With that size battery, you'll end up at pretty much the same weight, and the same amount of energy going airborne.
That means the speed, thrust and flighttime will all be very similar to the 6s5000 setup.

It would not surprise me if the ARCs on 4s outperform some of the cheaper motors being used on 6s!

Even if he does end up at same weight or less, with 170a combined on 2x4s 3700mah parallel (7400mah combined) he ain't getting much flight time.

7.4ah (60) = 444

444/ 170a = 2.6min

2.6min (.80) = 2.08min if WOT flight time

So if 50/50 on the throttle then he should be landing @ 2.5min no where near my landing on 5000mah 6s which has me landing @ 3.5min and still putting back 25-30% into my battery on charge.

I think the "Non-3D" 4S version of the Su was a 2D version..... just flat depron pieces....

Originally Posted by PeterVRC

I think the "Non-3D" 4S version of the Su was a 2D version..... just flat depron pieces....

ya a lighter and cheaper alternative to the 6s setup.

Originally Posted by IntheTubeDeep

Yes you're correct I planned on 2 x 4s in parallel, on my Su35 running 6s I have 2 x 3s in series, 3s 4500s and a set of 3s 5000s, they weigh approx 400g each x 2 = 800g, and the CG was good with these up against the cockpit wall(AS far forward as possible) stil have plenty of adjustment room for heavier batts. Now I'm leaning towards 3700 or 3850s

You know what.... it may just squeeze by as a sport flier so have fun with it.

Two 4500 40C to 5000mAh 35C batts will generally be over 1kg to get factory performance. I glanced back at the numbers and miscalculated. The 153g ARCs are heavier. I was thinking motor and fan not just motor. The factory was 179g. Mine with the 2W25 110g came out to 181g each. The new CS units are heavier 75g ea so with the ARCs you may be 456g vs factory 358g (98g diff). Add 8g on the ESCs and the extra 200-250g of extra battery weight to approximate the same run time, you have an extra 306-356g to produce about the same as factory thrust. It too is spec'd at 3kg on the bench but does more like 2.8kg. So thats vanilla'd and we haven't spoken about External 8amp BEC or what weight your servo choices have added up to. You may come in around 3.1-3.2kg with 2.8kg of thrust. You can go down on the battery size but capacity is more important to you on 4S than it is for us on 6S since we produce more power with less battery.
If it comes out the same as factory, thats a lot of extra money spent to just be on par with.

I look forward to the vid. and what numbers you get with the CS70/12 in the tube and in the air. Hopefully the CS12 will allow you to accelerate quicker and allow better throttle management.

I have a couple of Zippy Compacts, 6S 5000mah 25C packs that I use in my Euro. Can I use them in the SU?

Originally Posted by av8ersteve

I have a couple of Zippy Compacts, 6S 5000mah 25C packs that I use in my Euro. Can I use them in the SU?

As long as the demand is less than 125 amps (5000 mAh/1000)*C 25. I forget what your setup is but motor amp demand times two from batteries capable supply tells you if you'll fly or fry

Also Just try not to punish your battery flying WOT more than 50% of the time. The heavier your thumb the more likely your battery will puff, if you want your battery to last.

Originally Posted by Maxthrottle

As long as the demand is less than 125 amps (5000 mAh/1000)*C 25. I forget what your setup is but motor amp demand times two from batteries capable supply tells you if you'll fly or fry

It's all stock setup. I'm getting ready to maiden. It was set for today, but going to be tomorrow.

So the 25C packs should be ok as long as I'm not full throttle all the time, right?

Originally Posted by av8ersteve

It's all stock setup. I'm getting ready to maiden. It was set for today, but going to be tomorrow.

So the 25C packs should be ok as long as I'm not full throttle all the time, right?

Should be ok with stock setup. If I remember correctly stock esc's are only 55amp. Still dont want to push battery too much though as you are approaching its capacity.

Originally Posted by av8ersteve

It's all stock setup. I'm getting ready to maiden. It was set for today, but going to be tomorrow.

So the 25C packs should be ok as long as I'm not full throttle all the time, right?

Especially during the last minute or so of your flight time. Stock runs at about 50amps peak maybe 110 amps combined; may be more. Its fine periodically on the battery the same way its fine to go over the peak rating of an ESC for under 10 seconds or so. Only with a battery its a chemical pack not solid state like the ESC. As you deplete a lipo, pushing too hard against the compound can permanently alter the composition and the battery either puffs or progressively lacks ability to hold a charge.
Thus the use of higher C count batteries have advantages with EDFs because the properties of the compound not only has a lower resistance and performance but it also its chemical properties remain in tact longer.

