Improve That Design: How Aircraft Could Have Been Made Better

[XBe02Drvr]

@BiffF15 and X XBe02Drvr ,

I got a question, and this will probably sound stupid, but I'll ask it anyway: If you're breathing in pressurized oxygen and you lose consciousness, do your lungs inflate and pop? Or something else?

Your lungs inflate, your chest expands like a balloon, but if the regulator is working correctly (let's hear it for the aircrew equipment guys!), it won't overpressure and rupture your lungs, and the discomfort will make it difficult to drift off to sleep. And the likelihood of pulling enough G at those altitudes to black you out is pretty low. Terrestrial folk don't often think about it, but our ribcage is designed and muscled to expand against resistance, not contract. Exhaling is just the relaxation of the inhaling effort. When an outside force such as a pressure breathing regulator resists our efforts to exhale, we discover how weak we are in that direction.
The only other non - naval aviator in the chamber was some sort of clandestine warfare type (green beret/SEAL/CIA/UDT? - he wasn't talkative), just returning from a tour of staff duty and getting re-qualed to go out in the field. Whatever his billet was, he had to requalify at HALO (High Altitude, Low Opening) parachute insertions from 30+K altitudes, for which he had to get a refresher in the chamber. After they brought the chamber down and let me out, they let the jet jocks talk them into taking the chamber back up so they could carry on their little game of "who can pressure breathe the longest". The spooky guy outlasted all the jet jocks. The folks that ran the chamber said distance swimmers and SCUBA divers were usually the best at pressure breathing.
Cheers,
Wes

 

[XBe02Drvr]

Wes,

The 45k you reference above is actually at approx 60k and called Armstrong's Line. The Eagle could get above this easily enough and we were made aware of this during my time in the school house. I know of one now retired 3 star who has been through 75k and and still climbing...

Armstrong limit - Wikipedia

Cheers,
Biff

Thanks for the update. I don't remember the terminology of Armstrong's limit being used back in 1973, and the altitude numbers they gave were a little lower than what you and Wikipedia quoted. Perhaps a little safety margin to keep testosterone fueled aviators safe and mentally fit to get their precious chariots back aboard the boat?
Cheers,
Wes

 

[Zipper730]

I was thinking of something else: Was there any way the V-1710-59 could have been designed without it's flaws and been able to produce a higher ACA?

 

[XBe02Drvr]

I was thinking of something else: Was there any way the V-1710-59 could have been designed without it's flaws and been able to produce a higher ACA?

Of course; any designer with a functioning and properly maintained crystal ball knows ahead of time what features will turn out to be flaws and can avoid incorporating them in the design. That's why everything always works perfectly straight out of the box.
Cheers,
Wes

 

[pbehn]

Of course; any designer with a functioning and properly maintained crystal ball knows ahead of time what features will turn out to be flaws and can avoid incorporating them in the design. That's why everything always works perfectly straight out of the box.
Cheers,
Wes

Many design flaws are only considered so in comparison. If someone produced a 3,000 BHP V1700 engine in 1940 or one that ran for 1000 hours without being touched, all other engines would be considered to be flawed. People used to write to the Times when their car did 100,000 miles or ran at 100MPH for 10 minutes without blowing up.

 

[P-39 Expert]

I was thinking of something else: Was there any way the V-1710-59 could have been designed without it's flaws and been able to produce a higher ACA?

The -59 was the first V-1710 to use the 9.6:1 supercharger step up gears (up from 8.8) to increase critical altitude. Just like the other contemporary V-1710s except for the gear change. Turns out the gears wouldn't support the increased manifold pressure and they wore out too quickly. Fix was to widen the gears but redesign of the accessories casing took almost a year, from the end of '41 to November '42 to get the -59 (now the -83) into a flying airplane. Allison and the Army were still goofing around with backfire screens which reduced power a little but finally discarded those in mid '42 (Sept '42 for turbocharged P-38s). Would have been great if the original gears had worked (backfire screens didn't help) and the -59 would have been available from the end of '41, but the Army would have just negated that by figuring out how to make the P-39 even heavier.

 

[Zipper730]

The -59 was the first V-1710 to use the 9.6:1 supercharger step up gears (up from 8.8) to increase critical altitude. Just like the other contemporary V-1710s except for the gear change.

That I'm aware of: I'm just curious why they had so much difficulty with the higher-speed gear? It wasn't something that's never been done before, the Merlin's had a similar gear-ratio from what I was told.

Fix was to widen the gears

Are you talking about the teeth?

Allison and the Army were still goofing around with backfire screens

Why?

Would have been great if the original gears had worked (backfire screens didn't help) and the -59 would have been available from the end of '41, but the Army would have just negated that by figuring out how to make the P-39 even heavier.

Why would they want to do that?

