A hard lesson in CG
May 14, 2013
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A few weeks ago a 747 cargo plane crashed just after takeoff at Bagram Airfield in Afghanistan. The cause has been determined to be shifting cargo.
Shortly after takeoff the cargo broke free, shifting to the rear of the plane. The sudden shift in weight drastically changed the flight characteristics.
But there is a lesson we can directly apply to RC flight. Knowing and checking your Center of Gravity (or CG) can drastically change the behavior of your model.
A tail heavy plane will want to pitch up, causing lost lift and stalls. Depending on the stall characteristics of your plane there might not be a way to catch it.
In the video you can see this very thing happen. The weight shifts to the rear, the plane slows, pitches up, looses lift, and then stalls completely. Wing tipping hard to the right, the pilot tries to level her out but all forward momentum is lost.
A great rule of thumb when in doubt fly with a slightly nose heavy plane. This will cause the nose to want to drop and speed the plane up. The increased speed will cause increased lift counteracting the nose down motion. An easy method of balancing RC airplanes is to place the tips of your index or middle fingers under each wing, exactly on the line of the CG. A correctly balancing rc airplane, sitting on your fingertips, will either be level or have the nose pointing slightly downwards.
Remember to always check the plane in its flight ready configuration. Loaded with all batteries, RX, camera, and cargo
Remember to always check your CG before flight. After each flight process the planes behavior and adjust the CG for the next flight. An iterative adjustment process will lead the to best flight experience.
Good luck and wheels up!