Imagine the scenario when a plane is flying, then it turns off its engine and nose dives. After gaining a lot of speed, if the pilot pulls the stick back and the plane now points upwards again, will the plane fly upward? Surely if all the forces acting on the plane bring it toward the ground, how could it recover from this and pull and fly upwards?
7$\begingroup$ The same way a car coasting down a big hill, can climb a small hill, at the bottom of the big hill. $\endgroup$– Mike SowsunApr 24 at 19:16
$\begingroup$ @MikeSowsun that is basically an answer. Could you post is a one? $\endgroup$– DeltaLima ♦Apr 25 at 7:57
$\begingroup$ @zander -- seriously, you should google up a video of sailplane aerobatics. Completely unpowered aircraft performing all kinds of loops, zoom climbs, etc. Then you can can make your own glider (paper airplane) and configure elevators/elevons so they try to pitch the nose up and then you can throw the plane downward and have the experience of seeing it climb upward higher than your head. Understanding that this can happen is hardly rocket science, though a full analysis of the forces at play is a little complicated. $\endgroup$– quiet flyerApr 26 at 21:01
$\begingroup$ @zander -- if your question were more stated in terms of "exactly how does this happen" rather than "is this even possible" I'd be more inclined to answer, but the question as stated is just far too elementary. Just a few minutes spent googling around the web would be enough to show that such maneuvers are in fact possible. $\endgroup$– quiet flyerApr 26 at 21:01
2$\begingroup$ I’m voting to close this question because -- shows no evidence of any prior research (see guideline aviation.stackexchange.com/help/quality-standards-error ) $\endgroup$– quiet flyerApr 26 at 21:04
In the very simplest terms, you can compare it to a car coasting down a big hill with the engine shut off.
Gravity will cause the car to accelerate downhill and build up kinetic energy. If there is a small hill at the bottom of the big hill, the kinetic energy will easily allow the car to coast uphill as well.
A descending aircraft also has kinetic energy and can also do a climb at the end of a decent.
Bob Hoover used to do essentially what you are describing as part of his airshow performance. During part of his show he would shut down both engines of his Shrike Commander (a business airplane) and then proceeded to continue flying aerobatics. There's plenty of video of him performing if you search around, such as here: video of Bob Hoover aerobatics The answer is that one can exchange potential and kinetic energy. Gliders are also capable of flying aerobatics. Again, it's not hard to find video.
This is a very simplified answer, but it fundamentally comes down to energy and energy management. Aircraft can, essentially, trade altitude for speed and vice versa.
Lift, the ability to fly, is ALL about airflow which in turn is all about speed. The faster you go, the more lift you can produce. Pointing the aircraft down trades altitude for speed, which means you have the ability to climb when you want it.
Now, of course, physics dictates that you can't do this forever due to outside forces such as drag and gravity - it's not a lossless process. You can't start from 10,000 feet, dive 5000ft and get back to 10,000 ft at the same speed. You'll either be lower, or slower and will eventually run out of both speed and altitude.
Incidentally, fighter jets make use of this in an emergency situation by trading their excess speed for height. Smaller aircraft tend to have little excess speed, so do the opposite and immediately start trading altitude for speed, to keep flying.
$\begingroup$ I thought that even if the plane is flying downwards, very fast and pull up, it will still have the velocity of its dive pulling it down, surely when they pull up the velocity isn't converted from downwards velocity to forwards velocity, is it? Demonstration of what I mean in this photo: imgur.com/a/kDUIKmP $\endgroup$– user68613Apr 25 at 18:08
$\begingroup$ @zander The downwards pull creates speed, which allows you to create lift which is the counteracting the downwards forces. $\endgroup$– DanApr 25 at 18:26
$\begingroup$ This question (as well as the others) is missing a description of the mechanics on how the downwards velocity is converted into forwards/upwards velocity. $\endgroup$ Apr 25 at 23:04