CANSAT video

[Jamie]

http://www.youtube.com/watch?v=AxJ9xw85ync

 

This is the video from the onboard camera on the Gumby ARLISS – the canopy you see is the cockpit on “Gumby” the nose cone.

 

Interesting to note that the (2) 5/64^th shear pins didn’t hold the nose cone on when the main deployed – obviously larger shear pins are in order – I’ll do some ground testing to determine the optimum application.   

 

This video was made using keychain camera on a prototype mount I designed –  I plan to document making the mount at a later date (but well before next season).

 

 

[Geoff Huber]

Two 4-40 nylon screws will hold it in my experience.

 

Geoffrey Huber
(530) 891-0853 ext 3030
Geoff...@landacorp.com

[Jamie]

What diameter are the 4-40s? 

[Allen J. Palmer]

Geoff

 

You say

Two 4-40 nylon screws will hold it in my experience

 

The question is,

 is this an assumption or do you have video proof. There is a growing thought that the payloads are coming out at apogee due to shock pressure of the main deployment.

 

Allen Palmer

 

-----Original Message-----
From: arliss...@googlegroups.com [mailto:arliss...@googlegroups.com]On Behalf Of Geoff Huber
Sent: Tuesday, September 20, 2011 11:07 AM
To: arliss...@googlegroups.com
Subject: RE: [ARLISS Flyers] CANSAT video

 

Two 4-40 nylon screws will hold it in my experience.

[Seth Wallace]

I use 3 4/40's (and sometimes only 2 if I'm in a hurry) and I do have video proof from Tuesday that it holds the project in until the charge blows after the 6 second delay. I'll post it after I'm done editing it. SW --- On Tue, 9/20/11, Allen J. Palmer <aj.p...@mindspring.com> wrote:

[Seth Wallace]

3/32nds SW --- On Tue, 9/20/11, Jamie <ja...@dph.com> wrote:

From: Jamie <ja...@dph.com> Subject: RE: [ARLISS Flyers] CANSAT video

[Thomas Kernes]

Is that a problem?  IIRC, the 6 – second delay was to make sure the carrier was pointing downward, but in my experience, this isn't necessary for the payload to leave the carrier.

TK

From: "Allen J. Palmer" <aj.p...@mindspring.com>

[Geoff Huber]

Besides ARLISS I have flown the same rocket in Dual deploy without a problem.  I have video and have watched the rocket come down with the nose cone intact many times.  

 

http://www.youtube.com/user/aeroexperimental#p/u/11/p-1gDrNCNzs

 

 

 

Geoffrey Huber
(530) 891-0853 ext 3030
Geoff...@landacorp.com

 

[Jamie]

There is no doubt that the proper shear pins will do the job – but obviously the ones I was using (and maybe others as well) are inadequate.

I know that others have had this problem – I think Eric even has a similar video to mine.

 

FWIW – I plan to do two tests on my system.  A drop test, where I secure the shock cord to the payload section to a tall structure, assemble a reasonable payload weight (any suggestions?) and then drop it a good distance (10 feet or so) to see if the pins hold.

Then of course do an e-charge deployment of the carrier to make sure the pins will shear.

[Steve Wigfield]

If you are using the styrene pins, they do not have nearly as much strength as the 4/40 nylon screws.

 

Steve

 

---

[Erik Ebert]

Thanks, everyone.  This is a great discussion.

I really like that high-def, solid-state cameras have gotten so cheap now that we can get close up video of exactly what is happening at deployment, rather than guessing and making assumptions, and can use it to fine-tune our launch vehicles just like NASA does with their vehicles.  There's no substitute for first-hand information.


Ken and/or Dave, I think you have a copies of all the student presentations from the ARLISS breakfast.  Once you have settled in settled in back home and recovered from the launch,  can you post them somewhere and let us know?



