How The Spitfire Mk XIV Compared to the K4 and Other Questions

[GregP]

That would be an interesting count if you recall it. The month of collapse was April 1945. In that month we shot up more than ten times as many aircraft on the ground as in any other month of the war up until then. They were either out of fuel or just gave up. I think they were out of fuel, pilots, props, or all three.

Of the three, it is much more likely they were out of fuel entirely. Not because there wasn't any fuel, but because there were thousands of Allied fighters roaming about shooting up anything that moved and the fuel couldn't be delivered.

 

[Vincenzo]

land front was gone, a central germany city as Kassel was occuppied the 4th april

 

[Milosh]

This is the link, both Jan and April '45, Luftwaffe Orders of Battle 1945

Only counted fighter - no bomber or other types.

 

[Denniss]

I assume most K-4 built in 1944 an very early 45 were delivered with 1.8 ata boost to be used with B4+MW. The higher boost was still in experimental/test stage by then.
There should have been no change required to use C3 without MW if no B4 was available.

 

[drgondog]

Many aircraft would not burn when strafed from March forward.. and while April 1945 was a big month for strafing credits, only two FG's appreciably changed their rankings as far as ground scores - the 339th w/271(160 going in) and 56th with 172(147 going in). The long running 'pros' 4th, 352nd, 355th all had about 170 each - but each also had over 100 in April 1944.

 

[dedalos]

Thanks Milosh.

That's the report I came across many years ago and didn't save. As I remembered, the rich rating went from lower to higher. Looks like 110 to 125 - 130. That's not an equivalent to 115/145, but isn't bad at all. It is a virtual equvalent to 100/130.

Appreciae it. In times recently past I had the time but not the link. Almost no time these days.

Still, I've seen pics of a Bf 109K-4 with a B4 sign over the fuel tank. That tells me there were at least some late-war Bf 109K's flitting about on bomber fuel equivalent to early war fuel. It probably means a C3 fuel shortage rather than a desire to run B4. You could set the DB 605 to run B4 or C4, but it required a mechanical change and could not run either at will without having the change done first. In other words, it was configured to run either B4 or C3, but not either one at will.

I am given to understand the changeover wasn't difficult, but required a mechanic, the parts, and maybe two hours of work. That from an old Luftwaffe pilot who spoke at the museum some years back. Note he was a pilot, not a mechanic, so I don't know if it is accurate, but it is the only first-hand report I have ever heard. I'll take it on faith until we hear otherwise from a wartime DB 605 mecahnic.

Hey Biff,

As I recall, they have the idle circuit on the Jumo 213 engine, but the main jets, or equivalent for the fuel injection system, are simply missing. Could be the primary injectors.

So they can prime it and start it, but have no real way to accelerate it past idle speed. I'm sure a master mechanic could adapt an American or British carburetor or fuel injection system of some vintage to make it run ... but it would not be 100% completely authentic ... hence the reluctance. The adapter would no doubt require some minor modification, and should they ever find the genuine parts, then the modification would have to be undone.

With today's 3D printing, I'd think it wouldn't be all that tough to fabricate a 3D model and print a modified manifold for use with an adapted mixture device, and they could save the original for use when and if they ever find the real parts. That option wasn't really available 25 - 35 years ago, and it offers us a chance to see a real Jumo 213 run and fly should Paul Allen ever be so inclined. To date I don't think he is, but maybe ...

I believe that it would be extremely iresponsible to fly the D-13 even if it was complete or was possible to replace the missing parts.
It is a UNIQUE aircraft, represents the very last generation of german piston engined fighters. We are very lucky that survived and should always remain within the walls of the museum, nice and safe.

 

[GregP]

If the current owner believes like you, then he won't complete the engine and fly it, dedalos. That is his choice.

If I owned it, I'd fly it. I think we've had these discussions before and since neither of us is the owner, we can only wait and see what he does. I believe Paul Allen currently has no intentions of having it fly. He lets most of the rest of the collection fly occasionally ... not "often."

 

[Koopernic]

page 13 rich mixture rating 116% and 120% of US 130 grade
http://www.fischer-tropsch.org/Tom Reels/Linked/A5464/A5464-0638-0654 Item 6A.pdf

There seem to be a number of misunderstandings of this document, which only covers German fuels to 1943.

