Just a quick update on some things learned. With just 30 flights most of which had trim and a variety of speed controller and timer adjustments, flights 31 & 32 were a trial by fire as Elroy was taxed with high wind, severe turbulence and competition in a field including 2 World Champions and 6 Nats champs. Given the fact that his driver/pilot totally placed him in a “this can’t be good fatal position” by not detecting a wind shift in the hourglass he performed very well. While I was treated to a full 360 degree inspection of Elroy during the during that single maneuver he did not give up and somehow found a way to restore control to me!
Power components:
Plett 20-12
APC 13/4.5 pusher
Turnigy Nano-tech 4S-2650 and Zippy Flightmax 4S-2650 batteries
ICE-50 Lite ESC
Hubin FM9 timer system
Maxx Products arming switch
Airplane general specs:
55” span, approx. 615 sq in. area, small flaps
Flight weight: 62 oz.
PTG Skinny airfoil (14% root, 9% tip,) dynamic flow curve (different root and tip plots) includes flaps (they are part of the wing)
Moments: Nose 10.675”; tail 18.75” (hinge/hinge)
*Much more about airplane details and flight characteristics in the future
Things learned:
How to work with small, low overhead, lightweight, inexpensive batteries.
How to calibrate, record and adjust FM9 system to match ICE-50/Plettenberg combo.
How not to fly combat sized maneuvers during official flights.
So we’ll start with the easiest first:
‘How not to fly combat sized maneuvers during official flights’ JUST SAY NO!
With that out of the way lets move to batteries. I would be remiss if I didn’t credit my good friend Erik Rogers with finding, testing and logging virtually all of the info about these batteries. He is by far the most experienced CLPA electric pilot around here and has rapidly ascended the ranks of very stiff Advanced completion here in CA. One of the things I like most about competition is the idea of pushing the equipment performance limits. These little batteries can and do deliver very good performance if care is taken to do the following.
1. Charge them correctly
2. Closely match the motor KVM with practical flight RPM.
3. Control flight time
4. Closely monitor # of cycles and mAh usage on each battery
5. Check individual cells for voltage after fully charged
Always charge these and probably all other Lipo batteries in full balance mode. I learned by accident that not doing so can greatly shorten their usable life for competition flying. Elroy was first flown with Plett 20-14, which has 810 KV specs. The combination of charging without balancing and running this motor at relatively high RPM averaging 9300 resulted in the premature demise of several batteries. At first I was baffled when the Plett 20-12 rated 950 KV was installed and a couple of the batteries I thought were gone somehow recovered. After reviewing charging details on the individual packs I noticed that the low packs were not charged in balanced mode. This was farther verified by checking the individual cell voltage after fully charged. Indeed there was always at least one cell that had a lower baseline voltage than others. With over 100 flights Erik had concluded that if any single cell reading was 4.4 volts or less the pack is just too unstable to chance in competition. This proved to be the case in the dead packs for me. Also, mAh usage seems to be somewhat variable and generally not critical if under 2475.
Flight time is also important in maintaining performance of these packs. One thing to note is every airplane/prop/line type and length combination will have different actual power requirements during flight. Add to this flying style and wind conditions and things get really interesting. Given all these I settled on 5 min. 10 second flight time. Flying on 66 ft. Laystrate lines at lap times between 5.2 and 5.35 seconds there is plenty of time to complete the pattern and setup your landing approach.
OK, so we’re really on the ragged edge pushing these packs this way but given their very light weight (Zippy Flightmax = 9.59 oz, Turnigy Nano-tech = 9.45 oz.) the reward is well worth the risk when closely monitored and matched with motor/airplane/prop/lines.
One final note re. governing. In my opinion and much praise for Dennis Adamisin for his insight and work with APC, the 13/4.5 props seem to offer an RPM envelope that is close to ideal. Head speed plots of RPM in different wind conditions, with a wide variety of ESC settings and bigger battery packs with more overhead are remarkably consistent averaging between 92 & 93k and Elroy is very happy regardless of what my handle tells him to do!
The topic of calibrating, adjusting and recording the FM9/ICE-50, Plettenberg combo will come after as soon as notes are fully reviewed.