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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

 

FAA Oversight Of Part 135 Drone Operations: What Can Operators Expect?

Part 135 Drone OperationsAs you may know, the FAA is charged with oversight of the national airspace ("NAS") and aircraft operations conducted within the NAS.  This includes making sure that that air carriers (those who transport persons or property for compensation or hire - Part 121 and 135 operators) are complying with heightened regulatory requirements applicable to those operations.

Until recently, air carriers were limited to operations with manned aircraft.  However, that is no longer the case. The FAA has issued Part 135 authority to certain operators of unmanned aircraft systems ("UAS"). If you have received, or anticipate receiving, approval to conduct 0n-demand UAS operations under Part 135, you should know what to expect from the FAA.

The FAA's Guidance.

Fortunately, this isn't a secret.  In fact, the FAA recently issued an order (FAA Order 8900.527) updating the guidance it provides to its inspectors to explain the surveillance and inspections required for Part 135 UAS operators.  Not surprisingly, the guidance isn't too different from typical Part 135 oversight, but it does specifically address issues unique to UAS operations.

So, what will the FAA inspectors be doing? They will be conducting surveillance of both the airworthiness of the UAS being operated and the operations conducted by the air carrier.

Airworthiness.

With respect to airworthiness, this will include inspections of the following:

  • The operator's facility, including operator data, maintenance facilities, data and records and, of course, the UAS airframe, powerplant, critical systems and AD compliance, as applicable;
  • The operator's manuals and procedures; and
  • The operator's records and recordkeeping systems;

Operations.

With respect to the operator's use and operation of its UAS, the FAA will inspect the following:

  • The operator's air operator certificate;
  • The operator's Operations Specifications;
  • The operator's Operations Manual;
  • The operator's records, including trip records, crew records, PRIA records, and any additional records required by an exemption, waiver, or certificate of authorization;
  • The operator's training program; and
  • The operator's UAS, as well as the operator's actual use/operation of the UAS.

Conclusion.

This list is certainly not all-inclusive.  However, it gives operators a good idea the major items the FAA inspector(s) will be inspecting/reviewing to make sure the Part 135 UAS operator is conducting operations in compliance with the regulations.

And, of course, the length and scope of the inspections will vary depending upon the inspectors involved, the same as it does for Part 135 manned aircraft operations. But if you are familiar with this guidance, you will at least have a general roadmap of what to expect when the FAA conducts surveillance and inspections of a Part 135 UAS operation.

Greg Reigel is a partner at the firm of Shackelford, Bowen, McKinley & Norton, LLP in Dallas Texas.

Greg has more than two decades of experience working with airlines, charter companies, fixed base operators, airports, repair stations, pilots, mechanics, and other aviation businesses in aircraft purchase and sale transactions, regulatory compliance including hazmat and drug and alcohol testing, contract negotiation, airport grant assurances, airport leasing, aircraft related agreements, wet leasing, dry leasing, FAA certificate and civil penalty actions and general aviation and business law matters.

He can be reached via:
Email: GReigel@Shackelford.law
Website: https://shackelford.law
Phone: 214-780-1482

Tips for Noting the Wind on Ground Reference Maneuvers

Here's a short scenario:

You've just taken off from your home airport. You fly about 25 nautical miles out from where you took off and go find an area to do ground reference maneuvers.

Once you find an area you like you begin to get yourself set up to do your first maneuver: rectangular course for example. For rectangular course you have to enter it with a tailwind just like you would enter a typical traffic pattern. So now it's time to note the wind.

First rule: don't just use the direction the winds were at back at your home airport.

But it's just 25nm away, they should be the same right?

Wrong!

The winds can actually be blowing a completely opposite direction than they were back at the airport. This can be due to surface friction, the terrain of the area you're in, and of course what the weather is like for the day. If one area has thunderstorms blowing in the winds can be gusty and shifting, while 20nm away they're calm and skies are clear.

Remember this, especially on a check ride, when it comes to noting the winds. 

So, if you're just over an area with a bunch of fields and no airport to report the weather how do you find the wind direction?

Very simply: look outside.

Now, obviously you cannot truly see wind. But, you can see objects that it's blowing and the direction they're facing.

A great example would be the references that I use since I fly in Houston: refineries. The stacks are almost always blowing steam from the top and it's very easy just to glance at them and see which way the wind is blowing it.

Some other outside visual references would be trees, water, smoke if there is any fires out etc.

If there isn't any references to use and you have an avionics system on board, bring up the groundspeed display. You can always look at this and fly a 360 degree turn to set up for the maneuver and check where you groundspeed is fastest and where it is slowest.

This will tell you exactly where your tailwind is and where you have a headwind, so you can calculate from there how to enter the maneuver.

Using groundspeed also tells you a rough estimate of how strong the wind is blowing, so you can have an idea of how much correction you'll need during the ground reference maneuvers to hold your track. The bigger a difference between your slowest and fastest groundspeeds, the stronger the wind likely is.

Have any other tips you've found for your maneuvers? Drop them below!

We hope you're getting in the Christmas spirit this month, head over to Globalair.com to check out our cool Santa hat on the logo and see what's available on our website!

 

How to Determine Your Pivotal Altitude

Whether you're working on your commercial certificate now, going to be, or already have then you'll find this useful.

As part of the Commercial ACS, we as pilots have to learn Eight's-on-Pylons. This is a maneuver in which the plane flies around two pylons maintaining a visual sight reference with each one in relation to the lateral axis of the airplane. Drawing the plane's ground track, it looks like a figure 8, thus the term Eight's-on-Pylons. 

Picture from the Airplane Flying Handbook

One of the most important concepts to take from this maneuver is pivotal altitude.

So what is it?

Pivotal altitude is the altitude at which, for a given groundspeed, the projection of the visual reference line to the pylon appears to pivot. Simply put, it's what the plane keeps coming back to each time you're able to maintain the pylon off the wingtip and hold it. 

This is also something that is calculated before the maneuver is begun using the airplane's groundspeed. It's the groundspeed squared divided by either 15 for miles per hour or 11.3 for knots. 

Some things to note about pivotal altitude is it does not change with the angle of bank, given that it is not steep enough to affect the groundspeed (but if you do the maneuver and correct for wind properly you shouldn't have to over-steepen the bank where this happens). 

Pivotal altitude can be noted very easily while flying around the pylons. All you have to do is get the plane stabilized where you're holding the pylon off the wingtip with no pitch up or down correction, then look at your altimeter and note the altitude! This is what the plane will keep coming back to. 

You should also enter and exit the maneuver at the pivotal altitude; how close or far you are from it when exiting can exhibit how well the maneuver was performed. 

If you're needing help with commercial maneuvers, or just want to pursue a commercial certificate, take a look at our Aviation Training Directory to find somewhere near you to train.

Best of luck with your Eight's-on-Pylons and happy landings!

-Addi

 

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