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PML Cirrus Dart on I600

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m85476585

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I'm thinking about flying my Cirrus Dart on an I600. I just simed it, apogee is 9721 feet, max velocity is 1699 ft/sec (mach 1.5), max acceleration is 2180 ft/sec^2 (67.7 gs). Is this a crazy idea? Will the rocket survive? The whole thing is glassed, and there is a layer of tip-to-tip on the fins. All the glass it 3oz, but it is very rigid. The only electronics would be my Beeline tracker.

I painted it red (instead of the old yellow) for visibility on the playa, so it would be a 4 foot red rocket with a 6 foot red flame.
 

Adrian A

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Your sim altitude sounds a little low. Was that based on measured weight? Cjl flew an unglassed Cirrus Dart on an I600 a couple years ago and it did fine. It went to about 12kft AGL, but that was starting from an 5400 foot ASL launch pad. He needed electronic ejection because the apogee was longer than any available delay, so be sure to sim it based on the weighed rocket and polished surfaces to make sure that you won't get a premature chute deployment if you're planning motor ejection.
 

m85476585

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That's just based on everything stock in Rocksim. Mine is a little lighter, only about 16oz instead of 21oz since I left out the piston and drilled out the nose cone some, but if I lower the weight, it reaches a lower altitude!

The I600 is only offered with a medium delay for some reason. Can I use that delay interpolation table (and where can I find it?) to find a longer RDK for it, or is there a reason they only sell it with a medium delay?

edit: Putting in 3848 feet for the launch site elevation gets me just 54 feet short of 2 miles using the stock mass.

The finish is not very smooth, so I probably don't need to lower the CD at all. I don't really care what altitude it gets to since I won't have an onboard altimeter to compare the sim to. As long as it is up there, I'm happy.
 
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cjl

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Mine did have a professional auto paintjob, so that was a definite advantage. Mine was also around 16oz fully prepped without the motor, so that sounds pretty comparable. As for delays? Interpolating from the data I can find, and based on the measured coast time on my flight, you'd need a bit over 3/4" of delay to be right around apogee. That is pretty close to an RDK-16 (0.781"). That isn't a certified delay for that motor though, so I'm not sure of the legality. Still, that should give pretty close to dead on apogee, perhaps slightly late due to your higher drag coefficient.

Oh, and make sure you have a tracker. It will basically vanish off the pad :D

Here's the data from my flight:


And the liftoff shot:
 

m85476585

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Is there a reason it's only certified with a medium delay (at least according to the AT catalog)?

Also, does anyone have a link to that chart that interpolates all the RDK delays?
 

cjl

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There isn't any reason the longer delay wouldn't work, at least as far as I know. I don't have the chart, but as I said, the RDK-16 should be the right one for what you are looking for.
 

cjl

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I doubt that's the case, honestly. The delay should burn identically while the motor is burning, so the only difference should be post burnout.
 

mikec

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I doubt that's the case, honestly. The delay should burn identically while the motor is burning, so the only difference should be post burnout.
Hmm, I think in general the exact opposite is true. If you look at the delay interpolation, there are different slopes for each propellant type, because (as I understand it) the delay burn rate during thrust is a function of pressure, which varies with propellant. Since the I600 and the J420 are both Redline and have the same external geometry, there must be something different between them since the M delay elements are different. According to AT, the I600 M delay is RDK-10 and the J420 M delay is RDK-17.

Anyway, I am probably thinking too much, it's just odd that they didn't list an L delay.
You will certainly get a longer delay with a physically longer delay element.
 

blackjack2564

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Hey guys, if someone has the load..... all cross referenced delays are right on back of the yellow and black header card the reload is in.
 

cjl

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Hmm, I think in general the exact opposite is true. If you look at the delay interpolation, there are different slopes for each propellant type, because (as I understand it) the delay burn rate during thrust is a function of pressure, which varies with propellant. Since the I600 and the J420 are both Redline and have the same external geometry, there must be something different between them since the M delay elements are different. According to AT, the I600 M delay is RDK-10 and the J420 M delay is RDK-17.

Anyway, I am probably thinking too much, it's just odd that they didn't list an L delay.
You will certainly get a longer delay with a physically longer delay element.
Actually, I was saying that the delay would burn identically during the burn compared to the included M delay. It won't be identical to the burn for different motors of course :)
 

mikec

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Actually, I was saying that the delay would burn identically during the burn compared to the included M delay. It won't be identical to the burn for different motors of course :)
Yeah, I realized that finally. You're right of course. Sorry for the confusion.

BTW, I was curious about why the I600R even exists considering it uses the same case at the J420R. It can't just be for you altitude guys using near-full-I motors to go after the I record. :) Then I found an AT press release: "The I600R was specifically designed for use in this year's [2004] LDRS 'I-Lite' Bowling Ball Loft competition..."
 

m85476585

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Well, it worked just fine with the RDK16. I didn't count how long the delay burned for, though, so it might not have been the full time needed for it to reach apogee. I don't know how high it went since there was no space for an altimeter. This was by far my fastest and highest flight. I think my next highest flight was only about 4000 feet, and I don't know if I have flown anything supersonic before this.

