An Allison V-1710 with a two-speed supercharger in 1942 (9 Viewers)

[Simon Thomas]

Speaking of these fighters, anyone know the origin of this roll rate chart?

View attachment 871284

Fig 9-24, p366.
"AIRPLANE PERFORMANCE STABILITY AND CONTROL"
BY
COURTLAND D. PERKINS
Professor and Chairman, Aeronautical Engineering Department
Princeton University

ROBERT E. HAGE
Senior Engineer, Preliminary Design Department
Boeing Airplane Company

It doesn't give a specific reference for where they got the info, but they list this at the end of the chapter:
SUGGESTED READING
1. NACA TR 715, "Lateral Control Required for Satisfactory Flying Qualities
Based on Flight Tests of Numerous Airplanes," by Gilruth and Turner, 1941.
2. NACA TR 799, "Charts for the Determination, of Wing Torsional Stiffness
Required for Specified Rolling Characteristics or Aileron Reversal Speed,"
Pearson and Aiken, 1944.
3. USAF TR 5180, "Prediction of Aileron Effectiveness," by J. D. Bitner, 1945.
4. NACA TR 635, "Theoretical Stability and Control Characteristics of Wings
with Various Amounts of Taper and Twist," by Pearson and Jones, 1938.
5. NACA TN 825, "Wind-tunnel Investigation of Effect of Yaw on Lateral
Stability Characteristics. III. Symmetrically Tapered Wing at Various
Positions on Circular Fuselage with and without Vertical Tail," by Recant
and Wallace, 1941. (Also others in this series.)
6. NACA WR L-419, "Collection of Balanced Aileron Data," by F. M. Rogallo,
1944.
7. NACA RB, "Resume of Data for Internally Balanced Ailerons," by Rogallo
and Lowry, 1943.
8. NACA WR L-169, "Resume of Hinge Moment Data for Unshielded Horn-
Balance Control Surfaces," by J. G. Lowry, 1943.
9. NACA TR 548, "Effect of Tip Shape and Dihedral on Lateral Stability Charac-
teristics," by J. A. Shortal.
10. USAF MR ENG-M-51/VF 18 Add 1, "The Computation of the Critical Speeds
of Aileron Reversal, Wing Torsional Divergence, and Wing Aileron Di-
vergence," by L. N. Shornick, 1942.
11. NACA TN 1245, "Summary of Lateral Control Research," by Langley
Research Department, compiled by T. A. Toll, March 1947.

 

[Steamed_Banana]

Do you point out at Curtiss that made the P-40F & L reality with the V-1650-1, or at RR that made Merlin XX a reality?

Presumably the combination of aspiration for the engines with the engine itself working in the airframe is a combination of both. But the P-40F was in action by August 1942 and it seemed to make about that much power at altitude. The Merlin XX made 1150 hp at 18,500 ft and still 1040 hp at 21000 ft and 50" of boost, and what you were saying upthread about RAM effects on critical altitude and hp seems to indicate that we are at least in the ballpark.

I must be missing something, but it sounds like SR6 is saying that Allison can't make a two speed (or multi-speed / hydromatic) engine in 1942 which can produce 1,100 hp at 20,000 ft. Seems like RR did it with their 1940 design. Am I reading this wrong?

 

[Steamed_Banana]

Fig 9-24, p366.
"AIRPLANE PERFORMANCE STABILITY AND CONTROL"
BY
COURTLAND D. PERKINS
Professor and Chairman, Aeronautical Engineering Department
Princeton University

ROBERT E. HAGE
Senior Engineer, Preliminary Design Department
Boeing Airplane Company

It doesn't give a specific reference for where they got the info, but they list this at the end of the chapter:
SUGGESTED READING
1. NACA TR 715, "Lateral Control Required for Satisfactory Flying Qualities
Based on Flight Tests of Numerous Airplanes," by Gilruth and Turner, 1941.
2. NACA TR 799, "Charts for the Determination, of Wing Torsional Stiffness
Required for Specified Rolling Characteristics or Aileron Reversal Speed,"
Pearson and Aiken, 1944.
3. USAF TR 5180, "Prediction of Aileron Effectiveness," by J. D. Bitner, 1945.
4. NACA TR 635, "Theoretical Stability and Control Characteristics of Wings
with Various Amounts of Taper and Twist," by Pearson and Jones, 1938.
5. NACA TN 825, "Wind-tunnel Investigation of Effect of Yaw on Lateral
Stability Characteristics. III. Symmetrically Tapered Wing at Various
Positions on Circular Fuselage with and without Vertical Tail," by Recant
and Wallace, 1941. (Also others in this series.)
6. NACA WR L-419, "Collection of Balanced Aileron Data," by F. M. Rogallo,
1944.
7. NACA RB, "Resume of Data for Internally Balanced Ailerons," by Rogallo
and Lowry, 1943.
8. NACA WR L-169, "Resume of Hinge Moment Data for Unshielded Horn-
Balance Control Surfaces," by J. G. Lowry, 1943.
9. NACA TR 548, "Effect of Tip Shape and Dihedral on Lateral Stability Charac-
teristics," by J. A. Shortal.
10. USAF MR ENG-M-51/VF 18 Add 1, "The Computation of the Critical Speeds
of Aileron Reversal, Wing Torsional Divergence, and Wing Aileron Di-
vergence," by L. N. Shornick, 1942.
11. NACA TN 1245, "Summary of Lateral Control Research," by Langley
Research Department, compiled by T. A. Toll, March 1947.

Thank you!

 

[Shortround6]

I must be missing something, but it sounds like SR6 is saying that Allison can't make a two speed (or multi-speed / hydromatic) engine in 1942 which can produce 1,100 hp at 20,000 ft. Seems like RR did it with their 1940 design. Am I reading this wrong?

