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What parameter is used to follow a hot start procedure

Michael Wellenzohn

Michael Wellenzohn

Well Known Member
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Hi all,

Lately I found myself twice in a situation where I started the RV-10 after it sat on the ground after a previous flight and wasn’t sure if I should use the hot start procedure or not. What parameters & values do you use to go for hot start vs. standard?

Kind regards
Michael
 
Michael Wellenzohn said:
Hi all,

Lately I found myself twice in a situation where I started the RV-10 after it sat on the ground after a previous flight and wasn’t sure if I should use the hot start procedure or not. What parameters & values do you use to go for hot start vs. standard?

Kind regards
Michael
Click to expand...

All of our birds will exhibit slight differences in stages of starting. If I just fueled up, pushed out for the next guy, then check my fuel for water, I consider this a ‘Hot’ start and do not touch any fuel pump to start, just pull ICO all the way out, 1/4” on the throttle and it starts right up.

If I stop for a meal and the plane sits for an hour, then fuel pump comes on for about 5 secs and start like above.

Regards,
Bill
 
As Bill says, if in doubt, treat it as a hot start - no pump, ICO, cracked throttle.

If it doesn't work, give it a shot and all should be well. If you have just refuelled and do the hot start and it runs rough - panic not, vapour is going through the lines.

30 - 60 mins is the curious zone !!!!
 
Flooded

The assumption with a hot start is that the heat has pushed the fuel into the cylinders and you're starting in a flooded condition. If you assume a flooded condition and do not have one, then doing a hot start will not flood it more.

If you have a hot start (flooded) condition, and treat it as a cold start, you will flood it MORE, and end up spinning the prop and not starting.

So when in doubt, I always assume hot start if the engine has been running in the past few hours or it is sitting on a hot ramp. If I'm wrong a shot of the fuel pump and cold start procedure will correct it.

Incidentally, what works for me if to pull the mixture to idle cut-off and the throttle to wide open. Once I crank with the starter the engine will begin sputtering to life and I s-l-o-w-l-y transpose the two levers while continuing to crank. It works nearly every time as the engine goes from a flooded to a lean condition it will light off and I'll be on my way. It never takes more than a few blades of the prop.
 
Below are the steps for starting the IO-540 from the Lycoming Ops manual. They recommend the same procedure for hot starts as they do for cold (see last note). Kind of surprised by this.

In my plane, I’ve found that their recommended cold start procedure doesn’t work well for the first start of the day, but it works really well for hot starts. For my plane, I consider a hot start to be anything after the first run of the day up to 4-5 hours after the first flight.

For cold starts I use: throttle 1/2 travel, mixture rich, fuel pump 3-5 seconds, throttle cracked 1/2”, engage starter. After start I usually need to pull the throttle back a little to get the desired idle RPM, and I always lean it for taxi after starting.

As mentioned earlier, each engine probably has some nuance that requires experimentation. It took me quite a while to get hot starts down in my RV-10. The key for my engine is to leave the mixture in ICO position until the engine fires. On some starts this can seem like a long time, but if I move the mixture too soon it never fires.

FROM THE LYCOMING OPS MANUAL
“Page 3-2 b. IO-540 Series (Cold Engine).
(1) Perform pre-flight inspection.
(2) Set propeller governor in “Full RPM”.
(3) Turn fuel valve to “on” position.
(4) Open throttle approximately 1⁄4 travel.
(5) Turn boost pump on and move mixture control to “Full Rich” position until a slight but steady flow is indicated.
(6) Return mixture control to “Idle Cut-Off” position.
(7) Set magneto selector switch. Consult airframe manufacturer’s handbook for correct position.
(8) Engage starter.
(9) When engine starts, place magneto selector switch in “Both” position.
(10) Move mixture control slowly and smoothly to “Full Rich”.
(11) Check oil pressure gage for indicated pressure. If oil pressure is not indicated within thirty seconds, stop the engine and determine trouble.
NOTE
If engine fails to achieve a normal start, assume it to be flooded. Crank engine over with throttle wide open and ignition off. Then repeat above procedure.
Hot Engine – Because fuel percolates, the system must be cleared of vapor; it is recommended that the same procedure, as outlined on page 3-2, be used for starting a hot engine.”
 
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For me: Throttle full open, mixture full lean (off), prime 3 seconds, start and when engine fires, up with mixture, throttle back. I do that every start unless plane has been sitting for a few hours.
 
Michael Wellenzohn said:
What parameters & values do you use to go for hot start vs. standard?
Click to expand...

In terms of time or temperature values, I'm doubt there are any reliable hard numbers across the fleet. Kevin's approach is probably best...

krwalsh said:
The assumption with a hot start is that the heat has pushed the fuel into the cylinders and you're starting in a flooded condition. If you assume a flooded condition and do not have one, then doing a hot start will not flood it more.

If you have a hot start (flooded) condition, and treat it as a cold start, you will flood it MORE, and end up spinning the prop and not starting.

So when in doubt, I always assume hot start if the engine has been running in the past few hours or it is sitting on a hot ramp. If I'm wrong a shot of the fuel pump and cold start procedure will correct it.
Click to expand...

In effect, he is suggesting the sweep method. The engine will fire when a cylinder contains a mixture that is within a fairly narrow fuel/air range. So, the goal is to sweep the mixture through that range during the start process, either by beginning in a lean condition and moving toward rich, or beginning in a rich condition and moving toward lean. Either way, when you hit the sweet spot, it will light. Kevin (and many others) assume the hot engine is too rich, and sweep toward lean.

