Testing BP charges

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Maxter

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What is your method of testing BP ejection charges? For example, do you start with the payload section
with all the shock cords , parachutes and nomex in place? Do you plug the motor tube, etc.? Do you use a vacuum to check the computers? Or are you a just fill'em up and let it go bang kind of tester? Do you use online calculators and if so how accurate do you find them?I know the way I test but, I wonder how others are testing.
 
I start with online calculators- specifically on that used to be on ROL. I saved the page locally so I can still run it. Calculate that usually for 12-15 psi to determine charge.

I then load up the rocket sections with chutes, harnesses- flight configuration, and run cables through the vent holes. Pop the charges to makes sure things go as planned. Usually they do as the aforementioned calculator is pretty good. If running redundant altimeters/ charges I use the tested charge as the starting/ light charge, and the larger secondary charge is usually 10% larger.

I test altimeters with matches and a vacuum.
 
Only change i make to Marks testing process is to replace my chute with an equal size and weight bundle of old T-shirts, that way I don't risk scorching the chute with a weak ejection charge.
 
I fly the rocket in question low enough I can see the whole flight and use at least one known quantity to deploy main safely close to apogee, and any additional recovery is free to succeed or fail without damaging the rocket.
 
Do a calculator.
If it's a kit, perhaps ask someone that flys it successfully.
load it all up, ready to fly, with a empty motor tube that's plugged.
run your ematches into the ebay and out the baro hole.
I use 100 feet of speaker wire and a 9 volt battery
I do the apogee event first because that's the way it flys.
 
  1. Test altimeters with an Adept vacuum chamber and two LEDs.
  2. Use online calculators to get recommended ejection charges.
  3. Load rocket in final launch configuration (i.e., could walk to the pad with it -- motor loaded, chutes and harnesses, shear pins in, etc.).
  4. Disconnect wiring from one altimeter and send leads out through the static port, clearly marked for main/drogue.
  5. Tilt rocket on a small X-stand so that payload section is elevated and fins are on the ground.
  6. Attach Estes launch controller leads to drogue wires.
  7. Depress continuity button to eject (Estes are high current devices and the continuity check will light an e-match).
  8. Make sure section separated far enough to allow harness to unzip and drogue is free. If not, reload and repeat.
  9. Move booster off of X-stand, and place payload tube on X-stand.
  10. Connect Estes controller leads and depress continuity button to eject.
  11. Make sure nose cone separated far enough to allow harness to unzip and main chute is free.
  12. If not, repeat.
  13. If using back-up altimeter, add 10% - 15% to secondary charges.
 
Most of the answers are how I test. However, I have found the online calculators to be off by as much as 115%. I use them as a starting point but, would never rely on them without ground testing.
 
Calculators are a starting point. But to truly know the volume of the space you are trying to pressurize, you would have to take into account how far the motor sticks out past the forward CR, the topology of the AV bulkheads, the exact shape of the NC shoulder, etc.

Tightness of the components is a big one, too. A tight tube takes more powder to blow it out than a loose one, even with the same volume.
 
Like they said, start with an online calculator.. it will give you a good starting point..

I pack it all up like it is going to fly.. I use the motor case and I plug the end with cardboard. that way you have the volume of a used motor.
Use the same shear pins you are going to use on flight day.

I do my testing right on the ground. I don't support the back of it .. it will not have support in the air to stop the back. so I just let it fly.
Winter time in Michigan makes it nice with snow on the ground. the nose cone moves nicely.

[video=youtube;V8gPab-Mvi0]https://www.youtube.com/watch?v=V8gPab-Mvi0[/video]
 
Bat-mite said:
Tightness of the components is a big one, too. A tight tube takes more powder to blow it out than a loose one, even with the same volume.
Click to expand...

I haven't done any testing so I could be way off, but I think a tight, not over tight, tube can take less charge to open it then a loose tube. With a loose tube you lose some pressure around the connection. If it is tight, the pressure can build higher and pop it apart. That seems to track with my experiences. With that said, I'm not sure there is enough difference to be concerned about. Size the charge for a loose connection and you should be good to go.

Of course using shear pins negates most of that.
 
I like to test my altimeters during the BP tests. I do this by blocking all but one avbay vent hole and insert a 1/8" OD polyethylene tube into the remaining one. Onto this I push a length of 1/4" OD irrigation tubing hooked up to a large, modified slurp gun. When I pull the piston rod which normally is used to pick up water, a vacuum is created which slowly dissipates, simulating an apogee (or descending) event and the altimeter fires the charge. I change altimeter channels depending if I am doing an Apogee or Main test. I protect the nosecone with bubble wrap.

Here are a few videos from my L1 Matrix, L2 X-celerator and L3 Gizmo XL tests:

[video=youtube;Abn89NZo8Po]https://www.youtube.com/watch?v=Abn89NZo8Po[/video]

[video=youtube;HS5cQdjMpRA]https://www.youtube.com/watch?v=HS5cQdjMpRA[/video]

[video=youtube;i3VH0Tftq4s]https://www.youtube.com/watch?v=i3VH0Tftq4s[/video]

[video=youtube;D66t7yfLC_g]https://www.youtube.com/watch?v=D66t7yfLC_g[/video]

[video=youtube;fUag4HUHpgA]https://www.youtube.com/watch?v=fUag4HUHpgA[/video]
 
Last edited:
The Eggtimer TRS and Eggtimer Quantum altimeters allow you to test the deployment channels remotely. I was at TRASD last weekend and I had a flakey continuity reading on the Main channel of a Quantum in a Wildman Mini, so while it was on the pad (with the igniter OUT) I fired the main from about 50' away just to see if the problem was the igniter or the circuitry. It popped. Turns out I damaged a part by overtightening the screws on the board.
 

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