Dave47's Macdow 5.5" Black Brandt II Build for L3 Cert

[Dave47]

HI!

I'm starting a build thread for my L3 project. As the title says, it is a Madcow 5.5" Black Brandt II. The instructions from Madcow amount to just a parts list with a blown up diagram showing their relative positions in the build.



I've added a few things to the original kit, weighed most of the parts, and put together a Rocksim to get something like the following:

View attachment Black Brandt 2 B.rkt

So, on an Aerotech M1297W, I should get just under 12K ft. I still need to add some parts to the Rocksim and will do that while keeping track of the build weights. Some things not yet included are internal fin pockets, a thrust ring, and a flanged Aeropack 75mm retainer, the final size and weight of the electronics sleds and other miscellaneous hardware.

I've had this kit since BF2015, so I've done a lot of thinking about this. Now is the time for assembly and my target is to launch at Airfest in the fall.

David

 

[Dave47]

Reserved

 

[Dave47]

Below is a picture of all of the parts that I will be using in the motor mount. Some of the changes/additions to the Madcow parts list include:

1. Thrust plate and internal plywood retaining ring (Binder Design)
2. Extra plywood centering rings and G10 fin pocket system (Upscale CNC)
3. Aeropack 75mm flanged retainer
4. Lengthened the motor mount tube to 30" (it ships with a 16" tube) so I would have less volume to pressurize for deployment and so I can actually reach the U-bolts.
5. Dual SS U-bolts for recovery system attachment



I'm not sure how Madcow really intended the business end of the rocket to look, but the parts diagram seemed to suggest that the motor retention would be partially inside the boattail. Well, my goal isn't to have this model be totally scale or anything, so I was OK with a thrust plate and a retainer that sticks out. The dry fit of the retainer looks really good to me, anyway.



I will be beefing up the deployment attachment with an additional plywood centering ring.



The forward rail button will be attached to this centering ring. I also have another plywood centering ring inside the boattail to airframe coupler (not shown here) for the aft rail button.

I'll have some pictures of the gluing soon. I've chosen Proline 4500 epoxy for the MMT joints for it's higher temperature rating and rocketpoxy for cooler joints and fin fillets.

David

 

[rfjustin]

Subscribed...

 

[Nytrunner]

The fin pocket system isn't something I've heard of before. What's it entail?

 

[Flyfalcons]

Awesome, this kit is on my short list of ideas for my(probably distant) future L3.

 

[Tonimus]

The fin pocket system isn't something I've heard of before. What's it entail?

It consists of stringers running on both sides of each fin, allowing more surface area for glue when using small-ish fin tangs (or for fins that may habitually impact the ground before the BT), or for bolting the fins rather than gluing them.

 

[Onebadhawk]

I'm a big fan of scientific sounding rockets..
I had a Aerotech Arcas that flew more times over more years then I can remember..
My only complaint was that I had grown out of the 29mm motor mount...
That lead me to a MadCow Arcas,, all glass with a 38mm mount...
This is another one that's been up so many times you couldn't try to remember them,, twice on the Aerotech J 570 W though,, lol...
Just such an old favorite...
I have always wanted a Black Brandt... I have drooled over MadCows 4" at times and then drooled over this one,, the 5.5"...
I wish you the best of luck with this,, this is close to the heart...
Take your time on the build,, enjoy it...
Great move on the 2- U bolts 180 degrees apart on the top centering ring....

This is truly a special rocket for me....
When I get done with the one on my build pile that's supposed to be done already,, lol...
This one's next.....

Teddy

 

[farsidius]

Subscribed! I love BBs! I'm about to start my L3 build too, which of course will be BBII, but I'll be building the Rocketry Warehouse 6" version. Looking forward to following your progress.

-brant

 

[iqsy59]

Interested...

 

[blackbrandt]

I'm just happy that he put the D in Brandt.

Will be watching.

 

[Dave47]

Take your time on the build,, enjoy it...

I've had the kit almost a year already

Great move on the 2- U bolts 180 degrees apart on the top centering ring....

I got them from you, after all... We will talk when I need the rest of the harness.

David

 

[Dave47]

The fin pocket system isn't something I've heard of before. What's it entail?

