1. Flight Controls
The ailerons are flap-like, movable surfaces attached to the trailing edge of each wing, extending from perhaps mid-wing out to near the wingtip on typical ultralights. They are rigged so that when one moves up, the other moves down. Aileron deflection causes the plane to roll about its longitudinal axis to produce a bank.
A bank is required to make the aircraft turn right or left. A bank to the right gives a turn to the right, and vice versa. So, the ailerons play an important part in making the plane turn right or left. In fact, they work in concert with the rudder to give the pilot directional control of the plane.
Aileron deflection is produced by side-to-side movement of the stick. Or on planes that have a control yoke instead of a stick, rotation of the yoke controls the position of the ailerons.
When the stick is moved to the right, the right aileron is deflected upward while the left one moves downward. This causes the left wing/aileron combination to produce more lift, while the lift of the right wing/aileron is reduced. Accordingly, the plane will roll toward the right. That is, stick right, roll right. Moving the stick to the left produces the opposite effect.
When an aileron is deflected downward into the airstream, it produces more drag than its opposite member that is deflected upward. This effect gives rise to unbalanced drag acting on the wings, and the nose of the plane will tend to move sideways toward the aileron that is down. This effect is called “adverse yaw.”
It is “adverse” because it is undesirable. Ideally, aileron deflection should not cause the nose to move sideways at all. However, the adverse yaw effect tends to make the nose move in the direction opposite the resulting bank, which is opposite the direction of the desired turn. That is, the nose goes the wrong way!
Some planes have “differential ailerons.” Aileron movement on these planes is configured so that the aileron that moves up moves upward more than the other moves downward. This minimizes the drag associated with the down aileron and at the same time, increases the drag on the aileron that is up. This reduces the effect of adverse yaw.
The elevators consist of two movable surfaces attached to the trailing edge of the horizontal stabilizer. The horizontal stabilizer is the horizontal surface that forms part of the tail section. It's the little wing that flies behind the big one.
On most planes, the horizontal stabilizer consists of two separate “little wings,” one on the right and one on the left. And an elevator is attached to each one so that there are two elevators. They are rigged so that both move up or both move down at the same time.
The elevators control the up-and-down movement of the nose of the plane about the “pitch axis.” The pitch axis is a line running essentially parallel to the wings that passes through the center of gravity (CG) of the plane.
Elevator deflection is produced by fore-and-aft movement of the stick (or yoke). Pulling the stick back causes the elevators to be deflected upward. This produces a downward force on the tail and causes the entire plane to rotate about the pitch axis, the nose moving up. That is, back stick causes the nose of the plane to rise. Forward stick gives nose down.
Note that we did not say that the elevators make the entire plane move upward or downward. We said that they make the “nose” of the plane move up or down. Now in many cases, moving the nose upward has the effect of causing the entire plane to move upward, that is, to climb. But not always.
In fact, there are instances where pulling the stick back will cause the nose of the plane to rise but produce an overall effect that causes the plane to descend more rapidly that it otherwise would. And there are times when, if you pull back on the stick too much, the plane will come down even faster!
This is to make the point that it is not proper to regard the elevators as being the up-down control for the plane. It is just not that simple. True, they are involved in controlling the up-down movement, but other things come into play like airspeed, engine power setting, angle of bank, and so forth.
At the risk of being somewhat technical, the elevators control the pitch angle of the nose in relation to the “relative wind.” In turn, this controls the “angle of attack” of the wings.
The rudder is a movable surface attached to the trailing edge of the vertical stabilizer, the straight-up-and-down part of the tail section. Deflection of the rudder causes the tail of the plane to move right or left, and this causes the nose of the plane to move in the opposite direction as the plane rotates about the yaw axis.
Rudder deflection is controlled by two foot pedals operated by the pilot. When one of these pedals is pushed or rotated forward, the other one moves to the rear. That is, they operate with a see-saw or zig-zag sort of motion.
Pushing the left rudder pedal forward is “Left rudder.” This deflects the rudder to the left, which pushes the tail of the plane to the right, which rotates the nose of the plane to the left. That is, left pedal gives nose left. Right pedal gives nose right.
Rudder deflection alone will not cause the plane to make a turn in a graceful, dignified manner. It takes a coordinated application of both rudder and aileron to get a smooth turn. So, unlike on a boat, the rudder is “not” the turning control on an airplane. It's part of it, but not the whole thing.
