Interceptor 29mm

[TomSmith58]

So I have been inactive since LDRS. I had a Terrible, Horrible, No Good Very Bad Day and my name is not even Alexander. I pranged my three favorite rockets, packed up and went home. After that work ramped up to 60 hrs a week for a while.

One of those rockets was my Interceptor E. I got about eight flights on it before I wrecked it. Shortly after I bought it I noticed that Amazon only had two of these left so I bought them too. I always wanted to keep myself in Interceptors and I do not like the Cosmic Interceptor. This holiday I decided to dust one of the unbuilt ones off and start it.

I had always wanted to upgrade my next Interceptor to 29mm. I had another project in CAD I have never started in real life. I had designed an F-35-like nozzle for a 54mm with a 38mm motor mount. It was easy to scale it down to 2.00 in. by 29mm. I redesigned the bulkheads to fit the 29mm in CAD. I sent it all to Shapeways.com and had it 3D printed in nylon.

While I was at it I turned the bulkheads and motor mount into an ejection gas baffle. Here is a CAD image.

 

[dixontj93060]

All of us have had a bad launch or two. Glad to see you are back "in the saddle"!

 

[TomSmith58]

I ordered the parts from Shapeways. They came fairly quick. The nozzle detail came out nice. I am not super happy with the roughness of the finish though. Next time I will order white and paint it myself. I made these available for all to order at Shapeways, and I posted a 24mm nozzle for those who want to use the stock motor mount. You can find them by searching for scoutertom58 or Coyote Enterprises.

 

[TomSmith58]

Here is how the bulkheads, coulper and motor mount form a baffle.

I drilled eight 1/4in holes in the motor mount with my hand drill and a forstner bit. The entry is clean but the exit of those holes was messy. I had to clean the holes up with an Exacto knife.

The baffle is intended to allow launches without recovery wadding. The idea is the hot gasses go up the motor mount and out the holes into the chamber formed by the motor mount, the coupler, and the two bulkheads. The gases escape through the sixteen holes in the bulkhead. I intended to put some large gage steel scrubbing pad in the coupler as a heat sink. The scrubbing pad is like steel wool but with much larger gage strips of metal and there is lots of room for gasses to pass through. Aerotech sells rockets with this design.

The problem is that I got itchy and glued the coupler to the motor mount too fast and forgot the scrubbing pad. I will either glue it into the motor mount near the holes or glue it in on top of the bulkhead where the gasses exit. It will be fine.

Here it is glued together. The bulkhead in the middle is intended to be butt up against the front edge of the wing tab that is inserted through the slots in the body.


A friend pointed out that the hot gasses will impact the bulkhead. I added a 1/8 in. balsa plug. That should protect the bulkhead.

 

[TomSmith58]

I replaced the two piece wings and the vertical tails with basswood. I don't like the stiffening pieces that are referred to as wing supports that the kit calls for. They don't seem very wing-like to me. I know others consider them cool and techy, but I don't want them. I flew my last Interceptor on one piece basswood wings and fins and had no trouble.

Here is the dry fit. Note that the original tabs on the wings and verticals are sized for a 2.00 in. body tube and a 24mm motor mount. I sanded them down to fit the 29mm motor mount. Here you can see they fit with no daylight shining between teh fin and body, and I can wiggle them and hear them scrape on the motor mount. It seems like a good fit.

 

[dhbarr]

The scrubber needs to be removeable, IMO. The AT ones get corroded & compacted, need shaken out on occasion.

 

[TomSmith58]

The scrubber needs to be removeable, IMO. The AT ones get corroded & compacted, need shaken out on occasion.

So maybe I'll figure out how to encapsulate it. I am betting it will survive the longest if I put it at the bottom of the laundry chute (forward body tube).

 

[neil_w]

Nifty work so far.

 

[TangoJuliet]

Why would a Nomex re-usable 'chute protector not be a good candidate here? Granted, I've never used one, so I don't know the answer. But I've never built a baffled rocket either.

 

[TomSmith58]

I have some 6" chute protectors and I am considering using them. I think it's a bit of belt and suspenders but it is also a bit chicken. I think I will fly with one. They don't weigh much.

