Whoa, Joe! I don't have to defend the charts. They're FAA Approved Data!N1478D wrote:Come on now Geoge, look outside of your paradym!
First off, you are starting off all of your calculations using the imaginary number of 145 horsepower. Even if our airplanes were new, how many of them would have exactly 145 horsepower?
Second, I have never seen a pilot looking at the trees, whip out his calculator or chart and say, "OK, I have 122 horsepower, that will do it!". Owners practice and know their airplane and it's capabilities. Renters look at charts and they are either not allowed by the rental agreement or they just don't know the airplane well enough to go to tight places.
Cessna was probably required by the regulations to provide charts. Even with interpolation for the different atmospheric conditions we fly in, the charts would have a hard time accomadating all of the different ways airplanes are maintained, fuel quality, prop nicks, tire sizes, etc, etc. Those same charts say it takes 3 times as much runway to land than it really does.
It's like the accountant that eventually comes to believe that the real reason every one is there at the corporation making widgets is to help him count the widgets, not to make them. Those charts are just documentation George, you don't have to defend them. Take a survey and find out how many owner pilots refer to them.
145 isn't imaginary. It's a fact, based upon FAA certification of mfr'r data that if your engine turns 2700 rpm it's making 145 horsepower! (and if it's only turning 2250 static it's making 118 hp, etc.)
"Second": The pilot is required by regulation to determine his required takeoff distance prior to flight, and the data to do that is in the FAA Approved Flight Manual. If the airplane meets it Type certificate, is in airworthy condition, and is operated according to the recommended procedure...then it will meet the charted data. It's the reason we follow airworthiness standards when maintaining our airplanes.
Lastly, with regard to your observations regarding "owner" experience with their airplanes and "prop nicks" and "3 times as much runway": The airplane is to be maintained according to it's maintenance schedule and FAA regulations therefore if there are any "prop nicks" etc they'd better be within the specifications or the airplane will not meet it's performance data (the owner/operator is req'd to keep the airplane airworthy according to such requirements) and "owner experience" is a relative term. As is "3 times the rwy required" an anecdote, without factual basis....it's your commentary...not a proven fact based upon flight testing.
The aircraft performance by FAA definition is documented using "average" pilot technique as proven by the factory test pilots who certified the aircraft's performance. If an owner is especially adept, or personally more familiar with his aircraft or uses special operating techniques then he may exceed (or fail to meet) the published, approved data.
If you are looking at trees, then you'd better whip out your charts and confirm the takeoff data before you start the roll. Not only are you required to do so by regulations, it's also prudent.