Keep complaining about the P4, but I'm happy with mine! This flight was in 5-12mph winds the whole time. I can't believe that all these people complaining aren't posting any evidence of their poor performance, what a circle jerk.
I don't have a dog in this fight and I'm not arguing with you at all. (I've ordered a Phantom 4 but it hasn't yet arrived.) My interest is in learning the truth. I'm glad you are happy with your Phantom 4 and I hope I will be with mine as well.
At 21,332 feet in distance your flight was just about 4 miles long. I assume 21,332' is out and back. Because of it's curved arc your Phantom was less than 2 miles distant from your location at its furthest. You didn't nearly approach DJI's claimed 3.1 mile limit for radio control. Your flight then doesn't support or refute DJI's claim f 3.1 miles. (People have complained about lack of RC range.)
On a similar note, your 21 minute flight represents but 75% of the maximum flight time claimed by DJI, so it neither supports or refutes their claim on that subject either. I'm very curious if you made note of how much battery charge you had left upon the completion of your flight.
DJI's claimed 28 minutes includes the provisos of flying "in calm conditions with constant speed", although they fail to say so on their
specifications page which I regard as perhaps unethical, perhaps an oversight. I only saw the following disclaimers (below) after clicking on the Learn More link under the FLY FAR FOR LONGER section near the bottom right of
this page:
*In calm conditions with constant speed.
**Maximum range tested in unobstructed areas free of interference and may vary depending on local regulations.
DJI includes the following in the Phantom 4 User Manual:
"How many minutes of flight time can Phantom 4 achieve with the new Intelligent Flight Battery?
At sea level in calm environments when flying in ATTI mode, the Phantom 4 can achieve 28 minute flight times. This will vary due to different flight patterns, weather conditions and altitudes." I can understand why people are upset when they get less than 28 minutes flight time. I mean, DJI doesn't present "the whole truth and nothing but the truth" up front in (at least some of) their advertising or on its website specifications page for the Phantom 4.