Simple Electric Airplane Performance Calculations

Posted: August 3, 2014 in r/c airplanes

calculation

What you need: A Watt Meter and Power Analyzer that measures peak Amps and Watts like: a Watt’s Up or Turnigy

watts up

After logging the various measurements you can use these simple calculations to estimate your planes performance and to make sure that you are within the limits or your ESC and motor. Very helpful when experimenting with different prop sizes to find the right performance you’re looking for.

Let’s use these two examples of peak Amps and Watts taken with my Watts Up on my Carbon-Z Cub:

Peak Amps at full throttle = 56

Peak Watts at full throttle = 1,333

With just these two numbers we can determine expected length of flight time, watts per pound and the equivalent internal combustion engine horse power.

************************************************************

To determine the expected length of flight time, you’ll need the peak amps at a set throttle position and the battery capacity in milliamps:

The calculation is: Battery capacity in mAh divided by amps x 60

The result is: Flight time at full throttle = ~3.54 minutes

Of course you may not fly at full throttle the entire flight so take several readings at various throttle positions to help determine an average.

************************************************************

You can determine the expected flight performance based on the peak watts and the weight of your plane:

The calculation is: Watts divided by plane weight

The result is: Watts per pound = 157

Use these Watts Per Pound values to help determine if you have the power to match your needs:

  • 50-70 – Minimum level of power. Think Park flyers.
  • 70-90 – Trainers and slow flying scale planes
  • 90-110 – Sport / aerobatic and fast flying scale planes
  • 110-130 – Advanced aerobatic and high-speed planes
  • 130-150 – 3D and ducted fan planes
  • 150-200+ – Unlimited performance 3D and aerobatic and larger ducted fan planes

Bear in mind these are industry related  de facto numbers and I find that in the real world they are not all that reliable.  Use them as a starting reference point.

***********************************************************

You can also estimate your electric motor performance compared to an internal combustion engine

The calculation is: Watts divided by 746

The result is: IC equivalent = 1.8HP

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s