Piston engine start

Jake Simpson

Jake Simpson

Filing Flight Plan
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Oct 22, 2021
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cvgaviation
Good evening everyone,

I have been wanting to ask this question but a lot of people I ask don't have a solid answer and answers tend to vary. The question lies in how to start different sized piston engines and fuel injected vs carbureted. I have flown in many single engine piston aircraft including 152s, 172s, 182s, cherokees, warriors, archers, etc. Over half of my time was spent in aircraft with IO360s, so the start procedure was always mixture idle, mags start, wait for it to turn over and simultaneously release the starter and go full rich. This was in the brand new Piper Archer TX and C172S/R models. Other aircraft I've flown such as the smaller displacement carbureted warriors/cherokees were all started with mixture already full rich, so all you had to do was turn the key. I am wondering if this procedure is different for the method in which fuel gets to the engine (injected vs. carb) or displacement of the engine itself? I was confused because I logged around 10 hours in a 182 with an IO520 stc and we started that with mixture full rich as well. Still injected and large displacement. In my 200hrs of flying I've just consulted the POH and checklist for starting procedures but have never asked: Why do we start the engine this way? Can you start an IO360 C172 or Archer with full rich mixture? Is that frowned upon? Why do the methods differ? Would you rather start a cold engine with the mixture full rich or idle cutoff, what about a warm engine? Does it differ by brand? The IO360s in the archers and 172s were Lycoming whereas the IO520 in the 182 was continental.

The reason I ask is because I want a better understanding of why these procedures differ so I can feel more comfortable in various types of small single engine aircraft. This doesn't seem to be a common topic taught at most flight schools, but I'm sure it is for A&Ps etc. I'm also looking to purchase an aircraft of my own so this would help me understand the engine my plane will have.

Thanks so much!
 
Jake Simpson said:
Why do the methods differ?
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In general, its my understanding the differing starting techniques is due to the fuel delivery design. Each one requires a different approach. For example, its the reason some engines have a primer system and some do not. Even turbine engines have different starting procedures depending on type of fuel scheduling. Throw in ambient temp and hot/cold engines and it gets tweaked some more. But one thing I can say is that trying to second guess the established procedure can lead you to some unanticipated results.
Jake Simpson said:
but I'm sure it is for A&Ps etc.
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Not really. APs learn about general system theories vs specific starting procedures. But if you want to learn more all this info is available for you to study as well. Another good source specific to the aircraft or engine can be found in the "system description" sections found in a number of mx manuals that give an overview how the system works. To me these sections are an important part to learning the aircraft.
 
Look how a carburetor works vs fuel injected. One system depends on the engine sucking fuel to the cylinders and the other fuel is pumped (injected) to the cylinder. When vacuum is used, you have to make it easier for the fuel to be delivered. When pumping is used, you have to assure too much fuel isn’t being delivered,
 
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Lycoming fuel injected engines are started from idle cutoff to avoid fire in the intake plenum due to excess gas. That is my understanding anyway. This is not an issue with TCM fuel injected engines. Or at least the TSIO 360 I am used to. It's also not an issue with carbed engines in general.
 
It's a good question. The short answer is, and not to sound like a jerk, use the POH.

For the injected Arrow I sometimes fly, from memory, I believe to cold prime it's full rich, turn the electric fuel pump on for about 3 seconds or until you see fuel flow, then pump off, mixture to idle, and start. Because as Sac Arrow pointed out, otherwise you risk pouring fuel into the engine, which could cause a fire. Mechanical fuel injection systems in airplanes are not like computerized multi-point fuel injection in cars.

Similarly, over priming a carbed engine can result in a fire. Not to scare people, but it's possible. So again, POH. You can also read the engine manuals, but if they differ, it's back to the POH. Pulling up the manual on an injected engine can be an interesting read.
 
Starting procedures for both types of engines vary depending on if they are cold or hot. My cold start procedure for carburerated engines is to crack open the throttle, begin cranking mixture rich and then prime vigorously while the prop is turning. This ensures all the fuel goes into the cylinders and forces the mixture from too lean to rich enough to fire the engine. If the priming pump doesn't work you can prime by pumping the throttle while cranking and let the accelerator pump richen the fuel for you. Only do this while the engine is turning or most of the fuel will just run out on the ground. If hot no priming is required. Crack open the throttle, crank the engine with mixture rich and slowly open the throttle until it starts.

A fuel injected engine when cold primes with the engine stopped. Full forward on the throttle and mixture, turn on the boost pump for about 3-4 seconds, turn off pump then mixture to lean cutoff, throttle closed and cracked open slightly. Crank until engine fires then mixture full rich. If hot, run the priming pump 2 seconds with throttle and mixture closed to remove vapor lock, then open throttle to about 15-25%. Crank engine with mixture lean until it starts. Sometimes you may need to quickly open and close the mixture once to give it a quick shot of fuel, but hot fuel injected engines are usually too rich to start, not too lean. Control mixture while cranking with throttle position, open is lean and closed is rich until it fires and airflow increases.

Hope this helps.

PS There are a couple of good videos on hot starting fuel injected engines.
 
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The simple answer is, starting procedures vary from one airframe to another and one engine to another because their fuel systems vary. The aircraft flight manual is usually the best place to start looking for information on the recommended procedures but that can sometimes get challenging when STCs are applied or the manual isn’t very verbose. I would not advocate rolling your own procedure unless you know the systems well.
 
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