stupid question about S-300C mixture lever

[Reely340]

I'm asking about that prominent lever in the middle of the bottom end of the instrument panel:
http://www.aogheliservices.com/images/C-FIBC_FOR_SALE_files/image007.jpg

All FIs and AFMs call it mixture lever: "out" is fuel cutoff, "in" is rich (flight pos)

Why has it got that notched knob? :confused:
Can one adjust the mixture by turning it?

Why is the master fuel cutoff (bottom end left side) a simple locking push pull lever, and said mixture lever has such an inviting knob to frob with?

I didn't dare turn it, I was afraid some internal threading might pop out, and of course the AFM sez nothing about turning it so I didn't, but I genuinely want to know. :8

(that mixture lever must cost more than the master fuel cutoff on the left,
why did Hughes/Schweizer go with that extra expense? :suspect:)

[Hughes500]

Sometimes you have to turn the knob on the vernier thread to achieve full rich to take up the bounce in the cable. Bear in mind these cables are a universal manufactured item so are also used in machines that you can lean the mixture on

[Hawkeye0001]

Yes, you can adjust the mixture by turning it (no in-flight leaning!!!)

And regarding the master cutoff: you'd use it in emergencies (e.g. engine fire) and then you'd likely want it off-off, not just "a bit off", "half off" or "simmering heat" :)

[Reely340]

AHA! :suspect:


So how is that done?
Which direction for rich/lean?
When to turn that thing (only when all the way in or out, or anytime)?
Who is supposed to turn the control?
According to what behaviour/indicator/parameter ought it be set?
How can I check if the setting is off?

Especially 6. would be interesting, as various people starting the beast many times a year
might slightly alter the knob while doing so, unaware of its internal effects.

Background is I can lease two S-300C. One is really pulling well. The other one not so.
Said other one got a completely overhauled engine in 2012. Same lame power output.
This especially puzzled me as according to the mech "overhauled" means only the engine
case and crank stay, the rest is replaced. So with all new liners, rings, pistons, valves,
seats and camshafts the only reason for the noticeably worse performance might be
in the FI section (which to my knowledge is unchanged) setup.

TIA
Peter

[albatross]

All my piston time was in a Bell 47.
I came from a fixed wing job and was used to adjusting mixture in cruise.
My first instructor's first briefing was clear and loud.
"You are a fixed wing driver? See that knob? ( pointing to mixture control )
Do NOT repeat NOT touch that thing in the air!"

As it was explained later in fixed wing we leaned it out until it roughened up a bit and then enriched a bit to get it smooth. ( no EGT ) the flywheel effect of the prop kept the donkey running.
Due to the freewheel in a 47 if you did that and leaned a bit to much the donkey would quit cold leaving you with more problems than you wanted.

Long time ago in a galaxy far far away.

I am sure someone with more brains and recency than I will be along to provide truth and enlightenment.

Is the mixture control and proper use thereof not mentioned in the Flight manual? Perhaps ground adjustment is mentioned in the engine manual.

some carbs have an automatic mixture control. At the high power settings used in helicopters I would think you would want a pretty rich mixture anyway.

I hope you find the info you require.

[krypton_john]

That's as good an explanation as I've heard, Albatross.

The question remains though: why bother with the vernier adjustment when a fuel shutoff lever would do the same job?

Enjoyed the anecdote about your lesson too!

[HS125]

1. So how is that done?

You can either push the button and then push or pull the control or turn the control to change the mixture.

2.Which direction for rich/lean?

Push or clockwise for Rich, Pull or counter-clockwise for lean

3.When to turn that thing (only when all the way in or out, or anytime)?

Personally I'd just push or pull it, you only use Full Rich or Idle Cutoff and it isn't intended to be used for altitude leaning.

4.Who is supposed to turn the control?

The PIC

5.According to what behaviour/indicator/parameter ought it be set?

The checklist/POH

6.How can I check if the setting is off?

If I was concerned that the setting was different to that commanded by the control, then I'd get engineering to have a look at it double-lively.

[Hawkeye0001]

*Before* takeoff it can be used to lean at altitude - refer to the POH, I believe it was over 3000ft. Also comes in handy to burn off carbon deposits from the spark plugs if the mag-check was a bit rough.

The procedure we used was to run the engine at full RPM (3200 RPM), start leaning the mixture by turning the knob counter-clockwise until you notice a slight drop in RPM, then richen mixture again slightly by turning clockwise for one (or two?) turns and engine RPM recovered.

Edit:
Just found the reference for the S300 CBi: Leaning recommended over 3750ft. No leaning in flight (Ref. POH 4-20).

[spinwing]

Mmmm ....

Hawkeye is spot on WRT 'leaning' ..... engineers will do a similar thing with the injection flow control during maintenance checks to get a smooth engine idle.


... Why has it got that notched knob? ....

Because there are other 'vernier' type controls (also with different colour knobs ie: Blue or Black) which (in aeroplanes) are used to control other engine functions like 'Propellor Speed' setting or 'Throttle Position' and they also have different 'notches' or shaped so as to allow 'tactile' identification with out having to actually look at the control to know you have selected the correct one.

You have actually asked some very good questions ... well done.

:ok:

[HS125]

*Before* takeoff it can be used to lean at altitude

good catch I stand corrected!

[Reely340]

Prefect feedback thank you all ! I'll try Hawkeye's drill next time.

The only part I find odd is, that there is absolutely no info about mixture setting in the AFM! As if that adjustment facility didn't exits as of writing. I'll double check but I'm pretty sure I didn't overlook it.

The AFM I'm am referring to is not some copy of "appr. a Hu269",
it is is a copy for one of the very machines I am flying!

The general lack of knowledge about that PIC operated mixture setting might explain why those two S-300Cs are so extremely different to start, and might explain the appallingly different experienced power output.

[nocarsgo]

"The procedure we used was to run the engine at full RPM (3200 RPM), start leaning the mixture by turning the knob counter-clockwise until you notice a slight drop in RPM, then richen mixture again slightly by turning clockwise for one (or two?) turns and engine RPM recovered.

Edit:
Just found the reference for the S300 CBi: Leaning recommended over 3750ft. No leaning in flight (Ref. POH 4-20)."


That reference is for 300CB which is carbureted. The 300CBi is fuel injected as is the 300C. The CB and CBi are both model 269C-1 and have the same flight manual just with different notes depending on which engine you have.

Right after that section you marked (300CB) is this note for the CBi:
"Mixture FULL RICH
Note: (Helicopters with fuel injected engine - HIO-360-G1A) Leaning is not permitted."

For the 300C (Model 269C) which is fuel injected, the flight manual only uses full rich and idle cutoff as positions to use.

[Reely340]

For the 300C (Model 269C) which is fuel injected, the flight manual only uses full rich and idle cutoff as positions to use.Right!
And that is the exact reason for me asking.
Is turning the knob supposed to actually have any effect in the 269C?
Has anyone personally adjusted mixture to DA as described by Hawkeye prior to takeoff on the fuel injected 269C?

[Hawkeye0001]

@Noscargo: Thanks for pointing that out, I stand corrected!