How long for a hot start

[A64Pilot]

14 hours ago, Shadrach said:

Nice… Especially with a ground crew standing by to deal with any fires. I have seen Mooneys catch fire during a flooded starts.

I set my C-140 on fire many years ago doing the flooded hot start, just some paint discoloring from the soot.

Several years ago at Jack Browns sea plane base an instructor was demonstrating the flooded hot start to a new Maule owner, burnt that airplane down to the floats

Obviously neither of us did it right, we both over flooded which is an easy mistake to make

[Huckster79]

On 8/22/2022 at 9:43 AM, RLCarter said:

I could taxi from my hangar to the fuel pumps (1/4 mile, maybe) and the restart would require a “Hot Start” procedure. 

I learned that a few weeks ago! I didn’t think it would get hot enough but it sure did… one more fuel injected lesson learned…

[gwav8or]

5 minutes ago, Huckster79 said:

I learned that a few weeks ago! I didn’t think it would get hot enough but it sure did… one more fuel injected lesson learned…

Glad I'm not the only one that can taxi to the fuel pumps and still require a hot start.  The only procedure I've learned that works is to go mixture ICO, throttle full open, start cranking, slowly reduce throttle.  About half way to throttle closed, maybe a bit more it will start to fire.  Stop closing throttle and slowly advance mixture. 

[Shadrach]

1 hour ago, A64Pilot said:

I set my C-140 on fire many years ago doing the flooded hot start, just some paint discoloring from the soot.

Several years ago at Jack Browns sea plane base an instructor was demonstrating the flooded hot start to a new Maule owner, burnt that airplane down to the floats

Obviously neither of us did it right, we both over flooded which is an easy mistake to make

I am not a fan of flooding an aircraft engine (intentional or otherwise).  Back in the 80s, I saw my Dad intentional flood the engine after two failed hot start attempts. The plane caught fire as he was cranking. Luckily he persisted and the engine started. Flames shot out both cowl flaps as the prop wash filled the nacelle with air.  No damage save for some melting on part of the ram air cable sheath.   Had the plane not started, I am sure the damage would have been worse. 

A few years ago a Stearman on our field suffered a similar fate during a flooded start.  It also started but sustained enough damage to ground the airplane until repairs could be completed.

[Fly Boomer]

8 hours ago, zehutiman said:

That’s what I’ve been doing (idle cutoff).  If you run the pump with the mixture full rich, that’ll flood it, right?

Yep.  Idle cutoff=no gas.  Full rich=max gas.  For a hot start, try just pushing the mixture back in (if you usually leave it out after shutdown), and turning the key.  If it doesn't start, you aren't out anything, but once in a while, the answer to "how much should I prime?" is "none".  To purge vapor from the system, pull the mixture to idle cutoff and run high boost for a minute.  Whenever you start it, be ready with short jolts of boost to keep it going.  The fuel system in these engines is crazy complicated, and very few people have the tools and skills to set one up properly.  To make things more challenging, when you combine the complication of the system with the shortage of qualified people, you end up with widely differing engine behaviors.

[Shadrach]

25 minutes ago, Fly Boomer said:

Yep.  Idle cutoff=no gas.  Full rich=max gas.  For a hot start, try just pushing the mixture back in (if you usually leave it out after shutdown), and turning the key.  If it doesn't start, you aren't out anything, but once in a while, the answer to "how much should I prime?" is "none".  To purge vapor from the system, pull the mixture to idle cutoff and run high boost for a minute.  Whenever you start it, be ready with short jolts of boost to keep it going.  The fuel system in these engines is crazy complicated, and very few people have the tools and skills to set one up properly.  To make things more challenging, when you combine the complication of the system with the shortage of qualified people, you end up with widely differing engine behaviors.

Respectfully disagree.  Compared to modern fuel injection, these things are quite simple, with the Continental taking the win for most simple.  There is not a lot that is field adjustable, but that is more a function of the simplicity of these systems, not that they are "crazy complicated".  Both Continental and Bendix systems use differential fuel pressure to meter fuel. The Bendix System also uses differential air pressure which is why Lycomings compensate for altitude changes and Continentals do not.  

