Level 3 Documentation - 1/2 Scale Aerobee 150

[aerobee_guy]

Hi TRF,

I've been following the forum for a while and have learned so much from all the build threads and L3 documentation packages - so I wanted to return the favor by sharing details of my NAR L3 project:

https://sites.google.com/site/narlevel3/

The rocket is a 1/2-scale Aerobee 150 designed with transportability in mind. The certification flight (at LUNAR on November 5) was a success thanks in no small part to the club and its members, L3CCs David Raimondi and John Lyngdal, our hobby's vendors, and the friends and family who spared their time helping me.

Cheers!

Max

 

[Tim51]

A fascinating and inspiring read - very impressive engineering + very impressive analysis. Congratulations!

 

[Nick@JET]

Nicely done congrats on the big L3!! Great information and documentation. The AT M1939 is an awesome motor!
Those look like bolt on fins?

Did you have any issues with the liner split post flight?

 

[NateLowrie]

Hi TRF,

I've been following the forum for a while and have learned so much from all the build threads and L3 documentation packages - so I wanted to return the favor by sharing details of my NAR L3 project:

https://sites.google.com/site/narlevel3/

The rocket is a 1/2-scale Aerobee 150 designed with transportability in mind. The certification flight (at LUNAR on November 5) was a success thanks in no small part to the club and its members, L3CCs David Raimondi and John Lyngdal, our hobby's vendors, and the friends and family who spared their time helping me.

Cheers!

Max

Max,

Thanks for sharing. That documentation packet is very thorough and I like the attention to detail. A few questions:

• What program did you use for calculating fin flutter? I see the screen shot but it doesn't look familiar.
• What program did you use for the FEA work?
• How did the bolt on fins work? Did the brackets exhibit more or less drag than the simulations? i am try to get a feel for how they compare to the

Interesting use of the E-Stop for a button. The use of a new head that fit the hex tool for arming was pretty brilliant. I take if you are an engineer by trade? Your packet gives me some ideas for changes I may implement in the final version of my packet.

 

[Bat-mite]

That has to be the most comprehensive L3 package I have ever seen. Well done! I think they should pass you without a flight. :wink:

 

[watermelonman]

Did I ever get you the pictures? Probably not, I am slow!

 

[aerobee_guy]

Thanks for the kind words, everyone!

Nick@JET, thanks! By "liner split," are you referring to the liner in the M1939W? Everything looked good when I cleaned up the (awesome) motor.

NateLowrie,

• I used FinSim for flutter calculations. Timothy Dixon's L3 is some of the best work with FinSim that I have seen: https://drive.google.com/file/d/0B7...FjLWI1ZGItNDNmYzZhZjY4ZDYz/view?ddrp=1&hl=en#
• I used SolidWorks for both CAD and FEA of the aluminum parts. Very convenient to be able to update dimensions and re-run FEA in the same software.
• The bolt on fins rely on a machined aluminum bracket that has a flat surface for clamping the fins, and a curved surface for clamping the airframe. Inside the airframe, there are small machined pieces (capturing ordinary 10-32 nuts) that match the inner curved surface of the airframe. The torque clamping the fins is selected to avoid crushing the balsa core (although there are aluminum spacers that would take up the load before any serious damage was done). I have no idea how much these brackets impact drag, but for reference, I had to set the Cd to 0.8 in RockSim in order to match the altitude of the L1500T shake-down flight. The bolt-on design was chosen for fitting into my mid-sized sedan, not for peak performance
• I'd be happy to share the files or a Shapeways link for converting the E-Stop button, if you are interested - just send me a PM and I'll dig up the info. (And yes, I am an engineer!)

View attachment 305560


watermelonman, thanks for an awesome photo! Hope to see you out there again soon.

Max

 

[NateLowrie]

Thanks for the kind words, everyone!

Nick@JET, thanks! By "liner split," are you referring to the liner in the M1939W? Everything looked good when I cleaned up the (awesome) motor.

NateLowrie,

• I used FinSim for flutter calculations. Timothy Dixon's L3 is some of the best work with FinSim that I have seen: https://drive.google.com/file/d/0B7...FjLWI1ZGItNDNmYzZhZjY4ZDYz/view?ddrp=1&hl=en#
• I used SolidWorks for both CAD and FEA of the aluminum parts. Very convenient to be able to update dimensions and re-run FEA in the same software.
• The bolt on fins rely on a machined aluminum bracket that has a flat surface for clamping the fins, and a curved surface for clamping the airframe. Inside the airframe, there are small machined pieces (capturing ordinary 10-32 nuts) that match the inner curved surface of the airframe. The torque clamping the fins is selected to avoid crushing the balsa core (although there are aluminum spacers that would take up the load before any serious damage was done). I have no idea how much these brackets impact drag, but for reference, I had to set the Cd to 0.8 in RockSim in order to match the altitude of the L1500T shake-down flight. The bolt-on design was chosen for fitting into my mid-sized sedan, not for peak performance
• I'd be happy to share the files or a Shapeways link for converting the E-Stop button, if you are interested - just send me a PM and I'll dig up the info. (And yes, I am an engineer!)

View attachment 305560
View attachment 305561

watermelonman, thanks for an awesome photo! Hope to see you out there again soon.

Max

Max,

I meant to ask if you liked how the bolt on fins performed on the rocket and if you would use them again, not how they functioned. My bad for using a poor sentence choice.

Thanks for the other info. The E-Stop is a little big for what I am doing but thanks for the offer.

 

[Ccolvin968]

Now that's impressive!
Nice write up!

 

[cherokeej]

If you fellers like the write up, you should have seen the flight. It was outstanding. Sure was pretty hanging under main...

 

[aerobee_guy]

Hi NateLowrie,

Yes, I would definitely do the bolt-on fins again. It's amazing how much smaller the rocket is for transportation once you take the fins off, and it's also nice that I could bolt on different fins for a higher speed flight or in case the somewhat vulnerable balsa core incurs damage. Also, my gut feeling (confirmed by FEA) says the brackets could be much smaller.

Max

 

[NateLowrie]

Hi NateLowrie,

Yes, I would definitely do the bolt-on fins again. It's amazing how much smaller the rocket is for transportation once you take the fins off, and it's also nice that I could bolt on different fins for a higher speed flight or in case the somewhat vulnerable balsa core incurs damage. Also, my gut feeling (confirmed by FEA) says the brackets could be much smaller.

Max

It definitely has advantages. Out of curiosity, how would you approach a bracket system like this on a minimum diameter bird? Would you choose to tap the tubing and bolt directly to the frame?

 

[aerobee_guy]

I would be hesitant to rely on just a couple of threads grabbing into a minimum diameter rocket - if you were set on using the bolt-on fin method, I'd consider gluing on the brackets. Also, the drag from the brackets might be more relevant on a minimum diameter rocket, too, so I personally will use this method again only for rockets where extra drag isn't a big deal.

Max

 

[Hobie1dog]

Very enjoyable, thanks for sharing this with us.