I do indeed have video similar to Jamie's, and will post it as soon as I've edited it down to the useful bits.  It clearly shows the nosecone and payload being jerked out by the shock of the main opening at apogee.  And six seconds later you can clearly see the empty carrier being pushed out as the ARLISS charge goes off.    I'm using 5 styrene shear pins, but clearly that's not enough.


As for Thomas's question, why worry about whether we deploy the projects at apogee or six seconds, as long as we deploy, in the video you can clearly see the payload section thrashing about quite a bit when the main initially deploys.  With the weightt of the project behind the nosecone, that's what jerks the project out at apogee if the shear pins are insufficient.

By six seconds the payload section has settled down and is hanging pretty stably under the main.    A lot of the project failures seem to be stripped chutes.   There's nothing we can do about projects with poorly designed recovery systems other than keep reminding them, 'don't do that', but on the other hand we shouldn't be making it more difficult for them than it already is.  By making sure we always deploy at six seconds, I think we will be giving the students a much gentler ride with more opportunity for success.  



The missing piece of information is what Jamie was just asking, the average weight of the student payloads (and a reasonable assumption on max weight), for Jamie's drop test prior to a more expensive test flight.    We can probably get that from the student presentations from the ARLISS breakfast once Ken an Dave post them.


Pending the results of Jamie's test, I have a feeling the next ARLISS I will probably be going with 3 4-40 nylon screws, with suitable ground testing, of course, and a test-flight with high-def video at the next Mudrock.


  -- Erik

[Jamie]

I was using Nylon Screws – I’m thinking smaller than 4/40 -  I had them loose so I’m not sure, I had been using them I thought to some success until I saw the video.

 

I know I have larger nylon screws but these are 5/64^th  in diameter – so I’m thinking these aren’t 4/40s

[Steve Wigfield]

Here are the 4/40 specifications.

[Allen J. Palmer]

I think we are going to ‘’see’’ ourselves facing a trade off between conflicting goals.

 

We want to retain the nose cone / payload inside the rocket body against the shock of main deployment by using stronger screws in the nose cone.

 

This may require stronger charges to ‘’blow out’’ the carrier/payload against the stronger shear pins holding on the nose cone

 

This will result is greater forces being applied to the payload as it ejects out of the carrier.

 

I have been concerned about the G forces that we apply to the payloads and their chutes.

 

I think a plan of study and experiments is what is needed much as Jamie has listed

[Randolph Mitchell]

Erik Ebert wrote,

> As for Thomas's question, why worry about whether we deploy the projects at apogee or six seconds, as long as we deploy, in the video you can clearly see the payload section thrashing about quite a bit when the main initially deploys. With the weightt of the project behind the nosecone, that's what jerks the project out at apogee if the shear pins are insufficient.
>
> By six seconds the payload section has settled down and is hanging pretty stably under the main. A lot of the project failures seem to be stripped chutes. There's nothing we can do about projects with poorly designed recovery systems other than keep reminding them, 'don't do that', but on the other hand we shouldn't be making it more difficult for them than it already is. By making sure we always deploy at six seconds, I think we will be giving the students a much gentler ride with more opportunity for success.

Another reason for the six-second delay is to ensure the projects do not deploy until they are clear of the booster laundry.

Ranny

[Thomas Kernes]

With the parabolic flight of these heavy rockets and considering that they
actually deploy like dragster chutes, I don't ever see that being a
problem.

TK

[Jamie]

Anyone else is welcome to perform the same research, btw.  I see it only being beneficial.

 

I understand the concern about the G-Force shock from needing to go to a larger e.charge – I’m pretty sure it won’t resort to that.

 

The reality is  my video shows the payload going through more ‘trauma’ than I suspect the students  planned for – so if it does require extra g-forces to get it out at the proper moment, that may not be such a bad thing.

[david raimondi]

Ken has the presentations at the moment. One of us will be posting the information on the ARLISS site soon.

 

The cansats are limited to 350 grams and the open class I believe are limited to 1050 grams.

