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brynjames

Cessna Engine Start and Fuel Pump

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How should I start and stop the Cessna 172 engine without resorting to CTL-E? Can't find any clues in the learning centre.So far I've found I can shut down the engine by switching all magnetos off, or setting the mixture to an inappropriate position :)Starting the engine again seems more difficult. Moving the key switch to the start position cranks the engine: sometimes it fires, sometimes it doesn't. The fuel pump switch position doesn't seem to matter.I'd appreciate some guidance here, thanks.--Bryn

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*mixture full rich*just a bit of throttle*hold key in start position until engine starts--

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I don't recall on the Default 172 but many aircraft have a fuel "cutoff" position on the mixture control(full out) so it's not necessarily wrong to do what you did with the mixture control.

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>I don't recall on the Default 172 but many aircraft have a>fuel "cutoff" position on the mixture control(full out) so>it's not necessarily wrong to do what you did with the mixture>control.That is the proper way to kill the engine, before turning off the mags, electronic ignition, etc.

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The reason most GA aircraft are shut down using the mixture is to ensure there is no/minimal fuel left in the system after shut down.. as essentially you're starving the engine. So that usually is the correct way (as posted above) to shut it down..The fuel pump is not usually found on high wing GA aircraft (which is confusing as its in the default 172) as the fuel is gravity fed to the engine. Low wing aircraft need them to pump fuel up to the engine until the engine driven pump takes over (on start up) when they're no longer needed. They are however used in important parts of flight like changing tanks, flying the circuit.. landing/take off etc incase the engne driven pump fails. Fuel injected systems have fuel boost (auxiliary) pumps that are used for different reasons.. so perhaps thats what is supposed to be in the default Cessnas.

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>Fuel injected systems have fuel boost (auxiliary) pumps that>are used for different reasons.. so perhaps thats what is>supposed to be in the default Cessnas.Yes, that's the reason for having the auxiliary fuel pump in the default Cessnas which are the newer fuel injected models. Fuel injection requires a much higher fuel pressure than a carbed engine, and also has a return line back to the tank, for excess fuel that the injection system can't absorb.

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On an injected engine is vapor lock a bigger problem? I understood that the return line helped alleviate vapor lock. I also heard (?) that the return line is sort of discretionary. It makes some sense the fuel has more opportunity to over heat in a injected engine because of the additional distance it travels in close fitting fuel lines.DannyCZBB

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"That is the proper way to kill the engine, before turning off the mags, electronic ignition, etc."I thought that was the case but didn't want to say so in case I was wrong. When I sit as a passenger in my friend's Super Cub he always shuts it down that way. Thanks for confirming.

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Looking at my 172R Skyhawk manual. A return line isn't shown. And depending on the system, some high pressure aux fuel pump setups require them and some don't. A low pressure carb system requires 4-6 psi, while fuel injection can be in the upper 20's to the 40's. Return lines can be used for returning un-used fuel, so that the pump doesn't get into the 100 psi range, as well as for purging vapors. Some aux. pumps have internal regulators & bypass.Vapor lock can be a problem because the fuel injection system is laying on top of the hot engine. Purge systems are sometimes used to circulate cool liquid fuel through the lines to push any vapors/bubbles out. 100LL aircraft fuel is less likely to vapor lock than auto-gas. Fuel under high pressure is less likely to get bubbles than low pressure. Confusing -yes!

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Thanks for all the informative replies.So, in FS2004, what does that Cessna Fuel Pump switch actually do? I can't detect any change in sim behaviour with it on or off.I have just started using one of these boxes:www.desktopaviator.com/Products/Panel/Model_1010/index.htmVery reasonably priced, delivered here in the UK only 7 days after ordering, and immediate answers to any queries I have sent to the suppliers, and gives a nice feeling of doing something real, especially with the key switch for starting.The key switch only has two key positions, so the off position is programmed as "Engine auto shutdown" in controls assignments. This pulls out the mixture control automatically. The on position is assigned to "All starters on/off". There is no FS2004 assignment available for Fuel Pump (there was in previous versions) so the fuel pump switch is assigned to "Auxiliary fuel pump on/off". Since the switch in the sim doesn't seem to do anything this is just eye candy :)Today I have had no problems shutting down the engine and restarting, so don't know what the problem was before.--Bryn

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>>So, in FS2004, what does that Cessna Fuel Pump switch actually>do? I can't detect any change in sim behaviour with it on or>off.>In reality, the auxiliary fuel pump is just a backup, should the engine driven pump fail. These pumps also might be used to pressurize priming lines on some aircraft. IMO, the best use of the fuel pump switch is for practicing proceedure, according to the operating handbook. Forgetting to turn on, or turn off the fuel pump was one of my major "brain lapses" during flight training, and you'll still find other pilots forgetting to turn a pump off while in cruise, if they at least admit to it.By using the pump switch within a flight sim as standard operating proceedure, it becomes part of the memorization process. And thats the best use I can think of.L.Adamsonedit: I just checked the default 172's in both FS2004 & FSX. If you turn the master switch on, and follow startup proceedures with throttle & mixture control, then you'll see that the aux. fuel pump does provide fuel pressure on the fuel flow gauge, even though the engine isn't running.

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>>>>So, in FS2004, what does that Cessna Fuel Pump switch>actually>>do? I can't detect any change in sim behaviour with it on>or>>off.>If you turn the master switch on, and follow startup>proceedures with throttle & mixture control, then you'll see>that the aux. fuel pump does provide fuel pressure on the fuel>flow gauge, even though the engine isn't running.I'm not sure what I'm looking for here. The fuel flow meter is staying just off the 0 mark when the engine is off, whether the fuel pump switch on the 172 panel is on or not. How does the fuel flow meter give an indication that the system is pressurised?Probably obvious questions to folks whose lives depend on keeping the engine running in real life :)--Bryn

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I'll print part of the 172R "starting engine" checklist that I have here. The R & SP models are fuel injected. You should see results, especially when adding more throttle.1. Throttle --- open 1/4 inch2. Mixture -- idle cut off3. Propeller area -- clear4. Master switch -- on5. Auxiliary fuel pump switch -- on6. Mixture -- advance to obtain 3-5 GPH fuel flow, then return to idle cut off position.

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