Ejection Baffle Where do I place It?

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Brian Johnson

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I'm building a LOC 2.14 rocket seen below I have some problems.
1) I notice that AeroTech places their baffle at the bottom just above the motor tube.
2) Others on the TRF are saying they put their baffle up front?
3) I'm using a LOC 2.14 air frame which is almost a BT-70 and I can't find a baffle system to fit the tube. Is there a baffle that will fit with some sanding of the ends.
4) Do the baffles made of plywood work? Seems to me they would burn up over time.
5) Do metal mesh baffles clog up over time and will they set your rocket on fire?
6) Add last how much do they weigh I need to know so I can simulate where to put a baffle for best stability?
1589928778387.png

Thank You
Brian
 
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heada

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I place my baffle as far aft as I can so as to leave as much room for recovery devices as possible but not so far aft that it'll interfere with the motor or motor ejection. Bigger the motor, the bigger the ejection, the farther forward I place it.
 

neil_w

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It is always recommended that a certain amount of room be left between the motor and the baffle, but I don't think I've ever seen a proper formula for exactly how much that is.

My own inclination would be to put it as far forward as possible while still leaving comfortable room for all the recovery materials (plus some slop). Typically that probably puts the baffle at or in front of the loaded CG, *and* it keeps the shock cord further forward, so it's more likely to help stability rather than hurt it.
 

Leo

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I place my baffles as far forward as possible so the ejection gases "cool" down so not to scorch it too much but enough room for recovery equipment.
 

heada

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There is already a volume of air in the rocket that has to be moved in order for the hot gases to move forward in the rocket. My baffles block direct burning particles and I rely on the volume of air already there to mitigate the hot gases. No issues so far.
 

jrap330

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The official line is hot ejection gases (Estes, NAR,, etc) but everyone of my scorch Plastic chutes show damage that indicates individual burning pieces of propellant/black powder. So, Heada , nail it on the head....
 

BABAR

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The official line is hot ejection gases (Estes, NAR,, etc) but everyone of my scorch Plastic chutes show damage that indicates individual burning pieces of propellant/black powder. So, Heada , nail it on the head....
Actually it depends on the black powder motor. A young lady did a NAR Presentation (I can’t find it at the moment) that demonstrated using high speed photography and a glass plate to “catch” the ejected material that ZERO delay motors, which have no clay caps, eject only hot gas with no significant flaming bits. It is presumably the infrared light going up the open nozzle that ignites the sustainer, or the next booster in 3 or 3+ black powder staging. Which kind of explains why you can gap stage at least 50 inches between motors, when vented properly.

she didn’t do the test with standard delay motors, but these have a clay cap and from experience looking at the burn marks on chutes and balsa helicopter blades, these motors definitely spit flaming chunks.
 

kuririn

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My own inclination would be to put it as far forward as possible while still leaving comfortable room for all the recovery materials (plus some slop). Typically that probably puts the baffle at or in front of the loaded CG, *and* it keeps the shock cord further forward, so it's more likely to help stability rather than hurt it.
+1
As far forward as possible while still leaving room for the recovery laundry.
This will also prevent adversely affecting your CG by keeping the added weight forward.
Excellent article by Tim Van Milligan in Apogee's newsletter here:
Excerpt:
"Finally, I would recommend positioning the aft bulkhead disk of the baffle at least one body tube diameter in front of the engine mount tube. This will allow some space for the gasses to cool before having to go through the lower bulkhead disk. Further is better, but you don’t always have the extra room. "
(Highlights mine).
Since he has a degree in aeronautical engineering, he should know.
Laters.
 
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