Catapult launch VTOL

So here is the setup: my tailsitter VTOL plane will be submerged under water (held under by a rope with a release mechanism). When the vehicle wants to takeoff, it will cut the rope, thus launching itself into the air (due to the buoyant force). You can imagine this as a vertical catapult mechanism. The whole system will be autonomous. What i want is, for it to detect when it starts to move upward, then start the takeoff procedure. (Think of it like an ICBM launch from a submarine) I thought that the “catapult launch” section detailed here would be the closest to what im trying to achieve. Is catapult launch-hand launch supported for VTOL in arduplane? I wouldn’t want it to start the motors underwater as the ESC’s shut off due to the high water resistence. Will setting TKOFF_THR_MINACC and TKOFF_THR_DELAY be enough to achieve this effect? I will have a companion computer and i may use it to detect when the speed of the craft goes to zero (top of the arc it will draw as it shoots out of the water), then switch to TAKEOFF mode, but this seems a bit iffy to me. Any help for anything will be greatly appreciated! Thanks in advance!

As long as you have sufficient buoyancy margin to trip launch detector (high enough acceleration for required amount of time) it should work.

Do you have a plan to use speed sensor as IIRC it is recommended for planes and especially VTOL? How will you protect it from water?

Thank you, we wont be able to use a speed sensor as barometric sensors and water dont mix well afaik. We plan on having most of the electronics in a waterproof box, and cover the rest in nail polish/epoxy.

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