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  1. #1
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    Demystifying Deployment Bags

    There are several discussions on the go about how to use deployment bags, so I decided to start this thread. I will share what has worked for me and hopefully others will contribute their experiences, with either content or links to what has worked for them.

    I have been working with deployment bags since my 1st L1 attempt. I attempted to use a research deployment bag, in conjunction with a cable cutter. The idea was to hold the deployment bag flap shut and the pilot to the bag using a zip-tie. The pilot acted like a drogue from apogee until main @ 800’. At main the cable cutter would cut the zip-tie allowing the drogue to act like a pilot and pull the main from the deployment bag. This was on a 3” PML Bull Puppy, modified with a nosecone AV bay, which held my altimeter and tracker. May she rest in peace, or more like pieces.

    Although ambitious for an L1, the technique was well bench and ground tested. Unfortunately the day of my flight the main failed to deploy. Upon further testing I discovered that the gauge wire I used for the altimeter power was just too light. Something I was unable to initially detect due to the poor sensitivity of my ohm meter, which I replaced. This caused just enough resistance that prevented my igniter from firing the main, however it did fire my apogee event. Using a 9V in colder temps was also contributing factor, and explained why it did not show up in the half dozen bench tests while on my nice warm bench. Fortunately the rocket landed in nice soft mud which did not result in any damage from this attempt.

    Regardless, I abandoned that method and have been using deployment bags in a more orthodox manner ever since. That being the chute bridle connected to the 3rd loop of the shock-cord on my booster. The top loop of the chute connected to the deployment bag tether, and the top tether of the deployment bag connected to a pilot.

    I will go into detail of the setup in the pics below. The example below is on my 3” Darkstar, which is the smallest airframe I have used with a deployment bag. I have successfully flown this specific configuration twice and during the last flight I was lucky enough to capture a lot of the recovery events on my on-board Mobius. Once I finish editing the video I will post links in this thread.

    The components used in this example are the following:

    - One Bad Hawk 3 loop 25’ 11/32 Kevlar recovery harness
    - One Bad Hawk 3/16 and 1/8 stainless steel quick-links
    - Fruity Chutes 48” Iris Ultra Compact (main)
    - Fruity Chute 12” Classic Elliptical (pilot)
    - Fruity Chutes 3’ 1/4” flat Kevlar 2 loop extension
    - Fruity Chutes 3”x6” Deployment bag
    - Fruity Chutes 1.375 ID stainless steel slider ring
    - Topflight 12”x12” Nomex

    As mentioned above this is what I would call a standard setup, however there are other variations. One such technique is something I have heard referred to as “free-bagging”. Hopefully someone with some hands on experience will add this and other methods to the thread, and this will help others gain some comfort with the tech and techniques.

    First the proverbial “un-boxing”. Left to right, recovery harnesses, chutes, Nomex chute protectors and deployment bags, nosecone, payload and AV bay from my 3” Darkstar and quick-link/recovery hardware.



    This particular rocket is over-stable, so where I can I will eliminate forward weight. In this case I take the 3rd loop and the end of the recovery harness and loop it over the nosecone harness and through the other end of the recovery harness. I use quick-links everywhere else on this set-up. I realize that this introduces a weak point in the recovery harness, however it is simply holding the nosecone on, which is not under enough loads at any point to be a concern.



    Taking a look at how the 3-loop One Bad Hawk harnesses are made, you can see that there is a harness from one end to the other (black box) with a third loop sewn into the harness (red box). I always use the end-to-end harness to attach my chute to the booster and the sewn on, 3rd loop, is connected to my nosecone. Again no real loads to be concerned with if the stitches were ever compromised. Having said that I have yet to see any defects in a One-Bad-Hawk harness. Still I like to mitigate where I can. Going forward I am going to refer to the forward loop of the end to end, as the 3rd loop.



    The other end of the harness passes through the payload tube and connects to the forward bulkhead on my AV bay via a 3/16 polished stainless steel quick-link.



    This rocket uses machine screws to secure the payload tube to the AV bay via self-clenching nuts epoxied to the inside to the AV Bay. In this example I am just screwing down one, but there are three 120 apart.



