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barfo1983
05-18-2009, 09:46 AM
I saw an Allison V-1710 the other day and the supercharger seems quite large, roughly the same size externally as the Merlinís. Why didnít GM redesign the supercharger to incorporate multiple speeds and/or stages? A quick goggle search shows that they did give it a somewhat half hearted effort but didnít use intercoolers and other anti detonation devices that the Merlin designers used.

Why didnít they devote more effort? It seems to me that retooling the supercharger would be simpler than fabricating all the tooling that Packard required to produce Merlins (including the Merlin supercharger) Come to think of it, why didnít GM license build the Merlin supercharger if they couldnít get their own design correct? I know they were devoted to using a turbo for the second stage but there would have been a pretty good market for a high altitude Allison without a turbo.

Just curious. I assume there were technical or political reasons, or even that the Packard Merlin was just a better or easier solution.

Thanks

Viper2005_
05-18-2009, 10:31 AM
From a technological perspective, the US was heavily invested in turbosupercharger technology.

This had some important consequences for engine manufacturers.

The most obvious one was that they had no incentive to develop high pressure ratio superchargers themselves. This meant that they had no great incentive to develop efficient superchargers; naturally enough they therefore didn't invest the large sums of money necessary to do this and so they didn't actually have the technology base to draw upon. The real turbo-machinery experts in the USA until Frank Whittle arrived with design drawings for his jet engine were GE and Westinghouse, and they were busy building steam turbines and turbosuperchargers.

Politically and financially, Packard tooled up to build Merlins because the British Government wanted to buy them to supplement Rolls-Royce's production capacity from a source not subject to disruption by German bombing. Had a customer with equally deep pockets asked for V-1710s then I have no doubt that V-1710s might equally have flowed from the Packard factories in vast numbers.

As for re-designing the V-1710 to take a Merlin supercharger, although this might theoretically have been done, it would not have been a trivial undertaking as detail design was somewhat different on each side of the Atlantic. Allison also had plenty of orders for the engine as it stood, and so didn't have an especially great incentive to go cap in hand to RR to ask for help with their supercharger technology. The V-1710 might not have been quite as good as the Merlin, but it was hardly a commercial or engineering failure.

The Mustang came into existence because the British Government wanted to buy P-40s from NAA, but NAA didn't want to build them, and undertook to design and build a fighter of equivalent performance in the same amount of time that would have been required for them to tool up for P-40 production in the first place. NAA originally selected the V-1710 for their aircraft because it was available - it would have been used in any P-40s they would have built had they not proceeded with the Mustang.

The Mustang was fitted with a Merlin after flight testing by Rolls-Royce demonstrated that it had exceptionally low drag and was only held back by the poor supercharger fitted to its V-1710. Development proceeded in parallel on both sides of the Atlantic, with RR developing the Mustang X (a few of which saw limited operational use) whilst NAA developed the P-51B. Since the USAAF had displayed interest in the P-51A, it was logical for them to extend that interest to encompass the P-51B.

After the War, when Packard ceased production of the V-1650, Allison built advanced versions of the V-1710 for use in the P/F-82 Twin Mustang. They also fitted an advanced V-1710 to the P-51J which was used for engine development work. The V-1710 never quite caught up with the Merlin because Allison lagged behind with their supercharger technology. However, the V-1710 had stronger con rods than the Merlin, and many racing Merlins flying at Reno today have been modified to take V-1710 con rods.

staticline1
05-18-2009, 05:17 PM
Nice read there viper. Didn't the P-51H have a newer version of the allison?

Viper2005_
05-18-2009, 05:19 PM
The H was powered by a V-1650-9 IIRC.

http://home.att.net/~jbaugher1/p51_13.html (http://home.att.net/%7Ejbaugher1/p51_13.html)

ElAurens
05-18-2009, 05:34 PM
Being a big fan of Packard automobiles the story we hear is that Chrysler desperately tried to get the contract to build Merlins, but Rolls Royce selected Packard because they were the only company that could build the engine to the tolerances set by Rolls Royce, and in the numbers wanted by the RAF.

