Honey Badger 2 Build Thread and Flight to 57k!

Everyone loves a good build thread, so here it goes ....

Last year Oberth and I built a 4" rocket and made a build thread (https://www.rocketryforum.com/showthread.php?42436-4-quot-Min-Diameter-Rocket&highlight=honey+badger). We realized that it was overweight and under performing; while the propellant could be improved we realized our extreme performance rocket building skills needed some honing before we did so (or maybe just mine - Oberth has plenty of minimum diameter experience).

So we set out to shave weight, increase both max velocity and altitude performance and take lots of pictures along the way!

Starting at the top ...

Building a NC to a custom sized tube is a bit of a pain (more on that later). I had some experience with a 6.5" NC that I had made using a technique I saw Wedge Oldham use on his Black Brant II. The idea was to create a short adapter that fit the tube and carried the same angle as a commercially available nosecone that would slide into the top side of the adapter.



The Performance Rocketry 5:1 Conical NC is on the top and the Al adapter is on the bottom. When combined they make a continuous 5:1 nose. Also of benefit was that the RF transparent PR cone gave us a good location for radio transmitters, the only location on the all aluminum rocket.

Next we fiber glassed the internal profile of the PR cone to increase the stiffness. This was based on a "feel good factor" (ie the nosecone was flexible before, and not all after ) and added minimal weight gain (3 layers of 9oz satin). The layup was vacuum bagged - not an easy task through the ~0.75" hole in the tip.

An aluminum tip finished off the cone sub components - this served to retain the altimeter bay and provide a location to arm the electronics.

The fiberglass cone was epoxied into the aluminum adapter and the entire exposed surface was covered with a high temperature ablative that proved to be quiet a messy endevour but was ultimately fruitful. After application the entire cone was re turned to create a concentric cone.



The cone was then coated with 5 layers of BBQ paint coat followed by some high visibility paint. The shoulder was coated with a graphite lubricant to help keep the aluminum-aluminum surfaces from binding.

If you ever need a plug for a custom nosecone (especially for special/interesting projects), PM me. I've been writing software to load Rocksim / OpenRocket files and output gcode for a CNC machine. I cut a tiny one for maxvelocity a few weeks back. I've done up to 4" dia so far, but should be able to go larger:

18mm 7:1 Von Karman:
[video=youtube;Acfb3PAX-AY]https://www.youtube.com/watch?v=Acfb3PAX-AY[/video]

Moving to the bottom...

Our previous flight (Honey Badger 1, HB1) used traditional building techniques; fiberglass airframe, G10 fin material, high strength epoxy for the fillets and carbon layups. Aero heating was a concern with HB1 since it was expected to go well over mach 2 so we coated the fins and nosecone with several layers of BBQ paint. The paint helped but a small portion of the carbon layup did peel up.



For HB2 we wanted to make some improvements like: turn the motor case down to a 3.75” OD, shorten the fin span/improve fin shape, get rid of the fiberglass airframe and just use a 98mm coupler tube for the base of the fin can. A lighter case, smaller fins and smaller OD equals more speed, more aero heating and more altitude. Our goal was to use all room temperature cure epoxies that don’t require a post cure to make the build as easy as possible and keep costs low.

Unlike HB1, we decided on swept back fins in order to reduce drag and increase altitude. Fin flutter was definitely a concern since the back portion of the fin would be relatively unsupported compared to a traditional “mach diamond” fin shape. We like 4 fins instead of 3 because it allows for a smaller overall fin and, in our opinion, provides more dynamic stability.

So here's what we ended up with:

We used a 98mm coupler tube as the base, 1/8” G10 fins and high temperature epoxy for the fillets.


We applied 3.5 layers of IM-7 carbon using Aeropoxy 2032/3660 and vacuum bagged the layups.






I had always wanted to make a room temperature cure ablative coating so I decided to try my hand at it on this project. It’s still a work in progress but as the results will show later, it worked very well.



Finally, several coats of BBQ paint and a fluorescent pink were applied for good measure

Oberth said:

...I had always wanted to make a room temperature cure ablative coating so I decided to try my hand at it on this project...

Click to expand...

