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  #61  
Old 01-12-2009, 08:11 PM
rkt2k1 rkt2k1 is offline
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Default Updated Design - Predator Advanced BGM-18M

Quote:
Originally Posted by CPMcGraw
I agree, that C6-5 is the optimum motor in your list, and I would not recommend using any of the others. They are either at the edge of, or deep into, chute-shred territory. Getting about 670' on a C6-5 is good, though.

One thing I have to caution you on is the guide length. You call out a 36" x 1/8" rod, which is standard. However, you need to look at the flight summary. Double-click the line on the simulations screen where you flew the C6-5, and start reading through. You'll get to an area where it says "Launch Guide Data". RockSim says this design doesn't reach safe flight V until it's 38" up the rod. You're 2" short. This rocket needs a 48" x 3/16" rod using that motor, so that you get a full 38" of guide length. The extra won't hurt it.

Try simulating instead with the D13W-7. This is a composite D13 White Lightning. It jumps to velocity in only 20", reaches 1581', and has a Dv of just 5 FPS. Here is your optimum motor! Of course, it also has a Max V of 435 FPS, and an acceleration of 614 FPS/S. Really quick, but I think the TTW construction will hold up.

Good work for a RS9 first!


Craig,

Thanks for the feedback. I haven't got much experience with composite motors. Are 18mm composites readily available?

I tweaked and updated the design and found another black powder engine that seems to work. The Quest B6-4 (B6Q-4 in Rocksim) has both a higher total impulse and average thrust numbers than the Estes B6-4.

I also increased the launch rod length to 48". The tweaked design reaches safe minimum launch velocity using both the Quest B6-4 and Estes C6-5.

Name: Predator BGM-18M

Length: 22.1"
Diameter: 1.64" (ST-16)
Fin Span: 4.498"
Weight: 2.8098 oz

Engine Size: 18mm
Launch Guide Length: 48" x 1/8"

Motor......Max Altitude......Dep. Velocity

B6Q-4.........282.92 ft.........12.37 ft/s
C6-5..........668.50 ft..........1.88 ft/s
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File Type: rkt Predator Advanced BGM-18M.rkt (73.9 KB, 85 views)
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  #62  
Old 01-12-2009, 09:18 PM
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CPMcGraw CPMcGraw is offline
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Default RockSim Update Available

RockSim 9.0.1 F70 is available today.
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  #63  
Old 01-15-2009, 10:46 PM
rkt2k1 rkt2k1 is offline
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Default Design Help

Hi guys, I'm hoping someone can help with the latest design file I've been working on. After reading through the thread on the Centuri Bulldog #5354, I decided to try and sim it in order to clone.

I remember building and flying an original kit as a teenager and still have the BNC-70AJ from it. I used multiple transitions to duplicate the paper shroud detail on the nose cone. I used Semroc components in the Rocksim design and believe it to be a fairly accurate representation. Sim altitudes attained on both B6-4 and C6-5 engines seem to match those documented on the plan.

The problem I'm having is in getting the deployment velocity and minimal launch velocity off launch rod numbers in line. The DV numbers are at parachute shred levels and it looks like design requires a 48" launch rod which surprised me.

If anyone would like to take a look and make any suggestions it would be appreciated.

At some point I'd like to try the design with a 24mm mount.

Thanks,

... Bill
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  #64  
Old 01-16-2009, 12:47 AM
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Default

Quote:
Originally Posted by rkt2k1
Hi guys, I'm hoping someone can help with the latest design file I've been working on. After reading through the thread on the Centuri Bulldog #5354, I decided to try and sim it in order to clone.

I remember building and flying an original kit as a teenager and still have the BNC-70AJ from it. I used multiple transitions to duplicate the paper shroud detail on the nose cone. I used Semroc components in the Rocksim design and believe it to be a fairly accurate representation. Sim altitudes attained on both B6-4 and C6-5 engines seem to match those documented on the plan.

The problem I'm having is in getting the deployment velocity and minimal launch velocity off launch rod numbers in line. The DV numbers are at parachute shred levels and it looks like design requires a 48" launch rod which surprised me.

If anyone would like to take a look and make any suggestions it would be appreciated.

At some point I'd like to try the design with a 24mm mount.

Thanks,

... Bill


I'm looking at the design, and I've looked at the plans from Centuri. The primary motors for this monstrosity are the B8-5 and C5-3. These are cored motors, with sharp spikes to kick it hard. I don't think your simulation has any major problems, since you matched it close to the original. It's the motors, and the lack thereof of motors with any serious power. Your idea of converting to 24mm might be the only viable solution unless or until someone ever produces core-burners again.
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  #65  
Old 01-16-2009, 07:04 AM
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pantherjon pantherjon is offline
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Default

Quote:
Originally Posted by CPMcGraw
I'm looking at the design, and I've looked at the plans from Centuri. The primary motors for this monstrosity are the B8-5 and C5-3. These are cored motors, with sharp spikes to kick it hard. I don't think your simulation has any major problems, since you matched it close to the original. It's the motors, and the lack thereof of motors with any serious power. Your idea of converting to 24mm might be the only viable solution unless or until someone ever produces core-burners again.

