Henri Welker L1
hi Cenjars, I just launched NEWHORIZON on the 18th (Brian, my dad, and I found it in a tree) and I had a question regarding flight stability. I know that 1 - 2 cal is an acceptable range, but i need to make my fins a bit smaller because im worried they'll snap, is 1.51 cal okay for my L1 flight attempt? I normally go for 1.7 - 1.8. Thank you!
Quote from Henri Welker on October 20, 2026, 3:37 pmhi Cenjars, I just launched NEWHORIZON on the 18th (Brian, my dad, and I found it in a tree) and I had a question regarding flight stability. I know that 1 - 2 cal is an acceptable range, but i need to make my fins a bit smaller because im worried they'll snap, is 1.51 cal okay for my L1 flight attempt? I normally go for 1.7 - 1.8. Thank youAre you using OpenRocket? If so, share some more information about your rocket from OpenRocket.
Generally, a calibre between 1 and 2 is fine. Significantly more than 2 and the rocket can be over-stable, and it can have issues with crosswinds. Less than 1 should be avoided. Close to 1 is marginal stability.
What material are you using to fabricate the fins? Use a plywood of 3mm to 6mm and use through-the-wall fin attachment. The fin tabs glued to the motor mount tube help to transfer the thrust to the rocket and takes the load off of the centering rings. Such fins are also stronger overall as they're attached to the MMT and to the airframe.
I use 3 mm basswood, and cut it on a CNC so it's as precise as possible, then a use titebond 3 and make a big fin can, then slide that whole thing into my rocket, then make a bunch of titebond fillets
-Henri
Quote from Henri Welker on October 20, 2026, 4:24 pmI use 3 mm basswood, and cut it on a CNC so it's as precise as possible, then a use titebond 3 and make a big fin can, then slide that whole thing into my rocket, then make a bunch of titebond fillets
-Henri
Basswood isn't all that strong. It's certainly nicer and stronger than balsa but if you want to go HP, you should consider plywood.
Checkout OCooch Hardwoods for good quality plywoods. They package their product well for shipping so boards stay flat! OCooch products are all I've been using in my laser when cutting wood.
A CNC should be able to cut plywood. Jeff Myers (CENJARS member) has a CNC he used his to cut metal plate for me.
That is a good point. On my first L1 attempt, I used 3 mm basswood, and while the flight did have a big anomaly, the basswood audibly cracks when you wiggle it. How thick should I go for? and could I take 2 of my basswood sheets and just glue them together with the titebond III? and which wood type specifically?
-Henri
Quote from Henri Welker on October 20, 2026, 4:39 pmThat is a good point. On my first L1 attempt, I used 3 mm basswood, and while the flight did have a big anomaly, the basswood audibly cracks when you wiggle it. How thick should I go for? and could I take 2 of my basswood sheets and just glue them together with the titebond III? and which wood type specifically?
-Henri
If you insist on using the basswood, I'd suggest you go with your two piece plan. However, cut the pieces and glue them together so that the grain of each piece is at right angles. That will significantly increase the strength. TB-III is a waterproof variant to Titebond. I'm not sure how well it will seep into the basswood.
Another thing that strengthens woods like balsa and basswood is thin CYA. Coat your pieces with thin CYA and let it soak in. When it's cured, it pulls the grains together and make the wood very strong. It's also easier to sand and prep for paint.
I have to suffer NYC tomorrow. My youngest wants to go to the NAB show at Javits Center and he's not comfortable navigating NYC. I don't see the problem as it's cartesian. So, I need to smell sewer gas, auto exhaust, diesel truck exhaust and listen to interminable Nuwa Yawkahs speak for several hours. I suppose I could just sit in Stout on 33rd all day. I'm not sure if I want to lug my MacBook Pro along with me, so don't expect any exigent replies from me.
Haha! Good luck! The only reason I want to use basswood was because I just bought.... 30 sheets of it! So you suggest I coat them in cya, then sandwitch the sheets together? Its a 3 layer basswood, with 2 thinner layers and a thick one in between, and wood glue sticks to it pretty well. Whatever you think is best really, METRA's last launch is this November, and they don't start back up until March, so I want to hopefully get my JR L1 in November.
- Henri Welker
I'm not sure I understand why you mentioned the New Horizon rocket. Are you planning to re-build that for you L1 or do you have another kit that you plan to build?
Thanks,
Charlie
Hello Charlie,
The rocket in question was my scratch-built NEWMOON I launched at METRA in September. The reason I'm still going for my L1 is because my first attempt... went poorly (I had a camera pod, which most likely influenced the aerodynamics of it. After motor burnout, it's nose pointed towards the horizon, and my parachute was damaged along with my tube coupler, because I had an AV tube). I am making NEWMOON 2, without electronics, as to remove all variables and just get the certification. This started with me asking about a stability of 1.51 cal for a high power launch, then shifted toward fin material. Right now, I use 3mm basswood, but after NEWMOON's launch, they were cracking with light force, so I wondered if I should keep using 3mm basswood for my next launch, or shift to another material (possibly 3mm baltic birch plywood.....?). METRA's last 2026 launch is this November, so I really want to get the certification!
- Henri Welker