[EricJ]

1 hour ago, Fly Boomer said:

Yep.  Idle cutoff=no gas.  Full rich=max gas.  For a hot start, try just pushing the mixture back in (if you usually leave it out after shutdown), and turning the key.  If it doesn't start, you aren't out anything, but once in a while, the answer to "how much should I prime?" is "none".  To purge vapor from the system, pull the mixture to idle cutoff and run high boost for a minute.  Whenever you start it, be ready with short jolts of boost to keep it going.  The fuel system in these engines is crazy complicated, and very few people have the tools and skills to set one up properly.  To make things more challenging, when you combine the complication of the system with the shortage of qualified people, you end up with widely differing engine behaviors.

Continentals (TCM) are notoriously annoying to rig, but Lycomings (Bendix) are essentially the opposite and have very little adjustment.   They operate a bit differently as well.    

[Vance Harral]

1 hour ago, Fly Boomer said:

To purge vapor from the system, pull the mixture to idle cutoff and run high boost for a minute.

Every time I see this advice given without qualification of engine type, I feel obliged to point out that it's poorly understood.

First, this practice does very little in fuel-injected Lycomings with RSA fuel servos.  That's the power plant for all the "vintage" fuel-injected Mooneys (M20E, M20F, M20J), and also for some of the later big-bore models as well.  In the RSA fuel injection system, fuel has nowhere to go when the mixture is at idle cutoff.  There is no flow to move vapor bubbles anywhere or cool anything, no matter how much pressure the pump provides.  Therefore, the only thing you're doing is pressurizing the system between the pump and the fuel servo.  The 20-ish psi provided by the pump is very unlikely to collapse any vapor bubbles that have formed there, and even it if did, everything downstream of the fuel servo is unaffected.

Things are more interesting in the Continental system, which has a vapor return line to the tanks.  Running high boost with ICO mixture in these system does cause fuel to flow through the pump, both cooling the pump and moving vapor bubbles upstream of and inside the pump out of the system.  There is some residual cooling effect just downstream of the pump, but once you get very far away from there, the system is similar to the Lycoming.  However, the pressure provided by high boost in Continental installations is nearly double that of the Lycoming pump, and that higher pressure probably provides some benefit as well.  I don't operate a Continental, but this advice to run high boost for a minute prior to hot start is so well accepted that it almost certainly has some benefit.  In the mean time, though, Lycoming operators try this to no effect, and confusion abounds.

Anyone wanting to understand the mechanics of hot starts would do well to first understand the fuel injection system in their particular engine.  You can see schematic diagrams of both, side-by-side, at https://aviation.stackexchange.com/questions/71333/what-is-the-main-difference-between-continental-fuel-injection-system-and-ben

In summary, Fly Boomer's advice is good for Continentals, and harmless-but-ineffective in Lycomings.

[Shadrach]

5 minutes ago, Vance Harral said:

Every time I see this advice given without qualification of engine type, I feel obliged to point out that it's poorly understood.

First, this practice does absolutely nothing in fuel-injected Lycomings with RSA fuel servos. 

Agree with all that you wrote in the above post save for what I edited above. 

[Vance Harral]

2 minutes ago, Shadrach said:

Agree with all that you wrote in the above post save for what I edited above.

I actually wrote "does absolutely nothing" in my first draft.  But it does pressurize the fuel between the pump and fuel servo, which "might" have a few vapor bubbles due to heat cooking that line (unlikely given that that hose is below the hot parts of the engine, and heat rises).  Even if there are vapor bubbles there, the fuel pump pressure is unlikely to collapse them, and even if it did, that's well upstream from the part of the system that makes hot starts difficult.  So I guess I'd amend my comments to say, "very little in theory, and nothing in practice".

[Fly Boomer]

19 minutes ago, Vance Harral said:

In summary, Fly Boomer's advice is good for Continentals, and harmless-but-ineffective in Lycomings.

I was responding to (and quoted) the question from the guy with a 550 (Continental).