Many folks often forget that Packard was very savvy on the engineering side, and designed/built some very fine automotive and marine engines. The V-12 Packards of the late thirties had one of the best engines ever put in an automobile, regardless of country of manufacture. If you have ever heard one run you would know what I'm talking about.

And not to diss Allison. The turbosupercharged V 1710 in the P38 was a stellar performer once the bugs with the intercoolers were worked out.

IF the Army had not dropped the turbocharged Allison engine from the P-39 we might be speaking of the "Iron Dog" in a completely different light today.

horseback
05-18-2009, 06:13 PM
IF the Army had not dropped the turbocharged Allison engine from the P-39 we might be speaking of the "Iron Dog" in a completely different light today. Yeah--great performance, less firepower than the Jug, no legs.

But 601 Squadron would have had a LOT more fun in '41...

cheers

horseback

barfo1983
05-18-2009, 07:31 PM
Thanks for all the good info everyone

ELAurens When you mention Packardís auto and marine V-12s donít forget about the Liberty airplane engine and its even neater version, the 4M-2500 that was used in PT boats. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Iíve also heard about RR selecting Packard because they were the only manufacturer that could build the Merlin to their tolerances but I've never been able to find a good source for it. Have you? I can buy that Packard was the only company that had the manufacturing capacity available but why would they be able to build an engine to tighter specs than any other automotive company. Actually, the larger companies probably had more advanced automated machine tools than Packard, no? I used to be a machinist so I just find it kind of interesting. I know that Packard made a lot of changes to the design to aid manufacturing.

There are a lot of interesting pictures of the abandoned Packard plant on the web.
A good search string is ďPackard RuinsĒ

ElAurens
05-18-2009, 07:54 PM
Well, actually having worked on many pre war Fords, Chevrolets, Plymouths, and Packards, I can say that the "big three" could not hold a candle to Packard's abilities, especially in engines. I really don't think the big companies had the ability, experience, and more importantly, the mindset to do Rolls Royce quality work. Packard had the trained workforce and tools already in place, wheras Ford, Chevy, et al, would have had to invest in different tooling and undertake a major training program. Though Ford did build Pratt and Whitney radials, but that is a different kettle of fish entirely, and GM already had the Allison Division and more than enough work already building V 1710s.

Buzzsaw-
05-18-2009, 08:19 PM
Salute

Very interesting and informative material presented by Viper and El Aurens. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Question for you gentlemen:

The P-63A KingCobra used the Allison V-1710-93 with a single-stage supercharger and auxiliary hydraulic turbosupercharger. Who was the manufacturer and what was the model of this Turbosupercharger? Was it related to the one used on P-38's? Or was it a developed member of the same family?

I know the P-63B was scheduled to be powered by a V-1650-5 Packard Merlin, was there a problem with the Allison installation?

After that I understand Bell went back to the Allisons.

Thanks in advance

R_Target
05-18-2009, 08:54 PM
I've never read of a turbo on the P-63. What I have on the V-1710-93 installation says two stage SC with dry and wet Combat Power.

Buzzsaw-
05-18-2009, 09:00 PM
Originally posted by R_Target:
I've never read of a turbo on the P-63. What I have on the V-1710-93 installation says two stage SC with dry and wet Combat Power.

Maybe I'm wrong. I got the info from Joe Baugher's site, which is usually pretty accurate.

http://home.att.net/~jbaugher1/oldseriesfighters.html (http://home.att.net/%7Ejbaugher1/oldseriesfighters.html)

But as I said, I don't know a lot about this, hence my questions.

ImpStarDuece
05-18-2009, 09:15 PM
Joe Baugher's site states that the Merlins for the proposed P-63B were instead allocated to Mustang production. P-51s had higher production priority, as I understand it.

