Refueling Fuselage Tank only

Got a question about the fuselage fuel tank and the ordinance using fuel tanks.

In DCS the ground crew is refueling the Left and Right tank first before the fuselage tank get fuel, what is the reason for doing so?

Why should the Pilot use the fuselage tank first before using the wing tanks, have this something to do with the COG?

 

 

I have read something about Left tank needs fuel to start up the engine, but i did a test with 100% fuel running the wing tanks empty.

After touch down i turned off the engine and did a restart with empty wing tanks and a full fuselage tank.

 

 

I did a nice flight with the fuselage tank only, without any COG problems, and without the need to switch all the time between the left and right tank.

Maybe the COG is even better?

 

 

I realy love to fly the P51D but it bugs me using the wing tanks, reworking the trim all the time, it's a huge disadvantage in combat.

 

 

I would suggest to change the ordinance of refueling, or make it possible to refuel the wing tanks and fuselage tanks independently.

If the Left tank needs relay fuel for starting up the engine, give him 1%

Maybe someone can make a mod or ED can change it. If i could, i change a LUA, but don't know how?

 

 

Give me feedback about my idea, what you think, if its bad or good, please.

 

 

Happy Flying :pilotfly:

Filling fuselage tank is creating COG problem, so fuselage tank has to be burned first while cursing to the target.

Manual say that with fuselage tank filled every aerobatics are forbidden. I think fuselage tank filled up is making p-51 not recoverable from stalls spins, i guess this is the reason.

The effects of having fuselage tank filled up are rather mild in DCS compared to the competing WWII sim, though I'm not qualified to judge which FM is more accurate in this regard. The nose gets a little bit more wobbly during maneuvers and that's about it. You can do aerobatics, spin and recover left and right no problem; also, contrary to the module manual, trimming for hands off level flight is easy and comparable to tank-empty configuration.

 

I have read something about Left tank needs fuel to start up the engine, but i did a test with 100% fuel running the wing tanks empty.

After touch down i turned off the engine and did a restart with empty wing tanks and a full fuselage tank.

 

Not quite like that. Engine can start while being fed from any tank (not sure about drop tanks, haven't tried that :D), it's just recommended to do so from the left one, because this is where the fuel return line from the carb goes to (so you have to suck some fuel from it first to make space for any carb return coming).

Yes exactly if your left tank is full and you start engine on other tank fuel will flow out from left tank in to the ground, it is about 10 gallons/hour

Yes exactly if your left tank is full and you start engine on other tank fuel will flow out from left tank in to the ground, it is about 10 gallons/hour

 

Is that modeled in DCS and what conditions lead to it?

 

I've flown for over a half hour at a time in all kinds of environments (extreme heat/cold/altitude) and have never seen a measurable return to my left tank. (NOTE: if you're going to test this sometimes changing altitudes can give weird readings).

Is that modeled in DCS and what conditions lead to it?

 

I've flown for over a half hour at a time in all kinds of environments (extreme heat/cold/altitude) and have never seen a measurable return to my left tank. (NOTE: if you're going to test this sometimes changing altitudes can give weird readings).

 

Actually I've never tested it, and yes tank gauges sometimes may show different values after flying in not level attitude.

I don't know is it modeled or not , but half an hour flight it would give 5 gallons the difference on tank gauge would be very small.

But if this is modeled flying on right tank for an hour should bump up fuel level in left tank by about 10 gallons.

The easiest way to test it, would be to fuel p-51 as low as possible for example 10 gallons in each tank, fly on left tank till is dry then switch to right tank and after burning all fuel form right tank switch to left, there should be some fuel to keep it going

Edited November 24, 2019 by grafspee

the fuselage tank is behind the pilot and having it full is supposed to shift the COG to the rear. making the elevator authority weak.

but as mentioned I have no problems pulling out of a dive with the tank full.

maybe they will take another look at it with the new damage model.

Full fuselage tank was dangerous because stick force was reversed during tight turns and pull-out.

It means that force needed to move elevator (pull) decreased with increased G-force and pilot could easy ovecome structural plane G-limits and destroy it, or just reach "black-out".

 

It was reason why "bob weight" was instaled into elevator control line, to increase force needed to move it.

Is that modeled in DCS and what conditions lead to it?

 

I've flown for over a half hour at a time in all kinds of environments (extreme heat/cold/altitude) and have never seen a measurable return to my left tank. (NOTE: if you're going to test this sometimes changing altitudes can give weird readings).

 

Just tested this in DCS. unfortunately there is no fuel returning back to left tank.