 

[TomSmith58]

So I decided to replace the balsa wings and fins with basswood. I didn't like the seam right down the middle of the wing you get with the original balsa. I ran into a problem with the wing to strake joint. I wanted to paint the fins ahead of glueing to the body as you then have the best chance of sanding to a good finish. The problem is the stakes brake off during handling. So I made a splice like I see in Shaker furniture. Here is an example in the image.

There are two of those splices. The other is under the tape.

 

[TangoJuliet]

Good idea. :wink:

 

[hornet driver]

Well, I gotta tell ya, it's a nice clean design for the baffle. The assembly looks great! I have a couple concerns(probably unfounded) first is the 90 degree turn into the side of the baffle---I'd be concerned with heat damage to my paint---might not be a problem since it's such a short event. The only other problem I see is the size of the initial exit holes on the puffer tube. I guess their area is pretty close to the puffer but I might have added 4 more holes for better flow--29's are pretty energetic. That said, it's a nice design. I've never done a 90/90 baffle. I've just done the usual 180/180 and oversized the holes for flow. I really like the idea for the strakes--that's always a PIA area. As for the nozzles--I'm gettin some--very cool!!!

I've done a ton of Interceptors--most modified---we all have a go to kit--maybe I have one more left in me,been thinkin about a dual 29. That's gotta wait I need to finish the JQ and get the Herc built, so maybe next year! I'll watch this, interested how the baffle works. You gonna get outside the box with the paint/finishing?--H

 

[TomSmith58]

Hornetdriver
My outside the box on paint is Acur8 Phantom skins
Nothing like making a $50 kit come out to $250.

 

[neil_w]

I though the skins are only about $50 for the E? The Phantom skin is beautiful, please relay your experience with applying it.

In the meantime I was browsing Pursley's site and man oh man he has some beautiful new designs. I have my eye on this one and this one, may grab a Cosmic and Trajector while on sale just as an excuse to use those skins.

 

[TomSmith58]

You're right on the price. He gave me a sale price. Probably because he liked my 3D nozzle.

 

[Forever_Metal]

hows the application going? interested to see as i have 3 of his wraps.

fm

 

[TomSmith58]

I'm doing my fillets. I tried something new. I modeled my fillets in CAD and printed them. They cost me $11 to have them done on Shapeways.

Here they are glued on after I attached the wings and fins.


By the way I created some fin guides in CAD. I noticed that the fin slots on the body tube aren't at +/- 60 degrees. I also noticed that Pursley's skins don't have the stub fins in plane with the verticals. Furthermore I noticed that the Estes instructions have one stub fin .050" off. Measuring the snot out of the slots on the body tube as well as Pursley's skins I finally came up with a fin guide that isn't too far off. I still didn't match the verticals super well.

It worked fine for the Stub fins though.

Right now I am putting on a second coat of epoxy with micro balloons. I had to design my fillets with a chamfer because printers don't handle knife edges well. That means I have to fill in a wedge that is 1/64" deep the full length of the fillets.

Again this is an experiment. My goal is to see if it produces superior results with reduced effort. The jury is out until I finish my fillets. I consider the effort and the expense an extravagance.

I have an idea for high power MD designs. I would make molds for epoxy fillets. You would orient the sustainer tube nose down and pour epoxy into the back of the mold. I would need to get familiar with mold release. That idea might yield minimum fuss strong epoxy fillets. Later this year when I do my Mongoose I'll try it.

 

[dhbarr]

Yay! I had been thinking about large fillets routed out of balsa for cardbirds, but this makes a lot of sense.

What about printing an HPR fillet, carbon wrapping it, dissolving out the print, then backfilling with tooling epoxy? Especially under TtT it could be a strong win.

 

[cjp]

Here is how the bulkheads, coulper and motor mount form a baffle.
View attachment 308159 View attachment 308158
I drilled eight 1/4in holes in the motor mount with my hand drill and a forstner bit. The entry is clean but the exit of those holes was messy. I had to clean the holes up with an Exacto knife.

The baffle is intended to allow launches without recovery wadding. The idea is the hot gasses go up the motor mount and out the holes into the chamber formed by the motor mount, the coupler, and the two bulkheads. The gases escape through the sixteen holes in the bulkhead. I intended to put some large gage steel scrubbing pad in the coupler as a heat sink. The scrubbing pad is like steel wool but with much larger gage strips of metal and there is lots of room for gasses to pass through. Aerotech sells rockets with this design.

