Mailing List flyrotary@lancaironline.net Message #5486
From: Ed Anderson <eanderson@carolina.rr.com>
Subject: Re: [FlyRotary] Re: Air cleaner
Date: Fri, 23 Jan 2004 18:10:36 -0500
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Message
 
 ----- Original Message -----
From: TWJames
Sent: Friday, January 23, 2004 2:02 PM
Subject: [FlyRotary] Re: Air cleaner

Hi All,
I am so glad to read Rusty's honest appraisal of how it really works in this experimental stuff.  I'm thinking of naming my plane "Do & Re-do". 
 
Ten days ago in Pensacola, duh?, I set about to re-evaluate my mixture map.  (hint to Perry)(Thanks to Ed).  I found that the average setting, from 13" to 30" was 5-6 bars/10 on the meter.  I reset in Mode 1 to 7-8 bars.  Went flying and power was good. However, takeoff roll rpm was still low at 4500.  As we accelerated to 5400 in level flight, the mixture meter showed only 4-5 bars.  I adjusted to 7 and kept the mixture there for local flights at from 3-5000 with nothing but smoothness.
Questions: 
1.Why would the WOT mixture decline in flight vs. static WOT? 
2. Should I go for more TO power with slightly less pitch until it will generate 6000 +- with WOT in level flight?
 
Regards,
Tommy the lurker
ps WOT Temps never got above 197* with OAT at 60-65*, even at 80kt climb
 
Hi Tommy,
 
    I'll try to answer your questions.  First if your take off is 4500 rpm (which is low) and your can accelerate to 5400 rpm (which is not high) and your bars are in the 5-6 range then you are basically still below the air fuel mixture for best power.    I suspect that you may be encountering some airflow challenges with your intake as I would expect like to see you closer to 5000 rpm for take off and 5900-6000 rpm for the upper end.  OR you simple have more prop pitch than optimum for take off. 
 
   Here is what I would suggest.  I would set the prop so you can get 5000 rpm static (you might want to work up to that in several stages and noting how it effects your top end in flight).  AT 5000 rpm static (ready for take off roll), I would crank the manual mixture control up until I see around 8-9 on the LED.  Asssuming that max LED number 10 can be make to light up.  The reason I state that is the LEDs are measuring the O2 sensor voltage from approx 0 - 1 volt.  Depending on the O2 sensor (or the calibration of the LED indicator), its possible for the number 10 LED to be lit and yet you only have an air/fuel ratio of say 13 instead of the optimum for best power which is around 12.6:1. 
 
    Air/fuel ratio = POWER.  So you generally want the maximum - particularly for take off which generally means around 9-10 on the LED scale.  Also note your EGT, as long as it tends to increase that means the fuel is being used to produce power, if you advance the mixture too rich you will note that the EGT starts to drop off.  Now if you lean it too much the EGT will also drop off, but with the LED indicator its generally easy to tell which one is happening.  If you are at 10 LED and the EGT is dropping then you probably have it too rich.  IF you are 5 or below and the EGT is dropping then you are getting lean.
 
Its not unusually to have to manually adjust the mixture control to keep it where you want it for your particular regime of flight.  Many factors seems to affect its operating position.  When I lean out for economy cruise the LED are not lit - too lean to show on the scale and my fuel flow is around 6.7-7 gph.
 
By the way, once we get the fuel flow indicator working for you, you will find that with the LED and Fuel Flow indicator, you really get a much better picture of what you are doing with the engine.
 
Hope this helps.  Once you get the aircraft to NC , let me know and we can do some more "experimenting"
 
Ed Anderson
 
  
 
   
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