# Trivia Testers : Oooh, Dad!

Oooh, dad! Can I get one of those for my bike?
The world’s smallest jet engine (whether turboprop, turbofan, or turbojet) used in a “real” passenger carrying aircraft weighs in at

1. 19 grams
2. five pounds
3. 75 pounds
4. 225 pounds

Looking sharp, moving fast
Hypersonic vehicles do not generally have sharp-edged wings or noses. Why not?

1. Shock waves above Mach 5 are parabolic, not angular, and so they don’t need to be pointy. Blunter structures are stronger, not to mention cheaper to make.
2. Sharper and “pointier” objects have proportionally greater surface area to volume ratios. Therefore, they have more area to heat up, and less volume with which to absorb that heat. Even inconel, with a 1370 deg C melting point, cannot hold up to hypersonic flight when fashioned into something sharp, skinny, and pointy. That’s why the front end of the Space Shuttle looks about as sexy and suave as a sea manatee.
3. They can be sharp and spiky, actually. That surface area to volume stuff is fuzzy thinking. The more surface area something has per unit volume, the easier it is for it to radiatively dissipate heat.
4. Surface insulation tiles, like the curvy brick jacket of silica fiber tiles sported by the Shuttle, can’t take load deformation, which is sure as heck what they’d get if they stuck out into a Mach 5 breeze.

Answer: B. There must be enough material to absorb heat. A pointy object would be much more likely to get so hot it that would just burn off.

Vector analysis isn’t just tedious. Why, it can be exasperating, too!
In a constant rate climb, the lift produced by an airplane’s wing is

1. exactly equal to its weight
2. greater than its weight
3. less than its weight
4. equal to its weight, but only at L/Dmax.

Answer: C. In any sustained climb, the lift produced by the wing is actually less than the weight of the airplane. How can this be so? In unaccelerated straight and level flight of course, lift equals weight. Now take an F-16, climbing at a steady rate, straight up. The wings are contributing nothing; that GE or Pratt and Whitney is doing all the work. Okay, now take your Beetle Bomb Bug Smasher, climbing like a scalded ape at a dizzying climb angle of, oh, six degrees. Does the same thing hold true? Yup. When you pull back on the controls, whatever thrust is coming from that prop, multiplied by the sine of your climb angle (which would work out here to about one tenth of it) is what’s helping hoist you skywards. (So now only nine-tenths of that thrust is left to counteract drag forces, and guess what? You slow down.)