WW2 Aviation Mythbusters

parsifal · Dec 13, 2011

You would think the first thing to do with a captured ac would be to analyse the fuel.....

My extremely limited knowledge on this subject is that lower octane rated fuel is the same as standard versus super grade petrol, well, kind of. 87 grade standard burns quicker its ignition is more of a bang rather than a burn. Super grade petrol (which is 95 octane rating from memory), has lead added to it that acts as an ignition retardant. It has a longer, slower burn cycle, so that more of the power stroke of the piston is actually under power, and hence accelaration. This in turn generates more power at the drive point, which in a car is the flywheel in a plane is the prop hub.

thats how my schoolboy mechanics understands the process at least. If the wrong fuel is put into an engine rated and tuned for a higher rated fuel, it doesnt take long before pistons have holes burnt in them, valves are burnt as fuel ignites prematurely (and unburnt fuel ignites in the exhaust ports due to inadequate fuel/air mixing) and cranks tend to get broken from the jerky violent running of the engine .

At least thats my elementary understanding of fuel octane ratings and engines. if Im right, that means the engine had to be left running very rough for some time until it sh*t itself. Why would you do that

Milosh · Dec 13, 2011

Yes the Bf109 had great range. That is why some (between 15 and 60) of the lightened Bf109s that took off from Prague were recalled when the bombers turned north and were out of range during the Rammkommando Elbe mission. Then there was the 15 from Stendal were never given a target and returned to base due to fuel shortage.

On the Spit Performance site I believe there are some graphics which show the Bf109 had a combat range of 130mi.

wuzak · Dec 14, 2011

Edgar Brooks said:
Twaddle; the Spitfire climbed at over 4000'/minute at full throttle, so could reach 20,000' in less than 10 minutes

Indeed.

Spitfire LF.IX (Merlin 66):
Rate of climb at Sea level: 4620 ft/min
Rate of climb at full throttle height in M.S. supercharger gear: 4700 ft/min at 7000 ft
Rate of climb at full throttle height in F.S. supercharger gear: 3860 ft/min. at 18,000 ft
Rate of climb @ 30,000 ft: 2125 ft/min.
Time to 10,000 ft: 2.15 mins.
Time to 20,000 ft: 4.75 mins.
Time to 30,000 ft: 8.4 mins.
Height at which rate of climb is 1000 ft/min: 37,100 ft
Time to reach above height: 12.9 mins.

Spitfire HF.IX (Merlin 70):
Rate of climb at Sea level: 4390 ft/min.
Rate of climb at full throttle height in M.S. supercharger gear: 4530 ft/min. at 11,900 ft.
Rate of climb at full throttle height in F.S. supercharger gear: 3480 ft/min. at 24,700 ft.
Rate of climb @ 30,000 ft: 2600 ft/min.
Time to 10,000 ft: 2.25 mins.
Time to 20,000 ft: 4.85 mins.
Time to 30,000 ft: 8.05 mins.
Height at which rate of climb is 1000 ft/min: 38,000 ft
Time to reach above height: 12.6 mins.

These numbers are corrected to maximum boost of +18psi. Later in the war they were allowed +25psi.

The Mk XIV was similar - less than 5 minutes to 20,000ft, around 8 minutes to 30,000ft.

The ability to climb quickly was the basis for the defence system for the Battle of Britain. If it took an half hour to get to combat altitude then the RAF would have been much less succesful in the BoB.

Siegfried · Dec 14, 2011

FLYBOYJ said:
And if you're jumped by fighters?
We're not talking about the Spit nor were my comments made about the Spit. The -109 had a constant speed prop and any abrupt attitude changes will cause additional fuel consumption. QUOTE]

I'm not so sure about that, the latter Jumo and DB engines had a "Kommandogeraete" or "control apparatus" that handled prop pitch, engine rpm, prop overspeed in a dive and mixture settings in single throttle control. This was similar to the one famously used on the BMW 801. The Me 109's abillity to retain reasonable range in the face of massive weight and engine power increases with no increase in fuel tankage seems to relate to the very good fuel efficiency of the engine.

