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View Full Version : Oleg, question about fuel load distribution in P-51D-5NT / 20NA



PlaneEater
04-13-2004, 09:09 PM
Hi, Oleg. Congratulations to you and your wife on the little one! My fiancee and I are expecting out first in May. Maybe there's something in the water? http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

I have a question about the way fuel is loaded into the tanks of the P-51Ds when the different fuel loads (25/50/75/100) are selected.

I've noticed that with a 25% or 50% fuel load, the center (fuselage) tank is filled first, then the two wing tanks get the remaining fuel to fill out the load.

USAAC practice was to take off feeding from the left wing tank. Once airborne, they'd immediately burn off the fuselage tank as fast as possible--even before feeding from drop tanks. If it was a short hop, the fuselague tank wasn't even filled.

Would it be possible to switch things around, and distribute fuel between the two wing tanks first, then fill up the fuselage tank once the wing tanks are full?

Here's how that would load out (if I remember right, wing tanks on the P-51D are 92 gallons each, and the fuselage tank is 85).

25% fuel load:
33.625 gallons in each wing tank
Fuselage tank empty
--------
50% fuel load:
67.25 gallons in each wing tank
Fuselage tank empty
--------
75% fuel load:
92 gallons in each wing tank
17.75 gallons in fuselage tank
--------
100% fuel load:
92 gallons in each wing tank
85 gallons in fuselage tank


Even if my memory (and those numbers) are slightly off, the idea's there--filling the wing tanks before the fuselage tank as per USAAC practice, to avoid the center of gravity problems the fuselage tank caused when filled.

There aren't many of them left. They flew these things. They stepped off the earth, into the sky, in a pair of metal wings and a howling, living, fire-breathing beast of war, and they fought.

And they died.

And the least we can do is remember they were heroes.

PlaneEater
04-13-2004, 09:09 PM
Hi, Oleg. Congratulations to you and your wife on the little one! My fiancee and I are expecting out first in May. Maybe there's something in the water? http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

I have a question about the way fuel is loaded into the tanks of the P-51Ds when the different fuel loads (25/50/75/100) are selected.

I've noticed that with a 25% or 50% fuel load, the center (fuselage) tank is filled first, then the two wing tanks get the remaining fuel to fill out the load.

USAAC practice was to take off feeding from the left wing tank. Once airborne, they'd immediately burn off the fuselage tank as fast as possible--even before feeding from drop tanks. If it was a short hop, the fuselague tank wasn't even filled.

Would it be possible to switch things around, and distribute fuel between the two wing tanks first, then fill up the fuselage tank once the wing tanks are full?

Here's how that would load out (if I remember right, wing tanks on the P-51D are 92 gallons each, and the fuselage tank is 85).

25% fuel load:
33.625 gallons in each wing tank
Fuselage tank empty
--------
50% fuel load:
67.25 gallons in each wing tank
Fuselage tank empty
--------
75% fuel load:
92 gallons in each wing tank
17.75 gallons in fuselage tank
--------
100% fuel load:
92 gallons in each wing tank
85 gallons in fuselage tank


Even if my memory (and those numbers) are slightly off, the idea's there--filling the wing tanks before the fuselage tank as per USAAC practice, to avoid the center of gravity problems the fuselage tank caused when filled.

There aren't many of them left. They flew these things. They stepped off the earth, into the sky, in a pair of metal wings and a howling, living, fire-breathing beast of war, and they fought.

And they died.

And the least we can do is remember they were heroes.

hobnail
04-13-2004, 09:16 PM
The order in which tanks are drained is a limitation of the IL2 engine and was not a research mistake.

PlaneEater
04-13-2004, 09:31 PM
Drained, yes, filled, no.

I'm asking that the fuselage tank be *filled* last, and the wing tanks first, as was operational procedure, due to the stability and center of gravity problems the fuselage tank caused when full.

Currently, it is filled first and the wing tanks last. Therefore when selecting lighter fuel loads, the player is burdened with an exceptionally unstable and historically inaccurate fuel configuration.

I say 'exceptionally' because with the fuselage tank full, and the wing tanks empty--and unable to counter-balance--the center of gravity is shifted much farther back than USAAC operating guidelines allowed, and causes the aircraft to become far more unstable than it historically was allowed to be during operation.

