- Both terms are still used.
- As a general matter, fast swept wing airplanes do not have benign stalls like straight wing low speed WWII airplanes did. It’s far more important to stay well away from the stall or even near-stall environment in swept wing airplanes (setting aside fighters & such). Actually getting a bizjet, airliner, military transport, or bomber to the aerodynamic stall is a very bad idea.
So fly-by-computer airplanes will have envelope protection systems that will prevent the airplane from getting close enough to the edge to feel the actual aerodynamic burble.
Lesser bizjets and heavies will have artificial warning systems intended to fire off before the burble starts. If those fail or are ignored you’ll get to feel it.
3) “Burble” is a gentle rhythmic turbulence-like buffeting or vibration of the whole airplane caused by turbulent flow along part of the upper wing surface that’s physically shaking that part of the plane. And hence shaking the whole plane at least some. In a low-speed straight-winged airplane it feels kinda like driving over the rumble strips they have along the edge of the freeway to warn you that you’re drifting into the shoulder. But more like how those feel at 30mph than at 75. A shake, not a buzz.
FYI - “flutter” has a specific aerodynamic / structural dynamic meaning. Your use of it as a layman’s descriptive term was apt at that level, but dead wrong at the technical level. In a burble, the wings will be vibrating, but not “fluttering”.
“Mush” is used in a couple of different but allied senses.
- In any non-computerized airplane as you get slower the controls become less responsive. It takes more and larger pushing and pulling to make the nose move. At the same time, for non-powered controls as found in current lightplanes and WWII planes, the feedback is softer. At high speeds it feels like stirring a pot of fudge. At low speeds it’s like stirring a pot of beer foam. The control impression changes from a direct connection where you push against typical resistance and the airplane moves as expected to instead you push against little feedback and the airplane slowly wallows sorta where you’re trying to herd it towards. The polar opposite of “crisp” is “mushy”.
The other sense relates to power available versus power required. Which requires some background explanation.
Maintaining altitude requires different amounts of power at different speeds. The faster you go towards max speed, the more power it takes to do that. Eventually at max power you’ll discover the max level flight speed for the conditions you’re in. The only way to go faster from that condition is to start downhill.
So far, so like a car. Now it gets more complicated.
Because of the nature of aerodynamic lift, the *slower *you go below a middling speed, the more power it takes to hold altitude. In essence as you slow down the wing becomes less efficient and you need to make up for that decreasing efficiency with more power.
Depending on how powerful your airplane is, you may have enough power and then some to hold altitude while slowing all the way down to just above a stall. Or you may find that you run out of power before you get slowed all the way to stall. But unlike the high speed case that’s not stable. You’re slow and have insufficient power to maintain speed. What happens next is you continue to slow uncontrollably until you stall. Or you augment your power with a descent. Sliding downhill is another form of power to let you maintain speed above stall.
An unstoppable descent caused by lack of enough power at low speed is also called a “mush”. Near the ground a “mush” sometimes turns into a “crash.”
Note that both forms of mush occur together when a simple airplane gets slow. First the controls get increasingly uncrisp = mushy. Then if carried far enough beyond your power available, you completely lose the ability to maintain altitude and *will *descend gently or less so until something changes. Inherently low powered airplanes or even high powered airplanes when operated at extreme high weights, temperatures, and/or high altitudes are prone to mushing.