When do parachutes rip off?

[Zwer.ch]

Kello,

I'm wondering when do parachutes rip off the ship during deployment? E.g., is there some kind of rule-of-thumb how much mass could be attached by/to the parachute?

I feel that I tend to attach too many parachutes, maybe less would do. But I don't want to test this the hard way and crashland Jeb

Edited December 19, 2013 by Zwer.ch

[Geschosskopf]

It's more about speed at opening than anything else, although number of chutes also plays a part. The faster you're going when the chutes fully open at 500m AGL, and the more chutes you have, the harder the jerk.

To determine the correct number of parachutes, use the handy parachute calculator

To avoid going too fast, don't try to land directly from interplanetary transfer orbits .

In general, though, 1 small white chute = 2 radial chutes and can safely land up to about 2 tons. 1 big bluetip chute can safely land about 4 tons so is about equal to 2 small whites or 4 radials.

[Smidge204]

Like any part, the "joint" between the parachute and what it's attached to will fail at a certain force. That force is based on for fast you're going when the chutes deploy. So the slower you're going the less likely they'll rip off.

Using more chutes and deploying them earlier, so they remain partially deployed to slow you down, will help. Drogue chutes (the orange ones) can also help.

In extreme situations, you can use thrust to slow you down at the last possible moment so your chutes can deploy safely. Sepratrons are particularly good for this on heavier vessels.

You can also strut parachutes to the craft, increasing the attachment strength. I've had to do that with a large Eve lander... doesn't feel right, but it works!

=Smidge=

[Sirrobert]

If you are in physics warp, they will probably rip off when they fully deploy (on Kerbin, the big chutes deploy 500m above the surface).

[numerobis]

In general, though, 1 small white chute = 2 radial chutes and can safely land up to about 2 tons. 1 big bluetip chute can safely land about 4 tons so is about equal to 2 small whites or 4 radials.

What matters is the mass of parachutes; the small white one is 0.1t, radials are 0.15t, the big blue one is 0.3t, and effectiveness scales accordingly.

Parachutes deploy at 500m altitude. The speed you're going at that altitude is going to be terminal velocity almost no matter how fast you entered the atmosphere -- about 100 m/s at Kerbin or Laythe sea level, 65 m/s at Eve sea level. Duna is the only place with atmosphere thin enough that you won't have bled all your speed off yet.

Forces on your craft when parachutes deploy are gravity and drag. Drag on your parachutes is extremely high, which means huge force on the joint between the parachute and what it's attached to. Adding struts from the spacecraft to the parachute can help -- but then you still need to make sure what you attached to the parachute doesn't tear off from lower parts of the spacecraft. Another way to reduce the jolt is to add another force: thrust upwards right when the parachute is about to extend.

[Kasuha]

Another way to reduce the jolt is to add another force: thrust upwards right when the parachute is about to extend.

Or use drogue.

Come on, people. Drogues are the first thing you should be considering when you have problems with chutes tearing your ship apart.

[Tic-Tac]

Opening the chutes earlier is the first thing that comes in my mind,slows down faster.

I usually don't have enough area on my landers to put any drogue xD

[Smidge204]

Parachutes deploy at 500m altitude.

That's tweakable now. There's also fully deployed and partial deployed - 500m is the default fully deployed for normal chutes.

Which leads to...

The speed you're going at that altitude is going to be terminal velocity almost no matter how fast you entered the atmosphere -- about 100 m/s at Kerbin or Laythe sea level, 65 m/s at Eve sea level.

Terminal velocity is a function of drag, not altitude. Thanks to partially deployed chutes, your terminal velocity can be much lower than a craft without chutes... and the more chutes the lower it gets. So more chutes DO help, but it's diminishing returns.

Drogue chutes are fully deployed at 2500m by default, and provide more drag than a normal chute that's partially deployed but not as much as a normal chute fully deployed. They're a good way to slow down heavy craft coming in at steep angles (where you will NOT reach terminal velocity before reaching Kerbin's surface!) but you'll still need something extra for a safe landing.

=Smidge=

[Starwaster]

get Real Chutes by stupid_chris, the guy with the creepy deer avatar pullings hooves off like gloves and wriggling writhing fingers after...

[Skorpychan]

Drogue chutes are, generally, the best way to slow a craft down and prevent chute shock. They provide a hell of a lot of drag when they open.

Otherwise, pop the chutes as soon as you hit atmosphere, so they partially deploy and provide drag. Should slow you down enough to pop a drogue, then the regular chutes once you're at the right height.

If you don't have room for a drogue, make room. They're invaluable.

[Kasuha]

They're a good way to slow down heavy craft coming in at steep angles (where you will NOT reach terminal velocity before reaching Kerbin's surface!) but you'll still need something extra for a safe landing.

=Smidge=

The only case when I was over my terminal velocity when 500 m above Kerbin surface was when I was coming from Jool and trying to hit KSP which happened to be right in the middle of the globe. So I came at some 8 km/s straight down.

If you're using partially deployed chutes to slow you down before you reach 500 m, you're using way too many chutes instead of just a few drogues.

When landing anything bigger than just the pod, put one or two drogues on it. Just try it and you'll see the difference.

You can mount drogue radially using cubic octagonal struts, too. If you're not afraid of part clipping, you can stick the drogue to the point near the ship. It looks perfectly and works like charm because drogues don't produce enough force to rip the strut off.

I usually don't have enough area on my landers to put any drogue xD

Perhaps you can save some area by removing a few chutes?

[Zwer.ch]

handy parachute calculator

That one is indeed useful, thanks for that.

Thanks all for this heap of hints and the good discussion ...awesome community

Will make use of the drogues when the science tree allows for that.

[Sirrobert]

Terminal velocity is a function of drag, not altitude. Thanks to partially deployed chutes, your terminal velocity can be much lower than a craft without chutes... and the more chutes the lower it gets. So more chutes DO help, but it's diminishing returns.

Drogue chutes are fully deployed at 2500m by default, and provide more drag than a normal chute that's partially deployed but not as much as a normal chute fully deployed. They're a good way to slow down heavy craft coming in at steep angles (where you will NOT reach terminal velocity before reaching Kerbin's surface!) but you'll still need something extra for a safe landing.

=Smidge=

It is a function of air density though, which changes with altitude