VW-IceFire
04-13-2004, 09:41 PM
Do we know if fuel tanks are taken into consideration for weight and balance concerns in the FM? They may not be...

http://home.cogeco.ca/~cczerneda/sigs/tmv-sig1.jpg
RCAF 412 Falcon Squadron - "Swift to Avenge"

PlaneEater
04-13-2004, 09:54 PM
I'm pretty sure they are. You dive faster and climb slower with full fuel, especially in planes that carried a lot like the P-51 and P-47.

If fuel weight wasn't factored into weight and balance in the FM, then why does everybody go for 25% fuel on dogfight servers or small maps?

The problem is exagerrated with the P-51 because of its huge range. IL2 doesn't have any maps large enough for it to need full fuel to fly across the map (*maybe* Gulf of Finland, if you fly low), much less drop tanks. So when you fly it, it's common and smart practice to lighten up the plane by only bringing, usually, 50% or less... and that's where you run into the balance issues because of the fuselage tank being filled first.

PlaneEater
04-14-2004, 12:46 PM
You know, I've never had to do this before...

*bump*.

04-14-2004, 01:34 PM
Fuel load DOES affect aircraft weight. However, I am not certain that fuel load affects aircraft CG.

The only mention of CG I have read is a post where Oleg mentioned adjusting the Ta-152 CG aft to reflect installation of GM-1 bottles.

As far as I can tell, all fuel and armament does not affect CG. I shall have to try some stability tests in the P-39 with and without ammo. The full ammo load in the nose was supposed to make the Cobra handle nicer.

JR_Greenhorn
04-14-2004, 02:05 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by cosmokart:
As far as I can tell, all fuel and armament does not affect CG.<HR></BLOCKQUOTE>Blasphemy!
Well, I guess first I should ask if you mean it's not modelled to have an effect, or if it doesn't IRL?


PlaneEater has a good idea here, regarding fuel tank filling. I think this one is worthy of consideration by Mr. Maddox, or at least a response.

http://www.fargoairmuseum.org/F2G-1D.jpg

gates123
04-14-2004, 02:45 PM
Flying a mustang online with more then 25% fuel is practically suicide.

http://www.fortunecity.com/meltingpot/justin/1087/WWII/Images/Thumbs/TBf109AK.jpg
Did anyone see that or was it just me?

PlaneEater
04-14-2004, 05:55 PM
Gates, I'd say that right now, flying it with 25% fuel at all is far closer to suicide than we may realize.

I'm wondering how badly the stall and yaw characteristics are being affected by this.

Bull_dog_
04-14-2004, 06:56 PM
Before anyone says fuel does or does not affect performance...I'd suggest you go test...you might be suprised!

I found that fuel made no difference in Top end speed on a few of the aircraft I tested....I don't pretend to be scientific about it, but I was rather suprised... I did not test climb, dive or accelaration, turn rate or really anything else so I'd be interested in the results if anyone cares to try.

WUAF_Badsight
04-15-2004, 02:41 AM
id be interested to see a reply to this as well

its common knowledge that the middle tank was not helpfull to flight performance

it should be the last tank filled

this might be too much work to correct given the games engine

but it should be considered enough to be replied about because the Mustang pilots DID empty the middle tank first for better flight performance

SUPERAEREO
04-15-2004, 04:30 AM
P-51's were notoriously sluggish with a full fuselage tank, and US pilots would not have dreamt to enter combat in those conditions.

Said that, there was a warning at the release of the add-on saying that it had not been possible to model the tank system correctly (or words to this effect).

Still, it would be interesting to know if the Mustang in the game has the same flight characteristics it would have had in combat or not.
With all the surviving P-51's around, documentation on this should not be too difficult to obtain.

S!



"The first time I ever saw a jet, I shot it down."
Chuck Yaeger

Bull_dog_
04-15-2004, 07:01 PM
As I understand it... a full fuselage tank primarily affects the center of gravity of the mustang...

The affect of this manifests itself in high g turns where the center of gravity wants to switch and a pilot suddenly has to push on his stick to keep the aircraft from swapping ends.

