Packed parachute size in RockSim

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enderw88

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I recently purchased RockSim 9. I had been using OpenRocket for some time, and I was easily able to control the size of the packed parachute. I can't figure out how to do this in Rock Sim. The "thickness" of the parachute evidently helps it figure out parachute mass, and apparently changes the packed diameter. I cannot change the packed length which is pretty important. Am I missing something obvious?

The jury is still out on whether switching to RockSim was prudent.
 
I recently purchased RockSim 9. I had been using OpenRocket for some time, and I was easily able to control the size of the packed parachute. I can't figure out how to do this in Rock Sim. The "thickness" of the parachute evidently helps it figure out parachute mass, and apparently changes the packed diameter. I cannot change the packed length which is pretty important. Am I missing something obvious?

The jury is still out on whether switching to RockSim was prudent.

It's better to just override the mass and leave the size of the chute alone. As long as the mass is right the. You will be fine.
 
It's better to just override the mass and leave the size of the chute alone. As long as the mass is right the. You will be fine.

I do not agree. The size, especially length has a lot to do with how the rocket balances and can greatly effect Center of Mass.
 
I do not agree. The size, especially length has a lot to do with how the rocket balances and can greatly effect Center of Mass.

I fly all high power so the small mass if the chute doesn't effect much. I suppose if it was a lpr rocket then it would effect it more so it is important.
 
I fly all high power so the small mass if the chute doesn't effect much. I suppose if it was a lpr rocket then it would effect it more so it is important.

A 60" Sky Angle classic-II weights 18.2 ounces. Add in 30-40 feet of 1/2 inch cord and hardware, you actually have quite a bit of weight and where it sets in the rocket can make a huge difference.
 
A 60" Sky Angle classic-II weights 18.2 ounces. Add in 30-40 feet of 1/2 inch cord and hardware, you actually have quite a bit of weight and where it sets in the rocket can make a huge difference.


I agree I input the correct weight and put the chute where it will lie in the rocket however that has nothing to do with the ops question of the thickness and length of he chute. Like I said as long as the chute is placed where it will be in the rocket and the weight is overridden then they will be fine.
 
A 60" Sky Angle classic-II weights 18.2 ounces. Add in 30-40 feet of 1/2 inch cord and hardware, you actually have quite a bit of weight and where it sets in the rocket can make a huge difference.

Plus with high G flight, every thing could be shoved back moving the C/G aft. But wait!!! With the motor mass going out the rear, the two "might" cancel each
other out!!.

Seriously, I believe it would only be an issue if the CG/CP is marginal to start with. If that's the case, one better be careful. If there is a large margin of stability to
start with, will be no problem. Soooooooooooooooo............. Connor is right and RWW is right. Kurt
 
thanks Kurt I didn't want to start an argument. Thanks for clearing that up:)
 
thanks Kurt I didn't want to start an argument. Thanks for clearing that up:)

RWW is right that it could be a problem with marginal stability. Shift a sizeable parachute and shockcord to the rear and a marginably stable rocket could go haywire. With longer rockets with smaller recovery systems shouldn't be a problem.

The craziest flight I ever saw was with a research K with too far aft CG. Did 3 loops in the air, hit the ground flat, flopped around a few times and then took off at a 45 degree angle out away from us. I thought they would never find it but the flier did. When found, there were no fins left on the fincan. They all broke off.
The full scale Phoenix missile at MWP a few years back did loop and smashed into terra firma with an O motor burning. CG wasn't checked with the heavier motor. Kurt
 
I recently purchased RockSim 9. I had been using OpenRocket for some time, and I was easily able to control the size of the packed parachute. I can't figure out how to do this in Rock Sim. The "thickness" of the parachute evidently helps it figure out parachute mass, and apparently changes the packed diameter. I cannot change the packed length which is pretty important. Am I missing something obvious?

The jury is still out on whether switching to RockSim was prudent.

Wait, the program is supposed to predict how tightly you will pack a chute?!?! I think that is asking a bit much of a simulator.

I played with the RockSim parachute slider bars. The rocket CG doesn't move with them, so it seems the changing L and D of the chute in the graphics window is just for visual effect.

Override the mass and CG of your chute and put it where you think it should be.
 
In OpenRocket you can specify the length and diameter of the packed chute (it is not predicted). When designing a new airframe having that stack length modeled correctly is very important. I have a 14" Cato drogue chute. I can enter the deployed diameter and mass override to the measured weight but RockSim insists on showing it about 2" long. It actually packs at six inches. That is a four inch length difference that must be taken into account manually leaving lots of empty volume for nor reason.
 
In OpenRocket you can specify the length and diameter of the packed chute (it is not predicted). When designing a new airframe having that stack length modeled correctly is very important. I have a 14" Cato drogue chute. I can enter the deployed diameter and mass override to the measured weight but RockSim insists on showing it about 2" long. It actually packs at six inches. That is a four inch length difference that must be taken into account manually leaving lots of empty volume for nor reason.

I see. You want to specify the chute length and display it correctly in the graphics window. Perhaps you can create a dummy, zero-mass inner tube of the correct length and diameter as a surrogate for visualization purposes.
 
I see. You want to specify the chute length and display it correctly in the graphics window. Perhaps you can create a dummy, zero-mass inner tube of the correct length and diameter as a surrogate for visualization purposes.

That's a good idea. Just seems like an obvious thing to control the packed parachute geometry. I have been very surprised by the number of features present in OpenRocket that have no analog in RockSim. I can't comment yet on simulation quality.
 
If you want that on Rocksim, or a future version of it, you should email Tim at Apogee. He cannot add features if he is not aware of what folks want.


Mark Koelsch
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