 

dave

 

-----Original Message-----
From: arliss...@googlegroups.com [mailto:arliss...@googlegroups.com]On Behalf Of Erik Ebert
Sent: Tuesday, September 20, 2011 13:52
To: arliss...@googlegroups.com
Subject: Re: [ARLISS Flyers] CANSAT video

[Steve Wigfield]

When I pack my main I use and old Alcocer technique of taping break points into the shock cord. I think this helps reduce the high G forces when the main inflates by absorbing the forces incrementally as the break points break.

 

 

---

[david raimondi]

Ken and I discussed building a testbed sat to measure the forces of launch and deployment. The testbed should be sized to fit in the ARLISS K rockets and with an adapter, slip right into an ARLISS M carrier as well, with the appropriate simulated masses and at least 3 axis accelerometers.

 

dave

[Erik Ebert]

Perfect.  Thanks.

  -- Erik

[Jamie]

Yes, I use this technique and I wrap the chute in the shrouds and use a deployment bag with a pilot chute.   

 

Anyway – next time I plan to have both forward and aft looking cameras so that I might get a better understanding of what’s going on in the laundry department

 

I’m also thinking that of adding an additional 15’ to my main shock cord – just to give it more to run out, especially on days where the winds make it deploy horizontal.

[Seth Wallace]

Both of you guys have had premature deployment of the project, Dont both of you guys also keep all of your airframe on one shock cord? Perhaps thats a contributing factor. My booster floats away on its own chute unconnected to the forward airframe and project, maybe there is less of a yank between the forward airframe and the booster this way when the first event happens.

SW --- On Tue, 9/20/11, Jamie <ja...@dph.com> wrote:

From: Jamie <ja...@dph.com> Subject: RE: [ARLISS Flyers] CANSAT video

[Seth Wallace]

I don't think we need to be concerned about the g-forces we apply to the payloads and chutes, I think the students need to be concerned about the g-forces applied to the payloads and chutes, because when they graduate and start building satellites in real life, they are not going to be any less. For that matter the students should probably learn what a "launch window" is and practice making it on time SW

--- On Tue, 9/20/11, Allen J. Palmer <aj.p...@mindspring.com> wrote:

From: Allen J. Palmer <aj.p...@mindspring.com>

Subject: RE: [ARLISS Flyers] CANSAT video

[Steve Wigfield]

I recover my air frame in three parts with a separate chute for each part, similar to you Seth. I have not had a premature deployment yet, there is always a first time.

 

---

[Erik Ebert]

I thought of that, too, but I'm pretty sure I had the problem even before I switched to a single chute, although that was just trying to see what was going on through binoculars. 

I was more worried that was the case until I found out most people are using 2-3 4-40 shear pins, which is a lot more than I am using. Now  I think my shear pins were just too small.  Come to think of it I might even have some accelerometer data from my old flights with the old chute setup I can compare to be sure. 

  -- Erik

[Erik Ebert]

Hopefully I won't be increasing the charge size at all.  I have a feeling there is a pretty big sweet spot between 'amount of force the shear pins need to be able to withstand to hold a 1050 gram payload in against the shock of the main opening', and 'amount of force to reliably blow the carrier out against those shear pins without blowing it up.'   

I have a feeling that once we get the data I might even be able to reduce the size of my charges.

  -- Erik

[Jamie]

I’m not certain how often this configuration has deployed prematurely – all I know for sure it happened this one time because I can see it on video.  Until I saw the video, I had thought I was deploying ‘normally’ and we flew it 4 times this last meet.

 

It’s possible the booster is adding extra stress to the process, at least it’s easy to visualize that possible scenario but I would like to know for sure.

 

I do have footage from last year showing the deployment of the chute but the bird was almost perpendicular when it deployed so I can’t really rely on that to represent horizontal deployment.

 

If we do develop a good shock test dummy payload, it could also help in this research.

