What was the problem with the allison engine?

[wuzak]

When fitted with the GE turbocharger, the Allison put out more HP at altitude that the 2 stage/2 speed Merlins.

That all depends on altitude. Power for the V-1710 with turbo was almost constant up to the turbo's critical altitude, then power fell off rapidly.

Rolls-Royce had experimented with a turbo in the late 1920s (on a Falcon, IIRC, with the turbo in the vee), but didn't get great results. And as a mater of policy R-R didn't use turbos with their engines because of the exhaust thrust effect. As altitude increased the efficiency of the prop reduced and the thrsut from teh exhaust became more significant.

 

[wuzak]

2. When Allison added an auxillary mechanical supercharger stage to the V-1710 they left out an intercooler or aftercooler. The reason is clear - it is too hard to fit one in a sleek fighter airframe IF you make it an air to air cooler like was used in everything else BUT the Merlin 60 series. Have you seen the intercooler of a B-17? It is large and buried in the wing - not that much of a problem for a big bomber. Have you seen the intercooler for a P-47? It is huge and buried in the fuselage where the 2nd seat of its ancestor was (the P-35 was virtually a 2 seat airplane). That was the clear incredible genius of Sir Stanley Hooker. He solved the problem of getting all that draggy air in and out of the aftercooler by going to a liquid to air cooler. The fact that Allison and no one else did not copy that stunningly obvious idea is simply incredible. Using a liquid cooler would have solved the P-38's intercooler problems, made the 2 stage V-1710 as used in the P-63 and F-82 a more viable powerplant, and would have been useful in otehr engine installations as well, for everything from the P-61 to the B-28 to the Republic Rainbow.

The first V-1710s with two stage compressors had an aftercooler, which loked very similar to teh one atop the Merlin 60 series. However, using that meant redesigning the engine supercharger intake and carburettor, or moving the carb to the auxiliary stage. By not having the aftercooler Allison was able to use a common engine stage supercharger and carb for all their variants - single stage, two stage, and turbocharged.

The loss of the aftercooler meant that ADI was required.

btw two stage Merlins had intercooling and aftercooling. The aftercooler is obvious in pictures, while intercooling was achieved by cooling passages around the supercharger casing. Maybe not super effective, but still there.

 

[wuzak]

I seem to recall that the Allison was superior to the Merlin in North Africa due to less maintenance issues from the environmental conditions. I am going to check Bodie, but I think they did a study on using Merlins in the P-38 that surprisingly indicated a significant weight gain and no increase or possibly a decrease in overall performance. Have either of you read anything about these issues.

Lockheed did a few studies on the Merlin in the P-38. Usually the performance was similar or superior to the Allison version.

Merlin XX in P-38:

                                         Merlin XX    V-1710-F2 (-27/29)
                                        Reprt 2036           YP-38
Takeoff BHP                              1280/3000       1150/3000
Critical Altitude Military bhp                1170            1150 
Critical Altitude, feet                      21000           25000
Critical Altitiude max speed, mph              431             405
P-38 weight, pounds                          14500           14348
Sea level rate of climb, ft/min               3160
Sea level max speed, mph                       354
High speed cruise, bhp/rpm                875/2650       1000/2600
High Speed cruise mph/Alt ft             393/20000          /25000
High Speed cruise fuel use lb/bhp/hr         0.485
Range at high speed cruise, miles/gal         2.78             310*
Service Ceiling, feet                        38100           38000
Engine, with turbo  ducts, pounds            1430            1590
Normal range, miles                            640             650
Normal fuel capacity, gallons                  230             210

Merlin 61 in P-38

                                   V-1710-F17 (-89/91)           Merlin 61
                                    Military   Normal       Military   Normal
Altitude for max speed, ft             27000    25000          27300    30200
Maximum speed, mph                       418      395            423      403
Sea level                                360      326            343      326
5000ft                                   365      342            365      345
10000ft                                  382      358            386      364
15000ft                                  396      374            406      381
20000ft                                  408      386            406      395
25000ft                                  416      395            414      388
30000ft                                  414      383            419      402
Absolute ceiling, feet                 42300    38500          42300    41200
Service Ceiling, feet                  41600    37800          41600    40400
Climb in 5 minutes, feet               17800                   17800
Climb to 20000ft, minutes                6.2                     5.9
Climb to 25000ft, minutes                8.7                     8.4
Climb to 30000ft, minutes               12.2                    11.8
Distance to takeoff 
of 50ft obstacle, feet                  1640                    1770

A later study with an "advanced Merlin"