There will be more on this later, but the parts look like this unassembled...



They lock together like so...



I first saw this method in robertv2's 8 inch pike build thread.

As Tonimus mentioned, I chose this method because the fins are swept and will most likely be the first things to hit the ground. I don't want them popping off or anything. Also, since the fins wrap around the boat tail, there won't be any way to apply internal fillets by leaving out the aft centering ring until the last minute. The boat tail has to be attached before the fins. This seemed like an easy way to to get the fillets.

David

 

[Lowpuller]

Where did you get your work mat?

 

[Dave47]

Today, I cut out some some small blocks of red oak to glue on the two plywood centering rings. I will install the threaded inserts into them after getting all of the rest of the motor mount installed.



One of the centering rings goes inside the coupler that joins the boat tail to the rest of the airframe. Here it is by itself.



The next step is to epoxy it in and also to epoxy the forward G10 centering ring to the plywood centering ring.

David

 

[Dave47]

Where did you get your work mat?

I think I got mine from Hobbytown USA. It's a 24"x18" "Builder's Cutting Mat" made by Hobbico. It looks like you can get them from Amazon, too.

 

[NateLowrie]

There will be more on this later, but the parts look like this unassembled...

View attachment 306683

They lock together like so...

View attachment 306684

I first saw this method in robertv2's 8 inch pike build thread.

As Tonimus mentioned, I chose this method because the fins are swept and will most likely be the first things to hit the ground. I don't want them popping off or anything. Also, since the fins wrap around the boat tail, there won't be any way to apply internal fillets by leaving out the aft centering ring until the last minute. The boat tail has to be attached before the fins. This seemed like an easy way to to get the fillets.

David

I am so using this method on the next rocket I do. It would have made my Formula 200 build a lot easier. Thanks for sharing the details!

 

[Zebedee]

I've been lusting after one of these for a while - did you have specific reasons to go with the 5.5" vs 6" or was it just cost?

 

[Dave47]

I've been lusting after one of these for a while - did you have specific reasons to go with the 5.5" vs 6" or was it just cost?

I don't think they offered a 6" version a year ago when I bought my kit.

David

 

[Dave47]

OK. Spent some time over the weekend working on this. I apologize in advance for some of the focus issues. Also, these pieces were assembled the following way:

1. Wipe down with isopropyl alcohol.
2. Sand surfaces with 80 grit sandpaper.
3. Wipe surfaces again with isopropyl alcohol.
4. Mix and apply epoxy. I am using Rocketpoxy for outside joints and Proline 4500 for motor mount joints.

These are what the parts look like (top and bottom):



First, I epoxy in the centering ring that holds the thrust plate. I use the thrust plate, the retainer, the motor mount tube, and the top centering ring and coupler to make sure it is plumb and straight.

 

[Dave47]

I then attach the motor mount tube to the centering ring the same way.



Somewhere along the line, I missed getting a picture of this piece with the outter Rocketpoxy fillet, but it looks the same as the bottom centering ring.



I then mix and apply the two different epoxies so I can attach the top centering ring to the motor tube and the boattail at the same time.



I use some clamps to make sure the coupler is the correct height so it won't interfere with the fin tab after I add the CNC cut G10 centering ring on top (a later step).



When it is done, it looks like this.



The pencil line is the center of the block of wood for the lower rail button. Hopefully, all of this was clear?

David

 

[Dave47]

OK, I've been making some progress the last few days...

I prepared the forward centering ring / deployment attachment point. This is pushed up into the body tube into a bead of epoxy. Since I am using a longer motor mount, the epoxy bead is placed about 24 inches from the bottom of the body tube (around the pencil marks on the tube).



I have short arms and the epoxy needed to be 2 feet inside the tube, so the application was not as clean as I would have liked. It still worked OK, though. I got a nice bead on the top and bottom of the centering ring.



I've done it in this order so I can get epoxy on all four joints. I have these two fillets done. The third will happen when I insert the rest of the motor mount. The final one will be applied last.

Next, I applied some epoxy to the fin pocket set to hold everything together.



I then applied epoxy to the top of the boat tail coupler and centering ring.



The fin pocket set is then slid over the motor tube and clamped to the boat tail until the epoxy sets. I do have a centering line drawn on here to show where the block is for the rail button.



