Ground Testing AV Bay Charges

I am building my AV bay and started to think about what a ton of people have been telling me " Make sure you ground Test" I have never done it could someone tell me what would be the best way or ways to do it? Please
Thank you
Mark

If you have an altimeter that can run a test, like the Raven, you just set it to do that. Otherwise you can feed a wire into a vent hole and manually use a battery to fire your e-match and ignite the black powder.

Most altimeters have a test mode so that you can test the igniter that you want to use with the battery that you want to use. Use the same ones as you are going to fly... otherwise it's not a valid test.

You also want to test the payload bay/parachute section with a charge so that you have an idea of how much powder to use to give your nose cone and chute a good kick. There's plenty of guidance floating around on this, in general you're going to use between .5 g and 1 g of powder for each charge.

chefmarkt69 said:

I am building my AV bay and started to think about what a ton of people have been telling me " Make sure you ground Test" I have never done it could someone tell me what would be the best way or ways to do it? Please
Thank you
Mark

Click to expand...

this is how i do it. Estes R2D2 Launch controller attached to e-match out a vent hole

[video=youtube_share;qp98EBLZhVg]https://youtu.be/qp98EBLZhVg[/video]

Testing your altimeter (like a Raven) is different than ground testing your charges. It's best not to mix the two. If you want to ensure your e-matches, charge holders, charge size, shear pin combo works, it's best to fire them manually.

I had a test bench set up using only e-matches (no bp), turned on my raven, then realized I had not connected the USB cable for the test. I neglected to first turn off the Raven (so it' doing the beep beep boop thing), and when I connected the USB cable both e-matches fired. Very glad I didn't have bp in the mix. I was startled, but still have my eyebrows, eyes, fingers, etc.


So my personal rule is test the altimeter with e-matches, test the charges manually.

There is a third option in some cases. If your altimeter has telemetry you may be able to instruct it to fire remotely. I test that way with the Telemetrum. If I recall the process correctly, you pick the charge you want to fire, arm it, then fire it.

But without telemetry or remote control I'm a little hesitant to use an altimeter's built-in test mode for ejection testing. I don't like a process I can't control or abort. What if it doesn't go off when you expect? When is it safe to approach the rocket? Suppose the timing is wrong and it goes off early?

BTW, I'd highly recommend testing with all recovery gear loaded, just like it would be for flight.

Additionally, if your rocket will go moderately high ( > 10Kft) then a flight charge may have to be somewhat greater than a test charge. If > 20Kft things get more interesting than that. Those aren't hard numbers and I don't have the personal experience to guide anyone on this. But target altitude matters.

If you use a backup charge, you might consider making that one stronger, but setting it to perhaps a second or two delay compared to the primary. It is the insurance policy.

Gerald

I test using wires ran though a vent hole. I don't test with my electronics. Mainly a safety measure. What if your charge is oversized and you damage your e-bay and wreck your electronics. That would be bad. A fellow club member tested his L3 with over 12 grams (that is as high as he told us, his numbers said 20 grams) of 4fff in a 7.5" airframe. I had my foot against the e-bay bulkhead and we were testing the nosecone. Two members had a moving blanked about 5' away to catch the nose. I was thinking it was 5-6 grams. It went off, nosecone went clean through the blanket and then hit the end of the cord and pulled the airframe 10' away. It was a stout kick on my foot. He also caved in his 1" plywood bulkhead on his electronics bay. He would have wrecked them had they been in there. We now have the 'Ernie charge' named after him.

Edward

With a L3 it's probably better to find this out on the ground than in the air... whenever firing a charge you need to maintain a "safe" distance. In the case of a 1g charge in a L1/L2 rocket, it's probably only a few feet to the side; with something like this you may need a bunker.

I've had charges breach the bulkhead on small rockets, since the charge has already deployed the parachute the flight effect is minimal, but of course the electronics don't like it very much. Generally it causes a reset or hang; it doesn't seem to damage them, fortunately.

AlphaHybrids said:

I test using wires ran though a vent hole. I don't test with my electronics. Mainly a safety measure. What if your charge is oversized and you damage your e-bay and wreck your electronics. That would be bad. A fellow club member tested his L3 with over 12 grams (that is as high as he told us, his numbers said 20 grams) of 4fff in a 7.5" airframe. I had my foot against the e-bay bulkhead and we were testing the nosecone. Two members had a moving blanked about 5' away to catch the nose. I was thinking it was 5-6 grams. It went off, nosecone went clean through the blanket and then hit the end of the cord and pulled the airframe 10' away. It was a stout kick on my foot. He also caved in his 1" plywood bulkhead on his electronics bay. He would have wrecked them had they been in there. We now have the 'Ernie charge' named after him.

Edward

Click to expand...