 

From: arliss...@googlegroups.com [mailto:arliss...@googlegroups.com] On Behalf Of Seth Wallace

Sent: Tuesday, September 20, 2011 3:41 PM
To: arliss...@googlegroups.com

Subject: RE: [ARLISS Flyers] CANSAT video Question for Erik and Jamie

 

Both of you guys have had premature deployment of the project, Dont both of you guys also keep all of your airframe on one shock cord? Perhaps thats a contributing factor. My booster floats away on its own chute unconnected to the forward airframe and project, maybe there is less of a yank between the forward airframe and the booster this way when the first event happens.

[Allen J. Palmer]

AH contra my friend ……

 

I real life the payload team would be given parameters of the G forces to expect while in our case we have no spec’s. They (the students) have no idea what amount of black powder or size of CO2 cartridge, the length of shock cord that will be used. Are they to prepare for 5, 10, 50 G’s. I don’t think it is realistic to expect them to plan for unlimited G force on deploy.

[Seth Wallace]

FWIW heres the raw footage of just takeoff and deployment, the project has a red chute and the nosecone has an orange chute. The first event is at 26 seconds and the project deploys at 32 seconds.  It was pretty big project on a small chute I thought but it seems to float happily away. I don't have the proper codec on this computer so theres no audio http://www.youtube.com/watch?v=6UsYSrmPnhE

[Seth Wallace]

Tell them their project will be shot out of a cannon and if they plan for that they should be OK. :)

[Jamie]

Yeah – that’s pretty much perfect deployment there.  And you’re using 2 or 3  - 4/40s?

[Seth Wallace]

yep

[Paul Hopkins]

Jamie, any chance of putting 3 or 4 cameras around the airframe? Then combine the videos so it looks like you're looking thru the rocket.

> -------Original Message-------
> From: Jamie <ja...@dph.com>
> To: arliss...@googlegroups.com
> Subject: RE: [ARLISS Flyers] CANSAT video
> Sent: Sep 20 '11 14:29
>
> Yes, I use this technique and I wrap the chute in the shrouds and use a
> deployment bag with a pilot chute.
>
>
> Anyway � next time I plan to have both forward and aft looking
> cameras so that I might get a better understanding of what�s going on
> in the laundry department
>
>
> I�m also thinking that of adding an additional 15� to my main
> shock cord � just to give it more to run out, especially on days
> where the winds make it deploy horizontal.
>
>

> FROM: arliss...@googlegroups.com
> [mailto:arliss...@googlegroups.com] ON BEHALF OF Steve Wigfield
> SENT: Tuesday, September 20, 2011 3:15 PM
> TO: arliss...@googlegroups.com
> SUBJECT: RE: [ARLISS Flyers] CANSAT video

>
>
> When I pack my main I use and old Alcocer technique of taping break points
> into the shock cord. I think this helps reduce the high G forces when the
> main inflates by absorbing the forces incrementally as the break points
> break.
>
>

> --------------------
>
>
> FROM: arliss...@googlegroups.com
> [mailto:arliss...@googlegroups.com] ON BEHALF OF Jamie
> SENT: Tuesday, September 20, 2011 2:51 PM
> TO: arliss...@googlegroups.com
> SUBJECT: RE: [ARLISS Flyers] CANSAT video

>
>
> Anyone else is welcome to perform the same research, btw. I see it only
> being beneficial.
>
>
> I understand the concern about the G-Force shock from needing to go to a
> larger e.charge � I�m pretty sure it won�t resort to
> that.
>
>
> The reality is my video shows the payload going through more
> �trauma� than I suspect the students planned for � so if
> it does require extra g-forces to get it out at the proper moment, that may
> not be such a bad thing.
>
>

> FROM: arliss...@googlegroups.com
> [mailto:arliss...@googlegroups.com] ON BEHALF OF Allen J. Palmer
> SENT: Tuesday, September 20, 2011 2:18 PM
> TO: arliss...@googlegroups.com
> SUBJECT: RE: [ARLISS Flyers] CANSAT video

> On Tue, Sep 20, 2011 at 1:06 PM, Jamie <[LINK: mailto:ja...@dph.com]

