How to Set Drone CG: A Guide for Fixed-wing Aircraft

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This guide explains how to set drone CG, or “Center of Gravity.” If you didn't know what that was, it might be best if you keep reading!


Curt
Aug 9, 2016

Disclaimer: Manufacturers [usually] know best!

If you’re going to be modifying your aircraft, first ask yourself why you’re looking to change things up? Manufacturers of quality UAVs invest great amounts of time, money, and R&D into making their drones perform at their best; but keep in mind they’re often bound by safety regulations and maximizing profits. You should feel confident that the wing or rotorcraft they’re selling has been rigorously tested and is safe, but could they have done better?  When the use cases are specific, the answer is often “yes” as evident by the massive amount of aftermarket parts and add-ons available in the drone and RC market.  Sure, manufacturers can up the MSRP of their product to produce better build quality and enhance features, but mass manufacturing must target the mass market.

Always room for improvement?

Farmers are always thinking of ways to optimize performance and improve efficiency of their equipment as they seek to maximize what they can do with their demanding schedules.  Flying drones is no different, so when I decided to find ways to increase the flight times of our late-model AgEagle, I started looking at larger capacity batteries.  It may sound simple; throw larger batteries in and fly longer, but it’s not.  Larger, heavier, batteries towards the front of the wing greatly affect flight characteristics and the wing will struggle to stay aloft  if you do not counter-balance the weight to maintain the Center of Gravity (CG).  CG is the point of which the aircraft is balanced and is engineered by the manufacturer.  If is often marked on the wing or noted in the manual as a measurement from the trailing or leading edge of the wing.  In the case of our AgEagle, the point of balance is established from a solid red line 4.75 inches from the tail of the aircraft.

Proceed at your own risk!

Before making any changes to your OEM equipment, make sure you have a solid understanding that what you do (or fail to do correctly) may lead to disastrous outcomes.  Do not modify your equipment if you have no room for failure.  No one here at AgFlyers accepts any  responsibility for what you decide to do in your own workshop!  Make sure that the total amount of weight added is minimal as there is a threshold in which too much weight will exceed the intended performance of the wing.  In our case, the wing was designed to be able to handle the additional payload.  To that point, the amount of extra weight your wing is capable of handling should be confirmed with the manufacturer before you begin this process.

You’ll also need a means to balance the wing such as a CG Machine, but can be done with a homemade rig such as wooden dowels or PVC pipe (Google is your friend).

Let’s get Started!

The first step to set drone CG is to equip the wing with everything that you’d set up before a normal flight.  The goal is to get the measurements of the balanced wing as designated by the factory.  This means loading the factory specified payload (camera) batteries, prop, etc.

AgFlyers_Set_Drone_CG_01

Next, balance the wing on the CG machine.  

AgFlyers_Set_Drone_CG_02

Draw a straight line on a piece of masking tape and place it horizontally on the nose of the wing.  Measure and note the distance from the table top to the line on the masking tape.  We’ll want to duplicate this measurement later on after we’ve placed heavier batteries or a different camera in the wing.

AgFlyers_Set_Drone_CG_03

Make your modifications and remeasure.

Now we can make the changes to the payload such as using a different camera or larger batteries.  Again, in my case, I’ve placed larger, heavier batteries in the wing.

AgFlyers_Set_Drone_CG_04

Balance the wing on the CG machine again, and note the new measurement at the line placed at the nose of the aircraft.  The measurement will typically be higher if extra weight is placed at the nose of the aircraft as the wing has to “tip up” to remain balanced.

AgFlyers_Set_Drone_CG_05

Add weight to balance to original specs.

To bring the nose back down to our original measurement and still remain in balance, we’ll need to add weight to the rear of the wing.  The further back the weight is placed, the less weight you’ll have to use (think of the leverage of a teeter totter).  I like to use ½ oz Tape A Weights.  In my case, I had to add 1.5 ounces (three Tape A Weights) to the rear of my wing.  

AgFlyers_Set_Drone_CG_06

With these weights in place, my measurement now is now the same as the measurement with the factory designated payload.  When placing the weights, make sure you stay in-line with the longitudinal axis of the wing.  If the weight is placed on one side or the other, the wing can have a tendency to roll in the direction of the extra weight.  I also place gorilla tape to further secure the weights in place.

AgFlyers_Set_Drone_CG_07

Success! (with a big asterisk)

Our wing is now balanced back to factory specs, but keep in mind that it is now heavier!  The feel and performance of the wing will change because of the weight, but not to the extent it would have been with the incorrect balance.

Looking to enhance the performance of your aircraft? Need to set drone CG because of larger batteries or a different camera? Ask your questions in the link to the forums below!

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