One feature of the Spitfire was the introduction of extra fuel tanks. The Mk VIII was supposed to have a little extra fuel in its main fueselage tank plus a pair of 12 gallon tanks in each wing. The 'emergency' Mk IX generally didn't get these. Some Mk VIII had a tail tank of 44 gallons. The tail tank was of no use in combat due to the instabillity it introduced and was a ferry only tank; it was significantly worse than the P-51s tail tank C of G issues, which were more manegeable. The Mk XIV (Griffon) variant more or less used the Mk VIII fuel tankage to compensate for the thirstier Griffon.

PRU spitfire had leading edge tanks that eliminated the possibillity of armament. Recon Me 109's retained their armament.

The key issue with external tankage is that it generally needs to be jettisoned to engage in competitive combat and this ultimatly limits combat radious. The 3 x 66 gallon tanks possible with some armed Me 109 recons would certainly allow interesting mission profiles but the combat radious would still be about 3/4 of maxium range without drop tanks assuming reserves, combat allowance and the advantage of climbout being provided by the external tankage. The main advantage as I see it would be the abillity to provide extended combat air patrols eg to loitre above a ship or u-boat for several hours.

vanir · Dec 14, 2011

They got the range improvements on the later Daimlers by playing with blowers, not the integrated aeromechanical screw system (ahem "kommandogerät"), which is hydraulic and mechanical and still subject to getting tossed around a little bit by ambient pressures.
The retained throttle-twist prop pitch manual adjustment on every 109, 190 or 152 ever made, it wasn't for a backup on the ca. Aug41 autoscrew adoption (F4 onwards, might've been trialled on late F2/3 examples but I don't believe was standardised until F4). It was for vets who set it better than the auto system. Pilot request, thank Mölders for that. I believe one of the RAF write ups on a captured 109G mentioned a skilled pilot could squeeze improved performance using the handy throttle twist prop pitch adjustment, and commented on how great the option was.

The ASB engine superseded the DB engine over cruise range. They got it from the blower. Same with 605A vs 601A, actually the throttle altitude compensated for the higher fuel burn rate. It evened out on the range despite power increase using the same 400 litre capacity, it had a longer ranging normal cruise condition. The DB motor did exactly the same thing, 1.5ata military burns more fuel than 1.42ata military in the 605A-late, but the DB cruises with a lazy 100hp more at a thousand metres higher using about the same fuel consumption and rpm, it's got a better blower for ranged cruise, just floats the alt easier.

A lot of blower development of 42-45 for the Daimler 605 was all about cruise performance for ranging operations without increasing the weight of the aircraft. They needed more military power, and more cruise range on the same fuel load, those were the priorities. Oh and to do it all in synthetic fuels. I'm personally surprised the RLM didn't just ask for a partridge in a pear tree.

Siegfried · Dec 14, 2011

bobbysocks said:
This in my understanding this is where the LW lost the biggest wealth of its seasoned pilots. Herman the horrible, because of the LWs success at supplying the troops at Demyansk by air promised he could do the same at Stalingrad. the magnatude of this operation was much larger and so more pilots were needed. its easier to put a less experienced pilot in a single seat fighter by himself than in a multi engine ac loaded to the max. many veteran pilots were shifted from units or as instructors to supply stalingrad and then to air lift out. but in Demyansk the VVS wasnt as strong as it was in Stalingrad and the LW took some heavy punishment. in the few theings i have read i dont recall there being any escorts available.

Jenkoschenk made the commitment to air lift, when he checked his figures he realised the capacity of the SB 500 air supply parchute container was not 500kg but that the 500 refered to only the bomb shackle used. Von Richthoffen also said that it wasn't possible. It was more than just the parachute supply container issue of course. Jenkoschenk tried to correct his mistake but Goering wouldn't let him. Hitler had in a speach said that "we shall not retreate from this place" and was politically motivated not to retract his words and relieved that the airlift wouldn't force a tactical retreat.

The Ju 52's were worn out, engines couldn't develop full takeoff power which restricted load, their opperational availabillity was restricted, there was a pilot shortage, a sever one, as these men had been lost of Damyansk and Crete (due to enigma decrypt revealing specific drop zones). We thus had several women pilots supply Stalingrad.