There are many occasions when a pilot uses the rudder when he or she has no desire whatsoever to make a turn. One case is that of a forward slip, a piloting trick for losing altitude quickly. In this maneuver, right rudder may be applied along with left aileron to put the plane sort of crossways to the wind to create more drag and a greater rate of descent.
Another involves landing when the wind is blowing across the runway (crosswind). In this case, the pilot uses the rudder to counteract the tendency of the plane to act like a weathervane and turn sort of sideways to the runway. Appropriate rudder action will keep the plane pointed straight down the runway.
Flaps are cockpit-adjustable surfaces attached to the trailing edges of the wings, inboard of the ailerons. They are not movable in the same sense that the ailerons, rudder, and elevators are movable, but rather, they have certain “degrees of deployment” that the pilot can select by moving the “flap lever” to a different position.
Both flaps operate together. When one goes down, the other goes down. Not all planes have flaps. In some planes that do, the flaps are deployed or retracted by a mechanism driven by an electric motor. All the pilot has to do is flip a switch either up or down, and the flaps move accordingly. How nice!
Flap deployment is measured either in “degrees” or “notches.” Typical settings may be 0, 10, 20, 30, and perhaps even 40 degrees. This would correspond to “flaps up,” or 1, 2, 3, or 4 notches of flaps. The “notches” terminology grew out of the old flap-lever actuators that had detents or notches at the various positions.
When fully deployed, the flaps act like air brakes. They create a lot of drag with little or no increase in lift. This enables a pilot to lose altitude quickly in a steep descent without gaining airspeed.
When less than fully deployed, say with 1 or 2 notches, the flaps increase the lift of the wings with only a small increase in drag. This enables the plane to fly more slowly.
On some planes the flaps are somewhat oversized and may be capable of deployment all the way to 40 degrees, or 4 notches. This is great for descending quickly because of the very large drag produced by the flaps, but it is not good for climbing.
In fact, some planes can hardly climb at all when the flaps are fully deployed. This becomes an issue when a pilot is descending with full flaps to a landing and then, for some reason, has to abort the landing and go around. The first objective, in that case, is to get the plane established in as much of a climb as can be mustered, and then very carefully retract the flaps.
These are small aerodynamic surfaces that may be attached to the trailing edges of the ailerons, rudder, or elevators. Their purpose is to make a small modification to the attitude at which the plane will fly “hands off.”
Trim tabs may be cockpit-adjustable or ground-adjustable. One that is cockpit- adjustable will be connected to a small knob or lever that the pilot can adjust in flight. Ground-adjustable trim tabs can only be adjusted on the ground, usually be bending a piece of metal to a slightly different angle.
Most small planes will only have a cockpit-adjustable trim tab for the elevators. The elevator trim allows the pilot to trim the plane to hold the pitch angle desired for a given engine power setting. For example, in a long climb it is customary to adjust the trim so that it is not necessary to hold constant back pressure on the stick. And in level flight at cruise RPM, a tweak of the elevator trim can enable the plane to fly for extended periods without gaining or losing altitude.
Here's a curious point about the elevator trim tab, for example. The trim tab exerts a force on the elevator, and the elevator exerts a force on the tail of the plane. The trim tab controls the elevator which, in turn, controls the plane.
Suppose the trim tab on the elevator is adjusted so that it points upward slightly. Airflow over this tab will tend to push it down, and it will exert a downward force on the rear of the elevator, pushing it down. And when the elevator is deflected downward, the tail will be pushed upward and the nose downward.
There is a reversal of direction between the deflection of the trim tab and its ultimate effect on the nose of the plane.
2. Brakes and Steering
Control of an airplane on the ground is an important consideration, especially when operating on a ramp or in a parking area in close proximity to other planes. Therefore, brakes and steering systems represent important controls although they are not “flight controls” in the strict sense of the word.
Most tricycle-geared planes (nose draggers) will have the nosewheel coupled in some fashion to the rudder pedals so that operating the rudder also turns the nose wheel in the direction of the desired turn. This provides firm, mechanical steering that does not depend at all on aerodynamic forces.
Conventional-geared planes, with the small wheel back under the tail (tail draggers), do not employ such a coupling, largely because it is not needed. The tail wheel is simply allowed to caster and choose its own direction.
