Consumption Presumption

After spending the morning at the field with the DAO, I have multiple items of pretty good news to share. First, FPV with my new DIY biquad antenna (more on that in a later post) worked flawlessly on the plane. Second, we found flying with 12,000 mAh of 4S to be a piece of cake, we didn't notice any ill effects and, as you'll see below, it promises quite a bit of additional flight time. Finally, it seems as though we have remedied the problem of high power consumption on the new airframe. It looks as though the issue was pretty much unrelated to the airframe and instead a function of speed. When we flew on Tuesday we were cruising at ~14 m/s. By backing off the throttle a little today and keeping our cruise speed at ~10 m/s, we greatly extended our flight time. With those pesky laws of physics increasing drag force by the square of velocity, we really hurt ourselves with those 4 m/s. Check out below for a graphical representation of today's results.

This figure shows battery consumption during our first flight. The initial constant-slope portion is battery being burned sitting on the ground. From this we can see that its pretty important not to do that if we want peak performance. The rest of the slope is remarkably constant, despite the fact that this flight included a climb from 100 to 350 m over 2 km. That particular climb can be seen as the inflection point about 3/4 of the way through the time interval. You can clearly see the downward turn as it climbed and the flattening out as it rapidly descended.

This figure shows battery consumption during our second flight. During this flight we upgraded from 4S1P to 4S2P, for 12,000 mAh of capacity. As you can see, the slope is quite constant , but slight variations in slope can be seen as we climbed from 100 m to 200 m, descended, flew level, and then repeated the process. Also, don't pay much attention to the appearance of a large difference in slope between the two figures; they are shown over significantly different time intervals.

Our first flight, with lengthy loitering around the field, and 2 passes of a flight plan. The first pass took us from home to the right at 100 m, turned up river and climbed to 350 m, and then turned back for home while descending back to 100 m. The second flight was the same but the climb was reduced to 200 m. The flight path from the south to north end is 2 km. Total flight time was 30 minutes and the total distance traveled was 20 km.

Our second flight, with 4S2P configuration. The flight plan was the same as the other, with a climb to 200 m. Total flight time was just under 20 minutes and the total distance traveled was 14.5 km.

So, with all of that said, here is the really good news. With the 4S2P configuration we should be able to fly at least 45 km. We expended 26% of our battery over 15 km, which means that 45 km would leave ~25% in the tank (5% reserve). This calculation would also seem to be fairly conservative, as a climb to 200 m followed by pure straight and level flight should be significantly more efficient than climbing, descending, and circling. So, having that number, Miles and I did some back-of-the-envelope calculations and, based on that flight distance and the footprint of our images (with overlapping areas removed) and came up with 450 as the number of hectares we can map in a single flight. If we map 450 ha in a 1 hour flight and fly 4 times in a day, we can map 18 square kilometers in a day. I don't know about you, but by my standards that is a pretty big area.