L3 Project Construction Tips

[Doug GerrardParticipant]

Yes, I have a few you can buy off of me 😉 The device itself is OK. It has the advantage of the on board battery which is very convenient. It works reliably for general recovery.

The problems I have with it is (1) the software. You must view the data from their software. I switched to the G-Whiz MC because it allows exporting of the data. I found that very useful, particular if you wish to do side by side comparisons with other date, from other flights or other recorders for example. The other reason (2) I switched to the MC is that it is more versatile. For example, I can program the drogue to deploy some time after apogee or adjust the altitude I want to deploy the main. However, it does not have the on board battery.

The ALTACC is fine for many applications and I used them for my L3 but since then I’ve converted to the MC.

Doug

[Bruce R. Schaefer]

Thanks, Doug. I’m using a G-Wiz accelerometer along with the Blacksky for apogee, then–when I can afford it–the MWC radio controlled system as a backup for the main when I fly DD (or to replace the Blacksky for single deployment). I’m not sure, at this point, what configuration I’ll use for L3. I could remove the payload section and just fly single deployment (8k AGL). I’m taking this relatively slowly (mostly for financial reasons at this time) and step by step. While I could have my rocket ready before it snows, I really want to just prime it for the winter, then finish it next spring.

[Bruce R. Schaefer]

Well, as you can imagine, designs evolve. Wish we could insert pics in these posts. If the Blacksky altimeter works in flight test, then I’ll go with it, and a redundant MWC WRC2–on loan. Got my GLR TAC-9 B chute from Tim Thomas today. Man, is that thing solid! Feel like using the 7K pound harness and chute to jump off the roof. 😈 But, I weigh more than 42 pounds, and like the Coyote–of Roadrunner fame, it’d open right after I hit the ground. 🙂 Do not do this at home. 😉 Going to ground test soon, with a dummy TAC-9 B. Will let all know how it goes.

[Bruce R. Schaefer]

Well, time passes… here are links to two pictures of the main ground test:

http://www.putfile.com/pic.php?img=5245084

http://www.putfile.com/pic.php?img=5245085

You’ll see the booster attached, so Art could hold onto it–he likes fire, and the top of the upper section, two blankets, the dummy chute, and the nose cone (with a paper towel top to hold down the damage). Went very well on 6 grams. Shot it out cleanly, not aggressive enough to cause any damage, but aggressive enough to separate and deploy properly with (4) 6-32 shear pins. I apologize if I’m letting my duties to the club slip a little, but it’s just for this project. After a successful L3, I’ll be there for anyone who needs anything.

[Warren B. MusselmanModerator]

Unless you’ve gotten consistent separation with that amount of BP at least 3 times, I’d beef it up a hair. I’ve found that you want to use the lowest amount that gives consistent separation plus a bit more. Add a gram – you want it to a l m o s t extend the shock cord to the end.

Warren

[Conway StevensParticipant]

Unless you’ve gotten consistent separation with that amount of BP at least 3 times, I’d beef it up a hair. I’ve found that you want to use the lowest amount that gives consistent separation plus a bit more. Add a gram – you want it to a l m o s t extend the shock cord to the end.

Warren

I would disagree here. I do believe in a strong charge. Trust me on that ( I went to the JW charge school many years ago still have my diploma) As well as On my L 3 I used a 6 gram with #4 pins on one end (#6’s on the other) like Bruce did and it worked fine. Look at the photo and see how much distance is there betweens the 2 pieces. Thats plenty. Now if he were going to be going well above 10 or 12K in altitude I would say hey yea add another gram. (really most rockets will not need any additional for higher altitude unless they start to approach the 20K and above MSL then pressure and BP effectiveness do make a difference) looks to me like its let it out quite far enough in the photo. You never want it to have enough energy to almost push it to the end of the shock cord. Do not forget that the rocket will be under deceleration as well and that also will ad to the amount of yank that will happen as well. I like to have my pieces come to a fairly slow halt by the time they reach the end of the harness (and they always do reach the end) so no unnecessary extreme snaping back actions happen. If it were me I would be fine. Also doing the ground test 1 time successfully like that is plenty good. No need for more unless it failed with a specific size and you need to try a larger one.

[Bruce R. Schaefer]

you want it to a l m o s t extend the shock cord to the end

It separated just fine, so much so that in my always very careful state, I actually feel confident in the results. I want it to be aggressive enough to move away, yet not aggressive enough to JOLT the harness, as Conway said. Both the booster separation and main were much better than I hoped. I added half a gram to each online simmed calc, and it was perfect. Plus I have 60 foot between the booster and upper section and 40 foot between the nose cone all that dangles beneath, and trust me they’ll stay away from each other. It will deploy safely. Only going to 8k. Plus, just for grins, Art and I used 4 grams for the main separation, and it didn’t even shear the pins. 6 grams is absolutely perfect, and since NAR requires a redundant set of electronics, what if BOTH went off at the same time… do the math. As rare as that would be, since I’m using a WRC2 as the redundant system, this is the safe way to go.

[Conway StevensParticipant]

It would be very well near impossible for the 2 charges to happen at one time. BUT for added safety and redundancy I would add 1 gram more to the charge that has the WRC connected. That way JUST in case and I say as a back up precaution only if the first charge wasn’t enough the next one should be. The MOST ever important deployment is always Apogee (both are important BUT Apogee makes it or breaks it) That way a complete ballistic doesnt happen.

[Bruce R. Schaefer]

The MOST ever important deployment is always Apogee (both are important BUT Apogee makes it or breaks it) That way a complete ballistic doesnt happen.

Agreed, but that’s the nice thing about the WRC2; if the primary doesn’t fire at apogee, you can hit the redundant charge with a button. I really feel confident that what I tested will do the trick. Without the resistance of the ground, in flight, all separations should be just about perfect. Another gram won’t make that much difference. I will definitely consider that, Conway.

[Conway StevensParticipant]

You would be surprised how much 1 gram can do when topping it on to what exist. Look at the difference betwen the 4 and the 6 grams you tested. Not much there either. but it did the trick. Just a recommendation anyhow.

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