L3 Short Squat Design

I have been working on a TRA L3 cert design. It is based on the Gizmo. It will be a 7.5" PML Phenolic airframe with a fiberglass nosecone. It will have 75mm motor mount. I plan on fiberglassing the airframe and tip to tip on the fins. Fins will be 1/4" plywood. I've attached the OR file and a pic of the design. Also I tried to download some KC Royals logos and put them on the fins and the gold crown on the nosecone. I used the texture but as you can see from the studio shot it didn't work very well. Any help on that? What do you all think about the design?

I like squat rockets.

I kind of also got the idea from your L3 rocket. But mine won't be as big

Ha. Trust me. You won't regret it. Packing parachutes in fat rockets is way easier than skinny rockets!

I pulled the trigger and ordered my airframe, Nosecone, centering rings, motor tube, some Av-bay parts, & fiberglass cloth. My TAPs are Steve
Klausmeyer & Roy Polmanteer. Got to get cracking on the build. Want to certify at this years AirFest.

Fins are cut, leading edges rounded off. Centering rings are sanded to fit motor mount tube. Motor mount tube is cut. Av-Bay sleds are cut. Still need to get a small piece of basswood to make guides for the rods to slide through. I made the sleds bigger than they need to be but hey I have a 7.5" tube to fit them in so why not. Next big thing is to put two wraps of fiberglass on the big tube. Before I do that I have make sure I have enough West Systems epoxy. After talking with my TAPs I simplified the payload build. I lengthened the tube so I have room for the main parachute and don't have to put a chute tube in the nosecone. Just a bulkhead for the attachment and small bay for my BRB900 tracker. That will be easy just cut a hole in the bulkhead and put some T-nuts in it. I already have the cover and mount from my L2 rocket when I added the tracker to it.

Been working every night this week for a little while. Got the fin can all glued together tonight. Also used some left over epoxy to glue the av-bay sleds together as well. I messed up the other day when putting the CR's on the motor tube. I planned on three and didn't slide the middle one on before I put the forward one on. Probably would have been ok to leave it off but I decided to cut it in half and use it anyway. So every joint had a fillet made with my 1/2" CPVC coupler that I always use for fillets. Next I will work some more on the av-bay bulkheads. I have them cut just need to get holes for U-bolts, Charge holders, terminal blocks, and holes for the 5/16" all thread. Can't laminate the air frame yet. I had to order some more West Systems from Wildman.

Whoo Hoo! Fed Ex just showed up with a box from Loki!!!! 😃👍👏

I know nothing about getting your L3 but I do know a little about OR. How's this? I'm not real sure why OR is mirroring the emblem on the reverse side of the fins. I am pretty sure I can fix it. I can try to work it out later if you are interested, just don't have time ATM.

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I love short stubby rockets.

Mikes

That's ok just did it to show people my basic paint/graphics scheme

Yeah that's what I figured. Just thought I would give it a go. It will probably bug me now until I figure it out. HA

Fiberglassed the body tube tonight. Only my second tube. I practiced on a heavy duty commercial paper towel roll (about 38mm) with 2.5 oz to practice. The 7.5" tube with 5.8 oz was a lot harder. Lol. Took me about 50 minutes from start to finish. I lost count of how many double pump batches of West Systems I used.

I also got the Av-bay completed the other night. Well all except for the piece of motor tube up the middle of it since the motor goes up into the Av-bay.

Sweet rocket!
I like how the motor case is almost as long as the rocket itself, so cool! Good luck on your L3

Got the fin can built today and the nose cone bulkhead cut last night. I used my airframe slotting jig I built for my L2 rocket. It took me several days to build but it was definitely worth it. Fin slots are so easy and accurate to cut with my router.

I have a question though. I am going to do tip to tip on the fins but wondered if I should put fillets on the fin to the airframe first?

You know, the more I see of big squat rockets, the more I think I want one. I mean, you can fit your hands inside to access stuff. There's plenty of room in the avionics bay. They stand up on their own, don't need some kind of display. Yep, next rocket is going to be a wide and stumpy thing.

-Hans

HHaase said:

You know, the more I see of big squat rockets, the more I think I want one. I mean, you can fit your hands inside to access stuff. There's plenty of room in the avionics bay. They stand up on their own, don't need some kind of display. Yep, next rocket is going to be a wide and stumpy thing.

-Hans

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Annd there's the name....