The Ju 52 was also not up to the task: the Ju 252 could have opperated from far more distant airfields safe from Soviet attack, carried more load per movement thus relieving the congestion issue as well as of load quickly due to its trappoklappe rear loading ramp and sped through danger zones. The Ar 232's range was slightly better than the Ju 52 but it had far far better takeoff and landing performance than the Ju 52 and exceptional rought airfield abillity due to its 22 'millipeed' wheels it could cross ditches of several meters. It could have used very small rough improvised fields. Only a handfull of these aircraft were available as they had been relegated to low priority development or had not been allocated the higher grade engines they needed.

vanir · Dec 14, 2011

FLYBOYJ said:
I'd also bet dollars to donuts that a good percentage of the time there was a layer of cloud cover that actually limited or even prohibited combat at higher altitudes. Even during heated battles, you have to be pretty careful about punching into a cloud bank unless you know exactly where you are and the height of the terrain around you.

Mate that's precisely the kind of thing I was trying to say. That whole environment thing, I'm no great pilot but I've flown some planes a long time ago, and if I learned one thing is that complex evolutionary diversity is really complex.

Nowadays when I see something in history that doesn't make sense, especially when professionals have been doing or saying it, nowadays I tend to think I've got it wrong. Not they did.

vanir · Dec 14, 2011

wuzak said:
Indeed.

Spitfire LF.IX (Merlin 66):
Rate of climb at Sea level: 4620 ft/min
Rate of climb at full throttle height in M.S. supercharger gear: 4700 ft/min at 7000 ft
Rate of climb at full throttle height in F.S. supercharger gear: 3860 ft/min. at 18,000 ft
Rate of climb @ 30,000 ft: 2125 ft/min.
Time to 10,000 ft: 2.15 mins.
Time to 20,000 ft: 4.75 mins.
Time to 30,000 ft: 8.4 mins.
Height at which rate of climb is 1000 ft/min: 37,100 ft
Time to reach above height: 12.9 mins.

Spitfire HF.IX (Merlin 70):
Rate of climb at Sea level: 4390 ft/min.
Rate of climb at full throttle height in M.S. supercharger gear: 4530 ft/min. at 11,900 ft.
Rate of climb at full throttle height in F.S. supercharger gear: 3480 ft/min. at 24,700 ft.
Rate of climb @ 30,000 ft: 2600 ft/min.
Time to 10,000 ft: 2.25 mins.
Time to 20,000 ft: 4.85 mins.
Time to 30,000 ft: 8.05 mins.
Height at which rate of climb is 1000 ft/min: 38,000 ft
Time to reach above height: 12.6 mins.

These numbers are corrected to maximum boost of +18psi. Later in the war they were allowed +25psi.

The Mk XIV was similar - less than 5 minutes to 20,000ft, around 8 minutes to 30,000ft.

The ability to climb quickly was the basis for the defence system for the Battle of Britain. If it took an half hour to get to combat altitude then the RAF would have been much less succesful in the BoB.

riiiight, so initial climb is sustained climb now. nice to know but you might want to mention it to the war vets who say it took about half an hour to climb to combat altitude in a midwar fighter. It's on dvd.

Hop · Dec 14, 2011

riiiight, so initial climb is sustained climb now. nice to know but you might want to mention it to the war vets who say it took about half an hour to climb to combat altitude in a midwar fighter. It's on dvd.

If you look at a Spitfire manual, you'll see an engine rating called "maximum climbing 1 hour limit". It was set at 2,850 rpm, 12lbs boost. If you go to Spitfire Mk VIII Performance Testing you will see the climb figures for that engine rating.

20,000ft was reached in just under 6 minutes, 25,000ft in just under 8, 33,000ft in 12 minutes.

FLYBOYJ · Dec 14, 2011

Siegfried said:
FLYBOYJ said:

And if you're jumped by fighters?
We're not talking about the Spit nor were my comments made about the Spit. The -109 had a constant speed prop and any abrupt attitude changes will cause additional fuel consumption.

Click to expand...

I'm not so sure about that, the latter Jumo and DB engines had a "Kommandogeraete" or "control apparatus" that handled prop pitch, engine rpm, prop overspeed in a dive and mixture settings in single throttle control. This was similar to the one famously used on the BMW 801. The Me 109's abillity to retain reasonable range in the face of massive weight and engine power increases with no increase in fuel tankage seems to relate to the very good fuel efficiency of the engine.