    At this stage we just have the deployment bag assembly to deal with.



    Broken out here is how it all goes together. The recovery harness (beige) is connected to the booster and nosecone with a 3rd loop that connects to the bridle/shroud lines (white) of the chute. You need a top loop on your chute to do this but the Fruity Chutes Iris comes with one pre-sewn. You connect the top loop of the chute to the deployment bag tether (black), which passes right through the top of the deployment bag and connects to a 3’ Kevlar extension harness (beige) then to the pilot/Nomex. I use the 3’ extension simply to get a bit more distance from the dead air coming off the top of the main chute. I connect the top-loop to the inside (longer black) tether of deployment bag using a 1/8 polished stainless steel quick link. I use a lighter quick-link for this, as it is never subjected to enough loads to be a concern.



    Then using the method published by Fruity Chutes "
    Fruity Chutes Iris Ultra IFC-168 Parachute Packing - Part 1 and 2" (links below), I stuff the chute into the deployment bag. I also slide on a polished stainless steel “slider ring” (also mentioned in the video) then neatly arrange the shroud-lines and bridle. As Gene mentions, neatness counts, if it looks messy then do it again. The slider ring simply creates a slight delay in your chute inflating. This mitigates the shock loads that can occur on the recovery system when the chute inflates. Depending on your chute and configuration this may or may not be an issue, but the Iris chutes have a 2.2 CD so they can add more shock load than most chutes.



    Now that the chute is packed in the deployment bag I z-fold the recovery harness up to the 3rd loop and stuff it in the top of the payload tube.



    Next I z-fold the length of the 3rd loop and place it on the deployment bag package and slide it into the airframe. It is very important that the deployment bag is correctly sized for your setup and that it is free to slide out of the airframe.



    At this stage I z-fold the integrated tether of the deployment bag connected to the 3’ extension harness and place it my pilot/Nomex package and slide it in so it is resting on top of the deployment bag. Always last in so first out.



    Then I just pin my nosecone. In this case I use 3x2-56 nylon sheer pins 120 apart.



    Lastly here is the entire package pulled out of the airframe showing where everything lines up.



    Reference videos:






    Last edited by mpitfield; 14th January 2018 at 09:00 AM.
    Michael Pitfield
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  2. #2
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    Great write up and photos! Thanks for taking the time.

    Scott Wathey
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  3. #3
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    Nice write up and photos, i've recently had my own questions about using this method, i plan to get some experience with one of 4" rockets.
    Eric M
    NAR#85115 L2

  4. #4
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    Quote Originally Posted by mpitfield View Post
    ...Lastly here is the entire package pulled out of the airframe showing where everything lines up.


    Is the opening of the bag facing fore or aft?

  5. #5
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    The opening faces aft, with the shorter deployment tether that protrudes from the top of the bag facing forward. When I get home I will take some sequence pics that will illustrate how it unpacks during deployment.
    Michael Pitfield
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    Quote Originally Posted by mpitfield View Post
    The opening faces aft, with the shorter deployment tether that protrudes from the top of the bag facing forward.
    Then that's exactly what makes sense to me, because if the pilot is the only thing that gets into the airstream (i.e. weak ejection) then it has the best chance of still pulling the bag and/or chute out of the airframe.

  7. #7
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    Quote Originally Posted by jahall4 View Post
    Then that's exactly what makes sense to me, because if the pilot is the only thing that gets into the air-stream (i.e. weak ejection) then it has the best chance of still pulling the bag and/or chute out of the airframe.
    Your intuition is correct.

    Below is an attempt to illustrate the sequence of events based on my setup. Of course in reality what happens in the air-stream may result in a different result however that is true for every setup I know. Regardless of all the hypothetical outcomes, I would argue that using a deployment bag in this way mitigates issues resulting in a net gain, vs. not using one.

    We will start off with the main event deployment charge shearing the pins and separating the nosecone.



