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e-Electric General Discussion > About flying time
 
 
herbalist
Heliman
Location: Taipei, Taiwan

Hey all:
I have some questions about flying time.
When Lipo first came put, the demos all showed that ppl could fly elictric heli with hard 3d for 15 or even 30min.

But now after several years, most electric heli's flying time are still limited to 5~10 min.

So......... why?

and.......how? like make a trex500 fly for more than 15min with at least F3C aerobatics? is this possible without too much modifcations?
08-14-2008 08:47 AM
 
 
702nitro
Key Veteran
Location: Las Vegas, NV

hard 3d whats that? Today people are running higher headspeeds and doing smackdown 3d, which explains as mah ratings go up flight times still remain low and the same.

<b>ńīţѓő</b>
08-14-2008 09:03 AM
 
 
herbalist
Heliman
Location: Taipei, Taiwan

So ppl just like to push everything to the limits
08-14-2008 10:45 AM
 
 
MrMel
Elite Veteran
Location: Lidingo, Sweden

In terms of lipo development mah vs weight has NOT changed since the beginning very much.

Big development has been in how fast you can drain it and how good it hold its voltage.

RPM & Collective management is the big key for getting flighttime.
For sample, Each 100RPM extra will cost you 7-8% runtime.

I get 5 minutes hard 3D on all my machines, I have VBar on it, which is another way to "extend" the flighttime since it has less drag.


Team Autopartner - Team pilot
08-14-2008 05:53 PM
 
 
red_z06
Elite Veteran
Location: Dumont, NJ

Flight duration of 30min or two flights without changing the pack was not by choice.

Early on, the packs had 5-10c max dicharge compared to 50c burst of today's packs. So, in order to get the proper discharge current capacity, packs had to be parelleled to double or tripple the current output. As a result, while the voltage remained the same the capacity trippled or quadruppled. So, if each pack can handle 6-8min at 5c discharge, now you have a pack than can handle 4x 5c but at a 4x more duration. There were simply no other way back then.

But now, you hardly see parallel packs anymore so people can choose the cell size based on there flight time requirement as current delivery is there.

www.justinchi.com
08-14-2008 06:04 PM
HOMEPAGE  
 
 
fergus
Veteran
Location: Ireland

My first 10s lipo joker setup was 7400mAh packs ( two 5s3p packs in series). Now the norm is 5000mAh or less. As already stated the discharge capability of todays cells is the key.

Regards

Fergus
08-14-2008 08:27 PM
 
 
Richardmid1
Veteran
Location: Leeds, England

Hard 3D, smack down or whatever you want to call it requires the heli to be fairly light thus they use packs that will allow 3-4mins flight time. If your only doing mild 3D you can get away with using slower head speeds and big capacity packs that barely fit under the canopy and get around 10 mins.

Eat, sleep, 3D, crash, repair, repeat...
08-14-2008 10:31 PM
 
 
heli boi
Heliman
Location: Dothan, Alabama

So if one were to parallel a couple of small packs together it would yeild longer running times than one big pack? Under "normal" flying conditions that is...?
08-19-2008 06:43 PM
 
 
red_z06
Elite Veteran
Location: Dumont, NJ

3s2500mah + 3s2500mah parellel = 3s5000mah

So, if the big pack is 3s5000, and the pack health is the same, they should yield the same flight time.

www.justinchi.com
08-19-2008 07:23 PM
HOMEPAGE  
 
 
fergus
Veteran
Location: Ireland

if voltage remains the same ie 5s 6s etc. Then the larger the mAh rating the longer the flightime at the expense of higher weight. If this means using a 6s 5000mAh pack or paralleling two 6s 2500mAh packs the result will be the same. (provided similar C rated cells).

Things start getting a bit more complicated when the voltage ( series count) is changed as higher voltage will mean less capacity (mAn) is required to get similar performance. This is where watts come into play.

Regards

Fergus
08-19-2008 07:26 PM
 
 
splitboarder
Heliman
Location: San Diego, California

Im a newbie with a few questions on this. I have 2 packs 11.1 volt each 3s and 4350mah. Im using the Xtreme charger. I list charge the packs at the same time in series. I have been entering 6s 22.2 v 4350mah Should I change that to 6s 22.2 v 8700mah?

And I am charging at 4,2 volts per cell in the set up. It takes 1 hour to charge. Can I make it a bit faster charge? And how would I do that? Change the voltsper cell rating to a higher number?

I dont wantto burn them up but at the end of the charge they are room temp, not hot at all

Thanks
08-27-2008 11:20 PM
 
 
fergus
Veteran
Location: Ireland

Your right to ask. You should read up on this until you are very clear about it or the results will be disastrous if you do it wrong.

SERIES = s
PARALLEL = p

SERIES = positive of pack A connected to negative of pack B

PARALLEL = positive of pack A connected to positive of pack B and negative of A connected to negative of B

The thing to get your head around is SERIES increases VOLTAGE of the pack. PARALLEL increases CAPACITY (mAh)

Your packs are made up of cells each of which can NOT be charged over 4.2volts. 3.7volts is used for the nominal voltage of each cell. You have two 3s packs which means each pack contains 3 cells of 4350mAh capacity connected in SERIES (3s) 11.1volts (This is the nominal voltage not the full charge voltage which would be 12.6volts). The capacity is achieved through 1cell so the pack is actually 3s1p (For convenience the 1p is dropped) 2p and 3p packs are not as common nowadays as discussed already.


Here is what you are doing now :-

connecting two packs in SERIES. Its important to only do this with identical packs.

By doing this you are doubling the number of cells in series so doubling the voltage to 6s or 22.2volts.

You are not changing the capacity or mAh rating because you are not connecting in parallel. Your 'new' 6s pack is still 4350mAh.

You are charging at 1c if it takes 1hr to charge i.e 4.35amps approx. To increase the charge time you need to increase the charge current from 4.35amps. You should only do this if you are charging with a balancer which can shut of the charge current from the charger if a problem or out of balance situation develops. PLEASE BE CAREFULL WITH CHARGING OVER 1C. In your case charging at 9.7amps would be 2c (and would take about half as long).

I am not familiar with your charger so maybe someone can help with your specific example. The power rating of a charger will limit how fast you can charge and this is measured in watts. Watts is voltage x current. so if brand A charger is rated for 120 watts it can charge a 6s pack at a current of 4.7amps maximum (If this were your 3s packs in series that would be just over 1c and would mean a little under 1hour charge time)

As a side note - SERIES charging is not ideal as the two 3s packs may have a different voltage (As a result of being flown in two different flights for different times and under different loads) If you are connecting in series to charge then its important that the two packs are allowed to balance when connected to the balancer BEFORE being charged.

Regards

Fergus
08-28-2008 01:31 AM
 
 
splitboarder
Heliman
Location: San Diego, California

Thanks Fergus. Im clear on it now. I think I will just stay at the charging time Im at. I dont want to cook my batteries
08-28-2008 02:42 AM
 
 
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