Finicky design..One that lends itself to being a 'tweener'..One delay is too short and the next option is a tad too long..If 1oz of nose weight is added, the 18mm RMS loads look viable..Tho, again, it is a tweener..All the loads (D13,D21 and D24) show good DV numbers- but require shortening the 7 second delay to either 6 seconds for the D21 and D24 or to 5 seconds for the D13..DV numbers I got:
D13 11.32 @ 996 ft
D21 3.63 @ 1026 ft
D24 12.89 @ 938 ft
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  #66  
Old 01-16-2009, 10:52 AM
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Default

Quote:
Originally Posted by pantherjon
Finicky design..One that lends itself to being a 'tweener'..One delay is too short and the next option is a tad too long..If 1oz of nose weight is added, the 18mm RMS loads look viable..Tho, again, it is a tweener..All the loads (D13,D21 and D24) show good DV numbers- but require shortening the 7 second delay to either 6 seconds for the D21 and D24 or to 5 seconds for the D13..DV numbers I got:
D13 11.32 @ 996 ft
D21 3.63 @ 1026 ft
D24 12.89 @ 938 ft


Which brings up the question, If this model is such a pill to fly, what motors did they really test with? This model was a 1982 release, so what other motors did they have available in 1981 and 1982 (but didn't mention in the instructions) that would have flown the model reasonably well, and give a relatively soft Dv?
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  #67  
Old 01-16-2009, 07:27 PM
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Default Design Count Update

585...
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  #68  
Old 01-16-2009, 11:22 PM
rkt2k1 rkt2k1 is offline
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Default

Quote:
Originally Posted by CPMcGraw
Which brings up the question, If this model is such a pill to fly, what motors did they really test with? This model was a 1982 release, so what other motors did they have available in 1981 and 1982 (but didn't mention in the instructions) that would have flown the model reasonably well, and give a relatively soft Dv?


Craig, this is exactly what I was wondering when I working on the Rocksim design. I'm going to see what it looks like with the 24mm mount and engine options.

Thanks for all those who looked over the design file and provided feedback.

Thanks,

... Bill
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  #69  
Old 01-18-2009, 12:20 AM
rkt2k1 rkt2k1 is offline
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Default New (Old) Design - Centuri Bulldog with 24mm Engine Mount

Well I reworked the Bulldog with a 24mm engine mount and got much better performance numbers. Does a modification to a manufacturer design count as a Barclone entry?

... Bill


Design Name: Centuri Bulldog with 24mm Engine Mount

Length: 20.5"
Diameter: 2.217" (BT-70 / ST-13)
Fin Span: 6.967"
Weight: 4.822 oz (with 2oz nose weight and less engine)

Engine Size: 24mm
Launch Guide Length: 48" x 1/8"

Motor......Max Altitude......Dep. Velocity

Motor.....Max Alt......DV...

D12-5......735.91.......3.48
E9-6......1236.72......10.89
E30-7.....1727.58.......7.47
E15-7.....1808.73......11.03
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  #70  
Old 01-18-2009, 12:37 AM
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Default

Quote:
Originally Posted by rkt2k1
Well I reworked the Bulldog with a 24mm engine mount and got much better performance numbers. Does a modification to a manufacturer design count as a Barclone entry?

... Bill


Design Name: Centuri Bulldog with 24mm Engine Mount

Length: 20.5"
Diameter: 2.217" (BT-70 / ST-13)
Fin Span: 6.967"
Weight: 4.822 oz (with 2oz nose weight and less engine)

Engine Size: 24mm
Launch Guide Length: 48" x 1/8"

Motor......Max Altitude......Dep. Velocity

Motor.....Max Alt......DV...

D12-5......735.91.......3.48
E9-6......1236.72......10.89
E30-7.....1727.58.......7.47
E15-7.....1808.73......11.03


It does.

Those numbers are a lot better. The general rule-of-thumb goes something like this:

Over 25 FPS = Chute-shred territory.
Less than 20 FPS = Good, but not best. Can still inflict explosive chute openings and broken shrouds.
Less than 15 FPS = Better, and similar to most kits now available.
Less than 10 FPS = Great! Very few hard pops.
Less than 5 FPS = Smooth operator!
Less than 3 FPS = Perfection!
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