2009年4月6日星期一

The Basic of Flight ( 4 )

4. BASIC FLIGHT MANEUVERS

This section covers the basics of flight—takeoff, climbing, descending and landing—and outlines basic recovery procedures for stalls, a common occurrence.

TAKEOFF
Taking off from an airfield is a fairly straightforward procedure. First, lower the flaps to change the aerodynamic shape of the wing, and then apply full throttle.

Once you generate enough forward airspeed and lift, the tailwheel (if the aircraft has one) rises off of the runway surface. Gently apply rear stick to pitch the nose up approximately 10°. Be careful not to climb too steeply— if your airspeed starts falling, you'll need to reduce the pitch angle to avoid stalling.

..Lower flaps
..Increase throttle to 100%
..Wait until your speed is over 160 km/h. (Exact airspeeds for takeoff vary by airplane).

Gently apply pitch (pull back on flight stick) so that your climb attitude is around 5°
..Keep pitch steady (if airspeed drops, reduce pitch)

CLIMBING
After you take off, the next step is to retract the landing gear—it creates unnecessary drag, and once you're airborne it's important that you reduce drag in order to build up speed.
Keep your throttle on its full setting, and pitch the nose slightly upward until it's at about a 20° angle. If you start to lose airspeed or if the STALL warning appears onscreen, dip the nose down until you're again flying level. Then, resume climbing at a gentler angle.

As long as no approaching aircraft are in your flight path, you can maintain this climbing position until you reach the desired altitude. You can also angle gently toward your first waypoint, although turning will sacrifice some airspeed and lift.

Once you decide you're ready to level out, reduce the throttle until you slow down to the desired cruising speed (flying on full throttle quickly consumes fuel, and you might not have enough to make the return trip home). Make slight adjustments to the throttle setting until you're flying at a constant speed and altitude.

..Retract landing gear
..Maintain full throttle
..Pitch upward at a 20-degree angle
..Level out
..Reduce throttle to desired airspeed
..Make slight throttle adjustments until you have a constant speed and altitude

DESCENDING / DIVING
There are two methods by which you can reduce your altitude. First, you can reduce your throttle setting, which creates less lift and therefore drops your altitude. If you aren't particularly concerned with getting down in a hurry, this method is fine. You maintain level flight without losing noticeable airspeed (although you reduce the throttle, your aircraft gains some speed while descending due to gravity).

The second method is to redirect the nose by pitching down. This is the more drastic method—you bleed off altitude in a hurry and gain airspeed. The dive is often used to attack a lower-flying aircraft or as a recovery procedure following a stall.

Be wary of prolonged dives or extremely steep dives at low altitude—your aircraft's controls may "freeze" due to compressibility (air moves so quickly over the control surfaces that they're rendered useless).

..Decrease throttle to slowly lose altitude at the current airspeed
..Alternatively, pitch down to descend quickly and gain airspeed

BANKED TURNS
Turning is also know as banking, or combining pitch and roll maneuvers to alter your heading. By pulling the stick back and either left or right, you make a banked turn. You can also apply rudder in the intended direction of the turn to make the turn more quickly.

If you enter a banked turn without adjusting the throttle, you lose altitude, airspeed, or both by the time you finish turning. This occurs for two reasons. First, you change the angle of attack (angle of the wings as they meet the airflow).

This creates drag that slows down the aircraft. Secondly, lift acts nearly perpendicular to your aircraft's wings. If the wings are angled, so is the lift vector. You have less pure vertical force, so you drop in altitude.

If you want to maintain altitude and speed, apply extra throttle before you start banking.


..Push stick left or right to bank the airplane.
..Pull back on the stick to begin the turn.

LANDING
Landing sounds simple—you reorient your aircraft's nose so that it's pointing in the general direction of the airfield, bleed off some speed and altitude, lower the gear, and touch down. But in reality, many factors affect whether you land an aircraft safely or convert it into a junk pile.

Landing takes a steady hand and a smooth series of changes in throttle and pitch. When you're ready to land, you need a range of at least 5 km from the airfield. Make sure you are flying level at about 150 meters of altitude and that your throttle is set to about three-quarter speed. Drop the gear and lower the flaps—with flaps, you have more lift and can slow down without going into a stall. Gently pitch down to start your descent, striving for a maximum airspeed of about 190 km/h.

Once the aircraft reaches the edge of the runway, you should have between 6 to 9 meters of altitude. Pull the stick back firmly to raise the nose up past the horizon and chop the throttle to zero. The main wheels will touch down. As your skills progress, you may even touch down all of the aircraft's tires simultaneously.

..Line up with the runway 5 km out
..Fly level at 150 meters of altitude
..Reduce speed until you're below 190 km/h
..Lower the landing flaps
..Lower the landing gear
..Gently pitch down
..Reduce airspeed even further
..At the edge of the runway, with 6 to 9 meters of altitude, pitch the nose up 15°
..Cut the throttle to zero

STALLS
A stall is the loss of lift. They occur because your aircraft's speed has dropped below the airspeed required to maintain lift. Without lift, your aircraft falls toward the ground and your control surfaces are useless, much like a sail without a breeze to propel it.

Stalls are most commonly experienced during tight turns, steep climbs, loops, or takeoffs and landings. To solve a stall situation, let the aircraft fall and try to keep the nose oriented toward the ground (most aircraft nose down automatically). Make sure the throttle is set at 100%. Eventually, this buys enough airspeed to restore airflow over the control surfaces and let you regain control of your aircraft.

Let the aircraft fall to regain airspeed, then slowly level out when controls respond
Increase throttle to 100% if it is currently lower
Alternatively, increase throttle to regain airspeed

SPINS
A spin is a special type of stall that happens when one wing loses lift, but the other does not. More often than not, a spin occurs when you make a hard turn and have the nose pitched too steeply. Lift fails on one wing, and it begins to drop toward the ground. Meanwhile, the opposing wing keeps producing lift and rising. If the rudder is engaged, it rotates the aircraft about its yaw axis. The result is a spinning corkscrew motion.

All aircraft have a critical angle of attack, or a maximum angle at which the wings can still provide lift. If you nose up drastically at high speeds, you may surpass this angle and initiate a stall or spin.

To recover from a spin, you have to neutralize the aircraft's rotating motion. The best way to accomplish this is to center the stick and apply rudder in the opposite direction of the spin. Then, nose the plane downward. Hopefully, you'll have enough altitude to recover and break out of the spin.

..Restore stick to center position
..Apply rudder opposite the spin (if you're spinning left, apply right rudder)
..Pitch down
..When you stop spinning, level out