Luftwaffe after BoB: strategy, tactics, tecnology?

[tomo pauk]

The last is a common misconception. If your climb rate at 20,000ft or so is significantly worse than the defenders it means you get one firing pass at them and then you are out of the fight. It is also a misconception because it assumes that the defenders have a limited amount of warning time and are struggling to reach combat altitude as the bombers and escorts arrive.

One thing is to measure the climb rate with all internal fuel, another thing is to measure it after, say, 1/3rd was used up. For the P-40B, that would mean arriving at combat with 100+ gals aboard, a 300+ lbs difference. The Spitfire has 100 US gals aboard prior the take off, and will burn, say, 20 gals until it is at 20000 ft?
The defender cannot use the maximum power, but will instead climb at a lower power setting.

It is 165miles from Dover to Birmingham, over 45 minutes at the cruising speed of many bombers. Granted the defenders may not know which target/s the raid is going after but even without radar, deep penetration raids are going to find interceptors in the air and above them.

The attacker can throw all of their LR fighters in an approximate area where the bombers will be flying. Would all of the defenders be able to concentrate on the attackers? I'd say no, we can look at the BoB and inability of different groups to help the neighbor from another group.
Then, what will the defenders do, once they see the attackers? Forget about the escort, go after the bombers, only to be killed by the escorts (= LW in 1944)? Or deal with the escort, so the bombers can go unmolested?
What was the alternative to the LW anyway in 1940? Bf-110 - no go vs. the Spitfire, struggles with Hurricane, not enough of them any way. Unescorted bombers? Another no-go. Night bombing? Healthier for the bombers, but they will not kill the RAF.
We should look at a whole air force needs, not just whether one fighter is 5-10 mph slower than the other.

And like I keep saying, climb rate is an indicator of how well a plane can maneuver and fight at a given altitude. Many countries figured you needed a climb rate of 500 fpm just to fly in formation, let alone fight. Squadron of planes does a 180 degree turn at 25,000ft and above, outside planes have to speed up to maintain formation, using more power, all planes loose lift as they bank and need more power just to hold altitude as they turn. To actually engage in combat might require a climb rate of 1000fpm and a tight turn (anything around 2-3 Gs depending on altitude) will cause you to loose either height or speed.

As above - an attacker that burned 1/3rd of it's fuel will climb much better than with its full fuel.

I don't care if the quality was the same, I do care if we are comparing planes with self sealing tanks to planes without them, And the P-40C gained a lot of weight (and lost fuel) with it's self sealing tanks which were hardly of a 1944 type. Adding several hundred pounds of self-sealing tanks to some of these planes will affect their performance, climb and turn.

I care, since we are debating the abilities of planes that were using pre-1941 technology (though the P-40B was from 1941).

Thank you, apparently the Bf 109 was a real dog when it came to aerodynamics as it is about the same speed as a D.520 despite having around 20% more power. The D.520 carried more armament (weight) and more fuel for greater range too. Good thing for the Germans not many got into service.

The Bf-109E was a dog, aerodynamics-wise. The Bf-109F-0, with same DB-601A engine, was faster some 25 km/h, just due to the aerodynamic refinements (front of the plane, retractable tailwheel, no struts on the tailplane, wider shallower radiators, also one cannon less).

 

[Shortround6]

title of thread is "Luftwaffe after BoB: strategy, tactics, tecnology?"

After the BoB The Germans, British, Americans all figured that planes without self-sealing fuel tanks/armor were operational trainers. French are already out of it (D520 with smaller, heavier fuel tanks has range of ????Performance of???), Japanese didn't change and lost how many pilots and and aircrew?

Escorts may burn off fuel, they can't burn off the weight of the empty (or part empty) self sealing tanks. The P-40 gained 250lbs in weight just due to the extra weight of the self sealing tanks while empty. WHile the first P-40Cs don't show up (at the factory) until April/May of 1941 the Army had ordered the first P-40Ds in Sept of 1940 (middle of the BoB)
And escorts need enough fuel to fight for 15-20 minutes then fly 150-250 miles to 'neutral' airspace (say the channel) and then still need to cross the channel, find friendly field and land. The flying back from the target area to the channel CANNOT be done at 190-220mph at 10-15,000ft unless they want to provide target practice for the defenders.
I will assume that the escorting was done in relays so one group of fighters are not tied to the bombers for the entire flight. Going by the chart for the P-40D/E a P-40 would burn about 60 gallons an hour at 2300rpm map 28in (lean) to go about 280mph at 15,000ft. It would also burn 43-45 gallons to reach 20,000ft taking off at 8100lbs. Taking off at 8700lbs increase fuel to 20,000ft to 46-51 gallons.
Climb rate for a P-40E at 20,000ft was 950fpm at 7500lbs, 800fpm at 8100lbs and 650fpm at 8700lbs, At 25,000ft it was 550fpm, 400fpm and 250fpm for the three weights. Yes you burn off some fuel before engaging in combat but even an extra 500-600lbs has a significant impact on climb at the high altitudes. The P-40E at 25,000ft is climbing at 3/4s the climb rate at 8100lbs as it would at 7500lbs. At 5,000ft the heavier plane is climbing at about 89-90% of the lighter one so the difference is nowhere near as great.