Brakes are equally important for obvious reasons. It is standard practice to hold the brakes while starting the engine because sometimes an engine comes alive with a burst of power. Without effective brakes, the plane can easily begin to move forward, and quite rapidly at that. In fact, many planes will move across a paved ramp even with the engine throttled all the way back to idle.
In addition to holding the plane in place or slowing the plane while taxiing or during the landing roll, the brakes serve another purpose if the plane has individual braking systems for each of the main wheels (differential braking) . And that purpose is steering.
By applying a bit of braking pressure to one wheel only, the plane will turn toward that wheel. By using the brakes to lock one wheel in place, a tail dragger can be made to swing around in a very small circle, almost turning in place.
Brake systems for ultralights may be either hydraulic or mechanical. Typical hydraulic systems are similar to the systems found on motorcycles. That is, the master cylinder is operated either by a hand lever or a foot pedal, and disk brakes are the norm.
Mechanical systems couple the hand lever or foot pedal to the brake mechanism in the wheel by using a wire cable that runs inside a flexible housing. Throttle cables and choke cables are similar in construction, as are the throttle cables found on lawnmowers and many other small engines.
Mechanical brakes may utilize the traditional drum-and-shoe mechanism, or a system in which a band is tightened around a rotating drum (band brakes).
The preferred location of the “brake pedals” in general aviation (GA) planes is at the top of the rudder pedals, assuming differential braking. To apply the brakes, the pilot simply slides his or her feet upward slightly on the rudder pedals and then rotates the top of the pedals forward. Some ultralights have brakes set up this way.
Another option is to have a small pedal or tab mounted down on the floorboard near the heel of each foot when the feet are on the rudder pedals. Then, only a small movement of the heel is required in order to apply the brakes.Some ultralights have a motorcycle-style brake lever mounted on the stick. Such systems are usually hydraulic and are not differential. That is, brakes are always applied to both main wheels equally. Many options are available and many different systems are used, especially in the inventive world of experimental aviation.
Yes, you're right. The altimeter is not a flight control. However, before taking off, be sure to set the altimeter to the correct barometric pressure or field elevation.
The altimeter is the only flight instrument on an ultralight that requires “setting” before each flight.
3. Engine Controls
The throttle on an airplane is analogous to the accelerator pedal on an automobile. However, the throttle on a plane is always hand operated. It appears in the form of a lever or knob that is typically placed on the left sidewall of the cockpit or on the center section of the instrument panel. A pilot in a critical maneuver, like a takeoff, landing, or turn, normally flies with one hand on the stick and the other on the throttle.
The coupling between the throttle control and the carburetor is via a throttle cable. This is a wire or wire cable inside a housing, as mentioned above.
Among the many flight-critical components on an airplane, the system consisting of the throttle lever, throttle cable, and throttle linkage at the carburetor is right up there near the top. If the throttle mechanism breaks, binds up, or otherwise fails, you could be found riding behind a perfectly good engine sitting at idle while you frantically look for a place to park and do the repair.
Now suppose the throttle cable either breaks or comes loose so that the carburetor is left to do its own thing. Do you want the engine automatically to throttle back to idle, or would you prefer it to automatically go to full power in the event of a throttle cable failure? Yes, there is a choice.
On an automobile, motorcycle, four-wheeler, or other land/water-based craft, you clearly want it to fail to the idle position. But with a plane, an engine at idle is almost as good as no engine at all. Therefore, many throttle systems are set up so that force must be applied in order to reduce the engine to idle. That way, if the force cannot be applied, the engine automatically goes to full power.
Now, you say, you can't land with the engine at full power. True enough, but you can get to the airport (fast) and then shut the engine down for a dead-stick landing, which every self-respecting ultralight pilot should be able to do.
In-flight adjustable mixture controls are seldom found on ultralight planes even though the mixture control is a standard item on almost all GA planes.
The purpose of a mixture control is to give the pilot a means for leaning the mixture as the plane climbs to higher alitudes, and to enrichen the mixture on the way back down. However, the carburetors most commonly encountered on ultralights do this automatically up to altitudes of perhaps 10,000 feet, and few UL pilots fly higher than this.
Here's a minor ramification of not having a mixture control. To shut down the engine of a typical GA plane, you idle it down to perhaps 1,000 RPM and then lean the mixture all the way to the cut-off point. Without fuel, the engine stops.