RR had a supercharger with a larger impeller and housing in 1935/36 and they got to give the well known 1030hp at 16,250ft with 87 octane fuel. RR then put a two speed drive between the engine and supercharger in 1938. Somebody put a set of 9.089 gears in the single speed supercharger instead of the 8.588 gears to come uyp with the Merlin XII. Hooker goes to work for RR in 1939. He comes up with a much better intake and outer cover for the supercharger in 1940 (or very late 1939) they get the engine (Merlin XX into production in July/Aug 1940 with first Hurricane IIs in Sept. Allison is getting about 1040hp at a bit over 14,000ft. at the same time and were trying to get the long nose engine though the type test and they had to rebuild 277 (?) already completed engines to meet the new standard in late 1940. Just meeting their contracted deliver dates was taking up most of their time.

RR was 1-2 years ahead of everybody else an as we have tried to explain, the superchargers are not often separate pieces that can be swapped from engine to engine. You need a proper supercharger drive and as had been said, some of these engines (Allison ?)used a cast and machined recess in the back of the engine to form part of the supercharger housing. You may need to design new casting molds to use a larger supercharger. Allison was trying to get into large scale production in 1940 and they were trying to come up with new processes. They changed the way they cast the crankases and cylinder blocks in 1941. In an earlier post it was stated that Allison got one of the new RR superchargers but without a stiff enough mounting system the supercharger destroyed itself. RR used an accessory section at the back of the engine and mounted the supercharger behind it. The accessory section contained not just the supercharger drive but the drive gears and shafts for the Generator, vacuum pump, hydraulic pump and other things. Aircraft engines tended to try to make things do double duty but sometimes that made upgrading hard as sometime they had to redo several things in order to just change the one thing they wanted to change

As an idea of what they were dealing with an Allsion trying to flow 9,000lb an hour needed about 100hp to drive the supercharger using 6.44 gears (early P-38 engine) and needed about 190hp for 8.80 gears and needed about 225hp for 9.60 gears.
Now if you want more power you can use larger carbs and such an flow more air, Using the 9.60 gears you can flow 10,000lbs and hour which is good for about 1285hp but the engine needs/was making 1672hp in the cylinders with the difference going to Friction and 250-225hp to drive the supercharger at the higher flow.
It took Allison until 1942 to make an engine that could stand up to that level of power in the cylinders. They still could not get the power needed through the supercharger drive.
I would note that in England neither Bristol or Napier were making superchargers as good as RR.

You cannot just stick a 10.5in impeller in a housing that is made for a 9.5in impeller and get very far. The size and shape of the diffuser housing plays a big part.

 

[Steamed_Banana]

RR was 1-2 years ahead, ok. Allison wasn't making an engine that could stand up to 1600 hp in the cylinders until 1942. Ok.

We are talking about this happening in 1942. They have to make a new impeller, new housing, other new parts. This is two years after the XX was developed. The US has plenty of resources. The original Merlin XX copies have been around for two years to look at. There are Packard-Merlin XX copies / V-1650-1 already in the US by what, second quarter of 1942? Pratt and Whitney has their own two speed superchargers that Allison could also look at, if the government asked for this to happen.

I'm sure it's not "snap your fingers and it's done" easy. But it also seems unlikely that it's out of reach. And I'm not sure Allison's R&D was doing a lot that was tremendously more important. If they could get something viable into production by the end of 1942, you've got the new engines in fighters in 1943, and this very difficult year gets a little easier because you have P-39D+, you have more P-40F or L equivalents (or maybe a P-40L+ with a slightly better engine), you have P-51A+, maybe a P-38G+ with 2 / multi speed supercharger and no turbo. All your fighters can now fight at 20,000-25,000 ft. Rate of climb will be better for a much wider altitude range. You can cruise comfortably in the thin air on your way to and from targets. You can escort heavy bombers at least for operational / tactical raids.

The single speed / single stage supercharger on the main in-line engine for US Army fighters was a real liability for the US. It was a good engine, but it wasn't living up to it's potential. Everyone was betting on the turbos, but it would have been wise to have a backup plan. The two speed (or hydromatic) could have been that backup plan.

 

[BarnOwlLover]

I mean the P-51 model with the highest top speed was powered by an Allison so what's the difference then exactly?

I don't think so. Production P-51H hit 472 mph (fully dirtied up/combat ready) and 487 mph (clean). A XP-51F fitted with a V-1650-9 Merlin hit 491 mph. The XP-51G with the Merlin RM 14SM (Merlin 100) hit 495 mph. The XP-51J only made a few flights that were highlighted by engine issues and the pilots who carried out said flights highly disliked the Allison variant used in the J and those issues showed up in the F-82E/F/G/H that were built with late V-1710s after all but 22 Merlin powered P-82s (2 XP-82s, 20 P-82Bs, 1 each P-82C/D night fighter conversions based on P-82Bs and came from that production total) were cancelled.

And you don't have to take my word for it. Forum Mustang experts such as drgondog, Mustangtmg, and ColFord have the hard data, though the latter member focuses mostly on the wartime Mustang variants.

 

[tomo pauk]

Presumably the combination of aspiration for the engines with the engine itself working in the airframe is a combination of both. But the P-40F was in action by August 1942 and it seemed to make about that much power at altitude. The Merlin XX made 1150 hp at 18,500 ft and still 1040 hp at 21000 ft and 50" of boost, and what you were saying upthread about RAM effects on critical altitude and hp seems to indicate that we are at least in the ballpark.

Note that there is no Allison company in the P-40F story.

I must be missing something, but it sounds like SR6 is saying that Allison can't make a two speed (or multi-speed / hydromatic) engine in 1942 which can produce 1,100 hp at 20,000 ft. Seems like RR did it with their 1940 design. Am I reading this wrong?

You are reading this right.
I'll add: Allison might've probably been able to make a better S/C in a timely manner if they don't spread themselves thin with different versions of the basic V-1710, and the X and W engine concepts in the late 1930s/early 1940s.

 

[Steamed_Banana]

Note that there is no Allison company in the P-40F story.

No, it just speaks to the apparent relative ease of fitting an existing (if by now, 2 year old) engine with a two speed supercharger into one of the existing US fighters.

You are reading this right.
I'll add: Allison might've probably been able to make a better S/C in a timely manner if they don't spread themselves thin with different versions of the basic V-1710, and the X and W engine concepts in the late 1930s/early 1940s.

