Radial Parachute Numbers

[Jonfliesgoats]

Desired Vertical Speed (m/s) at Kerbin Sea Level.               Mass per Radial Parachute. (tons)

5                                                                                           .4  

10                                                                                       1.7

20                                                                                       6.8

40.                                                                                    27.2

[Xavven]

Nice! I wonder if we can get these numbers for Duna and Laythe, too.

[Jonfliesgoats]

Sure I just used the drag equation.  Substitute the rho (free stream air density) values.  I find from my experience on Kerbin that the above figures are pretty accurate.  

[Guest]

@Jonfliesgoats

FAR or stock? Or it does not matter?

[Jonfliesgoats]

Stock.  I am not sure about FAR.  

[swjr-swis]

11 hours ago, Jonfliesgoats said:

Desired Vertical Speed (m/s) at Kerbin Sea Level.               Mass per Radial Parachute. (tons)

You are missing the Spread Angle in this table. Makes a significant difference.

[Jonfliesgoats]

Very true!  I am playing on Xbox which is still waiting for 1.2.  Spread angle became a factor in 1.2.  You can approximate this, though.  If your canopy is offset less than thirty degrees from the slipstream (vertical) you should be within 90% percent of these.  If you are highly clustered, a 45 degree offset means your canopies are only about 70% effective.

IRL canopies also interfere with each other and generate lift rather than simple parasite drag (drag which varies as the square of dynamic pressure).  So canopies close together will jelly-fish, interfere with each other and really lose quite a bit of lift.

KSP doesn't model that stuff yet.

Edited October 30, 2016 by Jonfliesgoats

[KerikBalm]

the spread angle matters now? I thought it was just a visual graphics thing...

[m4v]

10 hours ago, KerikBalm said:

the spread angle matters now? I thought it was just a visual graphics thing...

yes it does, for some reason...

[crackerbal]

On 29/10/2016 at 4:53 PM, Jonfliesgoats said:

Desired Vertical Speed (m/s) at Kerbin Sea Level.               Mass per Radial Parachute. (tons)

5                                                                                           .4  

10                                                                                       1.7

20                                                                                       6.8

40.                                                                                    27.2

can u put a "0.4" better then ".4" on the first line thats realy confusing stuff

btw good job to post it !

[Meithan]

Back in the days we had this:

KSP Parachute Calculator

Sadly, it hasn't been updated in ages, last time being way before 1.0 came out (which heavily changed the aerodynamics of the game), so its results are probably not correct now. Calculating terminal velocity isn't hard, though, so it should be possible to mathematically deduce a rough rule of thumb for parachutes.

[samstarman5]

On 10/29/2016 at 9:30 AM, Xavven said:

Nice! I wonder if we can get these numbers for Duna and Laythe, too.

Schiaparelli would have liked to have known.

[Tyko]

On 10/30/2016 at 7:49 AM, KerikBalm said:

the spread angle matters now? I thought it was just a visual graphics thing...

Spread angle matters, but it's the reverse of what I expected - two or more parachutes with a higher spread angle produce more drag. A spread angle of 10 results in more drag from the 2 chutes than a spread angle of 1.

[KerikBalm]

Well, when at an angle, you may actually see lift effects, rather than straight drag... there may be real physics behind this

[Tyko]

2 hours ago, KerikBalm said:

Well, when at an angle, you may actually see lift effects, rather than straight drag... there may be real physics behind this

good point and I'm not sure if it was lift or drag causing the change...let me clarify     On a test vehicle descending under two parachutes my descent velocity decreases as I increase parachute spread - a spread of 10 resulted in lower descent speed than a spread of 1

 

[Jonfliesgoats]

IRL predicting how complex parachute systems interact with each other was very difficult.  As forces would change, the geometry of your lifting surface would change too.  This was one of those situations where there was really no substitute for actual wind-tunnel and flight testing until recently.  This is one of the reasons holes in the tops of round parachutes not only make the canopy more stable but even make it a more effective parachute!

Calculating parachute effectiveness in terms of drag is an antiquated method.  Parachutes, including round parachutes are lifting surfaces like any other wing, rotor, etc..  Still, if you need a quick 90%accurateish idea of what a simple parachute will do, the drag equations work.

In KSP, I find my cowardice makes for inefficient design.  So I needed to come up with a quick idea of just how much parachute to bolt on to a given mass.

[Terwin]

3 hours ago, Jonfliesgoats said:

In KSP, I find my cowardice makes for inefficient design.  So I needed to come up with a quick idea of just how much parachute to bolt on to a given mass.

The stage recovery mod(updated to 1.2), you can open a read-out in the VAB/SPH that will tell you estimated descent speed with full or empty fuel tanks of each of your stages.  I find it works well to hep me have enough chutes, but not too much.  (the default display is for empty tanks, but if I still have fuel, I can always turn on the engine just before I land to slow down if I am faster than I like).

[Jonfliesgoats]

Argh!  I can't wait for 1.2 to hit Xbox land!

[MitchS]

I can infer what "spread angle" means, I guess, but noting it has NEVER come up in my KSP experience. My KSP engineering style is "less is more," so I've always aimed for the lowest number of parachutes required and therefore have had to get a good feel for their behavior for effective landings... but are there dynamics of effective parachute usage that I'm not aware of...?