Ok. This piqued my curiosity.

Would you mind describing what it is and how you did it?

Greg

The single most massive part of the original rocket was the motor case. Some quick calculations showed that we had oodles of margin, and even shaving the case to 125 thousands gave us >1.5 capability with worst case material conditions at MEOP in both hoop and bearing loads. We did double check this with as made dimensions and ensured we were as close to perfect in the applications of our loads to the motor...more on that later.

The second most massive part of the rocket was the airframe, so, we eliminated it. By extending the motor case by 6" we had enough room for our single parachute (more on that later too). As Oberth mentioned this whole package was convienently sized to fit perfectly into a commerically available 4" coupler tube.

Motor case/airframe, the stack to the right are the grains showing how much of the rocket is propellant:


The closures for the nozzle and bulkhead were retained with hardened steel dowel pins. This application is as close to the perfect shear/bearing load case on which we were doing calculations - there were no threads to worry about, capability loss due to torquing features or drag inducing heads.



The forward bulkhead was pretty standard (and HEAVY) and coated with an insulative mixture prior to installation:

The nozzle was also retained with a pin ring which also served another of other purposes: fincan retainer, tailcone and expansion cone extension.



The nozzle this year had a graphite throat but included a phenolic extension between the graphite and aluminum portions of the exit cone. If you revisit the first honey badger thread you will see that our previous graphite -> aluminum design suffered some serious erosion.

The propellant was an 83% solids 12% aluminized formulation with moderate performance. Burn rate was modified with RIO. This propellant has a pretty low viscosity at room temperature thanks to the use of some 90 mic (it’s almost too fluid to pack). It was well characterized using strands, small sized characterization motors and full scale test motors.

This was the same grain geometry used in HB1 and gives a nice progressive burn profile. The motor comes out to be an N5000 delivering 16.5kNs, with Pc_max around 1200psi, and a burn time a little under 3.5s. The thrust to weight ratio just before burn out was calculated to be 146:1.

Confucius say....."motor that works always outperforms one that burns a hole through side!"

Tony

After a tedious final assembly, and the last minute welding of a tower the rocket was ready for the playa ...

The 6" recovery space proved to be slightly on the small side, but after some careful shock cord packing we got the NC on.



The arming wires were passed through the NC tip and after arming the tip was screwed on with loctite.

TFish and Burner helped us load the rocket on the pad, Thanks guys!

Liftoff was fast, really fast! The progressive motor profile could be seen in the way the rocket flew.

Burner took some AWESOME photos:

One video of the flight from the flightline ...

[YOUTUBE]U8mr0cdvwjo[/YOUTUBE]

Ryan,
Great work.
Randy

Post flight pics:

Here's how we found it. Everything worked as planned. We brought it in fast to ensure we stayed within the airspace. It landed 2.5mi away.



Here are some shots of the fin can. As you can see it got pretty hot and cooked nearly all of the paint off (including the BBQ paint). Unlike HB1, the G10 leading edges didn't hold up too well. We could have coated the leading edges with ablative too but we wanted to see what happened if we didn't.









The next photo shows a cross-section of the fin. If you look carefully you can see the ablative char layer, then the ablative unchared, carbon and finally G10.



There was some interesting case discoloration just in front of the fin can transition (possibly a localized hot spot?)



Here's the nose cone. It did suffer some damage from the landing but that was kinda expected. All the paint was cooked off.



And here's a close up showing the char layer on the nose as well



The nozzle worked great, Butalane's design held up well

Wow! You know you went fast when Friction cooks your Fins! :y: Holy Crap!

Copy of the GPS data plot

Well, not sure if anyone is following the thread...but if you are, we also go some onboard video! The rocket is moving around a lot the whole flight, but there are some cool freeze frames and you can see the fast liftoff!


[YOUTUBE]7BELQLjgOrU[/YOUTUBE]

tfish said:

Confucius say....."motor that works always outperforms one that burns a hole through side!"

Tony

Click to expand...

