Tommy wrote:Horse power is the single most dominant factor when one looks at performance, aerodynamics help, but it's not going to get you there in any big way.
Nope. Let's talk about speed (technically velocity) as one aspect of performance. Looking at the math, the force required to overcome drag increases with the square of velocity, and horsepower needed to overcome drag increases with the cube of velocity. So adding more horsepower provides diminishing returns if you want to fly faster.
But another way to go faster is to reduce the drag force (either coefficient of drag and/or less frontal area) with a slicker airframe. Reducing drag has the same proportional effect as increasing horsepower. We could get into a similar discussion in discussing climb rates, looking at factors like excess horsepower, coefficients of lift, etc. My point is that horsepower is no more dominant than other factors that aircraft designers must consider when evaluating aircraft performance.
Tommy wrote:Again, base line poh performance numbers are what should be looked at when comparing aircraft, nothing else.
Not sure what you mean by "base line," but it's obvious that people value a lot more than just performance when comparing aircraft, e.g., safety, economy, easy-to-fly, comfort, noise, etc.
Tommy wrote:Again Dave, you continue to cherry pick performance i.e starting at 5,000' or sea level.
I was simply refuting your claim that a DA42-VI can't out climb a BE58 Baron by providing the real-world circumstances under which it did exactly that. We never tried a climb comparison at sea level, but I'm pretty sure the Baron would easily win at that altitude. If I were trying to "cherry pick," we could have performed our testing at an altitude like 10,000 feet or higher where the turbo DA42 would more easily have out climbed the Baron.
Tommy wrote:There must be a reason why the manufacturer in the poh states thats the recommended cruise setting is 75% and not 92%. If it's not necessary and poses no degradation or ill effects why is it there?
The 75% power level is not stated as a limitation, and there's no prohibition on operating at higher power levels. 75% is recommended because of the point I made earlier: Because the amount of horsepower required in cruise flight increases with the cube of velocity, increasing power from 75% to 92% doesn't result in anything close to a proportional increase in airspeed. Instead, cruising at 92% causes the aircraft to operate less efficiently, burning more fuel/mile. Consider 75% power as sort of the "sweet spot" between fuel economy vs. actually getting to your destination in a reasonable amount of time.
Tommy wrote:There isn't and airplane made out there diesel or avgas that has not had nothing but problems with gear boxes.
I guess you've never heard of Rotax airplane engines that now dominate the Experimental and/or Light Sport aircraft markets, shipping in numbers approaching those of new Continental or Lycoming engines. A Rotax engine in cruise operates at about 5000 RPM with a gearbox that lowers the prop RPM into the 2000+ range. And based on years of experience, Rotaxes are now considered to be just as reliable (if not more so) than a Continental or Lycoming engine.