Effects of multi-speed superchargers (or lack of the same)

[Zipper730]

Well, 0 Low and High looks like 3 speeds to me.

Well, one stage only has one speed, the other has three speeds. I guess it's just harder to write down than to say "two-stage supercharging"

 

[MIflyer]

The fluid coupling used in the BF-109's DB engine gave it at least one tactical advantage over the Merlin Mustang and Spit IX. On the P-51 and Spit IX the low to high speed switch over occurred at about 18,000 ft, controlled by an aneroid device (y'all ever try to calibrate one of those?) . Canny BF-109 pilots knew that and tried to fight at that altitude, the speed switch going in and out and thus really screwing up the Allied pilot's throttle setting. And of course manufacturing and calibration tolerances meant that no two Mustangs or Spits were set up exactly the same, with the result that a lead and his wingman had a hard time staying together when maneuvering at around 18,000 ft.

Some Mustangs on Iwo Jima had their spring loaded supercharger high speed switches changed to regular toggle switches so they could engage the high speed manually at a lower altitude. The Packard tech reps strongly recommended against this practice.

Late in the war, or perhaps postwar the Merlin supercharger speed switchover was changed from an altitude setting to ram air pressure. I guess this makes sense, because it you are going slow presumably the throttle setting is low as well and there was less chance of overboosting the engine. Then when speed built up the high speed would switch over to low. I know someone who flies a Mustang regularly and says theirs has had the aneroid device removed, the manual supercharger high speed switch being operated for test purposes only once in a blue moon.

The Japanese tried 3 speed single stage superchargers in the Raiden.

 

[MIflyer]

Well, one stage only has one speed, the other has three speeds. I guess it's just harder to write down than to say "two speed supercharging"

Confusion is aided further by the fact that many older articles and books referred to "Two Stage Supercharging" when in reality it was "Two Speed Supercharging."

 

[tomo pauk]

Confusion is aided further by the fact that many older articles and books referred to "Two Stage Supercharging" when in reality it was "Two Speed Supercharging."

If there is one stage, and then another stage, that is a two stage supercharging.

 

[Deleted member 68059]

Confusion is aided further by the fact that many older articles and books referred to "Two Stage Supercharging" when in reality it was "Two Speed Supercharging."

Very true, including otherwise very well written books like "FIGHTER" By Len Deighton.

 

[Mike Williams]

The fluid coupling used in the BF-109's DB engine gave it at least one tactical advantage over the Merlin Mustang and Spit IX. On the P-51 and Spit IX the low to high speed switch over occurred at about 18,000 ft, controlled by an aneroid device (y'all ever try to calibrate one of those?) . Canny BF-109 pilots knew that and tried to fight at that altitude, the speed switch going in and out and thus really screwing up the Allied pilot's throttle setting. And of course manufacturing and calibration tolerances meant that no two Mustangs or Spits were set up exactly the same, with the result that a lead and his wingman had a hard time staying together when maneuvering at around 18,000 ft.

Not necessarily:

http://www.wwiiaircraftperformance.org/Oxsbring-72sqdn.jpg

http://www.wwiiaircraftperformance.org/mustang/ppf-p-51-mods.pdf

 

[MIflyer]

Very true, including otherwise very well written books like "FIGHTER" By Len Deighton.

I also have a problem with "Fighter" in that he describes BF-110's escorting bombers from Norway and leaving their rear gunners on the ground so they could carry the huge extra fuel tank, and that apparently never occurred.

 

[Reluctant Poster]

The fluid coupling used in the BF-109's DB engine gave it at least one tactical advantage over the Merlin Mustang and Spit IX. On the P-51 and Spit IX the low to high speed switch over occurred at about 18,000 ft, controlled by an aneroid device (y'all ever try to calibrate one of those?) . Canny BF-109 pilots knew that and tried to fight at that altitude, the speed switch going in and out and thus really screwing up the Allied pilot's throttle setting. And of course manufacturing and calibration tolerances meant that no two Mustangs or Spits were set up exactly the same, with the result that a lead and his wingman had a hard time staying together when maneuvering at around 18,000 ft.

