The Philippine Flight Simmers Group is one of the best communities on aviation in the Philippines. There are aviation enthusiasts of all ages, from pre-teens to retirees, and also a lot of active pilots on the Forum, from all over the world. PFSG deserves an article by itself, really.
PFSG’s Kevin and Iyoy, friends who actually care a lot, weighed in on that last takeoff from Baguio,via SMS.
We all learned in ground school that air becomes less dense with altitude. The higher you go, the thinner the air. Sort of like some politicians running for higher office. They get a 50-knot breeze between their ears… .
Thinner air means less “lift”, the upward force that, er, lifts airplanes into the air. This is highly simplified, but a more technical discussion would lift your eyes towards the sky.
Loakan airport is 4,250 feet above sea level. Small training airplanes usually fly at 1,500 to 3,000 feet. Sitting on the ground at Loakan, a young pilot could be higher than he has ever flown. Before even getting into the airplane, he is already in thin air.
Air also gets thinner with increasing temperature. The hotter it is, the thinner the air. Think of a packed gymnasium in summer. By afternoon, people stand farther apart from each other.
And you thought “Hot and High” was another article about pilot Angelina Jolie flying her airplane.
The aviator’s way of measuring the “thinness” of air is Density Altitude. When the air is hot, humid and therefore thinner, the airplane feels like it’s at a higher altitude. The apparent altitude at which the wing finds itself flying (or not flying) is density altitude.
The internet has density altitude calculators. I discovered this while looking for the latest babe Vice Presidential videos on YouTube (I typed in “Hot and High”). Instead I found a site that measures thin air.
The temperature at Baguio that day was 24*C, dew point 19*C, QNH 1021. The calculator gave me a density altitude of 6,296 feet, far higher than the 4,250-foot elevation at Loakan. Our wings were trying to take off in thin air. Then we had an inch of carb heat knob out, which I had failed to push all the way in.
Iyoy gave me of two more Density Altitude issues.
How many degrees more do u think d heated air is? Work dat into the DA and u know wat ‘hot and high’ really means for your internal combustion engine.
Iyoy has over a thousand hours in general aviation, but he flies Airbus jets now, so he tends to elucidate “Your internal combustion engine” like John Travolta would say, “Your Seiko”.
He’s right, though. With thinner air, the fuel-air mixture going into the cylinders would be short on air and rich with avgas. But we had already leaned our mixture for highest RPM. So that wasn’t the issue.
But he had more.
Also, don’t 4get ur prop is an airfoil too. U need xtra RPM 2 create req’d thrust at dat DA.
Note his use of “thrust”. Spoken like a real Airbus cockpit manager! Still, Iyoy hasn’t forgotten his propeller days.
It’s not just the wing that was grabbing at thin air. The propeller, a vertical wing biting into air, was struggling too. Few pilots think about that.
Iyoy has forgotten more about general aviation than I have ever learned. He used to fly airplanes to visit the girl who became his wife. I first saw him at a Philippine Hot Air Balloon Fiesta 8 years ago. He was in the process of winning the balloon bursting competition.
Iyoy flew with me once before he stepped up to the airline flight levels. He introduced me to oscillating stalls long before my aerobatic course with Meynard. He capped a thoroughly enjoyable afternoon by coaching me on minimum speed approaches for short field landings. The best aviators are those who get passionate about passing on knowledge.
But that’s another story.
Posted from Bangkok, Sep 29, 2008
Next: More from Kevin and Iyoy on hot and high