BNC80BB Design

My LHS had some balsa nosecones in the clearance box, so I bought a bunch of them. One was a very large, round BNC80BB:



Maybe it's backwards, but I tried to design a rocket around this nosecone (and other scrap pieces I have laying around), so I came up with this large, draggy, Big Bertha-esque design:



View attachment BT-80 Rocket.ork

Does this seem like a reasonable, mid-power rocket? I can start building tomorrow if it gets the TRF seal of approval.

looks reasonable to me. of course if one had say 48" of bt80 tube it would look like a super big bertha. should fly well on an E18.
Rex

Here's what I built when I came across one of those cones:


An upscale of an Astron Ranger, with 3X 24mm mounts. There are, of course, a lot of variations of that which you can do, those most people probably will think "Bertha" because of that cone shape. FWIW, I think that as long as it looks stable, build it if you like it - you certainly don't need anyone's approval...

EXPjawa said:

Here's what I built when I came across one of those cones:

An upscale of an Astron Ranger, with 3X 24mm mounts. There are, of course, a lot of variations of that which you can do, those most people probably will think "Bertha" because of that cone shape. FWIW, I think that as long as it looks stable, build it if you like it - you certainly don't need anyone's approval...

Click to expand...

That looks great!!

My advice - to go with this nose cone:

- Thru-the-wall light ply fins
- 29mm motor tube - you can always adapt down, and plain estes BT80 will easily stand up to "H" power.
- Kevlar shock cord
- Estes screw-on motor retainer

scsager said:

My advice - to go with this nose cone:

- Thru-the-wall light ply fins
- 29mm motor tube - you can always adapt down, and plain estes BT80 will easily stand up to "H" power.
- Kevlar shock cord
- Estes screw-on motor retainer

Click to expand...

You might want to consider building Dual Deploy with upper and lower parachute bays as well, cuz on a 29mm H its going outta sight

Started building yesterday:



Cut the rings from piece of Matt board with new Olfa circle cutter. Cut body tube and payload bay. Haven't cut fins yet. I think I will paper the fins for strength.

Probably have to wait until after Christmas to get more done...

Ill be watching this, I've been wanting to do an upscale Bertha/Ranger for a while now.

gna, looking good so far.

A bit more progress on my BT80:

• Printed out the Fin Pattern from OR on cardstock and cut it out. Bought a sheet of 1/8" balsa at my LHS, traced out fins, and cut out:
  
  
  
• Printed out the fin guide from OR, and marked fin and launch lug lines. Traced slots for fins on body tube, and cut with x-acto knife:
  
  
  
• Cut them out, and tried the fins. Looks solid:
  
  

I have to say, I'm really enjoying scratchbuilding. Open Rocket makes it easy.

Glued in the motor mount and sanded the fins. Quick papering question: do you paper the whole fin, including the tabs? I was reading K'tesh's guide and he says something about cutting a slot for the tab.

gna said:

Glued in the motor mount and sanded the fins. Quick papering question: do you paper the whole fin, including the tabs? I was reading K'tesh's guide and he says something about cutting a slot for the tab.

Click to expand...

I usually paper the whole fin unless I am going to do internal fillets.

OK, papered the fins. I used thinned Aileen's Tacky glue. I made "butterflies," so I papered over the leading edge. I tried to be extra careful and not get dirty glue fingerprints on the paper. I squeegeed with an old hotel keycard.

I weighed the fins down overnight with some big books:



I trimmed the paper, sanded, and sealed the edges with Superglue.

The BT slots were a bit narrow for the papered fins, so I had to widen them a bit. I used an emery board. I had some slight gaps when I was done, but the fins seemed solid. I double glued them in with yellow glue. I had made a payload bay template, so I think I got the alignment pretty good, but the tabs made it pretty easy to get just about right on.



I found this video from Apogee describing how to make a payload bay. Wish I had seen that before. I had a 4" section left over, so I thought I'd try to make into a payload bay. I thought the coupler I bought was too big so I had cut it in half, so I glued 1" in and left 2" out. On the original payload bay I thought 1 1/2" would be enough:



It looks okay with the 4" bay (and CWF'd nosecone):



Now for my favorite part: filling spirals and sanding.

gna said:

My LHS had some balsa nosecones in the clearance box, so I bought a bunch of them. One was a very large, round BNC80BB:

Click to expand...

But, that's a BNC-70BB.

-- Roger

jadebox said:

But, that's a BNC-70BB.

