MADCOW 2.6" BLACK BRANT II BUILD

[ozwald]

Hey all. Has anyone out there built the thin wall fiberglass 2.6" Black Brant II offered by MadCow? Any thoughts will be appreciated. Thanks Oz

 

[Wizard]

I have. I modified it to dual-deploy by adding an avbay and cutting the body tube. I'll have to look when I get home to see the dimensions of the resulting 2 sections. If the Jolly Logic Chute Release had been available then, I wouldn't have bothered. I found it built pretty easily, but it did take some effort to get the fiberglass reinforcing strips to lay neatly against the fin/tailcone without leaving a void. The FG tape really didn't like to fold very well. I think I wound up using a fairly heavy bag of sand and did them one strip at a time. Now I'd probably just use my vacuum bag setup. You can get an Aeropac 38 mm motor retainer in there, but it is a snug fit. I used one of the Doghouse Rocketry aluminum anchors, threaded to 8/32, and 1/8 Kevlar in the booster for shock cord. I know those aren't available anymore, so I'd probably just fall back to the stock arrangement, but still use 1/8 Kevlar. That's all I can think of offhand - let me know if you have specific questions.

One other thing - the fins are a tad vulnerable, so I'd target a descent rate on the slower side, especially if you have a hard landing surface.

David

 

[ozwald]

I have. I modified it to dual-deploy by adding an avbay and cutting the body tube. I'll have to look when I get home to see the dimensions of the resulting 2 sections. If the Jolly Logic Chute Release had been available then, I wouldn't have bothered. I found it built pretty easily, but it did take some effort to get the fiberglass reinforcing strips to lay neatly against the fin/tailcone without leaving a void. The FG tape really didn't like to fold very well. I think I wound up using a fairly heavy bag of sand and did them one strip at a time. Now I'd probably just use my vacuum bag setup. You can get an Aeropac 38 mm motor retainer in there, but it is a snug fit. I used one of the Doghouse Rocketry aluminum anchors, threaded to 8/32, and 1/8 Kevlar in the booster for shock cord. I know those aren't available anymore, so I'd probably just fall back to the stock arrangement, but still use 1/8 Kevlar. That's all I can think of offhand - let me know if you have specific questions.

One other thing - the fins are a tad vulnerable, so I'd target a descent rate on the slower side, especially if you have a hard landing surface.

David

Wow David, thanks for all the info. I thought of the chute release option also but considered the DD approach. It should be here today or tomorrow so I'll get a look at what's there. I may just keep things easy and go chute release. Planning on flying my 38/240-360-480 cases in it. What motors have you flown in it?

 

[crossfire]

I also have one to build. Is the FG strips for fins really needed?

 

[noffie79]

I love mine. I'd never used FG "tape" before. It was a mess as I only had BSI 30 minute epoxy. If I were to do it over again, I'd just use RocketPoxy and no tape. The fins are very vulnerable. I have one that's popped at the moment. Need to take the time to sand everything down and reattach. As for deployment, I use the Jolly Logic Chute Release and it's worked every time. I just need to use a larger thin mill chute in order to protect the fins in the future.

 

[Wizard]

I've flown it on 2 AT H148R (1314/1487 ft), 2 AT H165R (1005/1014 ft) and one AT H699N (1938 ft). I've flown it mostly at a field with a 2500' limit, so I've not pushed it too much. Note that in my configuration, it weighs 48 oz, which is quite a bit heavier than stock, the result of a 6" coupler/G10 bulkheads for the avbay and associated hardware. It is a really nice flier, and a great looking rocket. I've got the 6" version on my build table right now. Oh, yes- I cut the BT for DD into a 17.375" booster and a 15.5" payload.

I would definitely use the FG tape again - the fin/tailcone joint takes the brunt of the landing forces and I think the tape does a better job of spreading those forces over a larger area than a simple epoxy fillet. A bit of a pain, yes, but worth getting right.

David

PS - The H699N was a FUN flight.

 

[ozwald]

Wow, thanks for all the info guys. I have a built Cosmodrome but I've been very hesitant to fly it. At least now I'll have one that I can fly. Appreciate the comments.

