Budd Davisson instructs a student in his Pitts biplane at KSDL.
There are maybe a million questions that could be asked about any aviation subject. Actually, there are probably an unlimited number of questions, but what are some of the more basic ones that we should all be able to answer? We made up a quick list that includes general, basic questions that fit any airplane or condition, so they aren't specific to any given bird.
What's the conversion factor for changing knots to mph?
Just remember, it takes more miles to make up a knot, so you multiply by 1.15. (Easy way to estimate: Take 10%. Add half of that and add the total to the number
What's the conversion factor for changing mph to knots?
It's the inverse of 1.15 or .869 (1/1.15).
Use .85 if you're doing it in your head. Close enough.
What altitude and temperature are performance charts usually based on?
"Standard" test conditions are sea level, 29.95 inches of mercury and approximately 15 degrees centigrade (59F). As conditions go up from there, performance goes down.
Rule Of Thumb: How much gust factor before wheel landing a taildragger?
It depends a little on the airplane, but 15%-20% of its touchdown speed is often used.
If the battery dies, will the engine quit?
No, because it uses magnetos, which in the act of turning generate more than enough spark to run the engine. Except for starting, the engine doesn't need the airframe's electrical system to run.
Which is used to stop P-factor from turning an airplane in a climb—rudder or aileron?
Rudder. We're talking pure yaw.
What direction does P-factor push the skid ball in a climb?
Assuming a clockwise-turning propeller (as seen by the pilot), in a full power climb, the ball will be off to the right, because the P-factor tries to push the nose left. Right rudder is needed to center. The reverse is true in a power-off glide. The ball is off to the left, so left rudder is needed. "Step on the rabbit."
What's the purpose of the rudder?
The rudder's primary purpose in life is to correct unwanted yaw. It might be adverse yaw, while rolling into a turn, or that caused by P-factor. It's also used to control yaw in forward and side slips.
How does fuel load affect CG?
Aha! This is a trick question, because not all fuel tanks are located in the same place. In some aircraft, as fuel is burned, the CG moves aft, in others, it moves forward. So, it's a good idea to know which way the CG in your aircraft moves. It's possible to load an aircraft far enough aft that, as the fuel burns, the CG gets into dangerous territory.
How does an aileron cause the wing to move up?
The primary effect of an aileron (or flap, or rudder) changing position is that it changes the camber of the surface (the curve). If it goes down, it increases the curve, which increases lift.
How do flaps give a slower landing speed?
Same thing as a down aileron—they increase lift by changing the wing's camber line. See Fowler flaps below for another effect.
What's different about Fowler flaps, as on Cessnas?
Fowler flaps move aft as they go down, thereby increasing wing area, which also increases lift. Slotted Fowlers let the air bleed over the top of the flap through a slot, which lets the air stay attached longer. However, more lift always means more drag, so the nose must go down to maintain speed.
What is Glide Ratio (L/D)?
The Lift/Drag ratio determines how much altitude is lost for every foot moved forward. A normal, and good, glide ratio might be 10/1, 10 feet forward for every foot down. Some might only have four feet forward for every one down, so they come out of the sky quite quickly on approach. The ratio gets worse as flaps and gear come down.
How many magnetos does the average aircraft engine have?
Two, which is why there's a "right/left" marked on the mag switch.
How many spark plugs does a four-cylinder engine have?
Eight, two per cylinder, as in all aircraft engines. One top and one bottom, each fired by a different magneto. This is so there's a redundant ignition system in case of a mag failure or a plug goes bad. Some modern engines have one magneto and one electronic unit.
What color is 100LL gas?
It's very, very light blue. It's sometimes difficult to see the color, but if seen in the tank, the blue color is visible. This is important because jet fuel is colorless to a very light straw color. Also, jet fuel smells like kerosene (because that's what it is). When in doubt, check it carefully. Also, jet fuel has an oily feel when rubbed between the fingers.
Which of these is worse on landing—a quartering headwind or quartering tailwind?
The quartering tailwind is worse because not only does it increase the touchdown speed but, if strong enough, can give the controls a feel that can confuse a low-time pilot. A quartering headwind slows the airplane on landing and feels "normal."
Which is heavier, avgas or water?
Water is much heavier, which is why it sinks to the bottom of a fuel tank.
How much does a gallon of avgas weigh?
It's normally assumed to weigh six pounds per gallon, but in extreme cold (minus 40 degrees F), it can be as heavy as 6.4 pounds per gallon or as light as 5.9 pounds/gallon at 100 degrees F. For comparison, water weighs 8.34 pounds/gallon.
What does a fuel quick-drain valve do?
It's located in the low point of the tank or a fuel line where moisture, which is heavier than fuel, is likely to accumulate. It should be opened and run into a clear tester before every flight to see if there's water present. If there is, drain until no more water appears.
Will the wings fall off if the airplane reaches it's Never Exceed, red-line speed?
No. However, that speed is established by several criteria, one of which is gust protection. If at Never Exceed speed and a gust over a specific level is encountered, the Yield Limit of the airframe could be exceeded, and damage can occur. Also, the control force needed to exceed the airframe's G-limit is much lower, so a hard pull on the yoke, when fast, can cause damage. The Vne could also be set at a given level, because that's the highest speed for which it has been flutter tested. Red lines are to be respected.
How does an aft CG affect an airplane?
As the CG moves aft, the elevator pressures get lighter and lighter. If the CG is pushed out the back of the envelope far enough by too much weight, the elevator control pressures not only get feather light, but the airplane goes into an area of reverse command where it snakes up and down, and the pilot can't control it.
What does the FAA consider to be the average weight of a pilot/passenger?
Traditionally, the FAA has considered 170 pounds to be the average weight of those onboard light aircraft, but that assumption is under challenge, especially for bigger aircraft, and they're pushed up as high as 190 pounds. For weight-and-balance calculations for light aircraft, the known weight of each passenger on board should be used, and at least 10 pounds each added for clothes and modest answers. Few are truthful when asked their weight.
Define "Useful Load."
This is the combined weight of passengers, cargo and fuel that can be added to the empty weight of the aircraft and still be under its allowable gross weight. In most light aircraft, there will be a trade-off between passengers/baggage and the amount of fuel that can be carried. Only a few four-place aircraft can carry four FAA-sized passengers and full fuel, much less four "real" passengers that probably weigh 200 pounds each.
Is all the fuel in the tank available for flight?
It depends on the airplane, but most airplanes have a certain amount of fuel in each tank that's unavailable because the fuel lines don't access it. It's not unusual to have anywhere from one to two gallons that aren't usable. So, flight planning should never assume all of the fuel in the tank is available, even if the POH says it is. Always leave a margin.
There are lots and lots of other things we should know about the machines we fly. If, while we're looking at some part of the airplane and we ask our-selves a question, "Hmmmm, I wonder what if...?" it's time to seek the answer. Unanswered quessions aren't healthy in an aviation environment.