Adrian

LOL, yep, I think that is definitely going to be the name.
Time to start some basic planning.
Anyway, time to go back to lurking on this thread, no need to clog up the OP's fun with my own sillyness

-Hans

Took my fincan and av-bay to my local TAP for review. He liked everything except for the flexibility of the fins. If it wasn't for this being a cert flight they would have been ok. So he asked me to laminate them with 2 layers of fiberglass. Wasn't that hard to do but it is making the finishing much harder because now I have to a lot of bondo to smooth out the fins. Even with peel ply there is a lot of cross hatch and rough edges. Good thing I have all this week and this weekend to finish up. Still need to ground test the ejection charges though. After a couple coats of Bondo last weekend I decided to try Elmers wood filler we will see how that works after it dries.

You should always do the fillet first, fiber glass and carbon fiber have a very limited bending radius before the fibers start to break... which defeats the purpose of doing the tip to tip in the first place

davdue said:

Took my fincan and av-bay to my local TAP for review. He liked everything except for the flexibility of the fins. If it wasn't for this being a cert flight they would have been ok. So he asked me to laminate them with 2 layers of fiberglass. Wasn't that hard to do but it is making the finishing much harder because now I have to a lot of bondo to smooth out the fins. Even with peel ply there is a lot of cross hatch and rough edges. Good thing I have all this week and this weekend to finish up. Still need to ground test the ejection charges though. After a couple coats of Bondo last weekend I decided to try Elmers wood filler we will see how that works after it dries.

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When I use heavy weave fiberglass, I always "veil" the last layer with a lighter weight glass. There is still plenty of sanding to be done afterwards, but most of the weave will be tamed. For spot filling I recommend using Superfil from Aircraft Spruce It is a 2-part epoxy putty that fills and sands like Bondo, but also has the redeeming quality of adding a little strength to the filled areas...

junkyard said:

You should always do the fillet first, fiber glass and carbon fiber have a very limited bending radius before the fibers start to break... which defeats the purpose of doing the tip to tip in the first place

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Good point regarding the use of Carbon Fiber tip-2-tip. On my level 3 build, I did tip-2-tip with 6oz heavy weave glass, which conforms much easier that Carbon Fiber, then I built the filets. Then I did another round of tip-2-tip with the 6oz heavy weave, followed by a veil layer. Of course the route I chose was a "heavier" option over the Carbon Fiber, but it was proven quite effective.

junkyard said:

You should always do the fillet first, fiber glass and carbon fiber have a very limited bending radius before the fibers start to break... which defeats the purpose of doing the tip to tip in the first place

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I ended up not doing tip to tip but just laminating the fins for stiffness against fin flutter. My TAP felt like my structure with 3 CR's and all the fillets I put in there was plenty strong enough but the 1/4" fins could possibly flutter. Since this is a L3 cert flight we decided to error on the conservative side even if we didn't think it would be a problem.

davdue said:

I ended up not doing tip to tip but just laminating the fins for stiffness against fin flutter. My TAP felt like my structure with 3 CR's and all the fillets I put in there was plenty strong enough but the 1/4" fins could possibly flutter. Since this is a L3 cert flight we decided to error on the conservative side even if we didn't think it would be a problem.

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Interesting. I'm about to potentially put 1/4 fins on my L3 which is a 10" x 5' bird. What was it about the fins that was concerning - the static deflection from a side force (ie pushing on the fins)?

Yes he could take the fins and bend them. Now my fins have a big span too. They span 9". He is also an aircraft structural engineer and very conservative. He even said if it wasn't a very flight probably wouldn't need to do it.

davdue said:

Yes he could take the fins and bend them. Now my fins have a big span too. They span 9". He is also an aircraft structural engineer and very conservative. He even said if it wasn't a very flight probably wouldn't need to do it.

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Thanks for the reply. I'll have to see how mine come out. Can't remember the span off the top of my head, but they may have been shorter. The material I have doesn't have much give but it's harder to judge before it's thru-wall mounted.

Well things didn't turn out as planned. The rocket didn't separate at apogee and deploy the drogue. The charges fired but apparently something hung up. I ground tested and it separates but not real energetically so I doubled the FFFFg from 1g to 2g and went for it. The main fired at 900' but the rocket was already coming in ballistic by that time. The chute, Nosecone, & tracker survived but the shock cord seen loop ripped open. See before, during, & after pics below. Next time I will build it taller so the motor case doesn't come up into the av-bay. Interesting that this is the same design as the Gizmo XL dual deploy that Wildman is selling. Wonder if anyone has had this problem with it. It's fiberglass though.

Dude, that sux! Sorry to hear that...

On the positive side, the T2T fins held up nicely!

Still, sorry to hear...

-e

Didn't do T2T just laminated the fund after assembly with 2 layers of 5.8 glass.