Sunday, September 17th, 2006
This is interesting. Just the other day, I received some photos enclosed in an email describing what an airplane looks like precisely at the point of crossing from subsonic to supersonic speed. These were really great photos.
Ironically, today I was reading chapter 3 in the “Pilot’s Handbook of Aeronautical Knowledge” on aerodynamics and there was a discussion about this very topic. I thought there was an opportunity here…1. To show these great photos, and 2. To explain how this phenomenon happens.
Here goes, right from the book:
“When an airplane flies at subsonic speeds, the air ahead is “warned” of the airplane’s coming by a pressure change transmitted ahead of the airplane at the speed of sound. Because of this warning, the air begins to move aside before the airplane arrives and is prepared to let it pass easily. When the airplane’s speed reaches the speed of sound, the pressure change can no longer warn the air ahead because the airplane is keeping up with its own pressure waves. Rather, the air particles pile up in front of the airplane causing a sharp decrease in the flow velocity directly in front of the airplane with a corresponding increase in air pressure and density.
As the airplane’s speed increases beyond the speed of sound, the pressure and density of the compressed air ahead of it increase, the area of compression extending some distance ahead of the airplane. At some point in the airstream, the air particles are completely undisturbed, having had no advanced warning of the airplane’s approach, and in the next instant the same air particles are forced to undergo sudden and drastic changes in temperature, pressure, density and velocity. The boundary between the undisturbed air and the region of compressed air is called a shock or “compression” wave.”
So there is the boring stuff. Here is the cool stuff…
…and yes, in case you thought it couldn’t be done…a single prop small airplane has broken the sound barrier. Don’t ask me how this was done. Apparently this was a secret project and there were rockets propelling the craft. It is my understanding that this speed would tear the airplane apart, but from the article I read, there were modifications done that would prevent this.
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Wednesday, August 23rd, 2006
I was pretty excited to get going again. I had been watching the Private Pilot Ground School DVDs, so I was very motivated to put all of my new knowledge to use.
It’s funny, when you sit at a computer and watch a video on how to do something, you really think you can do it. The videos explained a lot on ground work, like the pre-flight inspection, taxiing and all that, but I am not sure it prepared me for what was to come during this lesson.
I showed up at Freedom Air at about 7:55. The flight instructor, Yigal, arrived a few minutes later. He and another person pulled a Piper Cherokee out of the hangar and we went over some basics for about an hour. Yigal covered some things like aerodynamics of an airplane wing, dispatch procedures, the use of checklists (which I now have laminated), certificates and documents, the aircraft preflight, decision making and judgement, engine controls, flight controls and fuel grades.
After all this, we got in the plane and it was suggested that I taxi to the runway. I did so, only after zig zagging all over the place. A little note, you steer an airplane with your feet. You also brake with your feet. Each pedel has two sections. This took a while to get used to. I also used the radio to make a few calls. I thought to myself that Yigal was really having me do a lot right off the bat. Well, right after I had that though, he instructed me to pull the airplane onto the runway, give it full throttle, and when we reach 65MPH, pull back on the control yoke (sort of like a steering wheel). I was wondering why he wanted me to do that, and then it struck me…he wanted me to takeoff! Ok, I was fine. I pulled out from the waiting area, made a right onto the runway, stopped, gave the plane full throttle and began to accelerate. For some reason, the plane kept trying to go to the left. Yigal kept saying, “Keep it in the center, keep it in the center.” Easier said than done when you are trying to steer with your feet and you keep thinking and any sudden move is going to tip the plane over. The reason planes pull to the left during takeoff is because of the torque of the engine, propeller slipstream and gyroscopic precession. So we hit 65MPH before I knew it and I began to pull back on the yoke. Strangest thing happened…we began to rise. We climbed at 85MPH until we hit 3000ft. Now that was pretty cool.
Now that we were up in the practice area, I controlled the airplane for about a half hour. Yigal had me practice left and right turns at a 20 degree bank as well as turns to specific headings. This gave me good experience feeling the turns, using the instruments and using the horizon as a guide. After this was done, Yigal took back the controls and landed the plane.
Next lesson, Sept. 1, 8:00AM.
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