Okay, I have seral doubts inside. First, I'd like to say what I know how to do. I know how to lean the mixture and how to get the EGT peak by monitoring the EGT instrument (Exhaust Gas Temperature).
I also know how to match the altitude and the temperature in the charts, so if I fly to 10000 feet and I have 69 Fº for the outside temp... I know I would have to look first the altitudes in the table 10000 feet and then the temp... so I find the range 10000 feet -8 Fº TO 10000 feet 28 Fº so accoring my exterior tempo, I find in that range the proper speed as indicated in the table.
I know how to do all that.
However, here I have several charts for cruise performances.
I see LEAN MIXTURE CHARTS and RICH MIXTURE CHARTS.
My first doubt is about what criteria should I apply to decide if I use a LEAN MIXTURE CHART or a RICH MIXTURE CHART.
What I think...if I am flying 9000 feet... normally at that altitude I would have the red lever almost back, to a 23%, so it is clear my mixture is lean. In that case I think I should apply LEAN MIXTURE CHART?
In the opposite case... I am descending, I am close to the runway and my MIXTURE IS FULL RICH... in that case I guess I must use the RICH MIXTURE CHARTS.
Is that correct?
That was my first doubt.
My second doubt is about the title of the charts...
I see there are charts for Inches of Mercury IN.HG.
Okay, that is what I use to calibrate the altimeter.
Then I see (OR FULL THROTTLE)...
And finally the RPM... 2100... 2300... 2500..
I am very confused with this.
Let's take an example... the first chart... RICH - 25.0 IN.HG (OR FULL THROTTLE) 2100 RPM - CRUISE RICH MIXTURE
I don't know if I understand this well or not...
I should use this chart if my altimeter is calibrated to 25.0 IN.HG or more and my RPM is 2100 maximum.
Is that right? or am I wrong?
Please, could you help me about how must I understand this?
`Lean` means you have achieved precisely what the charts require for ROP /LOP - 20° RICH or LEAN of PEAK EGT
Set Throttle
Set RPM
then
Tune for peak EGT
Once you have established that, you continue with mixture adjustment until you are EITHER 20° RICH or LEAN of what you saw as peak.
Depending on which side of PEAK you settle on, choose the appropriate cruise chart.
No door is closed to an open mind.
Cats open doors...
Hi Snave, I'm sorry but I don't understand you very well. This is a bit technical.
I tell you what I think it's EGT Peak.
I move rearward or forward the red lever and I watch the EGT needle. The goal is to maintain the needle in its higher possition.
Let's imagine we are flying at 9000 feet. In that case, if you move the lever forward too much, the EGT needle will go down, if you move the red lever back, the EGT needle will increase... but if you continue moving the red lever much more... the EGT needle will go down again.
So to find the peak, you have to move the red lever to the right possition back or forward until we get the EGT needle in its higher possition. Of course I take a look all the time to the EGT gauge in the cockpit.
That is for me EGT peak explained not so technically, but in plain words.
I don't understand very well what you said of:
`Lean` means you have achieved precisely what the charts require for ROP /LOP - 20° RICH or LEAN of PEAK EGT
ROP ?
LOP ?
20º ?
There are also several charts and seems to be there is a link about inches of mercury IN.HG and also RPM? I also don't understand that.
I would really appreciate practical examples to explain this instead too much technical vocabulary.
Cheers
I may not have been clear in a previous thread on this. The following diagram shows Rich to Lean in the horizontal - As you move the mixture out the graph values are rich to lean. This corresponds to an increase in EGT temp and then the more lean you get the EGT temp decreases.
The 150 degree point (example not real) is the peak EGT. The 130 degree points are 20 degrees Rich of Peak(ROP) (left side) and the other 130 point is 20 degrees Lean Of Peak (LOP) (right side).
So as you move the mixture the EGT needle will go up then stop and start going back down.
The other thing you misunderstood is that the in. Hg are for the Manifold Pressure, not the altimeter. The altimeter has nothing to do with the in Hg on the charts.
