The TAS numbers are statistically insignificant. The flow of the wing, cockpit width, etc make up for most of this. (btw, I’ve flown the Columbia 300 and the SR20 and put my money on the SR20 which I have since upgraded to an SR22).
Lancair’s numbers MUST be lean of peak or at peak. Running LOP is a complicated game that can only be safely accomplished with tightly balanced injectors and EGT/CHT from EACH cylinder. Note that Lancair and Cirrus do not offer this out of the factory though we are hoping that Arnav will be doing some of this for us. I’m guessing that the Cirrus numbers are 50-100 degrees rich of peak.
Again, with an apples-to-apples comparison, you would come up with very close numbers with fuel flow between the airplanes. Different cowlings can make a difference because of cooling issues. It will be interesting to note that, because every engine is a bit different, comparing an SR22 to an SR22 will not be exact.
Gami (the folks that make Gami injectors) have lots of articles on their web site discussing LOP operation. Read these before trying this in your airplane - especially with the 550. Unless you enjoy top overhauls!
The data below indicates that the Lancair Columbia 300 airframe produces a lot less drag than the SR22. Both at 8000 feet,
Cirrus SR22 (from Paul Traina’s web site)
RPM MP %HP GPH TAS
2500 20.7 69% 17.2 171
2500 19.7 65% 16.5 167
Lancair Columbia 300 (from Lancair documentation)
RPM MP %HP GPH TAS
2500 21 67% 14.4 174
2500 20 63% 11.9 169 >
The power settings and airspeeds are similar, but the surprising difference is in fuel flow. In the first comparison, the SR22 uses 19% more fuel (17.2 vs. 14.4 GPH), to get 3 fewer knots. The Columbia’s engine is operated at 50 degrees rich of peak.
In the second example, the SR22 uses 39% more fuel to get 2 fewer knots. In this case, and any case below 65% power, the Lancair manual calls for 50 degrees lean of peak operation.
If the manuals are accurate there must be big drag or propeller differences at play here.
Since both planes use the same engine, does anyone know if Cirrus specifies lean of peak operation below 65% power? Does the engine run smoothly in that mode?
I wonder if comparing planes gives the same results as comparing manuals? Any experience?