 

[ozwald]

I think i have decided to finish this one out in a little more non-traditional finish and look. Since I'm a huge Steelers fan.....I present Mark's latest creation

 

[ozwald]

I've flown it on 2 AT H148R (1314/1487 ft), 2 AT H165R (1005/1014 ft) and one AT H699N (1938 ft). I've flown it mostly at a field with a 2500' limit, so I've not pushed it too much. Note that in my configuration, it weighs 48 oz, which is quite a bit heavier than stock, the result of a 6" coupler/G10 bulkheads for the avbay and associated hardware. It is a really nice flier, and a great looking rocket. I've got the 6" version on my build table right now. Oh, yes- I cut the BT for DD into a 17.375" booster and a 15.5" payload.

I would definitely use the FG tape again - the fin/tailcone joint takes the brunt of the landing forces and I think the tape does a better job of spreading those forces over a larger area than a simple epoxy fillet. A bit of a pain, yes, but worth getting right.

David

PS - The H699N was a FUN flight.

Can you fill me in on the best way for getting a good square cut?

 

[Wizard]

I use my radial saw and a composite/fiberglass blade. The diameter is small enough that I don't have to rotate the tube. For 3-4" tubes, I'll clamp a block at the right distance, and another parallel to the fence but further out. then I can bring the blade into point contact and rotate the tube against the block into the blade. Larger than that I move to the table saw. The key is a smooth, steady, not too fast motion to avoid splintering, and a very sharp blade.

David

 

[ozwald]

I use my radial saw and a composite/fiberglass blade. The diameter is small enough that I don't have to rotate the tube. For 3-4" tubes, I'll clamp a block at the right distance, and another parallel to the fence but further out. then I can bring the blade into point contact and rotate the tube against the block into the blade. Larger than that I move to the table saw. The key is a smooth, steady, not too fast motion to avoid splintering, and a very sharp blade.

David

Awesome, thanks for the tips.

 

[crossfire]

I was thinking would it work to put fg strips on inside of body tube. It should work and one would not have to be so perfect laying down fg cloth.

 

[Wizard]

Love the color scheme, by the way.

 

[ozwald]

Love the color scheme, by the way.

Thank you. It should look cool. I'll post when I'm done.

 

[ozwald]

I was thinking would it work to put fg strips on inside of body tube. It should work and one would not have to be so perfect laying down fg cloth.

I'm not thinking that that will work as the lower section of the fin does not penetrate through the tailcone. This is realistically the area that needs reinforcement as it is not "through wall"

 

[cosmodrome]

Wow, thanks for all the info guys. I have a built Cosmodrome but I've been very hesitant to fly it. At least now I'll have one that I can fly. Appreciate the comments.

Why??

 

[ozwald]

Why??

I didn't build it. Two of the fins got knocked loose simply by my cat knocking it over

 

[ozwald]

I didn't build it. Two of the fins got knocked loose simply by my cat knocking it over

And please don't get me wrong, no diss on the kit. I Love it, just didn't build it.

 

[farsidius]

And please don't get me wrong, no diss on the kit. I Love it, just didn't build it.

I build a lot of Black Brant rockets and the Cosmodrome BBII is probably the best flying BBII rocket I have - when built correctly. It takes a lot of time and careful attention to detail (and maybe a jig) to get the wood fins beveled correctly. I think being able to shape those fins properly contributes to the excellent flight profile. You can't really do a proper BBII bevel on fiberglass fins. I also converted my Cosmodrome kit to dual-deploy.

And as others have said, it's really important to get the fins tacked to the boat-tail securely. I usually use strips of fiberglass and make a fiberglass fillet on the boat-tail. You can smooth out the edges of the fiberglass strips with some epoxy and sanding. It doesn't look too bad (everything down there gets painted black) and adds a ton of strength.

-brant

 

[ozwald]

I build a lot of Black Brant rockets and the Cosmodrome BBII is probably the best flying BBII rocket I have - when built correctly. It takes a lot of time and careful attention to detail (and maybe a jig) to get the wood fins beveled correctly. I think being able to shape those fins properly contributes to the excellent flight profile. You can't really do a proper BBII bevel on fiberglass fins. I also converted my Cosmodrome kit to dual-deploy.

And as others have said, it's really important to get the fins tacked to the boat-tail securely. I usually use strips of fiberglass and make a fiberglass fillet on the boat-tail. You can smooth out the edges of the fiberglass strips with some epoxy and sanding. It doesn't look too bad (everything down there gets painted black) and adds a ton of strength.

-brant

Thanks for your thoughts an tips. I'm presently working on a removable motor mount but haven't quite addressed all of the problems that it entails.