SHOULD the P39 have been able to handle the Zero? Was it training or performance?

[wuzak]

[QUOTE="MIflyer, post: 1392532, member: 42472]From a mechanical engineering standpoint it would have been child's play to add a 2nd speed to the V-1710's single stage supercharger. Given that the V-1710 was built in an automotive fashion, with engine block, gearcase, and accessory section as separate section it would have far easier than with the one-piece Merlin engine case and need not interrupt production. If required they could have gotten Continental or Maytag Washing Machines or some other company to build the new 2 speed section. Going the next step to a two stage two speed supercharger would have been more challenging, but well within their capabilities. As it was, Packard redesigned the Merlin supercharger for easier production and had Wright redesign the impeller. [/QUOTE]

Wright did not redesign the impeller of the Merlin. They produced the 2 speed dive for Packard Merlins, which was an epicyclic type, rather than the Farman type used by Rolls-Royce. The fact that Rolls-Royce used the Farman gearbox under licence may have had something to do with it.

Don't know that Packard did any significant redesign of the supercharger, to ease production or otherwise.

Packard Merlins retained the same ratings as their British equivalent, the 2 speed drives more or less had the same gear ratios as the Rolls-Royce equivalent.

Packard Merlins were 3 piece designs. There was the crankcase, the cylinder blocks and the cylinder heads. This was developed by Rolls-Royce as their single block head design was difficult to seal. Packard went into production with the separate head design from the outset. Packard developed their own method of sealing between the head and the block, but later changed to be the same as Rolls-Royce.

Merlins weren't designed to be as modular as the V-1710 was, that is true, so changing required some redesign of the crankcase.

 

[wuzak]

"It was a very special airplane, let's say, with the engine in the back, then those Italian maniacs always wanted do aerobatics, when they looped they came in this position and then had to continue, but it was too slow and instead of lowering the head, which it did not have ( for the position of the engine) they went in a flat spin and so they were screwed so a very good Genoese Pilot, Moresi left his skin, another Sergeant left his skin, even though they were saying, ehhhh, do you know what I say, if you loop, do it fast, but for me it was a fabulous plane because it had a tricycle undercarriage, on the ground it was driven like a car, apart from this tricycle undercarriage it had in the axis of the propeller a cannon of 37 and four machine guns on the wings the engine was a 1200 hp Allison a beautiful engine it was a very pretty airplane…"

I'm pretty sure I know what that means but just for clarification ( for my small brain ), I assume they were killed?

I'm pretty sure it means they were scared shitless, not that they did.

 

[wuzak]

The Merlin system worked but it was also a bit on the crude side (at first look) and many engineers were trying to go one better. The Merlin ALWAYS both impellers spinning at the same time and spinning at the same speed. Effective but not very flexible with a two speed drive. P & W's two stage (first flown in 1939 so two stage superchargers aren't unknown in the US) had a single speed supercharger on the engine and a two speed drive with neutral on the auxiliary supercharger drive given three possible combinations. Allison stuck a hydraulic coupling in the drive the auxiliary supercharger giving an infinite number of combinations between a high and low limit. More elegant from an engineering point of view but you had to pay for it somehow.

The advantage of the Merlin's system was that the two stages were always synchronised and matched for flow. With a separate auxiliary stage which could operate at different speeds to the main supercharger there was a risk of the superchargers being mismatched, causing surging.

The air to air intercooler is more resistant to battle damage. A liquid intercooler suffers just alike a liquid radiator from one or two minor hits. A couple pencil size holes in the airducts of an air to air intercooler isn't going to affect things that much. However keeping all those airducts air tight in day to day operation was more maintenance intensive. You pay your money and take your chances.

The air to air intercooler also had the problem that it needed to be in close proximity of the engine, or that the supercharger discharge goes on a world tour before getting back to the engine.

The liquid to air intercooler gave more options in the location of the radiator section, which could be quite remote from where the engine was.

 

[parsifal]

whats surging? I have an idea, but not certain really.

 

[wuzak]

Just my opinion, but what the Allison needed was not a two speed supercharger but a (mechanical, not turbo) two stage supercharger.

Not an unreasonable position.

We've had the two speed argument here before, and I still maintain that low gear's purpose is just to keep the pilot from overboosting the engine at takeoff and low altitude. The P-39 had plenty of performance at low altitude with their single speed unit regulated by the pilot in early models and the automatic boost control after mid '42. The Allison's single speed was in effect "high" gear, and the need for low gear was eliminated by the autoboost control. The whole two speed vs one speed argument is moot in my opinion.

You can maintain your opinion, but it is still wrong.

Yes, a 2 speed supercharger in high gear could easily overboost the engine at low altitude. The same could be said for most 2 speed engines' low gear as well. That is what the throttle is for - to control the boost. That is true whether it is high gear or low gear.

Throttling, of course, costs power.

A lower speed 2nd gear would have allowed more power from the V-1710 at low altitude.

But also needed a better supercharger.