 

[Shortround6]

Are you talking about the teeth?

The power needed to drive a supercharger impeller goes up with the square of the speed of the impeller as a rule of thumb.

An Allison supercharger using 9.6 gears needs 19% more power than one using 8.80 gears. Please remember that the turbocharged engines in the first P-38s used 6.44 gears on the engine supercharger. The supercharger drive had not been intended to handle such power as needed by the higher gear ratios. They needed to make the gears thicker (front to back) to handle the load. However, as mentioned above, the gear case was too thin to handle the thicker gears. The gear case was cast as part of the engine block (crankcase) so new molds had to be designed and built at the casting facilities. Using 9.60 gears the supercharger could easily take over 250hp to drive it.

Unlike many car engines, aircraft engines are not designed with a lot of extra space or room for "growth" as that means they are too large and heavy in the first models.

 

[wuzak]

That I'm aware of: I'm just curious why they had so much difficulty with the higher-speed gear? It wasn't something that's never been done before, the Merlin's had a similar gear-ratio from what I was told.

Single stage engines, at least the 45, had a gear ratio of 9.1:1, slightly higher than the 8.8:1 of the earlier V-1710s.

The Merlin XX series had ratios of 8.15:1 (MS/LO) and 9.49:1 (FS/HI).

2 stage Merlins had lower ratios than the XX.

The Merlin's gears were strong enough for those ratios because they were designed for those ratios and the power that the supercharger consumed.

The V-1710's gears were designed around a lower ratio, which meant that the supercharger consumed less power. From what P-39 Expert said, changing the gears for higher power/speed required a redesign of the accessories casing.

Another factor here is that the V-1710, for most variants, had an impeller diameter of 9", compared to 10.25" for most single stage Merlins. The 47, IIRC, had an impeller of 10.75" or 10.85".

 

[Zipper730]

The power needed to drive a supercharger impeller goes up with the square of the speed of the impeller as a rule of thumb.

So 19% for 9.6 vs 8.8 and 222.2% for 9.6 vs 6.44?

Please remember that the turbocharged engines in the first P-38s used 6.44 gears on the engine supercharger.

I'm guessing they used this lower gearing either because

1. They expected the turbocharger to take care of the rest and figured the least horsepower taken off the shaft would be best?
2. When the engine was designed in 1929, they didn't think the higher critical altitudes were important?

The supercharger drive had not been intended to handle such power as needed by the higher gear ratios. They needed to make the gears thicker (front to back) to handle the load. However, as mentioned above, the gear case was too thin to handle the thicker gears. The gear case was cast as part of the engine block (crankcase) so new molds had to be designed and built at the casting facilities. Using 9.60 gears the supercharger could easily take over 250hp to drive it.

And I guess they didn't realize the casing would have to be strengthened also?

Single stage engines, at least the 45, had a gear ratio of 9.1:1, slightly higher than the 8.8:1 of the earlier V-1710s.

Makes sense as they could operate at higher altitudes.

The Merlin XX series had ratios of 8.15:1 (MS/LO) and 9.49:1 (FS/HI).

And this was to allow more power for low altitude?

2 stage Merlins had lower ratios than the XX.

I would have figured they'd have been smaller in diameter but spun faster...

The V-1710's gears were designed around a lower ratio, which meant that the supercharger consumed less power. From what P-39 Expert said, changing the gears for higher power/speed required a redesign of the accessories casing.

The V-1710 did have a bolt-on provision off the bat for a turbocharger or a secondary supercharger stage, correct?

 

[Zipper730]

FL250 = 25,000ft from what I understand.

That's correct, starting at 18000 feet in the US (some lower amount in Europe), they start using flight-levels which are in blocks of 100 feet so FL180 = 18000 feet, and FL250 = 25000 feet. It goes up to 60000 feet because there's little operating up that high, and since we never fielded the SST, there was no reason to bring it up any higher.

 

[Deleted member 68059]

It was assumed by many in the planning departments/purchasing that the altitudes at which combat took place would keep going up. Which is why the Americans, British, Germans and others had designs/schemes for planes with pressurized cockpits all in the works in 1941-42. However, for a variety of reasons this did not happen with piston engines. At least not to the extent the planners thought.
...But some of the problems took too long to solve and the war was fought (mostly) with unpressurized aircraft.

This is all spot on, I have quite a few memos from British air ministry talking about getting Spitfires up to intercept high altiude German aircraft in 1941, it was expected to have to get up to engage at over 40,000 feet, and the reports state that even with Oxygen, the demands on the body caused by low temperature and pressure meant that the pilots would have to be hand-picked. I.e. some people just had a little more resistance due to their natural consitution, and the only way to actually operate at that altitude without a pressure cabin was to find such pilots. These papers say Supermarine regarded fitting out the Spitfire with a pressure cabin as immensely difficult (although they did, but it took a long time and a lot of effort).

