6" Diameter Smokin Rockets X-15 Build & L3 Certification

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So it begins... or does it?

Now it's early December 2023 and I'm trying to figure out how to modify the 6" X-15 for dual deploy. It's turning out trickier than I thought.

I had already successfully done it in my 4", so I figured I could do the same with the 6"; however, there was a significant difference. My 4" had the shoulder as a coupler separate from the nose cone and so I could use the coupler as an attachment between the dd bay (which is bolted on the end of the bay) and the nose cone (which is attached with shear pins).
(4" X-15 forward bay HED section showing coupler attached to bay and nose with shear pin holes.)

However, the nose cone for the 6" X-15 was a single piece of molded fiberglass with the shoulder already molded in. Additionally, the inside was somewhat rough, so I didn't feel that cutting off the current shoulder and using a coupler would work as well as it did in the 4".

I did still ponder it for a while though.

I had heard or seen two other attempts at converting a large X-15 to dd. One was a hatch, which I didn't have experience with and didn't feel confident enough with. Another was one where I believe they put the bay about 1/3 way down and made a cut below the shoulders (past the nose cone shoulder and possibly shortening it). I didn't like either method since the bay weight is further back and this requires even more nose weight to be added. Also I felt shortening the shoulder may become a problem under very high Gs combined with a lot of nose weight.

After about a week, I thought why not put the bay inside the nose cone shoulder?


(Mock up to check for chute space and bay size utilizing a large oatmeal can. AV band would not be used and bay would be cut down to the black line - please ignore the poor sketch of an eyebolt and quick link. )

I researched if something like this had been done before and I didn't find anything exactly like it - please comment if you have seen this in use; however, please wait until you see the entire setup (including the *internal body tube dowels*).

I decided to call it a Shoulder Cannon or HED Cannon. I thought that sounded cool. 😁 Additionally, the way I figured it, I can easily make it single deploy by just leaving out the bay. You can't do this with usual HED or a payload bay dd since the bay itself connects both parts. In this case, the bay is internal so you can actually omit it and hook up the booster strap to the nose cone anchor... a system to swap between DD and SD! This was something I tried to figure out a while back for a Polecat 5.5 Pershing, but I didn't get very far.

I know that a cert attempt isn't the time to try something new and to KISS (Keep It Stupidly Simple); however, I feel that using a variation of something you know should be doable given enough testing and approval of your L3CC/TAP. I was super lucky that my L3CC was actually involved in creating the HED system (he's also Wildman CT). I explained my idea to him and he said "sounds like that would work!". Woo hoo!

So if you're doing something out of the ordinary, use every resource you have to support what you're doing. Get the backing, support and confidence of your L3CC/TAP. I already had proven experience with a modified dd (I fly the 4" X-15 once or twice a year) and my mentor knew the HED system very well. Now I just had to build it and prove it.

I wasn't going to use this new idea untested in my L3 build, so I built it into a Loc 7.5 V2 first...
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Tick tock...

Now at this a point LDRS is 6 months away, so I have plenty of time, right?

Undertaking a project like this you HAVE to carefully manage your time otherwise you greatly decrease your chances of success.

If you read my other X-15 build threads, you know my background and how driven I am to meet deadlines.

I planned out the timeline and figured that I could build the V2 and HED Cannon system, have it ground tested and then ready to launch at our first club launch in March to show my L3CC, then get approval to start building my L3 rocket. At that point I have 2 months to build, iron out any problems/fine tune and test launch it during our April and May club launches.

Too bad fate had other plans...

If you really want to achieve something, time will often really test you on how much you actually want it.
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Amazing work Sir!

Nice rocket.

Smokin' Rockets - there's a name you rarely hear these days.

Nice job - great build, nice flight!


So glad for this thread! That rocket was (is) amazing, truly one of the highlights of LDRS for me. Felt privileged to see it fly.
THANKS!!! guys! It's really humbling getting such praise from others, including members I've admired for a long time. 🙏 :wos_love:
Bring the Boom!

