In Star Trek Beyond, they fix up the old Federation ship, USS Franklin. It wasn't made to fly in atmosphere, so in order to take off they need to propel it off a cliff and reach terminal velocity before the impulse engines can fire. (From what I can recall from a single viewing - if any of those assumptions are wrong please correct.)
What I don't understand is how does terminal velocity allow impulse engines to just "start working"?
The quote from the film is
Kirk: Scotty, can you get this thing started?
Scott: Started yes, Sir. Flying, that's a different thing. These old vessels, they were built in space. They were never supposed to take off from atmosphere.
then
Chekov: We have to achieve terminal velocity in order for the stabilizers to provide lift.
Quite why this is the case isn't explained other than it being treknobabble to explain why they need to push the ship off of the cliff.
Stabilizers are, at least in the Abramsverse, an integral part of starship atmospheric flight
“Mr. Sulu,” Spock exclaimed, “divert all remaining power to stabilizers!” “Doing what I can, sir,” the helmsman replied as he desperately fought to comply. “Doing what I can.”
Spock tried his best to see that the Enterprise’s vanishing energy resources were parceled out meticulously among the ship’s most critical active systems. While life support drew the most attention, he and Sulu attempted to steady the starship’s wildly skewing and rapidly failing artificial gravity. If he couldn’t stabilize it any better, there was a good chance a large percentage of the ship’s crew would never be able to make it to their assigned evacuation stations. Yet if he shunted power from life support to the precessers, there was a chance atmospheric pressure would fall too low and kill everyone on board.
Spaceships in atmosphere are usually depicted as flying due to downward force from an engine, like a hovering harrier. Since the Franklin wasn't designed to fly in atmosphere, it may not be able to direct sufficient force in a downward direction to effect a vertical takeoff.
So, if it can't just take off straight up, it must need to generate lift a different way. Assuming that the ship is producing lift via Bernoulli's Principle and an airfoil, needing a jump start makes perfect sense.
The lift generated by an airfoil is dependent upon the speed at which the craft is moving through the air. This means that the craft needs to get going fast before it can actually fly. This is why commercial aircraft require long runways, so they can get up to speed. As you may have noticed, there was no runway in front of the Franklin.
Therefore, before the ship could fly under its own power, it needed to get going fast enough that the stabilizers could keep it flying, despite providing minimal lift on their own. This required falling off a cliff.
In other words, it's just what Chekov said:
We have to achieve terminal velocity in order for the stabilizers to provide lift.
Even though I'm very late, was just rewatching this last night and came across this. Actually I think the 'jump start' was a wrong term that was used. What they were trying to do was trick the ship into thinking it was 'in space'. Though this is still accurate, it could explain why they needed to reach terminal velocity which means no external force in the ship. There is still the issue of newtonian vs relativity in terms of what justifies being 'space' but this explanation seems to fit better than the others. Unless they were just using terminal velocity cause it sounded cooler than same 500 m/s or so.
They specifically get the inspiration from the idea of the jumpstart. Then they basically "push started" the starship. So I'm assuming the older starships have a manual transmission, and they popped the clutch after getting up to speed. On a car, the wheels transmit the motion to the engine and engaging the engine suddenly can get the engine running without a battery. So, I guess there's something that rotates or moves on the basis of the air (or solar wind?) traveling on the outside of the hull, and engaging the engines suddenly allowed them to start without the power cells working.
But honestly, this part of the movie bothers me more than anything else they've done. It just makes no sense at all!