First of all consider that on page 8 that samples of German green dyed fuel (usually C3) is given as having an average RON/PN of 95/110 over 1942 (well down on the 100/130 that had taken over from 100 octane in allied service by then). Samples 285,305,311, 317,318-321 327, 328/9 256 had ratings of 97.5/118.5, 96.4/125,93.6/124, 95/125,95/125,95/125 respectively.

It is noted by British intelligence that the Germans didn't have an engine to take advantage of this improved rating of 96/125 that was achieved in 1943 but that the potentialities should be kept in mind. Of course that engine was the late 1943 BMW801 with increased boost (1.65ata and 1900hp) and with C3 einspriztung (1.65ata and 2050hp). The C3 rich mixture injection was never detected by allied intelligence.

Now in terms of the tests of samples AIR 336 and AIR 342 and their "120% of 100/130 rating". There were two tests for fuels with rich mixture RON ratings greater than the 100 of the iso-octane referenced RON test.

There was the well known performance number or PN test where the rich fuel was supercharged into the test stand engine to the point just below at which knocking occurred at which point a torque meter would measure the increased power attainable.

The other method was the 3C mixture rating which refers to AFD-3C standard, not to be confused with Luftwaffe C3 fuel. In this method iso-octane was used as a standard and the amount of TEL tetra-ethyl lead added to make it perform as the rich mixture under test was used as a reference standard. I read this as saying that the German fuel had 20% more lead.

The Germans simply had inferior quantities and qualities of duel available to them.

Higher PN fuels helped at lower altitudes, not at the altitudes where the XIV excelled.

Intercooling may have been heavier than simple ADI, but it never ran out. The performance afforded by intercooling was accessible at all times during a flight.

snip

I believe that the Mk 108 was a poor air to air weapon. While the round was heavier, it's muzzle velocity was only ~60% of the Hispano's. The Mk 103 was the great 30mm hope of the Luftwaffe, but it wasn't really sorted before the end of the war.

The use of 100/130 fuel surely allowed the Merlin and Griffon base set up, ie compression ratio and supercharger settings, to be optimally configured for standard use of 100 octane fuel as opposed to 87 octane and so indirectly improved its power at altitude, when 110/150 came along the engine was already preconfigured for a higher octane fuel.

The DB605L, with the two stage supercharger, seemed to require the higher octane C3 fuel. This is because pre-ignition is heavily a function of temperature which is a function of pressure ratio and compression ratio rather than manifold pressure and a two stage supercharger is likely to be producing pressure ratios of 5:1 at 10,000m and a rather larger temperature increase. Even an intercooler can't pull out all the heat.

Had the Daimler Benz DB605 series had a fuel as good as 100 octane fuel available the DB605 would have been mass produced in the variants with a higher compression ratio (8.4:1 rather than 7.4:1) This would increase power with no increase in fuel consumption and with no decrease in Full Throttle Height.

The introduction of the intercooler on the Merlin 61 added about 120kg to the 620kg Merlin 20 series. A 2000hp engine consuming fuel at an rich setting and sfc of 0.55 will use about 1100lbs (500kg or 500L) and hour. MW-50 would be added at about the same rate as the fuel so an 86L tank i.e. 190lbs would add about 10-12 minutes of WEP available. It seems enough given the other time limits on the engine.

The Mk103 was adequate to ranges equal to half its muzzle velocity, say 240 meters. It would be uncommon for greater ranges to be experienced and even with a higher velocity issues of the size of the target within the reticule become and issue.

Or DB gets really smart, lowers down the compression ratio of the DB 605, so it can do eye-watering 2.5 ata.

.

Not really that smart. Lets drop the pressure ratio of the 87 octane DB605A from 7.5 down to the same level as the Allison/Merlin ie around 6:5 (the merlin was even less) we've now lost about 13.33% of our expansion stroke and almost as much power while still burning the same amount of fuel. We can now increases the compression ratio of the supercharger but as this now forces more air and fuel into the engine and means that we must deal with much more waste heat and higher fuel consumption. The extra waste heat requires larger radiators and possibly higher coolant flows. The supercharger is now being used to over boost the engine and can no longer provide altitude compensation. We need a larger or a two stage supercharger. The heat increase at some point compels us to consider and intercooler. Our weight has gone up.

