Wednesday, May 30, 2012

Slow Flight - Is it Possible


With an Instructor aboard, if you are a student pilot in training, you will learn a valuable lesson about flying. 

After reaching a safe altitude for demonstrating aircraft flight characteristics, according to your Instructor's directions, trim your airplane for straight and level cruising speed. Once this is achieved cut back on your RPMs. Now do whatever is necessary to maintain your altitude. 

What I remember, it took a lot of back pressure on the stick to maintain altitude and the plane flew slower. The discovery that it could continue to fly, albeit slower, without stalling, was invaluable.

Think about it. The nose of the airplane was well above the horizon but it was maintaing a constant altitude at a slower speed. Most folks would think the airplane should be climbing - but it wasn't. The flight path of the airplane remains level.

Your lesson, slow flight is a great way to teach you about angle of attack. Angle of attack is defined, another way , as the difference between where the airplane points and where it goes - in his case straight and level flight.

Your flight instructor may warn you that, yes, you are close to a stall but the airplane has not stalled. As long as you maintain the same back pressure and power settings the plane will fly as long as you want it to.

This is "slow flight" training. The CAP uses this technique to carefully survey a site where a person lost in the woods can signal you and be found. It is a "search and rescue" technique.

With experience you will find many airspeeds, power settings and back pressures that allow slow flight to occur without the airplane stalling.

If you fly powerful single engine aircraft, like the Beechcraft Bonanza, they can maintain slow flight. Be careful though, they can heat up quickly that won't allow you to maintain slow flight for long periods. You can help the engine cool through the use of cowl flaps.

Newton's Law is very important in slow flight. The increase in angle of attack is necessary, at slower speeds, to force enough air mass downward to result in an equal but opposite force upward that exceeds the weight force of the plane. It keeps flying. The wing is "planing" through the air.

If you water ski you understand this well. When the towing boat first applies power the angle your skis make with the surface of the water is the angle of attack. It is high (angle of attack) at first, to reach a point where the downward push of water causes an upward force that begins to slowly force your skis and you toward the surface of the water. This occurs as the towing boat gains more and more speed. Finally you are skimming the surface of the water and the angle of attack in much lower. simple isn't it.