Estes Ninja BT-60 Upscale for 24mm power

[Flyfalcons]

Here's a project I've been working on that's just about ready to go. The Estes Ninja #0882 was my third or fourth rocket, and the first one flown that I actually got back. It wasn't in my stash of rockets that were kept from my childhood, so it must have had a short life or been retired early. I do remember it though, in that it was really cool looking! Inspired by EXPjawa's BT-70 upscale (see here), and with most of a Designer's Special sitting on my work bench, I decided to design a BT-60 upscale for 24mm power.

My design goals were as follows:
1) Closely resemble the original Ninja in BT-60 size, which is 222% of the original size.
2) Light enough for small field flights with a C11-5
3) Strong enough for an F44-8 for a real Ninja-like experience
4) Prevent the pointy fins from constantly taking damage on landing

What I ended up with is as follows. My original drawings from the standard Ninja have a slightly longer body tube and shorter nose cone. However, from the four BT-60 cones I had, the only one that was pointy enough to look good is 8-3/8" long, instead of the 6-3/4" that I was shooting for. So I had to compromise and shortened the body tube by 3/4" from true upscale. The result, I think, looks just fine. The base of the nose cone is pretty straight, so if you ignore the actual joint, the outline is still pretty close to original. This cone, by the way, came from the Estes BT-60 nose cone 3-pack assortment and not the Designer's Special.

To prevent fin damage, and to help withstand the 475mph shot from an F44-8, I selected 3/32" plywood for the fins. They are mounted through the wall in a simple arrangement: There is no middle centering ring on the MMT, just a forward and aft. The front of the fin tabs press against the forward CR. They are glued on with epoxy, no internal fillets, and wood glue for external fillets to help keep the aft weight down. The fins sit pretty far forward, and I moved the aft location from a true upscale 2.22 inches from the bottom of the tube back a little to 2 inches to help with CG issues. The fins themselves are a true 222% size and shape.

I included an engine block for flying with Estes C, D and E black powder engines, and a 24mm retainer for using composite motors. I set the engine block so a D12 with E spacer overhangs the MMT by 3/8". The bottom of the MMT sits flush with the bottom of the BT, then the inner retainer ring is glued on and overhangs the body tube by a small amount.

According to the simulation, 1 ounce of nose weight is needed to keep stable with the heaviest of the engines I may wish to use.

3/16" launch lugs were deemed appropriate for this size and weight rocket. I like using dual short launch lugs so that's what is on the sim.

That's pretty much it. This is a 3FNC design that just happens to look pretty cool. As can be seen in the simulation, performance should be great. A D12-5 should send it to 800 feet, an E20-7W goes to 1500, and an F44-8W should teleport the Ninja to 1660 feet. All while safely flying on a C11-5 to 360 feet at small fields. Before I left for my trip yesterday, I had basic construction complete. I just need to fill, smooth, paint, and add Stickershock vinyl decals and nose weight. Hoping to fly this at a local launch on the 17th this month, but I only have a few days at home between now and then so hopefully I can pull that off. Enjoy and hopefully someone can use the plans to make one of their own.





View attachment Estes Ninja BT-60 Upscale.ork

 

[Flyfalcons]

Here are some pics of the build. Not too many parts to cut on this one. Should look great dressed up in the all-black scheme with red vinyl decals.

 

[EXPjawa]

Cool! I'm glad to see you've got the fins on correctly. Too many seem to put them all the way back on the tube, which is probably more stable, but looks wrong. I used basswood for my fins, and was able to bevel the leading and trailing edges and bring the tips to a (near) point. I then CA'd them to add a little more robustness. Something like this is just begging for a ChuteRelease to get the full potential out of it...

FWIW, the decals really should be orange (assuming you're going for the original all-black scheme). Mark made mine from red vinyl, rather than orange. But I've since found my original Ninja and it definitely has orange decals.

 

[Flyfalcons]

Really, hmm it's been a while and I always remembered them as red. Interesting. Either way I have a black/red design on the brain, and red decals in my shop so red it is for me.

 

[TopRamen]

Lookin' good!

 

[K'Tesh]

Lookin' good!

+1!

 

[TopRamen]

I often build my LPR stuff like this, up-dogging to 24mm and whatnot, and just wanted to offer something that might be helpful.
I like to fly the C11 and D12 in my field, because that is about all it is big enough for in small, light rockets.

What ends up happening is I get a ring of BP ejecta crud in the motor tubes that I design with my lofty goals in mind.
Sure, I coat the inside of MMTs in CA, but they still get this ring when I fly them on BP motors.
My most recent rocket that is not MD, but uses 24mm and is built to handle composites, I made the MMT short and stumpy, so that the BP ring does not happen. This also keeps the weight down in the rear.

Not suggesting you should change anything, your build looks excellent, but when you do your black powder motors, make sure you wipe the inside of the mmt after each flight to keep the buildup to a minimum. An F32 and the other longer composite motors won't fit if that ring of crud gets built up like it did in my Centuri.

 

[Flyfalcons]

Top, do you use the orange spacers with the D and C motors? I seem to have good luck concentrating that crud within the spacers when I stick a C or D in an E-sized setup. Kinda keeps things channeled through the motor block that way. Yeah the longer MMT was part of the compromise with this design as I wanted the fin tabs to be somewhat centered on the fins. Thanks for the heads up on keeping the mount cleaned out!

 

[TopRamen]

Top, do you use the orange spacers with the D and C motors? I seem to have good luck concentrating that crud within the spacers when I stick a C or D in an E-sized setup. Kinda keeps things channeled through the motor block that way. Yeah the longer MMT was part of the compromise with this design as I wanted the fin tabs to be somewhat centered on the fins. Thanks for the heads up on keeping the mount cleaned out!

I've never used the spacer, so that makes sense why I'm having the issue with the build up. I don't generally put a thrust ring in the tube, so the spacer would not stay put anyhow. I guess I could glue a coupler to my C11 and D12 motors for use in my rockets with the long MMT to help with the build up.

 

[Flyfalcons]

You could probably just tape the spacer or coupler to the motor with scotch tape; I bet it would hold in place when the ejection charge fires. Those BP charges do leave a lot of crap in the tubes.

 

[TopRamen]

You could probably just tape the spacer or coupler to the motor with scotch tape; I bet it would hold in place when the ejection charge fires. Those BP charges do leave a lot of crap in the tubes.

That is probably the best idea, and I'll try it next time I take the Centuri to the park.

 

[EXPjawa]

That makes sense; I've seen a lot of build up on the spacers themselves but have never had an issue with it in the actual motor tube. Some of my rockets (like my Der V-3 clone) have seen a lot of flights, but almost always on a C11 or D12 with the spacer in place.

 

[Flyfalcons]

Finished it early enough to fly it today on a C11-5 and chute release set for a 300' open. Perfect flight! Video later. Finished weight minus motor and chute release came out to 5.4oz.

 

[TopRamen]

She's a beauty!!!

 

[EXPjawa]

Nice!