So in order to get the system for the X-15 tested, I first had to build and test in in the LOC 7.5 V2 I was building. I also used the V2 as a learning tool for some other techniques I didn't have much experience in (ex. glassing tubes). I found the build very enjoyable and the kit to be of high quality, a great value and very flexible with the Removable Nose Weight System (RNWS; however, I wouldn't be using this) and MMAS (Modular Motor Adapter System).

To create the HED Cannon, I first worked on creating a correctly fitting bay tube that would fit inside the nose cone shoulder. I did this by cutting and laminating some 7.5 Loc coupler tubing to make my custom size bay.

Notice that the Drogue side bay lid is larger so that it doesn't slip into the nose cone, yet is the same diameter as the nose cone so it slips into the booster. 2-56 Shear pins for the Main side are right above where the shoulder meets the rest of the nose cone.

I also show holes drilled into the shoulder and bay walls for the drogue shear pins, but I later realized that wouldn't be good (more on that later).

I did some ground testing of the bay with the Main first since the booster wasn't finished building, but made the mistake of sending the drogue side of the bay out without it mounted into the booster.

This basically just did a "cannon shot" of the bay out pretty far lol. At least it served to prove the toughness of my bay and the system aptly earned it's name at it's first trial!

View attachment 1000014830.mp4
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Sticky situation

So as I'm finishing the V2 booster, I'm starting to think that with the system the way it is, there is a danger (albeit small) of the bay shooting into the booster if the Main side fires first or at the same time as the Drogue. This would foul up the drogue and maybe (to a less likely extent) the main. Also the way it is now, I can't do a regular ground test of the Main where I just fire it out of the booster along with the nose cone.

So to fix this, I added two long dowels to the inside of the booster. This created a backstop for the bay while also strengthening the body tube considerably (helps to make everything stronger in a cert attempt) and there's also one more benefit which I'll find out later.

Note: I made sure that the dowels weren't in the way of anything on the bay lid.
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I also realized that having the Drogue shear pins through the bt, through the shoulder and into the bay (three layers) was a mistake. This is because a sheared pin will usually leave the rest of the shaft in the hole after it's sheared. This means that once the Drogue fires out and the nose and bay come out, there's still pin remnants from the drogue pins in the shoulder and bay and this can lead to it almost being held with twice the amount of pins, which is NOT good.

Always go through possible failures and what can go wrong. Better to think about it on the ground than see it in the air.

So to counter this issue, I had to figure out how to make it so that the Drogue pins only connect the booster and the bay...

I used Erector set pieces!


(Hole for pin to be drilled out.)

I did more ground testing and the system was working well. By now it's late January and I thought I was in good shape, so I started working on other rockets.
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So now I'm thinking I'm on schedule and in pretty good shape since I'll test and prove the system in the V2 during the first launch and then get the ok to start on my L3 build (can't start the build without your L3CC/TAPs approval).

Unfortunately the first launch got canceled!


When on a schedule to meet an important goal, assume things will go wrong. Really wrong.

I figured, it would be tight, but ok since I had allowed for at least a 1 month buffer in my original schedule. I'll just ask my L3CC if I could at least start on building the X-15 booster first.

I emailed and texted my L3CC; however, he became non-responsive. o_O
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Let's roll!

So my L3CC, Rick, was out of touch and our March launch was cancelled due to rain, but I heard that he'd be at the April launch. I didn't bother going out of my way to reach him since I respect other's privacy and usually I don't ask for direct contact info from people I meet at the field.

I later heard that he ended up having an accident and then knee surgery, so that explained him being incommunicado. Additionally, he later told me that he was the L3CC for *5* people at LDRS! (Of note is that all 5 got their cert under him on Saturday! Chuck Norris, right?)

So I showed up at the April launch and the field was very flooded to the right (looked like a lake and quite a number of rockets landed there due to the winds :eek:). Additionally, the farm on the left is very unfriendly and right behind us is a river, so that meant my test flight of the HED Cannon with the V2 should be low and landing as close to the pads as possible. I angled the V2 into the wind, expecting it to weathercock and launched it just as we were wrapping up flights for the weekend.

