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Schuyler

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I'm working on a simple scratch built rocket and hoping to certify at NERFF in August. I'm planning to use an altimeter for ejection but to use motor ejection as a backup. I'll use a delay that should be long enough to eject after apogee in case the altimeter fails. I bought a Perfectflight MAWD and some Newton's 3rd canisters. Here are my questions:

1) If the altimeter ejection system fails and the rocket is "saved" by the motor eject is that considered a failure?

2) Does buying black powder require a permit? If so, what is the best substitute? I have read that some substitutes are not reliable with these canisters.

3) I know I should test the ejection charge but I live in an apartment and I don't know where to do this without attracting unwanted attention. How do others get around this problem?

Any other advice is appreciated.
 

skycopp

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#1 I think it will still be a pass, but I'm not 100% positive.

#2 I don't think BP requires a permit. I bought some with just my driver's license. (try to get 4F, but I have 3F and it has been working fine for me).

#3 I use a friend's property. He is out of the city quite a ways. If all else fails, do it at the launch.
 

Pantherjon

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skycopp gets a 100! :D

As long as the rocket is recovered without damage that would prevent an immediate flight it will be considered a success- provided of course the laundry comes out..No laundry recovery with no damage still equals no certification..

BP can be had without a permit 'technically'..Meaning it is 'supposed' to be used in reloading ammo or muzzle load replicas..But, when I got my can of BP they didn't ask what my intended purposes were for it..And like skycopp said try to get 4F, 3F will work just as well, you will have a bit more soot from the 3F tho..

As far as the ground test..Yeah, if you live in an apartment, do it at the launch..

Good luck! ;)
 

hardinlw

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Most engine reload kits come with black powder. Because it is shipped as part of an exempt item, it is also exempt from the requirement to have an explosives permit. If you used only engine-based ejection and just used the altimeter to record altitude, you would not need a permit. There is a lot to be said for keeping the L1 certification simple. I did not start using altimeters until I started flying rockets that would go pretty high. That said, the altimeter removes all those nagging doubts as to whether you have the right ejection delay.

There is an exemption for black powder when used in antique firearms. If the gun shop does not ask what you want the black powder for, you could buy it; however, using it in a rocket does require an explosives permit. If a BATF agent attends a launch, sees you with BP other than what came with the engine, and asks to see your permit, you are in trouble. Maybe that's not likely, but the consequences could be pretty bad.

Ground testing is a requirement for L3 certification, but it was not required for L1 and L2 when I did those. I have never ground-tested ejection charges. For larger rockets, I've calculated what would be needed with an on-line calculator and it always worked. Now that I am building an L3 project, I will be doing ground tests. Your best bet in this regard is to go to the launch where you plan to certify and ask the person certifying you what he wants you to do.
 

Schuyler

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Thanks for the tips. Hopefully I'll be certified next month!
 

SpartaChris

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1) If the altimeter ejection system fails and the rocket is "saved" by the motor eject is that considered a failure?
I would talk to the person signing off on your cert to make sure they're on board. The recovery has to work as intended, so it is my belief that if your intent is to have a motor based back up to deploy the recovery, you should be fine.

2) Does buying black powder require a permit? If so, what is the best substitute? I have read that some substitutes are not reliable with these canisters.
Most people are using pyrodex or red dot. One thing about them is they need more containment for a complete burn than BP does. One way to increase the burn is to put the e-match in the top of your containment device rather than on the bottom. Some experimentation on your part would be a good idea.

3) I know I should test the ejection charge but I live in an apartment and I don't know where to do this without attracting unwanted attention. How do others get around this problem?
Find a friend with a yard. I've ground tested in the front and back yards of my friend's house without scaring the neighbors too badly. :)

Other advice- Make sure you ground test your altimeter with the e-matches you're planning on using. This makes you familiar with the altimeter before you fly and gives you confidence your setup will work. Also, if you have a bunch of nose weight or are doing a dual deploy, you might consider shear pins to help prevent possible drag separation. Otherwise, ave fun and come back with pics!
 

SpartaChris

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Ground testing is a requirement for L3 certification, but it was not required for L1 and L2 when I did those. I have never ground-tested ejection charges. For larger rockets, I've calculated what would be needed with an on-line calculator and it always worked. Now that I am building an L3 project, I will be doing ground tests. Your best bet in this regard is to go to the launch where you plan to certify and ask the person certifying you what he wants you to do.
Actually, it is not a written requirement though your TAP or L3CC may ask you to do it. Ground testing in general is just a good idea as you'd rather experience a failure on the ground than in the air.

Careful with the online calculators as they tend to be a bit high. My buddy used one for the ground test of his L3 rocket, and it told him to use 8 grams. I talked him into cutting it in half, which still wound up blowing the snot out of his rocket.

A simple rule of thumb I follow for ground testing- Start with .5 grams for rockets up to 2.5" in diameter and work your way up in .5 gram increments. 2.5-5.5" diameter birds, start with one and increase it in .5 gram increments. 5.5-8"- Start with 2 and go up in 1 gram increments. 8-12", start with 4 and go up in 2 gram increments. 12" up, start with 6 and increase by 1 gram increments.

It's not super scientific, but it's served me well every single time. In most cases, the starting amount winds up being exactly what I need or really close.

Also, if you don't want to burn through commercial e-matches, try making your own or using Christmas bulbs or something. By the time you get around to ground testing your rocket, you should already know whether your altimeter will fire your e-matches or not so you should only be testing the amount of ejection charge needed and not whether it will work with your altimeter.
 

als57

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Here are my questions:

1) If the altimeter ejection system fails and the rocket is "saved" by the motor eject is that considered a failure?
Usually the "motor backup" is used to deploy the drogue by most folks. So if there is no main deploy in a dual deploy situation ; then its a fail.

If your just using the alt to put out the laundry at the top. Then motor backup would save your cert as was mentioned.

Al
 

hardinlw

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Careful with the online calculators as they tend to be a bit high. My buddy used one for the ground test of his L3 rocket, and it told him to use 8 grams. I talked him into cutting it in half, which still wound up blowing the snot out of his rocket.
I flew my Basilisk at LDRS with dual altimeters as practice for my L3. The charges for the primary altimeter were the calculated .75 oz with the backup charges being 1 oz. Both times, the .75 oz charge was sufficient and did no damage, although it did seem a bit much for a 2" dia rocket.

For the L3, I asked Dan Michael what he used on his Der Red Max which is almost the same size. The calculator I used gave a result slightly larger than Dan's ejection charge and I know Dan tends toward larger charges. That supports your warning. My plan is to center my testing around half the calculated charge. The backup will be larger than the main, figuring that the chute will already be out.

At LDRS, one of the projects had 3 charges and the third one was really big. I overheard someone ask the rocket owner if that was a mistake. He said, no, it was his Hail Mary charge and if the parachute was not already out, he wanted to be sure to blow it out even if it came through the side of the rocket.
 
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