What I Did on Memorial Day

My airplane is pretty. It is an electric airplane. I fly it in the air. I went to the flying field on Memorial Day. I flyed it there real good. ;-)

I had a very nice flying experience today due to a combination of improvements:

– I used careful throttle management and was very happy to find that I got about 15 minutes in the air. Previously, I got about 5 minutes in the air mostly WOT. I have seen several reports of people that get “10 minutes WOT” with a 1700 mah battery… Those claims sound dubious (at least from my experience). And it seems to be the case that since my battery was draining slower, it also offered up more juice before giving out. As proof, when I went out last week, I got 5 minutes of flight time and then my peak charger put 800 mah back in. Today, it put 1,500 mah back in during recharge!

Twice I had a problem where I launched at full throttle, went about 5 seconds and then the engine cut out. I still had elevon control. Apparently, the battery voltage dipped and tricked the ESC into thinking the battery was almost dead. :-( After another start, I was ok. I guess the think to do is just keep off the full throttle until the battery is warmed up… or maybe pre-warm it on the ground.

– I fiddled with the CG, not to much effect. Though I’m going to put some more velcro in the tray so I can move the battery around more.

– Last night I reironed the Oracover. It had gotten crinkled up after some crashes. I think it helped with the aerodynamics. I’ve also got an issue with… ok, I’ll just come out and say it… when I first ironed it on, I didn’t take the protective film off. It stuck kinda-well, so I left it. It’s still on. Of course I’ll redo it eventually.

– I got in some inverted flight! Woo hoo! Unfortunately, I couldn’t quite maintain altitude, even by pushing all the way forward on the stick and all the way forward on the trim. I started at around 200 feet, was inverted at 175 feet and then started losing maybe 10 feet per second down to 100 feet, where I peeled out. I’ll keep at it though.

– As Yoda always said, “Control! You must learn control!” Improving my stick control is improving my flying. Of course, I still crashed 3 times… But that’s ok, I just brushed away the grass and mud, plugged the battery back in and zooOOM!

As for control surfaces… It always seemed to me that the horns were placed too close to the center of the plane. If they were moved out to the middle of the wing, the far end of the elevon wouldn’t have nearly as much of a chance to flutter or strain. Net result: more responsive flight. That’s my thought anyway. I haven’t seen any photos of such a configuration though. Thoughts?

– I learned a valuable lesson about near-stall speed flying and elevon airplanes. It had to happen to me twice before I sat the plane down in the grass, put my fluid dynamics hat on, played with the controls and thought about it for a while. The lesson is this: If you’re flying very slowly and pull a hard turn… lets call it a hard right turn, the right wing now has it’s elevon pointed up in the air like a flag. At stall speed, that wing isn’t going to bank and turn the plane. Instead the elevon will act as an AIR-BRAKE, slowing that wing down and sending the plane into a really cool though horribly tragic spin. What does the airplane doctor say about that? “Don’t do that!” “But Doctor, sometimes I find myself in that predicament when flying fairly low and then making a turning error.. Like for example turning away from the wind too quickly.” The doctor just repeats, “Don’t do that.” And I bow my head and agree.

– Could someone else put their stock zagi on a postal scale and crank it up to test how much thrust their motor is generating at full throttle? As I said before, mine comes in at 12 oz and the Zagi site shows 16 oz. Which is more normal? Of course, this number isn’t a totally accurate representation for flying because the prop might be stalling when there is no airspeed (in the test environment) but in the wild, when the plane is flying at 25 mph, the prop wouldn’t be stalling.

Cliff writes
>>How are you charging your battery? it should be at 2 amps max
>I’ve been charging at 2C to 2.5C, 3.4-4.25 amps. I’ve done that about 12 time

Hmm, I just reread the Zagi manual…. ”
SANYO RECOMMENDS CHARGING THE KR 1700AE CELL AT A RATE UP TO 1
AMP….SOME MODELERS REGULARLY CHARGE THEM FOR 40 MINUTES AT 2 AMPS.

Oop. My bad! But I so often hear about charging nicads at 2-3C…. ugh. I suppose slow charge time is part of the penalty for these batteries having such a good weight to energy density ratio. I’ll be good to my batteries from now on.
– The heavy aired misty day worked to my benefit. The wind was light and there was no one else there. If there’s glow planes on the field, it’s a bad idea to just walk into the middle of the field for the fun of having the plane fly by 5 feet away!

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Now I’m coming around to the Zagi way… I’ll probably be getting another battery pack and a brushless motor soon. Cliff has been good to me from the beginning so I’ll likely get it from him. :-)


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