4inch Hornet Upscale Scratch Build

[DabCat]

It's been a while since I did my last build thread on here, so how about another? This time I will be scratch building a 4inch upscale of the Estes Hornet. The Estes Hornet is actually a special rocket to me. It was the rocket I flew my first reload in. Way back, in the beginning of my rocketry journey, my dad was very into RC everything. At the top of his workbench, in a pile of long forgotten projects, was a rocket glider. For this rocket glider, he had a 18/20 and a pack of D2.3s, D13s, and D24s. While I don't remember exactly which reload was the first to fly in my Hornet, I do remember that all the reloads were flown. However, I do believe that it was the D24. The D2.3s were flown in a 3d printed UFO.

The upscale Hornet should stand at 58" tall, 43" being body tube. The motor mount will be a 54mm and will have 4 centering rings. You will see later in the thread why I used 4. The upscaled Hornet will be configured for dual deploy and will have dual StratoLoggers for redundancy. For the first flight, I'm thinking a 1 grain 54mm I of some sort. Most likely something in the Aerotech 54/426 case. It will fit the L1000, but I don't think I will fly anything larger than a 4 grain K in it. I will have a GPS mount though in case I'm feeling risky and have an L1000 in hand.

A while back, I was at Staples, and I came across this tube in one of the sale carts. The tube is 4"x48" and cost me less than $5. It seems plenty strong and still lightweight enough to be useful for a rocket. However, the catch is that the tube is an odd size. The inner diameter measures just shy of 4 inches and the outer diameter is about 4.15". No big deal. I just need to make my own nosecone for it.


First step was actually designing the rocket. I started by scaling up a openrocket file of the original Estes Hornet. I then fixed some minor details and added all the finer details. I ended out with this:


Next step was transferring these parts to CAD. First up was the fins:


Then the centering rings:


And that's all for this post. The nose cone can wait. Thank you for reading. Next up will be assembling the fin can.

 

[Tim51]

Nice choice for an upscale. I have a softspot for trapezoidal fin rockets, and the Hornet is a great one. Following with interest. The rocket in my avatar is 4", and designed to fly on 3 and 4 grain 54mm motors. It's a nice combo imho.

 

[DabCat]

Nice choice for an upscale. I have a softspot for trapezoidal fin rockets, and the Hornet is a great one. Following with interest. The rocket in my avatar is 4", and designed to fly on 3 and 4 grain 54mm motors. It's a nice combo imho.

I'm guilty as well. I love trapezoidal fins too. They look great and they don't hang down past the body tube, so they don't break as often. That's why I love the polecat goblins. I may or may not have a massive scratch build project involving a lot of fiberglass and a lot of goblins... that's for a future build thread though, and quite a ways off as well.

Anyways, back to the Hornet. Fins and centering rings are laser cut and the fins are beveled on the leading edge and trailing edge. And of course, a banana has been included for scale. Or a snack...

 

[jmasterj]

Are you going to 3D print the nose cone or something else?

 

[DabCat]

Are you going to 3D print the nose cone or something else?

Most likely 3d print it. I do have some spare foam and fiberglass though.

 

[DabCat]

Fin assembly is glued together. The small tabs are glued into the rectangular holes in the centering rings. Here is the bottom tabs being glued. I used the clips to hold the fins upright in the slots so they would be in place for the top centering ring. This helps to eliminate the part of juggling 4 fins with wet glue while trying to slide the top centering ring on.



The assembly is not glued to the motor tube yet, so the motor tube can be removed and reconfigured. The motor tube is there to hold everything in the correct position. The brick on top keeps everything pushed down and flat.



When this is dry, the motor tube will be removed and everything will be configured properly. Then all will be glued together, then internal fillets on everything, then it gets glued into the body tube.

 

[DabCat]

Some progress was made today. A little busy, so things are progressing a little slow.

First, the motor tube was removed from the fin assembly.


Next, the tube was marked. This is where the top of the rear centering ring will sit. The line was drawn at 2.335 inches, or at least approximately 2.335 inches. At that small of a scale, it doesn't really matter that much to me. All that soot on the tube is from the wood. Not a very clean laser cut, so I sanded the edges a little to clean them up a bit for better glue bonding.


Here is the fin assembly test fit at the proper location on the motor tube.


And here is what the final motor mount assembly should look like. The retainer will be mounted to the rear centering ring and the recovery harness will be mounted to the top centering ring. I may mount the shock cord through the top 2 centering rings though for redundancy.