                                    Standard  Advanced   Advanced      
                                       P-38J   Allison    Allison        Merlin
War Emrgency Power, bhp                 1600      1725       2000(wet)     2000
WER engine, rpm                         3000      3200       3400           n/a
Engine?propellor gear ratio           2.00:1    2.36:1     2.36:1        2.36:1
Propellor diameter, feet                11.5      11.5       12.5          12.5
Turbosupercharger, GE Type              B-33      B-39       B-38       Jet Exh
Fuel grade                               130       140        140       Special
Propellor activity factor               89.3      89.3        110           110
Propellor weight increase, lbs             0         0         51            51
Per engine weight increase, lbs            0         0         45           n/a
P-38 operational weight, lbs           16200     16200      17250         16500
Increase in maximum speed, mph             0        12         16            38
Increase in maximum climb, fpm             0       490        850          1300
Impact om manoueverability %               0        0?         -5            -1
Maximum sea level speed, mph             356       364        382           398
Maximm speed @ 30000ft, mph              436       448        452           468
Maximum climb in 5 minutes, feet       18700     21600      23000         25600
Timb to climb to 30000ft, minutes        8.7       7.2        6.2           6.2
Absolute ceiling, feet                 43900     43900      43700         43900

These are from Dan Whitney, Vees for Victory.

In that he also says that a two stage Allison version was proposed, but no performance figures were shown.

Notice that at some altitdes the turbocharged Allison has an advantage because of its more even power delivery with altitude, but at others is less.

 

[Readie]

And the Allison could have powered those Spitfires and Hurricanes in GB's hour of peril as it put out similar HP as the single stage Merlins of the day. When fitted with the GE turbocharger, the Allison put out more HP at altitude that the 2 stage/2 speed Merlins.

But, it wasn't and it didn't.
The Merlin steals the thunder and the worthy Allison is the also ran.
Cheers
John

 

[Milosh]

Not sure that Allison was ready to produce sufficient quantities of the V-1710 to power Spitfires and Hurricanes before 1940.

It is not about if there was enough Allisons but about that the HP produced. I am sure the Soviets would have preferred Allisons in the Spitfires and Hurricanes they received.

 

[Glider]

After having read Dan Whitney's excellent "Vees for Victory", I decided that both side of this arguement are right... and both sides are wrong. Allison engines were every bit as powerful at allitude the comparable Merlin engines, but...

What has condemed the Allison is that fact that it took their engineering department about two extra years to get their engines to the same level of development. It took Allison until nearly 1943 to get their 9.6:1 ratio high allitude single stage single speed blower into the field, while the comparable Merlin 45 was just a little too late for the Battle of Britian. The two stage mechanical Allisons had the same power at allitude as the Merlin 60 serieds engines but the Spitfire 9 with the Merlin 60 was being issued to the filed in late 1941, while the P-63 with two stage Allison was just starting into production in late 1943. The Allison G6 engines for the P-82 again were comparable in power at allitude to Merlin 100 series engines but again, Allison was about 2 years behind (1947 vs.1945).

And in battle two years is forever.

That is all I think I know.

Piper106

That fits my understanding as well, nicely put

 

[wuzak]

It is not about if there was enough Allisons but about that the HP produced. I am sure the Soviets would have preferred Allisons in the Spitfires and Hurricanes they received.

Why?

They just wanted as many aircraft that they could lay their hands on.

 

[Readie]

It is not about if there was enough Allisons but about that the HP produced. I am sure the Soviets would have preferred Allisons in the Spitfires and Hurricanes they received.

Why would anyone prefer am Allison to a Merlin?
Unless you mean that it was either a Spitfire / Hurricane with an Allison or no Spitfire/Hurricane at all.
Cheers
John

 

[Readie]

What has condemed the Allison is that fact that it took their engineering department about two extra years to get their engines to the same level of development. It took Allison until nearly 1943 to get their 9.6:1 ratio high allitude single stage single speed blower into the field
And in battle two years is forever.
Piper106

If we English had only the Allison I would be speaking German.
The Merlin is more than just another aero engine it represents our identity.
Cheers
John

 

[renrich]

SR, thanks for the correction and the link. I had forgotten the details on the Chrysler engine. I did not realise that Merlins powered the RN ships which were the major factor in keeping the Germans from definitely planning to invade England, along with the fact that Hitler never seriously planned on that invasion. The BOB was a very good effort on the part of the RAF but it is a myth that the Germans were kept from invading by "losing" the BOB. Even without the Merlin, I expect the British would have soldiered on and been a big part of the winning coalition.

 

[buffnut453]

The invasion was a bluff but Hitler absolutely wanted Britain out of the war and losing the BoB would have resulted in precisely that. Without the Merlin engine in 1940, Fighter Command would have lost the air superiority battle over southeast England to leave London completely exposed. Under those circumstances, it is entirely conceivable that the factions who wanted to sue for peace with Germany (and there were many in high places who wanted to do just that - Lord Halifax and his side-kick R A Butler were 2 of the more influential) would have removed Churchill and the world would be a very different place today.

