not as good as they should've been.

For my money, mix a separate ram air intake a-la P-40 + individual exhausts a-la Bf 109D + better carb, and there will be an easy 20 mph speed increase, as well as the better hi-alt abilities.

 

[Dave Smith]

Bad example.
The 35 liter DB engine ran at about 6.1lbs of boost, once they got a few niggling problems solved, like holes appearing in the piston tops. by the time the DB 605 appeared the Merlin was not only cleared for 12lbs of boost but 1942 saw boost cleared to 15lbs and later 18lbs with strengthened supercharger drive. Please note that 15lbs of boost is 2.02 Ata.
Amazing how an extra 42% of intake pressure (which in this case is mass air flow) can equal 30% extra displacement.

You are confusing two different things. A Merlin XX running 12lbs of boost had a temperature rise in the supercharger of 148 degrees C. This was the rise over the temperature of the intake air. The radiators had nothing to do with the temperature of the air in the intake tract, unless there was some sort of intercooler. A Merlin running less pressure would have a lower temperature rise. A Merlin using a lower gear ratio on the supercharger would have less temperature rise but would not have the same pressure available at the same altitudes.
This was why the Merlin VIII engine in the early Fulmars was rated at 1275hp at 9lbs of boost using 87 octane fuel. The low geared supercharger could only hold 9lbs of of boost to a very low altitude. The much slower turning impeller didn't heat the air as much.
The detonation limit in supercharged aircraft engines has very little to do with the detonation limit on non-supercharged cars/motorcycles. In the supercharged engine the intake fuel/air mixture at full throttle is very close to it's ignition temperature. Sometimes the pilot gets a warning in the form of conventional "knocking", which is local (in the cylinder) pre-ignition. Sometimes the entire cylinder flashes at once, instead of a controlled burn taking 30-40 degrees of crankshaft rotation all the burn burns in 0-2 degrees the resulting pressure breaks the piston/s, con rods, etc, In the case of radials it may blow cylinders right off the engine.
This is why the engine makers (and airplane) used intercoolers or water/alcohol injection. To cool the intake charge. Worrying about the engine overheating in 2-5 minutes came after you could get the engine to survive making the high power for even a few seconds.


For some reason the difference in speed between the DH and Rotol props was only a few MPH. There was a difference in performance. Performance covering all aspects, not just speed. The finer pitch end of the Rotol props gave better take-off performance and perhaps better climb. If you are trying to fly at 350mph you need the prop pitch to be correct for 350mph (or very close) otherwise the efficiency goes to pot real quick. All the engine and propeller people had figured that out (matching pitch to flight speed) in WW I with fixed pitch props.
The Speed Spitfire used a fixed pitch prop.
View attachment 772636
Getting the wrong pitch in 1940 that cost 20-30mph on a fighter was not impossible. what is close to impossible is that they never fixed it.
All two pitch or variable or constant speed props have the blades mounted in collars that allow the blades to changed in pitch. The hub may only allow a certain range of motion, like the already mentioned 20 or 34 degrees but the max or minimum pitch is adjustable on the ground and experiments would be very easy to do. easier than swapping a propeller (or carving a new wooden one). Now with the 20 degree props maybe you have to sacrifice something else but sacrificing 20-30mph of top speed for??????? shorter take off run? better climb at 120-140mph?
And when comparing different propellers we have the fact that they often used different shaped blades. The blades also were twisted as they went from the hub to the tip.
A prop tip has a shallower pitch angle than the mid part of the blade because the tip is moving much faster than the mid span of the blade in relation to the forward motion.
Different propeller companies may have had different ideas as what the change in blade shape could be.
Experimenting with different blade shapes/profiles is a lot harder than experimenting with different pitch angles.

Famous poor propeller is the early P-47. The speed didn't change much. The climb did, do the shape of the blades. More blade area.

I think you mistake my point regarding the increased cooling capacity of the Morris radiators, This has nothing to do with intercooling of the compressed charge whatsoever, but everything to do with increasing heat removal from the engine which was always an issue with the Whirlwind, If it removed heat more efficiently it would lower the engine temperature at max power condition, which was the controlling factor for detonation in the engine. If it ran cooler, extra boost could be applied until the safe limit for engine temperature inducing detonation was reached, thus allowing more power. I doubt the gains would be huge as most of the energy created in an engine goes into heat not power, but it would definitely be thereand an incremental gain, as was the reduced drag, so winner winner chicken dinner as they say

 

[Dave Smith]

Max speed a ~18000 ft was achieved with the +6.25 psi boost. Go ever lower from that altitude, and you can take advantage of the increased boost, provided the fuel of required octane/grade value is in use.
The +16 psi boost was available between SL and ~7000 ft, but not above that altitude.

(all values are with ram, as per chart; non-ram values are some 2000 ft lower)



Agreed.



+9 psi boost was on 100 oct fuel for the Merlin VIII (max power of 1275 HP).
Max boost on 87 oct fuel was +5.75 psi; for take off, that meant 1080 HP - 200 HP more than the Merlin III, despite a bit lower boost on same fuel and (low) altitude.
Shows how much power the superchargers were sucking up, and how much the throttle losses were a thing.