I'm not sure I buy that, but maybe at this point it might be worth taking a closer look at everything Allison R&D department was spending their time on in 1941 and 42. It seems to me that there could have been some overlap in design goals. For example, while it may have taken a lot of effort to create the 9.60:1 ratio supercharger, but that could have been the second gear for a theoretical two speed supercharger.

Then the priority becomes the impeller and whatever changes need to be made to carb etc., and a housing. It again seems to be like many of these components could be copied from the Merlin XX or one of the P&W superchargers.

Maybe to get this done we take some Allison R&D resources off of the project to make the quasi two stage supercharger for the V-1710-93 used by the P-63.

 

[Geoffrey Sinclair]

8th Air Force Raid on Lille 9 October 1942. From the Official History by Craven and Cate, initial bomber gunner claims 56 destroyed, 26 probable, 20 damaged, revised (no date when) to 21 destroyed, 21 probable, 15 damaged. The USAAF fighter escort made no claims, 4 bombers were lost plus a fifth written off. Craven and Cate researched the German archives and found Luftwaffe units operating in the west lost 11 aircraft that day with a further 11 with more than 60% damage (write off damage level). That is 22 aircraft from all causes of all types for all units. At this stage about 40% of the Luftwaffe aircraft losses were non combat related. After looking at the Luftwaffe fighter loss statements Craven and Cate conclude one (1) was the most likely number of fighters shot down by the bombers.

The above story is what many people initially interested in the USAAF rebound to after learning the B-17 (with an occasional little help and comic relief from its sidekick B-24), did not shoot down millions of axis interceptors just on test flights. Research tends to be left there, replaced by assumptions and estimates, the famed I know it is true as seen and proved on TV several times a night, ignoring the lead in the show has the great God Scriptwriter on their side, more and more necessary as seasons progress. Research largely confined to maximising audience share.

If anyone thinks the following is incorrect, provide the evidence, not the feelings.

The reality is the exchange rate USAAF heavies versus Luftwaffe interceptors changed over time. In To Command The Sky by McFarland and Newton they note that in Q4/42 5.8 heavy bombers were being lost per 100 cases of reported combat and this had climbed to 11.6 per 100 cases in Q1/44. In the book Brute Force by Ellis he lists the figures as in 1942 2.3 bombers lost per 100 combats and in mid 1944 17.7 bombers lost per 100 combats. Mostly as a reflection in the increase in average Luftwaffe fighter armament.

The interest in the 8th Air Force and B-17, along with the small number of raid days and the relative lack of non USAAF heavy bomber activity in 1942/43 makes it remarkably easy to obtain a good set of USAAF losses with causes for the period, down to serial number level and match them with Luftwaffe losses. Apart from the individual bomb group and other web sites things like B-17 Flying Fortress List by David Osborne, Mighty Eighth War Diary by Roger Freeman and the USAAF Statistical Digest (the latter acting more as a sanity check). The horrible grind that shows how even 1% losses times a mission every second day gives nearly 50% casualties in 3 months when measured against the starting force size.

Statistical Digest 1942/43 ETO
effective sorties, 20,883 heavy bomber, 5,533 medium/light bomber, 25,451 fighter
Combat flying hours, 162,059 heavy bomber, 23,735 medium/light bomber, 59,015 fighter
thousand rounds of ammunition used 651x0.30 and 27,761x0.50 heavy bomber, 5,533x0.50 medium/light bomber, 18x0.30, 1,265x0.50, 23x20mm fighter
enemy aircraft claimed destroyed in the air, 3,543 heavy bomber, 33 medium/light bomber, 458 fighter
US aircraft lost to enemy aircraft, 737 heavy bomber, 18 medium/light bomber, 171 fighter

When it comes to the Luftwaffe There are books like Day Fighters In Defense of the Reich by Donald Caldwell, for the study

A) Auswertung der Einsatzbereitsch der fliegenden Verb. Vom 1 August 1943 bis November 1944", which are the fighter losses for all units in the west and Reich. The figures quoted from this source actually stop on 19 April 1944.

B) Generalleutenant Josef Schmid "Day and Night Aerial Warfare over the Reich 1943-44", first published in 1954. Schmid was the commander of I Jagdkorps which controlled most of the fighters defending Germany. In checking his figures with the text of McFarland and Newton it looks like at times Schmid does not include write offs in his casualty list.

C) British translations of captured German Documents, "German Air Force Losses in the West 1 September 1943 to 31 December 1943" also losses for the area of Luftflotte Reich for the same dates and for the west and Luftflotte Reich for the period 1 January 1944 to May 1944. These are the documents from the Luftwaffe Quartermaster General and give cause of loss.

In summary it looks like the best rule of thumb for the 8th Air Force is for every 2 B-17s or B-24s destroyed by Luftwaffe fighters 1 Luftwaffe fighter was destroyed by the bomber's gunners. With the initial (1943) ratio being around 1.5 to 1 until the Luftwaffe gained experience in intercepting the B-17/24s then moving to a higher ratio as fighter firepower was upgraded then higher again as Sturm units and 30mm cannon came into use. It means in 1943 the 8th Air Force heavy bombers shot down around twice the number of Luftwaffe fighters as the USAAF fighters, while overclaiming by around an average of 7 to 1.

For on the ground, no claims until January 1944, the 8th AF fighters are credited with 4,250-23-2,886, the bombers 3,079 destroyed or damaged. The 9th Air Force 2,216-147-1,894, all by fighters. The USAAF Statistical digest reports MTO 7,003 enemy aircraft destroyed on the air, 2,494 on the ground, Pacific Ocean 575 and 219, Far East Air Forces 4,502 and 1,796, China Burma India 1,202 and 711, Alaska 89 and 24. Air to air claims end to have less overclaiming than air to ground ones.

The reported average of 18 to 20 hits of 20 mm cannon to bring down a B-17 is via causing structural failure, that is no fire, compared with 2 to 3x30 mm hits. US firing trials at Aberdeen using German 20mm incendiary rounds versus 40% full B-17 fuel tanks showed the chance of causing a fire per hit was 10% at 50 metres dropping to 2% at 2000 metres. Apparently a 13mm round's chance of starting a fire was 40% of the 20 mm. So the average number of hits to bring down a B-17 (and by implication other 4 engined types) would have been under the 18 to 20 figure, given the ones lost to fires.