Next, I scored the tube at the edges of the fin assembly and peeled the glassine for a better glue bond. Then I traced the fin assembly to help guide my glue placement. This is the first time I traced it like that, and I gotta say, it really helps. Definitely a step for future builds. I did have to be careful that my line stayed in the same spot, so I traced the rear centering ring, then peeled part of the glassine, then traced it again so that part of the original line still lined up with the new tracing on the peeled part. Once all the glassine was peeled, I had a guide for the location of the rear centering ring so I could trace the entire assembly.



Next up I spread some glue on all the traced areas, and slide the fin assembly over it. It seems that the raw and hairy cardboard seems to help prevent drips, because I was able to lay it on its side to dry and the glue did not shift as much as it would if the glassine was not peeled.


Next up is internal fillets. I managed to get 2 sets done before quitting for the day. The first set came out a little messy. Oh well, it shouldn't ever see the light of day again once the rocket is finished. If it ever does, I think there's bigger problems to worry about.



And that's all the progress for today. I'm not sure if I'll have time to work on it tomorrow, but if I do, I plan to finish off the motor mount assembly. I want to do something simple and cheap, but reliable for motor retention. I'm thinking about either a madcow style retainer, Z-clips, or washers.

 

[DabCat]

It looked like the images weren't showing in the previous post, so I think I've fixed it. Let me know if there are any errors.

 

[DabCat]

I had some time for 1 set of internal fillets. When I do the internal fillets, I make sure to get a fillet on the centering ring and the joint between the fin and the centering ring. The finished product is a bullet proof motor mount assembly.

 

[DabCat]

Between now and my last post, I had a chance to finish up the last internal fillet. With that part out of the way, it's time to start on the forward and aft centering rings. First up is the aft centering ring.

First up was marking where the holes will go. I decided to go with 4 washers for the retention. It's cheap and easy, and still perfectly functional. To hold the crews, I have some threaded inserts that screw into the centering ring.


Next up is drilling the holes for the threaded inserts. The left 2 holes were drilled without a backing and the right 2 were drilled with a backing. Big difference.


Here was a test fit with the threaded inserts threaded into the centering ring. Looks decent. I was a little worried about motors with large nozzles, so I test fit an L1000 and it fit just fine. Adaptors may be difficult, so I will probably just use my new set of expansion closures. This build may or may not have been for testing them out...


And now some epoxy. I smeared the epoxy on the threads and screwed in the threaded inserts. I've had great luck with this retainer design in the past, so I'm hoping to continue that.



And with that, the aft centering ring is complete. As soon as the glue is done drying, it's getting glued to the motor tube. Next step is the forward centering ring, which should be pretty easy. After that, the fin slots, then external fillets.

 

[DabCat]

Alright, next update. Over the course of yesterday and today, I've finished the whole motor mount assembly. Fin slots are currently in progress.

First up was gluing the forward and aft centering rings on. In order to prep the tube, I cut and peeled the glassine off and marked where each centering ring would go.


Then the centering rings got glued on.


Then I filleted all the centering rings.



Continued in the next post... file attachment limit

 

[DabCat]

And now the completed product. Note that in this picture, it is upside down.


Next up I drilled a hole and mounted a 5/16 eye bolt. This was originally un-welded. I grinded it down a little and welded it myself. We'll see how it holds up.


The eye bolt did rust a little, so I coated it in epoxy to hopefully reduce further rusting. It should also help keep the inside smooth since it was a little sharp from the weld.



And that's where I've last progressed. Fin slots are currently underway, but first the body tube must be cut into the right sizes. I decided to shorten the aft body tube and lengthen the forward body tube to give more room for the main chute. I think I'll design a separate av bay for this that provides a bypass so the motor can extend all the way into the nose cone. This would allow me to fly the contrail hybrid K motors. It may never fly one, but it gives me peace of mind to know that I could if I wanted to.

 

[DabCat]

Alright, time for the last update for today. I cut the tubes down and finished the fin slots. I decided to hand cut the fin slots with an exacto knife, since I don't have access to the laser cutter for a few days. It worked pretty well.

First up was marking the fin slots. I did this by clamping a piece of aluminum angle to each side of the fin and tracing it. This worked amazingly well.


And a magical little cut... and bam! the slots are all done! I'm happy with the way they came out. Not the cleanest, but still functional.


It took a pretty long time to cut them out, and they didn't come out super clean. If you want to save time, don't cut them by hand. And of course, to add to the frustration of how much time it took, I had to accidently test the blade sharpness. Only a minor cut, but still very annoying.