Pilots could and would engage with the fuel tank full, but they had to be careful not to enter high g turns or do acrobatics...so most would drain about half the tank when possible depending on the length of the mission.

At least this is how I understand the phenomenon to work...

Intersting that nobody tested any other flight characteristics...I was especially interested in climb rate.

DGC763
04-15-2004, 07:14 PM
Gents. The fill/drain order is an IL2 FB engine limitation. Hobnail was correct. The weight is taken into consideration but not C of G changes. Will be addressed in BoB I am lead to believe.

"Know the enemy and know yourself; in a hundred battles you will never be in peril." (III.31) Sun Tzu

PlaneEater
04-17-2004, 06:51 PM
Either way, I'd like to hear from Oleg about (*BUMP*)--rmm, excuse me--the issue, and how exactly it's currently set up in the sim.

kubanloewe
04-18-2004, 03:15 AM
a Pony flies with 100%Power at sealevel with 25% Fuel in FB about 34minutes thats more than 2times compare to a 109 !

A fat Jug flies with 25% Fuel with 100%Power
1 1/2 hours in FB !!

So I wonder why the US boy´s need such additional Tanks under the wings http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gifhttp://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gifhttp://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif

"The frist time I saw chuck Yaeger I shot him down..."
Petrosilius Zwackelmann (WW2 Hero)

"Finde den Feind und schiesse ihn ab alles andere ist Unsinn"
Rittmeister Freiherrr Manfred von Richthofen

Willey
04-18-2004, 03:40 AM
With 25% fuel only, turn rate gets 1,5-2s better than the initial 20-21s... http://ubbxforums.ubi.com/images/smiley/16x16_smiley-indifferent.gif. Then it almost turns like a 109F with wing/power load values worse than a 190D or 109K4 http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif

Willey
04-18-2004, 03:46 AM
@kuban: A 51C/D in FB has 269gal of fuel. That's 1022,2l http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif. So 25% is ~250l. With that a 109 also flies for more than half an hour :wink:.

But I wonder about the Ta-152! It burns some 100l in 4-5min! With almost 1000l of fuel, it can't even stay up for an hour! WTF? Also nice, that the 109A-8 and 9 fly half as long with more fuel than the 190A-5 has http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif. OK, they should have more fuel, and they don't have it. 515l instead of 400. Like the F-8.

PlaneEater
04-19-2004, 01:09 PM
Hmm. 25% of 'bump', loaded to the fuselauge tank, would be...

'P!'.

VF-10_Snacky
04-19-2004, 03:58 PM
Whether or not the Aux tank is modelled is a pretty big deal with the P51.
As with any aircraft the wings always get filled first and are last to be drained.

I often wondered if the 85gl aux tank was modelled in AEP and whether or not there was fuel in it. Since there is no way to select specific tanks in FB I would ask that the aux tank be left empty unless 100% fuel is selected. 25% and 50% should not have fuel in the aux tank.

"Son of a B**ch! That's gonna leave a mark."

PlaneEater
04-19-2004, 04:54 PM
Seawolf, the fuselage tank also needs to be there for a 75% fuel load.

At 75%, like I posted, the wing tanks are full (92 gallons each) and the fuselage tank picks up the extra, with 17.75 gallons.

Fillmore
04-20-2004, 12:13 AM
" Also, in FB source code current limitation prevents us from replicating the real world P-51 fuel
system."

From the readme. Exactly which aspects of the fuel system could not be replicated isn't said.

The effect of fuel loads is easy to see (at least in 190s, the planes I have most experience with) by how many trim steps are needed for level flight (higher fuel load you need less nose down trim for level flight). I am guessing this is due to differences in CG between different fuel loads. Oleg has stated that weight hasn't much effect on max speed irl.

One thing which I havnt' gotten around to testing is if weight/CG changes with fuel use, or is fixed from the initial selection, my impression at one time was that it was fixed (i.e. if you selected 100% fuel and flew till you have 25% left your plane will fly the same as it did from the beginning, and will fly differently than if you had started with 25%), but I never got around to testing it.

PlaneEater
04-22-2004, 12:44 PM
I still would really like to have Oleg comment on how this is currently handled in FB.

(*bump*...)