 

[tomo pauk]

Problem with the P-40 is that it gained weight, via installation of heavier armament, protection, structure and fuel system, while there was no gain in engine power. We cannot blame only the heavier fuel system for what it lost in the RoC vs. the lighter predecessors.
The European counterparts gained, sometimes, armament weight, a bit of protection, but they received more engine power every year, if not half a year, like sometimes the Bf-109 received. The Spitfire V with two cannons and 4 Brownings (= interceptor) should weight more than a Spit V with Brownings only and an empty self-sealing 30 imp gal rear tank (= longer range fighter), and would be also a bit draggier.

 

[tomo pauk]

Back to the engines again, this time BMW.
Forgetl the 802 and other bigger engines. All effort to the 801 model, but the fraction of the resources to slightly improve the Bramo 323 and BMW 132. The next step from the 801A/C might remain with a lower compression ratio, so there is less problems once the C3 fuel is used with greater manifold pressure?
Should also enable easier earlier over-boosting, above 1.60-1.70 ata, at a cost of some altitude power vs. the historical 801D, but still a bit better than the 801C, due to increased S/C gearing (from .
Improvements for the BMW 801 - the bigger S/C, a 2-stage S/C, both with or without intercoolers, explore the water injection application. Also the Polikovsky's 'swirl throttle', the increased power under 5-5.5 km (incl. take off) would be much appreciated by the bomber fighter-bomber A/C. Would also allow to have more power while remaining on the B4 fuel.
The compact turbo-supercharger, employing the turbine with hollow blades, looks interesting, too.

added: translation/additions/corrections by yours truly:

 

[Milosh]

Wasn't the first shipments of 100 octane fuel the Brits got suppose to go to the French? But, then the French were over run and capitulated.

 

[Shortround6]

Problem with the P-40 is that it gained weight, via installation of heavier armament, protection, structure and fuel system, while there was no gain in engine power. We cannot blame only the heavier fuel system for what it lost in the RoC vs. the lighter predecessors.
The European counterparts gained, sometimes, armament weight, a bit of protection, but they received more engine power every year, if not half a year, like sometimes the Bf-109 received. The Spitfire V with two cannons and 4 Brownings (= interceptor) should weight more than a Spit V with Brownings only and an empty self-sealing 30 imp gal rear tank (= longer range fighter), and would be also a bit draggier.

Just using the P-40 to help illustrate the point. But lets try something, still using the P-40D/E since it is a bit easier to get numbers for, granted in climbs like a pregnant hog but it's speed is pretty good for it's power which means it's drag isn't that far off. AND the P-40D/E has 123imp gallons of internal fuel and can take 43.3imp or 62.5imp drop tanks. Or use the P-40F.
Now figure out you combat radius;

1. Warm up and take off allowance.
2. Climb to altitude and form up allowance.
3. Combat allowance (5min military power and 15min max continuous)
4. reserve allowance (20-30min at most economical).
These are pretty much fixed and won't change much from mission to mission.

For a particular mission (and like the 8th airforce, lets assume you are escorting in relays) you need to figure:
5. cruise to meeting point with bombers.
6. Cruise speed while escorting bombers (if the bombers are doing 180-200 the fighters have fly faster and weave or else they will be flying to slow to quickly respond) and air miles flown vs ground distance covered due to weaving.
7. Separation point from bombers. Worst/best case is over the bomber target, Fighters defend and then break for home as Fresh fighter squadrons show up to escort bombers on return leg. What cruise speed and altitude is needed to minimize risk/losses as fighters withdraw from enemy airspace? It will NOT be most economical cruise.
8. At what point can you throttle back from "combat cruise" to something less as the danger of being bounced by fresh enemy fighters fades (like crossing the channel).

