Parachute

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Parachute

Postby Lablabla » Sat Jul 31, 2004 5:47 am

Hi,
I'm using FSDS 2.24
I'm making a model of a skydiver and i'm having problem with the parachute...
it acts as a spoiler to reduce the speed (high spoiler lift in the air file), the problem is how can i pack it in the "bag pack" that the skydiver carries?
I'm using hald a sphere for the chute... but the bag pack is much smaller... i had an idea but then i saw that in Animation mode, objects can't be Scaled...
any ideas and suggestion will be appreciated
thanks,
La bla bla
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Re: Parachute

Postby aceronzo » Sat Jul 31, 2004 3:17 pm

To make it just appear,name it spoilerwell_l,or spoilerwell_r. When you deploy the spoilers it appears,when you retract it dissapears.If you want it to unfold you will have to animate it in parts,sections,or however you want to build it.You can name it r_Spoiler or l_Spoiler.There's more people out there who know alot more than I do.They might help you more.
Best Regards,
Ronnie
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Re: Parachute

Postby Katahu » Sat Jul 31, 2004 10:44 pm

Having to model a parachute to unfold, and open up like in real life requires an enormous amount of patience and trial and error.

What you should do [as suggested by Aceronzo] is divide the chute in small sections. Each section will need a specific animation tag. Each tag [if you plan to use the same name] must have a unique suffix to help FS from being confused.

Ex:

l_spoiler
l_spoiler_01
l_spoiler_02

r_spoiler
r_spoiler_01
r_spoiler_02

This may seem easy from the start, but naming the peices is only the tip of the iceberg. You will then have to CAREFULLY link each individual piece of the chute together. Not only that, you then have to CAREFULLY animate them in such a way that even then it gets completely confusing.

Imagine a round tablecloth over a round table.

Pinch the center with you fingers and pick up the tablecloth until it hangs like a closed umbrella without a handle. Lay it on its side and roll it up.

Now that you have this in your imagination, imagine that process in reverse if you want to open the chute from a bagpack.

I am not trying to discourage you from going forward with your parachute project, I am just warning and preparing you on what lies ahead of you. If you ever do succeed with your idea, I'll give you credit for such work. All of us have encountered road blocks in our 3D-modeling lifetimes. Fortunately, we all have the ability to learn how to get around those road blocks and eventually you will too. ;D
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Re: Parachute

Postby Lablabla » Wed Aug 11, 2004 6:21 am

OK, i sorted that one out, next question is in the .air file, what should be the value of the Spoiler Lift in order to be as real as it gets?
is there a way to calculate this?
10x,
La bla bla
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Re: Parachute

Postby IanK » Wed Aug 11, 2004 11:21 am

Hello Lablabla,
it depends on which way your vehicle is pointing. If your nose points vertically down, then zero lift drag coef would be about 1.2 The wing area would be the canopy opening area and lift would be irrelevant unless you are doing a parafoil.

If you remain horizontal the vertical drag depends on the lift and with no horizontal motion what is the angle of attack ... a bit more difficult.

For more hacking go to AvHistory Decode Forum.

Ian
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Re: Parachute

Postby Lablabla » Thu Aug 12, 2004 6:45 am

Hi,
I've tried what u've said but the problem is that in order to land it needs to fly in like an aircraft - a thing that can't be done with such a slow airspeed (horizontal)
how can i alow that skydiver to land almost vertically without upward power?
thanks,
La bla bla
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Re: Parachute

Postby Lablabla » Thu Aug 12, 2004 6:54 am

Ian,
the model starts in horizontal position - if on the ground then it's as if the skydiver lies on his belly, when activating the spoiler the torso (the main part of the skydiver and the parents of all othere rotates to vertical position - if on ground then it's as if the skydiver stands on his feets
thanks,
La bla bla
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Re: Parachute

Postby aceronzo » Thu Aug 12, 2004 6:19 pm

Lablabla,

You mite try playing with the weight,less means slower drop.Too low means wind will carry you,of course you will have to cut power thrust also.Something to play around with.Hope this will help you.

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Re: Parachute

Postby IanK » Fri Aug 13, 2004 4:02 am

Hello La bla bla

So you want to model the full blown behaviour. I read up the Parachute section of Hoerner. Just for the ordinary chute you have to take into account the canopy porosity as well as the flow from the central opening if there is one. The book gives a full angle plot of CD vs. CL with loops!

Look at this stuff

Click Lighter than air then Aerodynamic Decelerators
beside chute photo. Ref to Hoerner is in there too.
http://www.aerodyn.org/



Ian,
the model starts in horizontal position - if on the ground then it's as if the skydiver lies on his belly, when activating the spoiler the torso (the main part of the skydiver and the parents of all othere rotates to vertical position - if on ground then it's as if the skydiver stands on his feets
thanks,
La bla bla
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Re: Parachute

Postby Lablabla » Sat Aug 14, 2004 4:51 pm

I'll try to be more specific...
when the skydiver "opens" the parachute the Vertical Speed goes down from -200 (if i remember correctly) to -10 and even goes up a bit to +15 or something like this.
the problem is that after a few seconds in that area it goes down back to -60... and it's impossible to land in Vertical Speed of -60 cause it's a crush...
i don't think that it matter how much lift i set to my spoilers it will always happend... just after a longer time period...
thanks again..
La bla bla
???
Lablabla
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Re: Parachute

Postby aceronzo » Sat Aug 14, 2004 7:31 pm

Lablabla,
Try adding drag to the spoiler(use maybe three digits),and try cutting the weight(to maybe 500lbs total empty).Is this one you built or are you modifying one.

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Re: Parachute

Postby Lablabla » Sun Aug 15, 2004 5:42 am

This is my own model... execpt the body.. the design and all is mine...
i'll try now what u said and let u know how it went..
thanks,
La bla bla
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Re: Parachute

Postby Lablabla » Sun Aug 15, 2004 6:02 am

It didn't work...
still... the problem is to maintain the low VS (Vertical Speed) of about -20...
if it's possible using other stuff aswell like flaps please tell me
any help will be appreciated..
thanks,
La bla bla
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Re: Parachute

Postby aceronzo » Sun Aug 15, 2004 6:52 am

Yes, you can add a lot of lift and drag to the flaps,try using 5 digits of drag with  the spoiler( 28000)in the airfile).You can also add lift to the spoiler(10.0).Put your weight to 0 (cfg file).You can adjust the flap lift and drag in the cfg.These are just numbers thrown out,you will have to play with them.It should float with the weight on 0.I assume it is for 2004.You will have to do a lot of trial and error,make copies and hang in there.Maybe someone else has a better plan.Goodluck!

Best Regards,
aceronzo
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Re: Parachute

Postby Lablabla » Sun Aug 15, 2004 7:45 am

Thanks,
I'm starting working on it right now... will let u know how it goes
thanks,
La bla bla
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