Left 270

The Airframe and Powerplant Mechanics Powerplant Handbook produced by the FAA gives a fairly detailed explanation of the systems.


PK

PA39

The lines up to the cylinder from the FCU contain no pressure once the mixture is at ICO.

OK, this is my observation of why it is the TCM and Lyc are different. In my opinion and observation a TCM will not pump much fuel at cranking RPM which is very very low. The overly rich situation eventually (and quickly) finds the right F/A ratio and lights off. The low RPM and thus low extra fuel delivery means no excess post-priming fuel will dribble in.

The Lycoming which is now primed up and overly rich, waiting for the F/A ratio to get optimal will start pumping fuel according to mass airflow immediately (and at the FR position this will be very rich….and will be too rich to start when combined with the primed amount.

Two different systems, two different techniques. :ok:

27/09

I tend to agree, cold ones present less opportunity to stuff up. One is not harder, just some find ways to create that scenario.

I would bet your local school 172's are not being started exactly as I describe. There will be all manner of throttle positions, mixture, priming and hence the problems.

The engine, provided it has good plugs, good mags and a F/A ratio that is right, WILL start every time. No argument. The pilot controls the F/A ratio and assuming the engine is "conforming to spec" all you do is get the F/A ratio right.

Some Lycoming operators who apply a bit of TCM start procedure (seen this a lot) always have problems. I bet that is what you are observing.

:ok:

As soon as I saw this thread go up, I thought, Jaba will be all over this very soon, and you did not disappoint!

I like my Contis for starting simplicity.... Prime it just shy of it catching fire and hit the switch and away she goes! :}

How much priming is just before catching fire? Well, that's the rub, isn't it!:E

I have no doubt you're correct on that score. Plenty of fried starters and flat batteries. :{

Agreed on having the F/A ratio correct.

I find with a hot start if it doesn't start after the first or second attempt you will need to prime. The amount of priming required can be hard to determine. On the next attempt after priming if there's not ignition after 4 to 5 blades I start opening the throttle to vary the F/A and almost always get a successful start.

Advancing the throttle on the first attempt at a hot start very often works as well.

ACMS

True - but then push down gear lever down after RH engine has shut down to check LH engine hydraulic pump

But - [ and there is always a "but" ] when checking LH hyd. pump on shut down, it may be a bit lazier due to higher hydraulic oil temp

Rotax 912 iS….no mixture control so no argument;)

What I do, for a conti semi-hot start on level ground, is...

1. Pat my head and rub my tummy
2. Flick the fuel pump on and off quickly five to seven times depending on the height of my shortest passenger
3. Say a short prayer
4. ....

Oh wait a minute, that's right. I don't any of those old wives tales and make up bull**** as I go along.

I just do what the AFM/AOM says on any type I fly - and LO AND BEHOLD.... it works every time.

Who'd have thought the AIRCRAFT MANUFACTURER would know the best way to start their aircraft, ey?

/End rant.

Pete, that is good. But not all POH's are created equal.

We (APS) know and actually highlight in class, several POH's that are, lets call it sub-optimal in terms of reliable information. One that springs to mind is inflight restarts. Don't ask me which one off the top of my head, but lets just say the book describes a process that makes it worse not better. ;)

So the idea is understand the science, then you can critically think through the POH and determine if the one you are reading is a gem POH, or a POS.

Cheers :ok:

27/09

That is about all there is to say about that! :ok:

gee wouldn't it be great if the manufactures provided a system that when running at or just above idle the engine actually took care of its on f/a mixture. perhaps they could call it lets say an idle circuit. omg what did you say they already do well ill be ???????

cold start
 

Yep Jabba...that's 100% correct. That's what I was trying to put across but went a little awry!...put it down to old age mate :(

I noticed that no one has mentioned the Lycoming IGSO-480s and Lycoming IGSO-540s.:cool:

Thanks Shytorque - I've been after a good explanation of this conundrum for years.

You land and then taxi to the ramp and cut the fuel to your hot fuel injected Lycoming by starving it of fuel by pulling the mixture.
Then as if by magic 5 mins later you start the engine with the mixture still cut off!

Heat soak! Simples

I've seen <insert name of nearby sausage factory> students in brand new 172's use the cold start procedure after refuelling and sit there wondering why it won't start. It's enough to make you weep. :ugh::mad::{

I have seen this at Parafield in Adelaide. The FCU's have to come off so often to get all the dye and goo cleaned off the diaphragm about every oil change! I kid you not.