> ja...@dph.com> wrote:
>
> There is no doubt that the proper shear pins will do the job � but
> obviously the ones I was using (and maybe others as well) are inadequate.
>
>
> I know that others have had this problem � I think Eric even has a
> similar video to mine.
>
>
> FWIW � I plan to do two tests on my system. A drop test, where I
> secure the shock cord to the payload section to a tall structure, assemble
> a reasonable payload weight (any suggestions?) and then drop it a good
> distance (10 feet or so) to see if the pins hold.
>
>
> Then of course do an e-charge deployment of the carrier to make sure the
> pins will shear.
>
>

> FROM: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com [mailto:[LINK:
> mailto:arliss...@googlegroups.com] arliss...@googlegroups.com] ON
> BEHALF OF Geoff Huber
> SENT: Tuesday, September 20, 2011 12:43 PM
>
>
> TO: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com
> SUBJECT: RE: [ARLISS Flyers] CANSAT video

>
>
> Besides ARLISS I have flown the same rocket in Dual deploy without a
> problem. I have video and have watched the rocket come down with the nose
> cone intact many times.
>
>

> [LINK: http://www.youtube.com/user/aeroexperimental]
> http://www.youtube.com/user/aeroexperimental#p/u/11/p-1gDrNCNzs
>
>
> GEOFFREY HUBER
> [LINK: tel:%28530%29%20891-0853%20ext%203030] (530) 891-0853 ext 3030
> [LINK: mailto:Geoff...@landacorp.com] Geoff...@landacorp.com
>
>
> FROM: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com [mailto:[LINK:
> mailto:arliss...@googlegroups.com] arliss...@googlegroups.com] ON
> BEHALF OF Allen J. Palmer
> SENT: Tuesday, September 20, 2011 12:03 PM
> TO: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com
> SUBJECT: RE: [ARLISS Flyers] CANSAT video

>
>
> Geoff
>
>
> You say
>
> Two 4-40 nylon screws will hold it in my experience
>
>
> The question is,
>
> is this an assumption or do you have video proof. There is a growing
> thought that the payloads are coming out at apogee due to shock pressure of
> the main deployment.
>
>
> Allen Palmer
>
>
> -----Original Message-----
> FROM: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com [mailto:[LINK:
> mailto:arliss...@googlegroups.com] arliss...@googlegroups.com]ON
> BEHALF OF Geoff Huber
> SENT: Tuesday, September 20, 2011 11:07 AM
> TO: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com
> SUBJECT: RE: [ARLISS Flyers] CANSAT video
>
>
> Two 4-40 nylon screws will hold it in my experience.
>
>

> GEOFFREY HUBER
> [LINK: tel:%28530%29%20891-0853%20ext%203030] (530) 891-0853 ext 3030
> [LINK: mailto:Geoff...@landacorp.com] Geoff...@landacorp.com
>
>
> FROM: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com [mailto:[LINK:
> mailto:arliss...@googlegroups.com] arliss...@googlegroups.com] ON
> BEHALF OF Jamie
> SENT: Tuesday, September 20, 2011 10:50 AM
> TO: [LINK: mailto:arliss...@googlegroups.com]
> arliss...@googlegroups.com
> SUBJECT: [ARLISS Flyers] CANSAT video
>
>
> [LINK: http://www.youtube.com/watch?v=AxJ9xw85ync]

> http://www.youtube.com/watch?v=AxJ9xw85ync
>
>
> This is the video from the onboard camera on the Gumby ARLISS � the
> canopy you see is the cockpit on �Gumby� the nose cone.
>
>

> Interesting to note that the (2) 5/64^th shear pins didn�t hold the

[Bob Feretich]

5/64" shear screws are M2 (metric) screws.
If they are new Nylon 6/6 (top quality) screws, each screw should retain 27-39 lbs. If the shear load was divided perfectly equally between the two screws and there was zero preload stress from tightening them, they would retain 54 to 78 lbs. (http://www.feretich.com/Rocketry/Resources/shearPins.html)

I had no problems with my ARLISS flights in the calm weather early in the week, but on Thursday the wind picked up and my flight arced badly to the south. It probably had 400 ft/sec of horizontal velocity when it reached apogee and deployed chutes. Previously, on similar flights my flight computers recorded 18-25Gs of acceleration upon parachute deployment.

