S-300C fuel system details
S-300C fuel system details
Guys, I'm trying to get behind the concepts and technical workings of the S-300C (Hu269) fuel system,
more precisely: the relationship between throttle grip and mixture lever.
The S-300C features a 4 Cyl Boxer with mechanical(?) manifold fuel injection,
I'm familiar with the AFM starting procedure:
1) 1/2" throttle open
2) fuel pump on
3) mixture full rich for 2.5/3 secs,
4) mixture full lean (idle cutoff)
5) fuel pump off
6) 1/8" throttle open
7) crank
8) wait till engine fires
9) mixture to full rich
Why? (Mind you I can read the AFM, I'm talking technics here only!!)
So, what exactly do the controls do?
Throttle: changes orifice for air intake and somehow "adjusts" injected fuel quantity,
thereby maintaining a combustible mixture (hence neither rich nor lean, just more or less of it)
Mixture: from "idle cutoff" to "flight mode" seems to reduce the mixture's fuel component only.
Technical guesswork for AFM starting procedure:
At 5) there must be a puddle of liqud fuel (or cloud of fuel mist?) sitting in the manifold cavern.
Phase 7) cranking is where the mystery happens:
a) initial phase engine draws in
air for 1/8" open throttle, NO fuel (mixture at cutoff) PLUS vapor of said puddle of fuel.
That is a very undefined mixture most probably way too rich
b) waiting for ignition phase engine draws in
air for 1/8" open throttle, NO fuel (mixture at cutoff) PLUS increasingly less vapor of said puddle of fuel.
ingested mixture becomes leaner
c) at firing point mixture is correct but rather volatile
as the fuel still comes from the diminishing puddle of fuel and NOT from throttle!
d) after firing
we are meant to set mixture to "rich" fast,
due to imminent fuel starvation as puddle of fuel is being used up
e) after mixture "full rich"
we did it, now the 1/8" throttle settings air is complemented from mixture fuel only, puddle is gone.
Needless to say you ever get to c), d) is the tricky spot, be slow and she'll die on you.
Besides being very awkward to set starting mixture by half flooding the engine and dynamically
passing mixture control from "puddle of fuel" to a measuring mixture lever, somehow this feels the
wrong way around to me, especially with warn engine:
I'd rather set minimal throttle (1/8" or even 0), start to crank and progressively shove in the mixture.
That way the mixture would start way lean, become increasingly richer until idle conditions are met.
This would have the advantage of avoiding any accidental flooding.
In my view that fuel system misses a cold start mixture enrichment choke postition/switch/thingy.
Example: Yamaha WR450F motorcycle carburetor choke opens a huge additional fuel passage
AND a small additional air passage, hence cold start works with zero throttle.
Anybody got a detailed exploded view of the S-300C fuel metering system, graphs, tables
picturing mixture vs. level position, anything that explains HOW the thing is working?
TIA
Peter
PS: how is ambient pressure induced mixture enrichment done?
Why doesn't it drown from overly rich mixture at FL100?
more precisely: the relationship between throttle grip and mixture lever.
The S-300C features a 4 Cyl Boxer with mechanical(?) manifold fuel injection,
I'm familiar with the AFM starting procedure:
1) 1/2" throttle open
2) fuel pump on
3) mixture full rich for 2.5/3 secs,
4) mixture full lean (idle cutoff)
5) fuel pump off
6) 1/8" throttle open
7) crank
8) wait till engine fires
9) mixture to full rich
Why? (Mind you I can read the AFM, I'm talking technics here only!!)
So, what exactly do the controls do?
Throttle: changes orifice for air intake and somehow "adjusts" injected fuel quantity,
thereby maintaining a combustible mixture (hence neither rich nor lean, just more or less of it)
Mixture: from "idle cutoff" to "flight mode" seems to reduce the mixture's fuel component only.
Technical guesswork for AFM starting procedure:
At 5) there must be a puddle of liqud fuel (or cloud of fuel mist?) sitting in the manifold cavern.