Some Mustangs on Iwo Jima had their spring loaded supercharger high speed switches changed to regular toggle switches so they could engage the high speed manually at a lower altitude. The Packard tech reps strongly recommended against this practice.

Late in the war, or perhaps postwar the Merlin supercharger speed switchover was changed from an altitude setting to ram air pressure. I guess this makes sense, because it you are going slow presumably the throttle setting is low as well and there was less chance of overboosting the engine. Then when speed built up the high speed would switch over to low. I know someone who flies a Mustang regularly and says theirs has had the aneroid device removed, the manual supercharger high speed switch being operated for test purposes only once in a blue moon.

The Japanese tried 3 speed single stage superchargers in the Raiden.

There was a difference between RR and Packard built 2 stage Merlins. Packard used the boost control unit from the Merlin 28. From Rolls Royce and the Mustang by David Birch: "The USAAC had reported oscillations of the boost control and its failure to control satisfactorily.........It was considered that the problem was caused by having too small a boost control unit.......Although a complete cure was not affected a considerable improvement was achieved by fitment of stronger springs in the boost aneroid and relay piston."

 

[MIflyer]

One thing I have wondered about. A friend of mine joined the RAF before Pearl Harbor and flew Spitfires and Hurricanes in the UK. I do not think he got past training over there because after 7 Dec 1941 he ended up in the Pacific flying B-24's. So he was likely flying Spit MK 1's and II's in training.

In any case he described having to reach down and "turn on" the supercharger in the Spitfire. This does not sound right but I have not dug into the pilot's manuals to see what he could be talking about. In any version of the Merlin could you engage and disengage the supercharger? That could be done with the R-1830 of the F4F and R-2800 of the F6F, F4U, and P-61 but was not possible with the V-1710.

 

[wuzak]

Spitfire Is had single speed Merlins, which did not have a neutral gear. The supercharger was engaged at all times.

Maybe manually adjusting the throttle. Not sure when they got automatic boost control.

The R-1830 of the F4F and the R-2800 of the F6F were two stage engines, where the auxiliary stage had High, Low and Neutral positions, while the main supercharger stage was always engaged and had a fixed speed relationship to the crank.

Most V-1710s were the single stage type, which was the same situation as the Merlin.

 

[Shortround6]

In any case he described having to reach down and "turn on" the supercharger in the Spitfire. This does not sound right but I have not dug into the pilot's manuals to see what he could be talking about.

He might possibly have been referring to the boost override switch. This had a number of nicknames.
Basically the British engines had an automatic boost limiting device (an aneroid device) that prevented the pilot from overboosting the engine. On the early Hurricanes and Spitfires they were limited to 6lbs of boost for most flying. However in an "emergency" a button or knob could be pressed that changed the aneroid device to a 12lb setting. If the plane was flying at near full throttle and below the critical altitude activating this switch would provide a very noticeable kick in the pants. About a 29% increase in manifold pressure if the plane was at the right altitude.

 

[MIflyer]

Yes, that would make sense. Eric Brown mentions the need to be careful with the early V-1710's, since they lacked an automatic boost control. I read of the RAF finding a number of Hawk 81A's still stored still in their crates and deciding while they were not much good for fighter duties they could be used for training bomber crews in dealing with fighter attacks. They assembled the Hawks, put RAF in them and sent them off. The first one was not up for long at all. The pilot had shoved the throttle all the way in and went roaring off, but the V-1710 blew its top right after takeoff.

 

[Kevin J]

Yes, that would make sense. Eric Brown mentions the need to be careful with the early V-1710's, since they lacked an automatic boost control. I read of the RAF finding a number of Hawk 81A'd still stored still in their crates and deciding while they were not much good for fighter duties they could be used for training bomber crews in dealing with fighter attacks. They assembled the Hawks, put RAF in them and sent them off. The first one was not up for long at all. The pilot had shoed the throttle all the way in and went roaring off, but the V-1710 blew its top right after takeoff.