I wonder how high that would have gone if the rocket was vertical...

AlphaHybrids said:

I test using wires ran though a vent hole. I don't test with my electronics. Mainly a safety measure. What if your charge is oversized and you damage your e-bay and wreck your electronics. That would be bad. A fellow club member tested his L3 with over 12 grams (that is as high as he told us, his numbers said 20 grams) of 4fff in a 7.5" airframe. I had my foot against the e-bay bulkhead and we were testing the nosecone. Two members had a moving blanked about 5' away to catch the nose. I was thinking it was 5-6 grams. It went off, nosecone went clean through the blanket and then hit the end of the cord and pulled the airframe 10' away. It was a stout kick on my foot. He also caved in his 1" plywood bulkhead on his electronics bay. He would have wrecked them had they been in there. We now have the 'Ernie charge' named after him.

Edward

Click to expand...

Just went through this a couple of months ago ahead of a weekend launch doing dual-deploy for the first time [went 4-for-4]. I have a Missileworks RRC2X. For testing the altimeter, I got a couple of 60mA lamps. I could run the test modes in my living room [that is, until my wife got annoyed by all the continuity beeping].

For ground testing the deployment charges, I read up as much as I could on the calculations. There's no shortage of "standard" sizes per airframe diameter that people use, but I was needing to calculate for a pretty small space. Anyways, I packed the charge, strung the wires that would go into the altimeter through the vent hole, and hooked them up to my launcher; that way, I was fully in control of when the charge would go off.

Thank you all for the info, I will take all of it and apply it and keep you posted on the turn out. Have a good day and thank you again.
Mark

I use old hand towels approximating the weight of the parachute when I do mine... don't want to chance screwing up my new 'chute on the ground if something goes wrong...


Later!

--Coop

I will probably get myself flamed out of here for asking this, but...
A quick search on me shows I have a problem with getting Aerotech Birds to separate successfully in the middle when required. You guys can tear me up for doing it wrong (not sanding/too tight a fit,
Several folks have suggested I augment the AT charge supplied with the 29mm reloads, and I want to do two things:
1) I want to easily access powder required to provide this ancillary force (NOT a pound)
2) I want to be able to ground-test in a 29mm reload casing.

I'm lucky to live in Arizona, which has pretty lax gun laws, but I'm not interested in trying to buy a LB of BP, because by my calcs, that will last 454 flights (g/lb and all). Can I instead buy a box of 22LR ammo, remove the slugs and collect the powder? Obviously there's some risk to this, but I think I"ll only need to open 5-6 rounds to get 1g.

If I do this, can I test the charge in my AT casings by:
1) installing an estes igniter in the hole in the casing normally between the BP well and the delay charge, then, filling with the AT powder charge + 1g
2) packing the chutes and cords in, and then counting down....

Please remember that I'm not trying for an L2 or L3 cert; I just want to fix a problem with motor ejection.

Thanks!

Don't use the powder from a .22. That is smokeless powder, NOT black powder. There is a very big difference in the burn rate and pressures created.

What mv1471 said. The smokeless powder from the 22LR will NOT work without being "contained". You can do that when you are using electronics. If you are just adding to the amount in a reload, it won't work well.
Just a guess here, but I would guess you have a G-Force. That seems to be the most common Aerotech rocket that has problems with ejection using Hobbyline reloads.

If you need more powder, and don't want to buy a lb. check with the vendor at your local site, or other fliers. They may be able to supply you with a small amount.

Anyone flying dual deploy flights will have cans of black power and will most likely share some with you. (happens all the time). If you are at a SARA launch in Tucson or any of the two day launches in Phoenix that I attend, I will give you some. Jack of "Whats up Hobbies" attends the bigger launches and will have it also.

terryg said:

Anyone flying dual deploy flights will have cans of black power and will most likely share some with you. (happens all the time). If you are at a SARA launch in Tucson or any of the two day launches in Phoenix that I attend, I will give you some. Jack of "Whats up Hobbies" attends the bigger launches and will have it also.

Click to expand...

That's very kind, Terry! I've not joined SARA yet, but am planning on doing so in 2013. I'll hopefully see you there!

No problem, the more flights I get to watch the better! Several of us have been sharing the same can of BP for a couple of years. 2013? Do not forget about this Saturdays launch (Dec 15). Never miss a launch opportunity! LOL

I can only recommend you test first..

here what happenz if not enough:

[video=youtube_share;Ql2rt-AKnHQ]https://youtu.be/Ql2rt-AKnHQ[/video]

now same rocket, same day, with corrected charges:

[video=youtube_share;8MaVSJrsXc0]https://youtu.be/8MaVSJrsXc0[/video]

conclusion: without this test the rocket would have been destroyed at first flight...