1 kg payload plus nosecone and payload carrier mass, lets say its 1.5 kg total mass.
25 Gs of acceleration times 3.3 lbs will exert a force of 82.5 lbs.
Plus we need to add the forces being generated by the internal/external pressure differential at 10,000 ft.

The math says that 2 new Nylon 6/6 M2 screws are guaranteed to shear under those conditions.

We should put more effort into "wind weighting" the flights. It's common for sounding rockets. If we knew the characteristics of the winds aloft, we could compensate with a launch angle the would minimize horizontal velocity. After my flight arced south, I helped Allen Palmer angle his flight as far to the north as the launcher would permit. It resulted in a nearly perfectly vertical flight. It was like watching a hook hit the pocket at a bowling alley.

Previously, there was a lot of chatter on the alias about weather balloons, gathering winds aloft data for flyers would be a very noble purpose.

Regards,
Bob

On 9/20/2011 10:50 AM, Jamie wrote:

http://www.youtube.com/watch?v=AxJ9xw85ync

 

This is the video from the onboard camera on the Gumby ARLISS – the canopy you see is the cockpit on “Gumby” the nose cone.

 

Interesting to note that the (2) 5/64^th shear pins didn’t hold the nose cone on when the main deployed – obviously larger shear pins are in order – I’ll do some ground testing to determine the optimum application.   

[Ken Biba]

I think we have an overall problem of mission consistency on deployment.

We are getting some apogee deploys. We have videos from several fliers that demonstrate that.

We are getting some deployment failures. There is a picture of one flight (for University of ElectroCommunications) in which the payload failed entangled in a broken carrier, a nomex protector and shock cord! Anyone lose a carrier?

We are getting VERY high deployment acceleration (sometimes) - I have gwiz files showing 39g deployments!

We MAY be having a very high level of vibration.

I will get the team presentations and then videos processed by end of week. Those of us that were there at the presentations likely remember (with me) several teams commenting that the vertical acceleration and lateral acceleration (essentially vibration) exceeded their expectations and helped contribute to mission failure. Now ... I do not believe we have given them good standards for those parameters.

I remember payload sizes of .5 to 1.2 kg.

I DO have data from variety of fliers over the past 10 years from their on board avionics ... and one snapshot of data I did with Pius on a test payload in 2001.

On the test payload - we flew an AltAcc within a test payload - and saw a 12g acceleration on deployment.

In quickly reviewing data from myself and other fliers over the past 10 years:

1. I am seeing acceleration spikes on apogee deployment on the order of 3-5gs ...

2. I am seeing acceleration spikes on payload deployment that are highly variable ... ranging from 6gs all the way up to 39gs with perhaps a median around 12gs.

These last measurements are taken from airframe - we can expect that the payloads are seeing significantly higher accelerations.

This variability is NOT a good thing .. and neither is deployment at 39gs.

I have a 6DOF sensor left over from 100K that I think would be perfect for this instrumentation - along with GPS. Welcome help.

Proper screws for shear pins are not the only issue here ... how much powder is also an issue as we can see.

I would argue that our standard for deployment should (at least) be:

1. Downward pointing under chute.
2. No more than 10gs (as seen by the payload) deployment acceleration.
3. No more than 12gs of boost acceleration.
4. No more than x lateral acceleration (vibration).

K

[save children]

i fly with a single main for the booster and payload sections. the booster has a 20' cord and the payload section is on a 40' cord. I have used this about 8 times and I use a slightly bigger second charge to backup. I have watched deployment once with binos and it seemed to deploy after the main deploy by 6 secs but the cameras are a great idea.