Phase 7) cranking is where the mystery happens:
a) initial phase engine draws in
air for 1/8" open throttle, NO fuel (mixture at cutoff) PLUS vapor of said puddle of fuel.
That is a very undefined mixture most probably way too rich
b) waiting for ignition phase engine draws in
air for 1/8" open throttle, NO fuel (mixture at cutoff) PLUS increasingly less vapor of said puddle of fuel.
ingested mixture becomes leaner
c) at firing point mixture is correct but rather volatile
as the fuel still comes from the diminishing puddle of fuel and NOT from throttle!
d) after firing
we are meant to set mixture to "rich" fast,
due to imminent fuel starvation as puddle of fuel is being used up
e) after mixture "full rich"
we did it, now the 1/8" throttle settings air is complemented from mixture fuel only, puddle is gone.
Needless to say you ever get to c), d) is the tricky spot, be slow and she'll die on you.
Besides being very awkward to set starting mixture by half flooding the engine and dynamically
passing mixture control from "puddle of fuel" to a measuring mixture lever, somehow this feels the
wrong way around to me, especially with warn engine:
I'd rather set minimal throttle (1/8" or even 0), start to crank and progressively shove in the mixture.
That way the mixture would start way lean, become increasingly richer until idle conditions are met.
This would have the advantage of avoiding any accidental flooding.
In my view that fuel system misses a cold start mixture enrichment choke postition/switch/thingy.
Example: Yamaha WR450F motorcycle carburetor choke opens a huge additional fuel passage
AND a small additional air passage, hence cold start works with zero throttle.
Anybody got a detailed exploded view of the S-300C fuel metering system, graphs, tables
picturing mixture vs. level position, anything that explains HOW the thing is working?
TIA
Peter
PS: how is ambient pressure induced mixture enrichment done?
Why doesn't it drown from overly rich mixture at FL100?
WOW! That'll make good reading, thanks a million!
Is that the exact type of fuel injection used on the HU269C?
From what I've seen from browsing the pages it appears to be a training manual,
still great stuff, thx again.
edit:
I've read that manual and found it very enlightening, except it appears that the metered fuel flow constantly runs through the injectors, regardless of the type of stroke the respective cylinder is operation in?
I'm not sure where the S-300C injects (directly into the cylinders chamber, into each cylinders intake manifold or into some central manifold area)
Only for single injector central injection I can imagine a requirement for a constant flow of fuel, as one of those four cylinders will be in intake stroke.
Peter
Is that the exact type of fuel injection used on the HU269C?
From what I've seen from browsing the pages it appears to be a training manual,
still great stuff, thx again.
edit:
I've read that manual and found it very enlightening, except it appears that the metered fuel flow constantly runs through the injectors, regardless of the type of stroke the respective cylinder is operation in?
I'm not sure where the S-300C injects (directly into the cylinders chamber, into each cylinders intake manifold or into some central manifold area)
Only for single injector central injection I can imagine a requirement for a constant flow of fuel, as one of those four cylinders will be in intake stroke.
Peter
Last edited by Reely340; 26th Jul 2013 at 19:29.
Join Date: Mar 2008
Location: England... what's left of it...
Posts: 161
Likes: 0
Received 0 Likes
on
0 Posts
I've read that manual and found it very enlightening, except it appears that the metered fuel flow constantly runs through the injectors, regardless of the type of stroke the respective cylinder is operation in?
This will explain why and how:
Continental IO-360 Fuel Injection - AVweb Features Article
At 5) there is a big puddle of fuel. This is in lieu of having a choke. At some point while cranking the fuel/air ratio will go from too rich to just right for a cold start. Mixture comes in later so you don't flood it.
Bryan
Bryan
Caution folks -
The link posted by Overdrive is for a Continental engine.
S300C is powered by a Lycoming with an RSA injector - Chalk and Cheese.
I would disregard the info on the Continental.
Full RSA Support Page
It "grew out" of a pressure carburetor which was designed to avoid icing.
