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Oct 19, 2019, 11:32 AM
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Quote:
Originally Posted by gquiring
With such an investment what's holding you back on using a 4s battery? The Grafas Maxi is going to weigh a little over 5 pounds and the battery is not just providing power but balance weight. A 3s battery will be much lighter requiring a lot of dead weight to get the CG right.
Yeah, well investment is relative... This would probably be my cheapest plane.

I'm not thinking much in economy but practicality, I hate having to deal with all different type of batteries.
If I could run all my planes with one and the same one I would .
Since that is not possible I try to consolidate my planes in as few options as possible.

And remember I have to order from abroad and lately the options for shipping of Lipos got very limited/complicated/expensive.

Anyway... I was just curious on what the procedure would be if I decided to drop one cell, after all it supposed to be a glider and I plan to use the motor only to climb up a few meters because there is no way these modern/light wing construction would stand the histart.
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Oct 23, 2019, 10:16 AM
lgs
lgs
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Quote:
Originally Posted by ferincr

I know the basics about batt cells ESC and motors but basically the question I have at this moment is:
I'm thinking in ordering the same motor/ESC combo (Gliderdrive+YEP) but the difference is that I'll be using a 3S batt.
So... to get the most of this setup should I change the prop size???

Having the same motor running at lower RPMs (I know I'll have less thust but) is the prop size linked to the motor size or RPMs?
Should I stick with the 11x6 prop? Or do I need to scale the prop accordingly? And if so which size you suggest?

Fernando
Hi Fernando, I caught your post about Battery vrs Prop Size and I want to let you know what I have learned.

There are a lot factors that go into the equation but to answer your first question, generally, the lower voltage uses a larger prop to generate the same amount of thrust measured in watts, as a larger (more volts) battery.

Lets say that you want a 100 watts per pound for the Grafas. 550 watts.

3S--- 550w / 12v = 45 amps That is pushing the limits for the Glider drive

so lets look at

4S--- 550w/16v = 34.7 Amps Much easier to achieve.

You are going to try different props to get to 550 watts The 3S will be larger than the 4S

I like to launch my planes to thermal altitude quickly I like getting to 400 feet, in 10 seconds cut the motor and still get another 100 feet from the momentum. If you are flying wench now that is the Zoom part. That equates to 150 watts per pound.

Top Model planes seem to need a lot of weight in the nose to balance the long tail. I found the 2 TM planes I built needed 3300 sized batts plus some lead to balance,

Besure to buy the YEP programing card The ESC is factory set for Heli flyers, very slow start up and no break. You dont want to rely on Beeps....

If you are flying with FrSky be sure to do the stick calibration or yo never get the motor to break. (stop spinning)
Oct 23, 2019, 11:12 AM
Registered User
Quote:
Originally Posted by lgs
Hi Fernando, I caught your post about Battery vrs Prop Size and I want to let you know what I have learned.

There are a lot factors that go into the equation but to answer your first question, generally, the lower voltage uses a larger prop to generate the same amount of thrust measured in watts, as a larger (more volts) battery.

Lets say that you want a 100 watts per pound for the Grafas. 550 watts.

3S--- 550w / 12v = 45 amps That is pushing the limits for the Glider drive

so lets look at

4S--- 550w/16v = 34.7 Amps Much easier to achieve.

You are going to try different props to get to 550 watts The 3S will be larger than the 4S

I like to launch my planes to thermal altitude quickly I like getting to 400 feet, in 10 seconds cut the motor and still get another 100 feet from the momentum. If you are flying wench now that is the Zoom part. That equates to 150 watts per pound.

Top Model planes seem to need a lot of weight in the nose to balance the long tail. I found the 2 TM planes I built needed 3300 sized batts plus some lead to balance,

Besure to buy the YEP programing card The ESC is factory set for Heli flyers, very slow start up and no break. You dont want to rely on Beeps....

If you are flying with FrSky be sure to do the stick calibration or yo never get the motor to break. (stop spinning)
Wow!!
Very comprehensive reply! And full of useful info too...
As I said electrics is a new concept for me, I only had a couple of those arf or RR little planes so I'll need to learn the ropes but this is a great way to start.
I might go with the 4S then just for what you stated (which makes a lot of sense) about the higher amp need with 3S.
I love to build and modify so I'll try to move as much weight forward as possible too.
Thanks,
Fernando


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