Winter Flying, Batteries and Cold Weather
 

In my area we fly year round between rain storms. Our clear Winter days can be down in the 20-30F range quite often. Most planes I fly wouldn't be too much of a concern if a battery went too flat and I had to land dead stick (other than it is hard on the batteries). However, I am currently working through the process of learning to fly a twin and it won't really fly dead stick or power reduced (to a point).

My question is: For fairly new batteries (less than two years) how much should the flying time be dialed back to avoid over-discharging the batteries or worse having to land dead stick or with too little reserve power?

Thanks,

Dave

There are too many variables to hazard a guess at flight time. Someone may guess on a percentage less flight time than on a 'normal' flight. But it would still be a guess.

I could depend on how charged the packs are, how long they have stood for, how cold the packs are, how much additional power is used, etc etc.

What's the twin ?, if it wont glide, (it won't really fly dead stick or power reduced), I can only assume it has a lot of drag, or horrendous wing loading.

I fly twins, (and a fours), and as there is always that risk of one motor cutting before the other I get a feel for when the motors are staring to loose their edge as the volts start to drop. Then it's gentle flying and start the landing circuit.

During the winter, try to keep Lipos warm, something like an insulated box or bag. Lipos loose their edge quicker if flown cold.

A while back, I did some testing on the 2300 Mah A123 cells, both at 75 F and at 32F. There was not much difference in voltage at a 15 ampere load. Didn't go any higher in current since that was the limit of my West Mountain CBAIII battery test unit.

Dave, I have similar winter flying conditions here on the West Coast of Canada, and don't find that the batterries lose that much power on cold days, as long as you keep them warm between flights. I precharge at home, and keep the packs in the cab of my truck during transport. At the field, the next pack to be used goes in an inner pocket of my padded vest, so it's getting body heat. Just be sure there's no metal of any kind in thast pocket! You can also cover up your cooling air intake on the model, so that the heat generated by discharge isn't lost too quickly in flight. I see a very slight loss in performance, and reduce my flight time by a minute, just in case, but have never had to land due to LVC in cold weather. Dress up warm, bring hot drinks, and enjoy that lovely new twin of yours. ;-)

Brad

It is a Cessna 310 with 55" WS and about 38 ounces. It is pretty lightly loaded but when it goes dead stick I feel like I am running out of elevator for sure. I was pretty conservative at the field that last time out and every one else was complaining about loosing power and battery capacity. However I fly a lot and I keep my batteries ready, fully charged and don't leave them sitting around to discharge. I fly them down to about 30-35% capacity and then recharge and every once in a while I do a controlled discharge, balance and recharge.

I am just being careful since I have had a long run without crashes and the planes I am building now have a lot of time invested in them.

Thanks,

Dave

I fly as much as possible and even in winter - If I can get a clear calmish day ... temps can be down to -20C at times ... last winter we hit -35C one night.

I keep spare LiPo in pocket to stay warm ...

One day - vid is on Youtube ... the 450 Heli would barely lift and stayed just a few cms of the ground ... showing that extreme cold did make a difference. The Lipo ... a 2280mAh 3S 30C good condition pack just couldn't work enough to generate heat and warm itself up ...

I have been thinking about pocket warmers as sold by Camping / Trekking shops .... maybe a PW fitted into a box could keep LiPo's ready for use ?

Anyway - flight times as original post was talking about ... I think if you fly to 45% or so on a LiPo as normal - then that's good enough in winter as well as long as temp is not extreme as I tried ... then to be honest - you can forget it as hands / fingers fail before the model !

I'm on the West coast of the U.S., at a high latitude, so it's cold and wet. I use a timer, and keep my winter flying to about 50% or so discharge, and have never had a problem.

I found they crap out in about 6 mins, but then, so do the fingers. :D I found the smaller ones, around 800 ma and smaller lose it even sooner as they don't have the mass to stay warm. I found the next size bigger prop helps, as the batt stays warmer. Bonus is a little better performance with the bigger prop, plus the denser air. If you can keep them warm in the plane by closing off the inlet and outlet ports you can get the full summer run time out of them. I use these little baggies on the profile planes made from the clear foam that electronics comes wrapped in. Tapes together with scotch tape and velcroed to the side of the plane with a velcroed closure. If the batt. comes out warm in your hand, your good to go.

Keeping them warm is the key. And don't buy those disposable hand warmers, that can get expensive. Simple dried corn or beans. I used to use a small bean bag size of it.
Minute or two in the microwave, toss it in a small foam cooler with a wash cloth over it. Kept the packs toasty all day long. Also corn or beans when heated give off moisture, the cloth also protected the packs from that.

And as a bonus, when I couldn't feel my fingers anymore, that nice hot cloth was a god send.

I picked up the cooler from the local pharmacy. Roughly 12x12x12 and had 3" thick walls. Was something they had meds shipped in. With the warmer inside, I could leave the cooler outside and the packs were still nice and warm.

Given that most of us have foam laying around, either from house repairs or our attempts at model building. That's same naterial basically as the cooler ... so with hot-glue gun and a sharp knife etc. - you could easily knock up a box to keep LiPo's warm in.

I will be doing it oncde I get home ... as winters drop to crazy numbers where I live ..