Some of these change depending on when in the war we are talking about. In 1940-41 the Channel was somewhat contested. You are NOT safe as soon as you are over water. Lets also remember that while the Channel was pretty narrow in the Dover - Calais area over much of it's length it is closer to 100 miles wide and for the British to hit Germany, they have to fly over Belgium or Holland. Germans have it a bit easier once they take France/Low Countries.

Now for the P-40 in US gallons 1 2 come up to about 40-50 gallons (lighter planes should do better, and perhaps in summer less warmup is needed?).
3. is about 38 gallons
4. is 11 gallons for 20 minutes.

So we are up to about 89 gallons already.

Now at about 233mph at 12,000ft it takes a P-40 23-24 gallons to fly 133 miles (distance from Ipswich to the Hague. And since you need to go both ways that is 135 gallons total, Granted the trip over will be done on the drop tank Or at leas t partially. Yo know have 13 gallons left plus drop tank for actual penetration into enemy territory while escorting bombers. The P-40 can do 280mph at 15,000ft on 60 gallons an hour or 4.33miles per gallon (engine is running lean, much faster and it has to go to rich. With a 52 US gallon drop tank you can theoretically penetrate about 140 miles past the The Hague but that does not count weaving.
IF you decide your fighters need to cruise faster for better response to an attack the P-40 does 297mph at 15,000ft but burns 85 gallons an hour running rich for 3.49miles per gallon. P-40D/E can do 316mph at 12,000 as long as the fuel holds out (max continuous) but is burning 112 gallons an hour or 2.82mpg.

Obviously other planes may differ a bit, especially as to altitude and max lean cruising speed but the general performance area is there. For the British an extra 20-30 US gallons inside and a US 50 gallon drop tank are barely going to get you to the German Border if you are formation flying and weaving over bombers and maybe not even that. Germans are a bit better off as they don't have to cross 100-150 miles of formally neutral countries to get to important targets.

 

[parsifal]

A word of caution on ranges. They are just not comparable between types and are often misleading. Manufacturers specs dont usually lie, but when a range is quoted, you cant know the operation state of the aircraft.

I was once involved in a simulation design and it was stated how superior the ranges of french aircraft were compared to both British and US. Then we started to look a little deeper...how far could an MS406, or a D520 go under combat conditions. turns out that 750 mile published range is a crock for operations. The D520 is marginally better than a Spit when operating in a combat role.

 

[fastmongrel]

Wasn't the first shipments of 100 octane fuel the Brits got suppose to go to the French? But, then the French were over run and capitulated.

Britain had been getting 100 octane from refineries in Venezuela, the Caribbean and Persian Gulf from about 1936 onward. US 100 octane was bought during the early years before Lend Lease but the majority of RAF fuel came from British owned refineries. I cant remember the exact figures but Britian had stocks of about 80,000 tons of 100 octane by May 40 which had almost doubled by Sept 40.

 

[tomo pauk]

This might help, in order to roughly calculate the range of the Bf-109 (unrelated to the topic: the length of the DB-601A is 1852mm, not 1352mm). The consumption is the last column, liter per hour:

 

[Aozora]

PLease, please, please......
Did the D.520 even have self sealing tanks? without them your escort fighters could be on a one way trip from only a few 7.6-8mm bullet holes. Performance for the D.520 is all over the place due to different engines, different power quotes even for the same engine. Very little data that has solid support and a lot of wild speculation on the web and from old books ( like this in wiki: "the 12Y-45 and -49s fitted to production D.520s used either 92 or 100 octane fuel.")

Now where the French were going to get 100 octane fuel is not mentioned. Nor is there any mention of what performance improvements there might be, and the Hispano design was getting pretty close to maxed out. The engines in the D520 may have require 91 octane fuel not the 85-87 octane of some of the earlier Hispano engines. ( most of the 860hp engines used a 5.8 compression ratio and ran on 85 octane, most of the over 900hp engines used 7:1 compression ratio and needed the 91 octane) The Hispano company had a lot of prototype engines or very low production number engines during the summer of 1940 and trying to figure out which airplane had which engine resulting in what for performance numbers is rather difficult.

And just so we are all on the same page here:

View attachment 276164

US 55 gal drum, 208 liters. 55 US gallons of fuel is about 330lbs or 150kg.