I am going to build a payload compartment for this rocket so I have space for an altimeter and my tracker. There was very little room for the tracker in the rocket as it was, and the antenna got bent stuffing it in. I think the bent antenna caused the tracker not to work well. At 100 feet, I only got about 5 (out of 9 or 11) bars with my directional antenna, and once the rocket was out of sight, I couldn't track it. Luckily, it landed very close to the pads (just past the away pads at maybe 500 feet), and I was able to pick up the tracker before it hit the ground, though it was visible at the same time. Once it was on the ground, I couldn't get a signal until I was within about 20 feet of it. I wonder if I can replace the built-in antenna with a piece of music wire or spring steel.
 

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I've been thinking a lot about a project just like this--trying to get to 10k AGL or greater with a 38mm motor. I move to Las Vegas NV in three weeks, so I am hoping that location enables a flight like this without as much chance of losing it. I was planning to use a BigRedBee w/o the GPS option.

With a weight like 16-21oz, is a single deployment streamer (like the new Flash one) an option if it's well built, even if activated via an altimeter? Seems like it should be, and would save more weight. Or, is that the going in assumption?

Also, just how much reinforcement is needed for supersonic flights like this? I tend to overbuild, but running some RS models shows that a heavy rocket can easily fall under the 10k AGL mark. I was planning to do one Soller composites CF/Kevlar sleeve with one layer FG tip to tip for the fins. Thoughts?
 

m85476585

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I used a homemade ~21" x-form chute, and it came down OK. A streamer might have been better if it was windy.

CF/Kevlar is unnecessary unless you really want to make it light. I used 3oz glass for everything, but the fins are G10, so they don't need as much glass as wood fins might (just enough to hold them on). It was just fine at mach 1.5, and I know the fins won't break even with a fast recovery. Mine weighs about 16oz.
 

cjl

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A bone stock Cirrus with a smooth paintjob and a lighter nose cone (I used one from Performance Rocketry) will break 10k just fine, and you do not need any reinforcement whatsoever. The stock Cirrus is unglassed phenolic, and the fins are 1/16 G10 with one layer of tip to tip glass (included). That's more than enough for a J350 or I600 in this rocket, both of which should be capable of 10k or greater. Adding a Soller sleve or something similar is just adding unnecessary weight, especially when the tube is very rarely the weak point on a rocket of this size.
 

MClark

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AeroTech made the I600 for the Bowling Ball Loft. When it was certified they sent us grains with 3 different core diameters, we fired all three sets and the one that was the highest impulse and still an I motor is the one they went with. It was certified with just one delay because it was at the last minute before LDRS that year and it was incredibly hot here in Phoenix where TMT was located at the time. The 38-720 J case is used because you can t get enough stuff in a 38-600 to get a full I.

Mark
 

m85476585

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I drilled out the nose cone in mine. I just drilled a series of ~1/4" holes being careful not to drill all the way through.
 

dlb

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A Cirrus Dart + I600 - Tracker = new case + new Cirrus Dart
:)
 

cjl

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A Cirrus Dart + I600 - Tracker = new case + new Cirrus Dart
:)
That's the truth, though even without the tracker, I would have found mine (it landed on the road that leads out of the launch site, about 3/4 mile from the pads :D)
 

m85476585

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Mine might as well have had no tracker. I couldn't get a signal until I could see it coming down, then when it was on the ground I couldn't get a signal until I was standing next to it. Luckily, we could see it part of the way down, so I knew where it landed.
 

m85476585

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I built an altimeter bay for this rocket for tomorrow's launch. I was able to fit a 9V battery, my HA45 altimeter, and my tracker in a 7"x38mm section of tubing. It's definitely the smallest payload bay I've done. The tracker antenna extends into a hole drilled in the once solid nose cone, so maybe it won't interfere with the altimeter too much. I know it won't get bent up, so the range should be better than last time even though I haven't tested it. I wired the altimeter to be able to do apogee deployment. I might set it up, or I might not since I'm lazy.

I will probably fly it on an I600 again.
 
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cjl

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Try a CTI I540. It'd be an interesting comparison...
 

m85476585

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Despite my tracker not working, I flew it on an I600 again. The altitude was either 8344 or 8433 feet. Since the tracker didn't work, we just drove around the lake bed until we found it. It was not where I expected based on the wind, but luckily it was not too far from the launch site.

I'll start another thread about the tracker.
 

cjl

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That low? Wow - how heavy is it and what's the finish like?
 

m85476585

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I don't know the weight right now, but it is probably fairly heavy. I ordered the wrong coupler from PML, so I had to make one by cutting a strip out of some extra 38mm tubing then internally glassing it. In the payload section I had a whole 9v battery in anticipation of doing apogee only deployment. The finish is definitely not low drag. The paint job on the booster section is OK, but the payload section is unpainted, and the transitions between them are probably not completely even. It also has 1/4" launch lugs in addition to surface mounted railbuttons (which stick out more than usual).

My rockets never go as high as predicted for stock kits.
 

cjl

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That explains it. Mine reached 11,950, but it had an auto paint job, was tower launched, and was lighter than stock (I used a hollow PR nose cone, and I ditched the piston).
 
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