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Author Topic: Urgent (easy) rocksim help! STealth Jr  (Read 3335 times)
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George

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« on: September 23, 2012, 04:37:11 PM »

My rocksim is broken, I can't calculate some things, right before Doomsday! I need a simulation for a Binder Stealth Jr on a G53, G138 and G80.
The stealth jr has a profile available from rocksim, but I can't access it, and my copy of rocksim is somehow missing the g53 and g138. If anyone has a minute, a quick estimate of optimal delay, stable yes or no, and maximum altitude would be very useful!

So if anyone is simming their rockets now and has a free minute to download the Stealth Jr profile and try it out on those motors, or anyone who has the Stealth Jr, it would be great if you could let me know how it goes.

Thanks!
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Nighthawk
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« Reply #1 on: September 23, 2012, 04:51:29 PM »

Gday George.

Have you had a look at OpenRocket? It works pretty much the same as RockSim but its an free open source program. It can open pretty much any Rocksim file (Im yet to come across one it cant).

Ive downloaded the Stealth Jr file and will put it through some runs for you now.

Cheers

Greg
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ARA Member #233
Level 1: 17/6/12 PML Callisto - H170M
Level 2: 29/9/12 PML AMRAAM 4 - J350W
Nighthawk
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« Reply #2 on: September 23, 2012, 05:10:17 PM »

G53FJ-7 gives about 1300ft
G138T-10 gives 2000ft
G80-7 gives 1600ft.

The delays Ive used appear to be pretty close to optimal for the stock built Stealth Jnr.

Is there any other details you need?

Cheers

Greg
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ARA Member #233
Level 1: 17/6/12 PML Callisto - H170M
Level 2: 29/9/12 PML AMRAAM 4 - J350W
George

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« Reply #3 on: September 23, 2012, 07:00:46 PM »

Excellent! I'll check it out. Thanks for the simulations!
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George

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« Reply #4 on: September 23, 2012, 11:13:15 PM »

Downloaded it, all good. Great program, for free! Just need to transfer my old simulation files across and I'm good to go. (So many scratch builds...)
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Lachlan

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« Reply #5 on: September 24, 2012, 11:24:38 PM »

For a quick and dirty sim method I use http://www.thrustcurve.org/

It only uses your rockets raw data: weight, diameter, motor mount, and Cd to calculate sims for every motor on their website (pretty much all current rocket motors available) that will fit in your rocket. Sims are calibrated based on the rockets dry weight (no motor) with each motors loaded weight being taken into account for the sims.

The outputs can be downloaded in excel format and printed off to take with you on launch day. Its good to know where your Cp is to know whether your rocket will be stable with the chosen motor however.

If you have an altimeter you can calibrate the sims based on the altimeters data to work out a more precise Cd, I find this isn't really needed though; most rockets are between 0.5-0.6 with 3 fins and near 0.75 for 4 finned rockets.

This is what I use for every rocket as it provides a lot of quick easy data, and the sims are really pretty accurate; for most 3000ft flights they are within 200-300ft.


PS I've got a stealth junior too, easily my favourite rocket, its last flight was on a H268R and that was a spectacular flight. I think the best motor for it is a G77R-M though - the reload.
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George

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« Reply #6 on: September 25, 2012, 12:27:45 AM »

I've got a G64-4 (No idea what to do, that delay is too short for any rocket I have), G53, G138 and some other G and F motors (hard to remember at the moment) and stuff to fly with this. Also got an I218 and an H170 for another rocket I've got, easily the two highest thrust motors I will have ever used  fangrin
This is probably twice as many composites as I've ever launched at any one event, and I've never launched an I before. Should be fun.  fangrin

(Wow, just looked up the H170 and I218, they're very similar... Like 10Ns difference... Weird...)
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Lachlan

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« Reply #7 on: September 25, 2012, 01:40:13 PM »

Quote
I've got a G64-4 (No idea what to do, that delay is too short for any rocket I have[/quote

One thing I've done before is for rockets that have payload bays, is to do a couple of simulations increasing the weight in the payload bay. You can then add this to the rocket and fly with a motor with a shorter delay.
I did this when I was flying my stealth junior on an H220, I think I ended up using about 200grams of wadding and a couple of bits of plywood, worked excellent and from what we could see the delay was spot on.

From my sims however the stealth seems to need a G64-10.

Another possibility is to ask around your other members and see if they would swap for a similar sized motor with a different delay, or try to find a rocket delay kit that will be suitable.
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RocketballSA
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Fantom on a H170 Sparky


« Reply #8 on: September 25, 2012, 09:28:07 PM »

I've got a G64-4 (No idea what to do, that delay is too short for any rocket I have), G53, G138 and some other G and F motors (hard to remember at the moment) and stuff to fly with this. Also got an I218 and an H170 for another rocket I've got, easily the two highest thrust motors I will have ever used  fangrin
This is probably twice as many composites as I've ever launched at any one event, and I've never launched an I before. Should be fun.  fangrin

(Wow, just looked up the H170 and I218, they're very similar... Like 10Ns difference... Weird...)

Yes the H170 and I218 is similar. They both go in the 360/38mm casing. Have flown a few of the H170s and noted it is on par with a small I motor. Lots of fun.  icon_thumright

These motors you have George such as the G138 and H170 come with 14 second delays. These delays will likely need to be cut back for what your planning on flying them on. For this will need the Aerotech drilling tool. If have not got one am sure someone at Dowerin may be able to help you out. Have fun.  icon_thumleft
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Rocketmad
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« Reply #9 on: September 25, 2012, 10:15:46 PM »

i have a delay drilling tool in my kit.
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George

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« Reply #10 on: September 25, 2012, 11:25:22 PM »

I've drilled delays before, not sure if with a knife or with a drilling kit, but they have gone well several times.
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