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

levi seaton said:

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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Looks like maybe you constructed the can?

Bat-mite said:

BRB900 and my name and phone number on the coupler. Got a call from two farm boys saying "we have your rocket."

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I've made a few stainless steel 'dog tags' from those engraving machines at wal mart with NAR number, name, and phone number.

Good on the farm boys! Glad you got your rocket back.

jahall4 said:

Looks like maybe you constructed the can?

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Yes. I turned down a piece of 4” aluminum tube to have a 5/32 wall and a snap ring for motor retention. Cut fins from 3/16 aluminum plate and beveled them with a router then tig welded them.

jahall4 said:

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?

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Yes, it has a library of the more common materials that we're using in rocketry.

Banzai88 said:

Yes, it has a library of the more common materials that we're using in rocketry.

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Awesome, thx!

levi seaton said:

Yes. I turned down a piece of 4” aluminum tube to have a 5/32 wall and a snap ring for motor retention. Cut fins from 3/16 aluminum plate and beveled them with a router then tig welded them.

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Very nice

Wayco said:

If you have the time, you could read my masters thesis on my L3 Darkstar Extreme:
https://www.rocketryforum.com/threads/wayco’s-dark-star-extreme.66950/

Way too much detail for most, but with both my TAP's in other states, I documented everything for them to review here on TRF.

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Absolutely thanks!

Did my L3 with a Wildman Darkstar Extreme and it went about 14.4k AGL on a M1780T (https://www.rocketryforum.com/threa...d-wildman-darkstar-extreme.57738/#post-604828). All told, my DSE has flown on three M motors, all went over 14k AGL, all went out of sight, and all required a tracker to recover. A lower, subsonic cert flight would be lower risk and in some ways more enjoyable to watch. YMMV.

If I were to do it all over again, I would buy a 5" or 6" project instead, like a Wildman Drago 5", Demon 5" or a smaller 6" using HED like the Demon 150 or Drago 6" (smaller is easier to transport & carry). Black Saturday and such sales are your friend if you can wait.

I did mine with a Wildman Drago XL, on a CTI 75mm/5G M1675 pink. Really awesome motor, went to a shade over 14K. Redundant everything, including trackers... an Eggtimer TRS in the nose cone (no deployments), and an Eggfinder Mini in the bottom (just in case there was a separation). Two Eggtimer Quantums in the AV bay, with enormous 1200 mAH Airsoft packs. They're long and skinny, and lend themselves to larger AV bays (3" and above).

Viperfixr said:

Did my L3 with a Wildman Darkstar Extreme and it went about 14.4k AGL on a M1780T (https://www.rocketryforum.com/threa...d-wildman-darkstar-extreme.57738/#post-604828). All told, my DSE has flown on three M motors, all went over 14k AGL, all went out of sight, and all required a tracker to recover. A lower, subsonic cert flight would be lower risk and in some ways more enjoyable to watch. YMMV.

If I were to do it all over again, I would buy a 5" or 6" project instead, like a Wildman Drago 5", Demon 5" or a smaller 6" using HED like the Demon 150 or Drago 6" (smaller is easier to transport & carry). Black Saturday and such sales are your friend if you can wait.

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Yep, that would be ideal, but I already have the components for 4" build bought and paid for save a 75mm motor tube. I like working with the glass and a 6" G12 nose and airframe ain't cheap. Don't mind aggressive builds/flights. My L2 was fairly tame but fully redundant. My L1 was 38mm cardboard to 4K and true DD.

I did L3 with a 4" fiberglass rocket on an M1297W. It went around 14k' if I remember correctly. I actually used a Wildman Extreme kit that I got on sale for the parts. Shortened the rocket up quite a bit and made the fins smaller/different shape. I used a Fruity Chutes 72" Iris in a deployment bag to minimize packing length with a Skyangle 24 for the drouge. It was my first time using a deployment bag and it worked great.

If I were to do it again, I would probably go with a shorter 4" or 5" rocket with HED. That being said, I still fly my level 3 rocket so maybe I would still go that route haha

tjsnakez said:

I did L3 with a 4" fiberglass rocket on an M1297W. It went around 14k' if I remember correctly. I actually used a Wildman Extreme kit that I got on sale for the parts. Shortened the rocket up quite a bit and made the fins smaller/different shape. I used a Fruity Chutes 72" Iris in a deployment bag to minimize packing length with a Skyangle 24 for the drouge. It was my first time using a deployment bag and it worked great.

If I were to do it again, I would probably go with a shorter 4" or 5" rocket with HED. That being said, I still fly my level 3 rocket so maybe I would still go that route haha

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That corroborates what I'd expect. Curious what you used for a pilot chute to pull you main from its bag?

Finsim is an excellent tool. I’ve used it on about five multistage supersonic rockets for University of Tennessee Chattanooga. None of our fins fluttered. We were testing M1.5-M2.4 on L1 motors. It has a material database for G10 and other materials. It will simulate more than trapezoidal geometry. It’s within twenty to twenty five percent. Has the NACA 4197TN method and other barrowman 2D and 3D methods. I’ve also ran Finsim on the forum R project. What’s concerning is once you have finsim you’ll realize some kits out there fail it’s flutter test. I typically run all my kits through finsim and scratch builds.

Sorry I can’t personally add anything to your L3 discussion. Haven’t gotten there yet.

I also did some manual calculations for the rockets I fly and most are well into the fin flutter regime. They always come back OK.

So what is the conclusion I should draw from this? It can’t be ‘avoid any fin flutter’, since as Andrew ASC says, vendors sell kits that way and mine seem to survive just fine.

Does flutter reduce rocket lifespan? Reduce aerodynamic efficiency? Or does it just look scary?

