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Fuel consumption and CoG...


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I know we do not ( yet ) have the chance to perform fuel management, but I wonder if fuel consumption does affect the CoG in aircraft that are sensible to it, especially under the following circumstances:

 

1) Longitudinally affected as fuel is consumed, especially on aircraft with a rearward fuel tank;

2) Asymmetry, not caused by not correctly managing wing tanks ( for aircraft with wing tanks ), which I believe are assumed to be managed in perfection by the virtual pilots, but rather due to fuel tank leaks;

Edited by jcomm
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I know we do not ( yet ) have the chance to perform fuel management, but I wonder if fuel consumption does affect the CoG in aircraft that are sensible to it, especially under the following circumstances:

 

1) Longitudinally affected as fuel is consumed, especially on aircraft with a rearward fuel tank;

2) Asymmetry, not caused by not correctly managing wing tanks ( for aircraft with wing tanks ), which I believe are assumed to be managed in perfection by the virtual pilots, but rather due to fuel tank leaks;

 

 

I believe that fuel does affect the aircraft's CG, at least longitudinally.  This was shown a few patches ago by JtD (IIRC) when he was conducting spin testing.  I seem to recall that spin recovery was markedly different depending on fuel load.

 

Anecdotally, I also tend to notice that the trim settings required at the end of the sortie are different than when you've just reached altitude and are heavy with fuel.

 

As for #2, I would be very surprised.  Note that if you shoot a Yak in one of the wings, the fuel will often leak out of the wrong wing.  I believe this indicates that the fuel system is abstracted, and I would strongly doubt that wing tanks have their weights modelled individually with the ability to change.

Edited by JG13_opcode
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  • 3 weeks later...

 

Take a 190 with full fuel, dive to 700 kph and pull up sharply (without using horizontal stabilizer), see.
 
After that, do the same with low fuel level, and see.

 

I haven´t the Fw-190, but  in game, I've tested the same in the Bf-109 and the neutral trim speed and power is the same, with fuel tank empty and full (with trim in +1º, default trim in game).. I feel the airplane a little more heavy in the pitch axis, with the fuel tank full. But the neutral trim speed and power is about 340km/h, at 0.6 ATA/2000RPM (stick & rudder free, and bank & ball centered.)  with trim indicator in zero.  

I ve tested with a SC-250 bomb, but  i haven´t found diferencies in the trim settings.

 

But if you read this Bf-109F Ladeplan. (Weight & balance chart) ...

22489801_10214780059997374_6422791159544

We can see that the permissible distance of the C.G is whithin 40.4 and 62.9 cm from EK1 (leading edge of wing rib No. 1, which is the first rib of the wing attaches to the fuselage).
Also we can see in the table, the distances of the C.G. with respect to EK1 in two different configurations, and with the airplane loaded, and flying empty.
- With 4 bombs of 50kg, and the airplane loaded (Voll)  the C.G. is displaced to 60.7 cm of EK1. TAIL-HEAVY
- with the ETC-50 bombs rack and the airplane empty in flight (leergeflogen) the C.G. would remain in 49.6 cm of EK1.
- With 1 bombs of 250kg, and the airplane loaded (Voll)  than the C.G. is displaced to 57.7 cm of EK1
- with the ETC-250 bomb rack and airplane empty in flight (leergeflogen) C.G. would be in 46.4 cm of EK1. NOSE-HEAVY
 
This means that with the 4 Bombs of 50kg the C.G. is displaced rearward more than with the 250kg bomb, and that when you release the 250kg bomb, and with low fuel,
the aircraft would become more nose-heavy, than with the ETC-50 bomb rack..

I think that, this is not modeled in game. 

 

BTW.  i ´ve checked in game the neutral trim speed & power setting with trim in zero, and I found these.

-Bf-109 E7 = 320 km/h @ 0.6ATA/1900 RPM

-Bf-109 F4 = 300 Km/h @ 0.6ATA/2000 RPM

-Bf-109 G2 = 340 Km/h @ 0.6 ATA/2000 RPM.

 

Almost 100 km/h less than the real cruise speed, and the power setting very different to the cruise power at 1.05 ATA/2100 rpm that Volker Bau tell us in our interview  

 

Edited by III/JG52_Otto_-I-
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I'd like to see if the FM does change dynamically as you burn fuel.

 

I can tell a difference if I begin a mission online with only 50% fuel. Not sure if I can tell a difference after burning a quarter or half tank of fuel though.

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Otto,

 

ran some test flights, Kuban Map, and indeed on the F4 flying around from a full fuel tank into an almost empty one didn't appear to creat any need for trimming in pitch.

