Automatic Boost Control

[P-39 Expert]

Agree, especially number 4. Early on the only experienced pilots were Pearl Harbor vets (one battle and only a few actually got in the air). The two squadrons at Port Moresby were just out of flying school except for one or two. Those IJN pilots opposing them were the best around due to their experience.

 

[Deleted member 68059]

The P-38 didn't suffer from bad turbocharger controls..

That is not what the Americans were saying at the time Greg, and it is nothing specific to the P38, it
applies to many Allied aircraft of the time too, but a twin engine with turbos places particularly
high demand on controls.

Wright-Field correspondance 31st March 1945, in connection with BMW801D Kommandogerat.

Archive File:
NARA - P301937 - Single Lever Throttle Control for P38 - Visit to Allison

 

[DarrenW]

That is not what the Americans were saying at the time Greg, and it is nothing specific to the P38, it
applies to many Allied aircraft of the time too, but a twin engine with turbos places particularly
high demand on controls.

Wright-Field correspondance 31st March 1945, in connection with BMW801D Kommandogerat.

Archive File:
NARA - P301937 - Single Lever Throttle Control for P38 - Visit to Allison

View attachment 567651

Am I to believe that United States aircraft engineers never investigated automated engine controls before they had a look the Kommandogerät ???

 

[MIflyer]

Automatic boost control was added to US engines later in the war. When the RAF started flying Hawk 81A's the V-1710's lacked auto boost controls and pilots used to the Merlin would shove the throttle in and go roaring off, only to have the engine blow its top. I believe the first airplane to have auto boost control with a V-1710 was the P-40M.

 

[GregP]

I should point out the 31 March 1945 is nowhere NEAR the early P-38 days and that, by then, the P-38 was past its prime.

The directive apparently went unnoticed since they immediately thereafter concentrated on jet engines, as history seems to say to me. I think the last gasp of the piston fighters was the SuperBolt, the CAC-15, and likely the Sea Hornet and Sea Fury. Only the British designs were produced, as you all know, though I suppose I could include the La-9 / 11. I'd say the Grumman Guardian doesn't count, but the Skyraider is another story altogether ...

 

[MIflyer]

Note that the P-38, unlike most other turbosupercharger equipped aircraft, had no direct control over the turbosupercharger. There was a linkage in the throttle controls that also worked with the turbo and that was it, other than other normal engine controls. In contrast, in the P-47 the pilot had the ability to adjust the turbo, being instructed to set the controls so that the turbo overspeed light blinked off and on, and of course on the bombers they had turbo controls.

When they added a manifold pressure regulator to the later V-1710 engines that caused problems. The engine manifold pressure regulator and the turbo regulator would fight each other, leading to a jerky flight. While no doubt unpleasant for the fighters, for the photo recon Lightnings this was a serious problem. You need smooth and steady flight for good pictures. So at the 9th Photo Recon Squadron, and probably at other recon units, the manifold pressure regulators were removed.

Generally speaking, Allison V-1710 equipped fighters had no supercharger controls at all. Even with the P-63C with its auxiliary supercharger, the pilot had no control over the speed of the auxiliary unit nor even if it was operating at all. On the P-63C they eliminated the prop controls and had the throttle set up to take care of that adjustment automatically.

On the F4U, F6F, and P-61 airplanes the pilot could make many more adjustments to the supercharger stages, which must have been a real pain in combat.

 

[P-39 Expert]

Note that the P-38, unlike most other turbosupercharger equipped aircraft, had no direct control over the turbosupercharger. There was a linkage in the throttle controls that also worked with the turbo and that was it, other than other normal engine controls. In contrast, in the P-47 the pilot had the ability to adjust the turbo, being instructed to set the controls so that the turbo overspeed light blinked off and on, and of course on the bombers they had turbo controls.