Flutter can harmonically destroy rocket fins with excessive vibrations. It looks real scary when that actually occurs. Of math theories it is one of the hardest phenomena to predict accurately. My initiative guess is Nick, your fins are fluttering slightly and the lifespan of the fin is reduced N cycles from whatever it’s max fatigue cycle limit really is. There are a bunch of dynamic loads on the fins during flutter as they twist and flex. The drag of the fin likely marginally increases. The real danger of flutter is losing a fin to it. You can reference HPR flutter videos of G-10 fiberglass literally flapping like humming bird wings at higher Mach, I personally dispise this. I would rather a design not flutter at all for a wide range of motors that fit into the airframe. Just because the kit manufacture gets away with it I personally don’t feel comfortable with it. They saved some material cost on a fin is how I look at it.

The real hard question to answer would be how much flutter can occur before my specific rocket falls apart? Nobody really knows easily. In this sense it’s safer to avoid flutter than dare enter it and find out. My opinion.
It may be easier to view it as every single rocket has its own maximum velocity never exceed before it literally falls apart.

Andrew_ASC said:

Finsim is an excellent tool. I’ve used it on about five multistage supersonic rockets for University of Tennessee Chattanooga. None of our fins fluttered. We were testing M1.5-M2.4 on L1 motors. It has a material database for G10 and other materials. It will simulate more than trapezoidal geometry. It’s within twenty to twenty five percent. Has the NACA 4197TN method and other barrowman 2D and 3D methods. I’ve also ran Finsim on the forum R project. What’s concerning is once you have finsim you’ll realize some kits out there fail it’s flutter test. I typically run all my kits through finsim and scratch builds.

Sorry I can’t personally add anything to your L3 discussion. Haven’t gotten there yet.

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No sorry, good info. Wouldn't surprise me at all to find that some kits are susceptible to flutter.

Thanks. I’ll just keep flying my MD screamers with the understanding of what factors can mitigate fin flutter.

jahall4 said:

That corroborates what I'd expect. Curious what you used for a pilot chute to pull you main from its bag?

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I've been using a regular 18" Top Flight flat parachute as a pilot chute with a small 1/8" kevlar leader attached to the bag. It's worked for 7 flights so far. That's about all I can say about it!

tjsnakez said:

I've been using a regular 18" Top Flight flat parachute as a pilot chute with a small 1/8" kevlar leader attached to the bag. It's worked for 7 flights so far. That's about all I can say about it!

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That's around the 20" I am calculating and hearing others use for a 6 to 7 foot chute.

Have you checked out the Level 3 document thread? Lots of great examples there of how to do your design doc.

Andrew_ASC said:

Finsim is an excellent tool. I’ve used it on about five multistage supersonic rockets for University of Tennessee Chattanooga. None of our fins fluttered. We were testing M1.5-M2.4 on L1 motors. It has a material database for G10 and other materials. It will simulate more than trapezoidal geometry. It’s within twenty to twenty five percent. Has the NACA 4197TN method and other barrowman 2D and 3D methods. I’ve also ran Finsim on the forum R project. What’s concerning is once you have finsim you’ll realize some kits out there fail it’s flutter test. I typically run all my kits through finsim and scratch builds.

Sorry I can’t personally add anything to your L3 discussion. Haven’t gotten there yet.

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Is this the tool you are referring to?
https://www.aerorocket.com/finsim.html

jahall4 said:

Is this the tool you are referring to?
https://www.aerorocket.com/finsim.html

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Yes

It is possible. In my experience, I see much more failures when folks build smaller and lighter rockets for level 3.

Some might be due to Mach and fin flutter. Some might be due to getting all the recovery into the small airframe.

You just have to think about the points of failure and decide the best option for your budget and field.

It's VERY possible. Recommended, actually (by me)
Use your TAPS to make sure your build plan and construction techniques are up to the task and go for it.

You might actually learn something instead of just "punching your ticket" with a low and slow flight.

This is a GREAT LEARNING and TEACHING OPPORTUNITY with two TAPS helping you -- use that help - go MACH!

Banzai88 said:

Yes

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Awesome just received the link from Mr. Cipolla

FredA said:

It's VERY possible. Recommended, actually (by me)
Use your TAPS to make sure your build plan and construction techniques are up to the task and go for it.

You might actually learn something instead of just "punching your ticket" with a low and slow flight.

This is a GREAT LEARNING and TEACHING OPPORTUNITY with two TAPS helping you -- use that help - go MACH!

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So far I have not taken the easy route on my certs, L1 was classic DD to 4K using a Madcow 38mm Tomach, L2 was scratch design using a prototype DD redundant Avbay, but I do like to watch big rockets make majestic flights to relatively low altitudes. To see it NOT arc over, but hang just for the moment as if defying gravity.

cerving said:

I did mine with a Wildman Drago XL, on a CTI 75mm/5G M1675 pink. Really awesome motor, went to a shade over 14K. Redundant everything, including trackers... an Eggtimer TRS in the nose cone (no deployments), and an Eggfinder Mini in the bottom (just in case there was a separation). Two Eggtimer Quantums in the AV bay, with enormous 1200 mAH Airsoft packs. They're long and skinny, and lend themselves to larger AV bays (3" and above).

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You have to use switches?

Cert how you like to fly. If you typically fly low and slow, cert that way. If you have a good amount of MD high altitude flight experience, doing that for your L-3 is fine.

What I would advise against is building a near minimum diameter L-3 bird because you can get the kit for cheap, when you never fly out of sight typically. Then you are into way too many things that are new to you on a certification flight.

FredA said:

You might actually learn something instead of just "punching your ticket" with a low and slow flight.

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Yep . . . You'll learn that you should have just gotten your "ticket punched" first and, then, you can go "raise Hell " and "show-off", after that !

Don't let anyone tell you how to cert, including me.