 

[MIflyer]

My friend Ward Duncan, maint chief for the 9th PRS,sad that they raised the V-1710 supercharger gear ratio because on the earliest P-38's the turbo was having to wind up to such a high RPM that it was coming apart. The "fins" you can see between the turbos and the cockpit are designed to protect the pilot from a disintegrating turbo wheel.

Above 45,000 ft without cockpit pressurization you have to "pressure breathe" which is a much more difficult situation than normal inhaling and exhaling - it is the reverse of normal.

A story I have yet to see told is how the RAF and Americans based their oxygen systems on captured German equipment

 

[Zipper730]

F7F-1 with a two-stage supercharger would be pretty hot-shit: There'd be a need for intercooling, and I'm not sure how much room would exist in the wings for that, but something like the F4U-4 could be done with a chin-scoop.

If I calculated my speed estimates using the cube-rule, I see a substantial benefit. With the exception of the Mach number listing, red will mean inferior in performance, blue will mean superior in performance, and black will mean no difference. The mach number will simply read black if below 0.65, and red above 0.65.

Military Rated Power (as was).............................with 2-stage blower

Altitude...TAS.............HP......S/C...................Altitude...TAS..............HP......S/C..............Mach No.
0'.............368....mph...4200...Low...................0'.............368...mph....4200...Neutral..........0.483
2000'.......376....mph...4200...Low...................2000'.......376...mph....4200...Neutral..........0.497
4000'.......384....mph...4200...Low...................4000'.......384...mph....4200...Neutral..........0.512
.........................................................................4400'.......385...mph....4200...NeutralACA...0.514
6000'.......391....mph...4200...Low...................6000'.......382.1 mph...3920...Neutral..........0.513
8000'.......399....mph...4200...Low...................8000'.......385.9 mph...3800...Low...............0.521
10000'.....397.5 mph...4200...Low...................10000'.....384.5 mph...3800...Low...............0.541
10167'.....407....mph...4200...Low/ACA........................................................................................
12000'.....405....mph...3900...Low...................12000'.....401.5 mph...3800...Low...............0.548
14000'.....403....mph...3590...Low...................14000'.....410.7 mph...3800...Low...............0.568
16000'.....400....mph...3200...Low...................16000'.....420.1 mph...3800...Low...............0.585
16250'.....399....mph...3280...High..................16250'.....422.5 mph...3800...Low................0.589
18000'.....406....mph...3200...High..................18000'.....429.9 mph...3800...Low...............0.603
20000'.....415....mph...3200...High..................20000'.....439.5 mph...3800...Low...............0.622
22000'.....425....mph...3200...High..................22000'.....450.1 mph...3800...Low...............0.642
.........................................................................23200'.....457.5 mph...3800...Low/ACA......0.656
23500'.....436....mph...3200...High/ACA..........23500'.....456.6 mph...3720...Low...............0.655
24000'.....432....mph...3130...High..................24000'.....448.8 mph...3660...Low................0.645
.........................................................................24200'.....453.6 mph...3600...High/Clutch...0.653
26000'.....429....mph...2960...High..................26000'.....465.4 mph...3600...High...............0.675
28000'.....427....mph...2640...High..................28000'.....475.7 mph...3600...High...............0.695
.........................................................................29200'.....484.1 mph...3600...High/ACA......0.711
30000'.....425....mph...2400...High..................30000'.....475.2 mph...3440...High...............0.701

 

[wuzak]

Makes sense as they could operate at higher altitudes.

The ratio was 3.4% for the Merlin 45 (9.1 vs 8.8), but the diameter was 7.9% greater (10.25" vs 9.5") so the tip speed was 11.6% higher for the Merlin 45.

That's the main reason it had a greater FTH, but not the only reason.

And this was to allow more power for low altitude?

The idea of having a 2 speed supercharger was to improve low altitude performance while maintaining, or improving, high altitude performance.

I would have figured they'd have been smaller in diameter but spun faster...

You'd be wrong.

The 2 stage supercharger for the Merlin required 2 different size impellers because they were fixed to a single shaft and spun at the same speed.

Initial production 60-series engines (61, 63) had an 11.5" 1st stage and 10.1" second stage. Later Merlins (from the 65/66) had 12.0" first stage supercharger.

There were a couple of different ratios for 2 stage engine, with the 61, 63, 70, etc., spinning faster for high altitude performance, while the 65 and 66 had a lower ratio for low(er) altitude performance.

The Packard 2 stage Merlins all seem to have had the 12.0"/10.1" supercharger from the start. The V-1650-3 and -9 had the high altitude gear ratios and the -7 had the low(er) gear ratios.