[Shadrach]

2 minutes ago, Vance Harral said:

I actually wrote "does absolutely nothing" in my first draft.  But it does pressurize the fuel between the pump and fuel servo, which "might" have a few vapor bubbles due to heat cooking that line (unlikely given that that hose is below the hot parts of the engine, and heat rises).  Even if there are vapor bubbles there, the fuel pump pressure is unlikely to collapse them, and even if it did, that's well upstream from the part of the system that makes hot starts difficult.  So I guess I'd amend my comments to say, "very little in theory, and nothing in practice".

Yeah I though about that prior to posting, but I think its a theoretical naval gazing. In my experience, vapor lock between the selector and servo has never a problem for these systems. 

[Hank]

On 8/25/2022 at 11:44 AM, jaylw314 said:

Ah, cool beans, thanks.  I still haven't had a chance to actually peek around a carbureted O-360

The fuel is simply dumped into the carburetor bowl.

Hot starts are simple, just advance the throttle a little bit, Mixture Full Rich, turn the key and push. It normally takes about twice as long as a cold start, runs a little rough for a few seconds then settles back down. Easy peasy, stone simple. Love my O-360!!

[EricJ]

1 hour ago, Vance Harral said:

I actually wrote "does absolutely nothing" in my first draft.  But it does pressurize the fuel between the pump and fuel servo, which "might" have a few vapor bubbles due to heat cooking that line (unlikely given that that hose is below the hot parts of the engine, and heat rises).  Even if there are vapor bubbles there, the fuel pump pressure is unlikely to collapse them, and even if it did, that's well upstream from the part of the system that makes hot starts difficult.  So I guess I'd amend my comments to say, "very little in theory, and nothing in practice".

That's actually one purpose of the pump, especially in carbureted airplanes, to increase the fuel pressure above the vapor pressure to prevent boiling in the lines.

[zehutiman]

5 hours ago, Shadrach said:

The Bendix System also uses differential air pressure which is why Lycomings compensate for altitude changes and Continentals do not.  

Does that have anything to do with the Continental’s altitude-compensating fuel pump?  Or, are you talking about something entirely different?  I’ve tried to find info on how this fuel pump affects leaning techniques in my Mooney, without much success.  

[EricJ]

5 minutes ago, zehutiman said:

Does that have anything to do with the Continental’s altitude-compensating fuel pump?  Or, are you talking about something entirely different?  I’ve tried to find info on how this fuel pump affects leaning techniques in my Mooney, without much success.  

The TCM (Continental) system runs essentially entirely based on regulated fuel pressure.    An altitude-compensated fuel pump changes the input pressure to the TCM system to try to adjust for altitude.   I've never used one but have heard that they generally work reasonably well.

The Bendix (Lycoming) system meters both fuel pressure and intake ram air pressure (I think as a reasonable proxy for Mass Air Flow), so once you set it for a particular air/fuel ratio it will tend to maintain it over power adjustments.   In other words, you still need to lean for altitude, although probably not as much as you would otherwise, but at a particular altitude and setting you can make power adjustments without affecting the mixture.

[Fly Boomer]

6 hours ago, Shadrach said:

Respectfully disagree.  Compared to modern fuel injection, these things are quite simple, with the Continental taking the win for most simple.  There is not a lot that is field adjustable, but that is more a function of the simplicity of these systems, not that they are "crazy complicated".  Both Continental and Bendix systems use differential fuel pressure to meter fuel. The Bendix System also uses differential air pressure which is why Lycomings compensate for altitude changes and Continentals do not.  

Check out the procedure in the M-0 manual.

[Shadrach]

1 hour ago, zehutiman said:

Does that have anything to do with the Continental’s altitude-compensating fuel pump?  Or, are you talking about something entirely different?  I’ve tried to find info on how this fuel pump affects leaning techniques in my Mooney, without much success.  

I have no experience with ACFP equipped aircraft.  Seems like a nice option but I've read that Continental had a lot of headaches with mechanics setting them improperly in the field.  An ACFP is essentially a regular mechanical fuel pump with a built in aneroid that controls output (Fuel Pressure) to the servo and thereby mixture. It is an option that if available for the engine, must be specified at overhaul. Cost delta is trivial as I understand it.  If I were doing an overhaul exchange on a Continental, I would opt for it.  I don not think they are as popular as one would think.

