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Author Topic: Efficiency in Selecting “E” Components  (Read 1918 times)

Offline Gil Mc Millan

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Efficiency in Selecting “E” Components
« on: January 01, 2014, 07:35:26 PM »
I have been flying E stunt for about a year now & am continually learning.it's finally getting through my very old, hard head. What I have trouble with is understanding what components yield the most efficient system..efficient in terms of battery capacity & therefore weight.
For Instance......
I have a 29 oz Ringmaster, with battery.complete flying weight.
E flite power 15 outrunner, 950Kv
Phoenix IceLite 50  ESC
Hubin timer
Turnigy Nano Tech 14.8 V, 1300 mAh, 45-90C discharge, battery
APC  11x5.5 EP propeller……RPM is set at 9,000
IT FLIES GREAT !
When building I assumed 100 watts per lb……100 x (29/16) = 181 watts
181 watts / 14.8 volts = 12.23 Amps…..1223 mAh……120% = 1500 mAh  for 6 minutes, therefore I thought that 5 minutes would be easy. WRONG, I get three minutes tops!
What did I assume that was wrong?
Should I have used 11.1 Volts, is that more efficient ?
Should I have used an E flite power 10?
Thanks, Gil
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Offline 55chevr

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Re: Efficiency in Selecting “E” Components
« Reply #1 on: January 01, 2014, 07:48:02 PM »
The 10 would be better sized for a Ringmaster ... and your battery is under what we use on our Ringmaster (Grandson). We use the same ESC and timer but 4S 1800 mah  and a 9 x 6 EP prop.


Joe
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Offline John Cralley

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Re: Efficiency in Selecting “E” Components
« Reply #2 on: January 01, 2014, 09:05:01 PM »
Joe is right --- too large a prop and too small a battery!! You are using the correct cell count for your motor (4S battery for the 950 KV) but you need more battery capacity. If you have a watt meter, check what amperage you are pulling with a 10" prop (or cut your 11" prop down). Vary the RPM to see how that affects the Amps being drawn (keep in mind that the Amps in flight will be less than what you pull in a static test). My guess is you need closer to a 2000 mah battery.
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Offline Gil Mc Millan

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Re: Efficiency in Selecting “E” Components
« Reply #3 on: January 02, 2014, 09:21:59 AM »
Thanks for the responses guys, I'm sure that what you suggested is correct & I'll make the changes.
My question was really what did I do wrong in calculating my needs, is 100 watts not correct ?  I was given that number by a friend with lots of experience. WHY do you make the suggestions given, is there no method other than trial & error ? That was my real question.
Thanks again, Gil
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Offline Mike Anderson

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Re: Efficiency in Selecting “E” Components
« Reply #4 on: January 02, 2014, 09:41:41 AM »
Your calculations don't consider the propellor that you chose.  An 11-5.5 at 9000 RPM with a 950 Kv is going to draw somewhere between 20 and 25 amps, whether mounted to some airplane or to a picnic table.  You came up with 180 or so watts as needed, but you are actually using about twice that.  The only real way to approximate the prop you will need, and the RPM you will need to turn it, is from experience, trial-and-error, or by going through some of the previously documented setups.
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Offline Tim Wescott

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Re: Efficiency in Selecting “E” Components
« Reply #5 on: January 02, 2014, 10:18:06 AM »
The rule of thumb that I've seen for stunt planes is 7W/ounce, which works out to 115W/lb.  But it comes with a caviat that as the plane gets smaller you need more power.  That still doesn't explain the super-short flight time, though.

Size the motor by using the rule of thumb of 11W/ounce peak power, and use that to choose the ESC and motor current rating.  I suspect that your power 10 would fit -- but do the math.

The propeller does seem to be awfully big for the airplane.  My Ringmaster flies quite well behind a 9-4, even if the only electron action involved in turning it happens when methanol vapor and oxygen violently rearrange themselves into water and carbon dioxide in a confined space.  Launch RPM with an OS FP-20 is about 12000 to 12500.

With that Kv and cell count you want to launch at something like 11K RPM tops.  That's a bit low for a 9-4, so you may want to try a 9-5.  If that works and you decide to spring for a power 10 (which will have a higher Kv) you may be able to run a 9-4 at 12000 RPM.  I'd certainly try a smaller prop before I did anything else.

Then tell us if it worked!!
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Gil Mc Millan

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Re: Efficiency in Selecting “E” Components
« Reply #6 on: January 02, 2014, 12:16:55 PM »
Can someone suggest a source of 9x4 & 9x5 pusher props?
Last year I started with the APC 9x6 EP & didn't like the performance, from what I'm hearing now, I didn't turn it fast enough, I'll try again at higher RPM.
Thanks, I still have lots to learn
Gil
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Offline Tim Wescott

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Re: Efficiency in Selecting “E” Components
« Reply #7 on: January 02, 2014, 12:39:47 PM »
Somehow the idea of going to the bother of putting a pusher prop on a Ringmaster just boggles my mind a bit.  It's like putting rubber-band tires on a Chevette, or a big four barrel on a Chevy 305.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Gil Mc Millan

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Re: Efficiency in Selecting “E” Components
« Reply #8 on: January 02, 2014, 01:08:05 PM »
Tim, I appreciate any help offered, but your sarcasm is over my head....why is using a pusher prop more bother ?  Wouldn't it be more trouble to now use a tractor prop ?  My motor turns correctly with a pusher prop.
I do realize that a Ringmaster isn't very sophisticated, but I'm trying to learn E stunt & apply what I learn to a "real" stunt ship without all the trial & error.
Gil

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Gil Mc Millan
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Offline Tim Wescott

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Re: Efficiency in Selecting “E” Components
« Reply #9 on: January 02, 2014, 01:13:30 PM »
All you need to do to reverse the motor rotation is to swap any two motor leads, which is no bother at all.  Unless I'm mistaken, the bother in using pusher props is in sourcing them -- there seems to be a lot more regular-rotation props available.

Once you get into "full sized" stunters then there are some nice APC pushers that are purpose-made for e-power, not to mention the carbon fiber ones that Alan Resinger is working on making, so it's easier to find a prop.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline William DeMauro

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Re: Efficiency in Selecting “E” Components
« Reply #10 on: January 02, 2014, 02:02:12 PM »
Gil,
Like the others have said, no doubt that your motor is too big, your prop is bigger than you need and your battery is too small. I've done 3 Flite Streaks for my kids and your Ringmaster is close enough to copy their setup. If it were me I'd use the Cobra C-2814/20 Brushless Motor, Kv=850 http://www.innov8tivedesigns.com/product_info.php?cPath=21_120_122&products_id=832  or any other motor in the same size class with a kv from 850-950. For a battery the Turnigy Compact 25c 4s 2200 mah will work well and is not expensive   http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=24619. You can use the APC 9x6 pusher or the Hobby king dollar clone. Spin it at around 10500 and work your RPM up or down from there to suit your plane and flying style. You can also easily spin the 10x5.8 pusher available from APC or Dennis Adimisin may still have some left. Start your RPM at around 9800-10000 and adjust from there. This set up will have no issues flying that plane. or any other plane in this size range. In fact this setup pulls Kevin's Gieskie nobler at 41 ounces with no effort through the entire pattern and uses about 1550mah out of the battery.
William
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