The problem is that I got itchy and glued the coupler to the motor mount too fast and forgot the scrubbing pad. I will either glue it into the motor mount near the holes or glue it in on top of the bulkhead where the gasses exit. It will be fine.

Here it is glued together. The bulkhead in the middle is intended to be butt up against the front edge of the wing tab that is inserted through the slots in the body.
View attachment 308163

A friend pointed out that the hot gasses will impact the bulkhead. I added a 1/8 in. balsa plug. That should protect the bulkhead.
View attachment 308156 View attachment 308157

I turn my couplers into baffles using 3 half moon disc coated with epoxy on the motor side to protect it from the hot gasses.The top of the baffle has a disc like yours with holes drilled around the outer edges and a I hook where the shock cord is attached.This is where I also have the tubes separate into a zipperless design.Don't know if that would work with your rocket but I do like your design.My baffle is easy to clean as you shake it after you remove the spent engine and shake out any loose stuff left from the injection charge.I heard the steelwool can clog up.I do not use any nomax chute protector and always have a clean chute that's damage free.Again that's mine and nothing at all wrong with your setup.If it works ,why change it?

 

[Steve Shannon]

I like the baffles. I've done them with chore boy material and without. There's really no need for it as long as hot particles don't have a straight path to pass through. I wouldn't add it.


Steve Shannon

 

[TomSmith58]

CJP
You said "This is where I also have the tubes separate into a zipperless design." Do you have any photographs of a rocket you built this way? I'd like to see it so I can maybe use your idea in the future.
Tom

 

[TomSmith58]

Dhbarr
You said "
What about printing an HPR fillet, carbon wrapping it, dissolving out the print, then backfilling with tooling epoxy? Especially under TtT it could be a strong win."

That sounds like a lot of work but if you try it I'd sure like to read about it

Tom

 

[dhbarr]

Dhbarr
You said "
What about printing an HPR fillet, carbon wrapping it, dissolving out the print, then backfilling with tooling epoxy? Especially under TtT it could be a strong win."

That sounds like a lot of work but if you try it I'd sure like to read about it

I'm trying to figure out if any of the 3D printers to which I have occasional access would allow this. I'll put it on the things-to-try pile

 

[cjp]

Let me find the pictures I posted on the zipperless design,it was a few years ago.

 

[cjp]

CJP
You said "This is where I also have the tubes separate into a zipperless design." Do you have any photographs of a rocket you built this way? I'd like to see it so I can maybe use your idea in the future.
Tom

I seem to have lost my pictures,zipperless design is not hard at all.Use the search engine for ideas.Should be some builds here showing it.The coupler that I make into a baffle is the separation of the body tube and the upper tube houses the parachute.The nose cone is held in place with screws.The baffle/coupler is epoxied into the lower tube.After every flight take out the single use motor or your motor casing and shake the bottom tube to get out the ejection particles that remain in the baffle.I hope this makes sense to you.qquake2k showed me a few years ago how to make the baffle and could also have shown me the zipperless design.I have learned a lot for him!!!He has the best build threads.

 

[TomSmith58]

I am still painting. I keep getting orange peel. Maybe it's the humidity in rainy California.
I hope to finish sand it today. If I don't get any sand-through spots I'll start the skins.

 

[TomSmith58]

The sanding went well. I plan on using 1/8 Kevlar shock cord. I want to use a heavier mount than the stock kit mount. I had some card stock for printing paper models that is roughly the same thickness as the standard Estes stock.

 

[TangoJuliet]

A little late now, but for future consideration, I would have avoided using the Estes "Tea Bag" type of shock cord mount completely and tied the Kevlar cord around the Motor Mount and up through the centering rings. It could also be protected in that area by sheathing it in a straw or even electrical heat shrink tubing. Even in my smaller Estes LPR models I'm getting away from the "Tea Bag" mount to minimize any hang-ups with ejection of parachutes/streamers.

 

[TomSmith58]

I worry about zippering. I also have had no trouble with chute hang ups. First flight is coming up March 23. I'm heading to Vegas with friends. We'll stop at Jean Dry Lake on the way up if it isn't too windy. We'll launch on Friday on BLM land when we take our hike. I'll post results.