The Hurricane and Blenheim units of the AASF of the RAF in France were being supplied with 100 Octane fuel;

http://www.wwiiaircraftperformance.org/hurricane/AASF-Fuel.pdf

http://www.wwiiaircraftperformance.org/hurricane/RAF-Component-15may40.pdf

the table below, dated 24 February 1940, lists supplies of 100 octane fuel "Overseas (West of Suez)" at 5,300 tons (or 12,720,000 lbs, or roughly 42,400 55 gal drums) as of 8th Feb. No doubt some of this was being transported, but I do know that there were tankers carrying avgas, from British oil refineries, that regularly docked at French ports, prior to May-June 1940

This table, dated 17 March, shows 6,200 tons as of 7 March

It doesn't take much of a stretch to think that the French AF may well have been able to get supplies of 100 Octane fuel from the British.

Also, what fuel did the French Curtiss 75s require?

 

[Shortround6]

Thank you for the tables.

The thing with 100 octane fuel and some engines is that you just can't pour the the stuff into the tank, twiddle the boost limit nut and magically get a few hundred extra HP.

Some engines will do very well if you do that, others tend to break real quick. Please note that anybody who developed the Hispano-Suiza 12-Y engine type to make significantly more power also increased the weight of the engines a considerable amount. The Swiss version used a crankshaft that weighed 30kg more than the French originals.

IF the french were planning on building hundreds of D.520s (and they were) then they had to plan to build hundreds of Hispano-Suiza 12-Y-45/49 engines (and they did) and they had to make these plans in 1939. So the question is NOT wither a few British tankers docked in France in 1940 with 100 octane fuel but where France thought it was going to get enough 100 octane fuel to run hundreds of planes on back in 1939 when they made their production plans.

The P&W engines used in the French Hawks would run on 87 octane and the Wright R-1820 G200-5 would run on 91 octane (or 91/96) and give 1200hp for take-off.

The P &W information can be found here;

http://www.enginehistory.org/P&W/R-1830/R-1830Index.pdf

and some Wright Cyclone information can be found here;

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/158515e26a46ef168525670b006c2d21/$FILE/E-219.pdf

 

[wiking85]

As an aside what could the LW have built if using our hindsight they don't produce the Me210 until its fixed, same with the He177, and the Ju288 is cancelled when the Jumo 222 runs into its 1940 problems? How about the effect of building the Ostmark engine facility around the Jumo 213, which would get the full support of the RLM once the Jumo 222 is dropped and probably be available a year or so earlier as a result? Or not gearing up for the Ta-154? https://de.wikipedia.org/wiki/Focke-Wulf_Ta_154#Produktion
Perhaps more Ju88Gs with earlier Jumo 213s? Or would we see more He-219s with Jumo 213s? Perhaps an earlier Ar234P for night fighting, or an earlier Me262B?

 

[Glider]

I am pretty sure that the French Airforce didn't have any 100 octane fuel. It only started to be used by the RAF in France in May 1940 and I do know that the French were asking to access it in April/May. I cannot be certain but I doubt that they would have had time to acquire, test and distribute it before the Germans rolled over everything in Europe.

 

[Greyman]

I am pretty sure that the French Airforce didn't have any 100 octane fuel. It only started to be used by the RAF in France in May 1940 and I do know that the French were asking to access it in April/May. I cannot be certain but I doubt that they would have had time to acquire, test and distribute it before the Germans rolled over everything in Europe.

The RAF was using it before then. Heck, the first RAF fighter kill in the war (Oct 30, 1939) was achieved with +12 boost.

My knowledge of French aircraft is quite low, but I have some information on the D.520:

Aircraft	Engine	Fuel
D.520 (1st 2nd prototypes)	12 Y 25/29	85/100 octane
D.520 (2nd 3rd prototypes)	12 Y 31	85 octane
D.520 (1940 production)	12 Y 45	92/100 octane
D.520 (1942 production)	12 Y 49	92/100 octane
D.523 (1 prototype)	12 Y 51	100 octane
SE 520 Z (1 prototype)	12 Z (2)	92 octane

 

[Shortround6]

Thank you for the information on the D.520 Hispanos.

Unfortunately it seems to open as many questions as it might answer.

From "Hispano Suiza in Aeronautics" by Manuel Lage:

Engine.............RPM............HP/altitude........HP/take-off...........compression ratio............compressor/ turning ratio.