When they added a manifold pressure regulator to the later V-1710 engines that caused problems. The engine manifold pressure regulator and the turbo regulator would fight each other, leading to a jerky flight. While no doubt unpleasant for the fighters, for the photo recon Lightnings this was a serious problem. You need smooth and steady flight for good pictures. So at the 9th Photo Recon Squadron, and probably at other recon units, the manifold pressure regulators were removed.

Generally speaking, Allison V-1710 equipped fighters had no supercharger controls at all. Even with the P-63C with its auxiliary supercharger, the pilot had no control over the speed of the auxiliary unit nor even if it was operating at all. On the P-63C they eliminated the prop controls and had the throttle set up to take care of that adjustment automatically.

On the F4U, F6F, and P-61 airplanes the pilot could make many more adjustments to the supercharger stages, which must have been a real pain in combat.

Regarding the P-63, the auxiliary supercharger was designed to be automatic and autonomous. The fluid coupling that drove the auxiliary stage automatically adjusted impeller speed to take in less thick air at low altitudes and gradually more thin air at higher altitudes. This relieved the pilot from having to monitor boost as he changed altitude or throttle position.

 

[tomo pauk]

Am I to believe that United States aircraft engineers never investigated automated engine controls before they had a look the Kommandogerät ???

Aircraft engineers have had nothing to do with engine controls (bar figuring the way to install them in the aircraft). Kommandogerät was a fruit of the people at Bramo, the engine company (later transpired into BMW), not of those in Focke Wulf or Dornier.

 

[MIflyer]

Yes, that is true and is what the P-63 pilot's manual says.

One of the disadvantages of mechanically driven supercharging was that it if automatic it usually had a specific speed shift point. For the Merlin P-51 and the Spit IX that was around 18,000 ft and was controlled by an aneroid device. German pilots knew that if they are careful to fight around that altitude the Allied pilots in Mustangs and Spits would be troubled with having to pull and push on the throttle frequently as their engines surged with power when the supercharger switched to high speed and then dropped back to low speed as the combat altitude varied. And if there were multiple P-51's or Spits in the fight, their unit cohesion was destroyed, since aneroid device setting always varied from airplane to airplane. The BF-109 had a fluid coupled supercharger drive and that eliminated such shift points, and I believe the FW-190D was the same way; the P-63 had that same feature as well.

Some of the P-51's escorting the B-29's had their spring loaded momentary "On" high speed supercharger switches replaced with regular toggle switches so they could defeat the automatic feature and use the high speed supercharger setting below the aneroid device setting. The Japanese knew to fight the Mustangs down around 15,000 ft, optimum altitude for their airplanes, but where the P-51 was starting to run out of steam.

Based on reading the various P-51 pilot's manuals I have on hand it appears that in late WWII or postwar the supercharger automatic switch was changed to one using ram air pressure. I assume that meant the switch occured at lower altitude if you were not going very fast.

 

[tomo pauk]

Yes, that is true and is what the P-63 pilot's manual says.

One of the disadvantages of mechanically driven supercharging was that it if automatic it usually had a specific speed shift point. For the Merlin P-51 and the Spit IX that was around 18,000 ft and was controlled by an aneroid device. German pilots knew that if they are careful to fight around that altitude the Allied pilots in Mustangs and Spits would be troubled with having to pull and push on the throttle frequently as their engines surged with power when the supercharger switched to high speed and then dropped back to low speed as the combat altitude varied. And if there were multiple P-51's or Spits in the fight, their unit cohesion was destroyed, since aneroid device setting always varied from airplane to airplane. The BF-109 had a fluid coupled supercharger drive and that eliminated such shift points, and I believe the FW-190D was the same way; the P-63 had that same feature as well.

If the German pilot is flying the Fw 190A, he also has the 'switch altitude' feature (~ 14000 ft). But switch or no switch, the Merlin Mustang is going to trash it above 17000 ft if Mustang's pilot is worth his salt - he knows better than to be sucked down under 20000 ft unless it is diving at the prey. Spitfire pilot should also know strong and weak sides of his aircraft.
Bf 109G pilot is on similar position - it requires co-operation of the Allied pilot to forfeit it's advantage (= high cruise way above 20000 ft) and come down to play.
Fw 190D was also outfitted with mechanically-driven S/C, the swirl throttle giving up to ~100 HP under the rated altitude.

