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 Post subject: Use all tanks on Mustang
PostPosted: Thu Nov 27, 2008 11:10 pm 
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Good day! I was wondering if someone knows how to set-up the P-51D Mustang to use "all tanks" or "drop tanks first then all tanks" rather than having to manually select each tank in order along the way and trying to keep everything balanced?

Thanks!


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PostPosted: Fri Nov 28, 2008 1:10 am 
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I believe this was not historically possible in the P-51D. I reviewed several historic P-51 manuals including the P-51D/K and later F-51 pilot training manuals for a definitive answer. While I haven't ascertained for certain whether the rotating fuel selector switch completely shuts off fuel flow from the unselected tanks, a set of wartime notes for the P-51D does describe the operation of the fuel switch in this manner:

Fuel lines from all five of these tanks lead to a selector valve and thence to a fuel shut-off valve. The selector valve, as its name implies, closes or opens the fuel line to the selector tank. The selector valve has five positions, each position connecting to one of the five tanks as indicated by the placard at the valve. When the selector valve is turned to either the left main, right main, or fuselage tank position, a micro switch automatically turns on booster pump in the tank selected if the booster pump switch is on. Only one of the three booster pumps operates at one time, depending on which tank is being used. The carburetor is vented to the left wing tank.

Most vintage manuals include a diagram of how the fuel system works. The set of notes referenced above does not include illustrations but it instead has the most detailed textual explanation of the fuel I've seen:

The engine is supplied from two main self-sealing tanks in the wings, a self-sealing fuselage tank which is located behind the pilot's seat and also from two droppable combat or auxiliary ferrying tanks, if they are carried. These tanks, when carried, are attched to the bomb racks. Each main tank and the fuselage tank is provided with Thompson submerged typed fuel booster pumps. These pumps are operated by a master booster pump switch located on the lower center instrument panel, which is wired in a circuit with micro switches incorporated in the fuel selector valve.

The main tanks, fuselage tank, and all lines from the tanks to the engine are the self sealing type. Fuel is supplied from the main system in the following manner: Each tank has a line extending from the booster pump to a check valve, which permits fuel to flow to the engine but it does not allow it to return. The two systems are joined at the check valve by a T fitting, and a line extends from the T fittings to a fuel shut-off valve. From the fuel shut-off valve, a line extends through a fuel strainer to an engine-driven fuel pump mounted directly to the engine. The auxiliary tanks consist of droppable ferrying tanks or combat tanks, one mounted to each bomb rack. When combat or ferrying tanks are used, the fuel from them passes through the fuel system selector valve and on the main fuel lines. The tanks are not interconnected, and it is necessary to switch from one tank to the other to maintain balance.

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PostPosted: Fri Nov 28, 2008 1:49 am 
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I asked myself, "If the plane is an equipped with an engine-driven fuel pump, could that pump be used to draw all tanks simultaneously?" (This was assuming, of course, that the fuel selector switch isn't a valve but only a booster pump control). The answer comes from the F-51D training manual:

Each of the main fuel tanks has its own gravity-fed submerged-type booster pump receiving power from the electrical system of the airplane. These pumps supplement the engine-driven fuel pump and will handle the fuel needs of the engine at all altitudes if the engine-driven fuel pump fails. If the the booster pumps fail, the engine-driven fuel pump will supply fuel only up to approximately 8500 feet. To prevent wing heaviness, fuel should be used alternately from the wing tanks.

The drop tanks have no booster pumps, but fuel is forced from them by a controlled pressure of 5 psi from the exhaust side of the vacuum pump. This pressurization will permit satisfactory flow of fuel from the drop tanks at all altitudes. If the pressure to the drop tanks fails, the engine-driven fuel pump is capable of pulling fuel from the drop tanks up to approximately 10,000 feet.

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PostPosted: Fri Nov 28, 2008 2:29 am 
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gw105 wrote:
...rather than having to manually select each tank in order along the way...

I found some interesting information about the sequencing of the P-51D's fuel tanks. The wartime operating notes I looked at suggest that the pilot should take off on the main fuselage tank, then at a suitable altitude to switch to the left main tank for ten minutes to create space for vented fuel vapors. The pilot would then switch back to the fuselage tank until it was drained down to 25 gallons remaining to give the aircraft the best center of gravity. Only then would he start to use the drop tanks or the main wing tanks.

The P-51D/K training manual from 1945 explains that fuel vapor recovered from the carburetor is sent to one of the main tanks:

Whenever the engine is running, vaporized fuel is returned from the carburetor to one of the fuel tanks through the vapor return vent line. On later airplanes, this line is led to the fuselage tank, while on some of the earlier P-51D's the vapor return is to the left wing tank. Find out which tank the vapor return line is connected by asking your engineering officer, and use fuel from that tank first to allow space for return. Also, check the tank occasionally in flight to make sure 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.

The F-51D pilot's training manual from 1954 advises this procedure:

Take-off and climb should be accomplished with fuel tank selector handle at Main Tank L.H. because the vapor separation line from the carburetor returns to this tank. Fuel vapors flow from the carburetor to this tank at the rate of approximately one gallon per hour. At altitude, use fuel from fuselage tank until 25 gallons remains, to have ideal CG condition for landing. Then cruise on drop tanks alternately until they are empty. Continue flight using main wing tanks alternately, to prevent wing heaviness, until they are empty. Then use fuel from fuselage tank during landing.
Warning --The fuel booster switch must be ON during flight to ensure an adequate fuel supply.

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PostPosted: Fri Nov 28, 2008 8:40 am 
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Hi Skycat, and thanks for your great informational replies! I 100% agree that the use of all tanks in the Mustang is not historically accurate... but I also think that certain allowances should be alright in FS9, given the nature of the flight sim, you already deal with certain "challenges" real pilots don't have to contend with, such as less manouverable visibilty, imprecise control inputs, and most of all lack of "feel".


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PostPosted: Fri Nov 28, 2008 9:07 am 
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Perhaps there is a way to edit the .air file; for example, make the main fuselage tank worth the total fuel capacity and the other tanks worth zero gallons. I think some FS models do have interconnected fuel cells so perhaps there is a way to simply edit what kind of fuel system is being used. But if such a 'fix' is possible it is beyond my technical expertise...my only solution would be to change the sim's difficulty settings to unlimited fuel.

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PostPosted: Fri Nov 28, 2008 3:51 pm 
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The A2A "H" model has a position for both wing tanks, real handy for long flights :D


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PostPosted: Sat Nov 29, 2008 8:17 am 
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I only have the P-51D model in WWII fighters, not the H model unfortunately. Does anyone know how to edit the D model to use all tanks?


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PostPosted: Thu Dec 11, 2008 6:49 am 
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Unfortunately I have no knowledge of editiing aircraft in this manner. Is there any shockwave support people here that might be able to tell me if there is a solution for this, or if it is not possible?

Thanks again.


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PostPosted: Thu Dec 11, 2008 1:07 pm 
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Unlimited fuel seems to be the option for you.

regards
ROB

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