12-Ydrs2.........2400...............930/950...................992..............................5.8....................................HS/8.31
12-Ycrs...........2400...............860/3300.................835..............................5.8....................................HS/10.0
12-Y-21..........2400...............910/3600.................880..............................7.0...................................HS/10.0
12-Y-27..........2400...............900/850...................950..............................5.8...................................HS/8.33
12-Y-29..........2400...............920/3600.................910..............................7.2...................................HS/10.0
------------------------------------------------------------------------------------------------------------------------------------
12-Y-31..........2400...............860/3250.................830..............................5.8...................................HS/10.0
12-Y-33..........2400...............955/2250.................960..............................7.0...................................HS/10.0
12-Y-37..........2400...............960/1250...............1050..............................7.0...................................HS/8.33
12-Y-45..........2400...............920/4200.................935..............................7.0...................................SP/10.0
12-Y-49..........2400...............910/5250.................910..............................7.0...................................SP/11.46
12-Y-51..........2500..............1000/3260..............1100..............................7.0...................................SP/11.46

Engines above the line use the old style connecting rods and have no crankshaft damper. Engines below the line have the new rods and dampers.
under compressor HS stands for Hispano-Suiza and SP stands for Szydlowski-Planiol. The SP supercharger was supposed to lower the intake temperatur by 60o​ C

The 12-Y-51 was supposed to have bigger intake valves, the extra 100rpm (which required stiffer camshafts ?) and reinforcement of the upper and lower crankcases for about a 10KG increase in weight.
Unfortunately the book makes very few references to fuel, and little or no mention of boost pressures.

The 12-Z got 4 valves per cylinder, ran at 2600rpm and went back to an HS supercharger. Only a couple of engines were flown before the surrender and at the time were using the same six carburetor set up as the earlier engines (or at least the same configuration, don't know if the same model carbs were used)

One could speculate that the 5.8:1 compression ratio engines ran on 85 octane and the others on 92 octane, what advantage the 100 octane brings I don't know as there is no mention of it and from the tables no real need of it (could very well be wrong on that) until you get to the 12 Z going back to the HS supercharger (or a modified one?) with it's higher intake temperature.

 

[Aozora]

The RAF was using it before then. Heck, the first RAF fighter kill in the war (Oct 30, 1939) was achieved with +12 boost.

Indeed, approval to use 100 octane fuel in Spitfires and Hurricanes, and constant-speed propellers for the latter, was issued on 24 September 1938.

http://www.wwiiaircraftperformance.org/100-octane/24sept38-spitfire-100oct-approval.jpg

http://www.spitfireperformance.com/spit1-12lbs.jpg

Paragraph 5 of the latter:

The operational limitations of Merlin engines when run on 100 octane fuel must be strictly observed.

The Merlins couldn't run at +12 lbs boost until they were equipped with modified cylinder heads and boost cut out controls and , although they were capable of using 100 octane fuel.

Is it possible the late 12-Y series engines were being modified to use 100 octane fuel, but had not yet been able to realise their full potential without more (possibly pending) modifications that were stymied by the surrender? It may well be the French had access to enough 100 octane to at least test the Hispanos, but not enough to use operationally.

 

[Glider]

The RAF was using it before then. Heck, the first RAF fighter kill in the war (Oct 30, 1939) was achieved with +12 boost.

The RAF were using it before then I agree but not in France. Hurricane Squadrons in France started using 100 octane in May, No 1 Sqd starting on the 18th May at Berry-Au-Bac

On a slightly different note but I would be interested to know which unit had the first kill in Oct 1939 using 100 octane. I say this as the use of the fuel depended on the supply of the fuel. In November formal approval was still not given for the use of the fuel and on the 7th December the RAF were yet to start distributing the fuel. The first instances that I am aware of the fuel being used in is Feb 1940.

 

[Greyman]

On a slightly different note but I would be interested to know which unit had the first kill in Oct 1939 using 100 octane.

1 Squadron. I think the action is detailed in Richey's "Fighter Pilot", my copy is not with me at the moment.

 

[Glider]

Thanks for this but according to the No 1 Squadron records they didn't get the fuel until May 1940 as mentioned before so something has gone wrong somewhere

 

[Shortround6]

The Merlins couldn't run at +12 lbs boost until they were equipped with modified cylinder heads and boost cut out controls and , although they were capable of using 100 octane fuel.

Is it possible the late 12-Y series engines were being modified to use 100 octane fuel, but had not yet been able to realise their full potential without more (possibly pending) modifications that were stymied by the surrender? It may well be the French had access to enough 100 octane to at least test the Hispanos, but not enough to use operationally.

One of the limiting factors (and a big factor) is the Hispano lacked the strength to withstand much of an increase in power, at least not without shortening it's service life.
Please note the modifications (and increased weight) of the Russian Hispano's, the VK series. The Russians used 95 octane and accepted (in some models) a shorter engine life.
The French may well have tested one or more Hispanos on 100 octane fuel but there was no big boost of power waiting to be unlocked.