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Spitfire Idle Cutoff Control


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No, right now idle cut off handle isn't working as supposed.And manual has error in that line. Moving mixture handle Aft will cut off the engine.


Edited by grafspee

System specs: I7 14700KF, Gigabyte Z690 Aorus Elite, 64GB DDR4 3600MHz, Gigabyte RTX 4090,Win 11, 48" OLED LG TV + 42" LG LED monitor

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Page 135 of the detailed Spitfire MK IX Manual says to pull the Idle cutoff control Aft after engine warm up!

 

 

 

Is this correct?

 

 

 

Spitfly

The stop valve must be aft as long as the fuel pump is active. Basically the fuel cutoff being forward floods the supercharger with gas, possibly causing a fire.

 

Not sure if it's modelled that way though. I pulled that from the actual pilots notes.

 

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Thanks for the responses.

 

I tested with the fuel pump on and off and the Fuel Cutoff Aft kills the engine operating from idle and also from 2000 rpm. Pushing it forward keeps the engine going even while it is sputtering to stop from the aft position.

 

Thanks again

Spitfly,

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Thanks for the responses.

 

I tested with the fuel pump on and off and the Fuel Cutoff Aft kills the engine operating from idle and also from 2000 rpm. Pushing it forward keeps the engine going even while it is sputtering to stop from the aft position.

 

Thanks again

Spitfly,

From what I've read, the fuel cutoff was actually the mixture control system in earlier models. Setting it aft was essentially Auto lean/idle cutoff, and setting it forward was auto rich. Later spits ditched the system for a completely automated mixture control system along with a pressure carberator which kept fuel flow during high g and negative g maneuvers.

 

I think the confusion is as to why the switch was kept in place in the mk IX, and what purpose it served. In DCS it essentially serves as a second fuel flow cock,and I can't find anything talking about what it did in the real mk IX.

 

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Okay I found it. The mixture control was retrofitted to be the carberator idle cutoff switch in later model spits. Essentially the fuel cock controls fuel from the tank to the fuel lines, and the cutoff switch controls fuel from the lines to the carberator.

 

The problem with having the valve open when the booster pump is active, has to do with the design of the carberator. Fuel and air are mixed inside the supercharger. This was a design choice to eliminate the need for a carberator heater, but it also meant that if the fuel cutoff was forward when the pump was operating, excess fuel would flood into the supercharger, creating a serious fire risk.

 

EDIT: To clear up further confusion, the fuel booster pump is an electric pump designed to deliver fuel to the engine during the startup procedure before the engine driven fuel pump takes over. This is completely different than the fuel pressure pump, which pressurizes the fuel system and should be used at altitudes above 20,000 ft.

 

Essentially the short of it is that there are two ways to start the spit. Booster pump, or manual using the wobble pump and cutoff switch. You can't do both at the same time.

 

In any case, if you want to use the booster pump: pull the switch aft to idle cutoff, run the pump for 30 seconds then switch it off, hit the booster coil and starter buttons, and once she sputters move the cutoff switch forward to run. Remember to release the starter once the engine catches, but hold the booster coil until the engine is running smoothly.

 

Hopefully that clears up some stuff.


Edited by Tiger4-2
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The cut off is not a mixture control. Earlier Spitfires with a manual mixture control, like the Mk I, II and early V and IX all had a manual mixture control and a Slow Running Cutout that served different purposes. Some Mk V had a Slow Running Cutout and an Automatic Mixture Control.

 

 

 

The slow running cutout was generally a knob or ring pulled out to choke the engine causing it to stop. The Idle cut off fills the same purpose but does it differently, controlling fuel flow at the carburettors. Mixture control is separate and automatic on our Mk IX

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According to spitfire diagram there is one fuel pump, which drain fuel from fuel tanks and pressurizing fuel system helping to operate at high alt.

As mentioned above. Our MK IX has only OFF/ON mixture handle position.

Mixture is controlled fully automatic.

Priming pump helping start the engine is at right hand side of the cockpit. It's operated by hand and unlike in p-51 which priming pump is electric.

Only miss behave of the mixture handle in DCS spitfire is that starting the engine is supposed to be done with mixture lever push all the way forward.In DCS spitfire starting procedure is identical to P-51 starting procedure.


Edited by grafspee

System specs: I7 14700KF, Gigabyte Z690 Aorus Elite, 64GB DDR4 3600MHz, Gigabyte RTX 4090,Win 11, 48" OLED LG TV + 42" LG LED monitor

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According to spitfire diagram there is one fuel pump, which drain fuel from fuel tanks and pressurizing fuel system helping to operate at high alt.

 

As mentioned above. Our MK IX has only OFF/ON mixture handle position.

There are two. Three if you count the pressure pump. One engine driven fuel pump, and an electric fuel booster pump.8dbe3be111f1651c18c23e50526e9b91.jpg03a5ac3b1462f8bd604345c3cc2c7e6e.jpg

 

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Yes. engine driven pump, electric pump, and hand operated priming pump.

There is additional handle for fuel tank pressurization, which just open valve which allow pressure enter fuel tank, but this has very little usage in spitfire, because it will vent fuel out when any leaks are present.

Edited, I forgot about hand operated fuel pump on right cockpit wall :)


Edited by grafspee

System specs: I7 14700KF, Gigabyte Z690 Aorus Elite, 64GB DDR4 3600MHz, Gigabyte RTX 4090,Win 11, 48" OLED LG TV + 42" LG LED monitor

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