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Lateralus_14
10-15-2004, 08:12 PM
Why wasn't this ever considered? According to most sources, the P-51 got an enormous performance increase from changing from an Allison to a Rolls-Royce Merlin engine. Considering also that the P-38 used the Allison for the duration of the war, why wasn't this arrangement tested or, evidently, even considered?

Where there technical problems? The Merlin doesn't seem to be physically much larger or heavier than the Allison, so that doesn't seem to be it.

The benefits seem to be numerous:

The performance benefits that the P-38 would recieve, particularly at high-altitude. Some recounts of P-38 pilots flying over Europe explain how the plugs would often foul, or some system, exactly which I cannot recall, would malfunction, resulting in two settings: one so low that it would not sustain flight, or another so high that it would blow up a supercharger. Others talk about how at altitude engine management was so difficult that it required all of the skill and focus of the pilot, not even considering going into combat in such a beast.

Ease of production. I'm not sure what other fighters used the Allison; the only one I can think of is the P-40, which by mid-war was not a first-rate fighter. If yet another fighter made the transition to using Merlins, wouldn't this make mass production easier due to streamlining of the manufacturing process?

DangerForward
10-15-2004, 08:42 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Lateralus_14:
Why wasn't this ever considered? According to most sources, the P-51 got an enormous performance increase from changing from an Allison to a Rolls-Royce Merlin engine. Considering also that the P-38 used the Allison for the duration of the war, why wasn't this arrangement tested or, evidently, even considered?

Where there technical problems? The Merlin doesn't seem to be physically much larger or heavier than the Allison, so that doesn't seem to be it.

The benefits seem to be numerous:

The performance benefits that the P-38 would recieve, particularly at high-altitude. Some recounts of P-38 pilots flying over Europe explain how the plugs would often foul, or some system, exactly which I cannot recall, would malfunction, resulting in two settings: one so low that it would not sustain flight, or another so high that it would blow up a supercharger. Others talk about how at altitude engine management was so difficult that it required all of the skill and focus of the pilot, not even considering going into combat in such a beast.

Ease of production. I'm not sure what other fighters used the Allison; the only one I can think of is the P-40, which by mid-war was not a first-rate fighter. If yet another fighter made the transition to using Merlins, wouldn't this make mass production easier due to streamlining of the manufacturing process? <HR></BLOCKQUOTE>

It was looked at, they tested a merlin powered P38J and calibration tests showed an estimated gain of 38mph in speed. Supposedly the project was discontinued for "political reasons". How's that for an uber-never-flown plane? http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Lateralus_14
10-15-2004, 08:48 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by DangerForward:
It was looked at, they tested a merlin powered P38J and calibration tests showed an estimated gain of 38mph in speed. Supposedly the project was discontinued for "political reasons". How's that for an uber-never-flown plane? http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif <HR></BLOCKQUOTE>

Is that the only statistic? 38 extra MPH? I'd be more interested in knowing the changes in high-altitude performance, the difference in range, acceleration, weight differences, etc.

As a small side note, why did the P-38 use three-bladed propellors? What are the aerodynamic differences between three, four, and five-bladed propellors? How is the number of blades on a propellor arrived at? Would the P-38 have benefitted from a four-bladed prop like on the Mustang had it switched to the Merlin, or even if it hadn't?

DangerForward
10-15-2004, 08:59 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Lateralus_14:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by DangerForward:
It was looked at, they tested a merlin powered P38J and calibration tests showed an estimated gain of 38mph in speed. Supposedly the project was discontinued for "political reasons". How's that for an uber-never-flown plane? http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif <HR></BLOCKQUOTE>

Is that the only statistic? 38 extra MPH? I'd be more interested in knowing the changes in high-altitude performance, the difference in range, acceleration, weight differences, etc.

As a small side note, why did the P-38 use three-bladed propellors? What are the aerodynamic differences between three, four, and five-bladed propellors? How is the number of blades on a propellor arrived at? Would the P-38 have benefitted from a four-bladed prop like on the Mustang had it switched to the Merlin, or even if it hadn't? <HR></BLOCKQUOTE>

I read it in the "Manual of the Eigth Air Force", but that's just about all they said. They had so many engine problems with the various P38 models over Europe that less and less were used by the 8th Air Force. The P38L supposedly fixed many of the high alt problems, but by that time it wasn't that important for the European Air War.

TgD Thunderbolt56
10-15-2004, 09:17 PM
The P-39 and the A-36 dive bomber used the Allison v1710 as well.

