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Parachute Testing
#1
This past weekend, at MDRA, I finally got down to the field late Sunday morning.  I would have been there an hour and a half earlier, however, the EMS gods did not find it necessary to let me go just yet... had to stay late to finish the paperwork.

So after working 25 hrs of my 24-hr shift, I arrived, all strung out on black coffee and having a wicked ammonium perchlorate jones.

First order of business was to get my Jolly Logic Alt 3 verified.  My trusty ol' Kraken did that job... 550' on a D12-5, with its standard recovery profile of helicoptering around on its small chute at a leisurely 16 FPS. 

Once data was verified from the on-board JL, we got to work.

I've been making a bunch of streamers for my dual-deploy rockets.  Last time, I recovered a number of MPR and smaller HPR rockets with a streamer as primary recovery, just to prove it could be done.  This time, I came with actual parachutes.

Sort of.

I'd brought three I wanted to test, yet, failed to bring the one MPR rocket I'd intended to use as a test bed, so I was reduced to two.  No worries.

First, was a 31" chute, a modification of a disk-gap-band type loosely based upon the Viking probes' mains. The object of the test is to determine the Cd.   It is a 12-gore canopy, with a slightly lower gore to width ratio than the Viking specs, and features a pull-down apex to a toroid shape.  This was in my Pem-Tech Bucky Jones... a rocket reminiscent of the 50's science-fiction serials, complete with gaudy gold and silver coloring, art deco swoopiness, and a dorsal cockpit.  She comes in horizontal to protect her swoopy, pointed fins by means of a kevlar tie-off to the shock cord. 

Bucky flew to 2,215 feet on a CTI H135-7.  Ejection was slightly before apogee, and she descended at 18 FPS.  At recovery, she weighed 2.6 lbs. 
Cd *S *0.5 *rho *V^2 = M  where Cd = Coefficient of Drag, S= reference area in square feet, rho = 0.002377, V = velocity in FPS and M = lbs at recovery.


Cd * (3.141 *15.5^2 /144) * 0.5 * 0.002377 * 18^2 = 2.6
Cd * 5.240 *0.5 *0.002377 * 324= 2.6
Cd * 2.017 = 2.6
From here, I just divide the weight by the calculated figure to get the Cd.
2.6/2.017 = Cd
2.6 /2.017= 1.293

Cd= 1.293


I'm pretty pleased with that, as my first attempts yielded a Cd of about 0.43, if memory serves.

Chute #2 is an evolution of the 31".  This is another 12-gore canopy, measuring 40", and is much, much flatter in profile, with a decreased gap, band width, and apex vent.  The object of this test was to verify stability of the design in such a profile, figuring that the venting characteristics, if they work on this pancake, will translate to stability across any gore: width ratio.  Also, to give a base point of Cd for future efforts.

Chute #2 flew in a slightly modified AT Sumo.  A 3-grain H163 was chosen for propulsion because this would allow better visual tracking of the entire flight.  Flight was to 1299 feet, with ejection slightly before apogee after cutting the delay to 7 seconds.  Descent was at 18 FPS also, and the rocket at touchdown weighed 2.7 lb.   There were no noted oscillations, helicoptering, or inflation problems--descent was stable, and due to weathercocking during ascent and drift during descent, I got to see the chute approach my position, pass in front of me, then drift off to its landing position.

I'm calling it stable as all get-out.

Applying the same formula for Cd:
Cd *S *0.5 *rho *V^2 = M

Cd * (3.141 *20^2 /144) *0.5 *0.002377 *18^2 = 2.7
Cd *8.726 *0.5 *0.002377 *324=2.7
Cd *3.360=2.7
2.7/3.360 = 0.803

Cd = 0.803

So, it was all a success for me: I got to see some friends, satisfy the AP spike in my brain, get some data, and --even better-- verify the design is stable.  Now to see if I can't get the Cd up where I think it should be...


Later!

--Coop
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#2
Hi Coop,

Very interesting chute results. I just read your previous post on streamers. Of note, after experiencing a "cracked fin" from a parachute descent at 26 feet/second utilizing a JL chute release (JLCR) activated at 500 feet, I became interested in utlizing a drogue & main chute with the JLCR. The rocketman sells drogue chutes with loops on top of the canopy to accomodate streamer attachment. However, like the "channel" built into your scratch made streamers, I thought it might work to run the kevlar strap through the streamer to the drogue thereby possibly saving on packing space in the payload section while still promoting increased visibility. That might be particularly advantageous in small diameter rockets with limited "packing space." Have you attempted this and what are your thoughts/results? Finally, in lieu of milar-what other reflective materials have you considered using?