The P-63C entry states that the engine for the P-63C was a V-1710-117, 1,500 hp dry rating, 1,800 hp WEP with water injection. As far as I can find (paper resources are all packed up from moving at the moment), the -117 was a two stage, two speed supercharged engine, not a turbosupercharged engine.

The P-63A reference contains a strange reference to the V-1710-93, with a "single-stage supercharger and auxiliary hydraulic turbosupercharger", which is odd.

I've got some fairly detailed references to P-63 engine and SC installations at home though, maybe I can clear it up there.

ImpStarDuece
05-18-2009, 09:34 PM
Just did a little digging on the NACA/NASA database.

What I could find was that the V-1710-93 had a "auxiliary stage supercharger", from a bunch of post war tests done to increase power output and altitude performance.

Some interesting documents there.

I'm not 100% sure on the terminology, but it seems to me that the NACA breaks supercharging down into "engine stage" (1st stage or MS in British parlance) and "auxiliary stage" (second stage or FS in British parlance).

Kettenhunde
05-18-2009, 09:49 PM
(1st stage or MS in British parlance) and "auxiliary stage" (second stage or FS in British parlance).

Interesting read, Viper.

Anybody know if MS and FS stands for "Motor Stage" and "Flight Stage"?

All the best,

Crumpp

M_Gunz
05-18-2009, 10:24 PM
Originally posted by barfo1983:
Actually, the larger companies probably had more advanced automated machine tools than Packard, no? I used to be a machinist so I just find it kind of interesting.

The big companies were used to running high production rates at cost-effective tolerances? How likely the
advanced part for them was in fast production rather than constantly adjusting for tool wear?
The difference could easily be in QC and shop management as well as a different attitude from the floor up.
Having extra-sharp shop foremen and machinists who work well together isn't something you just go hire.
It's like the difference between a production shop and tool-makers.

R_Target
05-18-2009, 10:45 PM
Cutaway view.

http://i43.tinypic.com/n2blzs.jpg

ImpStarDuece
05-18-2009, 10:56 PM
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">(1st stage or MS in British parlance) and "auxiliary stage" (second stage or FS in British parlance).

Interesting read, Viper.

Anybody know if MS and FS stands for "Motor Stage" and "Flight Stage"?

All the best,

Crumpp </div></BLOCKQUOTE>

I'm not Viper, but it was my post you were replying to.

Anyway:

MS = Moderate Supercharge(r)/ moderate speed
FS = Full Supercharge(r)/ full speed

The terms seem to have been used somewhat interchangably, although the majority of wartime literature I've read, particularly British technical documentation, tends to use the moderate/full supercharge(r) usage.

julian265
05-18-2009, 11:15 PM
Originally posted by barfo1983:
Why didnít they devote more effort?

Often this happens (private and government, in war and peace) because the people who make the big decisions don't have a clue about the stuff that they're deciding. They are also making judgements based on different criteria than the end user would use.

Kettenhunde
05-19-2009, 12:07 AM
The terms seem to have been used somewhat interchangably, although the majority of wartime literature I've read, particularly British technical documentation, tends to use the moderate/full supercharge(r) usage.


Thank you.

uppurrz
05-19-2009, 03:51 AM
Rolls-Royce went to Ford first. Ford of England built closer tolerance Merlins than did R-R. Negotiations with Ford of America fell through. Using the engineering drawings supplied by R-R, Ford of America went on to build its own V-12. After spending $2,000,000, they gave up. All was not lost thigh as 4 cylinders were removed from the V-12 to make a V-8. This engine was used in the M4 Sherman.

Has anyone noticed a red light on the instrument panel (to the left of the boost gauge) that comes on when the Merlin supercharger is in 'high' gear?

eindecker
05-19-2009, 05:42 AM
Originally posted by uppurrz:
Rolls-Royce went to Ford first. Ford of England built closer tolerance Merlins than did R-R. Negotiations with Ford of America fell through. Using the engineering drawings supplied by R-R, Ford of America went on to build its own V-12. After spending $2,000,000, they gave up. All was not lost thigh as 4 cylinders were removed from the V-12 to make a V-8. This engine was used in the M4 Sherman.