But this is not possible with an engine that does not have a mixture control. Therefore, you must shut it down some other way. What is done is to “kill” the ignition pulses going to the plugs by closing a switch that stops the magneto from working. (More about this below.)
The purpose of the choke is to produce a rich mixture for starting the engine. There is nothing new about this idea. The traditional “choke” controls a second butterfly valve in the throat of the carburetor. This second butterfly restricts the air flow severely when the choke is applied and results in a rich mixture for starting.
The popular carburetors on UL engines do not have the second butterfly valve. Instead they utilize some complicated plumbing to enrichen the mixture in a manner that does not depend upon restricted airflow. Nevertheless, the term “choke” is still used to refer to this apparatus even though the proper term is the “enrichener.” Details, details!
Many ultralight engine installations include a “primer” in lieu of or in addition to the enrichener. The primer consists of a tiny pump, like a syringe, that is used to inject raw fuel directly into the intake manifold of the engine. While primers are standard on GA planes, they are regarded as an option on most ultralights.
Now we turn to the electrical side of engine controls, the magneto switches, to be precise. These switches, of which there are two, “kill” the magnetos and prevent them from producing the high-voltage spark required by the plugs. They provide a means for shutting down the engine in the absence of a mixture control.
For those unfamiliar with magneto-type ignition systems, they are unlike the ignition systems found on automobiles which are powered by current from the battery. A magneto is a device that is completely self-contained. By way of magnets mounted on the rotating flywheel, a magneto generates its own power and is completely independent of the battery and electrical system on the plane.
The advantage in this is that a problem with the electrical system will have no effect upon the magneto. The engine will continue to run, with or without a battery being in the plane. In fact, many older planes as well as some modern ultralights have no battery at all.
The problem arises when we want to shut the engine down. Turning off the electrical master switch will have no effect at all on the magneto-driven engine. However, a magneto will always have a “kill wire” (to use a bit of slang), and when this wire is shorted to ground, it disables the magneto.
Further, because most aircraft engines have dual ignition systems (two spark plugs for each cylinder), there will be two magnetos, two kill wires, and two magneto switches. The magnetos are designated “Left” and “Right.” Both magneto switches must be OFF in order to shut the engine down.
Here is an important detail: OFF in the previous statement means, “Switch Closed.” That is, current must pass through the switch when it is in the OFF position as used here. The switch is in line with the kill wire from the magneto to ground. When the switch is open, the kill wire is not grounded and the engine will run. But when the switch is closed, the kill wire is shorted to ground and this “kills” the magneto so that the engine will not run.
The starter switch may appear in the form of a key-switch, like on an automobile, or it may be a separate, momentary contact pushbutton. Either way, it does the same job as the starter circuit on an automobile. There is nothing new here.
Key switches are available that combine the functions of the magneto switches and the starter switch. These are multiple position, rotary switches with selector points labeled .... OFF Left Right Both Start.
The switch function in each position is:
Left Left magneto active; right magneto disabled.
Right Right magneto active; left magneto disabled.
Both Both magnetos active.
Start Both magnetos active; starter circuit energized.
The switch with the key in an ultralight may be either the combination switch described above for the magnetos and starter, or it may serve as a master switch for the plane's electrical system. When used as a master switch, and when it is OFF, no electrical power is available to the starter solenoid, instrument panel, or accessories.
However, just because the master switch is OFF does not mean that the engine could not be started and the plane even flown ... without the key. The engine could be started by hand-propping and the plane would then fly just fine, but without any electrically powered instruments, radios, or fuel pump.
Fuel Pump Switch
Many planes include an electric fuel pump that serves as an auxillary or “boost pump” for the primary mechanical or pulse-driven pump located on or near the engine. Typically, this pump is only turned ON during the critical phases of a flight such as in takeoff and landing to provide backup in case the primary pump fails.
So, the fuel pump switch is the switch that turns the electric fuel pump ON and OFF. And that's it!
4. Communications and Navigation
These systems on ultralights usually consist of only a radio, which may be a hand-held unit adapted to the plane, a GPS unit, and an intercom to facilitate communication between the two pilots. The intercom will be tied in to the radio in some fashion.
Therefore, the list of “controls” is fairly short. Here are two switches that will be found on most installations.