In early 1944 the average Luftwaffe fighter in the west was given an armament upgrade as seen by the 8th counting the holes in returning bombers and noting what caused them. To Command The Sky by McFarland and Newton gives the statistics for the ratio of cannon shell to machine gun bullet hits for damaged bombers. The data reported on starts in August 1942 and ends in June 1944. The figures are date, cannon shell hits per 100 machine gun bullet hits.

8-12/42 40, 1-4/43 77, 5-8/43 70, 9-12/43 81, 1-2/44 88, 3-4/44 127, 5-6/44 135.

The Luftwaffe quite consistently month by month awarded 2 B-17 kills for each 1 actually shot down, the B-24 ratio was more like 1.8 to 1.

 

[Daggerr]

Any that is posted on this site?

It can be downloaded from NASA website:
Effect of Three Modifications on Performance of Auxiliary-Stage Supercharger for V-1710-93 Engine - NASA Technical Reports Server (NTRS)

 

[Frog]

8th Air Force Raid on Lille 9 October 1942. From the Official History by Craven and Cate, initial bomber gunner claims 56 destroyed, 26 probable, 20 damaged, revised (no date when) to 21 destroyed, 21 probable, 15 damaged. The USAAF fighter escort made no claims, 4 bombers were lost plus a fifth written off. Craven and Cate researched the German archives and found Luftwaffe units operating in the west lost 11 aircraft that day with a further 11 with more than 60% damage (write off damage level). That is 22 aircraft from all causes of all types for all units. At this stage about 40% of the Luftwaffe aircraft losses were non combat related. After looking at the Luftwaffe fighter loss statements Craven and Cate conclude one (1) was the most likely number of fighters shot down by the bombers.

The above story is what many people initially interested in the USAAF rebound to after learning the B-17 (with an occasional little help and comic relief from its sidekick B-24), did not shoot down millions of axis interceptors just on test flights. Research tends to be left there, replaced by assumptions and estimates, the famed I know it is true as seen and proved on TV several times a night, ignoring the lead in the show has the great God Scriptwriter on their side, more and more necessary as seasons progress. Research largely confined to maximising audience share.

If anyone thinks the following is incorrect, provide the evidence, not the feelings.

The reality is the exchange rate USAAF heavies versus Luftwaffe interceptors changed over time. In To Command The Sky by McFarland and Newton they note that in Q4/42 5.8 heavy bombers were being lost per 100 cases of reported combat and this had climbed to 11.6 per 100 cases in Q1/44. In the book Brute Force by Ellis he lists the figures as in 1942 2.3 bombers lost per 100 combats and in mid 1944 17.7 bombers lost per 100 combats. Mostly as a reflection in the increase in average Luftwaffe fighter armament.

The interest in the 8th Air Force and B-17, along with the small number of raid days and the relative lack of non USAAF heavy bomber activity in 1942/43 makes it remarkably easy to obtain a good set of USAAF losses with causes for the period, down to serial number level and match them with Luftwaffe losses. Apart from the individual bomb group and other web sites things like B-17 Flying Fortress List by David Osborne, Mighty Eighth War Diary by Roger Freeman and the USAAF Statistical Digest (the latter acting more as a sanity check). The horrible grind that shows how even 1% losses times a mission every second day gives nearly 50% casualties in 3 months when measured against the starting force size.

Statistical Digest 1942/43 ETO
effective sorties, 20,883 heavy bomber, 5,533 medium/light bomber, 25,451 fighter
Combat flying hours, 162,059 heavy bomber, 23,735 medium/light bomber, 59,015 fighter
thousand rounds of ammunition used 651x0.30 and 27,761x0.50 heavy bomber, 5,533x0.50 medium/light bomber, 18x0.30, 1,265x0.50, 23x20mm fighter
enemy aircraft claimed destroyed in the air, 3,543 heavy bomber, 33 medium/light bomber, 458 fighter
US aircraft lost to enemy aircraft, 737 heavy bomber, 18 medium/light bomber, 171 fighter

When it comes to the Luftwaffe There are books like Day Fighters In Defense of the Reich by Donald Caldwell, for the study

A) Auswertung der Einsatzbereitsch der fliegenden Verb. Vom 1 August 1943 bis November 1944", which are the fighter losses for all units in the west and Reich. The figures quoted from this source actually stop on 19 April 1944.

B) Generalleutenant Josef Schmid "Day and Night Aerial Warfare over the Reich 1943-44", first published in 1954. Schmid was the commander of I Jagdkorps which controlled most of the fighters defending Germany. In checking his figures with the text of McFarland and Newton it looks like at times Schmid does not include write offs in his casualty list.

C) British translations of captured German Documents, "German Air Force Losses in the West 1 September 1943 to 31 December 1943" also losses for the area of Luftflotte Reich for the same dates and for the west and Luftflotte Reich for the period 1 January 1944 to May 1944. These are the documents from the Luftwaffe Quartermaster General and give cause of loss.

In summary it looks like the best rule of thumb for the 8th Air Force is for every 2 B-17s or B-24s destroyed by Luftwaffe fighters 1 Luftwaffe fighter was destroyed by the bomber's gunners. With the initial (1943) ratio being around 1.5 to 1 until the Luftwaffe gained experience in intercepting the B-17/24s then moving to a higher ratio as fighter firepower was upgraded then higher again as Sturm units and 30mm cannon came into use. It means in 1943 the 8th Air Force heavy bombers shot down around twice the number of Luftwaffe fighters as the USAAF fighters, while overclaiming by around an average of 7 to 1.

For on the ground, no claims until January 1944, the 8th AF fighters are credited with 4,250-23-2,886, the bombers 3,079 destroyed or damaged. The 9th Air Force 2,216-147-1,894, all by fighters. The USAAF Statistical digest reports MTO 7,003 enemy aircraft destroyed on the air, 2,494 on the ground, Pacific Ocean 575 and 219, Far East Air Forces 4,502 and 1,796, China Burma India 1,202 and 711, Alaska 89 and 24. Air to air claims end to have less overclaiming than air to ground ones.

