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Oct 28, 2009, 07:05 AM
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Shorter flighttime with a 3s Lipo, than a 2s Lipo ?


I know that from a 3s 2200mAh I can get more Volts and amps, than from a 2s 2200mAh. But does it means that the flight time with a 3s 2200 mAh, will be shorter than with a 2s 2200mAh, if I did the exact same flying ?
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Oct 28, 2009, 07:36 AM
Proud to eat Kraut ;-)
Julez's Avatar
When flying WOT, your motor run time will decrease.

But if you fly a glider, WOT to gain altitude, and then glide, your flight time will increase.
Oct 28, 2009, 07:36 AM
Registered User
Yes.
Oct 28, 2009, 07:50 AM
Registered User
Quote:
Originally Posted by Julez View Post
When flying WOT, your motor run time will decrease.

But if you fly a glider, WOT to gain altitude, and then glide, your flight time will increase.
Sorry, but what does WOT means ?
Oct 28, 2009, 08:01 AM
Blessed by anvils from heaven
Chophop's Avatar
That is a complex situation. You could get a shorter flight from the 3S if you do not choose the correct prop. The wrong prop could end up beating air instead of moving the plane.
Like as with too much pitch, and in addition to simply beating air, the over pitch loads (slows) the motor down and allows waste current to flow in the motor, giving a double whammy.
Best to follow a program like Web O Calc to start. Then as you learn, you can optimize. I have been looking at variable pitch props to get the best maneuvering pitch for stunts or flip to cruise to fly around somewhat more gently.
The last time I compared a 2S vs 3S power system, I came up with 7 to 10% more efficiency with the 3S to produce the same thrust. So I would think changing from a generic outrunner to a Scorpion type motor, then also changing to a 3S from 2S power system would give about a 30% efficiency increase. You could start low and work up for a feeling of accomplishment or start at the top and work down. Your choice.

Ch
Last edited by Chophop; Oct 28, 2009 at 08:07 AM.
Oct 28, 2009, 08:07 AM
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everydayflyer's Avatar
Quote:
Originally Posted by SpookiePower View Post
Sorry, but what does WOT means ?


https://www.rcgroups.com/forums/showthread.php?t=441528
Oct 28, 2009, 08:54 AM
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Quote:
Originally Posted by everydayflyer View Post
Thanks
Oct 28, 2009, 08:59 AM
Registered User
Quote:
Originally Posted by Chophop View Post
That is a complex situation. You could get a shorter flight from the 3S if you do not choose the correct prop. The wrong prop could end up beating air instead of moving the plane.
Like as with too much pitch, and in addition to simply beating air, the over pitch loads (slows) the motor down and allows waste current to flow in the motor, giving a double whammy.
Best to follow a program like Web O Calc to start. Then as you learn, you can optimize. I have been looking at variable pitch props to get the best maneuvering pitch for stunts or flip to cruise to fly around somewhat more gently.
The last time I compared a 2S vs 3S power system, I came up with 7 to 10% more efficiency with the 3S to produce the same thrust. So I would think changing from a generic outrunner to a Scorpion type motor, then also changing to a 3S from 2S power system would give about a 30% efficiency increase. You could start low and work up for a feeling of accomplishment or start at the top and work down. Your choice.

Ch
I'm thinking about buying this motor http://aircraft-world.com/prod_datas...919-direct.htm. And I can see that there is a huge different in watt, if I choose the 6x4E prop and use a 2s or 3s battery.

I'm nut sure what "to much pitch" means. It is not listed in the "beginner dictionary"
Oct 28, 2009, 09:37 AM
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EricJ320's Avatar
Assuming everything is equal, i.e. same prop, same motor, same plane, than it's possible that the flight time is shorter, but it's just as likely as it could be longer, especially if you fly exactly the same, as you indicated. It all depends on how you fly it, and how you use the additional power the 3S will provide.

The plane doesn't care how much potential power the battery has, only how much it needs, or is receiving, to fly. Speaking generically, it takes a certain amount of watts to turn a given prop at a desired RPM. If you want to fly EXACTLY the same, then the amount of amps you would need to put in to your setup will be less to get the same amount of watts, since volts are higher on 3S. In other words, lower throttle position to achieve the same power as on a 2S, thus the amp draw would be less and flight times should be longer. But the 3S has more potential power, and can turn the prop much faster than a 2S, so as Julez said, at WOT, it will draw far more amps than the 2S could, and thus flight time will be less. But, thrust and speed will be much higher than the 2S could ever provide.

It all comes down to what you want out of your setup, if power is what you want, than shorter flight times might be acceptable. If you want longer flight times, prop it to the most efficient prop for each battery and flight times might not vary enough to notice. To me, it seems like 3S would give you a little of the best of both, longer flight times for the same performance using lower throttle settings, and the ability to get better performance by pushing the stick all the way up when needed or desired. Of course that route takes discipline to manage the throttle at lower levels, at least for me it does! My transmitter seems to have a spring loaded left stick!
Oct 28, 2009, 12:12 PM
Blessed by anvils from heaven
Chophop's Avatar
Too much pitch means too much twist in the propeller.
The drag of an airplane has what I call "the brick wall". Above a certain speed, it takes lots of power to make it faster than the wall allows. Watch your plane accelerate, It probably picks up speed slowly at first, then gains speed quickly and then sort of stops accelerating as quickly. Above certain throttle and pitch combos, you waste power trying to get past the drag. It's a worthless waste. That extra power can be used in a climb, and that's what I do. I note where the acceleration diminishes even though the prop is obviously speeding up. I keep at or below that point, except in a climb.

