January 2020 Aviation Articles

How CG Location Can Affect Airplane Performance

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?"

"Yes"

"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. 

Forward Characteristics:

-Nose heavy

-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

Aft Characteristics:

-Tail heavy

-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!

Initial Radio Calls for Beginners

Have you been working on radio calls lately and struggling to get them down?

Let's talk about how to at least make your initial call and go from there.

Ok so here's the scenario: you're sitting at a towered airport and completed all your checklists that were called for so now you're ready for taxi. Your hand goes to the PTT (push to talk) and your mind goes blank. What do you say?

This is the format to use on the ground:

-Who you're talking to

-Who you are

-Where you are

-What you want

So let's say this towered airport is KEFD (Ellington Field), your plane is a Grumman Tiger N9696W (this is just a fictional tail number I created), and you're in front of the FBO Signature there waiting to go on your flight to KACT to Waco. Using all of that information as well as knowing they have an ATIS there you need to listen to for information, let's put it together for a radio call.

"Ellington ground, Grumman 9696W at Signature, ready to taxi with information Papa"

Some people can argue you don't need to say direction of flight on the ground, only after you switch to tower, but I sometimes let ground AND tower know. I simply do this because often when I call ground at a towered airport, if I don't say it they come back with "say direction of flight." So here it's your preference, given that at the minimum you let tower know which direction you're headed.

Okay now let's say it's the same situation except you're at an uncontrolled airport T41 making an announcement call. This sounds almost the exact same (using the same format still) but you start AND end the radio call with who you're talking to. Remember at uncontrolled as well you're not asking for clearance, so you're only announcing what you're about to do.

Assuming there is a Signature there as well (though in reality there is not) and we want to taxi to runway 12 via Alpha here's what this radio call would sound like:

"La Porte traffic, Grumman 9696W at Signature taxiing to 12 via Alpha, La Porte traffic"

The call for takeoff would sound the same, except then we'd be announcing which direction we'll be departing to to let other traffic know. If we're going to Waco from T41, the direction is to the northwest. Here's what that would sound like:

"La Porte traffic, Grumman 9696W taking the active 12, departing to the northwest, La Porte traffic"

Still generally the same format as we first talked about. Just to keep elaborating, if I'm now holding short of 17R on Bravo at Ellington and ready to takeoff here's my call to tower:

"Ellington tower, Grumman 9696W holding short of 17R on Bravo, ready for departure VFR to Waco"

You notice how in every call they're all similar? The format may change in some calls as you'll learn the more you practice using radios, but this is always the basis most of them follow. 

There comes the subject of after making your initial call what to repeat back at a towered airport and what you don't need to repeat back, or in uncontrolled airspace how to communicate well with other pilots. There's a lot more that can be talked about with radio calls, so we'll likely talk about them another day. 

I hope everyone has a Happy New Year, stays safe, and sounds like a pro on the radios now!

Questions or comments concerning radio calls? Let us know below!

Happy Landings,

-Addi

 

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