 

I used the Autopilot first, in level flight, and watched the stick inputs ( enlarged view ), and then I flew it manually, with nill winds and turbulence.

 

No significative change in pitching moment, no change in trimmed speed and power...

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As the aircraft burns fuel ,it's weigh decreases so induced drag is reduced so wing has to produce much less lift to support plane weight, so it should start climb if other condition are constant right?

Weight has a very strong impact on takeoff length to, that could be tested to.

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I just concentrated on any pitching tendencies due to the CoG variation, but yes, those are important tests too!

I can confirm to you that there are no changes in pitch axis in game, due to changes of the CoG. The Changes in CoG are not modeled.
Moreover, i am thinking that the changes of the C.oP. (Center of Presures) are not modeled well in game , because changes of elevator trim in Bf-109 neither affect to CoP or CoG. in acording to "Jimbo" Reed  explain in this video.

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The THS  (trimmable Horizontal Stabilicer) of the Bf-109 is able to compensate the changes of CoG...same to today AIRBUS fleet.

True. But so can any trimmable elevator. That is what trim is for. But you claimed that the trim altered the centre of gravity. Or at least, that seemed to me to be what you were claiming.

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True. But so can any trimmable elevator. That is what trim is for. But you claimed that the trim altered the centre of gravity. Or at least, that seemed to me to be what you were claiming.

No that is not that i said. THS is a more powerful trim system than the conventional servo trim tabs system. THS can move the CoP respect to CoG distances.

 

""" The trimmable stabilizer's primary advantage is that it provides tremendous trimming power over the full speed range of the airplane. The system also reduces drag as the stabilizer surface and the elevator are in alignment whenever the aircraft is in trim. The stabilizer trim is normally adjusted to compensate for centre of gravity position prior to takeoff to ensure optimum elevator effectiveness."""

 

This system is not realistic modelled in game. In fact, the THS of the Bf-109 in game,have been "nerfed" with the patch V2012, Now the THS is anything, but nothing seemed to "tremendous trimming power". Moreover, the default elevator trim settings in the Bf-109 is worng, and we are flying in game at cruise speed with the trim setting in +1º (nose down) for long diving. ..In according with Volker bau said, It is zero trim for level flight at cruise speed and cruise power.

Edited by III/JG52_Otto_-I-
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Lol the stab wasn't nerfed. It's just as effective aerodynamically, it just doesn't move at superhuman speed anymore. So naturally 109-only pilots are upset they can't have their cake and eat it too.

The russian airplanes have not THS, ..But as Jcom said CoG changes are not modeled well for Russian planes too.
I suppose that you are that people who enjoy the magical Flaps of the Yak-1, ..Am i right? ..Or you don't eat that cake?  :P
Edited by III/JG52_Otto_-I-
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Burning fuel has to change place of CoG, so CoG will move with relation to center of pressure this produce rotational motion.

So pilot has to adjust to fly level in trimmed condition.

 

btw deploying flaps gives higher lift coefficient, they have lot of drag but near stall condition that is not that important - you know this too but we both don't know how much it should regardless Yak1

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No that is not that i said. THS is a more powerful trim system than the conventional servo trim tabs system. THS can move the CoP respect to CoG distances.

 

""" The trimmable stabilizer's primary advantage is that it provides tremendous trimming power over the full speed range of the airplane. The system also reduces drag as the stabilizer surface and the elevator are in alignment whenever the aircraft is in trim. The stabilizer trim is normally adjusted to compensate for centre of gravity position prior to takeoff to ensure optimum elevator effectiveness."""

 

This system is not realistic modelled in game. In fact, the THS of the Bf-109 in game,have been "nerfed" with the patch V2012, Now the THS is anything, but nothing seemed to "tremendous trimming power". Moreover, the default elevator trim settings in the Bf-109 is worng, and we are flying in game at cruise speed with the trim setting in +1º (nose down) for long diving. ..In according with Volker bau said, It is zero trim for level flight at cruise speed and cruise power.

What a load on nonsense. Either the elevator trim provided for an aircraft can provide the necessary adjustment for a given condition, or it can't. 'Tremendous power' (whatever that means) doesn't come into it, regardless of what some random Wiki claims. If you are going to cite sources, I suggest you find some that are (a) credible, and (b) relevant.

 

As for the 1 degree difference between the trim indicator in the BoS cockpits and the real aircraft, why does it matter? What measurable, independently verifiable effect does it have on aircraft performance as simulated by BoS? How would the developers correcting the trim indicator graphic benefit gameplay?

Edited by AndyJWest
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WTF is even going on here? I literally can't even. 