With the S300C start is just like "priming" a carburetor engine. When "hot" there is no need really to prime. Fuel pump "ON" for 5 secs - do NOT set mixture to "RICH" - fuel pump OFF. Hit the starter and when it starts slide mixture to RICH. Works every time as most times people over prime the things.
Be carfule on the S300 with worn mixture and throttle cables as they will break.
Also make sure that mixture is correct. Easy to check - on shutdown slide mixture slowly to cutoff and watch for RPM rise just before it stops. No rise Too Lean, Big Rise Too Rich. Should be around ~ 50 RPM Rise.
Of course if your idle mixture is out it will be a b!*ch to start. Some folk set up the S300 for certain conditions depending on the response you want on a "throttle chop" into auto. Sometimes they will "RICH CUT" which will brighten up your day!
The link posted by Overdrive is for a Continental engine.
S300C is powered by a Lycoming with an RSA injector - Chalk and Cheese.
I would disregard the info on the Continental.
Full RSA Support Page
It "grew out" of a pressure carburetor which was designed to avoid icing.
With the S300C start is just like "priming" a carburetor engine. When "hot" there is no need really to prime. Fuel pump "ON" for 5 secs - do NOT set mixture to "RICH" - fuel pump OFF. Hit the starter and when it starts slide mixture to RICH. Works every time as most times people over prime the things.
Be carfule on the S300 with worn mixture and throttle cables as they will break.
Also make sure that mixture is correct. Easy to check - on shutdown slide mixture slowly to cutoff and watch for RPM rise just before it stops. No rise Too Lean, Big Rise Too Rich. Should be around ~ 50 RPM Rise.
Of course if your idle mixture is out it will be a b!*ch to start. Some folk set up the S300 for certain conditions depending on the response you want on a "throttle chop" into auto. Sometimes they will "RICH CUT" which will brighten up your day!
Join Date: Mar 2008
Location: England... what's left of it...
Posts: 161
Likes: 0
Received 0 Likes
on
0 Posts
Caution folks -
The link posted by Overdrive is for a Continental engine.
The link posted by Overdrive is for a Continental engine.
From his posts so far I think he might realize that. His question that I quoted is addressed in the link, the principle of continuous flow injection.
When "hot" there is no need really to prime. Fuel pump "ON" for 5 secs - do NOT set mixture to "RICH" - fuel pump OFF.
From what I've learned reading the docs linked to in this very thread, the fuel pressure would build up against the closed valve of the mixture in idle cut off, hence no fuel at all would be delivered to the manifold, right?
Our school operates two S-300C, one of them has the high energy starter installed, fires up easier. The other one my buddy and me were flying an hour into the mountains, in current very hot days. We paid landing fee and refueled a bit and when trying to fire it up again it resisted. We tried various things for a minute or two, only to be suprised by sudden starting. We do not know exactly which sequence of actions it liked, but we certainly never did do your "prime at idle cutoff" trick.
So what's the "prime at idle cutoff" do, internally?
Last edited by Reely340; 28th Jul 2013 at 19:17.
MODEL RSA-5 AND RSA-10AD1
FIELD ADJUSTMENTS
STARTING PROCEDURES
5-1. The following starting procedures have proven successful; however, if there is a conflict,
information given in the Aircraft Operation Manual should be followed.
A. Cold Starts
1. Mixture control in the idle cut-off position.
2. Set throttle 1/8 open.
3. Master switch - ON.
4. Boost pump switch - ON.
5. Move mixture control to FULL RICH until the fuel flow indicator reads 4 to 6 GPH then immediately return
mixture control to cut-off position.
NOTE. On installations where a fuel flow indicator is not used allow 4-5 seconds in place of reading 4 to 6 GPH on the gauge.
6. Engage starter -- when engine starts move mixture control to full rich position.
B. Warm Starts
Use the same procedure for cold starts except the boost pump may be left "off" and step 5 eliminated.
DO NOT PRIME
FIELD ADJUSTMENTS
STARTING PROCEDURES
5-1. The following starting procedures have proven successful; however, if there is a conflict,
information given in the Aircraft Operation Manual should be followed.
