Aerospace Science & Technology

 A photograph of the airplane I rent at KGAI.

In order to do solo cross country flights, you have to have a current solo endorsement. My endorsement expired and I had to renew it. This is done by flying a few times in the pattern doing landings and takeoffs. The plane I flew was N51079.

Before starting the engine, I got the weather: winds 250@5, favoring runway 32. What I did not realize was how quickly they were changing direction because by the second landing the pattern had switched from runway 32 to runway 14. The engine start was performed via checklist.

After starting the engine, I taxied to the engine run-up area. The engine is set to 1700 rpm and the magnetos, controls, and engine gauges are checked. Upon takeoff, the aircraft almost leapt off the ground before I reached the rotation speed of 55kt due to its light weight (half tanks on each side and only me inside). I had to pitch the nose of the airplane down to gain speed before letting it climb. I was not expecting the handling qualities of the airplane to change so much at a lighter weight, but they did. That’s flight dynamics in action for you!

The first landing wasn’t so bad, but there was some turbulence near the runway. After my first full stop landing I taxied back to runway 32 and took off again. After flying the pattern to my base leg and final, I overheard on the radio someone else turning to base on runway 14 (the opposite side), and someone was holding short to take off (also runway 14).  Apparently the winds had changed directions while I was in the pattern.  I could have landed since I already called final, but since one guy was already on base and another holding short, I powered up and went around. Keeping in mind he was on base (soon to be final on runway 14), I would be climbing right over him as he was landing and we would both be in each other’s blinds spots. So I climbed upwind of runway 32 and turned to the left since he would be turning from base to final from the right. As I was climbing out I got a visual on him in my rear right window below my altitude. I reported I had him in sight and continued my climb. When I was three miles out I did a 180 degree turn and made a straight in approach to runway 14. I had to adjust my speed on final because the person who was holding short of runway 14 was taking off as I was on final. By the time I reached the numbers (end of the runway)  he was well upwind of me and turning to his crosswind.

One thing to note was that this flight was at 4:00 pm on a Friday. When the sun shines on the surface of the earth it heats it up. Depending on the surface being heated (road, grass, houses, trees) temperature gradients are formed that result in pockets of air that rise at different rates. When you fly thorough this air it is felt as turbulence due to thermal convection. From a sensory perspective you're flying along there is a sudden and strong kick (or sink) that makes the airplane jolt. After about a minute of this your back decides enough is enough.  

Another problem was that the winds were coming in the direction favoring runway 14. This end of the runway has a tree line that is close to it. As the wind flows over this tree line, it’s forced to go back down suddenly where the tree line ends. This causes the air to swirl or eddy. This form of turbulence makes it difficult to land as you get close to the ground and is known as mechanical turbulence and can be seen graphically in the picture.

A third effect that occurs is known as ground effect. The wings of an airplane generate lift partly by displacing the air downward (downwash). As the airplane gets close to the ground, the downwash is deflected back up by the surface of the runway. This deflected air hits the wing, pushing it upwards, resulting in more lift as you get closer the ground. This is the airplane glides for a few hundred feet before the wheels hit the ground on flare. In addition, the deflected air also strikes the tail surfaces at the back of the airplane, increasing elevator sensitivity. This increases the chances of porpoising the airplane (PIO- Pilot Induced Oscillations - which happened every time I landed). If the porpoising becomes severe, a prop strike can result. The severity of this depends on how light the airplane is: remember that a heavier airplane will always fly better in turbulent air.

The combination of the wind changing directions on me, the airplane being very light, a hot humid day with turbulence, ground effect, and my sloppy set ups for final approach was making this flight tiresome. It was becoming more and more draining   (physically and mentally) to get the airplane on the ground after each landing.

It was starting to get really choppy up there and I wasn’t sure if I wanted to do another landing or not. I should have just stayed on the ground after I landed, but I decided to give it another go since this time I would be in the pattern correctly and hopefully set up for final a little better. Even while being in the pattern it ended up being no better than before. It was bumpy, throwing the airplane all over the place. Making this worse I turned to final too soon and ended up left of the runway. I had to correct this by stopping the turn and flying towards the runway at an angle and then re-initiating the turn again to line up. Once lined up with the runway, the winds started to push me to the left and I touched down way off centerline (not a big deal), but it was porpoising far worse than the other landings. It touched the ground three times, but the amplitude of each bounce was equally strong ( It’s possible to get the airplane into a mode where the bounces amplify and can structurally damage the airplane.). With that in mind I added full power climbed out to try another attempt.  I ended being too slow in retracting the flaps because I was too busy watching the airspeed indicator to try and not to stall on climb out. The result was a very slow climb rate. After I realized this I threw the flaps up one notch to 20 deg. The loss of lift caused the airplane to lose a bit of altitude (as expected). After a second or two the airplane gained some speed and resumed climibing.

Next time I fly with my instructor I will make sure we go up on a hot day where the winds are favoring 14 and practice approaches in bumpy weather. Having him in the plane with me to point out my mistakes will be vital.