Some of the P-51's escorting the B-29's had their spring loaded momentary "On" high speed supercharger switches replaced with regular toggle switches so they could defeat the automatic feature and use the high speed supercharger setting below the aneroid device setting. The Japanese knew to fight the Mustangs down around 15,000 ft, optimum altitude for their airplanes, but where the P-51 was starting to run out of steam.

Based on reading the various P-51 pilot's manuals I have on hand it appears that in late WWII or postwar the supercharger automatic switch was changed to one using ram air pressure. I assume that meant the switch occured at lower altitude if you were not going very fast.

Same thing here - why would US pilot leisurely fly down to where the Japanese pilot can exploit strong suite of his aircraft? It is like willingly dogfighting with Zero at 250 mph.

 

[wuzak]

The P-38 didn't suffer from bad turbocharger controls.

Because there were no problems with overspeeding turbos due to the regulator control freezing there was no reason to switch the regulator from the engine carburetor inlet pressure to the exhaust pressure.

http://www.enginehistory.org/Piston/Allison/V-1710Details/turbochargercomponents.html

Note that the P-38, unlike most other turbosupercharger equipped aircraft, had no direct control over the turbosupercharger. There was a linkage in the throttle controls that also worked with the turbo and that was it, other than other normal engine controls. In contrast, in the P-47 the pilot had the ability to adjust the turbo, being instructed to set the controls so that the turbo overspeed light blinked off and on, and of course on the bombers they had turbo controls.

The turbo control was the wastegate, which was like an automatic boost control in that it adjusted a throttle based on pressure.

The throttle linkage connected to the regulator, and set the pressure at which the wastegate operated.

If the B-17 and P-47 had separate controls to set the regulator I do not know, but that was still not a direct control of the turbo. The wastegate system controlled the turbo speed and boost.

I would like to know about P-47 pilots setting the turbo at the overspeed speed. At what altitude did they do this?

Given that the overspeed was calculated based on the speed at which catastrophic failure would occur, that tactic seems slightly risky.

 

[MIflyer]

"Same thing here - why would US pilot leisurely fly down to where the Japanese pilot can exploit strong suite of his aircraft? It is like willingly dogfighting with Zero at 250 mph."

Imagine you are a P-51 pilot and you've flown all the way from Iwo and look down and see a Zero. Note attached cartoon. Not hard to understand his attitude! He is after all, a fighter pilot, and so by definition not entirely rational.

From the P-47 High Altitude and Acro Training Film, what is important is the max speed of the turbine wheel, 18,250 ROM. It is exceeding that RPM that causes the turbine wheel to disintegrate. The pilot is told that as the airplane approaches its critical altitude the light will blink (starting at about 18,100 rpm) until he reaches the critical altitude, at which point it will stay on and has he has to reduce manifold pressure to keep it blinking.

https://ia800200.us.archive.org/22/...t03-highAltitudeFlightAndAerobatics_512kb.mp4.

Note that the P-38 has shields designed to keep disintegrating turbine wheel fragments from hitting the pilot.

 

[slaterat]

I would point out that "automatic mixture control" is still a switch, its just once you have SET rich or lean... it then ensures that is maintained.

That is true for the Hurricane I and probably the Spit I and II, on the Hurricane II the mixture is totally automatic and the "Rich Lean" switch is deleted. This is confirmed in the Hurricane II manual, in both text and in illustration

 

[Zipper730]

So the basic reason the USAAF/USN didn't have automatic boost control early on was that the commercial users and multi-engine aircraft designers drove the decisions involved in engine-control?

 

[Greyman]

I think the correct answer is that no one here knows.

 

[Shortround6]

The commercial market in the US in the mid to late 30s was certainly larger than the domestic military market.

