flight time ?

[hawkeye20]

could someone tell me what would be the flight time on the stock BNF cub with stock battery at full throttle from take off to landing. would like to know so I don't fry my batteries the only so called extra weight on plane is a keychain cam and 3'' lite wheels. thanks

[iflyforfun]

Hawk, if you are trying to calculate a run time for your batteries then you need to measure the battery voltage right after landing. The theoretical calculation can be done but will give to no real world usable info. Ok lets go over this:
A 1300mah battery should be able(if you believe the lable) 1.3 amps for 1 hour.
If your using a 2200mah battery then it should produce 2.2 amps for 1 hour.

lipo capacity: 1300mAh
Divde that by 1000 to get A/h = 1.3

Now, if you knew how many amps your motor was pulling at full throttle then you would just simply divide the 1.3 by the amps and the answer should be your flight time in seconds.

I think(not 100% sure) that a stock super cub ESC is rated for somewhere around 13 to 15 amp. So lets asume that the motor will pull 15amps.

Take 1.3 and divide by the AMPS you will be pulling (15):
1.3/15 = .087 <-- This is how many hours you can fly

Multiply .087 by 60 to get minutes.

.087 x 60 = 5min 22sec

Do you really want to stop flying after 5 min because the theoritical calculation says you only have 5 minutes flight time. We all know that a SC can fly much longer than five minutes. So the real question should be, how do we calculate the safe flying time. 2 things will kill your lipo. Heat and over-discharge. The only way to tell if your going below a safe voltage is to measure it. I will mention that many ESC's have a LVC(low voltage cutoff) but many(like mine) have the high setting at 3.2 volts. That is still to low. You really want somewhere around 3.5 to 3.7 volts per cell.
You have a couple of options, you can buy a tiny voltage cell checker like this one:

www.headsuprc.com/servlet/the-1994/Battery-Checker/Detail

Or you can buy a good quality lipo charger that also reads out the cell voltages. (i have a icharger206b) and that does everything except cook eggs but I never take it to the field. I have that little voltage checker and it works great if you want to get a quick voltage reading.

So this is how you calculate your flight time.

1. Take a fully charged lipo and fly the hell out of it while keeping track of your flight time. If you can and your skills allow it then fly full throttle for about 8 minutes.
2. Land and check your cell voltages right away.( dont wait more than a minute because the cells voltages will start to rise again. You need the reading right away.
3. If your above 3.5 or 3.7( i use 3.5 ) then you now know that you can fly a minimum of 8 minutes at full throttle and not overdischarge your lipo.
4. Using this method repete the test untill the voltage is down to 3.5volts(per cell or the lowest cell is 3.5).
5. You now have your worst case full throttle flying time. Set your flight timer for 30 seconds less than this time and you should be good to go!!!!!

I keep a battery log and after each flight I punch my battery number and cell voltages into a spread sheet I have on my Iphone. This helps me keep track of any problem lipos.

Ifly

[hawkeye20]

thanks ifly that's helps the math part sux was never good at math oh

well i do have a pretty good charger this is the charger I have.

www.hobbypartz.com/thac6smbachw.html

I will check on the other part you talked about again thank you

[flydiver]

Sept 12, 2011 5:18:49 GMT 1 hawkeye20 said:

.. full throttle from take off to landing.

ifly gave you extensive excellent advice. I'm way too lazy to do that kind of figuring.
I would add this; do you really plan to fly an entire flight at WOT? I doubt it but, if so, you can do the calculations pretty much straight up. Most folks don't so the math doesn't work entirely.
It's like saying I have a pitcher full of water and I plan to pour it out at varying rates-when will it be empty? Without knowing the exact variables you can only guesstimate.

A useful rule of thumb is 1/2 throttle consumes ~ 1/4 the amperage. As you back off from WOT the amp draw goes down.... a lot.

Mostly you have to do this by 'feel' and experience, coupled with a decent timer and a good field voltage checker. you do not want to trust the LVC setting in the stock Cub, it's too low > ~ 8.8-8.9v. Many other ESC have LVC that is too low also. Make that a shopping criteria when you go looking for new ones.

[hawkeye20]

thanks flydiver no not going to fly at WOT I just wanted some Idea on how long flight time I could get if at WOT so I could figure how long flight would be at 1/2 throttle.

[flydiver]

Sure, but like I said, half throttle is not half time.

[10mistakhi]

Man I learned some stuff thanks Iflyforfun.

I bought a timer at dollar tree and drilled out the hole in the back and stuck on my antenna. I started out with 7 Min's and would test it after that and have moved up to 9 Min's and still have plenty of time to get it back on the ground. I just started this and figure I can safely get to 12 Min's or better but I keep testing it each time until I know I'm not dropping below 3.7 per cell.

[iflyforfun]

Very good Mistakhi!!! Glad you took the advise. Keep working through your lipos and soon you will have a safe running time that you can trust!!! Just remember that your flying style will dramatically change your flight time. You want to be pushing your plane as hard as your abilities allow when figuring your flight time. This will give you a saftey margin when flying normally.

Ifly

[freediverga]

I thought about doing this test on the ground with plane secured at half throttle though. Can you leave the volt check connected while its running or can you plug it while its running to get reading? I'm guessing it has to shut down to get a good reading.

[flydiver]

Do NOT do extensive motor tests with a stationary plane. The motor and ESC rely on air movement to help cool. You can potentially burn something up.
Short bursts of a minute or so are fine unless you notice things heating up.
The prop does not provide the cooling you would expect as there is little air movement near the hub where the motor is and the ESC is buried inside. That's what those holes in the Cub are for > ventilation. Very important.

You got one of those little matchbook voltage checkers? Yes, you can leave it hooked up. In fact you will notice that the voltage sags to a lower level the more throttle you give it. This is the actual flight voltage and that data can be more useful than the resting voltage. There is always rebound with resting voltage-that's why you are looking for a seemingly high 3.5 to 3.7v/cell at rest. That will correspond more with 3.0-3.2v/cell under load, depending on the load.

A wattmeter will show this info along with watts, amps, milliamps consumed, lowest voltage reached, AND hold on to it after you shut the throttle down.

Pay attention to the after flight voltage (write it down if necessary) along with flight time. Then see how that corresponds with the mA put back vs. the claimed capacity of the battery. It's best if you are putting back about 80% or less.

[freediverga]

Sept 13, 2011 23:56:29 GMT 1 10mistakhi said:

Man I learned some stuff thanks Iflyforfun.

I bought a timer at dollar tree and drilled out the hole in the back and stuck on my antenna. I started out with 7 Min's and would test it after that and have moved up to 9 Min's and still have plenty of time to get it back on the ground. I just started this and figure I can safely get to 12 Min's or better but I keep testing it each time until I know I'm not dropping below 3.7 per cell.

are those runs at full thtottle