Which lipo? A first world problem.

[Steve Colman]

About to invest in some 5S lipos to get a small performance improvement over the 4S lipos I'm currently using in an Avios Grand Tundra. All the electronics are fine up to 6S and I will be changing the prop to keep things within amps and watts limits.

 

I have a choice between 3300mah 40c or 4000mah 55c. The 3300's have around the same Wh as my current 4S and I'm assuming that provided I keep amps to a similar level when flying I'll achieve similar flight times of around 6.5 minutes, with the 4000's enabling slightly longer flight times of perhaps 8 minutes. The 5S 3300's are virtually the same weight as my 4S 4000's and the 5S 4000mah lipos are 150g heavier. If the C ratings are to be believed perhaps the 4000's might be a better long term and performance bet.

 

Because of an offer I can get three of the 3300's for just 7 euros more than 2 of the 4000's.

 

Which would you buy?

 

 

[Simon Chaddock]

Steve

If you keep the amps the same and the battery is the same weight you will suffer a 25% drop in duration if you use all the 25% extra power all the time. At the same level as your current performance you will achieve the same duration more or less. 

The 4000 mAh 5s battery would go some way to restoring the same full power duration you currently have with the 4s. Of course the extra weight would take a touch off the performance compared to the 3300 5s.

It comes down to what compromise suits you best.

Remember a 6.5 minute flight is only taking an average of 10c out of the battery. 

As a skinflint I would go for the three battery offer!   

[andyh]

I'd get the 5S 3.3Ah's just so they're the same weight as the 4S 4Ah's so you can use either without affecting the CofG.

[Andy48]

Steve, I think your view of performance is over simplistic. There are more factors to consider rather than just battery voltage and current.

1. The Tundra is a very draggy plane, and as drag is proportional to the square of the speed, thus adding more power will probably not result in any noticeable performance gain.

2. Adding weight, in effect reduces performance, hence above comment also applies.

3. What do you actually mean by "performance"? Go faster, longer flight time etc.

4. If you are after a longer flight time, don't fly on full throttle, once you get above 2/3 throttle with an electric plane, the current consumption rises dramatically with very little to show in terms of performance, linking in also with point (1) above.

5. Perhaps also consider battery life. Higher "C" ratings are generally better here, as is a lower current consumption.

 

I fly with a 5S 4000 in my balsa Wot 4, together with a larger motor and ESC, mostly to get the balance right. Its obviously a much heavier plane. I can easily get a 20 minute  flight out of that flying at 1/2 throttle. It will take off easily from grass with less than half throttle too.

[Steve Colman]

Thank you for your replies gentlemen.

Perhaps I should clarify what I mean by "performance" in this instance.

 

Firstly though, I must highlight that generally I rarely fly at full throttle, mostly preferring to cruise around doing low and slow passes along the runway with flaps down. As such, the Tundra flies in a manner that I would describe as "acceptable" on 4S but also somewhat lethargic at certain instances which is my main concern.

 

It is capable of flying loops, rolls, inverted flight and performing some basic aerobatics if I so wish when pushed. It's the "when pushed" bit that concerns me, as I get the feeling that it is lacking in oomph and could do with a tad more. This is especially so with reference to the low and slow flying with flaps down scenario as I don't feel the model has anything in reserve to enable me to punch out of a situation quickly with confidence.

 

So, essentially I'm wanting some reserve power to provide me with some headroom if and when needed. I could of course go to 6s but personally I think that's way too over the top. However, many do fly the Tundra on large 6s packs so I don't think the added 150 grams of weight for the 5s 4000's is too much of a concern given the model weighs in at 2.9kg.

 

Of the two battery choices I have, I am swayed towards the 4000's because I think it will cope better with how I like to fly the model. If the 3300's weren't on offer I probably wouldn't consider them.

 

     

 

 

Edited October 29, 2021 by Steve Colman

[Andy48]

In that case I'd experiment with different props, checking the current draw before buying any batteries.

[Ron Gray]

My Grand Tundra is powered by 6s 5000, brilliant performance and can do some crazy manoeuvres. I tried it on 5s but soon went back to the 6s!