The reported average of 18 to 20 hits of 20 mm cannon to bring down a B-17 is via causing structural failure, that is no fire, compared with 2 to 3x30 mm hits. US firing trials at Aberdeen using German 20mm incendiary rounds versus 40% full B-17 fuel tanks showed the chance of causing a fire per hit was 10% at 50 metres dropping to 2% at 2000 metres. Apparently a 13mm round's chance of starting a fire was 40% of the 20 mm. So the average number of hits to bring down a B-17 (and by implication other 4 engined types) would have been under the 18 to 20 figure, given the ones lost to fires.

In early 1944 the average Luftwaffe fighter in the west was given an armament upgrade as seen by the 8th counting the holes in returning bombers and noting what caused them. To Command The Sky by McFarland and Newton gives the statistics for the ratio of cannon shell to machine gun bullet hits for damaged bombers. The data reported on starts in August 1942 and ends in June 1944. The figures are date, cannon shell hits per 100 machine gun bullet hits.

8-12/42 40, 1-4/43 77, 5-8/43 70, 9-12/43 81, 1-2/44 88, 3-4/44 127, 5-6/44 135.

The Luftwaffe quite consistently month by month awarded 2 B-17 kills for each 1 actually shot down, the B-24 ratio was more like 1.8 to 1.

These are the probabilities when the shells or balls hit the target.
To be accounted for is the total number of shots fired.
According to this site (I don't take position about the accuracy of the information true or not), the average would have been 2 % of hits for a common pilot. this would then make alot of ammo fired.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.airandspaceforces.com/article/0993regensburg/&ved=2ahUKEwjJyOn82p-TAxUVOPsDHX78Li4QFnoECDMQAQ&usg=AOvVaw3lsBQdqE6XVVwf1SvwRY0R

 

[Steamed_Banana]

The ratios and success rates definitely did change, and not just due to firepower - the Germans (and the Italians and other minor Axis powers, who we typically forget about) quickly learned the same lesson the Japanese did, which was to attack heavy bombers from the front. You don't need to blast apart the fuselage or blow a wing off - if you put one or two bullets or some shell fragments into the pilot and co-pilot, the plane is probably going down.

This was then partly countered by adding the chin turrets to B-17s and B-24s but that took a while. Quick google says B-17G started to replace B-17F in November 1943. There were some analogous upgrades to the armament of the medium bombers which was improved substantially though they never got nose turrets. And of course bomber unit commanders adjusted combat formations and tactics to deal with the enemy fighter threat.

Luftwaffe would then make frontal attacks with larger numbers (i.e six or more instead of individual) of heavily armed fighters like Fw 190s and Bf 109G with the cannon gondolas flying at high speed, and then as we know the Luftwaffe cleverly came up with a host of other creative measures against the unescorted heavy bombers like using heavy / night fighters (Bf 110, 210, Ju 88 and others) with extra cannon, using rockets, mortars, oversized 50 mm etc. cannon etc..

Another option was to make high speed diving or climbing slashing attacks from oblique angles which either targeted tail gunners (weakening defensive firepower) and /or one of the engines, which could cause the bomber to fall out of formation and thus into a swarm of Axis fighters and rapid doom.

A 2 for 1 ratio of fighter to heavy bomber losses sounds about right. In the MTO medium bombers usually had some level of escorted, as I noted upthread, but seemed to often end up on their own and had to fight off enemy fighters for a while.

In the Pacific where distances were greater and enemy fighters had much longer range and endurance, both heavy and medium bombers often got into long, extended, dramatic duels with Japanese fighters during egress, which often only ended when they were able to find clouds to hide in, or sometimes (more rarely) when Allied fighters came to their rescue.

There were several cases where lone B-17s or little groups of two or three of them were engaged with multiple zeros for up to an hour or more, and they often survived - sometimes with no loss on either side, but with lots of damage, WiA and KiA on board when they landed. US medium bomber formations were sometimes harried for long distances coming back from certain targets.

There was one famous case where B-25s of the 41st Bomb Group flying out of Makin island were striking targets beyond the range of the locally based P-39s and P-40s, and during egress they were being hounded by multiple A6Ms for extended time periods. Another fighter unit, the 45th Fighter Squadron at the time stationed at a nearby atoll planned an interception of this running battle on it's way back to base, and 12 P-40s engaged the surprised Zero pilots who were busy engaging the B-25s, claiming ten victories (actual results were closer to two or three) but they saved the B-25s that day and subsequently the IJN units stopped pursuing the bombers so far.

 

[Frog]

The ratios and success rates definitely did change, and not just due to firepower - the Germans (and the Italians and other minor Axis powers, who we typically forget about) quickly learned the same lesson the Japanese did, which was to attack heavy bombers from the front. You don't need to blast apart the superstructure if you put one or to bullets or some shell fragments into the pilot and co-pilot, the plane is probably going down.

This was then partly countered by adding the chin turrets to B-17s and B-24s but that took a while. Quick google says B-17G started to replace B-17F in November 1943. There were some analogous upgrades to the armament of the medium bombers which was increased substantially though they never got nose turrets. And of course bomber unit commanders adjusted combat formations and tactics to deal with the enemy fighter threat.

Luftwaffe would then attack with larger numbers (i.e instead of individual) of heavily armed fighters like Fw 190s and Bf 109G with the cannon gondolas flying at high speed in frontal attacks, and then as we know the Luftwaffe cleverly came up with a host of other creative measures against the unescorted heavy bombers like using heavy / night fighters (Bf 110, 210, Ju 88 and others) with extra cannon, using rockets etc..

Another option was to make high speed diving or climbing slashing attacks from oblique angles which either targeted tail gunners (weakening defensive firepower) and /or one of the engines, which could cause the bomber to fall out of formation and thus into doom.

A 2 for 1 ratio of fighter to heavy bomber losses sounds about right. In the MTO medium bombers usually had some level of escorted, as I noted upthread, but seemed to often end up on their own and had to fight off enemy fighters for a while.

