Baffle not a good idea for some rockets?

Discussion in 'Mid Power Rocketry (MPR)' started by Mushtang, Jan 17, 2014.

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  1. Jan 17, 2014 #1

    Mushtang

    Mushtang

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    I'm building a Leviathan and the body tube has a LOT of room in there for the laundry to slide backwards in, or it seems like it would take a ton of dog barf at a launch.

    So the obvious choice to avoid all this is to put in a baffle. I'm in the middle of making my own out of a spare short piece of a body tube and some thick card stock for the ends.

    Before I install this permanently I thought I'd ask if there's any reason not to use a baffle in a Leviathan, or any other rocket?
     
  2. Jan 18, 2014 #2

    TopRamen

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    I've never heard a Negative/Con, about a Baffle. You could always just use a Chute Shelf like the Stock TLP Kits if you have reasons for not trusting a Baffle. I've been buying and installing Sunward Brand Baffles on my BT-80 size Kits, and on my latest, use the Baffle with its inherent Coupler in place of the Body Tube Coupler. Then, I'll be able to use the "Chute' Shelf" to keep the CG where it belongs, not letting the Chute' slide back when it launches.
     
  3. Jan 18, 2014 #3

    hcmbanjo

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    I don't see any reason to install baffles in small diameter models, BT-5 through BT-50s.
    You have to compare the cost of a baffle to the cost of a package of wadding.

    Are you going to fly the model enough times to justify the cost of the baffle?

    For me it's BT-55 and above can get a baffle.
    Like you are doing, make it yourself!
    Coat the punched card stock ends with glue and the baffle could last forever.
     
  4. Jan 18, 2014 #4

    hball55

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    The only negative I have found with baffles is that they have a habit of spewing crud out the back of my rockets at inopportune times, like when carrying the rocket over light-colored carpet.:jaw: A good shaking before taking rocket indoors cures that.
     
  5. Jan 18, 2014 #5

    dave carver

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    If your worried about the chute sliding down what I do is add a centering ring below the chute, no baffle. But I guess that's a baffle of sorts but not in the traditional sense. I just make sure there's enough room for wadding, shock cord and parachute. :)
     
  6. Jan 18, 2014 #6

    Mushtang

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    Okay, I think the consensus here is that a baffle isn't a bad idea and won't have negative results.

    To Chris M., the use of a baffle wouldn't be to save money exactly, the club I fly with (or at least the only place I could ever fly a rocket of this size) supplies dog barf for use without charge. My concern is the length of that open tube and what would happen to the chute during powered flight. Plus a baffle keeps the CG forward, eliminates wadding, and just makes everything easier. I was just checking to see if there were some negatives I hadn't heard about yet.

    So here's my home made baffle pieces after a layer of glue has been put on the sides of the card stock that will face the heat.

    Baffle.jpg

    I have another question. There are about 30 holes in the piece that only has holes around the outside (which I'll put on the bottom) and about 25 on the piece with the holes grouped in the middle (which will go on the parachute side). How do I know if there's enough free area with the number of holes I punched? Will putting too few holes cause the pressure to build up enough to damage the rocket?
     
  7. Jan 18, 2014 #7

    Maxx Mayhem

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    I like baffles on BT-5 rockets because it seems to me that there is less likelihood of of getting the recovery system jammed up. Especially if the rear is a larger tube, and you have a chute.
     
  8. Jan 18, 2014 #8

    thobin

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    For 29mm rockets I would say yes go with a baffle where you can. Once you reach 38mm my opinion on this has changed a bit and I would have to say not so much any more, it can limit motor options. As for LPR I would have to go with hcmbanjo anything BT-60 and lower is unnecessary.


    TA
     
  9. Jan 18, 2014 #9

    Darian Rachal

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    I recently purchased a Leviathan and was wondering about this myself. I was thinking about using one of those Kevlar chute protectors, if they are still available somewhere for a reasonable price. What I may more likely go with is flameproof sheets of crepe paper. I'm sure it is fairly inexpensive and can be purchased at Walmart or on sale at Hobby Lobby. I may even check at the Dollar Tree. :)
     
  10. Jan 19, 2014 #10

    bill_s

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    I think there may have been some calculator for it, but I presume the area of a 29 mm thrust block has to be sufficient, which is 1" dia. Area is pi * r^2 (radius squared), so 1" is pi/4. If you want to keep pi out of it, use (target diameter/holes diameter)^2 = number of holes, minimum. So with 1/2" holes you would need 4, 1/4" would need 16.

    Note the RMS ejection caps are 1/2". The baffle needs to keep those entirely out or allow them to pass through freely.

    As to "blowing up" due to too little area, possible, but more likely just impede ejection.
     
    Last edited: Jan 19, 2014
  11. Jan 19, 2014 #11

    blackbrandt

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    Just wondering, why do you not just run a dowel through the rocket sort of near the motor mount, and finish the ends, and have the chute rest against that? Seems like a baffle is just more trouble.
     
  12. Jan 19, 2014 #12

    Handeman

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    The only negative for a baffle in the Leviathan, and other large rockets with small motors, like the G-Force, is marginal ejection charges. These types of rockets tend to have more issues with standard ejection charges being insufficient, or marginal at time because of the large volume and relatively small motors. Adding a baffle could make this issue worse if you are having any problems already. On my Leviathan and other rockets like this, I usually add about 0.2g of BP to the Hobbyline ejection charges.
     
  13. Jan 19, 2014 #13

    cwbullet

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    Baffles work well in medium to low power. I have not seen them in high power.

    What is a chute shelf?
     
  14. Jan 19, 2014 #14

    gdjsky01

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    Biggest issue is with the baffle you are using you have to do a lot of shaking to get those Aerotech caps out. If ye be doin that.
     
  15. Jan 19, 2014 #15

    dave carver

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    I've been useing dollar store crepe paper for years. At 2 rolls for a dollar you can wad a lot of rockets. You have to be careful of one thing, I mixed yellow and red on one rocket. The ejection charge didn't blow the wad out, just partialy, so there were was red and yellow streamers hanging out which to my old eyes looks to be flame. I yelled the "FIRE" call and was totally embarresed when the gathered crowd saw what happened...:blush: :eek: :facepalm:
     
  16. Jan 19, 2014 #16

    bill_s

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    Yeah I was thinking about that too ... although reasonably that seems like at most it would produce a longer pulse of less pressure, a delaying, except for leakage through the motor, which would still be small. Don't know if there is evidence.

    Note the drilled baffle would trap ejection caps which would be hard to get to drop back through the motor mount unless flush with the ring.

    I would guess a chute shelf is a thing to stop the chute. A centering ring or a plank across the body. Seems like all you need then is a bit of wadding or a blanket around the bottom of the lower ball of stuff (usually shock cord but I've put the chute on the bottom too).
     
  17. Jan 20, 2014 #17

    Handeman

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    I don't have any evidence either, all I know is I've seen more G-Forces come down without chutes deployed because the nose cone popped and the chutes didn't come out then any other model. The worst wasn't because of a week ejection charge though, if anything it was too strong. The elastic broke and while the nosecone headed off to Kansas under parachute, the lower section went ballistic through a windshield. Made a nice 4" diameter impression on the dash.
     

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