It was a great flight (albeit lower due to the wind and angling) and my system worked just as planned!


Rick gave me the go ahead to start my build! 🤩
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Start building already! :p

Yes, I'm finally showing the build at Post 48 of a build thread. 😆

Now that I got my green light to build the X-15, the way I figured it, I had one month to build it so that I could do the first flight on a K motor at our local club's May launch and then maybe an L if I have time (there is a June launch scheduled, but that was the Saturday before LDRS and it may be postponed or cancelled, so I can't rely on that).

I had a talk with my wife and I told her that I may be spending all my free time over the next month trying to build this rocket. A rocket like this is quite an undertaking and I was currently working a full time job.

If you seriously want to reach a goal, you should be ready to put serious effort into it.

(Note: I did a bunch of the background research before I started the build.)

The first thing to do was get the parts out and reviewed and for me to try to determine what kit I have since it wasn't described and the seller didn't seem to have any idea given he sold it as a "Rocket Spacecraft". After a lot of research, I determined that it was most likely an early Smokin Rockets kit since it had a nose cone and tail cone which were each made from 2 pieces and by the shape of the rear fins (the newer and fg kits are more swept).

Here is a pic of the parts and you can see a seam on the nose cone and tail cone:

I believe it's the same kit as the one pictured on the Performance Hobbies page that everyone drools over:


The fins provided were 1/4" plywood, a bit warped and also very poorly shaped (maybe hand cut) with the fin roots uneven.

Additionally, the fin roots were cut for a 54mm motor tube; however, my kit came with a 75mm motor tube (which was great for me given I need that for my M1350 motor). This was very much a garage kit!
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Pain in the rear

The kit I got had a 75mm motor tube which was loose in the tailcone and no CRs were provided for that end, so I ordered two from Dragon Rocketry, stacked them and sanded them as well as the inside of the tailcone to fit (the two piece fg cones are thicker where the seams are due to reinforcement).

Pics from another post:

I used two stacked CRs for extra strength since this rocket will often land on it's rear.

I also taped off the end and bathed the CRs in epoxy.

Now the other end of this tail cone was confusing. The tail cone shoulder seemed too tall since the tail fins would go there and so the choice would be to either cut slots in the tail root tabs or to cut slots in both that shoulder and the rear bt CR.


In the end, I made my own third option to cut off the shoulder and also partly recess that CR. This way the tail cone doesn’t need a shoulder.

This allows me to keep the maximum amount of fin root for the most strength, which is important in a cert build since a broken fin will likely be a failure.

Around the same time (things were a blur lol), I started glassing the phenolic body tube using a Soller sleeve and shrink wrap. I had never done fiberglassing prior to this project and tried it on the V2 first - it was messy and full of voids and pits, but was strong and a good learning experience. This time it came out much better!



I also started marking the rear CR since I wanted to have the horizontal stabilizers canted downward like on the real X-15.

Canting the rear horizontal stabilizers helps bring it into the airstream vs. being directly behind the wings and this helps with stability (more drag at the rear end).

I also test fit the motor tube and marked it up as well. I then glued everything in with West Systems (my go to epoxy on this build).

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Flimsy Fins

The kit came with 1/4" fins and I felt that was too flimsy for this kit. Especially given it would be about 30 lbs empty and over 40lbs with an M motor. Additionally, the ones provided were poorly shaped and even the fin roots seemed to be way off somehow.
(1/4" thick Fins that came with the kit.)

Normally I'd shop for high quality plywood for such a build, but due to very limited time, I resorted to going to my local Home Depot the same day I decided to make thicker fins.

Just my luck* that the half-sheet plywood section was a complete mess and worse yet, the 3/8" plywood was extremely scarce - almost as if they were phasing it out. It was very slim pickings! (*Note: I'll touch on the "luck" aspect in a bit. I find it frustrating at times, but also amusing.)

I finally found an "acceptable" sheet and marked it for cutting, avoiding the ugly knots. 😆
I had traced the originals, but notice how I made corrections to the fin roots. Trying to determine the correct shape took a lot of time and figuring out for me. The wings were cut out on the remaining half that isn't shown.