Has anyone noticed a red light on the instrument panel (to the left of the boost gauge) that comes on when the Merlin supercharger is in 'high' gear?

Yes, Ford was first.
Allison did indeed built 2 stage supercharged intercooled
engines for the P-63 and the P-82.
The P-63 did see service during WWII.
So the myth prevails but the truth is Allison
had a very nice two stage set up.
The Allison high blower stage was a variable drive that did not
cause the stepping in boost
pressures at different altitudes.
It was arguably the best two stage supercharger of the piston era.

Eindecker

hop2002
05-19-2009, 06:46 AM
I'm not 100% sure on the terminology, but it seems to me that the NACA breaks supercharging down into "engine stage" (1st stage or MS in British parlance) and "auxiliary stage" (second stage or FS in British parlance).

MS and FS refer to supercharger speeds, not stages. See for example the test of the Spitfire XII, which had a 2 speed, single stage Griffon:


Max. level speed in M.S. supercharger gear 372 m.p.h. at 5,700 ft.
Max. level speed in F.S. supercharger gear 397 m.p.h. at 17,800 ft.
http://www.spitfireperformance.com/dp845.html

barfo1983
05-19-2009, 07:44 AM
I would disagree with Uppurz a little bit. Ford of England did build a limited number of Merlins, as you said, and Ford did try to get win the Merlin contract in America but the license and contract went to Packard. They still wanted a piece of the airplane engine market so they then developed there own 60 degree V-12 that was an original design and not based on the Merlin. It was actually a bit more advanced with 4 valves per cylinder instead of the Merlinís two and with dual overhead cams which where shaft driven. Merlins only had one cam per bank. The block was also a single casting vs the split casting on the Merlin. It did have the same displacement as the Merlin but that was the only commonality. This was the engine that became the GAA Sherman engine when it was reduced to a V-8. Very neat engine.

hop2002
05-19-2009, 08:25 AM
Ford of England did build a limited number of Merlins

Ford built 30,428 Merlins, nearly 20% of the total.


It was actually a bit more advanced with 4 valves per cylinder instead of the Merlinís two

The Merlin had 4 valves per cylinder.


The block was also a single casting vs the split casting on the Merlin

The early Merlins used a single piece block, they switched to a 2 piece later in production, I believe they approached Ford in the US with the single piece design.

uppurrz
05-19-2009, 11:21 AM
Originally posted by barfo1983:
I would disagree with Uppurz a little bit. Ford of England did build a limited number of Merlins, as you said, and Ford did try to get win the Merlin contract in America but the license and contract went to Packard. They still wanted a piece of the airplane engine market so they then developed there own 60 degree V-12 that was an original design and not based on the Merlin. It was actually a bit more advanced with 4 valves per cylinder instead of the Merlinís two and with dual overhead cams which where shaft driven. Merlins only had one cam per bank. The block was also a single casting vs the split casting on the Merlin. It did have the same displacement as the Merlin but that was the only commonality. This was the engine that became the GAA Sherman engine when it was reduced to a V-8. Very neat engine.

From Graham White's book Allied Aircraft Piston Engines of WW2

http://img.villagephotos.com/p/2005-12/1114844/MerlinFord2.jpg

VW-IceFire
05-19-2009, 04:43 PM
Originally posted by eindecker:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by uppurrz:
Rolls-Royce went to Ford first. Ford of England built closer tolerance Merlins than did R-R. Negotiations with Ford of America fell through. Using the engineering drawings supplied by R-R, Ford of America went on to build its own V-12. After spending $2,000,000, they gave up. All was not lost thigh as 4 cylinders were removed from the V-12 to make a V-8. This engine was used in the M4 Sherman.