Of course, I had to do a quick test fit. It's starting to take shape!



And that's all my progress for today. Next up is gluing the motor mount assembly in and doing the external fillets. As for the rest, I have a CAD for the nose cone. I haven't printed it yet. I'm working with a new printer with a slower print speed and smaller print bed. The height is too small for this nose cone, so I'm thinking about splitting it in half, or even thirds. Or I could just wait. I have intermittent access to a faster and larger printer. I do have some spare foam and fiberglass, and all my supplies are out from a different project. I could go that route, but I really don't feel like doing all that. We'll see what happens. As for the AV bay, I'm debating between 3d printing the coupler or using a piece of scrap body tube. I'm thinking of designing something fancy with screw together pieces if I go the 3d printing route. I'm leaning toward 3d printing it because I've never turned a piece of body tube into a coupler before. Maybe I'll change my mind. Any input about this?

 

[cwbullet]

Awesome build!

 

[Pepe Le Pew]

I have also used Staples 4" tubes successfully, great build!!!

 

[Off Grid Gecko]

Probably a dumb question here cause I've never used this approach. On your fin slots did you just do a slit all the way down to slide the fins through then plan to seal it back with PVA or epoxy? Or is there some other sorcery going on that I'm not seeing. Asking cause I can't see the slices in the image. Is this a normal way of doing things. I normally spend days meticulously loading one element at a time into my fin can, doing checks for straitness, etc.

 

[DabCat]

Probably a dumb question here cause I've never used this approach. On your fin slots did you just do a slit all the way down to slide the fins through then plan to seal it back with PVA or epoxy? Or is there some other sorcery going on that I'm not seeing. Asking cause I can't see the slices in the image. Is this a normal way of doing things. I normally spend days meticulously loading one element at a time into my fin can, doing checks for straitness, etc.

Yes, that is exactly how I did it. When the motor mount assembly gets glued into the tube, I will put zip ties around the tube aft of the fins to keep all the slots closed. Later on, I will use some filler to get it smooth again. In the picture, it looks like the slot is very wide. When a zip tied is applied, this gap will be completely closed.

 

[DabCat]

I've made the final decision about the nose cone. I decided to 3d print it so I could experiment with large 3d printed nose cones. I'm thinking about trying it for 2 5.5" projects and a 10" project. (Build threads coming soon?). The nose cone will be printed in 5 different sections and will take approximately 3-4 days of continuous printing. I'm gonna try out a new method on the printer that should speed it up a bit. Apparently the quality is worse, so I'll see how the first section comes out. I'm planning to glue the sections together and reinforce with centering rings if needed. I think I'll cut the centering rings with room for a 54mm case so I could fly a casing in it that extends into the nose cone. Once the nose cone is assembled, I'm planning to coat the whole thing with filler and sand it down. Hopefully that should remove the 3d printed texture. I haven't had time to glue in the motor mount assembly yet. I should have time tomorrow to finish that and a few other estes kits as well. Gotta start shrinking that pile...

I'm thinking about doing a layer of T2T for some of the long burn Ks. Thoughts? I want to keep it light enough to fly on 1 grain 54s but I also want it strong enough to fly some of the hefty K motors. It probably doesn't need it, but it would be nice insurance.

 

[Tim51]

I've made the final decision about the nose cone. I decided to 3d print it so I could experiment with large 3d printed nose cones. I'm thinking about trying it for 2 5.5" projects and a 10" project. (Build threads coming soon?). The nose cone will be printed in 5 different sections

What filament material are you planning to print with? The reason I ask is I had a 5.5" custom NC printed a while ago from PETG. I glued the sections with polyurethane glue and 'glassed the ID of the shoulder (the shoulder was not capped to allow a NC bay). All seemed very robust. Nevertheless the PETG shoulder buckled and cracked when the NC landed (under chute) on a hard dirt track. I hear ABS is better, but more difficult to print (..?)

 

[DabCat]

What filament material are you planning to print with? The reason I ask is I had a 5.5" custom NC printed a while ago from PETG. I glued the sections with polyurethane glue and 'glassed the ID of the shoulder (the shoulder was not capped to allow a NC bay). All seemed very robust. Nevertheless the PETG shoulder buckled and cracked when the NC landed (under chute) on a hard dirt track. I hear ABS is better, but more difficult to print (..?)