I did as i said, i burned all my fuel from left tank(engine died, fuel pressure drop to zero), then switched to right tank. I was flying good 30 minutes on right tank, then i switched to fuselage tank which was empty all the time i waited to burn off fuel from fuel lines then switched to left tank nothing, not a single drop was in left tank.

I think it will be next requested feature for P-51.

I think it will be next requested feature for P-51.

You mean, next requested feature be returned fumes on left tank? :doh: Yeah, seems legit :lol::lol::lol:.

 

 

S!

You mean, next requested feature be returned fumes on left tank? :doh: Yeah, seems legit :lol::lol::lol:.

 

 

S!

 

It's about 10 gallons per hour.

And it is not funny for me so don't throw roll faces and face palms on me

Edited November 25, 2019 by grafspee

It's about 10 gallons per hour.

And it is not funny for me so don't throw roll faces and face palms on me

 

 

You can use active pause an 10x time acceleration to speed up the process.

You can use active pause an 10x time acceleration to speed up the process.

 

i think you haven't tried flying p-51 level at 10x time acceleration :P.

Any way i testing this on MP servers. I did 30min flight with empty left tank, Not a single drop was send to left tank through carb return line.

after 30min it should drop 1-2 gallons at least.

Fuel tanks have good gages first scale range is from 0-5 gallons so it would be very easy to see if any fuel is returning back, which is not in DCS case.

Edited November 25, 2019 by grafspee

It's about 10 gallons per hour.

And it is not funny for me so don't throw roll faces and face palms on me

10 gallons per hour of FUMES? Does say that the manual? Haven't seen there.

 

 

S!

10 gallons per hour of FUMES? Does say that the manual? Haven't seen there.

 

 

S!

On fuel system diagram, return line from carb is present.

I heard it from pilot, that is about 10 gallons per hour, taking in to account that almost no one is flying p-51 at powers more then 40" for longer time so i would guess that this 10 gallons per hour happens while plane is at cruise power.

Edited November 25, 2019 by grafspee

On fuel system diagram, return line from carb is present.

I heard it from pilot, that is about 10 gallons per hour, taking in to account that almost no one is flying p-51 at powers more then 40" for longer time so i would guess that this 10 gallons per hour happens while plane is at cruise power.

That's why I ask if it's stated somewhere, manual or something. 10 gallons per hour is too much, almost half of the engine consumption (though that depends on regime, right). I don't think fumes return could of should be that much, I mean that doubles a small Cessna consumption per hour in fumes :huh: . More clear info on that would be needed before any feature request.

 

 

S!

That's why I ask if it's stated somewhere, manual or something. 10 gallons per hour is too much, almost half of the engine consumption (though that depends on regime, right). I don't think fumes return could of should be that much, I mean that doubles a small Cessna consumption per hour in fumes :huh: . More clear info on that would be needed before any feature request.

 

 

S!

 

I may shock you, but V-1650-7 fuel consumption is between 60-194 gallons per hour irc, this engine probably burning 10 gallons per hour at idle. And comparing p-51's fuel system to cessna's no real point of doing that.

P-51 pilot said that if you have full wing tanks and you start engine on any tank excluding left wing tank, plane will start draining fuel out on the ground.P-51 is equipped with injection type carb which mean that fuel is forced in to intake by pressure. This pressure must remain constant to ambient pressure so there should be some pressure regulator and pressure regulator always has return flow to tank.

From where did you get fumes anyway. Im talking about liquid fuel. And you are constantly adding 10 gallons of fuel fumes over and over and over again. Why?

And you state that you have flown for 1 hour on WEP in p-51 so you had to notice that you blasted through whole full wing tanks.

Edited November 26, 2019 by grafspee

I may shock you, but V-1650-7 fuel consumption is between 60-194 gallons per hour irc, this engine probably burning 10 gallons per hour at idle. And comparing p-51's fuel system to cessna's no real point of doing that.

P-51 pilot said that if you have full wing tanks and you start engine on any tank excluding left wing tank, plane will start draining fuel out on the ground.P-51 is equipped with injection type carb which mean that fuel is forced in to intake by pressure. This pressure must remain constant to ambient pressure so there should be some pressure regulator and pressure regulator always has return flow to tank.

From where did you get fumes anyway. Im talking about liquid fuel. And you are constantly adding 10 gallons of fuel fumes over and over and over again. Why?

Because what returns from carburator are the excess fumes, not liquid fuel. Do you understand how much fumes (evaporated fuel of course) volume that means compared to the liquid it was at first? If 10 gallons (american, that's ~38 litres which is roughly my car's fuel tank :doh:). That's A HELL OF A LOT of fumes mate.

