L2 cert flight anxiety

[richP]

So, I am planning on doing my L2 flight next month, and am in the process of driving myself crazy with motor choices and general failure.
I will be using the same rocket that I used for my L1, which is a 3" LOC Iris kit, converted to DD.
For L1, I flew it on an I170, and the entire flight was smooth.
Now, I will be jamming a much larger motor into it, and the sim'd acceleration/speed/G's are beginning to worry me. I have chosen the J285, mostly because it is somewhat tame, and has a 15sec delay. My other options were a J270; which is very similar, but has a shorter 13sec delay that might have been too short. And the J94, which would bring me very close to waiver, and doesn't have a motor ejection.
I guess my main concern is if the rocket can handle to speed that I'm gonna be pushing it to. OR says that I should be in the 700ft/s range.
Fins are 1/4" ply, and I used rocketpoxy for fillets both internally to the MMT as well as the BT. Coupler friction fit is on the tight side, and I have a pressure relief hole in the payload section. However, the more I read, the more I worry about fin flutter, body tube kinking, drag separation, etc.
Am I overthinking, or are these real issues when moving to the bigger motors?

 

[rharshberger]

Built properly it should handle the flight profile you describe, if (my opinion starts here) you can get a motor with the motor eject, that way you can use it as a backup to the apogee event from the altimeter, it might save the rocket in the event something goes wrong with your electronics.
Fin flutter and airframe buckling are very real concerns but from the sounds of it you have built the fincan section solidly, 1/4"fins should be okay for almost any J motor (caveat being fin shape has a lot to do with fin flutter, a mosquito style fin will be more prone to flutter than a short triangular or trapezoidal fin like a Lil Nuke or Tomach.

 

[Nytrunner]

Sounds like you mounted the fins securely.
LOC tube is sturdy. If you still feel iffy, throwing a coupler inside significantly increases the strength.
Pressure vent hole is good idea. Try picking the rocket up by the top. If the booster stays in place, but shaking makes it start to slide off, you should be good.

Video of my L2 rocket below
Big 1/4" plywood LOC fins, ~800'/s 5.5" airframe on a K750
You can see them wiggle, but nothing close to flapping/shred

 

[Eric]

A buddy of mine used a 3" LOC sandhawk for his L1, and L2. He built It lightly with 5 minute epoxy and title-bond.

It survived it's last flight on a J825..... Yours should be just fine.

 

[Big_Red_Daddy]

A buddy of mine used a 3" LOC sandhawk for his L1, and L2. He built It lightly with 5 minute epoxy and title-bond.

It survived it's last flight on a J825..... Yours should be just fine.

That's mine. It went 4941' and 1026MPH on a J825R. No problems whatsoever. Used the full 14s motor delay, no electronics other than altimeter, 20' long streamer, and JL Chute Release at 300' with a 48" parachute. It landed about 100 yards from the launch pad. You should be fine and if not then you try again. I failed my first L2 attempt last year. Learned from it and tried again.

 

[David Schwantz]

LOC are great kits. Did my L1 & L2 with 4" Phoenix. #2 was with a J250 and nothing other than a JLCR set at 500'. Keep it simple, your kit is a good choice.

 

[richP]

Thanks for the replies and reassurance.
One of the biggest reasons for my concerns was the discovery of what I thought was a cracked fillet after an "I" motor flight.

20190619_160128

• richP
• Jun 20, 2019

Fillet scratch

Turns out, after some sanding, that is was either a crack in the paint, or some sort of scratch. Re-paint and another shot of clear and it should be all set to go.

20190620_090640

• richP
• Jun 20, 2019

Fillet scratch post sanding

 

[Bat-mite]

Best wishes for your flight. Relax and enjoy it!

 

[mbeels]

I failed my first L2 attempt last year. Learned from it and tried again.

How did it fail, and what did you learn?

 

[Big_Red_Daddy]

How did it fail, and what did you learn?

No ejection charge. Electronics fail. Had a CATO the previous day. Forward closure blew through the top of the rocket. Should have torn everything down better and looked for problems but the electronics all reported ready to go. I learned to use redundant electronics.

 

[richP]

Thanks to all for the reassurances. Flight went well, up to 4000', main chute opened at 600' and landed 1/4 mile away. Very 'uneventful'. Was even convinced to go drogueless for the first time.
Not so much as a scratch.
Now on to L3.

 

[Hobie1dog]

Congratulations, now what rocket are you going to build next?

 

[GalantVR41062]

Welcome to L2, it's a journey not a destination.

~John

 

[richP]

Congratulations, now what rocket are you going to build next?

I'll have a better idea once I decide on either 75 or 98 mm.

 

[Flyfalcons]

Maybe get some experience running electronics before going 98mm?

 

[YodaMcFly]

Welcome to L2 ... Now open your wallet even wider than you did after L1.

 

[Handeman]

Congrats an welcome to L2.

Considering your anxiety with your L2 cert, I would highly recommend some L2 experience with K and L motors before moving on to L3. You could go with a 4" rocket w/ 54mm MMT or maybe a 5" with a 75mm MMT. The diameter vs. MMT will depend on your normal flying field and waiver height.
You may want to try fiberglassing LOC tubing, tip to tip glassing, or other building techniques on an L2 rocket before using them for a first time on an L3. It will give you more knowledge and experience before tackling the L3 and hopefully lower the anxiety on what is typically a much high anxiety cert then L2. Using the larger L2 motors will also give you a much better appreciation for the power of M+ motors which all goes into learning to fly the field.

Mostly have fun, be safe, and don't worry!

 

[Steve Shannon]

Congrats an welcome to L2.

Considering your anxiety with your L2 cert, I would highly recommend some L2 experience with K and L motors before moving on to L3. You could go with a 4" rocket w/ 54mm MMT or maybe a 5" with a 75mm MMT. The diameter vs. MMT will depend on your normal flying field and waiver height.
You may want to try fiberglassing LOC tubing, tip to tip glassing, or other building techniques on an L2 rocket before using them for a first time on an L3. It will give you more knowledge and experience before tackling the L3 and hopefully lower the anxiety on what is typically a much high anxiety cert then L2. Using the larger L2 motors will also give you a much better appreciation for the power of M+ motors which all goes into learning to fly the field.

Mostly have fun, be safe, and don't worry!

I greatly appreciate the wisdom in this post. Simply certifying for L2 does not prepare a person for L3.

 

[Rail Dawg]

Great thread! Nice L2 flight.

Lots of learning occurs with the K and L motors. They are a great transition to M power and time needs to be spent nailing down perfect (and some not so perfect lol) flights with them.

Well done!

Chuck C.

 

[Bat-mite]

Congrats. I'm not one to tell anyone if/when to certify the next level, but a good flight on a big L is no less exciting than a baby M.