    If your charge is correctly sized and the laundry is packed properly then this should result in everything being ejected into the air-stream. However in a worst case if the pilot was the only thing ejected, it would very likely result in a nominal deployment. Of course that is assuming everything is free to slide out. For the purpose of this example we will exaggerate the events and start off with the pilot.



    Once the pilot is out it will inflate rapidly causing the rocket to fall at a greater velocity and pulling the deployment bag out of the airframe.







    As you can see the deployment bag is inverted while in the airframe, with the top facing aft and the aft facing forward. This allows the shroud-lines and chute to be easily pulled free from the bag. If you hold a deployment bag upside down and shake it, the chute should come out with very little effort.



    The next couple of pics demonstrate how the chute would depart from the deployment bag. As you can see the chute is still packed but the shroud lines and recovery harness are out. More importantly they are below the deployment bag, including the rocket components. This also mitigates an inverted deployment, where the chute is ejected from the airframe but under something, such as part of the recovery gear or worse a component of the rocket. An inverted deployment happened to me last summer with a nose heavy rocket where the nose was dragging everything down in a line and when the main deployed the entire rocket went right through the chute. Fortunately the chute was partially inflated and everything landed without any damage, just a bit hard. This was on a 54mm rocket which does not have a deployment bag but the issue was resolved with the addition of a drogue located close to the nosecone.





    This is why neatness counts and why you have to be careful when packing your chute. This picture shows where the shroud lines and the bridle merge into one, as well as my slider ring (optional). Gene mentions this in his how to pack tutorial and it is very important. For anyone rigging this up for the first time I would pack and manually deploy on the ground several times to ensure you get the logic correct. If these components were under the elastics that organize the shroud lines, then they could get tangled and your main may remain in the bag. This would result in a failed main. Notice how it's packed on the outside so when the lines pull out everything is free.



    Once your shroud-lines are free then your chute would start to get pulled free. Here is how it would work and in my case how the slider would help to retard full inflation.







    At this stage your chute is completely out and inflating. As well the deployment bag would be moving away from the chute but still connected via the top loop. Notice the slider ring holding the shroud-lines together, but rapidly moving aft as the chute is forced open.







    Finally here is a close-up of the "top-loop" that is pre-sewn into the Fruity Chute Iris canopy. This is the part that is directly connected to the deployment bag via a 1/8 quick-link in this illustration.

    Last edited by mpitfield; 14th January 2018 at 10:33 PM.
    Michael Pitfield
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  8. #8
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    Don't use a long and slender deployment bag and if one uses one recommended by the maker or made by them they won't go wrong. Kurt

  9. #9
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    Thanks Michael that was exactly what was needed!

    BTW... my spill hole loop is at the end of a strap.

  10. #10
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    Quote Originally Posted by jahall4 View Post
    my spill hole loop is at the end of a strap.
    What make chute is it, can you post a pic? I am having trouble visualizing.
    Michael Pitfield
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  11. #11
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    Quote Originally Posted by mpitfield View Post
    What make chute is it, can you post a pic? I am having trouble visualizing.
    It's one of Julie Blehm chutes. I'd love it insert a graphic, but it don't work.

  12. #12
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    Quote Originally Posted by jahall4 View Post
    It's one of Julie Blehm chutes. I'd love it insert a graphic, but it don't work.
    Ah Sperachutes, yes they are nice and well made. I don't own one but I have seen the construction, although I don't recall the top loop.
    Michael Pitfield
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    Yes they are, and her service is awesome.

    Here is a link to a photo: https://www.dropbox.com/s/ikr4vthsdo..._9869.jpg?dl=0

  14. #14
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    Quote Originally Posted by jahall4 View Post
    Yes they are, and her service is awesome.

    Here is a link to a photo: https://www.dropbox.com/s/ikr4vthsdo..._9869.jpg?dl=0
    Okay sure, it looks like an extended top loop. I see advantages of this if you are using a pilot, if you want an extension. However if you don't use a pilot then that is a lot of "top loop" to have hanging around doing nothing. That is unless it is an option?

    I attached the pic you sent for quick reference.

    Click image for larger version. 