The two STAGE engine was needed to keep up with the two STAGE Merlin 61 and the two stage R-2800s. The two stage engine provided more power at higher altitudes because the first (or auxiliary stage whether it be mechanical or turbo) stage boosted the thin air at high altitude up to sea level thickness and discharged it into the second (internal) stage which boosted it even further to get those fantastic speeds at high altitude. In effect, the first stage fooled the second stage into thinking it had sea level (high density) air at 25000' boosting power tremendously.

Note that the P&W 2 stage engines, at least early in the war, weren't rated at very high altitudes.

The Merlins came in several varieties, of course. Low altitude versions, like the 66/V-1650-7 sacrificed high altitude performance for more at low and mid altitudes. The 61, 63, and 70 series had higher gear ratios and this higher critical altitudes.

In Merlin 2 stage superchargers there was no fooling the "second stage into thinking it had sea level pressure". The first and second stage both provided boost, as such, having similar pressure ratios (that is, for example, the first stage PR was 2:1, the second stage was 2:1 for an overall of 4:1. I am away at the moment so can't get the proper numbers, maybe SR could fill in the blanks).

The fooling you speak of describes how turbocharged engines worked, for the most part, in WW2.

Note that the 2 stage engines also had multiple speeds. The Merlin and Griffon had 2 speeds, except the Griffon 100 series, which had 3 speeds.

2 stage Jumo 213s had 3 speeds.

V-1710 had variable speed auxiliary supercharger.

P&W had 2 speeds plus natural on their 2 sage engines.

 

[wuzak]

whats surging? I have an idea, but not certain really.

I don't have a good explanation.

This might help Centrifugal Compressor Surge - EnggCyclopedia

 

[wuzak]

On the very early P-38's they had to change the supercharger gear in the V-1710 to increase the boost from the mechanical supercharger so they could reduce the boost required from the turbo at high altitudes. Early on they had a problem with the turbos coming apart at high boost. Those "fins" on the side of the booms between the cockpit and the turbos were shields to protect the pilot from disintegrating turbochargers.

The turbos came apart from overspeeding, which was traced back to the wastegate controls, which could freeze at high altitudes.

If P-38s had gears changed it was to give more boost and power.

 

[pbehn]

My head is now hurting. Can someone tell me any area of performance that the latest P-39 was superior to the Spitfire IX or XIV, P-51-B/C, P47 and F4U as of 25 December 1943?

 

[wuzak]

The fuselage was indeed lengthened by 1.75' but that was their solution to the extra 200# from the auxiliary stage supercharger. Adding 200# aft of the CG necessitated moving the wing back a little for balance, then the tail had to be moved back to preserve the distance from the CG to the tail for the same leverage. That is why the front cockpit door edge is before the wing leading edge (same as the P-63) while the normal P-39 front door edge is right about even with the wing leading edge. They moved the wing back.

Now is where I differ from what you have read. The engine compartment for the P-39E and the P-63 was still exactly the same size as the P-39. The distance from the front edge of the engine compartment (right before the exhaust stacks at the cockpit turnover structure) and the back bulkhead (almost to the back edge of the carb inlet scoop, you can see the panel edges) is EXACTLY the same.

Looks like the V-1710 is a tight fit in the P-39

http://www.fiddlersgreen.net/aircraft/Bell-P39-Airacobra/IMAGES/Bell-P-39-Airacobra-Cutaway.jpg

 

[MIflyer]

If you are getting hit in liquid cooled airplane the intercooler/aftercooler is the least of your worries! The aftercooler on the Merlin was right up there behind the engine and the coolant radiator was built into the main radiator. On the Spit IX the added coolant radiator for the aftercooler was located in the same under-wing housing as the oil cooler. Hard to see how you could get hit in either the aftercooler itself or the coolant radiator for it and not lose capabilities that were far more important - like engine cooling and oil.

Packard had to a lot of work on the Merlin because they could not use the RR approach of experienced craftsmen, who hand-selected each part. Packard wanted to put Merlins together like an American automobile engine, and to do that they had to make the parts to tighter tolerances than did RR.

 

[wuzak]

My head is now hurting. Can someone tell me any area of performance that the latest P-39 was superior to the Spitfire IX or XIV, P-51-B/C, P47 and F4U as of 25 December 1943?

It was far superior in the size and uselessness of its main cannon.

 

[wuzak]

Packard had to a lot of work on the Merlin because they could not use the RR approach of experienced craftsmen, who hand-selected each part. Packard wanted to put Merlins together like an American automobile engine, and to do that they had to make the parts to tighter tolerances than did RR.

Bollocks.

This is the biggest myth surrounding the Merlin, probably.

The Merlin had already be productionised in the UK by (or for) Ford, and this was used in most Merlin factories.

Rolls-Royce Derby possibly continued the practice of hand fitting stuff, but then they were doing most of the prototyping and development. And their production numbers were small compared to the shadow factories.

Packard had to change the drawings from 1st angle projection to 3rd angle projection so that their machine operators, inspectors, etc, could read the drawings.

Note that components built in Britain were interchangeable with parts from the US (excepting parts like the supercharger drive, which was of a different design for Packard).

 

[pbehn]

It was far superior in the size and uselessness of its main cannon.

I believe the Mosquito had a bigger cannon but size doesn't matter Daaaahling

 

[wuzak]

I believe the Mosquito had a bigger cannon but size doesn't matter Daaaahling

The Mosquito wasn't in the list .

