Hey everyone! I hope you all have had a good start to 2020, stuck to your resolutions, and greased all your landings so far. I heard a pretty good joke the other day that I wanted to share at the start of this post before we dig into some CG topics.
So we all know about Murphy's law right? It's very prevalent in aviation: anything that can go wrong will go wrong.
Well, here's how to get your friends on a good joke.
"So you've heard of Murphy's law right?"
"Well have you heard of Cole's Law?"
"No what's that?"
"Oh it's just sliced cabbage with some dressing."
Love it! So cheesy but it's funny.
Ok now let's dig into some topics of the center of gravity.
First off: What is it? Well according to the Pilot's Handbook of Aeronautical Knowledge it is "the point at which an airplane would balance if it were possible to suspend it at that point."
Think about when you would get bored in elementary school and try to balance a pencil on your finger. Remember when you'd finally get it balanced, but it had to be a specific spot on the pencil or it'd fall back off? That's exactly what CG is on a plane. It's where most of the weight is concentrated, so once we load up the plane if it's within the CG then it flies the most stable and safe. It's also important to note that a CG is not just a fixed a point but it can move depending on the distribution of weight throughout the plane.
But let's say we loaded the plane with too much weight or we didn't distribute it well and now we're out of CG limits. We can either be forward or aft (behind) that area.
-Difficult to impossible to lift nose for takeoff
-Better stall recovery
-Total lift required by the wing is increased
-Wing flies at higher angle of attack, resulting in higher drag and higher indicated stall speed
-Difficult to impossible to recover from a stall
-Violent stall characteristics
-Light control forces that make it easy to overstress the plane
-Wing flies at lower angle of attack, resulting in lower drag and higher cruise speed
It's also always important to ensure to not take off past the max takeoff weight, and if you do it's brought down quickly/easily due to fuel burn. The effects of being overweight are dangerous. It includes:
-Higher takeoff speed
-Longer ground roll on takeoff and landing
-Higher stalling speed
-Reduced climb rate
-Excessive weight on the landing gear that can cause a collapse
-Accelerating metal fatigue over time
These characteristics run for all planes too, whether you're flying a Cirrus SR-22 or a King Air A100 you never want to be overweight or out of CG.
When it comes to weight and balance there is also several important terms to know that we use in order to help us calculate properly. These include:
Arm: horizontal distance from the datum line to the CG of an item (measured in inches)
Datum: an imaginary line from which all horizontal distances are measured in order to balance the aircraft. This is picked by the manufacturer and is usually somewhere like in front of the engine firewall or the leading edge of the wing.
Basic Empty Weight: the standard empty weight of the plane and any optional equipment installed
Standard Empty Weight: the weight of the airframe, engines, permanently installed items in the airplane, unusable fuel, full operating fluids and oil.
Moment: this is the product of weight x arm and is considered to be the force that causes an object to rotate.
If you're ever trying to remember these and study some more check out chapter 10 of the Pilot's Handbook of Aeronautical Knowledge and your own operating handbook for whichever plane you're flying. There's always so much to talk about with weight and balance but if you remember anything know this: don't ever land overweight and never accept an aft CG! That's the two most dangerous scenarios.
Anything else to add about weight and balance? Drop it below!