Question about hot engine start

[einepilotin]

Hello, everyone
I have a question on hot engine start.
I learned that when shutting off the engine, I need to stave the mixture and get rid of remaining fuel/air mixture in the fuel line/cylinder. To prevent prop rotation in pre-flight inspection, right?

And within 1 hour from the last flying, I do hot engine start without priming.
How is that possible engine to be started without fuel in the cylinder in hot start then?

Thank you!

 

[kgruber]

Gasoline vapor.

 

[RotorDude]

Hello, everyone
I have a question on hot engine start.
I learned that when shutting off the engine, I need to stave the mixture and get rid of remaining fuel/air mixture in the fuel line/cylinder. To prevent prop rotation in pre-flight inspection, right?

And within 1 hour from the last flying, I do hot engine start without priming.
How is that possible engine to be started without fuel in the cylinder in hot start then?

Thank you!

"No primer" doesn't mean "no fuel" or "no throttle". You do need to crack open the throttle, so when the engine starts cranking (with the starter) it will suck in fuel-air mixture from the carb and the spark plugs will ignite it. The primer is only intended for a cold engine, and typically only on a cold day.

 

[einepilotin]

"No primer" doesn't mean "no fuel" or "no throttle". You do need to crack open the throttle, so when the engine starts cranking (with the starter) it will suck in fuel-air mixture from the carb and the spark plugs will ignite it. The primer is only intended for a cold engine, and typically only on a cold day.

Thanks for the replying, is the cold start and hot start about the temperature?? I've taught within 1 hour from the last flying, I do hot engine start procedure....

And if I shut off the engine with mixture starvation, there should be no more mixture left inside the cylinder isn't it?
Shouldn't I be very scared of going around prop while the pre-flight inspection then, what if the ground wire failed, and it rotates???

 

[Clark1961]

It is always good to respect the prop and stay out of its arc. Any time the prop is moved there is some small chance that the engine will fire. If the key is in your pocket and the mixture is in cut-off then the chance of the engine firing is almost negligible. The mag grounding wires should be checked periodically. The newer electronic tachometers check mag ground for you if you are paying attention.

Editing to add that if you are flying a rental then you really do need to use extra caution with the prop since you don't know how the last pilot shut it down.

 

[RotorDude]

Thanks for the replying, is the cold start and hot start about the temperature?? I've taught within 1 hour from the last flying, I do hot engine start procedure....

And if I shut off the engine with mixture starvation, there should be no more mixture left inside the cylinder isn't it?
Shouldn't I be very scared of going around prop while the pre-flight inspection then, what if the ground wire failed, and it rotates???

In general, you should get the Pilot's Operating Manual and follow the instructions for "engine start". They should have different procedures for cold and hot starts, both the engine itself and the environment.
If you want extra information, find out what engine you have, and get the engine manufacturer's manual for that model engine (very often available online). They typically have even more detailed instructions there, though the POM instructions take precedence in case of conflict.
And yes, you should be very scared of failed ground wires and props in general. Try avoiding turning them at all times, regardless of circumstances. Assume that if you touch it, it will start, always!
Be sure to warn your passengers about that, after you are rated. It will ruin their entire experience if one of them gets decapitated.
And speaking of props, let me mention another common hazard, esp. when it comes to kids. The prop has very sharp, hard and pointy edges and it's definitely not fun for an excited kid to run into a blade and end up crying, or worse. So keep all kids (and pax in general) away from the prop, and for that matter, no running and no horseplay on the ramp and near the plane.

 

[RyanB]

Thanks for the replying, is the cold start and hot start about the temperature?? I've taught within 1 hour from the last flying, I do hot engine start procedure....

And if I shut off the engine with mixture starvation, there should be no more mixture left inside the cylinder isn't it?
Shouldn't I be very scared of going around prop while the pre-flight inspection then, what if the ground wire failed, and it rotates???

If the cowling is warm to the touch a hot start procedure should suffice and no priming

By pulling the mixture to idle cutoff you are depleting the remaining fuel in the carb. If you just kill the engine by turning the mags off you run the risk of pre-ignition and the remaining fuel in the carb can go stale, making the following start nearly impossible. I didn't catch if you're flying a carb'd or fuel injected engine, but that's the basics on the technique and the reason for doing so.