Thanks,
Fred,
L2, ROSCO
KG4YGP
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#3
(09-26-2016, 01:46 PM)FMarvinS Wrote: Hi Coop,

 Very interesting chute results. I just read your previous post on streamers. Of note, after experiencing a "cracked fin" from a parachute descent at 26 feet/second utilizing a JL chute release (JLCR) activated at 500 feet, I became interested in utlizing a drogue & main chute with the JLCR. The rocketman sells drogue chutes with loops on top of the canopy to accomodate streamer attachment. However, like the "channel" built into your scratch made streamers, I thought it might work to run the kevlar strap through the streamer to the drogue thereby possibly saving on packing space in the payload section while still promoting increased visibility. That might be particularly advantageous in small diameter rockets with limited "packing space." Have you attempted this and what are your thoughts/results? Finally, in lieu of milar-what other reflective materials have you considered using?

Thanks,
Fred,
L2, ROSCO
KG4YGP

Thanks!  I'm sorry for the delay in replying...

If I'm understanding your post correctly, you're saying to use both a streamer and a drogue chute--mounting the chute to the streamer itself?

If so, I have not attempted this.  I've found that streamers do well just on their own, and I couldn't see an advantage to using a drogue chute in conjunction with them --but I'd think it would be possible (but would recommend using two loops at the top of the streamer and a Y-harness sewn in).

I did use a pilot to pull out a particularly large streamer from a tightly packed in a 3" tube (on my King Kraken) with good results... but the small pilot really didn't figure much into the descent--it was pretty much to yank the streamer out of the tube...


Later!

--Coop

(09-26-2016, 01:46 PM)FMarvinS Wrote: I realized I did not answer your question on materials...


The nylon I use is lightweight calendared ripstop.  Calendaring is a process where the material is heated and pressed, and leaves a shiny --almost satin-- finish on one side.  It also makes the material less porous.  While there is zero-porosity (ZP) nylon as well, I've found this to be of little benefit for streamers (my first ones were of ZP).  The shiny side is noticeable during recovery, and honestly, the large streamers do just fine in keeping the descending rocket trackable, shiny or no...

My L3 flight was nearly 11' tall, 7.5" wide.  I saw its 24"x24' streamer LONG before I saw the airframe as it came down from apogee.



Later!

--Coop
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#4
(10-30-2016, 10:13 PM)Coop Wrote:
(09-26-2016, 01:46 PM)FMarvinS Wrote: Hi Coop,

 Very interesting chute results. I just read your previous post on streamers. Of note, after experiencing a "cracked fin" from a parachute descent at 26 feet/second utilizing a JL chute release (JLCR) activated at 500 feet, I became interested in utlizing a drogue & main chute with the JLCR. The rocketman sells drogue chutes with loops on top of the canopy to accomodate streamer attachment. However, like the "channel" built into your scratch made streamers, I thought it might work to run the kevlar strap through the streamer to the drogue thereby possibly saving on packing space in the payload section while still promoting increased visibility. That might be particularly advantageous in small diameter rockets with limited "packing space." Have you attempted this and what are your thoughts/results? Finally, in lieu of milar-what other reflective materials have you considered using?

Thanks,
Fred,
L2, ROSCO
KG4YGP

Thanks!  I'm sorry for the delay in replying...

If I'm understanding your post correctly, you're saying to use both a streamer and a drogue chute--mounting the chute to the streamer itself?

If so, I have not attempted this.  I've found that streamers do well just on their own, and I couldn't see an advantage to using a drogue chute in conjunction with them --but I'd think it would be possible (but would recommend using two loops at the top of the streamer and a Y-harness sewn in).

I did use a pilot to pull out a particularly large streamer from a tightly packed in a 3" tube (on my King Kraken) with good results... but the small pilot really didn't figure much into the descent--it was pretty much to yank the streamer out of the tube...


Later!

--Coop

(09-26-2016, 01:46 PM)FMarvinS Wrote: I realized I did not answer your question on materials...


Coop-

 Thanks for the update.

Fred

The nylon I use is lightweight calendared ripstop.  Calendaring is a process where the material is heated and pressed, and leaves a shiny --almost satin-- finish on one side.  It also makes the material less porous.  While there is zero-porosity (ZP) nylon as well, I've found this to be of little benefit for streamers (my first ones were of ZP).  The shiny side is noticeable during recovery, and honestly, the large streamers do just fine in keeping the descending rocket trackable, shiny or no...

My L3 flight was nearly 11' tall, 7.5" wide.  I saw its 24"x24' streamer LONG before I saw the airframe as it came down from apogee.



Later!

--Coop

Coop,


  Thanks for the updated info!

Regards
Fred
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#5
This project continues...

Yesterday, the intent was to do a side by side comparison of my two newest parachutes... Mark V and VI. Both these are similar to the previous 4 or 5 versions in overall design, with evolutionary improvements to gore geometry and alterations to the gap width and the band.

It's rocketry. That things do not go as intended is kinda part of the gig.