I was planning to use PETG. I'm hoping that the centering rings should work better to strengthen the nose cone. Thanks for sharing your experience. Maybe I'll switch over to ABS. I'm thinking that I'll print the nose cone shoulder section first and test it out.

 

[cwbullet]

Do you have your own laser cutter?

 

[DabCat]

Do you have your own laser cutter?

I have free access to one, but I do not own it.

 

[BigMacDaddy]

What filament material are you planning to print with? The reason I ask is I had a 5.5" custom NC printed a while ago from PETG. I glued the sections with polyurethane glue and 'glassed the ID of the shoulder (the shoulder was not capped to allow a NC bay). All seemed very robust. Nevertheless the PETG shoulder buckled and cracked when the NC landed (under chute) on a hard dirt track. I hear ABS is better, but more difficult to print (..?)

Other benefit of ABS is that you can use Acetone+ABS (ABS Slurry / Glue) to weld parts.

 

[cwbullet]

I have free access to one, but I do not own it.

What brand?

 

[DabCat]

What brand?

It's an Omtech 100w CO2 laser.

 

[DabCat]

Sorry to leave this thread hanging. Things got a little busy for me and the Hornet moved to the back burner. It's going to be a bit before I continue. My 3d printer has been acting up, so now there's a backlog of parts that I want to 3d print. In addition to that, I'm also on vacation for 2 weeks! Terrible, I know! On a good note, I now have my own laser cutter, so new projects have materialized. One of which being finding a place to put it and setting it up!

 

[DabCat]

Alright, Hornet is off the back burner. Almost burned! Let's get back to work with this bad boy.

I left off with the fin can ready to be glued in. Dusted it off, picked off the cobwebs, and did just that:


I threw on some rubber bands and a handful of these sweet mini clamps I found at Harbor Freight to hold the body tube together and make sure the fin slots close. The clamps are my go-to for keeping the body tube pressed against the centering, and I've found it to work extremely well.


Clamps from the inside of the motor tube to the outside of the body tube


And if you direct your focus away from my messy fillet around the motor tube, you can see how well the clamps work at sealing that little gap and keeping the body tube pressed in place. Definitely a good investment if you don't already have a set of your own.

 

[DabCat]

Now... the coupler. How do you get a coupler for a completely odd size body tube?

I had an extra 6" length of the body tube kicking around, so I'll use that to make my coupler. This will be the av bay, so my plan is to have the top 2" be screwed into the body tube, and have the remaining 4" connect with the booster section. Hopefully since the 2" section is screwed on, it shouldn't fold there during flight. Let me know if my logic here is flawed.



Next I need to cut a slit across the tube, so I clamped a piece of aluminum angle and sliced away with an exacto.



And... done.


I folded the lip of the cut over the other and slid it into the tube to mark where the next cut will be


Aluminum angle is clamped on again


Bit of slicing later


Continued in next post

 

[DabCat]

My previous tube cuts were a bit messy, so I cleaned up the tube a bit with some sandpaper


Test fit the coupler in the tube, and voila! A near perfect fit! I'm very pleased with how it came out.


Now to make it permanent. I spread some glue along the seam, sealed over it with some blue tape, and slid it into the body tube to hold shape while the glue sets.


And that just about sums up my progress so far. I hope to have some time tomorrow to finish off the coupler and external fillets.

Now... back to the nosecone again. Since last updating this thread, I've actually gotten a few new toys. One of which being a nicer 3d printer. More reliable, better prints, and a larger print bed. My plan is still to 3d print the nosecone in sections and join them. We'll see how it comes out.

Do you have your own laser cutter?

I do now. I've got some pretty ambitious ideas about making rocket kits to sell, but we'll see what comes of it. I've always wanted to sell kits, but there's countless difficulties that having a laser cutter just doesn't solve. Certainly makes builds a lot easier now that I can just cut stuff out as I need it. Also works well for DIY Christmas gifts...



Now if anyone was ever curious what project pushed the Hornet to the backburner...
Any guesses? It's still unfinished, but now progress is moving slow enough that I can get some other things done.

 

[Handeman]

Test fit the coupler in the tube, and voila! A near perfect fit! I'm very pleased with how it came out.

Now to make it permanent. I spread some glue along the seam, sealed over it with some blue tape, and slid it into the body tube to hold shape while the glue sets.
View attachment 564243 View attachment 564244 View attachment 564245

For some extra strength, take the piece you cut out and glue it over the joint on the inside of the coupler. Just trim it a little shorter if you are going to have end caps that have an inside shoulder.