You proved my point in your answer. Even with any type of auto pitch or mixture control, you will still change RPM/ mixture settings that will also change fuel consuption. This system is very similiar to what is used in modern general aviation aircraft that have fuel injection and a constatnt speed prop. To maximize range one would have to fly straight and level with limited climbs or dives and hope they have a good tailwind.

Shortround6 · Dec 14, 2011

There is also a difference between a "combat" or intercept profile climb and a long range cruise climb. A slower climb will use almost the same fuel as the fast climb to reach a certain altitude but the plane will cover more horizontal ground. There is also a difference between a single ( or 2-3) planes taking off and climbing and 12 or more planes trying to take-off, form up and fly in formation.

parsifal · Dec 14, 2011

so, is it safe to come out of the trench and say that whilst it is a myth that the 109 had a combat radius of 700 km for normal combat operations (as a fighter), it certainly could undertake ferry operations and/or recon operations at much greater ranges, quite possibly the 700 mentioned by our esteemed former member?

Or do we still have peope claimimg it possible to fly a 700k combat mission?????

pbfoot · Dec 14, 2011

Siegfried said:
The Ju 52's were worn out, engines couldn't develop full takeoff power which restricted load, their opperational availabillity was restricted, there was a pilot shortage, a sever one, as these men had been lost of Damyansk and Crete (due to enigma decrypt revealing specific drop zones). We thus had several women pilots supply Stalingrad.

.

Hmmmm whats with the we

buffnut453 · Dec 14, 2011

The start of the Fourth Reich?

I'll get my coat!

wuzak · Dec 14, 2011

vanir said:
riiiight, so initial climb is sustained climb now. nice to know but you might want to mention it to the war vets who say it took about half an hour to climb to combat altitude in a midwar fighter. It's on dvd.

You can figure out that to 20,000ft the average climb rate is just over 4000ft/min, whereas the peak was 4700ft/min at 700ft for the LF IX falling to 3860ft/min at 18,000ft. The HF IX had lower peak climb rates, but at higher altitudes - 4530ft/min at 11,900ft, and 3480ft/min at 24,700ft.

These are climbs at combat power.

If it took a half hour to climb to fighting altitude during the BoB the RAF was lost.

cimmex · Dec 14, 2011

Sorry, BoB period means Spitfire MkI or MkII
The relevant data are:
Engine
Merlin XII:
Horsepower
1175 (1050 at 13,000 ft)
Max Speed: 357 mph at 17,000 ft
Range; 500 miles max, 395 in combat
Ceiling: 37,200 feet
Rate of climb: 2.995 feet/minute
Time to 20,000 feet 7 minute
Source:
Supermarine Spitfire Mk II

regards
cimmex

FLYBOYJ · Dec 14, 2011

parsifal said:
You would think the first thing to do with a captured ac would be to analyse the fuel.....

My extremely limited knowledge on this subject is that lower octane rated fuel is the same as standard versus super grade petrol, well, kind of. 87 grade standard burns quicker its ignition is more of a bang rather than a burn. Super grade petrol (which is 95 octane rating from memory), has lead added to it that acts as an ignition retardant. It has a longer, slower burn cycle, so that more of the power stroke of the piston is actually under power, and hence accelaration. This in turn generates more power at the drive point, which in a car is the flywheel in a plane is the prop hub.

thats how my schoolboy mechanics understands the process at least. If the wrong fuel is put into an engine rated and tuned for a higher rated fuel, it doesnt take long before pistons have holes burnt in them, valves are burnt as fuel ignites prematurely (and unburnt fuel ignites in the exhaust ports due to inadequate fuel/air mixing) and cranks tend to get broken from the jerky violent running of the engine .

At least thats my elementary understanding of fuel octane ratings and engines. if Im right, that means the engine had to be left running very rough for some time until it sh*t itself. Why would you do that

Good points! Even before that you should make sure that fuels and any other liquids pose no health threats and then start examining the liquids within the aircraft. To be even more detailed, you could look at residual grease on control cables and within wheel bearings. It's amazing what you can learn about your opponent's manufacturing and operational capability just by examining the smallest things.

fastmongrel · Dec 14, 2011

Could it be that the half hour to combat height was the time needed for the RAF 12 Group Big Wings to form up and get to the fighting height. If a single Spit took half an hour to get to combat height then the LW would have dropped its bombs and be over the channel before they were intercepted.