At your experience level, it would be best to let us know what you have, look at a typical specifications sheet for a model and type it all up like that, including motor and prop.

CH
Last edited by Chophop; Oct 28, 2009 at 12:21 PM.
Oct 28, 2009, 01:13 PM
Registered User
Quote:
Originally Posted by EricJ320 View Post
Assuming everything is equal, i.e. same prop, same motor, same plane, than it's possible that the flight time is shorter, but it's just as likely as it could be longer, especially if you fly exactly the same, as you indicated. It all depends on how you fly it, and how you use the additional power the 3S will provide.

The plane doesn't care how much potential power the battery has, only how much it needs, or is receiving, to fly. Speaking generically, it takes a certain amount of watts to turn a given prop at a desired RPM. If you want to fly EXACTLY the same, then the amount of amps you would need to put in to your setup will be less to get the same amount of watts, since volts are higher on 3S. In other words, lower throttle position to achieve the same power as on a 2S, thus the amp draw would be less and flight times should be longer. But the 3S has more potential power, and can turn the prop much faster than a 2S, so as Julez said, at WOT, it will draw far more amps than the 2S could, and thus flight time will be less. But, thrust and speed will be much higher than the 2S could ever provide.

It all comes down to what you want out of your setup, if power is what you want, than shorter flight times might be acceptable. If you want longer flight times, prop it to the most efficient prop for each battery and flight times might not vary enough to notice. To me, it seems like 3S would give you a little of the best of both, longer flight times for the same performance using lower throttle settings, and the ability to get better performance by pushing the stick all the way up when needed or desired. Of course that route takes discipline to manage the throttle at lower levels, at least for me it does! My transmitter seems to have a spring loaded left stick!
Thanks for your explanation. I do alot of aerial photography, so I need power to climb high, and the glide down while I take photos. I guess I should go for a 3s battery.
Oct 28, 2009, 01:18 PM
Registered User
Quote:
Originally Posted by Chophop View Post
Too much pitch means too much twist in the propeller.
The drag of an airplane has what I call "the brick wall". Above a certain speed, it takes lots of power to make it faster than the wall allows. Watch your plane accelerate, It probably picks up speed slowly at first, then gains speed quickly and then sort of stops accelerating as quickly. Above certain throttle and pitch combos, you waste power trying to get past the drag. It's a worthless waste. That extra power can be used in a climb, and that's what I do. I note where the acceleration diminishes even though the prop is obviously speeding up. I keep at or below that point, except in a climb.

At your experience level, it would be best to let us know what you have, look at a typical specifications sheet for a model and type it all up like that, including motor and prop.

CH
So far I only have and EZ* and I do a lot of aerial photography. I need power to climb high and the glide down while taking photos. I do not need
power to fly fast.

I have been looking at a Hyperion 1913-04 (186 watt/3s) or maybe a 1919-06(233 watt/3s) both with a 6x4E prop. I'm not sure if a 1919-06 would make to much pitch.
Oct 28, 2009, 02:19 PM
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EricJ320's Avatar
Quote:
Originally Posted by SpookiePower View Post
So far I only have and EZ* and I do a lot of aerial photography. I need power to climb high and the glide down while taking photos. I do not need
power to fly fast.

I have been looking at a Hyperion 1913-04 (186 watt/3s) or maybe a 1919-06(233 watt/3s) both with a 6x4E prop. I'm not sure if a 1919-06 would make to much pitch.
A motor doesn't "make" pitch, the blades of a prop are twisted to a fixed pitch, and how fast you turn the prop determines the pitch speed of said prop. Either of those motors will provide far more power than the Easy Star needs to climb. Gliders in general are low drag designs, and some are built for high speed, although not necessarily the Easy Star. Again, it all comes down to what you want from your setup, and what you are willing to trade off to get it. The 1913-04 will draw roughly 18 amps, and the 1919-06 will pull around 22 amps. Both would do well, the 1919-06, however, will just make it climb a bit faster to altitude, and would likely be my choice given the info you've provided.

Here is another motor that is pretty popular from Hobby King for the Easy Star, only $20 + shipping. People using 3S with a 6x4 are seeing 20+ min. flight times on a 2200mah pack, pulling roughly 23 amps. Just another suggestion for a motor that is proven to work well on the Easy Star, and is a drop in replacement and needs no modifications. That's what's going in my Easy Star, if it ever gets here! It's funny you asked this question about this plane, I am using this motor on 2S for my wife to learn on, and then switch her to 3S once she's comfortable with it. But with this plane, and many mid mounted pushers, you are somewhat limited in the range of prop sizes you can use, so it will be a 6x4 on both batteries. I'm just afraid the 3S will be a bit too much power for her early on in the learning process.

http://www.hobbycity.com/hobbycity/s...idProduct=5203


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