In the Pacific where distances were greater and enemy fighters had much longer range and endurance, both heavy and medium bombers often got into long, extended, dramatic duels with Japanese fighters during egress, which often only ended when they were able to find clouds to hide in, or sometimes (more rarely) when Allied fighters came to their rescue.

There were several cases where lone B-17s or little groups of two or three of them were engaged with multiple zeros for up to an hour or more, and they often survived - sometimes with no loss on either side, but with lots of damage, WiA and KiA on board when they landed. US medium bomber formations were sometimes harried for long distances coming back from certain targets.

There was one famous case where B-25s of the 41st Bomb Group flying out of Makin island were striking targets beyond the range of the locally based P-39s and P-40s, and during egress they were being hounded by multiple A6Ms for extended time periods. Another fighter unit, the 45th Fighter Squadron at the time stationed at a nearby atoll planned an interception of this running battle on it's way back to base, and 12 P-40s engaged the surprised Zero pilots who were busy engaging the B-25s, claiming ten victories (actual results were closer to two or three) but they saved the B-25s that day and subsequently the IJN units stopped pursuing the bombers so far.

The ratios and success rates definitely did change, and not just due to firepower - the Germans (and the Italians and other minor Axis powers, who we typically forget about) quickly learned the same lesson the Japanese did, which was to attack heavy bombers from the front. You don't need to blast apart the superstructure if you put one or to bullets or some shell fragments into the pilot and co-pilot, the plane is probably going down.

This was then partly countered by adding the chin turrets to B-17s and B-24s but that took a while. Quick google says B-17G started to replace B-17F in November 1943. There were some analogous upgrades to the armament of the medium bombers which was increased substantially though they never got nose turrets. And of course bomber unit commanders adjusted combat formations and tactics to deal with the enemy fighter threat.

Luftwaffe would then attack with larger numbers (i.e instead of individual) of heavily armed fighters like Fw 190s and Bf 109G with the cannon gondolas flying at high speed in frontal attacks, and then as we know the Luftwaffe cleverly came up with a host of other creative measures against the unescorted heavy bombers like using heavy / night fighters (Bf 110, 210, Ju 88 and others) with extra cannon, using rockets etc..

Another option was to make high speed diving or climbing slashing attacks from oblique angles which either targeted tail gunners (weakening defensive firepower) and /or one of the engines, which could cause the bomber to fall out of formation and thus into doom.

A 2 for 1 ratio of fighter to heavy bomber losses sounds about right. In the MTO medium bombers usually had some level of escorted, as I noted upthread, but seemed to often end up on their own and had to fight off enemy fighters for a while.

In the Pacific where distances were greater and enemy fighters had much longer range and endurance, both heavy and medium bombers often got into long, extended, dramatic duels with Japanese fighters during egress, which often only ended when they were able to find clouds to hide in, or sometimes (more rarely) when Allied fighters came to their rescue.

There were several cases where lone B-17s or little groups of two or three of them were engaged with multiple zeros for up to an hour or more, and they often survived - sometimes with no loss on either side, but with lots of damage, WiA and KiA on board when they landed. US medium bomber formations were sometimes harried for long distances coming back from certain targets.

There was one famous case where B-25s of the 41st Bomb Group flying out of Makin island were striking targets beyond the range of the locally based P-39s and P-40s, and during egress they were being hounded by multiple A6Ms for extended time periods. Another fighter unit, the 45th Fighter Squadron at the time stationed at a nearby atoll planned an interception of this running battle on it's way back to base, and 12 P-40s engaged the surprised Zero pilots who were busy engaging the B-25s, claiming ten victories (actual results were closer to two or three) but they saved the B-25s that day and subsequently the IJN units stopped pursuing the bombers so far.

First official flight of a B-17G model from Boeing on may 21, 1943.
First official G model delivered by Douglas on spetember 4, 1943.
But about 100 of the last B-17F leaving Douglas Long Beach had also the chin turret and technically were G models.

 

[Steamed_Banana]

Couple of quick examples of bomber overclaiming in the MTO. These are all around the Tunisia area.

2 January 1943 - British Spitfire pilots from 242 and 77 Sqn claimed 2 x Bf 109s and 2 x Ju 87s, (for the loss of 5 x Spifrire Mk Vb), US Spitfires from 52nd FG claimed 1 x Bf Fw 190 and 2 x Ju 87s, US P-38 units claimed 4 x Bf 109 and 1 x Ju 88 (for the loss of 3 P-38s), and B-17s gunners from the 301st bomb group claimed 14 x enemy fighters confirmed (not counting several more damaged or probable) for the loss of 1 B-17F written off after landing. Actual German losses were two Bf 109G-2 (one reported as 'shot down by Spitfire' and one as 'after combat with B-17s and P-38s), one Fw 190A 'collided with Spitfire', one more Fw 190 MiA, one more 'lost to AA', 3 Ju 87 shot down or crash landed, and 2 Ju 88.

So in this case it looks like 14-1 overclaiming by the bomber defensive gunners.

19 January 1943 - B-24 defensive gunners from 93rd BG claimed 6 x Bf 109 'confirmed' destroyed, for the loss of 2 x B-24s and one force-landed at Malta, as well as one B-1F crash landed and 1 P-38 MiA. German losses were1 Bf 109G-4 from JG 53 'Takeoff accident' and 3 Ju 87 to AA.

So here it's probably 6-0 overclaiming by tyhe bomber defensive gunners.

31 January 1943 - British Spitfire IX pilots from 81 Sqn and 322 Wg claimed 2 x Bf 109G (for the loss of 1 x Spit IX, 1 Hurricane, and one Spit Vb, 2 x Beaufighters also shot down), P-38s pilots from 1st FG and 82nd FG claimed 2 x Bf 109 and 2 x Bf 110 (for 3 P-38 shot down), P-40 pilots from 33rd FG claimed 1 x Bf 109 (for 2 x P-40F shot down), B-17F gunners from 391st BG claimed 6 x enemy aircraft confirmed destroyed, while B-26 gunners from 17th BG claimed another 3 x Bf 109s. German losses were 4 x Bf 109G (2 to Spitfires, one to B-17s, one unknown probably to the P-40s), 1 x Fw 190 to B-17s, and 2 x Bf 110 to the P--398s. 1 Italian MC. 202 overturned on landing after combat with B-17s.

