Calculate Flight Time

[protyne]

Found this formula on RCGroups to calculate flight time -

(Battery Capacity * 60) / (Average Current * 1000)

Is it accurate for me to calculate my flight time as follows:

Half Throttle: 7A ; Full Throttle: 22A

Flight Time @ Half T: (2170 * 60) / (7 * 1000) = 18.6 min
Safe Flight Time @ Half T: 0.75 * 18 = 13.5min

Flight Time @ Full T: (2170 * 60) / (22 * 1000) = 5.9min
Safe Flight Time @ Full T: 0.75 * 6 = 4min

Therefore if flying with 50%-75% throttle - 10min is definitely not an issue?

Is this the way to calculate?

Thanks!

[Artyspec]

7X1000 is to get ur amp draw in mA instead of A cuz ur batt is rated by mA/h. Yea, so your battery ma/h divided by your mA draw gets you the fraction of an hour your battery will last you. You then multiply that by 60 to get the number of minutes. That's the explanation for the formula.

Back to your qn, yes, 10 mins shd be no probs cuz you hav to rem that there is also a reduction in amp draw in flight as your prop unloads in flight. Safe bet is around 70% of ground amp draw. If not, you can always depend on ur instincts and land when u feel reduced performance!

[Unorthodox_Sniper]

since our current drain measurement is normally measured in amps (A) and not mA, instead of having to deal * 1000 in the formula, a slightly easier way to calculate flight time is to always remember to use Ah instead of mAh for batt capacity. so if your batt pack is 2170mAh, the capacity is 2.17Ah
so the formula => batt capacity / current drain = time in seconds then you just * 60 to get the results in minutes.

so eg, a 2.17Ah batt on a full throttle current drain of 22A
= 2.17 / 22 = 0.0986 * 60 = 5.9mins

However do be careful when you are calculating the above on a lipo because the above flight time is when you drain your lipo to almost zero capacity which is very dangerous for lipo as it means it could go below 3.0v during flight when the motor is spinning

In this thread which I posted http://www.daddyhobby.com/forum/showthread.php?t=16231 the capacity of lipo is roughly calculated as below.

4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.5V – 0%

When you land and find that your lipo are about 3.5v per cell the damage may already be permanent because during flying when the lipo is under load the voltage would already drop and go below 3.0v so the best is to keep each cell at 3.8v after you land.


there are 2 schools of thoughts that a prop will unload during flight so you can take about 70% to 90% of the ground static current drain. but some will say if you fly headwind your motor actually needs to work harder so current drain can in fact be higher.

for me personally, as I normally fly full throttle about 75% of the time if my calculation is 6 mins of full throttle flight time I will still set my Tx to 6mins and I will prepare to land when my Tx gives the 5th minute warning. And when you feel your plane is losing power it's time to land and not wait for the Tx to beep because as lipo gets older or over-used they hold lesser charge and your flight time will be shorter. And it is always good to have some batt juice left in case of aborted landing eg someone accidentally appeared in your flight path and you need to make an emergency pull up

[Artyspec]

Oh, i think the flying headwind rule does not really apply as when you fly headwind, your airspeed does not change, only the land speed does. Therefore, the prop should, in theory, unload the same whether in head wind, tail wind or no wind. Also take note that if you measure the voltage of the cells immediately after landing, the voltage will be lower than what the voltage would be after letting the cells cool down.

[protyne]

Thanks for your advises guys. I think I might be using an over sized motor for my Formosa or I'm too newbie so 70% throttle is as much as I can take.

Will try sticking to 9min of flight and the last min for landing/aborts/landing and take my voltage from there.

Noticed over the wkend I tried 6min (50-70% throttle) on 2 different batt: FP 2170mah 25C and DN 1350 20C.

Checked both batt 15min after landing, both registered 11.6v

Question is won't the bigger pack return more voltage reading after equal flight time as compared to the smaller pack?

Note FP is 175g and DN is 125g. The 50g of load made any significant differences?

[trickster]

Thanks for your advises guys. I think I might be using an over sized motor for my Formosa or I'm too newbie so 70% throttle is as much as I can take.

Will try sticking to 9min of flight and the last min for landing/aborts/landing and take my voltage from there.

Noticed over the wkend I tried 6min (50-70% throttle) on 2 different batt: FP 2170mah 25C and DN 1350 20C.

Checked both batt 15min after landing, both registered 11.6v

Question is won't the bigger pack return more voltage reading after equal flight time as compared to the smaller pack?

Note FP is 175g and DN is 125g. The 50g of load made any significant differences?

Protyne,

You can do what I do...
1. Plane - Check
2. Motor - Yup working
3. Esc - Check
4. Lipo - Charged
5. Prop - Got
6. Just fly
7. Batt hot and like a ballon ---- STOP!

Hahahahahahahahahahahaha!!!!

Save alot of Math!

[edmond22]

For me, I have gotten myself a charger that tells me exactly how much mah I put back into a battery when I charge.

I normally get some flight time simulated figures from Motocalc (indispensable if you are designing or building your own craft). You must check those amp draw with real life amp draw to see if they are close. Take those simulated timing, half them and fly. Charge the batts and see how much you put back. that should give you a really good idea on the kind of timing you can use.

This method works for me, just dun forget to activate the timer like I did twice . Hover and harrier until I elevator to the ground lol.

[durex]

Protyne, for me, I set my timer on the transmitter for 5mins, when it beeps at 4min 30sec, I know its time to land. I flew all my plane, big or small, using this timing, these way I know I'm not pushing the batteries and also to avoid further stress on my eyesight...

[protyne]

Guys i've adopted all your methods....

1. Charge and fly like trickster said.

2. Set timer for 6min and fly and land within time stipulated as Alfian said

3. Check amount to put in after flying as advised by edmond.

So far 6min - 10min flying time depending on batt capacity. Kinda not enough and most of the time thinking of pushing the pack for few mins more. But decided against to prolong batt life...

[HotDogBun]

Protyne,

You can do what I do...
1. Plane - Check
2. Motor - Yup working
3. Esc - Check
4. Lipo - Charged
5. Prop - Got
6. Just fly
7. Batt hot and like a ballon ---- STOP!

Hahahahahahahahahahahaha!!!!

Save alot of Math!

Sibei reckless Wait balloon gets too big you see one big fireball in the air
Oh, trickster's "double" appeared on the Picture thread with the beaver
" hee haa "