Has anyone noticed a red light on the instrument panel (to the left of the boost gauge) that comes on when the Merlin supercharger is in 'high' gear?

Yes, Ford was first.
Allison did indeed built 2 stage supercharged intercooled
engines for the P-63 and the P-82.
The P-63 did see service during WWII.
So the myth prevails but the truth is Allison
had a very nice two stage set up.
The Allison high blower stage was a variable drive that did not
cause the stepping in boost
pressures at different altitudes.
It was arguably the best two stage supercharger of the piston era.

Eindecker </div></BLOCKQUOTE>
Interesting...so now...why didn't it get used anywhere else? Show up too late to be used in the development of other types except the P-63C?

eindecker
05-19-2009, 05:11 PM
Originally posted by VW-IceFire:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by eindecker:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by uppurrz:
Rolls-Royce went to Ford first. Ford of England built closer tolerance Merlins than did R-R. Negotiations with Ford of America fell through. Using the engineering drawings supplied by R-R, Ford of America went on to build its own V-12. After spending $2,000,000, they gave up. All was not lost thigh as 4 cylinders were removed from the V-12 to make a V-8. This engine was used in the M4 Sherman.

Has anyone noticed a red light on the instrument panel (to the left of the boost gauge) that comes on when the Merlin supercharger is in 'high' gear?

Yes, Ford was first.
Allison did indeed built 2 stage supercharged intercooled
engines for the P-63 and the P-82.
The P-63 did see service during WWII.
So the myth prevails but the truth is Allison
had a very nice two stage set up.
The Allison high blower stage was a variable drive that did not
cause the stepping in boost
pressures at different altitudes.
It was arguably the best two stage supercharger of the piston era.

Eindecker </div></BLOCKQUOTE>
Interesting...so now...why didn't it get used anywhere else? Show up too late to be used in the development of other types except the P-63C? </div></BLOCKQUOTE>

As it was posted eariler the USAAF was heavily invested in turbocharging.
The two stage Allison V-1710 went into only two production aircraft
that I am aware of.
There were a number of prototypes and paper airplanes that were
to use the two stage or the turbo compounded Allison.
Notably the last P-51 prototype the P-51J
and the The Douglas B-42 Mixmaster.

Eindecker

VW-IceFire
05-19-2009, 05:13 PM
I know about the turbocharging...but it sounds like this Allison could have been useful to the P-40 as well.

I'm just curious I guess on the timelines. Was this an engine available in 1942 for instance or later on?

eindecker
05-19-2009, 05:27 PM
Originally posted by VW-IceFire:
I know about the turbocharging...but it sounds like this Allison could have been useful to the P-40 as well.

I'm just curious I guess on the timelines. Was this an engine available in 1942 for instance or later on?

P-40Q was fitted with the two stage Allison as well, it was a top performer
but was to late to see production.

Editing this to complete the answer.

Allison had run two stage engines before WWII began for the US.
My information says 1938.
One interesting little known fact is that the Merlin equipped P-40s
were at least as poor in performance as the Allison equipped planes.
Those Merlins in the P-40s were also not equipped with a two stage supercharger.
Curtiss P-40F and P-40L were equipped with Packard Packard-built Merlin V-1650-1 rated
at 1300 hp for takeoff and 1120 hp at 16,000 feet.
Performance was no better than the Allison V-1710-81 and most that remained stateside were re-engined to the Allison powerplant.

Eindecker

Kettenhunde
05-19-2009, 11:02 PM
I've never read of a turbo on the P-63. What I have on the V-1710-93 installation says two stage SC with dry and wet Combat Power.


The XP-63 was supposed to have a turbo-compound engine not turbocharged.

http://www.enginehistory.org/v1710tc.htm

All the best,

Crumpp

M_Gunz
05-19-2009, 11:39 PM
I've wondered how much you could tap exhaust flow without spoiling outflow from the cylinders.
I does leave me wondering what the Mustang would have done with exhaust directed into the rear
of the radiator box as Meredith had written about thinking of doing.

