MAYBE NOT EVEN STEVEN
For many Cessna singles, why will fuel burn NOT be the same between the two tanks when the fuel selector is on ‘Both’?
- Manufacturing differences, which may include slight variations in fuel line legths and drain forces, can favor one tank over the other by several percent.
- Flying just slightly wing low can effectively cancel the equal draw of the ‘Both’ position. (In this case, the higher tank will empty faster.)
- There is no bias, trim-induced or otherwise. ‘Both’ means both!
- The fuel vent, located below the left tank, is the culprit.
Answer: D. Older Skylanes in particular (prior to about 1979) had this problem.
Even with the fuel selector on ‘both’, pilots have often seen one tank (in this case, the left) seemingly empty faster than the other. Whenever fuel is used up, it needs to be replaced with air, lest a vacuum form inside the tank, which could lead either to interruption in fuel flow to the engine, or in the case of bladder tanks, simply deformation as they get ‘sucked dry’, or worse, with non-bladder tanks, structural deformation. First, there is an ‘L’ shaped vent tube behind the left wing strut, and this is connected to the upper outboard section of the left wing tank.
There is a vent interconnect line between the upper inboard areas of both left and right tanks, to equalize pressure between the two. But when the tanks are full—and the slight dihedral of even a high-winged airplane doesn’t help here—this interconnect line can actually be ‘submerged’. As fuel is used, air coming in from the vent tube pushes fuel through to the right tank, replacing fuel as it is used from it. (This can even continue as fuel drains below the level of the inboard interconnect tube via the occasional sloshing over the interconnect port.) This has been seen to occur even to the point that the left tank is reading only 1/3 full, and the right tank is still reading ‘full’. No fuel starvation will occur however, as the engine is still indeed accessing both tanks–although fuel exhaustion is never less likely if you let them both run dry! (Another nagging problem these vents cause is of course overflow, if you fill the tanks with cold fuel and the fuel warms enough, as the temperature rises.)
EARLY BEGINNINGS
Who was really the first person to design a balloon for lighter-than-air flight?
- Lao-tzu, 6th century BC
- Leonardo da Vinci, 1452-1519
- Francesco de Lana (Lana-Terzi), 1631-1687
- the Montgolfier brothers, 1782
Answer: C. In 1670, an Italian Jesuit (and professor of physics and mathematics) by the name of Francesco de Lana studied the principles of the balloon and designed a ship consisting of four spheres, from each of which the air was to be removed, and which would be attached to a basket. He correctly deduced that if the air displaced by the balloon is heavier than the balloon, then the balloon would fly. Of course, no vessel could be constructed, then or now, that would be both light and strong enough (even one of spherical shape) to lift even itself alone by means of a contained vacuum.
SLIDING HOME
You’re about to enter the traffic pattern in a retractable gear aircraft, and when you lower the gear, much to your consternation, you don’t see three greens. After trying everything possible, including switching bulbs, checking circuit breakers, sudden pull-ups, performing the manual extension procedure, and a tower fly-by, and after you had tried everything else you could think of (or sought advice for over the radio, from folks on the ground) the gear is still up, and it does not want to come down. Which of the following surfaces would be best to land on?
- water
- a foamed runway
- concrete or asphalt, hold the foam
- grass
Answer: D. It would also be advisable to take your sweet time and burn off as much extra fuel as you could, within reason. Using a hard surface runway causes the least damage to the aircraft, and usually no injuries to those on board. Foamed surfaces are actually too slippery and also give poor deceleration and can easily result in a loss of directional control. Grass, sand and other soft runways (as well as landing on a body of water) are liable to cause parts of the aircraft to ‘dig in’, resulting in violent deceleration or sudden directional changes, all of which greatly increase the chances of injuries and structural damage.
