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Bill Alderson

Lear 35 Center Fuel Tank Draining

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Hi,

 

I don't know if it's something I'm doing or not doing but after I take off in the Lear 35 with a full fuel load, the center fuel tank appears to to be draining.  I don't know where the fuel could possibly be going,except out into the atmosphere, because the wing tanks are still full and the transfer pumps are off.

 

Thoughts?


Bill Alderson

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It is not going over board it is being burned by the engines. Although this is not how the fuel system works in the real aircraft is an easier way to simplify how to make it work in this FSW version.I tried some fuel loading configuration checks using the load manager and observing which tanks were decreasing in flight confirmed that is what is going on.The FSW version of the fuel system has not been modeled with the same functionality of the actual aircraft fuel system.

 

In the actual Learjet 35 you would begin to transfer fuselage tank fuel when the tip tanks are empty.You do not wait until the wings are low on fuel to do this, if the transfer system failed you would be in a low fuel state with no way to get that fuel out of the fuselage tank.If the wings are full when you begin the transfer the tip tanks will receive the excess fuel from the wings and you will observe that on the fuel gauge as they begin to fill in flight As fuel is burned from the wings it is being replaced by the tip tank fuel until the tips empty again.You are not directly burning fuel from a tip tank, or the fuselage tank.All fuel being burned by the engines originates from the wings.

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Gary Stewart

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I also discovered that the center tank "drains" only when I start from a saved situation in FSX (BTW, the center tank doesn't wait until the tip tanks are empty before moving fuel, hence my bewilderment as to where the fuel goes when the wing tanks are still full).  When I start from Free Flight, the center tank will only transfer fuel when I run the pumps.  I guess that will put an end to starting from saved situations for the time being.  :wink:


Bill Alderson

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Flight sims can be very touchy to saved files. I know in some other aircraft if I even ctrl+e start the engines because I was lazy, it will only burn out of a certain tank and when that runs out it won switch to another tank. So the engines just die and that's the end of that. Just a simulation thing.


Mitchell Haughee

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Interesting to be reviewed by Flysimware.    I bet they checked this for V1.7, indeed fuel configuration/ussage was updated.

 

Thanks for sharing, interesting thoughs :wink:


Raphael Chacón

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FLYSIMWARE-SM#1378797

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Interesting to be reviewed by Flysimware.    I bet they checked this for V1.7, indeed fuel configuration/ussage was updated.

 

Thanks for sharing, interesting thoughs :wink:

 

Thanks for checking into this.

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Bill Alderson

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I also discovered that the center tank "drains" only when I start from a saved situation in FSX (BTW, the center tank doesn't wait until the tip tanks are empty before moving fuel, hence my bewilderment as to where the fuel goes when the wing tanks are still full). When I start from Free Flight, the center tank will only transfer fuel when I run the pumps. I guess that will put an end to starting from saved situations for the time being. :wink:

In the Lear 35, the engines can only take fuel from the wing tanks. Left engine is fed by the left wing tank, and the right engine by the right wing tank.

 

I'm not sure how the add-on is configured, but in the actual aircraft, the tip tank fuel will be used first. The fuel flows from the tip tanks into the wings, and then from the wings to the engines via jet pumps. The wing remains "full" (on the gauge) because whatever amount of fuel is extracted by the engines is immediately replaced by the fuel flowing in from the tip tanks. Once the tip tanks are empty, fuel is transferred from the fuselage tank into both wing tanks. Again, the fuel is replenished (from the fuselage tank) as fast as it is used by the engines, so the wing tanks remain full. (Although at high power settings, the engines may use fuel faster than the fuselage transfer system can replenish it, so the crew might see some decrease in wing tank quantity under those conditions).

 

Fuel flow to the wings from the tip tanks happens automatically, but transfer from the fuselage tank to the wings has to be commanded by the pilot with the transfer switch.

 

Once all tip tank and fuselage tank fuel has been used, THEN the wing tank fuel level will begin to drop, as that is the sole remaining source of fuel.

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Jim Barrett

Licensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.

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I'm not sure how the add-on is configured......

 

Well let's just they use some "artistic license" about the manner of things. :smile:


Gary Stewart

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In the Lear 35, the engines can only take fuel from the wing tanks. Left engine is fed by the left wing tank, and the right engine by the right wing tank.