-- Roger

Click to expand...

I just grabbed a pic off eBay. How about

?

Though I sense I'm being put on. Is that actually your image? Would you like me to redact it?

gna said:

I just grabbed a pic off eBay. How about

?

Though I sense I'm being put on. Is that actually your image? Would you like me to redact it?

Click to expand...

It's from our eBay store. That's why I recognized it. I don't mind you using it. I just thought it would be funny to suggest that I could tell the difference between a BT-70 and BT-80 cone against a plain background.

-- Roger

^
Okay, as long as you don't mind.

I used CWF and filled the sprials, and applied several coats to the nosecone. It's all ready for primer:



Unfortunately, it's -10F here, so I'm not going to get to priming any time soon. Maybe I can take it to work and paint in one of our shops...

Well, we have had some warmer weather, so I was able to get primer and then paint on this rocket. While cleaning off my dresser I found some stickers from a visit to Prague many years ago, and they matched, so I put them on:



Forgive the pun, but I've been calling it the "Bad Czech." I'm very pleased with how it turned out. The red paint isn't perfect, but I have learned to leave well enough alone. Hope to fly it on a D12-3, then move onto E motors, at the next launch.

gna said:

Well, we have had some warmer weather, so I was able to get primer and then paint on this rocket. While cleaning off my dresser I found some stickers from a visit to Prague many years ago, and they matched, so I put them on:

View attachment 285810View attachment 285811View attachment 285812View attachment 285813

Forgive the pun, but I've been calling it the "Bad Czech." I'm very pleased with how it turned out. The red paint isn't perfect, but I have learned to leave well enough alone. Hope to fly it on a D12-3, then move onto E motors, at the next launch.

Click to expand...

Hopefully it doesn't become a "Bounced Czech"
Beautiful work by the way.

Looks great!!!

Make sure you check your final weight lodaed and the off the rod velocities with blackpowder E Motors. A D12 may work great, but an E9 not so much.

TopRamen said:

Looks great!!!

Make sure you check your final weight lodaed and the off the rod velocities with blackpowder E Motors. A D12 may work great, but an E9 not so much.

Click to expand...

OK. I think I need a more accurate scale, so I can account for swivels, screw eyes, wadding, etc. I entered some approximate weights into OR, and it seems to be ok, but how slow is too slow? I'm in the 35 fps range.

gna said:

OK. I think I need a more accurate scale, so I can account for swivels, screw eyes, wadding, etc. I entered some approximate weights into OR, and it seems to be ok, but how slow is too slow? I'm in the 35 fps range.

Click to expand...

I can't say what kind of figure my Mindsim would come up with without knowing the weight, but in general, you have to keep in mind some of the comparable sized rockets that have succumbed to the E9 in various threads.
There are many that I recall, where someone just automatically figures that because it is an E, it must be more peppy than a D, and then it did not end well.

It might be fine, but I was just trying to be the one that mentions being cautious. I noticed in your Sim that you also simmed it on a C11, which with an apogee of 169ft. you must have recognized as not a good idea, but wanted to make sure you are looking at the thrust curve info, and not just what the sim spits out for stats.
What length rod or rail are you flying in factors in slightly too.

I ended up with a weight of about 8 ounces, so adding a couple more for wadding and weight of motor has me well under the 15 ounce limit for an E9. I flew it today on a D12-3 and then an E9-4, with an altimeter in the payload bay. It weathercocked some into the wind, but I hit 335 feet on the D12 and 657 feet on the E9.

Edit: Added some pics from video taken with camera on launch pad:



Looks like the plug is getting ejected in the first photo...

I flew my Bad Czech this past Saturday. My brother filmed with his camera, my daughter put my camera on the launchpad, and I got an 808 camera to work well. I wove them all together in a video. Forgot the altimeter, but I'll guess it went 600 feet or so. My nephew is in charge of the countdown.

[video=youtube;nZsb3VSrofI]https://www.youtube.com/watch?v=nZsb3VSrofI[/video]

Yes, I know it's not the year 2103. I can never get the date to display correctly...

gna said:

Forgive the pun, but I've been calling it the "Bad Czech." I'm very pleased with how it turned out. The red paint isn't perfect, but I have learned to leave well enough alone. Hope to fly it on a D12-3, then move onto E motors, at the next launch.

Click to expand...

Great Praugress!

Nice videos mix, and a beautiful rocket. Congrats on some nice flights!