Besides, the Mosquito wasn't a fighter, but a fighter bomber, and its cannon was useful!

 

[pbehn]

The Mosquito wasn't in the list .

Besides, the Mosquito wasn't a fighter, but a fighter bomber, and its cannon was useful!

I was of course (in that post) joking, but in principle I cannot see any advantage the P 39 had over any other allied fighter, bearing in mind the Allies as a group had to defend daylight bomber boxes, defend the UK from any attack by any type of aircraft S/E T/E or buzz bomb and achieve air supremacy over Italy, Normandy and the Pas de Calais ...That is just European requirements.

 

[Shortround6]

Packard had to a lot of work on the Merlin because they could not use the RR approach of experienced craftsmen, who hand-selected each part. Packard wanted to put Merlins together like an American automobile engine, and to do that they had to make the parts to tighter tolerances than did RR.

can we please, please, please forget this myth. Ford of England had already gone through that before Packard ever got involved.
I would also note that Packard in the 1930s was America's premier auto maker with more prestige than Cadillac. While not quite the craftsmen RR had Packard was turning out a fraction of the cars the mass auto makers were.

Such cars were not punched out by untrained labor.

 

[Shortround6]

My head is now hurting. Can someone tell me any area of performance that the latest P-39 was superior to the Spitfire IX or XIV, P-51-B/C, P47 and F4U as of 25 December 1943?

Lawn dart?

 

[Elmas]

I'm pretty sure it means they were scared shitless, not that they did.

No, they were killed, and they were just two of many, with P-39.
Even Teresio Martinoli, one of the top Italian scorers, was killed in a P-39, when a worn out Allison failed.
And for an accident in which a Pilot lost his life with a P-39 there were dozens of other scaring situations where a mallet was needed to insert a pin into a particular anatomical formation of a Pilot, which I do not intend to mention now.

"In june-july 1944, Italians Gruppi 12, 9, 10, 4 moved to Campo Vesuvio
airstrip to re – equip with the P39s.
The site was not suitable and in three months of training 11 accidents
occurred, due to engine failures and poor manteinance of the base.
Three pilots died and two were seriously injured: one of the victims on 25th aug
1944 was the "ace of the aces" Teresio Martinoli."

CURRENTJ.D., American Warplanes of World War Two, Pedia Press, p. 208

 

[P-39 Expert]

I would note that the main difference between a good mechanical two stage system and a good turbocharger tow stage system is that in the turbo system the auxiliary supercharger is driven by an exhaust gas powered turbine and not a driveshaft from the engine.
You still need the auxiliary impeller and casing and you still need the intercooler and ducting (or intercooler radiator).
Anybody who thinks you can have a significantly smaller mechanically driven two stage system is either settling for less performance or fooling themselves.

The big advantage of the Allison mechanical two stage over the turbo is it takes up much less internal volume. In addition to the actual turbo there was the associated internal ducting (14' per engine in the P-38). The exhaust had to be ducted back to the turbo, the compressed turbo air had to be ducted back up to the intercooler (in the wing on F,G and H) then that air had to be ducted to the carburetor. All this ducting had to be properly aligned and sealed for the whole thing to work right.

The Allison mechanical two stage engine simply ducted the ambient air from the external scoop to the carburetor on the first stage and a short duct to take that compressed air to the internal supercharger. The intercooler was not needed except for WEP and that was cooled by the water injection. All was enclosed in the normal engine bay of the P-63 except for the small water tanks in the leading edge.

The turbo developed a little more power at the expense of all that internal room needed. Turbos worked best on multi engined planes because of their greater internal volume. A single engined turbo plane is the P-47 which was huge for a fighter of that day.

 

[P-39 Expert]

Not only lacking wing gun drag, lacking around 1000lbs of weight compared to a service P-63.
The graphs give no description of the aircraft involved.

I also love the part in an earlier post about the V-1793 being in full production in May of 1943.
May of 1943 saw the engine fully prepared for the model test, which was not actually fully completed until Nov 27th 1943. Yes engines had been built, delivered and were flying in P-63s before Nov 27th but after that date the engines were released for unrestricted use. Except the WER rating test was done in Dec of 1943 so any fantasies of P-63s or Super Allison Mustangs flying around with 1800hp at sea level engines need a reality check. Especially considering that the long development time included modified pistons and piston rings to stand up to the water injection and extra power.

We must be reading the same book. The -93 was in production in May and the model tests were not yet completed but the Army had sufficient confidence in the engine to start putting it in airplanes prior to test completion. After a short rework of the jackshaft these engines were considered very reliable. The development of the piston rings etc. benefited all Allison engines, not just this one.

The -93 was not really a new "engine". The only thing new about the -93 was the auxiliary stage, the power section was the same as the other contemporary Allison engines. The auxiliary stage was just an impeller inside a diffuser driven by an external shaft from the engine. There were also the step up gears with the hydraulic coupling. Why it took from 1940 until late 1943 to get this auxiliary stage working properly is a mystery to me. This two stage Allison would have really improved the P-39, P-40 and even the P-51.