Estes 3" x 38mm 'Crossifre ISXL' scratch build thread -- L1 cert --

[shanejohnson2002]

Hello all!

I decided to attempt my L1 cert soon, but I also decided to stray off the beaten path with a scratch build. In this case, I'm upscaling an Estes Crossfire ISX. I already made a BT60 x 24mm upscale which turned out much better than expected, so making the choice to take it a step further was pretty easy. Plus, I like tinkering, designing, engineering myself into corners and then applying creative solutions to get myself out. So here we are.

Allow me to present the 3" x 38mm Crossfire ISXL.

The biggest reason I chose this one, other than the fact that I really like this model from Estes, is the rather inefficient nose cone shape and big, draggy fins and fin tabs should keep it fairly "low and slow" for a good L1 cert attempt. I know 3" is on the smaller side for an L1 build, but this design is as heavy and draggy as some 4"+ models.

With all of the latest changes, it finally looks like a good balance between weight, impulse, CG/CP, etc. There were a few compromises that had to be made, but we'll see how they translate into real life.

Everything you see in the sim has been carefully weighed on my reloading scale (or postal scale if it was too heavy), so the weight is as close to accurate as I can make it.

 

[shanejohnson2002]

Here's how everything started. I made a small order from LOC for a 38mm x 11" MMT, some rings, a 38mm coupler, and a nylon shock cord.

It's pretty funny that each version's MMT is the same size as the previous version's body tube.

 

[shanejohnson2002]

We had some terrible weather here at the time, so I decided to start with a baffle. I know these are controversial, but I chose to add it to protect the parachute and JLCR, which are easily the most expensive parts of this rocket.

This is a bog-standard half-moon zig-zag baffle design, so it's not very restrictive but blocks any direct path of an ejection charge

The construction is pretty simple: each section is 2 layers of 1/8" birch ply, glued face-to-face to make a laminate. The holes in the middle were originally for a 1/4" eye bolt, but it was one of the parts that had to be cut out to save weight. So, instead, I went with a 1/4" dowel.

The entire thing was coated with JB weld to protect it a bit and give it a longer service life.

 

[shanejohnson2002]

This is where I'm at today.

I ordered the nosecone from Performance Hobbies. It's slightly oversized by a few thou, but I can't find a good 3" 5:1 conical anywhere else. It was a bit heavy when I received it, but otherwise is built like a tank. I had to sand it to get it to seat into the body tube, and there's still plenty of sanding to be done but I think it'll be a winner.

I waited for LOC to get their 3" body tubes back in stock, but it has been slow. So I ordered from Rocketarium instead, and I'm going to cut/slot the tube myself.

The plans call for a 22" main tube, a 6" nose cone extension, and a 6" payload bay.

The cutting part was actually super easy. I already had a 90-tooth blade on my miter saw, which made the cuts super clean. The slotting part is a little more intense. I typically use masking tape to hold straight edge guides in place, then use a box cutter with a new blade and several passes to cut the slots. I'll probably do the same here.

The fins were an interesting case. I started by ordering 1/4" fins from Always Ready Rocketry (Thanks Dave!), but they were too heavy after double-checking them in my sim. So I ordered some 3/16" 5-ply from Wick's Aircraft. I figured the weight savings was worth the almost negligible amount of strength I would lose by going with a thinner sheet. I cut the 2x2 sheet into 4 1x1 sheets. The first sheet was a sacrificial test piece, as I've never cut anything that thick in my low-powered hobby laser (TwoTrees TTS-55). It took 10 passes each but the fins came out cleanly cut.

 

[shanejohnson2002]

Here's the SVG files I've put together so far, in case anyone is interested. I'm also including my fin alignment tool for when I build the MMT / fin can:

 

[SolarYellow]

Here's how everything started. I made a small order from LOC for a 38mm x 11" MMT, some rings, a 38mm coupler, and a nylon shock cord.

It's pretty funny that each version's MMT is the same size as the previous version's body tube.

At least that gives me an idea of what to do with one of my extra PNC-55BB nose cones. 29mm MMT all the way.

 

[shanejohnson2002]

Minor setback:

When I installed my baffle, I had a drip go down the inside of the MMT. Rookie mistake, I should have let it dry with the baffle at the bottom, and let it dry longer before I moved it.