View attachment 772684



Was there a ww2 fighter that suffered 20-30 mph due to a wrong pitch, that we know for sure that was the case?

It is not stated what if any modification to the superchargers was required, the changes to the Merlin on the introduction of 100 octane fuel are noted as small. and the situation with the whirlwind may have been similarly modest for a similar percentage gain in p

Bad example.
The 35 liter DB engine ran at about 6.1lbs of boost, once they got a few niggling problems solved, like holes appearing in the piston tops. by the time the DB 605 appeared the Merlin was not only cleared for 12lbs of boost but 1942 saw boost cleared to 15lbs and later 18lbs with strengthened supercharger drive. Please note that 15lbs of boost is 2.02 Ata.
Amazing how an extra 42% of intake pressure (which in this case is mass air flow) can equal 30% extra displacement.

You are confusing two different things. A Merlin XX running 12lbs of boost had a temperature rise in the supercharger of 148 degrees C. This was the rise over the temperature of the intake air. The radiators had nothing to do with the temperature of the air in the intake tract, unless there was some sort of intercooler. A Merlin running less pressure would have a lower temperature rise. A Merlin using a lower gear ratio on the supercharger would have less temperature rise but would not have the same pressure available at the same altitudes.
This was why the Merlin VIII engine in the early Fulmars was rated at 1275hp at 9lbs of boost using 87 octane fuel. The low geared supercharger could only hold 9lbs of of boost to a very low altitude. The much slower turning impeller didn't heat the air as much.
The detonation limit in supercharged aircraft engines has very little to do with the detonation limit on non-supercharged cars/motorcycles. In the supercharged engine the intake fuel/air mixture at full throttle is very close to it's ignition temperature. Sometimes the pilot gets a warning in the form of conventional "knocking", which is local (in the cylinder) pre-ignition. Sometimes the entire cylinder flashes at once, instead of a controlled burn taking 30-40 degrees of crankshaft rotation all the burn burns in 0-2 degrees the resulting pressure breaks the piston/s, con rods, etc, In the case of radials it may blow cylinders right off the engine.
This is why the engine makers (and airplane) used intercoolers or water/alcohol injection. To cool the intake charge. Worrying about the engine overheating in 2-5 minutes came after you could get the engine to survive making the high power for even a few seconds.


For some reason the difference in speed between the DH and Rotol props was only a few MPH. There was a difference in performance. Performance covering all aspects, not just speed. The finer pitch end of the Rotol props gave better take-off performance and perhaps better climb. If you are trying to fly at 350mph you need the prop pitch to be correct for 350mph (or very close) otherwise the efficiency goes to pot real quick. All the engine and propeller people had figured that out (matching pitch to flight speed) in WW I with fixed pitch props.
The Speed Spitfire used a fixed pitch prop.
View attachment 772636
Getting the wrong pitch in 1940 that cost 20-30mph on a fighter was not impossible. what is close to impossible is that they never fixed it.
All two pitch or variable or constant speed props have the blades mounted in collars that allow the blades to changed in pitch. The hub may only allow a certain range of motion, like the already mentioned 20 or 34 degrees but the max or minimum pitch is adjustable on the ground and experiments would be very easy to do. easier than swapping a propeller (or carving a new wooden one). Now with the 20 degree props maybe you have to sacrifice something else but sacrificing 20-30mph of top speed for??????? shorter take off run? better climb at 120-140mph?
And when comparing different propellers we have the fact that they often used different shaped blades. The blades also were twisted as they went from the hub to the tip.
A prop tip has a shallower pitch angle than the mid part of the blade because the tip is moving much faster than the mid span of the blade in relation to the forward motion.
Different propeller companies may have had different ideas as what the change in blade shape could be.
Experimenting with different blade shapes/profiles is a lot harder than experimenting with different pitch angles.

Famous poor propeller is the early P-47. The speed didn't change much. The climb did, do the shape of the blades. More blade area.

My experience with highly tuned motorcycle race engines is that detonation at full power gives little warning before complete melt down ,or mechanical destruction of the engine LOL!

 

[Dave Smith]

It is not stated what if any modification to the superchargers was required, the changes to the Merlin on the introduction of 100 octane fuel are noted as small. and the situation with the whirlwind may have been similarly modest for a similar percentage gain in power, but none of the bodies involved with the document seemed particularly exercised about it.


My experience with highly tuned motorcycle race engines is that detonation at full power gives little warning before complete melt down ,or mechanical destruction of the engine LOL!