From Joe Baugher's website "With the R-1830 engine, the Y1P-36 did so well that it won a 1937 Army competition, and on July 7, 1937, the Army ordered 210 P-36As, the largest single US military aircraft order since the First World War."
Another source says largest order for US fighter planes ever given up until that time. However that was just placing the order. Curtiss built 101 of them in 1938 and 105 in 1939.

Since twin engine airliners climb a lot slower (and generally don't dive as fast) as fighters the pilots (and co-pilots) had a lot more time to play around with mixture controls and boost settings. With twice the manpower and things happening at 1/2 to 1/4 the speed (vertically) the need for automatic engine controls was nowhere near as great in commercial market, not to mention that fuel economy might have a higher value to the owners.

 

[MIflyer]

The maximum you can fly without supplementary oxygen is about 10,000 ft. Given that pre-war airliners were neither pressurized nor carried oxygen, flying higher than 10,000 ft was as high as you would go, normally. You do not need auto boost control for that.

The C-54 was a godsend for the route over the Hump. But it was designed as an airliner and had to wait until air supremacy had been secured over Burma, since the higher routes were not available to it.

 

[P-39 Expert]

The maximum you can fly without supplementary oxygen is about 10,000 ft. Given that pre-war airliners were neither pressurized nor carried oxygen, flying higher than 10,000 ft was as high as you would go, normally. You do not need auto boost control for that.

The C-54 was a godsend for the route over the Hump. But it was designed as an airliner and had to wait until air supremacy had been secured over Burma, since the higher routes were not available to it.

I read that automatic boost control originated in airliners before the war.

 

[Joe Broady]

The "Pilots Handbook of Flight Operating Instructions" for the F6F-3 and -5 has a diagram of the induction system. The cockpit throttle lever directly controls the carburetor throttle valve (between the two blower stages) and also goes to an "auxiliary supercharger regulator". The latter senses 1st stage blower output pressure and positions a throttle valve in the 1st stage input.

Clearly that valve can have no effect in neutral blower, and in fact the manual reminds the pilot that when operating in war emergency power and "LOW or HIGH blower is being used the engine will automatically return to military power when the water supply is exhausted. When operating in NEUTRAL blower, the auxiliary stage regulator cannot control the manifold pressure and the throttle must be brought back beyond the limit stop immediately when the water has been exhausted."

After a supercharger "upshift" the regulator doesn't respond quite fast enough and so the pilot must help it to prevent a momentary overboost. The procedure is to reduce manifold pressure (rpm too, if time permits), make the shift smartly with the blower lever (just inboard of the throttle), then restore the power settings. "The amount which the manifold pressure should be decreased before shifting to the next higher blower ratio is best learned by experience. Until familiar with the airplane, reduce manifold pressure 3" to 4" before shifting. The amount of surge in manifold pressure depends on how quickly the auxiliary stage regulator reacts, and this may vary with temperature conditions, and from airplane to airplane."

A downshift requires no such precaution. However, the manual emphasizes that both upshifts and downshifts should be accomplished with a quick motion of the lever. That minimizes clutch slippage during the shift. By the way, full forward is neutral blower, center position is low blower, and full aft is high. To me that's exactly opposite the natural directions. Another peculiarity is the Hellcat propeller governor lever. It's on the rear of the throttle quadrant and moves up and down. Push down to increase rpm. I wonder if the word "ergonomics" had been invented yet.

 

[GregP]

They reduced manifold pressure to shift because the gears had to mesh and its both easier and less stressful to mesh gears at lower speeds than it is at higher speeds. Anyone who has ever shifted a manual gearcase will recall that. It's in all the two-stage pilot's manuals to reduce power to shift supercharger gears, and turbocharger gears operate the same way. It would be different, of course, if the coupling were hydraulic.

Still, even when shifting something like a Formula 1 transmission, they momentarily remove power from the geartrain by interrupting the ignition to ease the gear engagement. Every single button-operated motorcycle gear changer I have used (several) has had ignition interruption, too.