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    Michael Pitfield
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  15. #15
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    Quote Originally Posted by mpitfield View Post
    Okay sure, it looks like an extended top loop. I see advantages of this if you are using a pilot, if you want an extension. However if you don't use a pilot then that is a lot of "top loop" to have hanging around doing nothing. That is unless it is an option?

    I attached the pic you sent for quick reference.

    Click image for larger version. 

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    It's standard with Julie's cutes 84" and larger. The irony is that I did not plan on using a bag until the chute showed up. Got me thinking that maybe I should. Little review of research I did over a year ago, a look at Gene's bag and I'm hooked.

  16. #16
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    Thank you Michael. I've been scratching my heat a bit on this, and how you lay it out really makes sense. Question - If you're a moderator, are you one of the forum people who can make this a sticky? Just a thought.

    Paul B.

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    Quote Originally Posted by PBic View Post
    Thank you Michael. I've been scratching my heat a bit on this, and how you lay it out really makes sense. Question - If you're a moderator, are you one of the forum people who can make this a sticky? Just a thought.

    Paul B.
    Hi Paul, I am glad it provided you some clarity.

    I am only a "moderator" in the Galleries thread, and in fact I am not really a forum moderator at all. I volunteered to help keep the Galleries thread organized as threads and posts were created, and this function provides me certain moderator rights. The ability to create stickies, close, move, merge threads etc. in my case is limited to just the Galleries section of the forum. Furthermore on the "moderators" moniker. When I took on the responsibility to manage the Galleries sub-forum, I made a point to make sure that in my new role that I had no interest in managing users, so I am just a regular user like everyone else.

    More specific to the sticky question. At this stage I am not sure it warrants a sticky; I suppose if enough people contributed to it and it became a good sole source for the subject then someone could approach one of the "real" moderators/admins to make it happen.
    Michael Pitfield
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  18. #18
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    Great writeup and it is very helpful with the pictures. I do have one question on the d-bag sizing. When you use a d-bag, is the diameter of the bag sized so that it fills the body tube or is it significantly smaller than the body tube diameter? I am thinking about one for my 4" darkstar, but not sure what size bag I would need to get. Thanks!
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  19. #19
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    Michael, Excellent write-up on d-bags.... The photos make it much more understandable.

    You asked people to post about "free-bag" deployments. Just to make sure I understand the definition of "free-bag", that is when the pilot chute pulls the d-bag up and off the main chute, but it is not attached to the main and the d-bag is free of the main/rocket assembly. I also believe the nosecone is attached to the pilot chute to give it some weight so it comes down close to where the rocket lands. If it was just a pilot large enough to pull the d-bag off but only had the bag under it afterwards, it might never come down. The nose cone gives it a reasonable decent rate.

    With that definition of "free bag", I use a modified version of that. I guess you could call it a "non-free bag" set up. The pilot is attached to the d-bag and nose cone. I like this because the pilot is attached closer to the nose cone than the d-bag so even if ejection doesn't push the d-bag out of the payload tube, the nose cone only has to separate a little bit and will pull the pilot out and get it into the air stream. I don't have to depend on the ejection charge pushing any of the recovery parts out of the payload tube. I have argued in the past that deployment is only the nose cone pulling things out of the tube, but the reality is the charge can also push the recovery gear out. How much the charge pushes the recovery gear depends on how tight the fit, the tighter the fit, the more the push. If you have a loose fit, the ejection gases tend to pressurize the tube, popping the nose cone off, but not pushing the recovery gear out much. Just watch some ground test videos and notice how the nose cone flies off but no chutes come out until the shock cord is stretched out and pulls the chute out.

    The pilot is sized to bring the nose cone down about 3-4 ft/sec slower then the main will drop the rocket. I use a 100 ft length of 150 lb. Dacron line between the d-bag and the top of the main chute. That is what is the "non-free" part of the setup. I will z fold and tape the Dacron line and put that in the d-bag first. I've had several deployments where there were a few z-folds still taped together after the rocket lands so even though the pilot is sized for a slower decent rate to keep the nose cone above the main, there isn't much tension on the Dacron line. The 100 ft of line is probably more than needed, but I want to allow enough time for the main to open and slow the rocket so the tension on the Dacron line is just the difference in decent rates. If the line reached full length before the main opened, it would have higher loads on it. Of course you could use stronger and/or shorter lines.