Would it be reall woth it? could the little Me 109 frame cope with larger radiators and provide the space for an intercooler.

However, simply provide 100/130 fuel to the Me 109, increase the compression ratio with higher crowns on the pistons and it seems a win win: no decrease in full throttle height, more power with no increase in fuel consumption or thermal load. We only need to make sure the bearings can take the extra power.

 

[dedalos]

Would it be reall woth it? could the little Me 109 frame cope with larger radiators and provide the space for an intercooler.

Hi coopernic,
I wonder why the german did not use a nose, circular radiator in the bf 109 like they used it on the Fw190D9.
Propably would cause somewhat less drag than the undewing radiators , almosy surely would provide better cooling,would eliminate the long coolant tubes. Perhaps, they would even manage to fit an intercooler in it as well. And they could use the free space in the wings for fuel or better flaps
Was technically impossible or once again was a matter of the potential production loss?

 

[GregP]

Interesting question, dedalos, I never considered that one before.

It would certainly make a new look, wouldn't it?

 

[Denniss]

Too much weight forward, impaired forward visibility which may have required major mods to engine installation

 

[BiffF15]

Gents,
Someone please confirm the reasons the Germans used the inverted V installation with inline motors.
Thanks in advance!
Cheers,
Biff

 

[GregP]

From an old speech at Doug Champlin's Fighter Museum when he had some former Luftwaffe aces give a talk (circa 1981 or so):

If you look at the Rolls Royce Merlin, the Vee between the engine cylinders is packed with plumbing. There is no room left. The crankshaft is low, the reduction gear raises the prop shaft, and the engine is widest at the top, making the nose wide enough to block forward visibility significantly, but allowing good propeller clearance.

If you look at the Daimler-Banz DB 601 / 603 / 605, the Vee between the engine cylinders is almost empty. The crankshaft is high and the reduction gear lowers the prop shaft. The nose tapers, with the widest part down low and offers better forward visibility, but ground clearance is less, making for wider but shorter propellers. Since the vee is amlost empty, they could make the prop shaft hollow and fit a cannon in the engine vee. Since the engine as narrow at the top, they could also fit two machine guns, one on either side of the engine case.

The Luftwaffe was keen to have the armament on the centerline of the aircrft, and the inverted vee was the simplest way to achieve it. He did not say and I did not ask whether or not junkers settled on the inverted vee design after Daimler-Benz was successful with it or whether they chose it on their own. If I were hearing this talk today, and if I were allowed a question, I'd ask about that because I have wondered for 30 years about it.

I will say this about the above. It was said in a talk given at a Fighter Aces Museum by a former Luftwaffe pilot. I do not claim the information is true, although it makes sense. I am not sure why a pilot would be "in" on the real reason the choice was made. Perhaps he knew someone at Daimler-Benz, or perhaps it was just a good story.

I am looking forward to hearing from other people with other sources.

 

[Milosh]

https://en.wikipedia.org/wiki/Daimler-Benz_DB_600_series

"In 1929 Daimler-Benz begun development of a new aero engine of the 30-litre class: a liquid-cooled inverted-Vee 12-cylinder piston engine. This became the F4, and by 1931 two prototypes were running on the test bench."

https://en.wikipedia.org/wiki/Junkers_Jumo_210

"Development of the Jumo 210 itself started in 1931 under the designation L10."
"The L10 was first ran in static tests on October 22, 1932."

 

[wuzak]

Biff, it may have been that the Germans sought to improve the view over the nose.

The original concept for the Merlin was an inverted Vee, but the British airframe manufacturers preferred the upright model.

Greg, being inverted was not due to a central gun requirement. In fact, the DB could be turned the right way up and it would still have the possibility of the gun firing through the prop.

You rightly point out the intake architecture of the Merlin as a reason for no access for a central gun. The supercharger is also in the way for a gun mounted in the vee, being mounted at the rear of the engine and being rather large. The DBs had their superchargers off to the side - a feature, no doubt, designed specifically to allow for a motor cannon.