So in this one B-17 gunners claimed 6 and seem to have gotten 1 x Bf 109 and 1 x Fw 190 and (arguably) 1 x MC 202, so that is pretty good overclaiming rate of only 2-1. The B-26 gunners overclaimed at 3-0. Bomber gunners together were 9-3 or 3-1.

4 Feb 1943 - B-17 gunners from the 301 BG claimed 9 x Bf 109s and 3 x Fw 190s, B-17 gunners from the 9th BG claimed 9 x Bf 109s (plus a lot of damaged and probables from the bomber gunners of both groups) all for the loss of 1 B-17 to flak and 1 B-17 to fighters; P-38s claimed 1 x Fw 190 (for the loss of 3 P-38s), Spitfire pilots from 52nd FG claimed probable and damaged. One B-26 was also shot down but that unit made no claims. German losses were 4 x Bf 109, all attributed to B-24 and B-17 bombers. 1 MC 202 was also shot down by Marauder.

So the B-17 gunners claimed a total of 21 fighters and appear to have shot down 4, so 21-4 or 5.25-1, and the Marauder was 0 claims for 1 shot down.

7 Feb 1943 - Spitfire pilots from 249 Sqn claimed one Ju-52, P38 piltos from 1st and 82nd FG claimed 2 Bf 109, B-17 gunners from 301 BG claimed 2 enemy aircraft confirmed, B-26 gunners claimed 3 Bf 109s (losing one B-17). German losses were one Bf 109F 'hit by AA' which crash landed. They also lost one Ju 52. 1 MC 202 belly landed after being 'damaged by return fire'.

So here the bomber gunners claimed 5 for probably one MC 202 actually shot down / forced to crash land.

 

[Steamed_Banana]

First official flight of a B-17G model from Boeing on may 21, 1943.
First official G model delivered by Douglas on spetember 4, 1943.
But about 100 of the last B-17F leaving Douglas Long Beach had also the chin turret and technically were G models.

ok that is production but when do the B-17Gs fly their first combat mission?

 

[Steamed_Banana]

It's worth pointing out that US heavy (and medium) bomber losses in the MTO were pretty low compared to Western Europe, in part I think because the Axis didn't have as many of the heavily armed fighters and heavy fighters etc. available in the Med zone, and just had fewer fighters in general. Most of their fighters were not the super heavily armed variants since they were optimized for air to air combat with Allied fighters for the most part.

But it seems like even though they overclaimed a lot, the defensive gunners did their job which was to keep the bomber alive. Because these bombers were often on their own.

 

[don4331]

Let's be fair to Allison here:

Up to '38, Allison is a small company which has build a grand total of 19 V-1710s (Vee for Victory).
Then in '38, they get an order for 59 V-1710s! (RR is making more Kestrels per month, and they're building Merlins, Griffons and Vultures in addition).

If any company was "file to fit", it was Allison, pre-39.​

Allison doesn't have resources to design/manufacture its own supercharger - they sub-contract it our to GE. (So do P&W & Wright)

GE is the premier compressor manufacturer; unfortunately, they are getting paid cubic $$$ to develop turbochargers.
With the challenge of developing a turbine (temperature/pressure) and noting they are getting "free" energy from the turbine, not much effort is put into optimizing the compressor (Efficiency is in high 30%s/low 40%s)
Being fair it GE, the compressor of the Kestrel has peak efficiency of 37% at this point. Then, as note earlier, RR tasks Ellor with improving that and he does - to 70%!​

Again being fair to both Allison and GE, a 1710 in^3 with 6.5:1 compression only need 4" (2 psi) of boost (33" manifold pressure) @ 2,600 rpm to achieve the 1k hp which the USAAF specification requires. The difference between a 40% and 70% efficient supercharger is minimal.

Then sudden Allison has an order for 837 engines in '39 from USAAF! So:

The engineers who historically were designing the engine are now designed the machinery to build 300 engines/mo.
The project managers are coordinating the erecting of the building to house the machinery and all the materials needed to build 300 engines/mo,
And the machinists are training all the new people on how to run the machinery/ assemble 300 engines/mo.​

In middle of this France wants to buy ~784; and the USAAF demands:

a. Allison forgive $1M in development cost for the V-1710 to manufacture for a foreign country.
b. An increase of 132 engines to 969 on the USAAF contract as the cost/engine is decreasing by ~$3k/engine.​

So, where in the above mess, does Allison find the resources to develop a better supercharger compressor?

​

 

[Steamed_Banana]

Let's be fair to Allison here:

Up to '38, Allison is a small company which has build a grand total of 19 V-1710s (Vee for Victory).
Then in '38, they get an order for 59 V-1710s! (RR is making more Kestrels per month, and they're building Merlins, Griffons and Vultures in addition).

If any company was "file to fit", it was Allison, pre-39.​

Allison doesn't have resources to design/manufacture its own supercharger - they sub-contract it our to GE. (So do P&W & Wright)

GE is the premier compressor manufacturer; unfortunately, they are getting paid cubic $$$ to develop turbochargers.
With the challenge of developing a turbine (temperature/pressure) and noting they are getting "free" energy from the turbine, not much effort is put into optimizing the compressor (Efficiency is in high 30%s/low 40%s)
Being fair it GE, the compressor of the Kestrel has peak efficiency of 37% at this point. Then, as note earlier, RR tasks Ellor with improving that and he does - to 70%!​

Again being fair to both Allison and GE, a 1710 in^3 with 6.5:1 compression only need 4" (2 psi) of boost (33" manifold pressure) @ 2,600 rpm to achieve the 1k hp which the USAAF specification requires. The difference between a 40% and 70% efficient supercharger is minimal.

