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  #1  
Old 03-14-2011, 06:42 PM
James Pierson James Pierson is offline
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Cool Narcon 2011

NARCON 2011

Tim Van Milligan gave an excellent presentation at NARCON on Rocksim from beginner to advanced in which I learned few things. I personally could have spent most of the day asking Tim question but had to settle for the 1-hour presentation.

I personally never knew that in the flight sims screen that the parachute symbols has a black arrow on it. If the arrow is pointing up then chute deployment occurs before apogee and the opposite if the arrow is down. Something I never really noticed.

Tim is also suggesting the Velocity at Deployment is best under 50 mph which seems to be a much higher than the 20 mph that most rocketeers use as a standard.

Also Tim stated that the Velocity at Launch Rod Departure should be at least 30 mph to make the fins effective for stability.

A little about decal simulations was given. Decals work best if the decal is made more like a complete BT wrap in size and completely covering the BT desired with decal and background colors. Also change the BT’s color in Rocksim to a white and diffused for the decal wrap for best results.

I later had a chance to meet Tim and had a chance to ask him a few other questions. Yes I had the courage to ask about the Tube Fin/ Ring Tail drag calculation problem! Tim knows it is a problem and I am assuming it is on his list of thing to be improved at a later date.

Respectfully submitted,

James Pierson
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PS. How that for reportin' Jay-o
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  #2  
Old 03-15-2011, 12:26 AM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by JP
I later had a chance to meet Tim and had a chance to ask him... about the Tube Fin/ Ring Tail drag calculation problem! Tim knows it is a problem and I am assuming it is on his list of thing to be improved at a later date.


Good to hear from you, JP!

Having that acknowledgement from TVM about something we've suspected is reassuring, really. We weren't just imagining it...

Quote:
Tim is also suggesting the Velocity at Deployment is best under 50 mph which seems to be a much higher than the 20 mph that most rocketeers use as a standard.


My standard for LPR, using thin plastic canopies and tape disk attachment points, is the slower the better. If you can hear the canopy "pop", the Dv is too high. Period.

Quote:
A little about decal simulations was given. Decals work best if the decal is made more like a complete BT wrap in size and completely covering the BT desired with decal and background colors. Also change the BT’s color in Rocksim to a white and diffused for the decal wrap for best results.


Meaning we're stuck with calculating the exact diameter of the BT and making a flat 'decal sheet' with everything in place before applying it. Pi, anyone?

(Pi R round, Cornbread R square!)
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  #3  
Old 03-16-2011, 11:05 AM
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Tau Zero Tau Zero is offline
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Talking Inquiring minds want to know...

Quote:
Originally Posted by James Pierson
NARCON 2011

Tim Van Milligan gave an excellent presentation at NARCON on Rocksim from beginner to advanced in which I learned few things. I personally could have spent most of the day asking Tim question but had to settle for the 1-hour presentation.

Tim is also suggesting the Velocity at Deployment is best under 50 mph which seems to be a much higher than the 20 mph that most rocketeers use as a standard.

Also Tim stated that the Velocity at Launch Rod Departure should be at least 30 mph to make the fins effective for stability.
The deployment velocity that Craig and I have been shooting for is 20 *feet per second.* Guys, what does 50 mph translate into f.p.s.? (I'm nowhere near RockSim right now.)


Quote:
PS. How that for reportin' Jay-o
*Dude.* *Sweet!*

James, you freakin' rock. *Again.*
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Old 03-16-2011, 11:11 AM
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Quote:
Originally Posted by CenturiGuy
The deployment velocity that Craig and I have been shooting for is 20 *feet per second.* Guys, what does 50 mph translate into f.p.s.? (I'm nowhere near RockSim right now.)



My rule of thumb is that 1 mph is about 1.5 fps, so 50 mph -> ~75 fps.


Bill
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Old 03-16-2011, 11:27 AM
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Doug Sams Doug Sams is offline
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Quote:
Originally Posted by Bill
My rule of thumb is that 1 mph is about 1.5 fps, so 50 mph -> ~75 fps.
That's mine, too. It's nearly exact. (60mph=88fps. So the true conversion factor is nearer 1.467.) 1.5 is close enough 90+ percent of the time.

Doug

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Old 03-16-2011, 11:41 AM
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Seems to me it would be easier just to use bullet-proof chutes, shock cords and attachment methods than focusing too much on DV.
In this area a little can go a long way as delays for certain manufacturers motors are notoriously inaccurate.
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Old 03-16-2011, 11:55 AM
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Quote:
Originally Posted by ghrocketman
Seems to me it would be easier just to use bullet-proof chutes, shock cords and attachment methods than focusing too much on DV.
In this area a little can go a long way as delays for certain manufacturers motors are notoriously inaccurate.
It's not so much bullet-proof, GH, as it is shock absorbing. I agree they need to be sturdy, but the key is damping. I prefer tape loops on the shock cord. That way, during a hard deployment, the tape gets torn thus dissipating the shock. (Elastic will dampen, but it stores the energy, then releases it in the form of pulling the nosecone crashing into the rocket )

The damping allows the use of lighter shock cords and parachutes, which reduces the overall system stresses. The other key is making sure the shock cord is wide thru the opening of the rocket to minimize zippers.

I've had so-called experts tell me the best solution is selecting the right delays, but I know better. Too much crap can happen, especially in the Texas wind, to get it out at the top with minimal DV every time. So a robust recovery system is needed, and is not overkill.

This rocket is a great example. With a four-motor booster staged to a single motor sustainer, with the higher likelihood of one booster motor out, flying in the nearly perpetual cross wind here, high DV is almost unavoidable. It has to be built to tolerate the hard jerk that often occurs at deployment. Doug .



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Old 03-16-2011, 09:40 PM
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Is the heat wave distortion of the background hills due to the motors or the local temperature? Either way, it makes for a striking photograph!
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Old 03-16-2011, 10:24 PM
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Quote:
Originally Posted by blackshire
Is the heat wave distortion of the background hills due to the motors or the local temperature? Either way, it makes for a striking photograph!
Thanks. The photo was taken in November (2006), so I must assume the motor heat is the sole source for the distortion.

Doug

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Old 03-16-2011, 11:27 PM
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Quote:
Originally Posted by Doug Sams
Thanks. The photo was taken in November (2006), so I must assume the motor heat is the sole source for the distortion.

Doug

.
You're welcome. That effect must be present even with 13 mm mini motors, but without just the right lighting and viewing angle it must not be captured on film or CCD detectors in pictures very often.
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