New MMT has already been ordered, but since the fins cut so well, I think I'll roll my own centering rings out of 3/16" ply to save a tiny bit of weight. I also have to decide how I'm going to attach the shock cord. U-bolt is my preferred method, but we'll see. I'm worried it might be too heavy, but the weight savings with the lighter CRs *might* offset it enough to work.
My current options are:

1/4" eye bolt in the new baffle. I like this because it's centered.

1/4" eye bolt in the centering ring. I feel like offsetting like this could lead to a zipper.

U-bolt across the top centering ring. I prefer this, but it adds a bit more weight and takes up a bit more space. It'll also make changing the shock cord easier in the future, should I need to do that.

Epoxy a kevlar leader to the MMT. This would be the lightest method, and most likely as secure as the others...but it's still offset by a small bit.

 

[shanejohnson2002]

While I'm waiting on the new MMT to arrive, I managed to get some other things done.

I designed my own payload bay. There's nothing really special about it. It's designed to accommodate a 1/4" eye bolt on either end. The sled is 1/8" craft ply, since it's not load-bearing. Thats held in by 2 #8 all-thread rods. The end caps are made from leftover 3/16" fin stock, since they ARE load-bearing i wanted to make them out of something tougher than craft ply. They also have 1/8" craft ply rings on the inner faces for alignment.

I don't have any plans for what will be mounted to the sled yet, except for my JL Altimeter 3.
Maybe down the road I'll add a DD system or something.

The rest of the day I plan on starting to round the fin edges. My plan for this is to make a jig using my table router and 1/4" round bit. I'll route a half-round channel in a scrap 2x4, and glue in some 100ish grit sandpaper. That should give me perfectly rounded leading and trailing edges.

After that, I'll do some more surface prep on the nosecone. The base is still proud of the body tube by a few thousandths, so I'll be trying to get it more flush.

 

[shanejohnson2002]

More progress:

1) fins and mid/fwd rings glued to MMT / fun can.

2) Nosecone shoulder trimmed to 3" long

3) Avbay screw holes drilled, plywood-backed tee nuts installed.

4) fin slots cut

5) test fit everything

 

[shanejohnson2002]

More progress:

1) New baffle put together. I decided to forego the coupler and install the baffle directly into the MMT. Before installation, I coated everything with a layer of JB Weld to help it survive the heat a bit better. I also added a fillet of JB weld around the top of the MMT.

2) U-bolt installed and loctite applied.

3) Nylon shock cord tied to U-bold in a removable manner. If/when it deteriorates, I can easily replace it with a coat hanger (or one of my kids' arms....my hands a bit too large to fit in the tube). "

4) (no pictures yet) fin can / MMT assembly glued into body tube.

5) (No pictures yet) glue fillets applied to rings inside body tube

6) (No pictures yet) MMT retainer roughed up with 100 grit and installed with JB weld.

7) Finished installing all of the avbay tee nuts. Secured inside nose extension with #6 screws and finishing washers.

8) vent holes drilled in avbay / nose extension.

 

[jmasterj]

Too late now, but with a baffle in the MMT you've limited your motor length options. How much room do you have left?

 

[shanejohnson2002]

Too late now, but with a baffle in the MMT you've limited your motor length options. How much room do you have left?

Honestly I'm not really worried about that. I'm not building this rocket for maximum performance or to put the biggest 38mm motor I can find into it.

Limiting the motor length was a trade-off I actually planned on from the beginning. To me it's a small price to pay to have additional protection for the most expensive parts of the rocket (chute and JLCR).

As it is now, there is 9.5" of space, enough for a 480 AT casing. That's plenty big enough to allow H impulse needed for L1, and some I impulse as well.

 

[shanejohnson2002]

It's beginning to look like an actual rocket!

Remaining tasks:
1) fill spirals and nosecone transition seam
2) glue fin tabs
3) apply fillets
4) install recovery laundry/ electronics
5) sand smooth (especially the nosecone)
6) prime
7) sand/fill
8) paint

I think I want to do a shakedown flight between #4 and #5. We'll see.

 

[shanejohnson2002]

Completed today:

Nosecone epoxied into avbay / extension.

Fin tabs glued to fins

Nosecone sanded to meet body diamter more closely (about 80% of the way there).

 

[shanejohnson2002]

Fillets applied.

 

[86mustang408w]

Nice man! Finally found it here!