A. Cold Starts
1. Mixture control in the idle cut-off position.
2. Set throttle 1/8 open.
3. Master switch - ON.
4. Boost pump switch - ON.
5. Move mixture control to FULL RICH until the fuel flow indicator reads 4 to 6 GPH then immediately return
mixture control to cut-off position.
NOTE. On installations where a fuel flow indicator is not used allow 4-5 seconds in place of reading 4 to 6 GPH on the gauge.
6. Engage starter -- when engine starts move mixture control to full rich position.
B. Warm Starts
Use the same procedure for cold starts except the boost pump may be left "off" and step 5 eliminated.
DO NOT PRIME
Usual caveats apply but trust me it works. Why? Its too many years since I have worked on these things!!
@RVDT
You lost me somewhere on the road, you said
Classic priming for cold start, boost pump ON + mixture full rich for a couple of secs. Ok so far. 
This is the "skip priming" procedure, because boost pump is off, and mixture is not temporally set to rich, well known from the AFM.
But you were recommending something different:
That'll be "boost pump pumping against the closed (idle cutoff) mixture valve".
I definitely never came across this one.
So was that a typo and you meant the standard don't prime regime or
is that a special, born out of experience, procedure?
You lost me somewhere on the road, you said
Quote:
MODEL RSA-5 AND RSA-10AD1
<snip>
A. Cold Starts
1. Mixture control in the idle cut-off position.
2. Set throttle 1/8 open.
3. Master switch - ON.
4. Boost pump switch - ON.
5. Move mixture control to FULL RICH until the fuel flow indicator reads 4 to 6 GPH then immediately return
mixture control to cut-off position.
MODEL RSA-5 AND RSA-10AD1
<snip>
A. Cold Starts
1. Mixture control in the idle cut-off position.
2. Set throttle 1/8 open.
3. Master switch - ON.
4. Boost pump switch - ON.
5. Move mixture control to FULL RICH until the fuel flow indicator reads 4 to 6 GPH then immediately return
mixture control to cut-off position.
B. Warm Starts
Use the same procedure for cold starts except the boost pump may be left "off" and step 5 eliminated.
DO NOT PRIME
Use the same procedure for cold starts except the boost pump may be left "off" and step 5 eliminated.
DO NOT PRIME
But you were recommending something different:
When "hot" there is no need really to prime. Fuel pump "ON" for 5 secs - do NOT set mixture to "RICH" - fuel pump OFF. Hit the starter and when it starts slide mixture to RICH.
I definitely never came across this one.
So was that a typo and you meant the standard don't prime regime or
is that a special, born out of experience, procedure?
@Overdrive
From his posts so far I think he might realize that.
Umm, *blush* thanks for that compiment 
Was good reading indeed, thanks a lot for the link!
Quote:
Caution folks -
The link posted by Overdrive is for a Continental engine.
Caution folks -
The link posted by Overdrive is for a Continental engine.
His question that I quoted is addressed in the link, the principle of continuous flow injection.
Reely,
Habit. Universal procedure. You give a bit of fuel pressure to deal with once you move mixture to RICH in case there is some vapor lurking before the servo. Watch the gauge next time you do it.
Take a look at the fuel lines with respect to residual heat.
The reason they start when warm is the residual fuel that must bleed out of the lines into the inlet when hot after shutdown is a theory.
Lots of folks do it this way. It works.
Your S 300 if properly maintained should start just like your car. If it doesn't there is something wrong with it.
Habit. Universal procedure. You give a bit of fuel pressure to deal with once you move mixture to RICH in case there is some vapor lurking before the servo. Watch the gauge next time you do it.
Take a look at the fuel lines with respect to residual heat.
The reason they start when warm is the residual fuel that must bleed out of the lines into the inlet when hot after shutdown is a theory.
Lots of folks do it this way. It works.
Your S 300 if properly maintained should start just like your car. If it doesn't there is something wrong with it.