WTE_Galway
10-15-2004, 09:18 PM
most likely there was a surplus of allisons by that stage of the war and every merlin or US made merlin equivalent was needed for other planes.

bear in mind that if the P38 used merlins every P38 made would mean TWO less P51D's



as far as the European theare goes I recall reading one major problem with the p38 in Europe was its total unsuitability to cold conditions

WUAF_Badsight
10-15-2004, 09:22 PM
P-38 K Super Lightning (http://home.att.net/~C.C.Jordan/P-38K.html)

wayno7777
10-15-2004, 09:28 PM
I do think the main reason was two engines per plane meant less P-51's

WUAF_Badsight
10-15-2004, 09:32 PM
P-38 was a $120 K plane

P-51 was a $50 K plane

wayno7777
10-15-2004, 09:35 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by WUAF_Badsight:
http://home.att.net/~C.C.Jordan/P-38K.html <HR></BLOCKQUOTE>

Thx for that site. Super! http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

heywooood
10-15-2004, 09:51 PM
for P-38 with twin merlins see Secudus....


http://www.1000aircraftphotos.com/APS/2115.jpg

...and the Westland Whirlwind...

I wish I could have heard one of these do a flyby...WOOOOOHOOOO

SkyChimp
10-15-2004, 09:59 PM
According to my sources, no P-38 with Merlins ever flew, nor were any ever fitted. Lockheed drew up plans and projected performance. But that's as far as it got.

Anyways, unless there was a significant redesign, any increase in high altitude speed would have presented a problem for the P-38. The critical mach of the P-38 was fairly low, and it could nearly be reached in level flight. Any signficant increase in level speed at high altitude would have caused comressibility problems.

FI-Aflak
10-15-2004, 10:47 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by WUAF_Badsight:
http://home.att.net/~C.C.Jordan/P-38K.html <HR></BLOCKQUOTE>

So its a lightning, but faster with better climb.

I admit, it'd be nice, but it is still a huge target, unweildy in a knifefight, and you have that "issue" at high speeds.

I'd rather fly in a Jug.

But I might take the 38K over a pony.

WUAF_Badsight
10-15-2004, 11:06 PM
dont take FB & RL as the same thing

k5054
10-16-2004, 03:11 AM
You can find a lot of stuff about the Merlin in the P-38 in 'Vees for Victory', Dan Whitney, the story of the Allison V1710.
The Merlin was expected to make the P-38 faster and better climbing, at the expense of range. The weight of the Merlin being all at the front, with no balancing turbo back down the boom, gave CG problems, and I don't know how they planned to fix that. Also, the plan p***ed off GM, who owned Allsion and had big pull on the War planning board (or some such name). As previously mentioned it made more sense to put the Merlins in P-51s. The Pacific would take all the Allison P-38s that could be made.

The Merlin p-38 would have been so fast that the a/c could get into compressibility problems in level flight (468mph with a notional 2000hp merlin), or a verrrry shallow dive. It was the wing that spoiled the 38, coming as it did direct from the Electra transport (the section and the planform, not the actual wing). Engine improvements could not really make it better. Turbo'd Allison had a far better sfc than the two-stage Merlin.

Blottogg
10-16-2004, 04:22 PM
Lateralus_14, as far as blade count goes, there are several things affecting how many blades get put on a prop.

In general, fewer blades is better, since there is less airflow interferance between the airflow (especially tip vortices) coming off each blade the further apart they are in the prop disk.

Countering this is the fact that the blades have to be made longer and/or wider to absorb the engine's power with fewer blades. Wider blades tend to be less efficient (just as wings with a lower aspect ratio tend to have worse lift/drag curves), and longer blades mean that the tip speeds start getting pretty fast. When the tips go transonic/supersonic, that portion of the blade becomes very inefficient. Usually designers will try to make the blades as long/thin as they can, using as few blades as possible, while keeping all/most of the blade subsonic. Note that the German answer to increasing power was to make the blades broader instead of adding blades like the Brits did with the late model Spitfires. Both are viable solutions to the problem, but with different tradeoffs.

Another factor is ground clearance. The P-51 needs enough clearance to keep the prop out of the dirt in a two-point attitude on the ground, defining a tradeoff between blade length and gear length. The P-38 has tricycle landing gear, and thus a little better control over prop-to-ground clearance. Making the gear long enough to keep a three blade prop clear of the dirt wasn't a big problem with the Lightning, so that's the solution they went with. FWIW, early Mustangs with Allison engines (which had less power than the later Merlins, especially in the thin air at high altitude) had a three blade prop, too.

p1ngu666
10-16-2004, 11:31 PM
they could upgraded teh entire plane given 2-3week stop in production

fix teh wing so it dont have compressablility, add merlins or griffons http://forums.ubi.com/images/smilies/59.gif and other improvements.

p1ngu666
10-16-2004, 11:33 PM
oh btw, remmber we are gettin teh mossie http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif http://forums.ubi.com/images/smilies/11.gif http://forums.ubi.com/images/smilies/11.gif