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Somethin' Extra electric conversion

Old 08-16-2020, 10:35 PM
  #1  
prowler53
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Default Somethin' Extra electric conversion

Well here she is after 17 years of hanging in a bedroom and never flown. I removed all the covering and gave it a fresh look, Made some Mods for the conversion. Added a hatch at the front for battery and a hatch under the front fuse for ESC. Dubro landing gear and 2 1/2" wheels for prop clearance. I have a 13x8 on her right now but probably room for a 14" If I decide to go larger. E-flite Power 46 and 60 amp ESC. 4S 4500 mah Lipo. Extended The Rudder and covered in Monokote. I used Oracal 651 vinyl for the graphics. She still comes in a little tail heavy with everything moved forward, so I'm thinking about a larger battery & prop spinner. 5.4 Lbs right now without adding more weight, so I think I'm going to end up around 6 Lbs when ready to fly. A little heavier than I wanted but I think it should be ok.

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Old 08-17-2020, 03:19 AM
  #2  
Turbojoe
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That looks AMAZING! Nice work!

Joe
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Old 08-17-2020, 10:54 AM
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ron_van_sommeren
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Originally Posted by prowler53 View Post
... I have a 13x8 on her right now but probably room for a 14" If I decide to go larger. ...
Both current and power drawn are proportional to diameter⁴, here they would increase by factor (14/13)⁴=1.35, 35%more.
(Ignoring higher voltage losses in battery, wiring, controller, motor due the higher current).

What's the current draw with the 13"diameter prop?

14" is better but you may need to reduce pitch should current get too high. Current drawn is proportional to pitch (also proportional to #blades, voltage≤ and Kv≥).

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Old 08-17-2020, 11:05 AM
  #4  
ron_van_sommeren
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It is a good practice to have some headroom built in.
About derating motors, controllers, batteries, electronics in general:
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Old 08-17-2020, 09:25 PM
  #5  
prowler53
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Originally Posted by Turbojoe View Post
That looks AMAZING! Nice work!

Joe
Thanks Joe
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Old 08-17-2020, 09:27 PM
  #6  
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Originally Posted by ron_van_sommeren View Post
Both current and power drawn are proportional to diameter⁴, here they would increase by factor (14/13)⁴=1.35, 35%more.
(Ignoring higher voltage losses in battery, wiring, controller, motor due the higher current).

What's the current draw with the 13"diameter prop?

14" is better but you may need to reduce pitch should current get too high. Current and power drawn are proportional to pitch (also proportional to voltage≤ and Kv≥).
I'm not sure of the draw yet....I have a Watt meter ordered and should be here this week.
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Old 08-23-2020, 03:04 PM
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Watt meter arrived but now I'm waiting on my transmitter that is being repaired or replaced because of the faulty scroll wheel switch. I was bored yesterday and took an hour drive to the closest r/c hobby shop. Ended up coming home with an E-flite Night Timber x BNF.
I heard good things about this plane, and thought it would be good to get some practice with before flying the Somethin' extra. Now I just need my transmitter to get flying.
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Old 12-06-2020, 08:03 PM
  #8  
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Well It's been a few months and I still have not flown this plane yet. I guess It will be next spring till I get her out for a maiden. I Switched the wheels to 3" for a little more prop clearance and I've not ordered a larger battery yet. Still unsure about the prop size so maybe someone could help me out with that. Here's what I have so far....
Total flying weight is 5.9 pounds with a 4s 4500mah 50c Lipo
E-Flite Power 46
E-Flite Pro 60 amp ESC
13x8e APC prop
at full throttle I'm pulling around 600 watts and around 40 amps with this prop. Do you think I have room for a 14x6?
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Old 12-06-2020, 10:49 PM
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ron_van_sommeren
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Current and power drawn are proportional to pitch and to diameter⁴
Going from 13◊8 to 14◊6, current and power change by factor (6/8)=0.74 and again by factor (14/13)⁴=1.34, giving a net product/result of 1.01.
Current and power drawn increase by 1%



The 'full' story.
Current and power drawn are proportional to pitch, #blades, voltage≤ respectively voltage≥ Kv and diameter⁴
So even a small change in setup can result in quite an unexpected increase.
Increase in current with one or two cells added simple table

Smoking examples.
Going from 2s to 3s, a 50% increase, would (3/2)≤=2.2fold current, more than double, 120% extra.
A 25% increase in velocity konstant Kv would (1.25)≥=2fold current, 100% extra.
A mere 10% increase in diameter would (11/10)⁴=1.1⁴=1.4 fold current, 40% extra.

Silly examples.
Doubling voltage would, 2≤=4, four fold current.
Doubling Kv would, 2≥=8, eight fold current.
Doubling diameter would, 2⁴=16, sixteen fold current.
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