Avionics Master Switch
During engine start, and to a lesser extent during engine shutdown, the electrical system voltage will be subject to wide fluctuations and voltage spikes that could be potentially damaging to the electronics on the aircraft (known as “avionics).
For example, when the starter motor is first energized, the system voltage will drop to a value as low as 6 V for a brief period until the starter motor comes up to speed. Then, when the starter solenoid is released, the collapsing magnetic field within the solenoid can generate a short spike that may reach 100 volts or more. This is “a very ragged time” to have sensitive electronics systems connected.
Therefore, it is good practice to include a switch that isolates the electronics until after the engine is started and running smoothly. This switch is called the “avionics master switch.” It is not turned ON until after engine start, and it is turned OFF prior to engine shutdown.
Push to Talk Switch (PTT)
This is the pushbutton switch the pilot presses in order to key the radio transmitter. That is, the pilot pushes the switch when he wishes to talk over the radio.
This switch may be mounted on the stick or any other convenient place, and there may be more than one. Obviously, the switch ties in to the radio, or in some cases, the intercom. In this latter instance, an electrical signal must be sent from the intercom to the radio in order to key the radio to the transmit mode when the PTT switch is pressed.
Without getting into the specifics of a particular radio, the controls you can definitely expect to find in some form are (1) Off/On; (2) Audio volume; (3) Channel selector; (4) Squelch; and perhaps (5) An automatic noise limiter (ANL) or an automatic noise reduction (ANR) switch. Of these, only the last two may be unfamiliar:
This is a circuit inside the radio that senses when a signal is present and turns the audio circuitry ON when a signal is detected. That is, the squelch circuit keeps the audio turned OFF except when a transmission is being received. This reduces the amount of noise and static heard in the headset.
The squelch control sets the threshold signal level at which the audio section will be turned ON. For example, if you wish to hear only strong, local transmissions near a particular airport, you can set the squelch control until only a strong signal will trigger the audio. But if you wish to hear all the transmissions, even those that may be at distant airports using the same frequency, you can adjust the squelch so that a very weak signal will be heard.
What is done, typically, to adjust the squelch is to open it fully so that you hear everything, including the noise and static, and then go the other way until it “just shuts off.” This ensures that no local, but weak, transmission will be missed.
Automatic Noise Reduction
The tiny, and not so tiny, clicks and pops that blend together to create at least a portion of the static in a radio receiver share a common characteristic. And that is, they all involve signal voltages that change very rapidly.
Electronic circuits have been devised that will recognize these rapid voltage changes and eliminate them. This is the basis of the noise reduction features found on many radios.
However, the system is not perfect. Sometimes, these circuits tend to eliminate part of the desired signal as well as the noise, and even with the best of them, some noise will get through anyway.
Most radios having this feature will include a switch that will turn the system OFF if it is desired to have maximum signal sensitivity. This switch may be labeled, ANL, ANR, or ANC, for automatic noise cancellation.
A typical intercom has only three controls, namely, the On/Off, Volume, and a Squelch if the intercom has the voice-activated feature.
The cockpit is a noisy environment, and the mikes will pick up this noise and send it to the headsets. However, the squelch control can be set so that it will keep the audio turned off until a large signal from a mike is detected. In this way, it operates much like the squelch control on the radio.
As a general rule, headset microphones should have muffs to reduce wind noise, and the mikes should be placed as close to the lips as possible. It is not unusual for a headset without a mike muff to be totally unusable. You might not expect this, but the mikes are quite sensitive.
Also, it has been observed that it makes a difference in wind noise pickup whether the mike boom wraps around your face toward the right or toward the left to the lips of the speaker. In most cases, less wind noise will be picked up if the mike boom extends toward the inside of the cockpit if the plane has side-by-side seating.
All are somewhat similar but yet different. Just remember that it takes a while (sometimes up to 5 minutes) for the unit to find itself after it is first turned ON. So turn it on early, right after engine startup, to be sure it will be available when you need it.
And that's it! Just keep in mind that, except for the flight controls, the controls on an ultralight aircraft are likely to vary widely from one to another, even for the same type aircraft. This article gives only an idea of what to look for.
Be sure to check out the article Controls 201 for more details about how the flight controls are used to actually drive the plane around through the sky.
Author: Doc Green