[Shadrach]

43 minutes ago, Fly Boomer said:

Check out the procedure in the M-0 manual.

I should have been more specific.  The system is simple (comparatively speaking).  The set up is time consuming and the M-0 manual is apparently not well written nor well organized.

[Bobaran]

On 8/21/2022 at 8:15 PM, jaylw314 said:

Hot starting has more to do with fuel than temperature.  On shutdown, the fuel in the lines above the motor warms up and pushes out the injectors into the intake manifold, so you have a mildly flooded intake.   Since the throttle is mostly closed, it can hang around for a surprisingly long time, even a couple hours.  On top of that, now you have no liquid fuel in the fuel lines, so it can take a few seconds for fuel to fill them up again even after the engine starts.

What you don't want to do is crank the motor with the throttle closed too much, give up after a few seconds and prime the intake to try a cold start.  You can end up flooding the intake even more.  That's the genius of Don Maxwell's technique, you keep the throttle open enough that only a few seconds of cranking should suck in enough air to light a typically flooded intake.  On the off chance that the motor doesn't catch in 5 seconds or so, it'd still be smart to open up the throttle and continue crank a couple more seconds to make sure you've cleared out the intake before trying a normal cold start.  Some people argue for flooding the engine to do a flooded start (which does of course work), but on the rare occasion DM's technique fails, I've never found that necessary, and a subsequent cold start always works out fine.

The empty fuel lines can result in the motor catching, opening the mixture, then having to wait a few seconds for the fuel to fill the lines while the prop spins freely.  Even though it seems like it won't happen, it almost always does, it's just a little unnerving.

"...fuel in the lines above the motor warms up and pushes out the injectors into the intake manifold, so you have a mildly flooded intake.   Since the throttle is mostly closed, it can hang around for a surprisingly long time, even a couple hours."  

This explains why the hot engine can start even though the mixture is closed or slightly open.  I had no idea of WHY this would work until now.  Thanks Jay.

[Denis Mexted]

On 8/25/2023 at 12:11 AM, Fly Boomer said:

Yep.  Idle cutoff=no gas.  Full rich=max gas.  For a hot start, try just pushing the mixture back in (if you usually leave it out after shutdown), and turning the key. 

Someone showed me that in a Chieftain once. With the addition to once the mixture is rich, open and close the throttle.

It worked beautifully. Problem was I only flew another 50 hours in it. The thousand before hand with lots of turnarounds it would have been handy.

It's been decades since I've operated a fuel injected piston engine aircraft regularly but good conversation guys.

[Echo]

Seriously, This thread is a mess. Somebody that knows the hot start procedure for a fuel injected vintage Mooney (E and F) NOT flooded start, NOT Continental start, NOT Continental with auto adjustable injection in climb:Please succinctly state procedure for hot start.  Thanks 

[ArtVandelay]

Seriously, This thread is a mess. Somebody that knows the hot start procedure for a fuel injected vintage Mooney (E and F) NOT flooded start, NOT Continental start, NOT Continental with auto adjustable injection in climb:Please succinctly state procedure for hot start.  Thanks 

Throttle setting to 1000+ (ie where you set it at cutoff), turn engine over, wait for it to start to catch, push in mixture, if it runs rough, turn on boost pump and gently increase power so rpms increase to 1200+ and it starts to run smooth.

[ArtVandelay]

Also, adjust mixture based on your altitude.

When on final, open cowl flaps to cool the engine as much as possible so your restarts may be a little quicker.

How long it takes before engine starts to catch depends on how much time has passed.
I find 15-30 minute starts the most difficult, especially in the summer months. The 1-2 minute restarts are easy.
I use the hot start method after changing my oil, so 1-2 hours later, starts nicely as well.

[EricJ]

2 hours ago, Echo said:

Seriously, This thread is a mess. Somebody that knows the hot start procedure for a fuel injected vintage Mooney (E and F) NOT flooded start, NOT Continental start, NOT Continental with auto adjustable injection in climb:Please succinctly state procedure for hot start.  Thanks 

The procedure in the manual works great.

Don Maxwell made a vid: