Custom Rockets Matra (#10018) build with modifications.

Back_at_it

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Every once in a while a rocket comes along that you absolutely love to hate but at the same time hate to love. For me that is the Custom Matra. I built this rocket back in about 1996-97 when it was still on store shelves. At the time I was still at a point where I believed that the manufactures knew what they we doing so I believed that everything needed to be built exactly to the instructions of something bad was going to happen. Unfortunately for me the issues with the Matra's design became apparent as soon as I was done building it and tried to pack the chute for the first time.

If you look at the design you quickly realize that there is no room for the recovery gear in the upper tube section. Instructions tell you to pack wadding and the chute into the smaller inner BT50 tube which is a bad idea as everything falls into the main tube when launched. Then there's the issue with the three fins on top and four on the bottom that triggered my OCD and kept me up at night :)

In all of the years I owned this rocket I flew it maybe 8 times total and had only two successful parachute deployments and this was only after adding 5 inches of additional tube up top for the recovery gear. All others were partial deployments which resulted in dented tubes, broken fins and a lot of colorful language. With the added length I figured I had finally tamed the beast until a failed ejection charge (didn't break the clay) on a D12-5 ultimately ended Matra's life. I was absolutely certain this rocket was cursed.

Even with all those issues I loved the design but knew I needed to fix a few things. With the bench clear I decided it was time to build a new Matra but this time fix everything that was wrong with the original. In the photos below you can see the remains of the original Matra off to the side. These were kept so I could have dimensions and fin patterns. For this build everything except the nose cone will be new. Over the last couple of nights I got everything needed cut and read for assembly.

Parts list.
BT60 main tube - 18" long
BT60 center tube - 2" long
BT60 upper tube - 3.5" long
BT50H motor mount tube - 4" long
BT50H upper tube - 5" long
Stock Matra nose cone.
Qualman BT60 Baffle.
Various BT 50 to BT60 centering rings in plywood and fiber.
3/16" screw eye.
4 (yes 4) upped fins cut from 1/8" Basswood.
4 lower fins cut from Basswood. Added fin tabs for TTW construction.
1 BT60 bulkhead (not shown).

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Started the build a little differently than normal with this one. I first marked and cut the slots for the lower fins in the tube. The outside of the tube was then sanded where the fins would attach.

Next it was time to insert the baffle. I wanted a fillet around the top of the baffle to help it stay in place. To do this the baffle needed to go in from the bottom which required it to go in first. This is a Qualman baffle that I opened up the holes a bit with a Dremel tool. These work just fine stock and look a lot nicer than when I got done with it but I just can't leave anything alone even if it works just fine. The baffle was assembled with TBII and given a coating of thinned TBII to give it a bit of fire protection. Next I added some 500# Kevlar to the screw eye for an attachment point for the shock cord.


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With the baffle in place we can see a nice bead around the top of the baffle.
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That is as far as I got last night. Picking this one up again this weekend.
 
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Back_at_it

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Built the motor mount next. Using a plywood upper ring and a fiber lower. With the TTW fins, the centering rings don't really carry any load but I wanted something a bit stronger up top due to the baffle. For now only the upper ring will be glued in place. The rear will be loosely fitted for installation but will be removed to allow for internal fillets. A BT20/50 ring was also used as a motor block.

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Once dry and a fillet added around the upper ring, I inserted the motor mount.

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With the motor mount drying I turned my attention to the upper fins. For this I lightly sanded the upper tube then marked the fin locations. The fins attach 1.5" from the bottom of the tube. A piece of tape was wrapped around the tube at the 1.5" mark to keep the fins aligned.

The fins were attached with TBII and fillets were added. Due to the design, I feel like it's going to be easier to fill, sand and seal the upper fins before final assembly.

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With the upper section completed I turned to the lower fins. I did need to open up the slots slightly to get the fins to fit. A little 100 grit opened them right up. All fins were attached using TBII. Ignore the bottle of Thick and quick, it was used as a weight to keep the tube from rolling around.

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Today will be internal and external fillets along with launch lugs and some filler work on the upper section.
 

Cape Byron

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Cape, There is 3.25" between the top of the motor mount and the bottom of the baffle.

At that distance I’d be tempted to coat the bottom of the baffle with epoxy, but if you can’t get to it now just check it occasionally. I think David likes 6” from MMT to baffle but I don’t have that email from him to hand.
 

Back_at_it

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At that distance I’d be tempted to coat the bottom of the baffle with epoxy, but if you can’t get to it now just check it occasionally. I think David likes 6” from MMT to baffle but I don’t have that email from him to hand.

I coat the entire baffle with a couple of coats of thinned wood glue for fire protection. In the past I’ve built models with the baffles as close as 1 inch from the top of the motor tube.

Even at that distance, I’ve not seen any issues with baffles coated in wood glue. I have used epoxy in the past and it works great but in my opinion isn’t mandatory. That said, if I’m mixing up a batch I’d absolutely spread some on the bottom as I’m all for doing something only once.
 
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Back_at_it

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Got a little bit more done. First thing on the list was getting a coat of wood filler on the upper fins and letting that dry. For this I used DAP brand wood filler. I like this stuff as it sands so easily that you don't need to worry about the excess. Just be sure to sand it outside as it creates a very fine almost Talc like powder that gets everywhere.

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Next it was time to do the fillet on the lower section. After doing the first coat of external fillets and letting that dry, I moved to the internal fillets. Nothing fancy to see there, Basically made a mess of the inside with TBII and let it dry. Afterwards it was time to close up the rear with a fiber BT50/60 centering ring.

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With the fillets drying I began building the upper tube. This rocket will will separate below the upper fins so I'm basically creating a payload section. For this I'm using a 2" section of BT60 tube and a 2.5" section of coupler. The coupler was inserted 1" into the tube with 1.5" exposed. Next I installed a bulkhead into the bottom of the coupler with a screw eye. This will be the attachment point shock cord. Once that was dry I inserted a fiber BT50/60 centering ring inside the body tube one inch down from the top. This will be the lower ring for the upper fin section.

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Wrapped up the evening with gluing the launch lugs in place. For this I decided to go with the 3/16" lugs. Since this could fly on 24mm E motors and composites I wanted something a bit more substantial.

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Woody's Workshop

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I built one of these in my younger years. I can't remember what ever happened to it.
I've been looking for one for decades. I even contacted Custom to see if they had plans.
All they send me was a diagram and parts list. Which I printed and can't find now.
And like an idiot, I deleted the Email instead of saving it.
So...If you have a parts list and diagram, I would greatly appreciate it if you could Email it to me.
Thank You Kindly.
 

Back_at_it

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I built one of these in my younger years. I can't remember what ever happened to it.
I've been looking for one for decades. I even contacted Custom to see if they had plans.
All they send me was a diagram and parts list. Which I printed and can't find now.
And like an idiot, I deleted the Email instead of saving it.
So...If you have a parts list and diagram, I would greatly appreciate it if you could Email it to me.
Thank You Kindly.

Woody,

If you wish to build it similar to what I have done here you can use the parts list in the first post. If you wish to build one stock (which I don't recommend) you can follow the link below as it lists what you would need. There is one difference. The builder below increased the upper tube length from 3.5 to 6.0 inches which it needs if you plan to have it separate at the nosecone. The only issue will be finding the nose cone. It's different than anything I have seen from Estes but I'm sure you can fins something that is close enough.


I do have a set of the original instructions that I can scan and send to you as well.
 

MALBAR 70

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I built one of these a few years ago, and I too had some OCD issues with the three fins on the top (and four on the bottom:eek: ). I built mine with four fins on top as well. I ended up gluing a piece of toothpick across the bottom of the recovery compartment, to keep the laundry from sliding back.
 

Back_at_it

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Minor update.

Did one additional fillet on the main fins using thick and quick to get a nice smooth surface. Next steps on the main body will be wood filler and sanding sealer on the fins then move on to primer.

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Major change. I had to get rid of that black cutting mat. Was making me crazy so I picked up a nice new green one :)

With the filler dry on the upper section I sanded the fins with 400 grit to get an acceptable surface for sealer and primer.

At this point I decided to add the upper and lower centering rings. These will center the transition section between the upper and lower body tubes. These were installed using TBII. I want crisp lines on the fins and rings so fillets were only added to one side of the centering rings. I'll get this into primer later today.

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Hoping to have this one in flying condition by Saturday for the club launch.
 
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Back_at_it

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Getting close. Pushing hard to get this one in flying condition for tomorrows launch.

Shot on 3 coats of SEM high build and let it cure for a day before sanding. Had to do some minor filler work after priming but nothing major. Did the bulk of the sanding so this will be less of a headache when it's all assembled.

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Next it's time to assemble the upper section. I began by inserting the upper fin section into the lower body tube. I placed glue around the inside of the lower ring along with a bead around the tube. Glue was also spread around the inside of the lower tube and the outside of the upper ring. These were inserted until the centering ring was flush with the top of the tube.

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After letting that dry for an hour I came back and attached the upper tube. Same as the lower, glue around the inside and outside of the rings and inside the tube. Pieces were assembled until the centering ring was flush with the upper tube. It was also at this moment that I realized I had forgotten the do a fillet on the upper ring so a fillet was added after the photo.

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With the upper section completed I turned to the lower fins. Two thin coats of DAP wood filler has been applied to the fins and a little to smooth out the fillets. These were left to dry over night.


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I couldn't resist putting it together for a quick peek of the assembled rocket.

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Still needs a shock cord and some sanding but I think this one will make tomorrows launch.
 
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Back_at_it

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Back with an update. I don't feel there is really a need to photograph the primer process. Basically hit the rocket with three coats of SEM high build primer and let it cure for a day before sanding with 400 then 600 grit. Some minor touchups were done then and it was ready for paint.

I started with the upper section. The upper fins were painted with three coats of Krylon bright white and let cure for a couple of days. Later today I'm planning to mask off the white and paint the upper and lower tube portions of the upper section Krylon Regal Red.

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Next it was time to put the second coat of primer on the nose cone. The cone was painted black way back when this rocket was first built. I don't know what paint I used back then but I can tell you that 20+ years later it didn't like SEM or Krylon Primer. I first shot on SEM high build in a very light mist coat. The paint immediately bubbled and cracked. This was sanded down and I decided to try Krylon. This too immediately cracked any of the original black paint it came in contact with.

After letting that sit for a few days to cure I sanded once again. This time I hit it with Duplicolor primer and didn't have any issues. Two coats were shot on and let dry.

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I also got two nice coats of Krylon Regal Red on the main body tube.


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Back_at_it

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Didn't get any work done on the Matra this weekend as I attended a local launch with PDawg. The Matra flew for the first time on a D12-5. While it was an absolutely perfect day to fly, the Matra weather cocked slightly but still managed a respectable 390 ft. Delay felt a tad late as well but mostly due to the weather cocking. Had it gone straight up the delay might have been much closer.

Recovery was a bit of a walk and I did have to get it out of a small tree but no harm done. The rocket was unharmed. Thinking the next flight will be on an E30 but in the meantime I'm hoping to get the vinyl applied this week.

08272022 Matra 1.jpg 08272022 Matra 2.jpg 08272022 Matra 3.jpg
 
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