So test bed is a scratch-built 4" Phoenix with a 54mm MMT, with a mid-mounted av-bay (between the forward fins), into which a Raven III has been installed. In the nose, there was the Jolly Logic Altimeter Three--a unit which really gave me fits at the beginning, but today has proved its worth. More on that later.

Phoenix is 6.1875 lb dry. I tried to select a motor that wouldn't send it too high, as we would be looking at the recovery more than the flight, which led me to the CTI 6XL I-243 white motor. Extra advantage of being a bit cheaper than 54 or 38mm was, admittedly, attractive as well.

Range opened, I RSO'd and weighed her in. She came to ~7 lb loaded with motor, 54-38 adapter and the 38-29. She flew well, straight on through the crosswinds without weathercocking to an apogee this side of 1,500 feet. Chute opened, and she began drifting down...

... A bit more on the "drift," than she did the "down," if you dig. Across the field... Over the flightline... The far field... Aaaaand into the trees.

Mordor, if you will.

So off I went to try and locate her.

Some time later, I found her, WAY up in a tree. The telescoping pole the club has was too short by a long way. But I did manage to drop a pin on the GPS location with hopes of a later recovery.

I did, however, manage to download the data off of the Jolly Logic unit. I had to fully extend my arm and stand on my tiptoes to keep the bluetooth connection, but I did manage it.

Descent at 15 FPS.

I'm still reeling.

That's far better than I had hoped. I obviously do not have a recovery weight --guessing about 6.5-6.75, once you figure in the loss of propellant and dog barf. For the preliminary calculation, I'll be using the average of these two --6.625lb-- with revisions later on as necessary.

Our formula, again is:--
Cd *S *0.5 *rho *V^2 = M
Cd * ((24^2*3.141)/144) *0.5 *0.002377 * 15^2= 6.625
Cd * (576*3.141)/144) *0.5 *0.002377 * 225=6.625
Cd * (1809.216/144) *0.5 *0.002377 *225= 6.625
Cd *12.564 *0.5 *0.002377* 225= 6.625
Cd * 3.360=6.625

6.625/3.360= 1.971

Cd= 1.971

1.971! Far better than anticipated... I'd very very much like to get that rocket back in-hand so I can weigh the thing and get more accurate data from the on-board Raven 3.

I'm disappointed in that I did not get to recover the rocket immediately, but am very thankful that I was able to download the data from the Jolly Logic unit whilst still treed. The initial results are very encouraging. I do believe I'm on the right track, here. I'd like to see what the Mark VI does vs the Mark V. I believe it will be comparable, perhaps slightly better, as far as Cd. Where I expect a notable difference will be between the opening force at dual-deploy speeds... which will be the next phase of testing.


Later!

--Coop
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#6
All that, and Coop was still able to help my daughter launch her Predator on a C6-5. Wink
John S.
NAR #96911
TRA #15253
MDRA
Level 1, 2014-Mar-15 -- Aerotech Sumo, H133BS
Level 2, 2014-Jun-21 -- Giant Leap Vertical Assault, J240RL
Level 3, 2016-03-12 -- MAC Performance Radial Flyer, M1101WH, 13,028 feet
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#7
(11-21-2016, 11:27 AM)Bat-mite Wrote: All that, and Coop was still able to help my daughter launch her Predator on a C6-5.  Wink

She was JUST a bit too short to reach the rod by herself--but not for lack of trying!


Later!

--Coop
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#8
For what it's worth, I did eventually get this rocket back.

Later!

--Coop
http://www.paramedichutes.com
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#9
The Arboreal Phoenix continues to fly.

This past weekend at the sod farm, she proved Bob Utley wrong by actually flying straight without benefit of an F-14 launch platform up to 1,480 ft on a twice-stepped-down (54mm to 38mm, 38mm to 29mm) 29mm 6XL I-243.

She ejected her nose slightly before apogee using motor delay (slightly supplemented with some spare 4F I had sitting around not doing much), With a http://www.paramedichutes.com BLS-48 burrito wrapped in some Nomex, bound by a Jolly Logic chute release set to 400'. Data suggests chute was released 309 feet (where one sees a corresponding 5.74 G spike, with approximately 2 seconds of elevated g-forces, as chute is released, lines extend, and main fully inflates). Chute is released at 29.6625 seconds. Inflation complete at 31.4325 seconds, 242 feet. Landed at an altitude of 5 feet at 45.8320 seconds.

Main inflation time: 14.3995 seconds.
Starting altitude: 242 ft.
Ending altitude: 5 ft.
Total descent: 237 ft.

237 ft/14.3995 seconds=16.459 ft/sec.

48" diameter chute. Measured recovery weight of 6.283lb.
Cd: 1.553


I'm going to fly this thing until the centering rings rot out of it.

Later!

--Coop
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