Tony,

This was actually considered when we turned down the motor casing. Although I don't know the thermal diffusivity of Al off the top of my head, we were slightly concerned that the reduction in thermal mass of the motor case would affect the temperature, our material properties and most importantly our material properties. On HB1 the bottom half of the liner was charred to ash and almost completed gone from the motor. Although this is a low solids, low aluminum propellant, the thermal effects were still a bit concerning. We bonded the grains in with some high temperature material and took some extra precautions at the grain interfaces to ensure there was plenty of thermal protection for the case. Upon inspection we found the liner to be fully intact, and to be charred very little. So, in increasing thermal margins we took a hit on burnout mass . Looks like we need more aluminum!

I will try to snap a picture of the liner.

Oh MAN that was a sweet boost! Like you said, you can really see the progressive profile. Wicked fast too. :grin:

Thanks for sharing!

Edit: Max Speed?

Alex

Pyramid lake at 57sec!

Aksrockets said:

Edit: Max Speed?

Alex

Click to expand...

Hey Alex,
Unfortunately our altimeter didn't record the data onto the sd card correctly (even though the sd card was installed correctly and the altimeter was potted for high g flights) so we don't have the flight data in a readable form, just a 2mb junk file :bang:. Luckily the altimeter fired the charges correctly but for our next flight, an improved altimeter that can handle the acceleration is a must. The only data we got was from the big red bee gps so we have altitude.

The altitude was within 2,000ft of the RasAero sim which predicted ~Mach 3 for top speed. That seems pretty reasonable to me.

Awesome rocket and flight, fantastic writeup!

I think we've talked about this in email or PM or something already, but the charring on the fins looks like it's the effects of the conical shock from the fincan lip washing over the fins themselves; the pressure transient in the shock alone would be enough to make the fin erode more severely at that point.

I'm tempted to say that right down at the fincan lip, the conical shock might have transitioned to a bow shock ahead of the lip edge by a centimeter or so, depending on the turbulent layer thickness there; would that explain the aluminum discoloration? I had similar discolorations in my 7075 body tube on BN, ahead of the threaded transition to the motor case (there was a slight, <1mm seam between the two parts because the CTI case had rounded edges).

I didn't have similar discoloration of the case ahead of the fincan on mine, but the scalloped fincan probably prevented any steady shocks from forming, and the CTI case anodizing would have prevented the discoloration.

Nice job on the fins! I'm very curious to hear more about your room-temp cure ablative; it clearly worked well, since the fins are still smooth, and the aeropoxy-only CF is intact. This result makes me rethink composite fins for an N5800 flight...


Also, re: case thickness; the CTI 6GXL case is 0.125" wall thickness nominally. Actually it's a few mils thinner (of actual aluminum) because of the anodizing, and it measures to about .129" (because of the anodizing).

Very nice stress test of materials. Thanks for sharing.

and heres another flightline video
https://www.youtube.com/watch?v=qFDihljhH8s

select 'original' to view in 2.7K quality if desired. load time will tank. most displays cant do it anyhow. but its there.

Awesome flight!

Thanks for posting the video!

That video sure did get up quickly to where the air is dark

No wonder you scorched the thing

Being out at the away cell seeing this thing launch was seriously so sick. I was so pumped that I think I screamed louder than both of you guys haha. I don't think most people understand what an accomplishment this flight was, if you had flown any cti 6gxl load this thread would be 3 times longer with replies. It's great you both are sharing the details of the construction too, good ideas. The only thing that sucks is that you bested my 98mm minimum diameter rocket by ~700'! Lol once again great flight guys.

I'm very impressed, if I didn't make this clear. =p

I've got a question, though. You said something about the "arming wires" being passed through the nose tip? what on earth are you talking about?

Thoroughly impressed. Honey Badger doesn't give a s**t! It just flies faster than a bat out of hell into dark space!

Thanks James! Btw, we decided on the fin shape because of your flight last year, makes a big difference!

"arming wires" being passed through the nose tip

Click to expand...

Our nose tip was threaded so we could retain the avionics bay via a piece of all thread. We were about to drill another hole in the nose shoulder for the arming wires but then realized we had a big hole up front if the tip was off So we loaded the rocket on the pad without the tip on (wires hanging out of the front part of the nose), armed the altimeters, then screwed the tip on.