Kettenhunde
05-20-2009, 12:21 AM
I've wondered how much you could tap exhaust flow without spoiling outflow from the cylinders.
I does leave me wondering what the Mustang would have done with exhaust directed into the rear of the radiator box as Meredith had written about thinking of doing.


That was the major issue with the radiator thrust production in the Mustang. The outlet temperature was too low to produce anything usable.

IIRC, Focke Wulf experimented with this as well and found it problematic keeping the EGT high enough with the radiator located mid-fuselage.

All the best,

Crumpp

ImpStarDuece
05-20-2009, 01:14 AM
Originally posted by eindecker:

Performance was no better than the Allison V-1710-81 and most that remained stateside were re-engined to the Allison powerplant.

Eindecker

Given that the full throttle height was about 8,000 feet higher, performance and climb at altitude was significantly better with the P-40s equipped with the V-1650-1 rather than with the V-1710-81. Conversely, climb performance and speed at low altitude was much worse with the V-1650 fitted.

The V-1710-81 in the P-40N/P gave 1,200 hp at take off, but 1,480 hp at 10,500 ft at 57.0" mainfold pressure.

The V-1650-1 in the P-40F gave 1,120 hp at 48" manifold at 20,000 feet, or 1,280 hp at 19,000 at 52" manifold. The engine was eventually cleared for 1,380 hp at 56" manifold, but I'm unsure if this was used operationally on P-40F/Ls

Above 15,000 feet the V-1650 powered P-40s are clearly faster, by as much as 25 mph at some altitudes. Rate of climb is only marginally better, probably due to the V-1650 variants being more than 1,000 lbs heavier when loaded.

Buzzsaw-
05-20-2009, 01:48 AM
Originally posted by Kettenhunde:

That was the major issue with the radiator thrust production in the Mustang. The outlet temperature was too low to produce anything usable.



Not according to a lot of very knowledgeable people:


To complement the aerodynamic efficiency, the placement of the drag-producing radiator and oil-cooler intake was another engineering success. The design engineers wanted to avoid placing the air scoop in the conventional position under the nose thereby reducing the drag factor on the airplane. The radical placement of the redesigned streamlined scoop on the underside of the fuselage, just aft of the pilot, resulted in significantly less resistance. Initially this location proved inadequate in terms of cooling efficiency of the engine, so the engineers then lowered the entrance to the scoop about one inch which bypassed the turbulent layer of air on the underside of the fuselage. This position not only reduced drag and produced an efficient cooling system, but completely by accident, the radiator design actually provided about 300 pounds of jet thrust in a manner similar to a ramjet as the heat energy thrust was dissipated from the exit scoop.

From the USAF Thesis I linked in another thread:

http://www.google.com/url?sa=t...VOWcCn8TSo1Z6cx6ht-w (http://www.google.com/url?sa=t&source=web&ct=res&cd=18&url=https%3A%2F%2Fwww.afresearch.org%2Fskins%2Frim s%2Fq_mod_be0e99f3-fc56-4ccb-8dfe-670c0822a153%2Fq_act_downloadpaper%2Fq_obj_d1d0fb6 b-72fa-4abe-8ec1-1a8b43d032ab%2Fdisplay.aspx%3Frs%3Denginespage&ei=IaMTSoKvB5m-tAP88PnuDQ&rct=j&q=Naca+evolution+of+fighter+aircraft&usg=AFQjCNGdjDFYzSVOWcCn8TSo1Z6cx6ht-w)

(please note the references)

Kettenhunde
05-20-2009, 02:30 AM
but completely by accident, the radiator design actually provided about 300 pounds of jet thrust in a manner similar to a ramjet as the heat energy thrust was dissipated from the exit scoop.



the drag created by momentum loss in passing through the radiator can be reduced from some 400 pounds to close to 30 to 40 pounds because of the offsetting momentum of the jet thrust from the radiator exit (V2).

