L2 rocket scratch build

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Ben Martin said:
I don't have the motor or exam as there should be a vendor and don't I get the test onsite? I'll be flying it on L1 54mm motors to test it before flying on a small J motor for L2.
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What Rex said. Contact the NAR Section President about bringing the exam and the scoring key. I think you have a year after you pass it to fly for certification. I am guessing you've been drilling on the questions?

Likewise, you've confirmed with the vendor that there will be motor for you to buy?

And bring your NAR card and the signed temporary card from your L1 application.
 
jlabrasca said:
What Rex said. Contact the NAR Section President about bringing the exam and the scoring key. I think you have a year after you pass it to fly for certification. I am guessing you've been drilling on the questions?

Likewise, you've confirmed with the vendor that there will be motor for you to buy?

And bring your NAR card and the signed temporary card from your L1 application.
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I've been using the study guides, are there better resources? Might just take the test this month and do the flight next month after I test the rocket on an I.

I confirmed that the vendor will be there and have the motors I need.
 
Ben Martin said:
I've been using the study guides, are there better resources?
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I just drilled with the questions from the pool

https://www.nar.org/pdf/HP-question-pool.pdf

I've seen folks recommend making up flash cards.

Since so many of the questions rely on rote memorization, and because I am a very poor student, I printed off the questions and blacked out all the wrong answers. I recited the questions and answers -- backwards and forwards -- a bunch of times. Then I ran the practice exam bunch of times to review. It was tedious and unrewarding exercise.
 
Practically complete. Only thing left are the exterior fillets which I need more epoxy for. I'll be filling in the gap on the transition with epoxy putty.20181109_001645.jpeg
 
Good luck with this! I highly recommend taking your test well ahead of your cert flight. That's what I did and it took so much of the pressure off - I only had to worry about my flight on that day. Not sure what it the rule is for NAR, but for TRA you have a year to do your flight after passing your test. Also, if you just need a small quantity of black powder for a few flights and ground tests, you can buy a ejection charge kit at buyrocketmotors.com (sorry having trouble posting a link for some reason)
 
there is something to be said about building and flying saucers, do it right and they don't need ejection charges :).
Rex
 
What size exterior fillets do you guys recommend? I'm thinking small due to all the interior reinforcement, but exterior could help stiffen it even more.
 
well...unless you plan on putting a CF rod into each fillet you're not going to gain much(except mass) by applying large fillets on the outside. I would use enough to smooth things out and call it good. I've been using micro balloons mixed with epoxy (creamy peanut butter thick) to do exterior fillets.
Rex
 
You might want to shoot a quick coat of primer on the tubes to minimize water damage if there is any rain. Bare cardboard tubes like that love to soak up water.
 
I will be disassembling it tomorrow to see how the printed parts held up. This will allow me to make modifications and create guidelines for future builds. I know that it really melted my motor retainer so I will see how bad it is.
 
Nice work all around.

I forgot to mention I think that the stiffening things with CF comes from the RC plane world where some additional stiffness on expanded-foam craft really help with performance due to reduction in aeroelasticity. That's where I have used it anyway.
 
Congratulations and nice flight, sounds like things worked well, and the printed parts held up as well as you could hope for. Just out of curiosity did you consider the grain orientation of the layers in the printed fins? I understand that the CF rods added a large amount of strength perpendicular to the orientation of the layers, but could you have printed on an angle so the layers were oriented parallel to the leading edge? I am thinking of wood and how the gain of balsa wood is always oriented in this way in order to prevent breaking of the fins along the weak axis. Nice project, I'm looking forward to seeing the L3
 
LawnDart2020 said:
Congratulations and nice flight, sounds like things worked well, and the printed parts held up as well as you could hope for. Just out of curiosity did you consider the grain orientation of the layers in the printed fins? I understand that the CF rods added a large amount of strength perpendicular to the orientation of the layers, but could you have printed on an angle so the layers were oriented parallel to the leading edge? I am thinking of wood and how the gain of balsa wood is always oriented in this way in order to prevent breaking of the fins along the weak axis. Nice project, I'm looking forward to seeing the L3
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Thank you.

About the orientation: My initial design without holes was printed vertically due to greater layer strength. When I added the holes printing vertically was no longer an option due to overhangs. I printed with PETG pretty slow and at 250C so that it has incredible layer strength, making it equivalent to the vertical orientation. In addition, the carbon fiber rods were epoxied in, helping to hold the layers together.

Then again, only time will tell how well they hold up.

L3 project will probably be in a few months as L2 already breaks the bank. Doesn't hurt to get started on the design though.
 
Makes sense, most of my printing experience has been with PLA which is weak over the grain layers and substantially stronger perpendicular to the grain lines. I wonder how well your fins would handle mach speeds.
 
LawnDart2020 said:
Makes sense, most of my printing experience has been with PLA which is weak over the grain layers and substantially stronger perpendicular to the grain lines. I wonder how well your fins would handle mach speeds.
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PETG is known for its excellent layer adhesion. Only one way to find out how it would handle it.
 
LawnDart2020 said:
Makes sense, most of my printing experience has been with PLA which is weak over the grain layers and substantially stronger perpendicular to the grain lines. I wonder how well your fins would handle mach speeds.
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This recent launch on a J250 got it up to around 500mph (mach .7). The max motor has it going at mach 1.7, that would be quite a show.
 
Without knowing the diameter and length it could just means it's more susceptible to weathercocking. Get it going fast enough and and that shouldn't be too much of a problem ( it'll just arc over more near apogee)

Is this your L2 rocket?
 
Congrats on the L2. Every time I say to myself, I'm going to try scratch-building, I end up buying a kit. :eek:
 
Nytrunner said:
Without knowing the diameter and length it could just means it's more susceptible to weathercocking. Get it going fast enough and and that shouldn't be too much of a problem ( it'll just arc over more near apogee)

Is this your L2 rocket?
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Yes, this is my L2 rocket.
 
boatgeek said:
It comes off the pad at 2 calibers, so that's pretty reasonable. If it's very long and skinny (20:1 L/D), it might even be a little light on stability.
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It's 63in long and 3in diameter. The advise I got earlier was 2cal off the pad. Keep in mind that this is OpenRocket, which tends to be less generous with stability than RockSim.
 
I'm guessing these higher stability numbers are due to adding electronics as you continue to experiment?

Ben Martin said:
Keep in mind that this is OpenRocket, which tends to be less generous with stability than RockSim.
Click to expand...

This is true. Especially when you stick a boattail on the end.
 

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