The MP is shown below:
Now you need to do a lot of reading to understand what all the charts are for and how to use them. I admire your interest in this, but it is a complex topic.
In a trainer (C150) you have the
Throttle - shows power with Tachometer (RPM)
Mixture - shows performance by listening for rough engine and notice a slight change in RPM or Air speed.
In a more complex aircraft (bonanza)
Throttle - shows power with Manifold Pressure (MP) - Higher - more power - more fuel
Mixture - shows performance by adjusting Mixture and looking at EGT - Rich - more fuel wasted, Lean less fuel wasted
Prop - Set the RPM for a constant speed propeller by looking at the tachometer.
The charts are used based on what YOU want to do when you fly. Do you want to go from Point A to B fast, but use lots of fuel or do you want to go from point A to B a liitle slower and used less fuel. The POH says stay ROP, so only use the Rich charts.
It is very difficult to teach you this in a thread on a site. This is basically 3 hours of ground school and 2 hours of inflight lessons.
`Lean of Peak` and `Rich of Peak` are standardised aviation expressions.
Use Google search to get additional information - Using the search term `rich of peak vs lean of peak` In Google presents the first reply from AOPA boards. It's all you need to educate yourself on the principles involved.
There's little point to use explaining the vagaries of an individual cruise chart unless/until you get your own understanding of the basics. P3D does over-emphasise the mixture adjustment IMHO, requiring mixture adjustment from too low a density altitude, so it's a key lesson to learn.
No door is closed to an open mind.
Cats open doors...
Hi ronh (again Impressed for the quality and quantiy of technical information you give)
Hi Snave
First, I am sorry for my delayed reply, however since last wednesday until today I had an extremely complicated week. I can breathe a bit now, so here I am.
I also did the homework and I was talking with a friend, pilot for the 737/800 in a very known "low cost" airline.
He explained me a lot of things via whatsapp and I think I have the ideas clear now, however I'd like to comment it here, so you can tell me if I am wrong or not
First thing: Mistakes, Missconceptions.
I will show what I did not know or confused.
- I did not know which was the funcion of the Manifold Pressure instrument, and I thought those inches of mercury were the same or had a relationship with the altimeter. BAD, of course not.
- I did not know why I had in the chart those 20 famous degrees lean or rich. Where do I find those 20 degrees? what are those 20 degrees? how do I calculate those 20 degrees?
- I did not know why rich or lean. When I am flying rich or lean. Because I move the red lever forward or rearward, but I don't know exactly when my flight is being considered lean or rich? - great confussion about this -
- I did not know why the cruise performance tables showed me a value in inches of mercury...
Second thing: Clarifications
- My friend, the Manifold Pressure Instrument. The manifold pressure instrument indicate me the air pressure for the INTAKE MANIFOLD (something we call in Spanish COLECTOR DE ADMISION), because to make the engine work we need air. Without air, things don't burn. Even more exactly, that air need oxigen... and here we have a problem... as long you ascend, the air is less dense and we have less oxigen. Things don't burn so well at 10,000 feet than they would burn at 1,000 feet. Due we need to create a mixture, fuel and air, we need to measure the air pressure of the intake manifold, because the air is less dense as long we ascend. For that reason we have the Manifold Pressure Instrument. We measure the air pressure, and we have that value in Inches of Mercury, basically this instrument tell us the amount of mixture we are using for the combustion. SOMETHING VERY COMMON IN PISTON AIRCRAFT IS THAT BY INCREASING THE ALTITUDE, THE PRESSURE IS REDUCED AND THE AIR DENSITY IS LOWER. HOWEVER, THE FUEL PRESSURE IS NOT AFFECTED. WHAT HAPPEN WITH THIS IS THAT, BY DEFAULT, THE MIXTURE IS ENRICHED AUTOMATICALLY. For this reason we have to lean, to get the maximum engine efficiency. We need to put more air in the combustion to make the things burn better at higer altitudes (the air have less oxigen, so we need more air to burn the fuel), and we need to put less air and more fuel in lower altitudes (we have more oxigen, we don't need so much air).