 

[shanejohnson2002]

I'll be pausing this project until after Halloween. My son wanted to be a Space Marine from WH40k, which means I had to learn how to make foam costumes cosplay style. That's not something I've ever done before and it's taking up quite a bit of time and effort. That's a price I'll gladly pay, but it will prevent me from making any progress here for at least 2 weeks.

In the meantime, I have a Rocketman parachute selected and ordered, and decided to add an 808 camera shroud from Additive Aerospace. I also have the plastic snap-in cradle for my JLA3 on the way as well.

As of right now, the first flight / sanity check will probably be early next spring on an Aerotech 29mm SU F67-4W, which sims to just shy of 400'.

 

[tsmith1315]

My son wanted to be a Space Marine from WH40k

Well, who wouldn’t?

Have fun with that, those days don’t last long enough!

 

[shanejohnson2002]

Parachute arrived. The sims show a nice 12-15fps descent speed with all of the motors I plan on using.

There is a potential catastrophic problem though.

My wife is an Alabama fan.....and the parachute is orange and blue.

 

[shanejohnson2002]

Well, who wouldn’t?

Have fun with that, those days don’t last long enough!

Here's the result. Now to take a few days off of any projects, and get back to finishing the Crossfire.

 

[Co-leader of the LRP]

That’s a very fancy-looking costume, don’t play that type of game but from a quick search it seems very accurate too. For halloween I’ve mostly had random mismatching stuff from the thrift store (two years ago (the last time I had a costume) I was a cowboy-pirate-wizard with one of those hawaiian flower necklaces lol)
Anyways, the rocket is looking good so far, hope all goes well with it The crossfire ISX was my first rocket, I thought the long nose cone looked pretty cool too.

 

[shanejohnson2002]

That’s a very fancy-looking costume, don’t play that type of game but from a quick search it seems very accurate too. For halloween I’ve mostly had random mismatching stuff from the thrift store (two years ago (the last time I had a costume) I was a cowboy-pirate-wizard with one of those hawaiian flower necklaces lol)
Anyways, the rocket is looking good so far, hope all goes well with it The crossfire ISX was my first rocket, I thought the long nose cone looked pretty cool too.

Fun fact: I don't really play that game either. I had to do some deep research when he mentioned he wanted it, and I still got some minor details wrong... but I don't think he cares. We're making good memories.

 

[shanejohnson2002]

That’s a very fancy-looking costume, don’t play that type of game but from a quick search it seems very accurate too. For halloween I’ve mostly had random mismatching stuff from the thrift store (two years ago (the last time I had a costume) I was a cowboy-pirate-wizard with one of those hawaiian flower necklaces lol)
Anyways, the rocket is looking good so far, hope all goes well with it The crossfire ISX was my first rocket, I thought the long nose cone looked pretty cool too.

The long nose is definitely cool. When I was building the BT60 upscale in my profile pic, I accidentally discovered that the "extension" part of the nosecone makes for a fantastic avbay / payload bay on MPRs / HPRs. It actually has a 3" BT-60 coupler held in with plastic rivets, and I'll usually toss my JLA3 in there. So that cylindrical area just below the nose turns out to be a very handy design feature. It'll also be very easy to make this a dual deploy in the future, and use the space inside the nosecone for another parachute / ebay.

For me though, it's more the fin tabs than anything that draws me to this design. They make so much sense from an aerodynamic / stability standpoint. They definitely contribute to quite a bit more fin drag than you'd get otherwise, and I can't prove it but I feel like they help with flutter, too. Kind of like the big wing fences on some MiGs. I'd love to see a CFD model of the fins with/without the tabs, just to confirm my suspicions (or destroy them).

I ended up settling on this design because it's not the usual fare you'd see at launches. LOC IVs / EZE-65s, Apogee Zephyrs, Madcow DX3s etc. Those are all very cool and I considered them for my L1, but I ultimately wanted something different. I also got to stretch my rocket design/building muscles a good bit trying to convert it into an HPR. But it was really very easy to do, as it's a very forgiving design.

 

[-Slick-Ice]

What a great project!

