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BobKK47

Version 2.6 confused about inflight fueling

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With version 2.6,  I'm having a problem with how fuel is sent from the tip tanks to the wing tanks.

 

I believe that in the real aircraft, fuel flows first from the tip tanks to the wing tanks and, when that is exhausted, fuel can be transferred to the 

wing tanks from the fuselage.   This is the way it seemed to work before version 2.6.   Now, I'm not seeing any fuel flow from the tip tanks to the wing tanks. 

 

According to the 2.6 update at the flysmware website:

 

1.  "'tip tanks are now externanl (sic) in the cfg. file so fuel never burns from the tip tanks"

 

2.  " Fuel valve now transfers tip tanks to wing tanks when tip tanks are 50%".  

 

First question.  Where is the valve that transfers the fuel from the tip tanks to the wing tanks?   (I thought this was an automatic process).

The only related item I can locate is the switch on the console which transfers fuel from the fuselage to the wings but has no effect on transferring fuel from the tip tanks.

 

2nd question.   The second statement does not seem to make sense.   Should it not say, "Fuel valve now transfers tip tanks to wing tanks when WING tanks are below 50%.

 

Thanks to anyone who can answer and clarify this for me.

 

 

 

Bob

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I don't know what the Flysimware guys were writing up there, but it is supposed to work as follows on the Lear 35A:

 

Fuel feed from the tips and wings is automatic. First you will notice the tip tank quantity drops as this fuel is pumped into the wings by the Jet Pumps. The wing quantity does not reduce until after the tip tanks are empty. Each tank has a gauge. If the quantities do not add up exactly, the total reading is the more accurate. However, I personally operate on the least indicating amount (individual gauge totals versus the Total reading).

After the wing quantity starts reducing it’s time to take some fuel out of the fuselage fuel cell. We refer to this cell as ‘the bag’. Select the FUS TANK transfer switch to XFER. The Crossflow Valve will automatically open and the Fuselage Tank Transfer Pump will start pumping fuel down into the wing cells. This will continue until the fuselage cell is empty at which time a fuel pressure switch will sense there is no more flow and the EMPTY light will illuminate. The Fuselage Tank switch must then be selected to OFF.

 

(From: Flying the Classic Learjet, by Peter D.  Condon).

 

 

For me, in the Flysimware Lear it works exactly like described by Mr. Condon. Also, with 2.6, the transfer light will not stay lit but only momentarily light up so as to indicate the transient valve/switch disagreement, as it should be.

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Thanks.   Should the transfer switch be in the neutral position?   Because unlike previous versions, I'm not seeing fuel being transferred to the wing tanks from the tip tanks.   The fuel runs out in the wings and then I have to transfer from the fuselage.   I'm probably not doing something correctly. 

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I had the same issue. Not only were the tip tanks not feeding, but, if I tried to transfer fuel from the center tank then stopped the fuel would just slowly drain out of the center into nowhere (I know now how it should be done just as outlined above). I had to go to a different ad on and hit auxiliary pumps on then back to Lear to get it to work.

 

Thanks to another member's tip I saved a flight with the Lear then use it for my Lear flights. You will be able to tell right after engine start because the tip tanks will start feeding immediately.

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For 2.6 we tried to simulate the fuel system more accurately. Unfortunately it's not well documented. So let me shed some light on this:

 

Fuel from the tip tanks can be gravity fed to the wings until the tips are about half full. For the lower half the jet pumps are needed, as internal obstructions prohibit any more fuel from being gravity fed. This is correctly simulated. So the jet pumps will not starve an engine when shut down, as they are only used for transfer.

The standby pumps only come into play during startup and if an engine driven pumps should fail; there is no mean to verify their operation though, at least with the equipment simulated in this particular Lear. In the real world there is a retrofit option that includes lights in the switch assembly as a visual feedback that the particular pump is operating.

The fuselage tank will fill up the wings only, and its pump will shut off automatically if the wing tanks are full. So when you select the switch to transfer, the wing is filled up intermittently, as the engines consume fuel out of this tank. So you will see the wing fuel level be staying full and the center tank decreasing.

 

Normal operations should be: Standby pumps always off, jet pumps always on. Let the tips drain empty, then use the wing tanks. Once around 600 pounds per tank used, you can fill the wings back up with the center tank. If you are certain that you indeed loose fuel, PM me with the configuration you had and I will try to verify that behaviour.

 

Always start your sim with a saved flight using a standard aircraft with everything switched off (as it is recommended you any advanced addon).

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Matthias,

 

Thanks very much for that very helpful information.   Thinking back to my last flight with the Lear, I'm almost certain that the reason I  assumed I was not getting fuel from the tip tanks to the wing tanks was that I failed to insure that the jet pumps were on.    Although, as you indicate in another post, gravity feeds the fuel from the tips initially and the jet pumps only come into play when the fuel in the tips goes to less than about 50 percent.   I definitely will monitor this on my next flight.

 

As you suggest, I always start FSX with a previously saved flight specifically,  the stock Cessna 172 sitting at my "home" airport, KCMA, in a "cold and dark" start situation.

 

Thanks again,

 

Bob

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Mathias is correct in his statement, when the wings and tips are full the fuel is burned from the wing tanks and is constantly being replaced by tip fuel until the tips are depleted.It is an automatic process as long as the jet pumps are on.If the jet pumps are off the tip fuel can only gravity feed to about 600lbs and would remain trapped in the tip tank unless the "motive flow pressure" has been restored from a jet pump.At that point you would see the wing fuel level start to decrease.Fuel transfer from the fuselage tank would normally occur once the tip fuel is depleted.

 

Regarding the standby fuel pumps, they will automatically turn on during engine start and when filling the fuselage tank using the fill switch.They can be manually activated by the pilot when balancing fuel wing to wing with the cross flow valve open, or in the event of a low fuel pressure situation where the normal low pressure fuel circulation (which is provided by having a jet pump switch on) has been interrupted from contamination or a blockage for example.The standby pumps are not able to supply adequate fuel pressure to keep an engine running if the engine driven fuel pump were to fail.It is a mechanical pump in the engine accessory section and if it fails the engine will flame out.

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