As long as your mags are grounded, the chance of an inadvertent start by turning the prop is low. However, always treat it as if it could fire at any time.

 

[MAKG1]

Even with injected engines, you usually hot start without priming. There are a few exceptions (like a Cardinal RG, which will vapor lock if you try that).

Stopping the engine with fuel starvation doesn't completely drain the fuel system. There is still some left, and the engine will usually fire on it. But not for very long.

What it does give you is a maximum amount of fuel. If you do prime a hot engine, you can make it backfire.

 

[Scrabo]

So I have a follow up question along the same line.

Say you shut down using mixture, so you do anything like open the oil door on the cowling to aid cooling, when you know you would be firing up the engine maybe within the hour?

I read somewhere that a shutdown engine becomes heat soaked between 20 & 40 mins after shutdown

 

[coloradobluesky]

Use what works. Different planes are different. Just remember, if it flooded, which tends to happen when its hot, give it NO GAS, and MAXIMUM AIR. That usually means mixture all the way lean(NO GAS) and throttle all the way forward (MAXIMUM AIR). Some fuel injected engines might be different.

If the engine has fuel injection, it may be different. All engines seem to have their peculiarities. I flew one that would start when you let go of the key (and it cranks one last time and starts!). Like I say, they all have their peculiarities.

 

[denverpilot]

Hello, everyone
I have a question on hot engine start.
I learned that when shutting off the engine, I need to stave the mixture and get rid of remaining fuel/air mixture in the fuel line/cylinder. To prevent prop rotation in pre-flight inspection, right?

And within 1 hour from the last flying, I do hot engine start without priming.
How is that possible engine to be started without fuel in the cylinder in hot start then?

Thank you!

Can you describe exactly what engine and aircraft you're flying?

Different aircraft and engine combinations and fuel delivery systems will behave differently. The POH will have appropriate procedures.

You're correct, shutdown on most piston aircraft is via fuel starvation by mixture pulled to the leanest setting. Not all. Again see POH.

You're also correct that it's about an hour in cold weather before you need to cold start. Probably more. You can feel the engine heat through the cowl during pre-flight. If it's still warm, you'll know. One hour is just a rule of thumb.

To answer your question, it's possible to start most piston engines when there's no fuel in the cylinders because rotation of the engine (by the starter) drives the mechanical fuel pump attached to the engine's crankshaft. On some aircraft you'll also have to engage a secondary/auxiliary electric fuel pump to assure enough pressure is available during start. All depends on the aircraft and engine combination.

Over time you may even learn some airplane specific tips that any particular airplane and engine like better even than the POH information. An example is my own airplane which at our high altitude starts better with the mixture pulled back a significant amount. Or the turbocharged carbureted twin that I fly which needs the mixtures at idle/cutoff during cranking for hot starts with a rapid move to full rich as they start to fire. Both engines need prime when cold but the 182/O-470 needs very little while the Seminole needs 4-5 seconds of electric primer button held in.

Propellers: I have a t-shirt. Front says, "What doesn't kill you makes you stronger." Back says, "Except airplane propellers. They'll flat out kill you."

Don't mess with props. There's very little call for them to be moved by hand at all. Always treat the ignition system as "live" and assume there's enough fuel/air mixture to fire up the engine if you turn the prop. (Is there really? You don't know. That's why you treat it as if there always is.)

Stay out of their arc even when they're stopped, and remember they're nearly invisible when turning. Isn't a pilot or mechanic here probably who's been doing this long enough, that didn't know someone, directly or indirectly, who was killed by one.

Clark talks about having the key in your pocket. That's a good habit. (Mine is the key is attached to a very bright safety orange keychain and it goes on the dash where it can be seen from anywhere up front when it's not in the ignition.) Have a system for where the key goes and a way to confirm that it's there before doing things near the prop.

But also keep in mind that many airplanes don't have keys. One person bumping a starter switch with the master on, while they're messing around in the cockpit, boarding, or otherwise not paying attention, while you're bending over to look at landing gear or something else, will ruin your whole day if you're in the prop arc.

Might not kill you outright, but it's definitely going to hurt.

*You* may not be able to effectively stop "prop rotation", if it's caused by someone else. Just be ready to get away from it.

As far as you causing prop rotation, don't. Don't turn it unless there is a real reason to do so, and then only with a plan.