EGT PEAK
When we reach the proper quantity of air / fuel in the mixture by leaning it, moving the red lever rearward, we have reached what is called EGT peak and we have the maximum engine efficiency. Fuel burn as it should, because we have adjusted properly the air for the combustion. But reaching the EGT peak is not enough... we need to do more things.
ONCE WE ARE ON THE PEAK WE HAVE TWO OPTIONS WITH THE RED LEVER. OR WE PUT A LITTLE MORE FUEL IN THE MIXTURE (ENRICH, MOVE THE RED LEVER FORWARD) OR WE REDUCE A LITTLE THE FUEL IN THE MIXTURE (LEANING, MOVE THE RED LEVER REARWARD).
What will happen with this is the EGT gauge needle will drop. It's the same you enrich or you lean after reaching the peak, the EGT needle will drop and the gases temperature will drop too.
How much is that bit? How much do we need the gases temperature to drop? 100 degrees? 1 millon of degrees?
No, just what it is indicated in the cruise performance tables, 20 degrees from the peak.
For that reason we have that misterious number there, 20 degrees rich, 20 degrees lean... of course, regarding the EGT PEAK.
20 DEGREES RICH / 20 DEGREES LEAN ?
To calculate this, we need to find the EGT peak first, and then, enrich the mixture or lean the mixture, making the temperature drop in the quantity of degrees indicated before (what is indicated in the cruise performance tables). In this case, 20 degrees.
- If my EGT peak is in 680 degrees, I will be flying in RICH MIXTURE MODE if I move the red lever a bit forward and my EGT instrument is showing 660 degrees (20 degrees less from the peak, as indicated in the cruise performance table, 20 degrees rich / lean). Then I need a RICH CRUISE PERFORMANCE TABLE.
- If my EGT peak is in 680 degrees, I will be flying in LEAN MIXTURE MODE if I move the red lever a bit rearward and my EGT instrument is showing 660 degrees (20 degrees less from the peak, as indicated in the cruise performance table, 20 degrees rich / lean). Then I need a LEAN CRUISE PERFORMANCE TABLE.
The goal when reaching the EGT peak is to decide if whe move the red lever a bit forward, in that case we will be flying with RICH MIXTURE and we will need RICH CRUISE PERFORMANCE TABLES... or we can move a bit rearward the red lever, in that case we will be flying ECONOMIC, and we will need LEAN CRUISE PERFORMANCE TABLES. Always dropping the gases temperature as it is indicated in the CRUISE PERFORMANCE TABLE (20 degrees from the EGT peak).
Okay... now what?
We have calculated the EGT peak... We decided we fly rich or lean by enriching or leaning the mixture to make the gases temperature drop in 20 degrees, what is indicated in the cruise performance table... but is that enought?
No. Now we need to take the the cruise performance table that better match with the value of the manifold pressure instrument. I have cruise performance tables for 21, 23 and 25.
If my manifold pressure is showing 25... I will take the table of 25. Which one? rich or lean? I will take rich, if I am flying rich, and I will take lean, if I am flying lean. How to fly rich or lean, was indicated before.
HOW SHOULD I FLY, LEAN OR RICH?
Flying rich. Better technical maintenance, more expensive, better engine cooling, more safe perhaps, faster flight (just 2 or 5 extra knots, it's not light speed, but it's better than anything).
Flying lean. Better for the pocket, worse for the engine, more autonomy, abusing this, whiten exhaust pipes and even we can rot them.
I think this is a summary about what mean that number of 20 degrees, what is that thing of the manifold pressure and those inches of mercury and what is flying rich or lean...which were my first doubts initially.
If I am wrong in anything, I'd like to learn as much as possible. Please, correct me in anything you want.
You have written correct information and now understand how the engine works and is set.
The EGT dial has 20 degrees per division labled on it so each white mark is 20 degrees C. You find the highest point the needle goes and the reduce by one division. (white mark). You don't need to know the absolute temperature just the peak point.
As rich or lean? The POH says always rich, I feel the lean ones are for emergency low fuel issues, but not really sure.
Read the part leaning with EGT in the bonanza POH - Shift+2
