|Oct 31, 2013, 06:07 PM|
Joined Oct 2013
Hi, I am new to electric flight. I have a couple of nitro powered planes that I want to convert. Is there any hard and fast rule regarding comparisons?
I have a high wing trainer that has been flying on an Irvine 40. What motor and ESC would I need?
It appears to me that the higher the kv rating, the smaller the aircraft, but I feel that one could waste an awful lot of money buying stuff they don't need
Many thanks Pat
|Nov 01, 2013, 04:15 PM|
Letchworth, Great Britain (UK)
Joined Jul 2004
The rule-of-thumb that's usually quoted is watts per pound: The normal range would be somewhere between 50 and 200 watts per pound ready-to-fly weight including battery. What number you pick depends on your model and your flying style -- I have a couple of 72" wingspan 9lb models (Sukhoi SU26 and an Extra-style model) which have 200 watts/pound available, but usually cruise on less than 1/4 of that. My 60" trainer-style model has 85 watts/pound, and is more sprightly than when it was propelled by an OS48FS engine.
Motor kv is a measure of how fast it will try to spin for each volt input. Higher kv means you use less volts and/or a smaller prop than with a low kv. The motor in my trainer-type model has a kv of 760, and with it I spin a 12x6 prop using a 5S A123 battery (nominal 16.5v). That's the same size prop that the OS48FS engine used. Most manufactures give examples of what prop size for different voltages for their motors.
Not knowing about the watts/pound rule when I first started into electric conversion, I went by the manufacturer's power rating for my engine and then converted it into watts (1hp = 746 watts, I think) for my electric motor.
|Nov 01, 2013, 08:26 PM|
United States, ID, Shelley
Joined Dec 2011
Step 1: Determine your models weight.
Step 2: You can determine the power requirements of a model based on the “Input Watts Per Pound” guidelines found below, using the flying weight of the model (with battery):
• 50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
• 70-90 watts per pound; Trainer and slow flying scale models
• 90-110 watts per pound; Sport aerobatic and fast flying scale models
• 110-130 watts per pound; Advanced aerobatic and high-speed models
• 130-150 watts per pound; Lightly loaded 3D models and ducted fans
• 150-200+ watts per pound; Unlimited performance 3D models
Step 3: Divide the total desired watts by battery voltage to determine necessary amps.
Watts / Voltage = Amps
Step 4: Determine the Voltage to /Currant ratio by dividing the given Amp by the Voltage.
Amps / Voltage = V/C Ratio
Voltage/Currant ratios should be fairly low; 2 or 3 to 1 being ideal.
Examples: 900w / 11.1v = 81a 7:1 ratio
900w / 14.8v = 60a 4:1 ratio
900w / 18.5v = 48a 3:1 ratio
900w / 22.2v = 40a 2:1 ratio
Step 5: Determine the battery discharge rate (C-rating) by divide the desired Amps by the battery
pack capacity, expressed in Amps (A).
Required amps / Capacity (A) = C-discharge rate
Example: 40amps / 4 (4,000mAh) = 10C
Step 6: Determine the Max. full throttle flying time, full discharged battery time by dividing 60
minutes by the C-rating.
60min / C-discharge rate = Max. full power time
Example: 60min / 10C = 6 minutes
Step 7: Determine the 80% discharge flying time by multiplying the Max time by 0.8.
Example: 6 minutes x 0.8 = 4.8 minutes.
|Nov 02, 2013, 04:08 PM|
Joined Oct 2013
Thank You, sounds simple now, at last
|Thread||Thread Starter||Forum||Replies||Last Post|
|Question DLE 20 comparison to Glow 1.20 two stroke or 1.5 FS||Alcuy||Engines||30||Oct 26, 2013 01:49 PM|
|Electric vs. Glow.... an unbiased comparison.||Jim Walker||Electric Plane Talk||50||Jun 13, 2005 04:27 PM|
|Electric/Glow Comparison-AXI 2820/12||challenger_i||Power Systems||3||May 22, 2005 05:31 AM|
|electric to glow comparison||sopwith99||Power Systems||10||Sep 09, 2004 06:40 AM|
|Glow vs Electric power comparison||Giz||Power Systems||7||May 21, 2004 09:03 AM|