Yes, you'll have to TOUCH it. Feel the leading edges and make sure it's smooth and ready for flight. But place your body in such a way that you can move away from it and if startled or surprised, you won't fall forward into it because your stance is body weight toward it.

It won't bite. It's not about fear, it's about respect for a few hundred pounds of metal that might whir and whack you. Just always be wary around props. Your location and motions should be deliberate and thoughtful around them.

 

[GRG55]

...Shouldn't I be very scared of going around prop while the pre-flight inspection then, what if the ground wire failed, and it rotates???

You should not be "scared of going around the prop", but as others have posted you should always have a very healthy respect for it when in close proximity, and always treat it as if the mags were live.

With respect to an un-grounded magneto, that is always a possibility. As part of managing that risk you should be doing a live magneto check just prior to every shut down. The procedure to do that will vary a bit depending on whether your plane has rocker/toggle switches for the mags or a rotary switch with a key.

 

[coloradobluesky]

About that prop. Don't take on passengers or let off passengers with the engine running. Allow no one in proximity to the plane while the plane is running. People just dont see that spinning prop and get injured by it.

 

[denverpilot]

About that prop. Don't take on passengers or let off passengers with the engine running. Allow no one in proximity to the plane while the plane is running. People just dont see that spinning prop and get injured by it.

And if someone approaches, gets too close, and won't stop, don't be slow about just shutting it down.

You wouldn't believe the stupid things people will do on ramps -- and you know that whole "texting and driving" thing? I've seen people walk under single engine aircraft wings that had engines turning, and do really stupid stuff while poking at their phones.

Don't be worried about grabbing mixture, the key, both, whatever... and doing a "proper" shutdown... if someone is walking toward your prop. Just kill it.

So far, I've only had one completely oblivious person walking directly toward one, and they were just far enough away that slapping the landing and taxi lights on, got their attention. My hand was on both mixture and the key when they noticed and altered their walking course.

I'm also not too enamored of line guys who were taught to be directly in front instead of off to the left side where the "official" marshaling texts say they should be. If my brakes fail, they'd better be ready to move quick, and I'll be cutting the mixture and key, but it's asking for trouble they don't need. I don't need them standing on the line to see the line, I need them to marshal correctly. If they're indicating straight ahead or a turn, they can do that from the side.

Plus they can do a better dance routine off to the side.

 

[MAKG1]

And if someone approaches, gets too close, and won't stop, don't be slow about just shutting it down.

You wouldn't believe the stupid things people will do on ramps -- and you know that whole "texting and driving" thing? I've seen people walk under single engine aircraft wings that had engines turning, and do really stupid stuff while poking at their phones.

Don't be worried about grabbing mixture, the key, both, whatever... and doing a "proper" shutdown... if someone is walking toward your prop. Just kill it.

So far, I've only had one completely oblivious person walking directly toward one, and they were just far enough away that slapping the landing and taxi lights on, got their attention. My hand was on both mixture and the key when they noticed and altered their walking course.

I'm also not too enamored of line guys who were taught to be directly in front instead of off to the left side where the "official" marshaling texts say they should be. If my brakes fail, they'd better be ready to move quick, and I'll be cutting the mixture and key, but it's asking for trouble they don't need. I don't need them standing on the line to see the line, I need them to marshal correctly. If they're indicating straight ahead or a turn, they can do that from the side.

Plus they can do a better dance routine off to the side.

I once arrived at a major CAP event where cadets were marshaling arriving aircraft, but there weren't enough of them. So one individual decided he could handle two positions. This involved running between them with multiple spinning props on the ramp. That is the one and only time I've ever yelled at a cadet. I told him it was better to just let the pilots do it and he should get his butt inside 'cause I didn't want to spend my morning picking up bits of cadet off the ramp.

They ARE trained for this sort of thing. But not for mission myopia.

 

[James331]

I don't really trust marshalers much, especially kids, they are a extra set of eyes but end of the day it's on me.

Hot start (piston)

Don't bother opening stuff up.

Method one, don't prime, mixture rich, crank as you slowly advance the throttle, once it catches ofcourse bring the throttle back.

Method two, when one doesn't work, mixture ICO, full throttle, crank till it catches and mixture in and throttle to idle, helps if you have large enough hands to do that in one motion with one hand.


That works great for me in a IO520 and IO550.