Then sudden Allison has an order for 837 engines in '39 from USAAF! So:

The engineers who historically were designing the engine are now designed the machinery to build 300 engines/mo.
The project managers are coordinating the erecting of the building to house the machinery and all the materials needed to build 300 engines/mo,
And the machinists are training all the new people on how to run the machinery/ assemble 300 engines/mo.​

In middle of this France wants to buy ~784; and the USAAF demands:

a. Allison forgive $1M in development cost for the V-1710 to manufacture for a foreign country.
b. An increase of 132 engines to 969 on the USAAF contract as the cost/engine is decreasing by ~$3k/engine.​

So, where in the above mess, does Allison find the resources to develop a better supercharger compressor?

​

Good points but doesn't this pressure and 'newness' ease up slightly ... eventually? We are talking about 1942 here not 1940.

 

[don4331]

Good points but doesn't this pressure and 'newness' ease up slightly ... eventually? We are talking about 1942 here not 1940.

Actually, it gets worse...

In '40, UK places order for 3,500 engines, as does USAAF (3,691 technically). So, instead of building 300 engines/mo, Allison needs to build 600+/mo.​

And that gets into the next level of problems: The "C" series Allision with their internal tooth gear reducer (and very large bearing) need custom, complex machinery to cut the teeth - so you have a limit on number of engines which can be manufactured*. The "E" and "F" with their external tooth gear reducers can be cut using much less complex machinery. So, redesigning the speed reducer is much higher priority.

The other part that SR6 alluded to - Allison has spend big $$$ on custom machinery to machine the rear accessories cover for the V-1710. It is not capable of being easily modified to accept a thicker gears, let alone additional shaft(s) for 2 speeds.

*Back to our frenemies at RR. They originally developed a 2 speed mechanism which only added 0.5" to the engine! Unfortunately, it used internal tooth gears. And as noted above, while the internal teeth were great for the prototypes; they weren't good for mass production.​

​

So, RR bit the bullet, crossed the channel to France and started negotiations with the Farman brothers for their 2 speed drive. Unfortunately, the Farman brothers went bankrupt. But they were too important to national security, so their company was nationalized. And the gov't of France wanted their £ (my attempt at humour) for the patent. As a result, RR only made a limited number of Merlin X engines in '39-40 as they were paying lots of ₣ to the French gov't. Then, the Germans invaded France and the French gov't waived the patent royalties so long as UK was fighting the Germans. Which is why suddenly a lot of RR engines got 2 speed drives using Farman's patent. RR sets up different machinery at different plant to build 2 speed engines, but they are turning out Merlins like hot rolls (to quote Goering)​

​

We will note the Farman 2 speed drive added 2" to the rear accessory cover of the Merlin. If your machinery won't accept the additional 0.25" for thicker gears, how will it accommodate 2" for 2 speed drive? And where does Allison get the $$$ for the patent royalties?​

​

Lastly, you don't hire/design/test/order & manufacture overnight. Especially, when every company is hiring/ordering machines as fast as they can...

Allison certainly could have added a 2nd speed but it would take a couple years from concept to mass production. And they (or USAAF) didn't see the need in '38.​

 

[Steamed_Banana]

Actually, it gets worse...

In '40, UK places order for 3,500 engines, as does USAAF (3,691 technically). So, instead of building 300 engines/mo, Allison needs to build 600+/mo.​

And that gets into the next level of problems: The "C" series Allision with their internal tooth gear reducer (and very large bearing) need custom, complex machinery to cut the teeth - so you have a limit on number of engines which can be manufactured*. The "E" and "F" with their external tooth gear reducers can be cut using much less complex machinery. So, redesigning the speed reducer is much higher priority.

yeah but, V-1710 "F" series are already in full production in 1941, or else what am I missing? First flight of the P-40D was in May 1941. delivery of what would be 560 P-40D / Kittyhawk I with Allison V-1710-39 / F3R to the British was in mid 194, first combat in the middle east was right around January 1942. This seemed to go smoothly on a design level by the way in spite of the need to make some rather substantial changes in the nose section of the Hawk 87 type P-40 to accommodate the new engine as we know.

So whatever work designers are doing to create external tooth gear and production of same would presumably be winding down by this point. They did do some work on strengthening the F3R (bearings, crank case and crank shaft) for the V-1710-73 / F4R but these would seem to be incremental changes. And of course we know that the higher speed supercharger was still in the works at this time but that seems like it went fairly quickly as well (P-40M with V-1710-81 / F20R delivered in November 1942) and presumably work on the 9.60-1 could overlap with a new two speed supercharger.

The other part that SR6 alluded to - Allison has spend big $$$ on custom machinery to machine the rear accessories cover for the V-1710. It is not capable of being easily modified to accept a thicker gears, let alone additional shaft(s) for 2 speeds.

I think it's obvious that the 'integral' supercharger & housing etc. would have to be replaced for a two speed, no doubt about that.

*Back to our frenemies at RR. They originally developed a 2 speed mechanism which only added 0.5" to the engine! Unfortunately, it used internal tooth gears. And as noted above, while the internal teeth were great for the prototypes; they weren't good for mass production.

So, RR bit the bullet, crossed the channel to France and started negotiations with the Farman brothers for their 2 speed drive. Unfortunately, the Farman brothers went bankrupt. But they were too important to national security, so their company was nationalized. And the gov't of France wanted their £ (my attempt at humour) for the patent. As a result, RR only made a limited number of Merlin X engines in '39-40 as they were paying lots of ₣ to the French gov't. Then, the Germans invaded France and the French gov't waived the patent royalties so long as UK was fighting the Germans. Which is why suddenly a lot of RR engines got 2 speed drives using Farman's patent. RR sets up different machinery at different plant to build 2 speed engines, but they are turning out Merlins like hot rolls (to quote Goering)

We will note the Farman 2 speed drive added 2" to the rear accessory cover of the Merlin. If your machinery won't accept the additional 0.25" for thicker gears, how will it accommodate 2" for 2 speed drive? And where does Allison get the $$$ for the patent royalties?​

I think Allison could afford patent royalties and the Free French would be unlikely to drive a hard bargain in this case.

​

Lastly, you don't hire/design/test/order & manufacture overnight. Especially, when every company is hiring/ordering machines as fast as they can...

Allison certainly could have added a 2nd speed but it would take a couple years from concept to mass production. And they (or USAAF) didn't see the need in '38.​

Sure but how about in 1940 or 41?