German 'jet program' - how to do it?

[Acheron]

Gasoline (Petrol) is highly refined oil.

Kerosene (#2 and Pearl) and Diesel (all grades) are a basic refinement of oil.

So, gasoline powered tanks needed more highly refined fuel than fighter aircraft?

 

[SaparotRob]

Insert "nose armour" joke here.

 

[Shortround6]

Yes, no, maybe

If we are talking about oil that comes out of the ground you get a chart/process like this

oil from different oil fields will give different percentages of product per barrel (ton?) from each other.

You can "tweak" the product at times to swing the middle products back and forth a bit. A little more gasoline and little less kerosene for example, you can't do much with the refinery gases and the fuel oil and residue. Or you may do better making a little less gasoline and get more diesel and bit less lubricating oil?

This is a straight run distillate. The "best" you are going to get is about 70 octane gas which means if you need higher octane you need to add something even if you are trying to run trucks on it. If your crude oil only gives you 55 octane gas you really need to do some extra refining/blending. Some oil fields would not even give 40 octane gasoline after one trip in the cracking tower.

The next "trick" is that they found out pretty quickly that "straight run" gasoline (or diesel fuel) didn't work very well under extreme conditions. And octane was not the only requirement. If the fuel "boils" too quickly it can result in vapor lock in the fuel lines even if the temperature is low. This is related to vapor pressure of the fuel in comparison to the pressure of the air as much as it is to actual temperature.

You can also have problems with diesels starting in cold weather. This lasted to this day although modern fuel (well after WW II) has gotten better.

Now the real trick starts to come into when you grab all the higher "grade" gasoline for aviation fuel and your cars/trucks/WW II tanks are trying to run on what's left.
The Fuel companies were already making "cat cracked" fuel in the 1930s so they could sell motor fuel cheaper than "straight run" gasoline. The cat cracking allowed more gasoline to be made per barrel and less of of the heavier/ larger molecules.

Trying to make 100/130 in large quantities required a lot of cat cracking and a lot of additives. A small batch could be made with a lot less blending and additives.
Truck fuel can vary tremendously too, Yes it was almost always cheaper/easer to make that aviation fuel.

Warning, do not try to use truck fuel even in a training plane that used 'equivalent" octane because the vapor pressure, allowable varnish and other details won't be the same.

 

[Thumpalumpacus]

Insert "nose armour" joke here.

I heard the Tiger was pretty good at low-altitude ops but sucked at high alts, as well.

 

[delcyros]

Lippisch actually designed his fighter initially (in mid 1940-1941) around a BMW jet engine in parallel to a design revolving around rocket propulsion. There were multiple iterations (P01-113 from june. 17th, 1940, P01-116 from June 12th, 1941, P09 from oct. 28th, 1941) of which the single JUMO-004 engined Lippisch P20 proposed on april 16th, 1943 was the last one before Lippisch left Messerschmitt. The project was later used by Messerschmitt for internal comparisons, which lead to the refined MeP1101 and -1111 series. This was around 1,5 years prior to the He-162 and I have always thought that this was sort of a missed opportunity as it would have allowed an earlier emergancy single engined jet fighter (later known as He-162), but with benign flight controlls at the expense of some speed.

drawing

MTOW: 3629 kg
Rüstgewicht: 2589kg
wing area: 17.3m^2 (22° wing sweep at leading edge)
wingload: 210kg/m^2
apsect ratio: 5
engine: 1 JUMO-004C rated 1000 kp thrust
thrust/weight: 0.276
speed: 905km/h calc.
initial climb: 18.5 m/s
service ceiling: 11,500m
fuel: 750 kg
max flight duration: 2 hours at 11 Km
max range: 940 km at 11 Km


armament: 2 MK108 + 2 MK103 & ammunition

Now, with some induction, we can calculate back the plane´s weight and performances, if only two 30mm MK 108 and one BMW-003A was used instead of the JUMO-004C and the mixed MK108 & MK103 armement to create a competitor for the He-162. The BMW-003 was considerably lighter (and smaller) than the JUMO-004 and has somewhat better specific fuel consumption (1.31 vs 1.4 at SL and 265kg/h at 11Km vs 315 kg/h at 11 Km, each at 100%). It also provides 20% less thrust, though. Also, the high velocity 30mm MK103 are really heavy (148 kg not incl. mounts per gun (the ammo is heavier, too) as opposed to 157kg for two MK108 incl. mounts and electric circuits). The principle idea is to replace the JUMO-004 with BMW-003 and to delete the two long barreled, high velocity 30mm MK103.

The weight break down for the given P20 reconstructed looks like (bold are from sources, rest is approximated from data or derived):

airframe weight: unknown, presumably 1200-1250 kg
equipment: 60 kg (assumed, for comparison He-162 with ejection seat: 95kg)
armoured parts: 57kg (assumed same like He-162)
powerplant and tanks: 800kg (same like He-162 with same JUMO-004C)
2 MK 108: 157kg (same like He-162)
2 MK103: >300 kg (assumed, single weight per gun without mount: 148kg)
Rüstgewicht: 2589kg

crew: 100kg (single crew standart)
fuel: 750kg
2x 60 rpg MK108: 70kg (58kg for 50rpg in He-162)
2x 50 rpg MK103: 120kg (assumed rpg calculated weight)
MTOW: 3629kg

The modified P20 weight with BMW-003 and 2 x MK108 comes out at:

airframe weight: unknown, presumably 1200-1250 kg
equipment: 60 kg (assumed, for comparison He-162 with ejection seat: 95kg)
armoured parts: 57kg (assumed same like He-162)
powerplant and tanks: 680kg (same like He-162 with BMW-003)
2 MK 108: 157kg (same like He-162)
Rüstgewicht: 2169kg

crew: 100kg (single crew standart)
fuel: 750kg
2x 60 rpg MK108: 70kg (58kg for 50rpg in He-162)
MTOW: 3089 kg
endurance: 45 min at low level and 100%, 2 hours at altitude
thrust/weight: 0.26
wingload: 179kg/m^2

In the end, this variant is at least half a ton lighter than the original P20 and about as heavy or only marginally heavier than the later He-162A. The lower wingloading (180kg/m^2 vs 210kg/m^2 for the Li P20 and 240kg/m^2 of the He-162A) indicates a correspondingly lower landing speed with good low speed maneuverability, a better rate of climb and the potential for a somewhat higher service ceiling. It would also indicate operability from limited airfield lengths. The resultant plane would have -in comparison to the later He-162A- a somewhat lower top speed at all altitudes (800-820 est. as opposed to 840km/h at 800Kpe) and would not have such a high roll rate on account of its longer span. It would still remain a 500mph+ airplane. On the positive side, it would have more endurance and generally employ tested aerodynamics.
The freed up space in the wingroots for the long barreled MK103 could be used for the MK108 (same mount as Me-163), thus requiring less changes from the Me-163s wing. Alternatively, the space could be used for fuel tanks, which would provide another 300kg or another pair of 30mm MK108 if the updated BMW-1003A2 with 920Kp overrew thrust is aviable later. There is more internal space in the BMW-003 powered Li P20 due to the lower height of the turbine jet assembly with the potential to reduce the airframe height by 8 in, cutting some fuselage drag.

The main advantage here is time. The LiP20 was proposed already by mid april 1943, which was 14 months before the predecessors of the He-162, the Heinkel He P1073 design was proposed (June 1944). Even with JUMO-004B engine (890Kp), the proposal remains reasonable. Particularely, if one would be willing to give up on the long barreled MK103 or replace them with MK-108, instead or else, change all four of them for 2cm MG151 (in terms of weight one may swap 2 or 4 x MK108 with 50rpg for 2 or 4 x MG151/20 with 120rpg). Speed would be similar to the Me-262A with better handling, low speed characteristics and climb.

 

[Snautzer01]

I heard the Tiger was pretty good at low-altitude ops but sucked at high alts, as well.

They were great at low altitudes

Spoiler: Wanna see???

 

[tomo pauk]

... of which the single JUMO-004 engined Lippisch P20 proposed on april 16th, 1943...

Agreed 100% - a 1-engined jet fighter is a must.

 

[delcyros]

just a minor addition. The Me-163 handbook provides data for the 20mm MG151/20 and ammo weights. Two guns , incl. mounts and electric circuits require 125kg (MK108=157kg) and ammunition weight (100 rpg for both guns) was 55kg (60rpg for two MK108 = 70kg, 50rpg =58kg). I have not yet come around MK103 weights. But I believe my estimate of 320kg for two guns (incl. mounts) and 120kg for 50rpg ammunition probably is a bit too low. Give or take, you get the idea.

a LiP20 mod with Jumo-004B and 4 x MG151/20 (100rpg) would then weight in about approx. 3,334 kg with tr/wt = 0.27, very approx, in effect slightly less than with 4 x MK108 with ~530-540mph top speed at opt. altitude.