 

[bobbysocks]

Too much weight forward, impaired forward visibility which may have required major mods to engine installation

that was my first thought too. all that weight near the extreme end of the airframe would cause a weight and balance issue. to counter that might negate any advantage gained.

 

[GregP]

Hi Wayne,

I don't believe you could turn the DB over and still have a cannon through the hub becasue all the bits and pieces that need to be at the top would be in the cylinder vee, just as in the Merlin. Instead of being at the top inside the case, the top part of the case would have to go on the NEW top, right between the vee. There are things that have to be at the top of the engine, and since the DB was an inverted vee, they didn't have to plug up the vee with those bits and pieces.

As for too much weight forward, there is nothing that says the radiator had to be at the front. Why not fit it around the rear of the engine and use ducting? There is usually a way to mitigate any undersirable features.

 

[wuzak]

The Me 209 II had an annular radiator

http://www.aviastar.org/pictures/germany/me-209-2.jpg

The extra weight forward could be compensated by ballast or by lengthening the rear fuselage.

 

[wuzak]

Hi Wayne,

I don't believe you could turn the DB over and still have a cannon through the hub becasue all the bits and pieces that need to be at the top would be in the cylinder vee, just as in the Merlin. Instead of being at the top inside the case, the top part of the case would have to go on the NEW top, right between the vee. There are things that have to be at the top of the engine, and since the DB was an inverted vee, they didn't have to plug up the vee with those bits and pieces.

Greg, the intake piping to the cylinder heads was still in the vee, but placed above where the cannon would go, and the ducting arranged to give the cannon clearance.

http://aircraftwalkaround.hobbyvista.com/db605/DB 605.JPG

The main change for changing the DB from inverted to upright is the sump arrangement - and that would make more clearance on top of the heads and, possibly, in the vee.

 

[stona]

Gents,
Someone please confirm the reasons the Germans used the inverted V installation with inline motors.
Thanks in advance!
Cheers,
Biff

The origin of the inverted V-12 German Aero engines goes back to 1928 when a committee of aeronautical experts was assembled in Berlin at the bidding of the R.V.M. Representatives from the Army, the D.V.L. research centre, the Navy (airships were at their peak in 1928 ) and Deutsche Lufthansa were instructed to make an in-depth study of of the international scene regarding aero-engines and then produce specific guide lines for the future development of large air and liquid cooled motors.
Along with others, Prof. Wunibald Kamm, Ing. Wolfram Eisenlohr and Dr. Helmut Sachse (later heavily involved in the design of the B.M.W. 801) served on this panel. The specifications drawn up by this "think tank" were very detailed and incorporated some very advanced features including, for the liquid cooled engines:
1) 12-cylinder, inverted installation,
2) mono-block cylinder banks,
3) wet cylinder liners,
4) propeller reduction gear,
5) supercharger,
6) fuel injection,
7) high temperature glycol cooling,
8 ) provision of a cannon tunnel in the V.

Tender documents were sent to Daimler-Benz, Junkers and B.M.W. all of which eventually produced a V-12 engine model in response although none was able to incorporate all of the required features immediately.

Wolfram Eisenlohr was interviewed in 1980 regarding the 1928 requirement for inverted V-12s and he cited three reasons for the decision.
1) more compact installation.
2) better pilot view for single engine aircraft,
3) less exhaust flame dazzle during night flying.

This is confirmed in a Rolls Royce report titled "Comments on Visit to Germany, July 24th 1945 to August 12th 1945". In the report the RR engineers comment that:

"A good example of Air Ministry control lies in the inverted Daimler-Benz engine. The D.B. people said that both from a technical and production point of view they would have preferred to make an upright engine but they were compelled to make it inverted by the Air Ministry."

There were problems with the inverted V. The same report says that the DB engineers acknowledged this.

"It was very difficult to obtain consistent oil consumption and due to the rotation of the crankshaft, one bank gets more oil than the other. For this reason the engine is built with a lower compression ratio on one bank than the other."

Which may have answered another oft posed question.

Cheers

Steve