 

[Milosh]

If we English had only the Allison I would be speaking German.
The Merlin is more than just another aero engine it represents our identity.
Cheers
John

In 1940, the Allison performed just as well the Merlin. If the Allison had powered the Spitfires and Hurricanes in 1940, they would have performed just as well as the Merlin powered a/c.

Wuzak, Merlins in Soviet use had very bad serviceability, while the Allisons did not.

The P-40 was powered by both engines and there wasn't much, if any difference, in the performance with either engine.

 

[buffnut453]

So why were the Allison-powered Mustangs relegated to Army Cooperation tasks? Answer - because the Allison lacked altitude performance which was vital for 1940 because it didn't have the 2-stage supercharger as discussed previously in the thread.

Bear in mind that you can't just drop in an engine in June of 1940 and expect it to work. The Merlin had been available since 1938 in sufficient numbers to support re-equipment of fighter command. What was the Allison's performance in 1938? Also, there's the challenge of securing export for the Allison in 1939 and enabling licence-building of the engine in the UK.

The Allison was a good engine but in no way was it ready for the combat environment of the BoB.

 

[Lighthunmust]

I
Wuzak, Merlins in Soviet use had very bad serviceability, while the Allisons did not. .

Which should increase the importance of the Allison in the minds of everyone when you factor in that the Russians did most of the dying and killing during WW2. It appears that the Allison was the superior engine whenever maintenance operations were conducted under adverse conditions not found at a fighter base in Britain and where high attitude combat is rare.

 

[buffnut453]

Undoubtedly so, but Hitler didn't attack the USSR until after he'd lost the BoB. The fact remains that having Britain as an adversary to the west diverted resources that were badly-needed for the Eastern Front. With Britain a non-combatant, there would have been no campaign in the Western Desert. What impact would Rommel and his forces have had on the Eastern Front? Again, the Allison was an excellent engine but it wasn't ready for the combat environment of the BoB.

 

[Lighthunmust]

Undoubtedly so, but Hitler didn't attack the USSR until after he'd lost the BoB. The fact remains that having Britain as an adversary to the west diverted resources that were badly-needed for the Eastern Front. With Britain a non-combatant, there would have been no campaign in the Western Desert. What impact would Rommel and his forces have had on the Eastern Front? Again, the Allison was an excellent engine but it wasn't ready for the combat environment of the BoB.

No doubt the Merlin was in the right place at the right time. The BoB definitely affected Barbarosa, the extent of which is not agreed upon from what I have read. I was speaking of the importance of the Allison during the entire war. The campaign in North Africa also bolstered the reputation of Allison serviceability being better than the Merlin in adverse conditions.

 

[buffnut453]

No doubt the Merlin was in the right place at the right time. The BoB definitely affected Barbarosa, the extent of which is not agreed upon from what I have read. I was speaking of the importance of the Allison during the entire war. The campaign in North Africa also bolstered the reputation of Allison serviceability being better than the Merlin in adverse conditions.

Fair enough. Incidentally, is there definitive evidence of Allison serviceability being better than the Merlin in the Western Desert or is it simply that the P-40 was more associated with that campaign due to the publicity given to 112 Sqn's sharkmouthed aircraft?

 

[Readie]

SR, thanks for the correction and the link. I had forgotten the details on the Chrysler engine. I did not realise that Merlins powered the RN ships which were the major factor in keeping the Germans from definitely planning to invade England, along with the fact that Hitler never seriously planned on that invasion. The BOB was a very good effort on the part of the RAF but it is a myth that the Germans were kept from invading by "losing" the BOB. Even without the Merlin, I expect the British would have soldiered on and been a big part of the winning coalition.[/QUOTE

The BoB kept the Germans at bay.
From your comment about it being a 'good effort' I honestly think that its difficult for Americans to really understand the threat of invasion and attack on their country. Hitler wanted to beat us before the Commonwealth and our allies could arrive. The thought of losing the BoB was unthinkable and is one of the pivotal points in our modern history.


http://www.yalumba.co.uk/Framesets/British Power Boat Co.

Not just one but, three Merlins. Petrol and Naval ships are not the best combination though...
There were the last of the WW2 Air sea rescue boats stationed in Plymouth in the 1960's and boy, could they motor.
Cheers
John

 

[Shortround6]

While Merlins were used in some coastal craft the majority of fast craft were powered by either Hall-Scotts (many of the Fairmile Launches) or Packard Marine engines which were NOT Merlins but a 2500cu in engine derived from a late 1920s aircraft engines.

 

[gjs238]

And the Allison could have powered those Spitfires and Hurricanes in GB's hour of peril as it put out similar HP as the single stage Merlins of the day. When fitted with the GE turbocharger, the Allison put out more HP at altitude that the 2 stage/2 speed Merlins.

Which is why in other threads I keep pondering how to effectively accomplish this in a single-engined fighter. A forward cockpit rear engine/rear turbo layout seems a good way to accomplish this with minimal ducting.