Your experience certifying L3 with a 4” (or smaller) fiberglass rocket…

jahall4

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Interested in hearing your experience certifying L3 with a 4” (or smaller) fiberglass rockets… Success, failures, caveats, etc... Thx
 

TimothyG

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Currently doing a 98mm min dia L3 project. On a small M it projects around 15000 plus or minus a couple thousand depending on many things. I’m really enjoying the challenge of it as well as finally having an opportunity to build my own fincan. Other than the fincan it’s actually easier than the 6”/98mm motor rocket I designed and flew at school. Less parts less electronics no motor mount etc.
 

C.O.B.H.C.

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I did my Level 3 with a Performance Rocketry Competitor 4 on an Aerotech M1315W. It went 16,345 feet which was the average between the two altimeters a Perfect Flight MAWD and a Perfect Flight HiAlts45K. I used a 30" PML Parachute for the drogue and an 84" Fruity Chutes for the main. It did have internal carbon fiber over the internal fillets as well as a single layer of tip to tip carbon fiber.
 

OverTheTop

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I would suggest you fly the flight you want to certify with. It sounds like a 4" (or 3") bird to a decent altitude is your hankering ;). Just make sure your TAPs are happy with that. Some are happy to certify off the data showing the drogue and main deploying properly, others like to see the entire flight to verify. You can make enquiries to find the requisite TAPs to suit your flight.

Have fun, and good luck!
 

jahall4

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I did my Level 3 with a Performance Rocketry Competitor 4 on an Aerotech M1315W. It went 16,345 feet which was the average between the two altimeters a Perfect Flight MAWD and a Perfect Flight HiAlts45K. I used a 30" PML Parachute for the drogue and an 84" Fruity Chutes for the main. It did have internal carbon fiber over the internal fillets as well as a single layer of tip to tip carbon fiber.

You mention "CFing" tip-to-tip weren't the fins 3/16 glass?
 

jahall4

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I would suggest you fly the flight you want to certify with. It sounds like a 4" (or 3") bird to a decent altitude is your hankering ;). Just make sure your TAPs are happy with that. Some are happy to certify off the data showing the drogue and main deploying properly, others like to see the entire flight to verify. You can make enquiries to find the requisite TAPs to suit your flight.

Have fun, and good luck!

Thanks, I have already communicated with my TAP (Actually it will be under NAR so he is L3CC) he is familiar with my experience and okay with a 4" bird.
 

jahall4

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I have flew my 4" Broken Arrow 2 times on AT M1297 twice with no problems. No tip to tip or internal fillets. Just used West Systems epoxy.

Love that kit, seen the 5" version fly more than once. Did you build the 4" with a 75mm motor mount?
 

ChuckH

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I did my L3 with a scratch built 4" diameter rocket on a AMW M1350. It flew great to just under 16K and earned me my L3 on the first attempt. That was almost 15 years ago; looking back now the rocket is too long and spindly. If I were going to do it again I would use a single piece of airframe and do out the top dual deploy.
 

jahall4

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I did my L3 with a scratch built 4" diameter rocket on a AMW M1350. It flew great to just under 16K and earned me my L3 on the first attempt. That was almost 15 years ago; looking back now the rocket is too long and spindly. If I were going to do it again I would use a single piece of airframe and do out the top dual deploy.

Construction? Tracking?
 

Bat-mite

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My L3 was a MAC Performance canvas phenolic Radial Flyer 4" on a CTI M1101. Flew over Mach 1 to 13,000. Came down over a mile away.
 

jahall4

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Airframe and coupler is Hawk Mountain fwfg. Fins are 1/8" G10. Internal fillets are West Systems and chopped carbon fiber. Tracked using a RDF transmitter.

Was flutter a concern/issue using 1/8" G10? That's one of mine.
 

ChuckH

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Was flutter a concern/issue using 1/8" G10? That's one of mine.

It could be depending on the fin shape. Honestly, my L3 fins are probably a poor shape in that regard (similar shape to a LOC Magnum), but they held. I think a mitigating factor was that the overall size and weight kept the speed down to a manageable level. That being said it went Mach 1.3. I've been toying with the idea of ditching the upper airframe and just flying the booster with out the top dual deploy. But I doubt I would fly an M in it in that configuration, due to flutter concerns. I've personally witnessed a minimum diameter 4" rocket fly on a very large N to probably over Mach 2 with 1/8" G10 and no tip to tip reinforcement; so that is another data point to consider. Again, fin shape matters. Any more I like to do one layer of carbon and one layer of S glass, both for minimum diameter and non-MD. For non minimum diameter I like to do the tip to tip on the motor tube and then mount it in the airframe afterwards. That way I get the strength I'm after without having to do a bunch of filling, sanding and shaping on the airframe to smooth it all out.
 

jahall4

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If you're concerned about fin flutter, FINSIM is a free download.

Thanks I'll give it a look-see. My investigation so far suggests with a app or spreadsheet in hand it ought to be pretty simple for a trapezoidal fin, just enter a few figures that describe of the geometry of the fin and its rigidity, bit it seems the nobody describes the rigidity with the same units. Does FINSIM provided some good guesstimates for commonly used material like G10?
 

levi seaton

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I did mine with a 4” md rocket. I rolled a cf tube. Welded aluminum fin can. Rocket cost about $80. That was the best part. Went to about 18,500 on an m1419.
 

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jahall4

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It could be depending on the fin shape. Honestly, my L3 fins are probably a poor shape in that regard (similar shape to a LOC Magnum), but they held. I think a mitigating factor was that the overall size and weight kept the speed down to a manageable level. That being said it went Mach 1.3. I've been toying with the idea of ditching the upper airframe and just flying the booster with out the top dual deploy. But I doubt I would fly an M in it in that configuration, due to flutter concerns. I've personally witnessed a minimum diameter 4" rocket fly on a very large N to probably over Mach 2 with 1/8" G10 and no tip to tip reinforcement; so that is another data point to consider. Again, fin shape matters. Any more I like to do one layer of carbon and one layer of S glass, both for minimum diameter and non-MD. For non minimum diameter I like to do the tip to tip on the motor tube and then mount it in the airframe afterwards. That way I get the strength I'm after without having to do a bunch of filling, sanding and shaping on the airframe to smooth it all out.

Thank, like the idea about T2T glass on the motor tube, but of course the design has to accommodate that.
 
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