Dog barf in LPR

What is ratio for Dog Barf in LPR rockets? This will be my first weekend using the stuff. I decided to try it since the glorified toilet paper keeps melting my parachutes.

Take a look at this post:

https://www.rocketryforum.com/showthread.php?27184-Dog-Barf-Mass&p=241758#post241758

Well, my answer is "just enough," which is maybe sort of helpful. I add enough that I feel comfortable that any still-burning BP pieces from the ejection charge will hit a piece of barf before the parachute. If it's too tight, of course, you will have ejection problems, or could blow out a weak spot in the airframe. I haven't been able to pack it that tight by accident, so I am not sure how hard it would have to be.

In a narrow airframe, it's possible to have several inches of loosely packed barf come out without a problem, in my experience. Others may get mathematical about it, but I've either been lucky or there is a large margin of error. When my son packs the barf, I like to take the nosecone off and see how much just pours out the top. I want most of it to stay in. I also sometimes take the motor out and look through the BT to see how much light gets past the barf (I want very little, as i don't want the BP to have a line-of-sight path right to the chute). Do not point the tube toward the sun when you do this: you will get an eye full of barf and then be blinded.

Dog barf is an almost perfect component: it works as well or better than the commercial wadding, is a small fraction of the price, and is biodegradable so we're not littering our fields. And every once in a while it contains an interesting bit of newsprint (maybe I'm examining the barf too closely?). I have not discovered a downside to using it.

How they make dog barf . . .

Another good idea I discovered is the use of small and standard sized cupcake baking cups with the barf. This is good for mostly BT 55 to BT 80 sized rockets. Cupcake shell goes in the tube bottom side first and I usually push it all the way in and keep it straight. The bottom of the cake shell will cover the motor tube. Use the usual "blackjack" recommendations as in the previous post for barf. This helps insure that the ejection will not creep through a loose portion of the barf and burn your chute. They are heat resistant after all. Werxz fer mee.

I use a 3-to-1 ratio +1. That is I start with a single sheet of wadding and add enough "dog barf" to the tube equal to 3 times the diameter of the tube in barf height. Loose fill mind you. Don't pack it down like a muzzle loader!

Jerome

Lots of variety and they all work.
BT50 and smaller I use 2x tube diameter loose dog barf. BT60 and above I use 2-3 sheets of wadding laid flat over the top of the tube and pushed down with a smaller tube like the cupcake papers. This keeps the ejection charge from blowing a hole through the dog barf. Then 1.5 - 2x tube diameter dog barf. No problems so far.

Mike

JeromeK99 said:

I use a 3-to-1 ratio +1. That is I start with a single sheet of wadding and add enough "dog barf" to the tube equal to 3 times the diameter of the tube in barf height. Loose fill mind you. Don't pack it down like a muzzle loader!

Jerome

Click to expand...

It's been quite while since I loaded a LPR, but I tend to put some dog barf in a sheet of wadding and push that down and then fill the dog barf on top leaving just enough to get the chute and nose cone on. Seems to work well.

use just enough so that there is no holes through the insulation. the ejection charge will compress the dog barf, protecting the recovery device. you dont have to use a lot and it should not require a degree in insulation packing to figure it out. fill the tube so there is some protection for the recovery device. Thats enough. By the way, if you purchase this insulation, expect to will it to your children.

FWIW, I don't use dog barf on rockets smaller than BT55. I just can't get it to work without melting the parachute. I can get the Estes style wadding to work great.