 

I'm not sure how the add-on is configured, but in the actual aircraft, the tip tank fuel will be used first. The fuel flows from the tip tanks into the wings, and then from the wings to the engines via jet pumps. The wing remains "full" (on the gauge) because whatever amount of fuel is extracted by the engines is immediately replaced by the fuel flowing in from the tip tanks. Once the tip tanks are empty, fuel is transferred from the fuselage tank into both wing tanks. Again, the fuel is replenished (from the fuselage tank) as fast as it is used by the engines, so the wing tanks remain full. (Although at high power settings, the engines may use fuel faster than the fuselage transfer system can replenish it, so the crew might see some decrease in wing tank quantity under those conditions).

 

Fuel flow to the wings from the tip tanks happens automatically, but transfer from the fuselage tank to the wings has to be commanded by the pilot with the transfer switch.

 

Once all tip tank and fuselage tank fuel has been used, THEN the wing tank fuel level will begin to drop, as that is the sole remaining source of fuel.

Yes this is how our fuel system works. Nice job explaining this as we have this info in our updated manual for V1.7.

 

We redesigned the fuel system so the engines can only burn from the wing tanks. Our older version we burned from the tip tanks then the wings to simulate gravity transfer. But in V1.7 we created a whole new code that actually tranfers fuel from the tip to the wing by gravity and as we decided to make the fuel system spot on. This took around 8 hours of re writing the code as it can cause conflicks since every time we create another process you must stop another one or the total fuel would change. For example if you are transferring fuel from the center to the wing the gravity system will be on hold until your finished. This is the downsides of FSX fuel coding. 

Hi,

 

I don't know if it's something I'm doing or not doing but after I take off in the Lear 35 with a full fuel load, the center fuel tank appears to to be draining.  I don't know where the fuel could possibly be going,except out into the atmosphere, because the wing tanks are still full and the transfer pumps are off.

 

Thoughts?

This makes no sense. I always suggest creating a new default saved flight with the king air as this solved a similar issue from another customer who would only have the left wing tank drain. His default was the ultra. Although i tested changing from the ultra to the Lear and i could not repeat the same issue. Also our coding is designed to change the hidden fuel selectors on aircraft reload. So saved flights should also have no issue if your last saved flight was working perfect before you saved. So this may be why someones saved flight has issues. 

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This makes no sense. I always suggest creating a new default saved flight with the king air as this solved a similar issue from another customer who would only have the left wing tank drain. His default was the ultra. Although i tested changing from the ultra to the Lear and i could not repeat the same issue. Also our coding is designed to change the hidden fuel selectors on aircraft reload. So saved flights should also have no issue if your last saved flight was working perfect before you saved. So this may be why someones saved flight has issues. 

 

I'm not sure what you mean by this.


Bill Alderson

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I'm not sure what you mean by this.

I mean if fuel is being supplied to the engines from the center tank then your default flight might have this fuel selector stuck on. Another customer had this issue until he changed his default saved flight. Default saved flights can get corrupted and cause weird issues as nobody else has fuel loss from the center tank. Our aircraft on re load uses only the wing tanks for the engines. Can you try reloading aircraft and then see if you lose fuel? Also what version do you have now?

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Agree on that.  Using saved flights is getting the LJ35A crazy

   

 

Avoid usage of saved flights =  Very academic pleasant flights :dance:


Raphael Chacón

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FLYSIMWARE-SM#1378797

FS2C #72243 #71201 #69299 #43560 #52175 #68068 #68152 SM#1325481

PMDG #431793 #371950 #333135 #332876 #292207 #280217 #247845 #206809  #178218 #171813 

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I mean if fuel is being supplied to the engines from the center tank then your default flight might have this fuel selector stuck on. Another customer had this issue until he changed his default saved flight. Default saved flights can get corrupted and cause weird issues as nobody else has fuel loss from the center tank. Our aircraft on re load uses only the wing tanks for the engines. Can you try reloading aircraft and then see if you lose fuel? Also what version do you have now?

 

My default flight is the FSX default 737-800, sitting at the gate with all systems off. It's been the same for years.  From there, I have setup a situation where my saved flight is the Lear parked at the FBO at Chicago Executive Airport (KPKW).

 

I believe I have the latest version of the Lear (1.7 if memory serves) and after reloading from free flight I have no problems.


Bill Alderson

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V1.8 is out......    

 

Run for your life!  :dance:


Raphael Chacón

158745.png

FLYSIMWARE-SM#1378797

FS2C #72243 #71201 #69299 #43560 #52175 #68068 #68152 SM#1325481

PMDG #431793 #371950 #333135 #332876 #292207 #280217 #247845 #206809  #178218 #171813 

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