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Weekend - September 21/22, 2019
Posted: Sat Sep 21, 2019 3:18 pm
Another great morning today at SP! There is no doubt that winds were more challenging but they were mostly steady which helped. Good turnout this morning. Rick had new member Frank (welcome!) up for a few training flights and that is going well.
Thanks to Bob for filling in some of the holes added to our field from someone presumably using a metal detector and digging in our main landing area. Wouldn't it be nice if people using the space were just a little more considerate?
Bill had an unfortunate stall in the wind to the right of the landing area. This really demonstrated the height of the thorn bushes... they must be 8-10' high in places. I grabbed some crappy iPhone pictures which depicted the area.
Tomorrow is looking less gusty but will still be a bit higher than we would like.
See you then!!
Re: Weekend - September 21/22, 2019
Posted: Sun Sep 22, 2019 7:59 pm
Another fantastic morning at SP!! Temperatures were cooler for sure but the winds were light and there were lots of smiles!!!
Jerry was back and we had two flights with the club Apprentice. He is nailing every aspect of the hobby and those rusty fingers were soon limbered up with the sticks!
Frank was up again with Rick for another few flights. Better conditions today for flying for sure.
Jayla, daughter to Andrew C, was at the field and we were able to get her up for two full flights. She did great... first mastering beginner mode and then in intermediate mode. Smooth take-offs and level flight. I hope that she enjoyed the experience!
The last round of help was with Paul's P51. He and I were buddy boxed just to have another person nearby. We identified that he needed more power as soon as he entered level flight (after taking off).... we were determined to bring it down after it passed over the field under full power... but labouring for sure. It did not make it to the flight line and the motor had stopped. Into the thorns. Lots of gracious help from HEFA members and the plane was recovered.
- We figured that the 2200mAhr 3S battery was the culprit but it was reading 3.9V per cell. So that should have been ok....
- We checked the internal resistance - less than 10 milliOhms per cell (4 milliOhms and 5 milliOhms in the others)... should be okay.
- We installed a power meter in-line and noted that the large 4-blade prop was pulling in excess of 50Amps... and that the voltage dropped significantly during that heavy draw.... below 10V. The battery is a 30C so it *should* be able to provide 66Amps but could be over rated.
- A 4S battery (70C) was tried and I believe that results were similar.
I am guessing that the ESC shut-down on overtemperature or excess current. It is supposed to be a 40A ESC stock.
Re: Weekend - September 21/22, 2019
Posted: Sun Oct 20, 2019 4:18 pm
Re 3s2200 at 3.9v.
A reading of 3.9 volts per cell, sure is a loong way from fully charged. 3.85 volts is the 30% storage voltage for long term storage of LiPo .
So I suspect that the battery was at least part of the problem. Also was the pack broken in or brand new?
A new pack has to be used at lower current levels and partial discharge and charge for 3-5 cycles before it starts to deliver full capacaity. During this process certain chemicals applied during manufacture get broken down. Unless buying packs that are tested and balanced, some of these chemicals may still be present after 3 full cycles.
Also under load, a pack that shows 3.9 volts would likely trip the Low voltage shutdown of the ESC under full load. Did the flight controls work when the motor shut down?