I've always wondered what happened to each Mohawk they received, because there's uncertainty between different sources as to the exact number received and operated. Does anyone know?

 

[MIflyer]

Some of the French Mohawks were left, still in their crates, in various French colonial possessions and rotted away.

The Profile publication on the Hawk 75 describes the various versions and some info on where they ended up.

 

[Kevin J]

Some of the French Mohawks were left, still in their crates, in various French colonial possessions and rotted away.

The Profile publication on the Hawk 75 describes the various versions and some info on where they ended up.

Thanks, but I was looking for something more detailed than this.

 

[soaringtractor]

Much has been discussed here of multi-stage superchargers, but less of multi-speed single-stage superchargers.

The DB engines used a hydraulic fluid coupling with a barometric control to achieve multi-speed drive with a seamless power curve.
Other engines featured multiple speeds, kinda like a stick/manual/standard shift transmission in a car, with a jagged power curve.
The V-1710 was stuck with one speed.

- Wasn't one reason for using the V-1650 in the P-40 because it had a 2-speed drive?
- Could an excellent multi-speed drive somewhat mitigate the effects of having only one stage?
- Which engines and aircraft had multi-speed drives? Which had only single speed?
- Whatever else comes to mind

BULLSHIT !!!! The P40 with the Allisons still out performed the Packard V1650-1 merlin in speed, climb, the only slight advantage the P40F Melin version had was a slight advantage in service ceiling, giving up top speed, climb to the Allison version, according to the performance figures I read !!!! nd remember the merlin was about 300# heavier !!!!! negating any slight increase in HP !!!

 

[tomo pauk]

Is that a new standard of conversation?

 

[Shortround6]

New standard of facts?

A number of squadrons did overboost the Allison engined P-40s before the WEP rating came out in late 1942.
But that only works below the critical altitude of the engine, which for the 8.80 geared airplanes was around 12,000ft without ram and depended a bit on intake manifold and backfire screens.
the high powers quoted for the Allison in the P-40E and K are for altitudes of around 5,000ft and under (including some RAM).

climb figures (time to altitude) are hard to compare because the Allison used 3000rpm for the first 5 minutes and then used 2600rpm for th erest of the climb while the Merlin powered versions used 2850rpm for the entire climb and not the full 3000rpm at any point in most tests.
Given the above limitations the P-40F was over a minute faster to 20,000ft.

The Allison powered P-40s were better at low altitude if over boosted. But once the altitude got into the low teens there wasn't much contest. The Merlin steadily got better.

 

[MIflyer]

In regard to the presence of bovine excrement, note the attached chart form "America's Hundred Thousand"

It would have been child's play for Allison to have built a two speed singe stage V-1710, and given that the V-1710 supercharger/accessories section was a separate part from the main block and the reduction gear sections, commonality could have still been maintained. And either the V-1650-1 or a two speed V-1710 in a P-51 would have been a heck of a performer, no P-51B in speed, but still better than just about anything else around in 1942.

Also the "300 lb heavier" compares a single stage V-1710 to a two stage Merlin 61.

 

[Shortround6]

Also the "300 lb heavier" compares a single stage V-1710 to a two stage Merlin 61.

Well, the V-1650-1 is supposed to weigh 1510lbs according to RR.
The V-1710-39 in the P-40E is supposed to weight 1310lb so there is 200lbs, not 300lbs.

I haven't looked up the difference in radiators, coolant, oil system and other "accessories".
And there may be a difference it what was considered "dry weight" depending on source.
Usually generators, starter motors/systems, gun synchronizers and any auxiliary pumps (vacuum, hydraulic, etc) are not included. Sometimes the exhaust gaskets, flanges, nuts and washers are but pipes/stacks are not.