Airborne Battery Pack Duration

[Tosh McCaber]

Having somewhat reluctantly converted from i/c to electric, what bugs me about lipo batteries, apart from the constant background danger from their overheating/ catching fire/ failing, is their short charge life. Compared to my 10- 15 minutes flight time with my previous i/c powered aircraft, I am constantly looking at the stop watch starting around the 6-7 minute time, to make sure the battery won't run out on me.

Has anyone any inside knowledge of any battery developments on the horizon to produce a more efficient cell, to give us a longer and safer flight time??

[Simon Chaddock]

Tosh

I fear if an energy density significantly higher than that of a LiPo is achieved it is likely to make make such a battery potentially even more dangerous.

The best answer for duration at the moment is to make best use of the advantages of electric to allow a bigger battery capacity without increasing the wing loading.

[Peter Jenkins]

Tosh, just consider that a whole FAI aerobatic sequence can be flown in 7 - 8 mins. Do you really need 10-15 mins flight time? That is a long time to be just flying around doing nothing in particular. You might be using the time to practice stuff but for me, and I stress it's for me, I am more than happy to have around 7-8 mins air time. I find that I've used up 70% of capacity in that time and don't really need to bother with listening to the timer which starts with a set of warning beeps with 30 secs remaining - it is set to 8 mins. That's more than enough time to land unless there is a queue of aircraft waiting to land.

Does your radio support telemetry? If yes, but you don't have the sensors then it's worth getting a sensor to measure the flight pack capacity remaining and using one of your alarms to sound off when you have reached the minimum remaining capacity limit you have set.

If you want longer flight times, and weight, space or CG position is not an issue, then see if you can fit in 2 packs in parallel to double the capacity and flight time back to your IC times.

[Chris Walby]

IMO I am with Peter J on this and find about 7 minutes more than enough time to fit a good session. I have also noticed that when instructing three or four 7 minute sessions are a much as a trainee can take before their performance starts to roll off.

The only times I need more time is on a maiden where I set the timer to 4 min and IC when I have a model that is hard to land and I might need a couple of go arounds to get it set up right.

I have an edf that did 2 min 30 sec and landed with 4% (killed the lipo) and the esc's were backing off....no chance of a go around with that! And as a flier it breaks a major rule (for me) in not having a viable plan B.

If you want longer flight times go back to IC, get a glider or go slope soaring

[Nigel R]

Is it just me, or would fitting a larger lipo be out of the question?

I try to get 8 min flight as a minimum, 10 minute if possible. Guess we're all different though.

[leccyflyer]

20 years ago one of the main criticisms of electric flight was that of short flight duration. Back then we were typically using 500AR cells in small models, which gave 500mah but flights were around 6 minutes, compared to up to 10-12 minutes for a similarly sized glow model. Moving up in model sizes the other common pack would be made up of 2400mah sub-c cells and again, 6-7 minutes was common, larger model, more power, more current draw needed. Motors were typically brushed and or geared, so mostly relatively inefficient.

Nowadays small models very often use the "standard" 3s1p 2200mah lipo, and the brushless motors are a wee bit more efficient, so flights of >7 minutes are definitely achievable, plus for models that can stand a bit of extra weight, packs of 3s1p 4200mah and larger are readily available, so you can cut your cloth accordingly. These are still lighter than the old NiCd/Mimh packs.

If stuck on using the 3s1p 2200mah packs then flight duration can be hugely extended by putting another pack in parallel, making a 3s2p 2200mah pack, which will then give you 4200mah to play with. Have a word with Jim J next time you see him at the field, he makes great use of those packs both in parallel and in series configuration. With a larger pack, as described above you can stay aloft until you get bored - have a look at Derek's Twinjet that can stay up for a fortnight with it's 3s1p 4200mah pack.

As pointed out above by several others though, personally I find around 7 minutes is perfect for me and I typically don't use a timer that often -not that I recommend that. With a model that I know well I can tell when the power is starting to drop off and time to land.

[Peter Miller]

I find that 6 or 7 minutes is quite a reasonable flight time. When I used ic engines I usually landed with quite a bit of fuel left as I liked to avoid dead stick landings.

With electric power I am learning to fly round on cruise power between sets of aerbatic manouvres which does extend flight times quite a bit.

[Rob Ashley]

Hello Tosh,

Must admit, I agree with you. The endurance of electric models is generally quite poor (this is also true of full size) - although there are some that have an endurance of over 10 mins and others may argue powered gliders much more. Most of my electric models have have flight times of 7 - 8 mins, which is a little short especially when you reach that time there is not much left for a go around if something / someone causes you to abort your approach.

I have an EDF F-14 that last 5 mins and no more on 2 x 6S 5000 mAh - another EDF model I have (a Hawk) lasts 7 mins if used very carefully on a 1 x 6S 5000 mAh, compare that to my longest IC flight of 42 mins they are in stark contrast. Granted most of my IC flights last about 12 mins, but 13-14 mins not uncommon if the circuit is active and I need to wait for an electric model to land before me. I actually find IC refreshing as I don't have to worry about throttle management or time as much, but still, most of my models are now electric.

Electric is a little more flexible than IC, in that a change of prop can mean the world of difference to the performance (either speed, thrust or endurance) setup of your model - much more so than IC. Alas, I don't think there is another huge step forward in battery tech for a while yet - although I could be wrong. Until then It really is worth spending time putting the correct prop on your motor as this will ultimately determine the amps you draw and therefore your flight time. I have often found the recommended prop from the manufacturer wasn't the one that fitted my setup the best.

