Walter Atkinson

(225) 939-7508

On Jun 27, 2013, at 8:45 = PM, Robert R Pastusek wrote:

From: Lancair Mailing List = [mailto:lml@lancaironline.net] On Behalf Of Walter = Atkinson
Sent: Thursday, June 27, 2013 = 9:05 AM
To: [LML] Re: GAMI = test

Based on = hard data, there are some significant misstatements in your post. = I will comment in line.

**To run a TSIO 550 lean of peak, it must be = operated below 75% = power.**

Many of = these engines are operated above 75% power as a matter of routine while = controlling CHTs. This usually requires operating it LOP. As = Confucius say, "Do not tell man something impossible when he already do = it!" = <g>

**but it=92s important that you know--and operate = the engine at lower power settings--if you want to run = LOP. **

There is = absolutely NO reason not to operate the engine LOP at high power = settings. Literally, thousands of pilots are doing so quite = successfully.

**When you run rich of peak, some of the fuel is = used directly for cooling and passes through the engine without burning. = As a matter of course, it cools by evaporation, and leaves nasty lead = and other deposits behind=85on plugs, valves, etc. = **

The heat = of vaporization of any extra fuel in a ROP mixture is not even a blip on = the radar screen in BTUs available for cooling. The reason a = richer mixture runs cooler than, say 50dF ROP, is that the richer = mixture burns slower placing the thetaPP further from TDC. This = results in lower internal cylinder pressures and fewer BTUs transferred = across the thermal boundary layer. Extra fuel does NOT cool a = cylinder. A full rich mixture relying on heat of vaporization for = cooling would not be 1 degree = cooler!

**So when you run LOP and eliminate this source of = cooling, you must offset it by either reducing power (total heat = produced) or increasing cooling (better baffling). = **

When = LOP, the leaner mixture slows the burn even mores than a richer mixture = and cooling is even better. It is possible, therefore, to operate = at higher power settings LOP with the same CHTs as ROP, or at the same = power setting with cooler = CHTs.

**So as you lean the mixture toward max cylinder = EGT, you=92re reducing the amount of fuel available for cooling and the = CHT=92s go = up.**

No. = See = above.

**With most Continental engines, this doesn=92t = happen at the same fuel flow for all cylinders, that is, one cylinder = reaches peak EGT at a given fuel flow (around 16-17 GPH if you=92re = running about 65% power) as you lean, while the other cylinders are = still rich of peak EGT. You need to note the fuel flow when the first = cylinder reaches peak EGT. As you continue to lean, the EGT (and CHT to = a lesser extent) of the first to peak starts going down, while the = remaining cylinder EGTs (and CHTs) continue to go up. Eventually, all = cylinders reach peak EGT and start decreasing. Note the fuel flow when = the last cylinder reaches peak EGT and just starts to decrease. The = difference in fuel flow between first and last cylinder EGT to peak is = the =93GAMI lean test.=94 Ideally, the fuel flow between first and last = should be less than 1 GPH; use of GAMIs can tune this to less than half = a gallon per hour, BUT NOTE THAT THIS IS OPTIMIZED FOR ONLY ONE = POWER/RPM setting, so you should test/set up the engine at the = normally-expected cruise power = setting.**

Well, = sort of. You have correctly explained the GAMI Lean Test. = The spread between the first and last to peak in GPH is called the = GAMI Spread. 1gph is pretty poor. GAMI shoots for a Spread = of 0.3 and most engines will run "smooth enough" with a Gami Spread of = 0.5 or below. While the GAMIjectors were originally "optimized at = 2300rpm (not any particular power setting) testing has shown them to = remain quite well balanced along a wide range of rpms and power = settings. The GAMI Spread will change very little UNLESS you have = induction = leaks.