    I don't have pictures, but here's drawing of how things are set up.

    Click image for larger version. 

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    My d-bag is home made and sized so the full bag with shrouds under the elastic straps (like the one you use) will be a relatively loose fit in the 6" payload tube. My main chute is also home made and 9 ft. diameter. It is stuffed into the bag and is very tight. It will not fall out of the bag. This still works quite well, it just puts a lot of stress on the bags connection point to the pilot chute. The first time I used it, the bag tore. I have since reinforced it by sewing 2" nylon straps to the bag at the stress points.

    With all that said, I have only used this on 5 flights of a 6" diameter, 50 lb., L3 rocket. All the flights have deployed perfectly, but I haven't used it on anything smaller.
    Handeman

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    Quote Originally Posted by Crazyrocket View Post
    Great writeup and it is very helpful with the pictures. I do have one question on the d-bag sizing. When you use a d-bag, is the diameter of the bag sized so that it fills the body tube or is it significantly smaller than the body tube diameter? I am thinking about one for my 4" darkstar, but not sure what size bag I would need to get. Thanks!
    I don't know that there are any hard fast rules on this as it is more the right sized deployment bag for the chute and payload bay. Obviously the important things are that the deployment bag does not get stuck in the air-frame and the chute does not get hung up in the deployment bag.

    One thing I have always done with all my deployment bags, and I have nine of them now, eight for 3" air-frames and one for a 4" air-frame, is to work with the chute manufacturer or supplier. Most (seven) of mine are from Fruity Chutes so I always run the scenario by Gene and work with him to come up with a solution.
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    Quote Originally Posted by Crazyrocket View Post
    Great writeup and it is very helpful with the pictures. I do have one question on the d-bag sizing. When you use a d-bag, is the diameter of the bag sized so that it fills the body tube or is it significantly smaller than the body tube diameter? I am thinking about one for my 4" darkstar, but not sure what size bag I would need to get. Thanks!
    This should help: https://fruitychutes.com/buyachute/deployment-bags-c-3/

    The Fruity bags are sized for the frame and when you pack the chute you scrunch it down so it fill the bag. The dia will always stay the same, but the packed bag will be longer for bigger chutes. I bought a 4x9 for a 4" frame.

  22. #22
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    Quote Originally Posted by Handeman View Post
    Michael, Excellent write-up on d-bags.... The photos make it much more understandable.

    You asked people to post about "free-bag" deployments. Just to make sure I understand the definition of "free-bag", that is when the pilot chute pulls the d-bag up and off the main chute, but it is not attached to the main and the d-bag is free of the main/rocket assembly. I also believe the nosecone is attached to the pilot chute to give it some weight so it comes down close to where the rocket lands. If it was just a pilot large enough to pull the d-bag off but only had the bag under it afterwards, it might never come down. The nose cone gives it a reasonable decent rate.

    With that definition of "free bag", I use a modified version of that. I guess you could call it a "non-free bag" set up. The pilot is attached to the d-bag and nose cone. I like this because the pilot is attached closer to the nose cone than the d-bag so even if ejection doesn't push the d-bag out of the payload tube, the nose cone only has to separate a little bit and will pull the pilot out and get it into the air stream. I don't have to depend on the ejection charge pushing any of the recovery parts out of the payload tube. I have argued in the past that deployment is only the nose cone pulling things out of the tube, but the reality is the charge can also push the recovery gear out. How much the charge pushes the recovery gear depends on how tight the fit, the tighter the fit, the more the push. If you have a loose fit, the ejection gases tend to pressurize the tube, popping the nose cone off, but not pushing the recovery gear out much. Just watch some ground test videos and notice how the nose cone flies off but no chutes come out until the shock cord is stretched out and pulls the chute out.

