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Old Oct 18, 2013, 10:31 AM
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The Netherlands, NB, Tilburg
Joined Feb 2007
52 Posts
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TF P-47 Razorback: which of two e-power options would be best?

Not sure if I'd post this in the "Glow to Electric Conversions" or in the "Power Systems" forum, but I guess this is the most appropriate category. If not, feel free to give feedback or for mods, move my thread.


I'm halfway through the build (balsa-wise) of my P-47 from Top Flite (10 lbs, 63" ws) and I've made a lot of calculations and looked up lots of example setups. Now I narrowed my choices down to two options and I would very much like to get some feedback before I spend this kind of money on my first glow conversion project (been flying electric for some years, but this is the first setup I've configured myself).

Requirements:
  • About 1400 watts
  • Four bladed prop
  • Good quality setup

Option 1: Scorpion 15"
  • Scorpion SII-4035-250kv
  • 8S 4000mAh 35C lipo
  • 80A HV ESC
  • 15"x11" four-bladed varioProp

Results from e-Calc on average charge state:
  • 53A max. current
  • 6211 rpm
  • 1478 Watts
  • 67 mph pitch speed
  • 156 W/lb (good for a warbird imo)
  • 7.7 min mixed flight time
  • Pros: Lower current, lightest prop, higher output
  • Cons: Close to max. RPM of prop (6.500 rpm) depending on actual kv of motor


Option 2: Hacker 16.6"
  • Hacker A50-16L (265kv)
  • 6S 5000mAh 35C lipo
  • 80A ESC
  • 16.6"x14" four-bladed varioProp

Results from e-Calc on average charge state:
  • 65A max. current
  • 4743 rpm
  • 1374 Watts
  • 66 mph pitch speed
  • 143 W/lb (suited for a warbird imo)
  • 7.9 min mixed flight time
  • Pros: Prop closer to scale size!
  • Cons: Prop is heavy (twice the weight of the 15" prop), high current (may peak around 70A, doable with good cooling, but nonetheless high)

I'm kinda leaning towards the Scorpion 15" prop setup, as it seems lighter overall and it's a cooler setup. The heavy 16.6" prop with low revs and cell count, and a high current, may be too much for the motor or so it feels. Only thing is that I hope I'll get it to run the 15" prop below 6.500 rpm, don't want to disintegrate that nice scale prop.
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Old Oct 19, 2013, 12:30 PM
Oh no, not again!
jhspring's Avatar
United States, LA, Carencro
Joined Dec 2005
5,594 Posts
Robert, I am building a similar-sized (1/8) Hawker Typhoon. I am on a budget and whenever I can I use the biggest motor I can fit to help with c/g (I hate adding lead).

You can buy a Tacon Bigfoot 110 from HobbyPartz for $51. Ecalc says that on 6S it would swing a 16/10/4 for 1400 W in, pitch speed of 65 mph. My experience with the Tacon motor is that they are very good value for money and pretty much bullet-proof. It weighs 16 oz and the weight is right where you need it. http://www.hobbypartz.com/96m607-big...325-295kv.html


FWIW,
Jeff
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Old Oct 19, 2013, 02:20 PM
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Thanks Jeff! I'm not familiar with that brand (Tacon) here on the other side of the pond, but I'm actually looking in what's the best option between the two. On the other hand, the fact that you say bigger is better regarding weight distribution, wouldn't make much difference for my options, they're both equally heavy (the lighter setup with 6S has a much heavier prop (250 gram vs 120 gram) and the motors do not differ that much).

Btw, if I enter your suggested setup in eCalc, I'm only getting 1150 W with a pitch speed of 53 mph. Would be great to know what's the difference, because a 16/10/4 prop on 6S would be great! Maybe you could paste a screenshot of your eCalc form?
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Old Oct 19, 2013, 05:44 PM
Oh no, not again!
jhspring's Avatar
United States, LA, Carencro
Joined Dec 2005
5,594 Posts
Robert, you're right, I miscopied my prop numbers. Try a 16/12/4, that will give you a little over 1395 W in, pitch speed of 65 mph.

I have no experience with Hacker motors, however I did buy one second hand Scorpion. I can see why they are expensive, they are extremely well made and can handle very high current loads.Sorry not to be of more help.

Regards,
Jeff
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Old Oct 19, 2013, 07:10 PM
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Australia, ACT, Kambah
Joined Feb 2001
3,267 Posts
I recently flew a 9-10lb 67" Phoenix Corsair on 2 different electric setups: 6S 5000mAh, Hyperion Zs4025-14, 16 x 12 (Kv=370, ~ 400g) and 10S 4000mAh, Himark 6332-260 15 x 10 (Kv=260, ~700g). I was getting about 1200W on the 6S and nearer 1500 with the 10S. Weight was very similar because I needed a lot of lead up front with the 6s. BTW, the Hyperion is A50-xxS size.

The 6S setup wasn't bad, the 10S setup was every bit as good as a 17cc gas setup in the same model.

Especially with the higher power you are seeking, I'd lean toward the higher cell count. Given the way I tend to fly a warbird which is at pretty high throttle settings, I felt the higher cell count was better able to manage the power demands. Even though you're using fairly large packs, if you can keep the current nearer 10C than 20C, through flight performance will be better, and they should (might?) last longer overall.

I feel 6 cells is adequate for lighter models flown with much more power variation, eg my 7lb 50e pattern model, or slower flyers with much lower wing loading (eg 9lb 80" Pawnee) but struggles with the higher wing loading, higher speed, higher average power models.
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Old Oct 20, 2013, 05:28 AM
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The Netherlands, NB, Tilburg
Joined Feb 2007
52 Posts
Thanks guys! These experiences reassure me that the 8s Scorpion setup is the best one:

Quote:
Originally Posted by jhspring View Post
(...) I have no experience with Hacker motors, however I did buy one second hand Scorpion. I can see why they are expensive, they are extremely well made and can handle very high current loads. (...)
Quote:
Originally Posted by scirocco View Post
(...) Especially with the higher power you are seeking, I'd lean toward the higher cell count. Given the way I tend to fly a warbird which is at pretty high throttle settings, I felt the higher cell count was better able to manage the power demands. Even though you're using fairly large packs, if you can keep the current nearer 10C than 20C, through flight performance will be better, and they should (might?) last longer overall. (...)
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