David

 

[Dave47]

I have a few more steps completed...

After the fin pocket set is firmly attached, I applied epoxy to all of the joints and centering rings. Here are the top and bottom centering rings.



And the fillets for the stringers.



I was careful to keep most of the epoxy out of the fin slots. I very small amount squished in at a couple of places, so I'm going to have to try and get it back out if it interferes with the fin root edge.



Next step is to sand this whole assembly to make sure it will slide smoothly into the body tube. I have to try and apply three epoxy fillets at one time and I don't need the motor mount to bind up at a bad time while I'm inserting it. Maybe more pictures in a day or two. I'm off work until the new year, so my goal is to have the fins on and external fillets by then.

I'm also considering cutting two more blocks for rail buttons. I haven't totally decided where they will go, so I'm keeping my options open.

As for the fin attachment... I measured the volume of the fin pocket to be about 3 cubic inches. The fin will take up most of that. My hope is that I can fill the fin pocket up with just enough epoxy that when I insert the fin, it fills the entire pocket and forms both the top and bottom fillet. We will see. Anyone know what the density of Proline 4500 is in gm/cubic cm? I didn't see it in the datasheet that I found online.

David

 

[Onebadhawk]

Really meticulous work Dave...
It's coming out great...
Solid as a rock,, lol...

Teddy

 

[Dave47]

Thanks, Teddy! I really hope so.

No more big updates for me until my L3CC gets a chance to look it over in person. Lucky for me, he only lives 2 suburbs over.

David

 

[Steve Shannon]

I have a few more steps completed...

After the fin pocket set is firmly attached, I applied epoxy to all of the joints and centering rings. Here are the top and bottom centering rings.

View attachment 307740View attachment 307741

And the fillets for the stringers.

View attachment 307742

I was careful to keep most of the epoxy out of the fin slots. I very small amount squished in at a couple of places, so I'm going to have to try and get it back out if it interferes with the fin root edge.

View attachment 307743

Next step is to sand this whole assembly to make sure it will slide smoothly into the body tube. I have to try and apply three epoxy fillets at one time and I don't need the motor mount to bind up at a bad time while I'm inserting it. Maybe more pictures in a day or two. I'm off work until the new year, so my goal is to have the fins on and external fillets by then.

I'm also considering cutting two more blocks for rail buttons. I haven't totally decided where they will go, so I'm keeping my options open.

As for the fin attachment... I measured the volume of the fin pocket to be about 3 cubic inches. The fin will take up most of that. My hope is that I can fill the fin pocket up with just enough epoxy that when I insert the fin, it fills the entire pocket and forms both the top and bottom fillet. We will see. Anyone know what the density of Proline 4500 is in gm/cubic cm? I didn't see it in the datasheet that I found online.

David

Beautiful work.
Personally I don't like more than two rail buttons. Two form a straight line, but once you add more there's a chance to knock one out of line and end up with buttons that bind.
It says here that the specific gravity is 1.17, so it would be 1.17 grams per cc: https://www.wildmanrocketry.com/pdf/Epoxy_Glue/Proline Epoxy Specs.pdf

However, since you already know the volume you're trying to fill, you could just measure it out by volume, weigh it, and then calculate how much hardener to add. The density of the hardener and resin are slightly different but as an approximation that should be close enough. If you want to get really close measure out 87% by volume of resin, weigh it, add 16% of that weight of hardener and it should be nearly perfect.



Steve Shannon

 

[Dave47]

Beautiful work.

Thanks!

Personally I don't like more than two rail buttons. Two form a straight line, but once you add more there's a chance to knock one out of line and end up with buttons that bind.

I really only planned on using two. The extra blocking is to I can decide which two to use. I'm afraid the aft block I currently have will be too low and the extra blocks would give me options. I'm not trying to set any altitude records with this one, so the extra weight doesn't bother me too much.

It says here that the specific gravity is 1.17, so it would be 1.17 grams per cc: https://www.wildmanrocketry.com/pdf/Epoxy_Glue/Proline Epoxy Specs.pdf

However, since you already know the volume you're trying to fill, you could just measure it out by volume, weigh it, and then calculate how much hardener to add. The density of the hardener and resin are slightly different but as an approximation that should be close enough. If you want to get really close measure out 87% by volume of resin, weigh it, add 16% of that weight of hardener and it should be nearly perfect.

