I ran across this while looking for a database of performance numbers. I like the table format, but do the numbers look right to you? I think these are the marketing numbers that the airplane manufacturers put out.
PA-28-161 Warrior II recommends cruising at 110, but 100 is a realistic number.
Obviously "cruise speed" is a moving target with too many variables to mention in a chart like this. Commonly, when quoting "cruising speed" of normally-aspirated piston lightplanes, the manufacturers pick the true airspeed, at max gross weight, obtained at the highest density altitude at which 75% of rated hp can be produced. That's usually in the 7500'-8000' range. (There are exceptions, for example cruise speed of the Cessna R172K "Hawk XP" is quoted at 80% of rated power, because the engine was de-rated from 210 to 195 hp.)
But how were the tests run? Did they use a production airplane with all the antennas, lights, assist steps and other drag-producing goodies a customer would normally order, or was it a stripped-down, unpainted factory "mule" used only for the certification testing? Certainly the tests were flown by expert test pilots, the engines were new, doors and seams were tight, everything properly rigged, and exterior surfaces free of damage, hail dings and wrinkles. Forty years on, or more, it might be tough to find an airplane that completely meets that description. You might even have a 5-7 knot variation between consecutive airplanes off the assembly line when they were new.
Some manufacturers had a reputation for being more realistic in their spec sheet performance numbers; others not so much. In the '60s, Piper tended to be straight-arrow about their performance claims. It paid off with good publicity when Piper airplanes frequently won the Powder Puff Derby and other handicap races that were popular in those days, because it was not difficult to beat the book numbers.
To your question about the Warrior: 118 KTAS, as shown in your chart, looks about right to me for a PA-28-161, with the 1978 or later full factory wheel fairings. What's odd, though, is that 118 KTAS is quite a bit
less than what Piper itself was claiming in its advertising. Here's a screenshot from the 1982 Warrior brochure:
I flew a lot of 1980-1990 Warriors when they were nearly new, but never one that would do 127 KTAS at 75% in level flight. For 1977, the only year the PA-28-161 had the old-style wheel fairings, Piper quoted 116 KTAS, then 127 KTAS for 1978, the only difference being the new fairings.
I have a C-172N, but it has been heavily modified, so it's not an apples-to-apples comparison with the chart. But the chart lists 122 KTAS cruise for the 172N, which in my experience with the unmodified airplane, would be about 5 knots on the high side, at least. And that would not be unusual with Cessna.