 

[shanejohnson2002]

I'm going to post my next steps just so I don't lose track of where I'm at when I pick it back up this week:

1) Continue sanding nose cone, especially the nose cone / extension seam
2) Attach camera shroud - I added an Additive Aerospace 808 shroud so I can capture my flight. It should be here this coming Thursday.
3) Order / Add additional laundry (FR cloth, kevlar leader, anti-zipper system, etc.). I'm also considering adding a small streamer for visibility at Apogee eject.
4) Install JLA3 bracket in avbay
5) Finish filling seams / plywood surface

I'm going to order the paint sometime over the winter also. My wife selected Kustom Canz flake paint for this rocket, since the original had Rustoleum Glitter. I don't plan on doing much more than applying a high-build filler and sanding until the weather warms back up.

One thing I did do this week was an ejection test of sorts. I wanted to see if the coupler was too tight or too loose, so I blew into the rocket from the MMT retainer. The nosecone ejected with just the right amount of force, I think. It was enough to make me believe the ejection will be easily successful, and there will be no drag/pressure separation.

I also have some 4 inch shipping tubes that I bought for my son's halloween costume. I have some plans for those as well. It'll be a modular 54 / 38 / 3x29 / 5x24 design. I'm sketching it up in OpenRocket at the moment and, at least so far, everything works.

 

[shanejohnson2002]

So after a long break over the holidays, waiting on bad weather to stop, and a bout of 'rona AND flu...I'm back at it.

No pictures unfortunately, but I applied some Deft Lacquer Sanding Sealer to the fins yesterday, and I plan on applying some Dupli-color high-build primer this afternoon or tomorrow. I also need to build the 29mm motor adapter, which isn't a big deal but has to be done.

The camera shroud came in. It's a TIGHT fight, but after some sanding I managed to get it to work. I plan on finishing it separately and making it a detachable piece. It'll thread into the lower body tube, with the camera looking at the fins.

I also received the test flight motors in the mail. Aerotech single use F64-4W. Sims to about 350ft and 47 ft/sec off the launch rail. Pretty impressive for one of the smaller engines this rocket is built for.

Once my new launch rail gets here, I'll go to the biggest city park I have near me and send it. Hopefully everything will go to plan. That's what the test flight is there for, though...to nail down the pre-flight process and ensure a successful L1. There will be another shakedown / confidence flight before that with a G of some sort. I'm not on my home computer at the moment so I don't remember what G motors I spec'd out for it. I believe it's a G80-7T single use though.

All of this is, of course, after the paint is finished. The weather has been nice where I live lately but it'll be getting rainy again soon. I'm trying to get as much done as I can, but I don't want to rush and have a finish I'm less than pleased with.

It really feels like I'm in the home stretch now!

 

[Handeman]

Biggest Park? What altitude are you expecting on the G?

Double that for the cert flight on a small H?

Looks like this is going to be a very high flier. Good Luck and have fun!

 

[SolarYellow]

Did you roll your own nose cone for the BT-60 version?

 

[shanejohnson2002]

Biggest Park? What altitude are you expecting on the G?

Double that for the cert flight on a small H?

Looks like this is going to be a very high flier. Good Luck and have fun!

Quite the opposite. I'm trying to keep it "low and slow" for cert flight purposes. That's exactly why I picked a model that had fins with a large surface area and draggy features like tabs.

I plan on doing the cert flight at DARS in Dallas, which has a field with a 4k limit. The H will get it to about 1500ft. After that, I'm definitely pushing it higher just for kicks. The biggest motor I've simmed for it is an I357-10, which puts it at 2200ft / mach 0.5.

The G motors are all around 600 ft, plus or minus.

I choose the biggest park I can find locally because I *really* don't want to risk losing it to trees, power lines, or roads...*especially* on a test flight. There's no reason for me to impart unnecessary risk when I have a massive public soccer complex 30 minutes from my house.

Even in my neighborhood park with LPRs/MPRs, I try to keep my flights within 500 feet or so. I also monitor the wind with the Windy app, so I get current conditions and sounding at various altitudes. By being smart about it, I have never lost a rocket at that location, even surrounded by trees and powerlines. I've even had a few land within a few feet of the launch pad, with two getting their parachutes hung on the launch rod itself.

I guess bottom line for me is I'm not an altitude nut. If anything, I'm more of a 'successful flight' nut. I like to keep the rockets visible, where I can see all of the flight events as they happen. This is especially true with the more complex rockets in my collection (clusters, staged, multiple chutes, etc).

 

[shanejohnson2002]

Did you roll your own nose cone for the BT-60 version?

Ordered it from eRockets:

https://www.erockets.biz/semroc-balsa-nose-cone-bt-60-8-0-conical-sem-bnc-60sm/