I love my Ryobi tools! Have been using them since the 90s and the new lithium ion batteries fit the old tools.

Here I was cutting a bevel on the two horizontal fins that would angle down 15 degrees. (I think.)

It's now Mid-April. 😬
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Let's talk about luck...

Ok, remember how I said I'd discuss being unlucky, etc.? Well, here's a good place. It's hard to argue that one factor you have no control over in a project like this is luck. You can have bad luck which sets you back or good luck which moves you ahead. It's my view that things even out in the end. Yin Yang. 🙂

Still, in my life there's things that follow me that I can't explain and even my wife had to admit it. I'm driven by logic because I've had so many illogical things happen to me. :p

Ok, one of those weird things is that the number 13 seems to keep popping up for me. I'm not religious and neither am I superstitious, but that number keeps haunting me.

Remember the distance between fins was 13" above? Well, with this one "good enough" piece of plywood I found, after I got it home, I saw it had a number stamped...



Good thing I'm not superstitious!

Now ask yourself... would you buy and use a piece of wood with the number 13 stamped on it for your uber important cert project? Gotta have guts sometimes. lol
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Liquid Gold

For fillets, I was lucky in that I had some Rocketpoxy left and had ordered and gotten a new set as well just before it becameunavailable. So despite it being unobtanium now, I wanted to use it since it was much quicker (and imho safer) than using epoxy thickened with silica. Quicker was important here!

Looks gross, but it'snot. 😛

I also used dowels to help further strengthen the motor tube, help support the CRs, help with fin alignment and also create epoxy dams for them. Dowels were cheap and strong!


This resulted in one beefy assembly!
20240419_231238.jpg 20240420_004031.jpg
Note that I aligned the U-bolts so the retaining nuts weren't in the way of the wings to be inserted.
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X-15s good for certs?!?

Argue Polar Bear GIF by Pudgy Penguins

As I'm building this beast, I was thinking "boy, this is one stout rocket! It should be able to take hard landings pretty well!"

One of the more important parts of a cert is that your rocket (assuming you got it back) is not substantially broken. Making a rocket with strong construction is one way to lessen the chances of failing on that.

Why would this X-15 be good for a cert?

  • First off, there is a stout tail cone which often hits the ground first, so the rear fins are less likely to break on a hard landing.
  • Then look at the above fin and motor tube assembly. There are a lot of big TTW fins as well as large wings that support multiple CRs all the way down without a gap in support.
  • Additionally, there are side chines (shrouds) that in this case are fiberglass and further support the wings and two of the fins like TTWW).

This builds into a very, very strong rocket. Twice my 4" rocket had a main chute issue, but both times it survived the faster landing without need for any repairs.

Of course this also becomes a heavy (chonky?) rocket, but that's ok for when you don't want it to go too high. That actually works for me being an East Coast flier with a local club waiver of 4,500'. Plus I like to be able to see the entire rocket in flight vs. just following its exhaust trail.
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I'm done except for paint!


I'm just fooling you lol. This is a mock-up I set up to determine where to cut the tail and wing slots in the chines/side shrouds. I actually added the wings temporarily to the tail assembly and held it down with a CR on top and then placed that behind the body tube with the shrouds taped on. Magic of perspective!

So once I had an idea of where to cut everything, I marked it up and started cutting. First I cut the two opposing slots in the body tube to be inserted over the vertical tail assembly. This was the "easy" since it's just on opposite sides.


I examined the cut out pieces to see how well the fiberglass had bonded on and it looked great to me!


Slipped it over the motor stack assembly to check fit and then also marked the location of the canted horizontal tail fins.


Marking up the slots for the wings here.


Test fitting the cut wing slots with a scrap piece.


A quick shot of it all together to see how it's looking...


3 weeks until May club launch. 🫨
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Warped situation

So after I glued on the top vertical fin (the biggest one), it showed warping. :facepalm:

I think having the largest fin on your rocket curving to one side isn't a good thing.

