I live at the SE corner of Stingray Point, Deltaville, VA, USA, on the water (Chesapeake Bay). Was given a Phantom 3 SE as a present last month. Am a newbie. Testing height and distance variables, yesterday I flew it straight out, SE, over open water toward Gwynn's Island, abt 2.5 miles away.
For the first leg, I flew at a height of 50 feet until I got 1,500 feet out, offshore.
The wind at Home point, ground level, was between 1 to 2 mph, from the N. (I flew out SE.)
In the track image you will see a squiggle almost near the end. I had the drone do a 360 for video of the land and our house, and altered course slightly, hoping to see the Piankatank River marker, Green # 3, on the screen. Could not as it is abt 1.5 miles offshore. Then, at 1,500 feet distance out from Home, I told it to RTH. Per my settings (cause of lots of tall pines inland) it rose to 250 feet, then flew a straight line back.
Later, I uploaded my files to the Airdata website.
Attached is a screenshot of both the track at Stingray Pt and, more significant to this discussion, the info re the wind during the trip.
At an elevation of 50 feet, en route out, the wind ranged from 3.16 to 3.51 mph.
For the RTH, at 250 feet, the wind jumped up to 10.69. So, it appears that the wind increased almost three fold, presumably, three times the speed and also three times the force on the body of the aircraft. WRONG!
While the speed increase was threefold, the wind force/pressure was much much greater.
As a sailor, it is my understanding that, as wind speed increases, the force on the sail increases four times. So a doubled increase from 3.5 mph to only 7.0, in terms of opposing pressure on the aircraft body, is a four times increase. Change facts, assume 5 mph v. 10 mph, a quadruple increase in wind force against the AC body.
So, for an elevation change from 50 feet at 3.5 mph wind, to 250 feet and wind at 10.69, the wind impact on the AC was much much stronger. When the AC left Home, there was hardly any wind at ground level. Fifteen hundred feet out from shore, at an elevation of 250 feet, there was a strong wind force opposing the RTH.
If I had gone to 400 feet, or perhaps 500 feet, twice as high, I too might have had difficulty with a successful RTH.
It was a real eye opener for me and, with this thread I am going to revisit my RTH height to a point perhaps only 20 feet above the highest trees.
Very enlightening thread. Thanks.
