There are lots of antennas and objects sticking out all over your training aircraft that may be a mystery to you. Truth be told, they just may be a mystery to experienced pilots, too. Here are some that are basic, and one that you can use to test your instructor.
Communications antenna
Most often the VHF communications antenna—the one that enables you to talk over the radio to people on the ground or other aircraft—is a stiff white stick swept backward at a rakish attitude. It’s one of the longer ones on the aircraft, and usually is above the cabin. It can come in a variety of shapes. A clean antenna is a happy antenna, since dirt can interfere with signals. Does your aircraft have two radios? Look for two antennas.
Temperature probe
If you see a short, small metal rod protruding into the outside airstream from the top of the cabin or, sometimes, the side of the nose, a good guess is that you’re looking at a temperature probe. Knowing the outside air temperature (OAT) is useful to determine airplane performance, but it also can alert you to the dangers of potential airframe icing. In the cabin you may see a dial marked OAT. The probes can be in a variety of locations. However, if you see a short metal rod on the bottom of the airplane, usually with a ball on the end, that’s usually a transponder antenna used for automatically reporting your position and altitude to air traffic control radar.
Static wick
What look like very stiff candle wicks protrude from trailing edges of flight control surfaces on many aircraft—especially high-performance aircraft and others that can be flown in bad weather. Without them, electrostatic charge can build on an airplane, interfering with communication and navigation radios. The wicks bleed the electrostatic charge into the airstream. Precipitation or dirt particles, even electrically charged clouds, can cause electrostatic charges that result in a hissing or static sound in radios. If you are going to fly in instrument conditions, make sure the static wicks haven’t been broken by a pilot walking close by during the preflight inspection.
Air vent
Especially on high-wing aircraft you’ll often see a large hole, usually covered by a screen, at the wing root near the cabin. That’s how you get cabin air, especially while flying in the summer. In the Cessna 172 pictured, the inboard holes supply air to the pilot and copilot seats via overhead adjustable ventilators, while the outboard vents duct air to the rear passenger ventilators.
ELT antenna
A thin wire that easily bends in the breeze is the best way to describe some emergency locator antennas. They usually have a conical rubber base and are located on top of the fuselage behind the cabin. On a modern Cessna they are fixed, as shown in the photo. In a few crashes the ELT transmitter has been torn away from the antenna connection inside the cabin. Make sure the ELT is securely fastened, if you can see it during preflight inspection.
Trim tab on the tail’s horizontal stabilizer
You need to picture this in your mind, or use an actual model airplane if one is handy. Let’s say you are flying along and you raise the tail’s elevator—the moveable portion on the back of the horizontal stabilizer—by pulling back on the yoke or control stick. It is easy to see that relative wind—that’s the wind always coming at you, even if you are headed straight down or up—will push on anything sticking up into the breeze. In this case it pushes the tail down, the nose rises, and (assuming you have enough power) you are climbing.
Now let’s take a small area at the trailing edge of the elevator; add a hinge, and a control in the cabin to move it up or down. Here’s how the trim tab works. If we move the trim tab up into the relative wind, the air pushes this smaller tab down. Since it is connected to the elevator, the elevator also goes down. Now relative wind pushes on the bottom of the elevator, the tail rises, and the nose goes down.
The trim tab is used to refine a climb, descent, or level flight already in progress. Set the attitude of the aircraft using the control yoke or stick, and then trim away any pressure you feel to keep it there. The trim tab is useful for helping to keep the airplane from climbing or descending while at a constant power setting during cruise, and to stabilize a climb or descent. If the aircraft is climbing, force the nose to a level attitude, let it accelerate, and then trim away pressure you feel. Here’s something neat: If you trim for a climb at 70 knots indicated airspeed, the aircraft will maintain that speed hands-off, assuming you don’t change the power setting. Reduce power to idle and the aircraft descends, but at roughly 70 knots! It’s like cruise control on a car.
Plastic light tube
Clear plastic tubes are like a riverbed for light. Shine a light in one end and you’ll notice a glow at the other. So that you can assure your wingtip navigation lights are working at night, some aircraft manufacturers install plastic tubes running from the light and jutting above or below the wing—someplace where you can see it from the cabin. If you see a clear plastic rod near the wing tip, it’s there to glow at night so you’ll know your wingtip lights are working.
Shimmy damper
Shimmy dampers—especially on older single-engine Cessnas—are notorious for failing, and most experienced pilots can quickly realize the problem. Vibration in the nosewheel during high-speed ground operations usually means a piston—a tube with a metal bar coming out that is mounted horizontally on the nose gear—has failed. The quick solution is to lighten the load on the nosewheel by pulling back a little on the control yoke or stick. A better idea is to take it to a mechanic. Usually the vibration is just an annoyance, something to be reported to the flight school.
Pitot tube
This is easily spotted, usually as a probe jutting from beneath the wing of a Cessna trainer, or it can be a vane on other aircraft. It was invented by French hydraulic engineer Henri Pitot in 1732 to measure the speed of water in rivers and canals—but you knew that, right? Be sure to keep ice and insects out. The ice is the easiest part; use pitot covers while on the ground and many aircraft have heated pitot tubes to melt ice once in the air. Insects can find their way in if determined to make your pitot tube a new home, or they can be scooped in during flight—that requires not only superhuman eyesight on your part to see the insect, but amazing piloting skills to spear it with your pitot tube.
Inspection ports
You see circles of metal affixed with screws all over the airplane. They are inspection ports, designed to easily be opened so mechanics can inspect the innards for the condition of control cables or pushrods, any corrosion or cracking in metal parts, and anything else that needs inspecting.
Fuel vent
A tube from the fuel tank mounted under the wing allows air to enter as the fuel exits, thus preventing a vacuum that would stop the fuel from flowing. If fuel heats up in the tank and expands while the airplane is sitting on the ramp, you’ll see fuel dripping out of the vent tube to keep pressure in the tank from building. Why is the fuel vent hiding behind the wing strut on a Cessna 152? That position prevents ice, dirt, and bugs from blocking the vent. If the airplane has been sitting awhile, look in the tube as best you can to make sure no bugs have set up housekeeping, thus blocking the vent—and stopping the flow of fuel to the engine.
Static port
This usually is a small hole on the side of the nose; sometimes, it can be co-mounted with the pitot tube. Without a static port you won’t know your airspeed. Its measurement is based on the difference between ram air pressure into the hole in the pitot tube, and the air pressure at the static port. The static port also drives the altimeter and vertical speed indicator. You may already have heard an instructor say to be careful after an airplane has been washed or waxed to make sure the static port is open (it might have been covered with a piece of tape for protection—and the task of removing that tape occasionally is overlooked). An alternate static port is sometimes included in another location. Make sure you know where the static port is.
CFI stumper: lightening holes
Here’s one to fool your flight instructor. Go beneath the wing and lift the aileron to expose the interior space between the aileron and wing. You’ll notice the back of the aileron has holes, large ones, in the metal and the edges of these holes are flanged or beveled. Ask your flight instructor why they are there. The real reason is to lighten the weight of the airplane, and the beveled edge is to prevent cracking or tearing of the edge of the hole. Maybe you can mislead the instructor, asking if the holes are there to assure no water is trapped in the aileron.