Minor point...fuel dribbling from the injector nozzle doesn't go into a cylinder. The nozzle is above the intake tube.
 
KiloWhiskey1 said:
FROM THE LYCOMING OPS MANUAL

(1) Perform pre-flight inspection.
(2) Set propeller governor in “Full RPM”.
(3) Turn fuel valve to “on” position.
(4) Open throttle approximately 1⁄4 travel.
(5) Turn boost pump on and move mixture control to “Full Rich” position until a slight but steady flow is indicated.
(6) Return mixture control to “Idle Cut-Off” position.
(7) Set magneto selector switch. Consult airframe manufacturer’s handbook for correct position.
(8) Engage starter.
(9) When engine starts, place magneto selector switch in “Both” position.
(10) Move mixture control slowly and smoothly to “Full Rich”.
(11) Check oil pressure gage for indicated pressure. If oil pressure is not indicated within thirty seconds, stop the engine and determine trouble.
Click to expand...

This is what I follow for hot starts, though I just use 1 second for step 5, as we are not refilling the whole system or need a prime like in the cold start. FYI, I never use full throttle to start a plane and feel no one should either. 260 HP on the ground can create real problems if you are having a bad day or not prepared for exactly what will happen when that amount of power comes on in an instant and starts rapidly moving your plane, not to mention what that blast is going to do to the plane right behind you gassing up. I cannot tell you how upset I would be if some guy went full throttle right next to me while I was fueling my plane, especially if the prop blast was pointed my way (do you put a gust lock on when fueling? I know I don't). If you really like the full throttle start, I recommend that you first practice by rapidly going WOT on the taxiway and be sure you can control it. This many not be an issue for the 360 guys, but I am sure you have noticed how hard a 10 will pull once it gets to 2700.

As mentioned, after shut down the fuel in the 1/8 tubes boils and moves to the intake chambers. This does two things. First it leaves the lines empty and need to be refilled. Two, it leave an excessively rich mixture in the intake chamber. So, if you stop for 10 minutes, then start, you get an overly rich mixture for a few revolutions, then it starts and then it goes lean as the lines refill. If you sit for a longer time, the lines are still empty, but the rich mixture in the intake chamber is now gone thanks to evaporation. Step 5 is key to make the approach work in all cases, as it refills the lines before starting and leaves either a rich or really rich mixture sitting in the intake chamber. This works pretty well in the second scenario, but makes it REALLY rich in the first scenario. Therefore the amount of cranking time to get it to kick will be variable, but it will always work. Basically the engine won't kick until the proper mix of fuel and air is achieved, but it will gradually go from over rich to just right if you follow the above steps

Larry
 
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Tooch said:
For me: Throttle full open, mixture full lean (off), prime 3 seconds, start and when engine fires, up with mixture, throttle back. I do that every start unless plane has been sitting for a few hours.
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Very same for me! After almost 500 hrs now I’ve got it down to where the rpm ramp up isn’t an issue.

Mike
 
You've gotten great advice on hot starts, so I won't repeat any advice on that. But it took me a while to find the best procedure for cold starts in my 10. Thought I'd share my cold start experiences in case others could benefit.

For cold starts, I used to prime at full rich for 5-6 seconds, crack throttle 1/4" and mixture to ICO. Engine would ALWAYS fire right up, but about 50% of the time it would cough and die right after no matter how quickly I moved the mixture to full rich. Seemed to be different every time (sometimes it would die, other times it didn't) based on time plane had been sitting in hangar between flights. (i.e., one day or 1 week)

Then found a little nugget of advice in the AirFlow Performance manual. It says to prime based on engine monitors fuel flow rate, not time. On my 10 I have found that the fuel flow rate of 5.8 Gallons Per Hour is perfect. So, I prime with throttle 1/2 open and mixture full rich until my fuel flow rate hits 5.8 GPH (this sometimes takes 5 seconds, sometimes it's 8 seconds) but once I hit 5.8, I quit boosting, set mixture to ICO, crack throttle 1/4" and it fires QUICKLY everytime and NEVER stumbles and dies right after.

I have been flying for 15 years and never knew you could prime based on fuel flow instead of time. Hopefully others can benefit from this slight change of technique on their cold starts too.
 
rvanstory said:
For cold starts, I used to prime at full rich for 5-6 seconds, crack throttle 1/4" and mixture to ICO. Engine would ALWAYS fire right up, but about 50% of the time it would cough and die right after no matter how quickly I moved the mixture to full rich. Seemed to be different every time (sometimes it would die, other times it didn't) based on time plane had been sitting in hangar between flights. (i.e., one day or 1/QUOTE]

My -7A with an IO-360 behaves the same way but my solution is to keep the starter engaged through the cough and it quickly comes to life.
Click to expand...
 
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Engine Start

rvanstory said:
I have been flying for 15 years and never knew you could prime based on fuel flow instead of time. Hopefully others can benefit from this slight change of technique on their cold starts too.
Click to expand...

I do the same on my IO-390, and it makes complete sense as it is the right amount of fuel that matters, not time. With one caveat - temperature. Where I live in Chicago we can see starts from 20 to 95 degrees, so I adjust that flow rate according to experience. Unfortunately that takes a bit of trial and error, but luckily there doesn't seem to be that big a range to it.

The other thing that has greatly improved my cold starts, usually less than a full turn of the prop, has been the change from magneto to SureFly EI.
 
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