Hitech, Fuel consumption questions

[F4UDOA]

I have been doing some research to explain my earlier post so I could show you what I mean.

Here is an example of what makes sense to me.

JoeBlogs did this chart in a prior post when I provided the manual data for the F4U and F6F.



It shows very basic info. What I look at is the SFC based on fuel consumption and HP.

SFC = Fuellbs/HP/HR

The R2800
Burns 42GPH at min cruise for a best SFC of .44
Burns 290GPH at mil power .870 which is
290GPH*6(pounds per gallon)=1740lbs/2000=.87

In AH the F4U-1D has 237gallons of internal fuel. and burns 290GPH. That gives the F4U-1D an endurance of 49 minutes at mil power. In the MA at 2.0 multiplier the endurance should be 24.5 minutes. It is 28 minutes so it is 3.5 minutes high.


Easy Cheesy right;)

The SFC is always best at minimun cruise and increases with power output.

Ok

The P-38 (one engine)
Burns 33GPH at min cruise 425HP =SFC .46
burns 167 per hour at mil power at 1425HP
167*6=1002LBS/1425HP=SFC.70
Better than the R2800 at mil power but slightly lower at min cruise. Results well within reason.

The P-38L had 410 gallons of internal fuel buring 167GPH*2 = 334GPH. 73 minutes of endurance at mil power. In the MA at 2.0 36.5 minutes of flight time.

In the MA the P-38L has exactly 37minutes of flight time. Well done.


Great.

Here is what does not make sense and I believe to be impossible.

The La-7
I don't have min cruise data.
Mil power 1650 HP 122gallons of internal fuel.

In AH it has 28 minutes of flight time at 2.0 fuel burn so that means 56 minutes IRL to burn 122gallons of fuel. In one hour that would be 130 gallons.

130*6=780lbs/1650HPmil power=.47SFC

This is what the P-38L Allison and R2800 SFC are at Min Cruise. I do not believe the La-5/7 engine (Ash-82) could do this or that any engine is as efficient at mil power as it is at max cruise. And this is with 87octane fuel!

Also I have German document on the La-5 with the same engine and fuel capacity that states that endurance at normal power was 30 minutes. At mil power that would be less than the MA without the fuel multiplier.

Here are some other anomolies IMHO

The BF109G-10 Puts out more HP than the La-7 and only has 106gallons of fuel!! How is that possible when this A/C couldn't hardly fly across the channel and back at cruise?I don't know what the mil power HP is but this doesn't sound right.

The Spit IX
Every reference I look at shows a max interal fuel capacity of 85 gallons imperial which is 102 gallons internal. But in AH it has 136 gallons. Why?

Also it has a Merlin 61 I believe that put out approx 1400+HP. How can this A/C have a duration of 35minutes which would indicate a real life endurance of greater than an hour at mil power. That would indicate less than 136 gallons per hour at mil power. And that is assuming its not really 102 gallons. This really sounds odd too.

The P-51D
At 150GPH as you have stated.

150*6=900lbs / 1490HP= .60SFC very low compared to the Allison which puts out less HP.

Here are the endurance numbers I am using.


FYI I have an entire German AFDU type doc on the La5

[GScholz]

Remember altitude decreaces fuelburn. The 109G10 has a 25 min fuel duration on mil power in the MA at sea-level. the 109G10 never saw action over Britton, that was the 109E . The 109E had 30 minutes of combat time over England during the BoB, and that's without any provisions for DT. Altitude is the key to increase your range, I use this a lot in the MA flying 109s. The 109F uses a quarter tank just to get to 20k, howerer at 20k I can cruise for what seems as an hour or more on the remaining 75% on mil power. With a DT I can cross the map flying that high.

[F4UDOA]

Gsholz,

I don't care about range. I know how to do it but that is not my point. I am only talking about duration at mil power.

Do you know what the G10's mil power HP rating was?

Also I know it was the 109E over Briton. My point is that the E did not have nearly the HP of the G10. The more HP you create the more fuel you burn. The Merlin and Allison engines did not produce the HP the G10's engine did and they burned at least 150GPH. I don't see how the 109 could burn any less. And the 109 has a tiny little gas tank.

[Batz]

109-e4

[Tilt]

Originally posted by F4UDOA


I do not believe the La-5/7 engine (Ash-82) could do this or that any engine is as efficient at mil power as it is at max cruise. And this is with 87octane fuel!

Also I have German document on the La-5 with the same engine and fuel capacity that states that endurance at normal power was 30 minutes. At mil power that would be less than the MA without the fuel multiplier.

FYI I have an entire German AFDU type doc on the La5

Can I have a copy of your German La5 stuff please.........

btw re octane the Ash82FNV figures I have state the design fuel was 90 Octane which I would believe to be the octane used in Russian tests.

I believe the LW however had two standards of Octane (early109's used lower octane fuel and the 190's used a higher grade)

I agree with the generalisation that mil power endurance for the la5/7 would be about 28 to 30 mins. I do not know what you refer to as normal power is.

It seems to me that AH fuel presents many opportunities for revision.....

a)actual burn rates mil power (AH full throttle no WEP)
b)actual burn rates at various (engine)rpm and levels of boost/WEP.
c)fuel availability at different field fuel attrition levels.

[GScholz]

Originally posted by F4UDOA
Do you know what the G10's mil power HP rating was?

I believe it was 1475hp mil power and 2000hp with MW50 boost, 0.45 lb/hp/hr at sea level at mil power. Although I might be mistaken.

EDIT: All the 109's had a 400 liter /88 Imp. gallon tank.

[F4UDOA]

Gscholz,

The E4 according to Batz document burned 114 gallons (433litres) per hour to create 1175HP. You can see by that chart the more HP you create the more fuel you burn. In order to create 1475HP you will be burning in the 150+GPH range.

The best SFC of any WW2 fighter was .40. The P&W R2800 was very good at .44. But this is at min cruise. No WW2 fighter could run full Mil power and maintain SFC. It's like your car milage staying the same regardless if your cruising on the highway or drag racing full speed.

What I believe HTC did was apply the SFC of min cuise to A/C in which the specific fuel consumption was not available. So the SFC never changes regardless of power setting.

The 109E produced 1175HP at max power and burned 114GPH it would have 56minutes of flight time IRL and 28 minutes in the MA.  Which means that the 109E is 3 minutes short in duration in the MA according to the MA chart I posted. However the 109G10 would create 300 more HP reducing flight time at mil power dramatically.

The SFC for the 109E at max power would be
114*6=684lbs/1175HP=.58

That is good but remember that number gets worse with more HP created.

Tilt,

The wording in the translated German document I believe is rated power which is typically max continious or Normal rated power.

I will zip and post it.

BTW the performance of the German La-5 is much lower than what we have in AH however they considered the handling excellent.

Also can anyone tell me why the fuel tank is so big on the Spitfire??

[F4UDOA]

Gents,

If there is one point I am despritely trying to make is the fuel burn and HP are a direct ratio.

The more HP you create the more you burn. And most WW2 engines were almost equal in burn rate.

Take a look at the E4 fuel burn to create 1,100HP and compare it to the P&W and Allison Engines I posted creating the same HP.

All Sea level.

109E4
1100HP= 84GPH

F4U/F6F/P-47
R2800
1070HP= 83GPH

P-38L
Allison V-1710
1100HP= 113GPH!!

They all are almost the same with the inline allison being highest.

So how does an Aircraft with a 100 gallons fuel tank fly in the MA for 28minutes at a 2.0 multiplier while buring enough fuel to create 1600+HP??

[Batz]

About that e4 info,

I am not sure how accurate it is because here the power settings that seem to be agreed upon most

DB601A-1

SL@1100PS@2400rpm@1.40ata (1' minute) takeoff

SL@990PS@2400rpm@1.30ata (5' minutes) climb

SL@910PS@2300rpm@1.23ata (30' minutes) combat

SL@810PS@2200rpm@1.15ata cruise


4.5km@1020PS@2400rpm@1.30ata (5' minutes) climb

5.0km@960PS@2400rpm@1.23ata (30' minutes) combat

5.7km@890PS@2400rpm@1.15ata cruise


DB601N

SL@1175PS@2600rpm@1.35ata (5 minutes) climb

SL@1020PS@2400rpm@1.25ata (30 minutes) combat

SL@910PS@2300rpm@1.15ata cruise

5.5km@1190PS@2600rpm@1.35ata (5 minutes) climb

5.4km@1060PS@2400rpm@1.25ata (30 minutes) combat

6.1km@970PS@2300rpm@1.15ata cruise

As you can see there slight variations(I know the image shows hp and the data above is ps).

Maybe some one with better info can confirm.

[214thCavalier]

This may be useful for comparison.

One PS is approx 98.6% of a HP

To convert from BHP to PS multiply by 1.01387

[HoHun]

Hi F4UDOA,

>The E4 according to Batz document burned 114 gallons (433litres) per hour to create 1175HP. You can see by that chart the more HP you create the more fuel you burn. In order to create 1475HP you will be burning in the 150+GPH range.

Well, you're using the very wasteful 1 min power setting for comparison. The 5 min power setting was more economical, and in fact the DB605 didn't burn 150 GPH at 1475 PS but just 480 L/h (127 GPH).

By the way, the equivalent to "MIL" power is "Kampfleistung" ('Combat Power'). The DB605A was rated at 1310 PS Kampfleistung, burning 400 L/h (106 GPH).

(Data from "D. (Luft) T.3605 A-B, 0 u. 1 Motoren-Karte")

Regards,

Henning (HoHun)

[VO101_Isegrim]

Originally posted by F4UDOA

Also I know it was the 109E over Briton. My point is that the E did not have nearly the HP of the G10. The more HP you create the more fuel you burn. The Merlin and Allison engines did not produce the HP the G10's engine did and they burned at least 150GPH. I don't see how the 109 could burn any less. And the 109 has a tiny little gas tank.

Sorry, but it doesn`t works this simply... Unlike you would expect, the fuel consumption of DB60x engines actually decreased proportionally to the power they developed with later engines.

Why? Because German engineers increased compression ratio as well, not just boost. More fuel effiencient. Also, more volume, better effiency again.

The increase in fuel effiency with the development of Daimler Benz engines can be seen from their compression ratio increase:

CR values:

DB 601A : 6.7 : 1
DB 601N : 8.2 : 1 (100 octane)
DB 601E : 7 : 1    
DB 605A : 7.5 : 1
DB 605D: 8.5 : 1


Comparing them the Merlins is not a very good idea... Merlins operated at  low CR values (all of them at 6 : 1), were low displacement engines, meaning worse fuel effiency. I can`t say for Allisons, I don`t know them for detail.

As for G-10 details, I am still waiting for more data on the DB 605D engine fuel consumption, I only have parts of details. However I will attempt to give it for Kampfleistung (30min limit for 1370PS for DB605DC), for which I have data, consumption is given as 225 gram/PS/h.

This would give 430 lit/hour consumption for 1370 PS power. In other words, 400 liter internal tankage was enough for 1 hour 4 minutes.

According to German docs, at this power G-10 could do 653 kph+ at 9km altitude.

So range about 650 km, endurance 1 hour at Kampfleistung/Military rating.

This is of course NOT economic cruise !! That would give around 1 h 30min endurance, and ~750 km range, taking into account takeoff, climb etc., but no combat. (=ferry range).

Assuming Sondernotleistung spec. consumption was somewhat higher (235 gr/PS/h assumed), this would mean (.235 x 2000)/.7205 = 650 lit/hour consumption of fuel.  400 liter int. tank enough for 37 minutes at WEP.
In addition, 180 lit/hour MW50 liquied is consumed, which would run out after about 30 mins.

So at WEP settings for G-10, Range = 425 km, Endurance = 37 min.

[VO101_Isegrim]

Ie, specific consumption for DB 605 A-1 to see how efficient it was, in Imperial units, at rated altitude:

Min. (economic) cruise :

WEP, 1355 PS at 18 700ft = .517 lbs / HP / h
Military*, 1250 PS at 19k ft = .484 lbs / HP / h
Max. cruise, 1080 PS at 18k ft = .473 lbs / HP / h
Eco/Min cruise, 890 PS at 18.7k ft = .454 lbs / HP / h

*Military rating : 30 min

So don`t be surprised if you experience that 109s - as opposed to urban myths -  have rather long endurance compared to their small tankage. They had probably the most fuel efficent aero engines of WW2 installed !

[GScholz]

Eh ... compression ratio does not have anything to do with fuel mixture. Increased CR increases power output (and actually limits boost unless fuel grade is increased as well).

[HoHun]

Hi Isegrim,

>Assuming Sondernotleistung spec. consumption was somewhat higher (235 gr/PS/h assumed), this would mean (.235 x 2000)/.7205 = 650 lit/hour consumption of fuel.  400 liter int. tank enough for 37 minutes at WEP.

Actually, specific gasoline consumption at "Sondernotleistung" decreased compared to combat power. Only the specific total liquid consumption (gasoline + water-methanol) increased.

I don't have any figures for the DB605, but for the Jumo 213, specific fuel consumption went down from 268 g/PS/h at "dry" war emergency power to just 221 g/PS/h at special ("wet") war emergency power.

This is an 18% decrease, which was countered with a 22% increase in total liquid consumption due to the injection of MW50.

By the way, the fuel injection used by German engines did contribute to their relatively good fuel efficiency, too. For comparison: The Jumo 211G was 8% more efficient than the Jumo 210Da of identical bore, stroke, rpm and power. That's a major advance.

When comparing mechanically supercharged engines like the Merlin or the DB605 to turbo-supercharged engines like the Allison or the R-2800, it's important to consider that in addition to the shaft power, the former also delivered considerable exhaust thrust - unlike the latter. That makes them a bit more efficient than the bare SFC figure suggests - the higher the speed, the greater the gain.

(The German conclusion was that turbo-supercharged engines were better suited for bombers and mechanically supercharged engines were better for fighters. That didn't stop them from experimenting with turbo fighters, though, but they couldn't get them operational.)

With regard to the most fuel-efficient WW2 aero engine, I'd suspect that the Jumo 205 Diesel would be the winner with an SFC of 0.35 lbs/HP/h :-) It wasn't a fighter engine, though.

Regards,

Henning (HoHun)