25C is better for props because prop jobs often with much lower wing loads have much less demand at the end of the flight. An EDF you still need a lot of juice to make the field and hold altitude etc. So note the formula, the volume of stored amps, 5000mAh potential stored energy, times the C count rating. As the amps deplete, the stored energy depletes and its no longer 5000*C but 2000 or less so the deliverable amps from the battery start dropping and intern threatens the battery composition. So for with that C count the do not exceed the last 20% is more important to your battery as V8 explained.

Ok, So, what should be my MAX flight time with 25C? No go-around left, just have to land time. You guys are better at running the numbers than I am. Thanks.

Originally Posted by av8ersteve

Ok, So, what should be my MAX flight time with 25C? No go-around left, just have to land time. You guys are better at running the numbers than I am. Thanks.

This is the exact setup that I use. I use to fly for 4 mins then land and have around 30-35% of the pack left. I always check the pack % remaining on my gizmo. This setup leaves a couple of missed approaches. I now fly for 3:45 with a flight type of 1-2 mins of vertical flips, hover etc. The rest of the flight is varied with loops, rolls, 4 point roll and stalls. A couple of low passes and the buzzer goes off. Setup for landing which is usually the first approach and taxi back to the pits. Again 30-40% left of the total pack. I generally fly very scale which is an average of 70% with occasional full power climbs. I would start at 3 mins and keep checking until your routine is nailed and increase accordingly.

Hope this helps.

Mathematically.... you will draw about 100Amps or so - the low C having high IR will limit the current draw, compared to if you have higher C batteries.
5A (5000mAH) / 100AMps = 0.05 hrs x 60 = 3.0minutes
That is if you drew 100Amps all flight.

You most likely wouldn't - but certainly many people could try! hehe

5000mAH x 25C = 125Amps "Capability" for the battery.
For a batery to cope 'somewhat esily' which will then allow it to operate at just a 'warm' temperature, instead of hotter, you need a battery with a 'capability' that is 1.5x what you will use, based off the WOT current draw. That is my minimum I try to stick to, or even 2x. But in some cases, if you test the setup, you can go lower because of the way you might use power in that aircraft. So I do have some that are almost down at 1x the battery capability - more so if they are CHEAP and thus more expandable in the longer term calculations of costs.

So in this case, at 100 Amps area (could go a bit more at WOT really), that 125 Amps capability is marginal for optimal battery life/survival. What you will see is that you will come down with it hotter than a higher C would..... and more and more so if you deplete it more. Lipo's just get hotter and hotter as they deplete more.
eg run it down 2/3 and it is is temp X, but go to 3/4 and it will be hotter than X - even if you flew identically in power terms. It is not actually exponential, but it is some faster and faster rising curve like that... ever increasing heat for the same power used.

What this all means is that:
1) You really should test the current draw with a power meter on the ground first. So you can work out all the base numbers to expect. Then you can already know if things are going to be marginal before even trying, or that they should have good leeway etc.

2) Test fly it...a SHORT flight. Probably 2.0 minutes to landing. Prefereably no more than 2.5mins till stopped.
Most 'half usefull assessments' of what battery to use will at least come out within a reasonable accuracy of what it can do. eg like here, mathematically 3.0mins of WOT. So 2.0mins will keep it well within that range, in case things are quite amiss in those assessments....
It also assures you have not taken the battery down to 2/3 or more, where heat starts to rise more rapidly.

Land.... go and check the battery temp..... this will tell you how much it struggled, and what it was like at this shorter safer time period.
If it was just 'warm', you can pretty well say you are safe to go for the 3.0mins as calculated - you don't even need to know the capacity that was used, because if it was only warm it is all but assured it was WELL short of using it all. You still want to check the recharge amount later (mA put back), but you can already safely know it was nowhere near 80% used.

If it was 'hot'.... now 'hot' is a relative term, but 50degC makes you go "OUCH!" and it won't burn you, but it is getting close to that. "Luke warm", well I will take it that anyone knows close enough what luke warm is... you have no 'watch out for this' response to such a lowish warm temperature. So for "hot", it is lower than the 50degC 'ouch!', but hotter than luke warm and you will be thinking "this can't be too good for something (except a heater!)". So at that level you are in the ball park of as hot as you really want to be seeing it!
This will also mean you have a problem... it couldn't even cope with 2.0 mins adequately. Maybe it really was marginal and will be ok overall... but it means TEST things!! You are not in the range, like the first example of it being cooler, this is no issue at all so I can just use it as it is (other batteries and fly again).