400lbs of drag minus 300lbs of thrust equals 100 lbs of drag.....

The radiator produces no net thrust.

http://findarticles.com/p/arti...29/?tag=content;col1 (http://findarticles.com/p/articles/mi_qa3897/is_199906/ai_n8870829/?tag=content;col1)


The "lot of very knowledgeable people" is one Air Force Officer writing her a paper for a War College assignment. The quote is correct but is taken out of context.

The unknowledgeable come along, see it out of context, and get suckered into claims they don't understand.

Physics says if you get the outlet temperature high enough it will produce thrust.

Facts are though the radiator just could not heat the air high enough.

It did produce some thrust and for a radiator quite a bit of thrust. It certainly helped to offset the drag of the system and contributes to the over all low drag of the design.

You can believe what you wish on this subject. In fact, you can lump it in with your ďinteresting in a train wreck sort of wayĒ theories on the effects of laminar flow.

Take care and good luck, Buzzsaw.

All the best,

Crumpp

eindecker
05-20-2009, 05:52 AM
Originally posted by M_Gunz:
I've wondered how much you could tap exhaust flow without spoiling outflow from the cylinders.
I does leave me wondering what the Mustang would have done with exhaust directed into the rear
of the radiator box as Meredith had written about thinking of doing.

Merideth effect in the P-51 cancled drag.
It's still thrust.

There are two different ways to recover exhaust energy in
a turbo compounded engine. Blowdown and pressure turbines.
The Allison used the pressure turbine.
Curtiss Wright used the blowdown on it's R-3350TCW radials.
The primary difference is the blowdown turbine harness the shock wave when the exhaust valve is opening.
Pressure turbines harness the hot flow mostly devoid of the shock wave.
Pressure turbines give greater recovery at high power settings but also cause greater back pressure. Little or no power is recovered at low power settings.
Blowdown types give greater power recovery at all power settings from idle
to cruise settings. They cause little or NO back pressure.
Generally about 20% was recovered with both types.
The Allison could recover nearly 30% at WEP power.

Eindecker

Kettenhunde
05-20-2009, 06:02 AM
Merideth effect in the P-51 cancled drag.
It's still thrust.


It produced drag just like all radiators.

It produced less drag than other radiators designs.

M_Gunz
05-20-2009, 08:58 AM
From Meredith's notes I have seen that it only gets the low net drag at high speeds.

eindecker
05-20-2009, 06:26 PM
Originally posted by M_Gunz:
From Meredith's notes I have seen that it only gets the low net drag at high speeds.

The military cruise speed (maximum sustainable speed without over heat)
for a P-51D was about 390mph at 25,000 feet.
High speed was the realm of the P-51, the Meredith effect
was real and helped to provide thrust to override parasitic drag.
Call it what you will, the radiator installation in the P-51 was very low drag.

A quick note on Turbo compounding, power recovered in the Allison
tests was about 750HP.
The Wright R-3350TCW series saw wide spread use and development.
Peak power recovered was nearly 1000hp.

Eindecker

Kettenhunde
05-20-2009, 08:38 PM
the radiator installation in the P-51 was very low drag.


Correct!

A very different statement and concept from one of the system producing thrust.

All radiator systems have an outlet that cancels some of the drag of the system.

It's designed that way!

http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

All the best,

Crumpp

Tully__
05-26-2009, 06:11 AM
I've cleaned up.
Those whose posts are missing, you may be getting a PT from me. If you don't get one, you're safe.

Doug_Thompson
05-26-2009, 10:35 AM
I look forward to reading all of this thread when I get the chance.

In the meantime, Packard should be given its due (if it hasn't already and I've just missed it.)

They did make important engineering and manufacturing improvements on the Merlin. They had high quality but had considerable technical expertise too. They did more than build the engine to the same high standard.