---

From: ja...@dph.com

To: arliss...@googlegroups.com
Subject: RE: [ARLISS Flyers] CANSAT video Question for Erik and Jamie

Date: Tue, 20 Sep 2011 16:00:31 -0700

[Erik Ebert]

Here are links to my deployment videos.  The Youtube "HD" still doesn't have the full HD resolution.  The dropbox files are the original full HD.


This is the full deployment sequence from just before the main goes until just after the carrier goes:

http://www.youtube.com/watch?v=0WMl0WlepQs
http://dl.dropbox.com/u/42582674/ARLISS2011_deploy_sequence.mov


The Aichi payload leaves as soon as the main goes.  

For Kyushu, you can hear the click as the main goes and the nosecone hangs on for 5 seconds or so as the payload section thrashes around before it gives up.  By six seconds when the payload section has stabilized, the payload charge goes off and the carrier is ejected, but the payload has already left.

The  Tokyo Institute of Technology sequence is somewhere in between.  You can hear the click when the main deploys again, and the nosecone hangs on for a couple of seconds before it gives up but not close to the full six seconds.


This one is more for fun.  It is just zeroed in on the payload being deployed, slowed down to 1/20th of real time:

http://www.youtube.com/watch?v=HcJXMdT1Tv4
http://dl.dropbox.com/u/42582674/ARLISS2011_deploy.mov


And this is the full test flight on Saturday with the camera looking down at the ground and at the main deploying:

http://www.youtube.com/watch?v=7wFDer9U29o
http://dl.dropbox.com/u/42582674/ARLISS2011_Test.mov

[Erik Ebert]

I probably shouldn't  be opening this can of worms again, but I finally got around to going back and looking at the data from long ago when I was flying with two chutes and more recent years when I have been flying with one chute.

With two chutes, the deceleration when the chute inflates averaged around 7.5 feet/sec^2
With one chute, the deceleration when the chute inflates averaged around 10 feet/sec^2

So definitely a bigger shock with one chute than two, which makes sense because it is a bigger chute inflating.   But even before, with two chutes, the wimpy styrene shear pins I was using were insufficient and I was getting early deploys.   I'll probably be going with 4-40 nylin screws next year (ground testing, of course).



On whether 10 feet/sec^2 shock of the larger single chute opening is too much for the project:

The boost acceleration is  6.5 feet/sec^2 acceleration.  So one chute or two shock of the chute opening is more than the boost, and yes, the shock of one chute opening is more than the shock in a two-chute configuration.


But then compare that to the shock when the payload deployment charge goes off.

Chute opening = (10 ft/sec^2 deceleration  ) X (approximately 2 pound payload) =
 = approximately 20 pounds force (lbf)


Cansat deployment charge:

1.5 gram charge in a 18" long by 6" diameter compartment = 5.7 PSI  (according to the infocentral BP charge calculator)

5.7 PSI (lbf/in^2)  x 3.14 x ( 3" radius base of the cansat carrier)^2 = 161 lbf.


And a 1.5g charge is probably the ragged edge of how small you'd want to go, depending on the size of the shear pins.  I personally prefer a little larger.  So one chute or two, the shock of the chute opening is insignificant compared to the shock of the cansat deployment charge.


Yes, some people have been going to CD3s, but there are tradeoffs there in size, cost, and complexity and I don't think CD3s should be required equipment.   No, we don't want to intentionally give the payloads too harsh a ride, but on the other hand part of the challenge is designing a project that can survive a standard ARLISS trip, and well-designed projects have been surviving BP deployments for years before CD3s even existed. 


  -- Erik

[save children]

Great information thank you very much. I haven't seen many worms yet. It is a cansat so you expect something to come out of a can.

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Date: Mon, 17 Oct 2011 12:52:31 -0700
Subject: Re: [ARLISS Flyers] CANSAT video Question for Erik and Jamie
From: eeb...@gmail.com
To: arliss...@googlegroups.com