Siegfried · Dec 14, 2011

FLYBOYJ said:
Good points! Even before that you should make sure that fuels and any other liquids pose no health threats and then start examining the liquids within the aircraft. To be even more detailed, you could look at residual grease on control cables and within wheel bearings. It's amazing what you can learn about your opponent's manufacturing and operational capability just by examining the smallest things.

You can find quite a lot of Allied fuel intelligence analysis files at http:/www.fischer-tropsch.org Basically the Germans had two major fuels: B4 which was a nominal rating of 87 octane and was dyed blue and C3 which had several ratings depending on period. It was initially rated around 94/115 and latter became 95/125 and latter 96/130. It was dyed 'green'. These were synthetics but there was also C2 which was a mineral oil version of C3.

In 1943 allied fuel intelligence (usually from examining drop tanks, crashed aircraft or captured drums) picked up the big increase in C3 rating and speculated that this was preperation for a powerfull new engine.

This gives a flavour of one of
http://fischer-tropsch.org/Tom Reels/Linked/A5464/A5464-0638-0654 Item 6A.pdf the reports

B4 fuel was produced by pressurising a coal/tolulene slurry at 700 atmospheres with hydrogen. The special alloys and turbo-compressors were quite an achievment. An gasoline was distilled of (as well as tolulene for backfeeding) and this gasoline, of about 72-77 octane was enhanced with TEL to about 87 octane. C3 was produced by adding about 20% pure iso-octane.

Iso-octane was produced by passing syn-gas over a chromium catalyst that produced iso-butanol, this was dehydrated over aluminium choride to iso-butylene which was polymerised to iso-octane.

A serious supply bottleneck for the Germans was that they iso-butylene was also needed for production or buna-n and buna-s synthetic rubber.

Allied 100 octane fuel relied on two processes:

1 the Houdry catalytic cracking process developed in the United States, which produced 100 octane.
2 the alkylation, which was used to produced Britains 100/130 (initially it was made from exotic imported fuels).

US 100 octane was not focused on the rich mixture rating as US aircraft were interested in range.

Cracking, at least thermal cracking was not applicable to the german hydrogenation product while the alkylation plants the Germans started building in about 1940 could not be completed during the war, a few started opperating in 1943 but they soon came under bombing attack in early 1944. This forced a big disruption in German engine plans, as the engines all had to be configured to be able to run on 87 octane.

The rating of C3 fuel as 96/130 means two things:

The 96 rating means that when a fuel is tested and compared with a muxture of pure octane heptane consisting of 96% octane and 4% heptane is tested in a standard variable
compression engine it start pre-igniting knocking at the same ratio.

There can not be a test fuel of greater than 100% octane so fuels with greater knock resistance can be given a PN or performance number. Normally a fuel is burned stoichiometrically at 14.2 part of air to 1 part of fuel by mass for complere combustion. By running the mixture rich (about 13:1) the 'octane' or rather Performance Number can icrease knock resitance.

The 2nd number in 96/130 indicates that 130% of the power of a pure octane fuel can be generated. Unsuprisingly this is associated with a 30% increase in supercharger boost pressure to increase the amount of air.

A standard atmosphere is 14 psi. A Merlin with a boost of 14psi has an absolute pressure of 28psi. A German would refer to this as 2 ata (atmospheres) while and amercian would refer to it as 60 inches (of mercury) with 30 inches equaling 1 ata.

bobbysocks · Dec 14, 2011

parsifal said:
You would think the first thing to do with a captured ac would be to analyse the fuel.....

My extremely limited knowledge on this subject is

everything you want to know about AVGas and were afraid to ask....its not only the octane rating but the way its manufactured and the additives...

http://www.eaa.org/autofuel/autogas/articles/1Autogas vs Avgas.pdf

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/5abbef4b4ef9830c862569ba006f6e01/$FILE/AC91-33A.pdf

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