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Old Aug 12, 2004, 05:00 PM
sloping addict
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France
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props results on B50-6S with 10 cells

Hi all,

has anyone got some data with 10 zapped 3300 cells on a B50-6S for a light frame (about 1.6kg / 57 oz AUW) with various props ?

My data shows 100' motor runtime, with Aeronaut 17*11. That gives an average of about 115A, probably with 140A peaks / static. Climbs are awesome: about 30m/s or 6300 fpm instant climbs - everyone on field quite agrees this is what I truly get.

What may I get swapping to 17*13 ? It seems average draw may be way higher with like + 20A all the time: is it worth it ? The cells may also become very hot then ?
Interested in real life data...

Assuming 3.2 mOhms / cell Motocalc says roughly the speed at which thrust / weight goes below 1:1 would rise from a speed of 30.5m/s (17*11) to a speed of 37m/s (17*13).

Results with RFM props (climbs / average draw / acceleration) would also be interesting.
thanks
...Proto
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Old Aug 12, 2004, 05:28 PM
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I did these tests some time ago, do a search for soholingo and b50 6s, I am sure you will get a lot of results. My experience is that you have the best prop for fast/impressive climbs. If you want go faster go with the aeronaut 16x13 for easy launching, and 16x16 slim for zipping across the sky. You may enjoy these props more the spectators watching will enjoy the 17x11 more...

j
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Old Aug 12, 2004, 08:04 PM
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Proto, these numbers are close to meaningless, but here we go......

With a cold and nearly empty 10-cell pack of zapped GP3300 hooked up to a B50-6s, a RFM 16x16 drew 85 amps and the Aeronaut 17x13 drew 102-105 amps. Yes, the RFM shrieked (stalled) and yes, the Aeronaut pulled like a tractor and even blew a 5x7 carpet in my shop up and off the ground.

Using the basic (charge current in)/(motor run time) yields an average draw of 130-132 amps for the RFM 16x16 over a 50 second motor run. Assuming some efficiency losses in the charging process, this value goes up even higher. The cell temp 5 minutes after a 10 minute F5B style flight measured 165 degrees F (about 1.5 seconds in your hand). Being more aggressive w/ the throttle can get the cells so hot that you can not touch them more than 1/4 second (did not have the thermal thermometer handy). No cooling and the plane is 55 oz.

Perhaps when everyone gets back from York they can start divulging their secrets.

Don - swapping out the Deans Ultra for those 5.5mm connectors tonight.
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Last edited by down_shift; Aug 12, 2004 at 08:06 PM.
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Old Aug 12, 2004, 08:34 PM
tic
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New Cumberland, PA. US
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Unfortunately, I bought a B50-7S for my new scorpio.. I just re- tested the aeronaut 17x11 and find I prefer it to the 16x13 now... ten GP-3300 cells.. Maybe 5,000fpm climb rate.. The great thing is that this motor is easy on the cells..I get 30min. flights in dead air and the cells come out cooler than when they go in.. I usually get the packs up to 120-130 F before flying... Agressive flying results in 160 F packs,,but I would think the 6S would toast the cells if flown the same. I may ask Santa for a B50-6S .. Do you guys think it's worth it?... BTW....I am finding my GP-3300 packs with approx. 200 cycles on them are starting to fade.. Still the same voltage and capacity, but they fly a bit flat compared to a new pack.... Would LOVE to see some real world results on cycle life verses temp.. etc. etc.
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Old Aug 12, 2004, 09:28 PM
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tic, you have two choices....

Buy the b50 6s

Or add two cells to your battery packs...

I wouild do which ever is easier/cheaper...
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Old Aug 12, 2004, 10:53 PM
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Guys, this is a dumb question, but I'm very new at this & trying to learn. What gearbox are you using, or are you speaking of direct drive?? Excuse my ignorance.
Thanks
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Old Aug 12, 2004, 11:06 PM
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Generally when you see the b50 6s mentioned it is in the use of a 10 cell fast sailplane, turning a large prop 15" or greater... In these cases the motor will have a gearbox, and most likely it will be a 6.7:1 maxon gearbox.
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Old Aug 13, 2004, 01:41 AM
sloping addict
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Yes, unless it is about pylon planes and less than 7" props, we mostly talk about the geared version (for 60" and larger sailplanes/holtiners/F5B...)

All geared Hackers apart from special orders are factory fitted with:
4.4:1 for the B20 series
4.4:1 for the B40 series (except some special carbon cased FAI versions)
6.7:1 for the B50 series
Those using a different gear ratio than standard (eg: 5.2:1) usually mention it.

Just such that calculations are OK for all,
Average amp draw = discharged (amp*hours) * 3600 / runtime

Say if Don used in reality 3000 mAh of battery, his amp draw would come down to:

3 * 3600 / 50 = 216 A!!! (Don, I guess/hope you only used less than 2000Ah from your pack !)
I believe we can take discharge capacity = 0.8 * charge back (assuming thus 80% charge efficiency). But some chargers may adapt the number already while others will give raw data... Or you could discharge the pack after one use, to see what was left of it. I assume 3300 will fade, and we shall stop, once we reached at most 3000 mAh discharge.

...Proto
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Old Aug 14, 2004, 03:26 PM
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For the b50 6s and any fast ten cell ship, one prop that is very underated and not mentioned much is the Aeronaught 15 x 13. I have the pleti with 5:1 10 cell job, cant remeber all the number right now..... but it goest better with the 15 x 13 aeronaught than it does with the 16 x 13 aeronaught and was drawing more amps static, 125 amps with hot gp3300's. Sometimes I wonder if we go in the wrong direction with prop sizes, Smaller diamter spinning faster with the same pitch providing the ship is light enough may be the way to go....

S
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Old Aug 14, 2004, 03:39 PM
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> 4.4:1 for the B20 series

Actually the ratio on the Hacker B20 series is about 4.05:1 (nominally 4:1)

Neil.
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Old Aug 14, 2004, 06:34 PM
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mitc99d,

Thanks for the info on the plettnburg. I have one sitting and I was wonder what would be a nice prop for it. It appears my rfm 15x15 will be the ticket...
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Old Aug 14, 2004, 11:32 PM
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Soholngo,
It may not be the ticket, the RFM are just so different to the aeronaughts, but definatley worth a try.

Shaun
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Old Aug 15, 2004, 02:14 AM
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Adding in a couple of lipo results for a 3S4P TP Gen 2 pack the B506S +6.7 is 130 amps on RFM 16x16 skinny and 110 on RFM 15x15 skinny.

those numbers are measured with a clamp meter.
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Old Aug 15, 2004, 09:26 AM
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dave are you going to put that setup into the air? I was going to try the same setup (well fai f5f 5L) but the MG won't hold so many cells...
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Old Aug 15, 2004, 09:39 AM
Bob W
Rock Hill, SC
Joined Jul 2003
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Which wire are you clamping around?
I've often wondered at the similarities between measuring at one of the three motor leads (AC) clamp-on and measuring in series between the battery and the controller, not possible at these currents. Is there a difference in readings? How do they compare?
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