Oddly I have more flights with my electric models (albeit shorter flights) as I don't want to take home charged Lipos - with IC that never seems to matter so I don't feel I 'have' to fly them. Odd really.

Rob

[Jonathan M]

I'd say it depends on the model, the power-train and what kind of flying you do.

e.g. on the usual mix of circuits and aeros, my balsa ARTF Wot-4 with its big 4s 4250mAh packs can very comfortably do 12mins with a 3547 motor (710 watts) or 10mins with a 4250 motor (980 watts), each typically ending flights with 30-40% capacity left. (The smaller motor is okay but the model really needs the bigger one to come properly alive, especially in any kind of breeze.)

Previous experience with a Max-Thrust Riot on the usual 3s 2200mAh pack limited flights to 7mins or so (from memory). I wonder whether smaller, lighter foam models are somehow less efficient - with more of the already limited capacity being used up just to keep dragging the airframe through the air?

By comparison, with exactly the same sort of flying, I used to get an easy 12-14mins with my 70FS powered ARTF Acrowot with plenty in reserve, and currently getting similar with the 46 powered Boomerang.

I'd say that 10-12mins is more than enough to do everything I want to do before concentration falls off, but sub 8mins never seems enough to get into my stride.

[MattyB]

Posted by Tosh McCaber on 20/09/2020 21:48:36:

...Has anyone any inside knowledge of any battery developments on the horizon to produce a more efficient cell, to give us a longer and safer flight time??

The internet is littered with tales of incredible new battery technology that is on the cusp of going mainstream, but so far 100% of those seem to have failed to emerge! The last great leap for us was Li ion Lipos, and that was how long ago now? Personally I wouldn't hold your breth for any new battery tech oin modelling for at least 3-5 years - even if something was discovered today it would take time to build manufacturing capacity, and even then all the production will be gobbled up for automotive and commercial use.

[Bob Cotsford]

What type of model are you flying Tosh? In my experience it's not hard to get 10 minute flights on electric - unless you fly non-stop aerobatics, 3D or an EDF. Admittedly small foam models like Riots or Wot4s can chew through packs in 6 or 7 minutes without trying but like Jonathon I could get an easy 10 minutes from a Wot4 ARTF on 4S throwing it around a fair bit, though on one occasion fling a mix of aerobatics and circuits and bumps I was airborne for well over 20 minutes!

Electric flight does need a bit more throttle management to get the best out of the power train compared to IC, but then I've flown a few IC models where 7 minutes flying meant landing NOW or landing quiet!

[FlyinBrian]

If you set up your tx timer to run when the throttle is above say 20% and set it at 8 minutes you will get a 10 min flight time if you a/ fly at less than full power most of the time and b/ climb high and do some gliding for a minute or two.

My Whizza is fast and climbs like a homesick angel but 10 min flights are normal with 20 to 25% left in the pack afterwards (4Max 2200 LiPOs)

[_AL_]

Multiplex fun cub with an upgraded motor & 2200 3s Lipo gives me enough grunt to climb vertical, or aerotow a 2m glider, or cruise around for 15 mins + doing touch & goes & low level aerobatics.

A 2700 battery would last even longer but I've never felt the need.

Use a radio with telemetry & you don't have to guess how much battery power you have left.

Al

[Tosh McCaber]

Having been given some background info and advice above, I'm a bit more relaxed. From what I see, even if the battery stops supplying energy to the motor, I still have the option to glide back to base, if I'm not too far away? I had visions of complete loss of control when the battery went low.

I actually started the thread to see whether anyone knew whether there was any alternative battery technology on the way. From the replies, it would appear not. However.... by sheer coincidence, I have just come across this article relating to that Electric Man, Elon Musk:

https://www.msn.com/en-gb/money/technology/teslas-future-battery-might-use-diamonds-could-transform-the-industry/ar-BB19iVzo?li=AAnZ9Ug&ocid=mailsignout

Who knows, in another 10 years- although using diamonds, the technology may be very expensive??

Thanks for the replies

[MattyB]

Posted by Tosh McCaber on 22/09/2020 17:52:33:

Having been given some background info and advice above, I'm a bit more relaxed. From what I see, even if the battery stops supplying energy to the motor, I still have the option to glide back to base, if I'm not too far away? I had visions of complete loss of control when the battery went low.

Yes, that’s correct - if you run to o the ESC low voltage cutoff you will still always have enough power for your RX and servos (assuming the BEC is suitably sized for the load on it under normal running of course). However it’s bad for you batteries to deep discharge them regularly, so try to use telemetry and/or timers in order to make sure you land with no lower than ~3.6V/cell.

[Cuban8]

Throttle management!! With IC the temptation is to set the throttle to a comfortable setting (sometimes full wack for a few) and leave it there for the whole flight. With a big tank it doesn't matter that much. Depending on the electric model type, try to modulate the throttle and only use higher settings when really needed, might need a bit of retraining of one's habits (particularly with EDFs) but it can give surprisingly longer flights with a bit of care. Don't forget that in windy conditions duration will fall off sooner as well.

Good and efficient motor/prop/battery selection plays its part as well of course - a rotten set up will never perform satisfactorily..

Edited By Cuban8 on 23/09/2020 10:15:10

[Adrian Smith 1]

Yes Cuban8 you are absolutely right.

Since turning leccy, most of my flying is done at 50% or 75% throttle depending on what I am doing. 100% throttle only gets engaged when entering aerobatic moves such at stall turn, loop etc. As you say set up is everything. I try to make sure the whole shebang is as light as possible from airframe to motor combo selection. On windy days I reduce the timer warning by 10% which has served me well.

[Tosh McCaber]

How long do you set your timer for normally Adrian?