OK, here goes ----
While some of us have heard and read the words of George Braly and what’s his name (AvWeb guy - Oh, I remember John Deakin, with the twin), we are still confused. Why? Well, let me speak for myself. I find no comfort hearing about high flying sixes, some turbo charged, with caveats like “fixed ignition timing”, dyno tested, etc. Most flying Lancairs are equipped with little 4 cylinder engines, many pushed to their limits. No matter, I have no cylinder envy, nor even inches (cubic) envy. I just want to operate at best power, or max power (for racing) or even economy power for the strange reason of stretching endurance on a long cross country. My confusion in understanding comes from the following:
- “Prop efficiency goes down after 2500 rpm.” Even though Klaus runs rings around larger engined planes when he is operating in excess of 3000 rpm? Does the efficiency go down, but thrust HP is increased? Am I losing power by operating at 2660 rpm (a felt sweet spot)?
- What is 75% power for my Lycoming I/O 320 engine equipped with a 70 inch Hartzell constant speed prop? I have made the following adjustments:
- Different pistons were used to raise the compression ratio from 8.5 to 9:1. How was that done? Did it reduce my cubic inches or somehow increase the stroke?
- A non-filtered induction ram air system is used which raises the manifold pressure 1.5” Hg at 180 KIAS (195 KTAS). What affect is this on power charts or do I just artificially add1500 feet to the chart scale?
- The added LASAR ignition system has 2 effects:
- A hotter spark, burning more fuel in the cylinder. The consequences are a 15-20 degree rise in cylinder head temps and a 90-degree reduction in EGTs. This seems to lead to increased torque, thus increased thrust HP because the prop pitch is increased to retain the RPM. This is seen as a sprightlier take-off run, a higher climb rate and better general performance. What is the affect on determining % power?
ii. At some RPM/MAP point, the “spark” is advanced, resulting in higher power and more efficiency. How does this affect % power at full power and best power? What is the affect when running LOP?
- The addition of a harmonic dampener, which for fixed pitch props generally, increases the full power rpm by 100. Does this improve my power also by increasing the flywheel affect (allowing an increase in prop pitch to retain rpm)?
Another words, what are the gross parameters I can use to operate LOP? What are the steps I can use when operating ROP and how many degrees (EGT) rich at certain power levels.
With the above listed modifications that appear to affect power, should I increase the takeoff fuel flow to something greater than its current 15.1 gph?
Someone help us little guys with answers to our questions! How else can we achieve harmony with the universe? Huh? Huh?
Grayhawk, AKA Scott Krueger
Sky2high@aol.com
LNC2 N92EX IO320 Aurora, IL (KARR)
PS Formulae accepted.