Doug, that is solid advice. The online calculators are a decent STARTING point, but that is it. I'd never dream of flying a bird w/o a ground test first -- unless I had a very, very similar rocket that I could cross reference.

Our "O" project will definitely have a lot of ground testing. It is just senseless to risk something that entails so much work.

I'm quite often surprised when I ground test-- sometimes it takes a lot less powder than I expected, and sometimes a lot more than anticipated. That is why I tend to test all the time.

Incidentally, on smaller charges-- the type of ematch will definitely affect things. In other words, an Oxral w/ 0.5g is often way different than a Davey 28BR w/ 0.5g of the same powder. If you change ematches, re-do your ground tests when using less than about 1g of powder. On bigger charges, the effect of a different brand of ematch is minimal.

JW

Thats interesting on the ematch differences there. Any Idea why? Has anyone used the quickburst ematches yet?

My tests were done with Quickburst. Mostly because I have a hard time finding any others.

Doug

Thats interesting on the ematch differences there. Any Idea why? Has anyone used the quickburst ematches yet?

The reason is because some of the ematches have differing amounts of pyrogen. IIRC, the difference between a 28B and a 28BR is that one of them has 3X the pyrogen vs. the other. On a some of my rockets I use 0.25g. I'll bet the ematch has that much oomph.

There is a very clear difference between ematches -- no doubt about it. Not a problem, though-- just test, and record your ematch and your charge and go from there.

The reason it is not a factor on a 4g charge is because the BP/Pyrogen ratio is way up there. If the ematch = 0.25g or 0.5g of energy, that pales in comparison to 4g of FFFF. OTOH, if you aren't using that much powder, say 0.25g, then your ematch is (potentially) doing some of the work.

JW

Doug as all of my experince has been on Davey Fires or Oxral how did you like the Quickburst?

I always like Davey Fires but as I mentioned I just can't find them anywhere. I picked up Quickburst at LDRS and they are in just about everyway comparable to Davey Fires. They list their spec on the package (and probably their web site) and I have tested nearly a dozen so far (all on the ground) and they have all worked. So far, I can't say anything bad about them except one little thing.

When I bought them I wanted the 2m lengths and the guy thought I was strange for wanting such a long igniter. They have only 3 foot leads. So for your M's and other long applications, you get to solder used leads to make them the length you need. BTW, when I asked about getting them he said he couldn't get any that long, if you believe that. The only other item maybe worth mentioning is that the lead also seem to be smaller than Davey fire but I don't know what gauge wire it is.

Bottom line is, I'm using them in Freeze Frame, which requires eleven of them per flight including the motor ignitors.

Doug

Cool Doug. Thanks for the info. I bought a box of 100 of the Quickburst and they do look very simular to Davey's. But I to wish I could get the long 3m length. I use the left over wires for my ignitors as well. I know tons of people that like them for that very reason. I was mainly concerned with the rekiabillity and quality was all. Want to be able to have some faith or trust that my chrges will work when I do my L3 cert.

Once again Doug Thanks again. And boy I cant wait to see your set up.

I'm going to use, and ground test first but haven't yet, the Quickburst 1-12gm. canisters for my L3. Heard very good things about them. I'll probably test at a launch, since I don't want to shoot anything through my fence. 🙂 This is a great and needed post.

Actually when I ground test I do a net/catch assembly with a large blanket or 2. keeps it from going throug the fence. And I have tested up to 7 to 8 grams before.

Actually when I ground test I do a net/catch assembly with a large blanket or 2

Absolutely, always rig something to catch the potential projectile. Many ask a couple friends to hold the blanket in front of the rocket. That works well as long as their life insurance is paid up...

Doug

Actually when I ground test I do a net/catch assembly with a large blanket or 2

Absolutely, always rig something to catch the potential projectile. Many ask a couple friends to hold the blanket in front of the rocket. That works well as long as their life insurance is paid up...

Doug

Doug, That was SO funny. I couldnt stop laughing... I had some pretty funny images of friends in full football or hocky gear come to mind trying to catch the parts. Like hey Dave Go long.. Then all the sudden flash.. A nosecone is sticking through Daves mid section (kinda like the Arrow through the head gag) and he says to me that he thinks he will go home now... ROFLMAO.. sorry guess ya gotta be there.. LOL

I'll ask my wife to hold the blanket, and our dog can hold the other end. I know hers is paid up. No, won't work, she'll have to hold both somehow, our dog hates loud noises. 🙂 Conway, I think you said you had calculated about 5 grams as an optimum charge to start with for yours. There are online calculators, but they always need to know the pressure needed to blow things apart. Is there a rule of thumb on calculating the pressure needed per volume, or body tube size, or anything else? I was going to start with 4 grams... I've used the empirical method, just took a guess, then went up or down from there depending on what happened during the initial test. Now, for a 5" diameter G10 FB tube with 24" effective length inside (two 6" couplers take 12" away from the 36" tube), giving a volume of 150 sq. inches. I'm starting with (4) 2-56 screws, with the option of drilling larger for (4) 4-40. I love fiberglass! 😉

Using one of the calculators as a guide. Start there and use a charge for that appropiate space. See how weak or strong it is when you test it. Then make adjustments from that point. Lets say it shears the pins and blows it out with auhtority. Maybe you will try a little less and see what happens. Maybe a little less is to weak. well you now know you need to go back up. Im a firm beliver that a more aggresive charge is always better then a weaker charge. At least then you know its coming out. Then be sure to use a long harness to absorb the energy from that charge and your good to go. I normally go a little bit big.. ok maybe a fair amount bigger then what some maybe do. but I have yet "knock on wood" to ever not deploy. I am willing to bet that when I am done testeing my set ups I am close to 5 to 7 grams per event.. leaning more towards the larger myself.

Bruce, if you haven't check out the video I put on my site you should look at it before you test. I have 24" of 6" tube and the online calculators said I needed at least 3 grams just to shear the four 4-40 screws, I decided to start with 2 grams and practically put a hole in the wall. Well it was a Styrofoam wall but it was MORE than adequate to do the trick, hence the posting on the forum. The calculators are overkill. Think about it this way, if you ground test and your charge is too small, so what? You might be embarrassed by your lack of performance but if it is too large you could impale you catcher and you might have to do some explaining.

Doug