    The pilot is sized to bring the nose cone down about 3-4 ft/sec slower then the main will drop the rocket. I use a 100 ft length of 150 lb. Dacron line between the d-bag and the top of the main chute. That is what is the "non-free" part of the setup. I will z fold and tape the Dacron line and put that in the d-bag first. I've had several deployments where there were a few z-folds still taped together after the rocket lands so even though the pilot is sized for a slower decent rate to keep the nose cone above the main, there isn't much tension on the Dacron line. The 100 ft of line is probably more than needed, but I want to allow enough time for the main to open and slow the rocket so the tension on the Dacron line is just the difference in decent rates. If the line reached full length before the main opened, it would have higher loads on it. Of course you could use stronger and/or shorter lines.

    I don't have pictures, but here's drawing of how things are set up.

    Click image for larger version. 

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    My d-bag is home made and sized so the full bag with shrouds under the elastic straps (like the one you use) will be a relatively loose fit in the 6" payload tube. My main chute is also home made and 9 ft. diameter. It is stuffed into the bag and is very tight. It will not fall out of the bag. This still works quite well, it just puts a lot of stress on the bags connection point to the pilot chute. The first time I used it, the bag tore. I have since reinforced it by sewing 2" nylon straps to the bag at the stress points.

    With all that said, I have only used this on 5 flights of a 6" diameter, 50 lb., L3 rocket. All the flights have deployed perfectly, but I haven't used it on anything smaller.
    Thank you Handeman,

    Yes the "free-bag" term, as I understand it, is as you described. I don't know if that is the correct term for the rigging but that is how I have heard to it refereed to as out in the rocket pastures I frequent.

    I have seen your setup as well, and I get the advantage of having everything come down together, I will call it a tethered free bag. Most times I have witnessed this setup one chute descends at higher rate than the other. So the nosecone/pilot are either draping over the main and dragging it down, or the other way around. Obviously you are aware of this and have made some effort to get the sizing correct, which seems to be a big part of getting this config right.

    Than you very much for adding this. Can you share how you calculated the "right" size for the chutes, was it just a calculation or did you do any test-out flights? Chute sizing for the pilot seems to be where the magic is in this config? Also if you can post pics on how you pack everything then that would also help?

    One other observation about your technique and "free-bagging" is that I have noted that they have almost been exclusively for larger heavier rockets, which I would include your 50lb rocket.
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    Mike, if I understand your setup, then the configuration below depicts how things might "unfold" upon deployment. The cone shoots downward, pulls tension on the pilot, and the chute springs out of the bag. If the drogue does it's job, then the main deploys into clean air and there is no problem. If the air frame is not pointed outward, though, then there could be issues. Do you see this happening differently than what I've drawn?

    Jim
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Quote Originally Posted by JimJarvis50 View Post
    Mike, if I understand your setup, then the configuration below depicts how things might "unfold" upon deployment. The cone shoots downward, pulls tension on the pilot, and the chute springs out of the bag. If the drogue does it's job, then the main deploys into clean air and there is no problem. If the air frame is not pointed outward, though, then there could be issues. Do you see this happening differently than what I've drawn?

    Jim
    The only thing I see about that is the time it takes for the pilot to pull the chute out of the bag. Once the pilot catches air, even if it is under everything else, it has to pull the bag out, pull all the shrouds out of the elastic, and then pull the chute from the bag. The pilot should be well above everything by the time all of that happens.
    The failure I see is if the upper parts catch and foul the pilot. Then the main never deploys and you are going to land hard.

    It's really a matter of having a proper drogue set-up which should prevent that from happening. With a proper drogue setup, no matter where or how the pilot deploys, it should be above the fin can. It is after all a system. You need to have all of it working, not just some of it.

    Click image for larger version. 

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    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  25. #25
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    Quote Originally Posted by Handeman View Post
    With a proper drogue setup, no matter where or how the pilot deploys, it should be above the fin can.
    Click image for larger version. 

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    Exactly

  26. #26
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    Quote Originally Posted by Handeman View Post
    The only thing I see about that is the time it takes for the pilot to pull the chute out of the bag. Once the pilot catches air, even if it is under everything else, it has to pull the bag out, pull all the shrouds out of the elastic, and then pull the chute from the bag. The pilot should be well above everything by the time all of that happens.
    The failure I see is if the upper parts catch and foul the pilot. Then the main never deploys and you are going to land hard.