I tried using cement slabs with weights to flatten it after a coating of epoxy, but it didn't seem to do much good.

In the end, I decided to sand down the middle of the curve on the side where it was sticking out and sand the edges of the opposite side (I haven't heard of this fix before) and then just apply a heavier fiberglass and epoxy coat when I do a tip-to-tip fiberglassing.

The sanding worked out very well! The fin was now straight, but if you look at the middle ply, you'll see it curves!
Phew! 😅

In aircraft design, a chine is a longitudinal line of sharp change in the cross-section profile of the fuselage or similar body. The term chine originates in boatbuilding, where it applies to a sharp profile change in the hull of a boat.
Wikipedia Source

So now it's time to attack one of the more daunting parts of an X-15 build... the side shrouds or "chines".

I had heard that the newer kits come with the chines already cut for the wings and fins and that this alone is worth the extra cost of the fiberglass kit (from what I recall reading). I would find it hard to argue that considering how much work was involved with cutting and trimming mine! The one good thing about not having them precut was that I could cut in the slots for the canted horizontal stabilizers without having to fill in any holes that were cut there for the non-canted fins (later I found out even that didn't help much).

So one of the first things to do was to remove the long flashing all around the chines. At first I thought I'd use some saw, but in the end I found that a reciprocating cut-off tool worked great. However, it was very dusty (N95 worn for this work).


I also used a jigsaw to cut the slots after drilling starter holes.

Test fitting:

Unfortunately in my rush, I wasn't too good on getting the position of those canted fins correctly and ended having to repeatedly cut it lower and then I had to insert a large scrap piece to fill in the gap. Always keep some scraps pieces just in case!


(Later pics here, but shows how I filled the big gaps.)

If you goof up, learn from it, then fix it and keep going.

I then checked my notes again (always keep notes on what you need to do now as well as later):
So I jumped over to Fillets and T2T glassing. More Rocketpoxy goodness!


Note the large holes drilled next to the mounting points (some taped). These were used to inject epoxy in after I had glued on the bt in order to create internal epoxy fillets between the CRs and bt.

View of the injected epoxy from the open wing slot :

(Earlier) To prevent the epoxy from covering the wing and fin areas, I used cut down pieces of chopsticks to form dams.


Tip to tip - I marked out the patterns for doing tip to tip.


I had some plan figured to have the entire section from the wings on back to be covered with 2 layers of 6oz fg cloth and then peel ply.

(Note how I marked a low spot to fix later.)

Remember that curved top vertical fin? I didn't forget about it. I had sanded it down, so now I had to finish "fixing" it by using pooled epoxy to fill any low spots and to strengthen it after the tip to tip. I made sure to use a level and checked several times before pouring the epoxy.

I think this looks beautiful! 😍

It is now early May. Less than 2 weeks to first test launch. :oops:
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Why this complex kit for L3?

General wisdom is that you should pick a simple, proven rocket to do your cert on and that it's the time to show that you've learned enough and have the skills to fly at a higher level. Don't do new or difficult things on a cert attempt otherwise you increase your chances of failure (and also possibly lose the confidence of your certifier and peers).

I actually agree with this and I usually recommend the same!

Well, there's another opinion...
Haha! Just kidding! 😂

The general wisdom applies when you have a desire to fly bigger motors and plan to continue. For me, this wasn't the case because my local field has a 4,500' waiver and I'm happy flying L motors and under. Plus the price of the bigger L3 motors is a bit out of reach for me after the crazy inflation and given I haven't started making my own motors yet. Last I saw, the retail price of an M1350 was $769?!?

In my case, this was more of a bucket list item, plus I enjoy a challenge every now and then. I was also fortunate enough to still have the M1350 motor I had purchased back in 2015 for $250 when I first considered trying for L3. I might try another M motor in the future, but not anytime soon.

It just made sense for me to try it this way and I was fairly confident that I could do it. If you're going to try a bucket list item, why not make it memorable? (As long as it's safe and within reason of course.)

A cert attempt is a good opportunity to prove your knowledge and skills as well as to learn how much you were lacking them!