The Packard Merlins had slightly different ratios to the RR Merlins because they used a different supercharger drive.

The V-1710 did have a bolt-on provision off the bat for a turbocharger or a secondary supercharger stage, correct?

As the turbocharger could be basically bolted onto any engine, you could say all engines had this provision. Some worked better with it than without.

The main "provision" the V-1710 had to run the turbocharger was a lower supercharger drive ratio for models to be used with a turbo.

EDIT: Corrected the numbers for correct (9.5") V-1710 impeller size.

 

[wuzak]

My friend Ward Duncan, maint chief for the 9th PRS,sad that they raised the V-1710 supercharger gear ratio because on the earliest P-38's the turbo was having to wind up to such a high RPM that it was coming apart. The "fins" you can see between the turbos and the cockpit are designed to protect the pilot from a disintegrating turbo wheel.

I don't believe the supercharger ratio had much to do with the turbocharger overspeeding and flying apart. The problem persisted after the ratio was changed.

The issue is that wastegate regulation was unreliable due to how it was operated. This was changed it later models, and even later was changed to a different system.

The turbocharger was designed to provide sea level pressure to the engine, not for boost, so the engine's supercharger gear ratio was moot regarding the turbo's speed control.

 

[Zipper730]

The ratio was 3.4% for the Merlin 45 (9.1 vs 8.8), but the diameter was 7.9% greater (10.25" vs 9.5") so the tip speed was 11.6% higher for the Merlin 45.

That's the main reason it had a greater FTH, but not the only reason.

What were the other reasons, reasonably speaking?

The idea of having a 2 speed supercharger was to improve low altitude performance while maintaining, or improving, high altitude performance.

That adds up

As the turbocharger could be basically bolted onto any engine, you could say all engines had this provision. Some worked better with it than without.

Oh, I thought it would have been possible to bolt on a second-stage supercharger and the inter-cooling to go with it. How did the airflow requirements of the R-1820 or R-1830 compare with the V-1710.

I don't believe the supercharger ratio had much to do with the turbocharger overspeeding and flying apart. The problem persisted after the ratio was changed. . . The issue is that wastegate regulation was unreliable due to how it was operated. This was changed it later models, and even later was changed to a different system.

How did it regulate the wastegate?

 

[wuzak]

What were the other reasons, reasonably speaking?

Better impeller design, better intake.

Oh, I thought it would have been possible to bolt on a second-stage supercharger and the inter-cooling to go with it.

They could and did. Mainly I was responding to the turbocharger comment.

The 2nd stage of a 2 stage V-1710 was very much a bolt-on, unlike that of a Merlin, or just about any other 2 stage engine.

How did the airflow requirements of the R-1820 or R-1830 compare with the V-1710.

A little bit less than a V-1710, I would say, but well within the capabilities of the B-series turbocharger.

How did it regulate the wastegate?

Poorly!

An air line was connected from the compressor discharge to the regulator, but water would freeze in the lines and stop the regulator from working.

Then they changed the line to connect to the exhaust nozzle box.

The final solution was an electronic regulator.

 

[Shortround6]

Poorly!

An air line was connected from the compressor discharge to the regulator, but water would freeze in the lines and stop the regulator from working.

Then they changed the line to connect to the exhaust nozzle box.

The final solution was an electronic regulator.

I believe the early method was actually to measure the back pressure (exhaust pressure) before the wastegate and control the waste gate so it would maintain a certain value (or range) of exhaust pressure in the system to simulate sea level. It was thought that this would mean a turbo rpm and compressor pressure that would mimic sea level conditions as far as the carb on the engine supercharger was concerned (no real overboosting going on at this point). However, as anyone who as seen a car engine run on a cold day knows, there is water in the products of combustion and this water would freeze the sensor or the control.

I don't know how many changes they went through but the final solution was to measure the air pressure before it entered the carb (which was actually the important part) and then arrange the control box/linkage to open and close the wastegate to give them the desired intake pressure (supposedly sea level air pressure unless overboosting).

I sure don't want to get into an argument over electric or electronic and the definitions of each so I will leave my contribution as above. The locations if the sensor/s and actuator/s

 

[Zipper730]

I believe the early method was actually to measure the back pressure (exhaust pressure) before the wastegate and control the waste gate so it would maintain a certain value (or range) of exhaust pressure in the system to simulate sea level. It was thought that this would mean a turbo rpm and compressor pressure that would mimic sea level conditions as far as the carb on the engine supercharger was concerned (no real overboosting going on at this point). However, as anyone who as seen a car engine run on a cold day knows, there is water in the products of combustion and this water would freeze the sensor or the control.

Ouch...

While this might be a silly question, where is manifold pressure measured from? The fuel-air manifold, or the cylinders? It sounds like it should be what it says on the box, but...