    It's really a matter of having a proper drogue set-up which should prevent that from happening. With a proper drogue setup, no matter where or how the pilot deploys, it should be above the fin can. It is after all a system. You need to have all of it working, not just some of it.
    I would say that the pilot could be above everything by that time, but it often isn't. And, the drogue often doesn't result in that perfect "V", although I have seen some beautiful examples). When I was testing my stabilization system, where the cone/stabilization portion was heavy, I can guarantee you that the chute opened below everything else. I suspect that the weight of the "cone" and the ejection velocity play a role in making the system work.

    Jim

  27. #27
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    19th January 2009
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    Quote Originally Posted by JimJarvis50 View Post
    I would say that the pilot could be above everything by that time, but it often isn't. And, the drogue often doesn't result in that perfect "V", although I have seen some beautiful examples). When I was testing my stabilization system, where the cone/stabilization portion was heavy, I can guarantee you that the chute opened below everything else. I suspect that the weight of the "cone" and the ejection velocity play a role in making the system work.

    Jim
    You didn't increase the size of the drogue when you added weight to the cone?
    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  28. #28
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    18th January 2009
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    Quote Originally Posted by Handeman View Post
    You didn't increase the size of the drogue when you added weight to the cone?
    The problem was an imbalance in the weight of the fin can versus the weight of the upper air frame. With a large drogue, both pieces hang down. With a smaller drogue, the fin section just flies above the drogue and the upper section still hangs down. I don't believe there is a drogue size that would make the parts fly properly. So, I arranged for the cone to be separate from the pilot/main, and for the chute not to open until it got above everything (per the pic).

    My case is somewhat unusual in that the upper air frame tended to be pointed more downward than what you want due to the weight distribution. I needed a way to make the main skinny so that it could get past everything before opening. My deployments for this special case got much better (had two bad deployments with the conventional approach and then two good deployments with the revised approach). Now, I just use this technique for everything, as I have not found a reason not to.

    Jim
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  29. #29
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    7th July 2013
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    Quote Originally Posted by JimJarvis50 View Post
    Mike, if I understand your setup, then the configuration below depicts how things might "unfold" upon deployment. The cone shoots downward, pulls tension on the pilot, and the chute springs out of the bag. If the drogue does it's job, then the main deploys into clean air and there is no problem. If the air frame is not pointed outward, though, then there could be issues. Do you see this happening differently than what I've drawn?

    Jim
    Hi Jim,

    Thanks for your input.

    In regards to the illustrations you posted of my set-up. In general I agree with both Handyman and jahall4 that drogue sizing and placement has a lot to do with how well the recovery "system" functions and it's chances of success. I can see that both outcomes you presented are possible, based on just the use of a deployment bag in the manner I presented. After all there don't appear to be any absolutes with any recovery method.

    When it comes to drogue sizing and placement. I typically perform at least two shakedown flights on any new build. I do this in a practical effort to uncover issues and tune the system. I did this on my L2 bird and the practice has proven to be invaluable on many occasions, not just for uncovering technical issues but logistical ones as well. If my L3 ever gets off the drawing board I have a plan to do this as well. When I do these "shakedown" flights I put a lot of emphasis on recovery, so I do low and slow in an effort to witness the events as they roll out. I also download all data sets and perform a relatively thorough analysis post flight, in an effort to identify anything that could use a tweak.

    Specific to your nose-heavy scenario, I experienced something similar this past summer with a new 54mm build that is nose-heavy but does not use a deployment bag. This nose-heavy issue is also something that I have witnessed from the flight line on several occasions over the years. I put a bit of thought in how to resolve my issue and came up with the idea to attaching a small drogue to the base of the nosecone. It is early to tell if this is a net plus or a minus but it has mitigated the issue to a large degree.

    Michael Pitfield
    TRA 14579 L2
    NAPAS BoD
    URRG
    MARS
    CRC

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