Electric Flight Systems

1
Electric Flight Systems

• Part II
• Selecting components for your airplane

2
Where Do I Start?

• Most manufacturers recommend a set-up that
  makes for a good starting point.
• Typically there are many tried and proven
  set-ups reported by others on-line.
• Dont re-invent the wheel when you dont have
  to!

3
OK I dont have a suggested set-up, now what?

• Ballpark your AUW then start from
• 70-90 watts/lb. - trainer and slow flying
  aerobatic models.
• 90-110 watts/lb. - sport aerobatic and fast
  flying scale models.
• 110-130 watts/lb. - advanced aerobatic and high
  speed models
• 130-150 watts/lb. - lightly loaded 3D models and
  ducted fans.
• -150-200 watts/lb. - unlimited performance 3D
  models.

4
A few real-world examples . . .

• Steves Corsair
• AUW 3.2 lbs
• Approx. 360 watts
• 360 / 3.2 113 Watts per pound
• Steves big F-86 EDF
• AUW 5 lbs
• Approx. 1300 watts
• 1300 / 5 260 Watts per pound
• Garys Taylorcraft
• AUW 2.2 lbs
• Approx. 290 Watts
• 290 / 2.2 132 Watts per pound
• Steve Gary like well-powered airplanes!

5
A quick and dirty watt estimate for glow
conversion. . .

• Double it and add a zero
• Double the 2 stroke glow displacement size and
  add a zero.
• Example A .40 size glow plane would need
  roughly 800 watts (40x2 80 then add a zero
  800 watts).
• A .60 size glow roughly 1200W.
• 746 watts 1 HP (assuming 100 efficiency)

6
What voltage should I use (how many cells) ?

• There are many ways to achieve the same of
  watts
• i.e. We can make 800 watts is several ways
• (2s) 7.2v x 111 amps 800W
• (3s) 11.1 x 72 amps 800W
• (4s) 14.8 x 54 amps 800W
• (5s) 18.5 x 43 amps 800W, etc.
• Practical considerations like weight, cost,
  flight duration, what size packs fit, what
  batteries or ESC you already own already, etc.
  can also factor into the decision

7
As a rule of thumb, for best efficiency, the amps
should equal 3x-4x the volts

• Some ballpark efficient ranges
• Cells Nominal voltage Amps Watts
• 2S 7.4 22 30 164 - 219
• 3S 11.1 33 44 370 - 493
• 4S 4.8 44 59 657 - 876
• 5S 18.5 55 74 1027 - 1369
• 6S 22.2 67 89 1479 - 1971
• 7S 25.9 78 104 2012 - 2683
• 8S 29.6 89 118 2628 - 3505
• 9S 33.3 100 133 3327 - 4436
• 10S 37 111 148 4107 - 5476
• 11S 40.7 122 163 4969 6626
• 12S 44.4 133 178 5914 - 7885

8
Select your propeller

• Propeller selection is more critical to electrics
  than glow.
• Glow motors create power that is then absorbed by
  the prop
• The prop pulls the power from an electric
  motor.
• Static thrust is primarily determined by prop
  diameter.
• Speed is primarily determined by prop pitch.

9
Propellers continued

• What kind of flying will you do?
• High static thrust is important for hovering,
  vertical, etc
• High pitch speed is for goin fast!
• 12 is a fairly typical starting point i.e.
  10x5, 12x6
• Ballpark - if you step up 1" in pitch you need to
  step down 1" in diameter to keep the same amp
  draw.