**Here=92s the rub: You need to be sure all = cylinders are at least 30 degrees below their peak EGT when operating = the engine in cruise power, and this is critically important when LOP. = Ideally, all cylinders are all operating at about the same amount below = their individual peak EGTs, but the actual temperatures are not = significant=85it=92s the peak value and delta below--for each = cylinder--that=92s significant. If the fuel flow is not well balanced = among the cylinders, the first to peak EGT will get so lean by the time = that you get the last to 30 degrees below peak EGT that the first to = peak starts mis-firing. My = cylinders start mis-firing at = about 120 degrees LOP as a reference point. Mine are well enough = balanced (no GAMIs) that I can operate the richest cylinder at 60 = degrees LOP and the leanest cylinder (first to peak when leaning) will = remain below 100 degrees LOP. That equates to about a 0.5 GPH fuel flow = difference FOR MY ENGINE=85but this varies a lot from engine to engine, = and with the power/RPM = setting. **

How far = LOP one should set the mixture is dependent upon the power being = produced, not some magic number that always works. For example, at = 65% power, 20dF LOP is adequate. I operate routinely at 87% power = and set the mixture at 70-80dF = LOP.

**BTW, the = TIT=92s ARE CRITICAL, and you=92ll want to watch these while you=92re = fiddling with the EGTs. Continental says the max TIT is 1750 and the max = continuous is 1650. I am more conservative, and have a =93yellow = warning=94 set at 1550 and a =93red alarm=94 set at 1650. As you lean = the engine, TIT=92s will increase with EGTs, and will continue to = increase for a short time after the first EGT peaks are reached, and = then start decreasing. I normally see about 1500 on my TITs in cruise = flight; I lean the mixture more if they go above 1550 in cruise = flight.**

I know = of no scientific data to support your recommendations of keeping TITs = under 1550. Doing so may keep you 100dF ROP or more, but it is = doing nothing for the life of the turbo. The 1650 TIT limit is for = max rotor speed at max temperature. The turbo may be safely = operate at 1649 all day long without concern. A s a matter of = fact, that number is conservative unless one is at critical = altitude.

Continental says the max CHT is 460 degrees. I am = pretty convinced you=92ll cook your cylinders if you operate them = anywhere close to that in normal cruise flight. I have a =93yellow = warning=94 set at 400 and a =93red alarm=94 at 420. I only see these = temps during high power climbs between about 12,000 and 16,000, when the = engine is still producing lots of power but the air is starting to = thin/provide fewer molecules to carry away the heat. In any case, when = my CHT=92s get to 420, I increase the fuel flow (low boost if not = already on) , richen the mixture control (climbing ROP anyway) and/or = increase airspeed. As a last resort, I=92d pull the power back, but have = never had to do = this=85yet.**

**As to CHTs during cruise = flight. Get the fuel flow to the cylinders balanced first=85effectively = you are making each cylinder produce approximately the same amount of = power (yields a smoother running engine)--and heat. Remember that this = will be optimized only for a small range of power/RPM settings. Then go = to work on balancing the CHTs. This is (at least theoretically) much = easier than balancing the fuel flows and EGT peaks because you can do = many things to change the cooling air flow across the cylinders--and = that=92s the only variable IF you=92ve balanced the fuel flow/cylinder = power output. Working CHT=92s first just won=92t yield good = results=85you=92ll wind up doing it over and over=85**That's excellent = advice.

Back = to precautions you asked about:

1) If you=92re running LOP, be sure you have the engine = producing less than 75% of its rated power; below 65% if you=92re = conservative.

&= nbsp; &nb= sp; = ; WHY???

2) Be sure that every cylinder is LOP and that the = hottest EGT is at least 30 degrees below the cylinder=92s max EGT = (without consideration of the actual value, nor the values of any other = cylinder)

&= nbsp; &nb= sp; = ; That depends on the power being = produced.

3) Keep the TITs below 1650 degrees; ideally below = 1550.

&= nbsp; &nb= sp; = ; No scientific reason for this = recommendation concerning = 1550.

4) Keep the CHT=92s below 420; ideally below 400 (If = you do the above things, they will likely be in the 300-340 degree = range)

&= nbsp; &nb= sp; = ; Excellent = advice.

I hope my = response has improved your appreciation of the issues. If I can = expound on any of these, feel free to ask. You would benefit = significantly by taking the APS class as all of these things will be = shown with data to support what I have said = above.

Best = regards,

Walter = Atkinson

Advanced = Pilot Seminars