 

[Dave Smith]

Well folks, thank you for your contributions, I seriously doubt that any more definitive understanding of the document is likely to happen 80 years after it was written, but it is fascinating nevertheless, and demonstrates that before the decision to terminate the Whirlwind, improvements in performance were being actively pursued. Of course the Peregrine although deemed "unreliable" was a sight better than the early Merlin's which were clearly a greater issue for the country

 

[tomo pauk]

It is not stated what if any modification to the superchargers was required, the changes to the Merlin on the introduction of 100 octane fuel are noted as small. and the situation with the whirlwind may have been similarly modest for a similar percentage gain in p

A complete overhaul of S/C will be required for the Peregrine to make close to 1000+ HP at 20000 ft - same as it was required for the Merlin to start making ~1100 HP at 20000 ft.
Merlin III was unable to do it, on any fuel; Merlin 46 and 47 were doing it, while featuring the 4th, if not 5th generation of the Merlin's superchargers.
The as-is Peregrine, just as-is Merlin III and the like, was running happily with the hi-oct fuel and higher boosts at lower altitudes.

Well folks, thank you for your contributions, I seriously doubt that any more definitive understanding of the document is likely to happen 80 years after it was written, but it is fascinating nevertheless, and demonstrates that before the decision to terminate the Whirlwind, improvements in performance were being actively pursued.

Westland, as other companies, were eager to sell their designs to the costumer. So they took the ball (= promise of the major power increase for a small cost involved) and tried to make a run with it, and nobody should blame them IMO.
Unfortunately, for every Whirlwind, UK industry would've been delivering 1,5 to 2 Spitfires, with comparable performance - and that math was very real so the UK went with that, thus Peregrine was cancelled, together with Whirlwind. RR had more resources to improve Merlin, and Westland started making Spitfires.

Of course the Peregrine although deemed "unreliable" was a sight better than the early Merlin's which were clearly a greater issue for the country

Peregrine was probably very reliable.
Contemporary Merlins (III, let alone the X) were better engines, though, and already by 1940 RR was making even better Merlins.

 

[Shortround6]

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.

Of course the Peregrine although deemed "unreliable" was a sight better than the early Merlin's which were clearly a greater issue for the country

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.

 

[Bretoal2]

it would lower the engine temperature at max power condition, which was the controlling factor for detonation in the engine.

No. About detonation, the main problem in the enormous capacity aero engines (20 x , 30 x or 40 x times a motorcycle engine....) is inlet temperature. See that ADI is injected in the induction circuit, not in the cooling system !

 

[Shortround6]

Unfortunately, for every Whirlwind, UK industry would've been delivering 1,5 to 2 Spitfires, with comparable performance - and that math was very real so the UK went with that, thus Peregrine was cancelled, together with Whirlwind. RR had more resources to improve Merlin, and Westland started making Spitfires.

That is the metric often used. However the actual metric should have been what was the cost of the pair of Peregrines (or Whirlwind) for each Typhoon or Tornado with their 24 cylinder engines. Compared to the Tornado they weighed within 100lbs of each other empty, held a similar amount of fuel, Whirlwind carried a little less ammo (if they had given it belts) and in 1940 they didn't have belt fed 20mm guns to stick in any airplane.

A 1940/early 1941 Spitfire with four 20mm guns possible. It didn't have the performance they were looking for.
They needed to get rid of Whirlwind production in 1940 in order to build more Lysanders

 

[tomo pauk]

That is the metric often used. However the actual metric should have been what was the cost of the pair of Peregrines (or Whirlwind) for each Typhoon or Tornado with their 24 cylinder engines. Compared to the Tornado they weighed within 100lbs of each other empty, held a similar amount of fuel, Whirlwind carried a little less ammo (if they had given it belts) and in 1940 they didn't have belt fed 20mm guns to stick in any airplane.

I don't think that for between the late 1940 and late 1941 the cost comparison between the Whirly and Typhoon/Tornado mattered. Not just because Westland was introduced as the another source of Spitfires after the Whirlys.

A 1940/early 1941 Spitfire with four 20mm guns possible. It didn't have the performance they were looking for.

A Spitfire with Merlin XII and 4 cannons would've offered similar speed and a bit lower RoC.
A Spitfire with Merlin XX or 45 would've offered a tad better speed and probably no worse RoC.

They needed to get rid of Whirlwind production in 1940 in order to build more Lysanders

Air Ministry should've canned both the Lysander and the Whirlwind by early 1939, while making a contract with Westland to make Spitfires.

 

[ThomasP]

FWIW

The standard Peregrine I using 87 grade fuel:
885 BHP with 3000 rpm at +6.75 lbs boost at 15,000 ft
765 BHP with 3000 rpm at +6.75 lbs boost for TO

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

The prototype Whirlwind Mk I in standard trim (no SSFT mods or bomb racks) was good for 354 mph TAS at 15,800 ft during RAE tests.

At some point it was decided necessary to add SSFT (the report of the speed tests after modification is dated 19 June 1941). Part of the mods for installing the SSFT required the wing section to be "thickened" over the area of the SSFT. Subsequent testing at RAE of a production Whirlwind in standard trim (with SSFT mods but no bomb racks) revealed a Vmax of 338 mph TAS at 15,200 ft. It was noted in the test report that the airframe used for the tests had seen some service and that some of the degradation in performance could be attributed to wear and tear on the airframe. How much degradation was due to wear and tear was not specified (or looked into as far as I know).

In 1941 at least one improved 1-stage/2-speed Peregrine was looked at on paper, and a standard 1-stage/1-speed Peregrine 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 Peregrine 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