 

Oldest Trope of Aviation: What goes up, must come down at some point. 

Second oldest Trope of Aviation: Your Elevator makes the Speed, your Engine makes the Climb. 

 

Following that: Speed is Adjusted by Adjusting the Elevator Trim. 

 

The 109 has a very Effective Elevator Trim System in that it allows it you to adjust for Speeds of Vne++ to Vmin--  while a LaGG-3 for example is only able to Trim for Speeds between 500 and 250, a Yak-1 is a bit more flexible, but not much. 

 

The P-40 appears to go through large CoG Changes from Full Fuel to about 60%. 

In a Climb that means that with 100% Fuel and full back Trim you climb at roughly 230kph, while with 60% Fuel (Range Extender Tank empty) it climbs less steeply, at 260kph as the CoG moved forward. 

So I would say CoG changes by fuel change, at least on the longditudinal Axis are implemented. However, I do not think they are for the Lateral Axis, since these Tanks at least all feed at the same time. 

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I indeed believe they're modeled, even longitudinaly...

 

I am running more tests with other aircraft...

 

OTOH, the Devs have long been clear that complex fuel management might come in the future - but we chose to have other features dealt with in the first place, so, we have to wait !

 

Presently, in aircraft with wing tanks, we have to accept the virtual pilot is correctly managing the source to keep the lateral balance as close to neutral as possible.

 

Armament thrown out of the deck asymmetrically sure has quite an impact too, and that is evident in the aircraft that allow for it in game.

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What a load on nonsense. Either the elevator trim provided for an aircraft can provide the necessary adjustment for a given condition, or it can't. 'Tremendous power' (whatever that means) doesn't come into it, regardless of what some random Wiki claims. If you are going to cite sources, I suggest you find some that are (a) credible, and (b) relevant.

 

As for the 1 degree difference between the trim indicator in the BoS cockpits and the real aircraft, why does it matter? What measurable, independently verifiable effect does it have on aircraft performance as simulated by BoS? How would the developers correcting the trim indicator graphic benefit gameplay?

Obviously you have no idea that we are talking about.. And no whatch my video

By the way, .. I've performed myself with my squadmates, the interview to Volker Bau about the elevator trim behavior of the Bf-109G in the Berlin airshow last year. Have you other source better than this?

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I realise that English isn't your native language, but given your self-evident inability to understand a couple of simple comments, I can see no point in discussing this further. Welcome to my ignore list.

Edited by AndyJWest
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Anyone attempting to measure trim changes due to fuel consumption needs to bear in mind that there are going to be two effects: one due to the reduction in mass (which normally would be expected to lead a plane trimmed to fly level to start to climb at a constant trim and power setting), and the other due to change of CoG. If the fuel tank is behind the CoG, it is entirely possible that the two factors can cancel out, or at least work against each other, making the effects less obvious. Similar points may also apply when looking at the effects of dropping bombs.

Edited by AndyJWest
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I realise that English isn't your native language, but given your self-evident inability to understand a couple of simple comments, I can see no point in discussing this further. Welcome to my ignore list.

Yes, the half of the world have not the english as native language, like many people here. ..But I´m not a racist.  :rolleyes:

 

Anyone attempting to measure trim changes due to fuel consumption needs to bear in mind that there are going to be two effects: one due to the reduction in mass (which normally would be expected to lead a plane trimmed to fly level to start to climb at a constant trim and power setting), and the other due to change of CoG. If the fuel tank is behind the CoG, it is entirely possible that the two factors can cancel out, or at least work against each other, making the effects less obvious. Similar points may also apply when looking at the effects of dropping bombs.

Basically, That is what we are talking about from the beginning of the tread, It seem that you understand finally.  ;) 

Jcomm and me thinks that CoG changes, are not modeled, especially the effect in the lateral stability when a wing fuel tank result drained due to battle damage, and the airplane continued flying with a wing tank empty, and the opposite full. 

Btw the fuel consumption affect very little to the trim setting in the Bf-109, due to the fuel tank is near to the CoG. But if you read the "Ladeplan" (Weight Balance chart) posted before, the bombs weight affect a lot of to CoG position in the real airplane, and that would  affect to the stab trim setting but that's not felt in game.

Edited by III/JG52_Otto_-I-
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Well, anyway as I pointed out above, fuel imbalance is in the Devs  TODO list, a long one given the many requirements we users have...

 

And I still have to make further tests ...

 

And, above all - truth is - we do not have anywhere near the overall quality of flight Dynamics, damage model / overall physics modelling in other civil or combat sims presently available, so...

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