When it is cold, recharge it and see how many mA it needed put back. Because the heat you felt can be from one, or both, of two reasons.
Heat will come from excessive current draw.... so even though the battery 'capability' was 125 Amps according to manufacturers specs, the truth will show when you DO use it... you will see what that particular battery can really do, and/or brand, versus 'claims above reality' (lol) etc.
Heat will also come from depletion of the battery.
So there is an interaction you need to try to separate.... how much heat was from current, and how much was from depletion. The recharge will give good info on working this out.....
If you used towards 80% capacity... or went further than that... than a lot of heat will have come from that. How much?? Well, that needs experience to just 'know' that. If it only used 50% capacity (possible because even though you 'flew 2 minutes' out of a potential 3 minutes, you would not have used WOT all flight, thus could easily have used only 50% or even less) then the heat was predominantly because the battery was over-stressed delivery the currrent (Amps) that you used. This straight away means that at least THAT battery was not up to the task.. and probably that 25C isn't.

You MUST do a short flight (or flights) FIRST!!! It is to save your battery from excess duress. It is to save you possibly ending up with no power, if it drains too much and the battery heat drags its power right down. In the very worst cases the battery can get so hot it bursts into flames!!
Mathematically I would expect the 5000mAH 25C will at least be on the lower end of 'acceptable'... if you used 15C it would probably be more towards "here comes flames!" LOL. So you should not have to be worried about this 25C one... just fly that 2.0 mins test flight to CONFIRM things!

If you can test the current (Amps) draw BEFORE flying it.
If you do not have a Power meter.. BUY ONE!! They are pretty well a MUST HAVE thing for electric models, especially EDF's more so than Prop aircraft.

You want one of THESE (below). There are tons around shops, eBay etc. All this same design. HobbyKing has one of teh best prices for it.
https://www.hobbyking.com/hobbyking/s..._Analyzer.html

For myself, I would NOT use 25C is this plane. I have numerous twin 70mm and 90mm, and they generally run from 90Amps out to 120Amps. Even the 90Amps level ones are a bit tough on 5800mAH 30C - which is 5.8 x 30 = 174Amps 'capable'. Part of it is because they are 'cheaper' brand batteries, which will have a bit higher IR than a more expensive battery.

Side-track:
BUT, I did tests of buying a Turnigy Nano 25C, which are much lower IR than average/cheaper batteries, against a plain Turningy 25C version and they ran NO BETTER at all. Undetectable in the plane.... only smallish static test differences too. I didn't do a full discharge static test, and I SUSPECT the Nano would maintain the higher power levels for longer - they should..... but in flight you couldn't tell a thing. I would think you need to really do detailed 'checks' to see the difference - I am sure some difference is there. But you would need to have some way to measure things, other than just by sight. Speed needs ever increasing power just to rise the next 1kph more.... thrust to weight is almost impossible to measure unless you hovered and saw a line of sustained climb over 'cant do it', and once away from that line it becomes imeasurable visually, like speed. (unless LARGE difference - which a normal to Nano will not show)

So anyway:
My Su draws between 110A and 120a (max, and of course not all flight ) and the 5800mAH 30C is not overly impressed with it. it is OK in temperature terms, but getting to heat levels I consider "Just passable but I would rather not".
I wouldn't even buy a 5000mAH 25C for it. At 5000mAH I would want 40C ("200A capable" to have more towards the 2x leeway), and I have some 5000mAH 65C Nano's but I don't consider they were really worth the extra cost they were. They are better, but you pay a non-linear ratio for the result.

OH!! Another good static test is to check the VOLTAGE the power meter shows, because higher IR batteries will drop more voltage across them, and that leaves less for the real use - the motor. This is where you will see a better battery flex its muscles..... but you can choose to use higher IR batteries (lower C, or cheaper) to PURPOSELY limit total power too! As long as you do all those heat tests to ensure the battery being used is actually operating in an appropriate load range for it. (eg not getting too hot). The higher IR makes it drop more volts over the battery, and thus less current draw in the system (to the motor), thus a lower power operation - and lower current/power possibility means the capacity will last longer - at the slower speed etc it will also have. But very often aircraft models can fly MUCH faster than they truly 'should' to scale anyway, so very often you don;t truly need the max power you could get from "better" batteries.
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