Thanks for that. I didn't know what the definition of specific gravity was and now I do. This will help a lot.

David

 

[Steve Shannon]

Thanks!



I really only planned on using two. The extra blocking is to I can decide which two to use. I'm afraid the aft block I currently have will be too low and the extra blocks would give me options. I'm not trying to set any altitude records with this one, so the extra weight doesn't bother me too much.





Thanks for that. I didn't know what the definition of specific gravity was and now I do. This will help a lot.

David

That makes perfect sense about the button options. Good planning.

Specific gravity is simply the ratio of a material's density to water. Water has a specific density of 1.0, which also means Water's density is 1 gram per cc. It can be confusing because specific density has no units.


Steve Shannon

 

[Dave47]

All right... Work continues.

I decided to only add one more rail button mount. After I thought about it, the other locations didn't make as much sense. So, here it is epoxied to the motor mount.



At this point, I intended to get a few good pictures of the insertion of the motor mount into the body tube. Unfortunately, I ended up having to work faster than I had planned to get all three epoxy joints applied and didn't get any pictures along the way. I will explain what I did, though.

1. Mix up Proline 4500 epoxy for the top of the motor tube to bottom of recovery centering ring joint.
2. Mix up Rocketpoxy for the top fin centering ring to body tube and top of boat tail coupler to body tube joints.
3. Wait ~5 minutes for the Proline to set up some more.
4. Notice that the Proline has gone off and isn't usable anymore (too thick and clumpy).
5. Quickly mix up some more Proline epoxy.
6. Rocketpoxy is getting thick, but is still OK.
7. Apply Rocketpoxy to the inside of the body tube just aft of the top of the fin slot. I will push the motor mount into this joint.
8. Apply Proline to the top of the motor tube so it will push into the recovery harness centering ring.
9. Push motor mount ~3/4 of the way in so the top fin centering ring is about halfway up the fin slots.
10. Apply rocketpoxy to the inside of the aft end of the body tube keeping it between the fin slots.
11. Push motor mount the rest of the way into the body tube.
12. Check that the fin slots align with the fin pockets and make any final adjustments.

Whew! After all of that excitement, I realized I didn't have any pictures. The next picture I got was the final motor mount fillet between the motor tube and the top of the recovery harness centering ring.



I now skip ahead to the next step where I have sanded all of the fins (50 grit) and dry fit all the fins with the fin alignment guide I made from foamboard. I got the drawing from payloadbay.com.



Everything is well cleaned and sanded, but sanded green on unsanded green doesn't really show up with a lot of contrast. So, you can just barely see the difference.

I went through the volume computations to figure out how much epoxy should be needed to fill up the slots after the fins are inserted.



This was sort of close at ~20 grams of epoxy, but I ended up needing closer to 28 grams to really fill up the slots. I must have been off 0.1 inches in a spot or two. I then pour the epoxy in and use a skinny dowel to make sure it is spread around inside the fin slot.



I press the fin into the slot and try to clean up some of the epoxy that squishes out.



Do that times 3, remove the fin guide, et voila, something that can stand up on its own and actually looks like a rocket.



The next step is to sand some of the Proline that squished out a little to rough it up and then measure, tape off, and apply the external fillets with Rocketpoxy.

David

 

[Dave47]

Hey! I haven't made a post in a long time, but I have been working. And, since Airfest is approaching, I thought I better get a move on. So, here are some updates.

For the fin fillets, I used a piece of 3/4 inch PVC pipe for my guide. I painted the edge of it with some red sharpie ink and then used it to make the marks along the fin and body tube. I placed the tape along these marks. I used Rocketpoxy for the fillets to which I added some of the manufacturer's black dye. I mixed up the epoxy and dye, spread it on some aluminum foil, popped bubbles for about 5 minutes, and then spread it on the joint. I pulled the epoxy with the same piece of pipe that I used for the marks, waited a few more minutes, and then pulled the tape. Repeat 3 times. The fillets looks pretty good.





David