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Parachute efficiency question


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I am seeing inconsistent behavior from the parachutes. At least, behavior inconsistent with my naive idea that all parachutes are basically equal and depend only on weight.

This thing is a Digger. It weights 80 tons (with tanks empty, as is the case right now), and it has 8 radial parachutes, so 800 kg, so 1% of its mass.oyF91Cu.png+

Here it is seen rocket braking just before the landing. But in the next picture, taken from inside the cockpit, it's just gliding down, and you can see it's going at 30 m/s

8fAWzCW.png

And the next ship is Stool. Stool weights 15 tons when full, as was the case in that landing. It has a single Mk3 parachute, so 300 kg, so 2% of its mass

PeA37Xz.png

Yet it's coming down at almost 50 m/s.

It's still pretty high up there, and it slowed a bit more before reaching the ground. Still, it was falling at more than 40 m/s.

So, Stool has twice as much parachutes by weight, and yet it falls faster than Digger. Digger was landing at a mildly lower altitude there (5000 m for Stool, 2500 for Digger), but even taking that into account, it's not enough to justify the difference in terminal velocity. Heck, it would not be enough to justify the difference if the parachutes were equal! I once landed a Digger at 5000 m, just a few km from where I eventually landed Stool, and it was still going slower than 40 m/s.

 

How is it possible that more parachute mass results in less parachute efficiency? Is the Mk3 parachute crappy? Are multiple overlapping parachutes more effective because of some glitch? Were parachutes reworked in the last update? (Digger landing is around january, while stool is from earlier this week). Is there some other reason?

 

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It's fairly easy to test this on Kerbin. Use an identical craft that has both types of parachutes, and probably a SRB, so that the launches are identical. Launch straight up from the launchpad and test. Open one set of parachutes or the other, and check their terminal velocities while descending.

I think you will find that the efficiency of the parachutes do not scale with mass, and the MK3 parachute is crappy. Also, mulitple overlapping parachutes are more effective because of a glitch. Also, the more you increase the spread angle, the more effective the parachutes are.

 

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Parachutes mounted in symmetry give around an n^1.5 bonus don’t know why if that’s relevant.

If only there were a mod you could use to calculate parachute requirements before you even launched.....

 

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