 

 

Checking Pilot's notes Mustang consumption is 165 US gallons per hour at 3000/67" with rich mixture and low altitude and that's the highest it can reach, 46" makes it half that and lower cruising can be in the 40's to 30's, even 20's gallons, which is a lot but expected for a big piston engine. I believe your numbers are in the higher guesstimate :smilewink:.

 

 

 

S!

Because what returns from carburetor are the excess fumes, not liquid fuel. Do you understand how much fumes (evaporated fuel of course) volume that means compared to the liquid it was at first? If 10 gallons (american, that's ~38 litres which is roughly my car's fuel tank :doh:). That's A HELL OF A LOT of fumes mate.

 

 

Checking Pilot's notes Mustang consumption is 165 US gallons per hour at 3000/67" with rich mixture and low altitude and that's the highest it can reach, 46" makes it half that and lower cruising can be in the 40's to 30's, even 20's gallons, which is a lot but expected for a big piston engine. I believe your numbers are in the higher guesstimate :smilewink:.

 

 

 

S!

 

pls explain to me where do you have fumes in p-51's carb?? Because this is pressurized carb so i have no idea where do you take those fumes from :P beside fumes in fuel tanks and intake manifold

165 US gallons is for -3 engine -7 burns 194 gallons at 46" 2700 rpm is 109 US gallons which is a little more then half but it is still a lot.

You will not go lower then 50 maybe 40 gallons unless you cursing at super low rpm like below 2000 rpm which is harmful for engine for longer periods. At max cruise that is 36"2400 rpm this engine burns 66 gallons at 14k ft and 64 gallons at 23.7k down low it will bur more.

And you mentioned that you took those data from DCS manual. Ha i found another miss match, Fuel consumption listed in DCS manual is for -3 engine not for -7.

Yes you are right it is called carb vapor return in diagrams. So i m thinking how engine driven fuel pump and tank boosters work if they pump fuel against a wall. Because if it is only fuel vapor that would take enormous volume . (engine rpm 3000 and thorrle shot off so very little fuel is exiting carb so those fuel pumps are still pumping at max power.)

Edited November 26, 2019 by grafspee

pls explain to me where do you have fumes in p-51's carb??

Carburators do run on fuel fumes indeed, not liquid gasoline :huh: . I don't know what you mean.

 

 

S!

Carburators do run on fuel fumes indeed, not liquid gasoline :huh: . I don't know what you mean.

 

 

S!

 

You are wrong, Carb is feeded with liquid fuel thus carb is injecting liquid fuel in to intake where fuel is mixed with air and gradual evaporating down the road.

Carbs run on liquid fuel, engines run on fumes.

Injection type carb is much closer to single point injection very little common with classic carb.

Anyway im leaving this topic be, maybe those pilots were mistaken i don't know.

Edited November 26, 2019 by grafspee

(OT so posted in a new thread): https://forums.eagle.ru/showthread.php?p=4119169#post4119169

 

From the manual 51-127-5 page 22:

 

(Concerning the vapor return): "Also, check the tank occasionally in flight to make sure that it isn't completely full. If you don't do this, the recovered gas, which may amount to as much as 10 gallons per hour depending on operating conditions, will be lost through the overflow pipe."

 

When I read this I tested it (about a year ago). It suggested that there were only specific conditions that would result in 10 gph. I remember GUESSING that conditions conducive to vapor lock would result in a higher vapor return rate, but my tests at that time didn't detect a discernible vapor return.

 

I tested max heat at SL and at max altitude. Since I couldn't find anything I just assumed that I didn't know what operating conditions caused the max vapor return rate. If I was operating the aircraft such that the vapor return rate was only 2-3 gallons per hour, I wouldn't have been able to detect the return with the tests I did.

 

DCS has far more subtle engine effects modeled, so I would describe this as a bug rather than pedantic aviation nerd rage.

 

EDIT: UNLESS it is modeled and I just don't know how to cause it.

Does anybody know for sure what "operating conditions" would cause the most vapor return? Is it just the engine setting, or would it be affected by ambient temp and atmosphere?

Actually, this is OT so I'll start a new thread: https://forums.eagle.ru/showthread.php?p=4119169#post4119169

Edited November 27, 2019 by Theodore42

It's really irrelevant to range etc if they model the actual fuel burn and then ignore both sides of the evaporate > scavenge equation. (as if recovery is effective, they net off to zero)

 

If you feel they're taking 10 gallons an hour of vaporisation and removing that, then not returning it, there's an effect on range / consumption, but if all they're doing is effectively adding it back to whatever tank the fuel is coming from, not always to the left tank - is that really the most urgent thing you can think of to request developer time is spent on ?