Heroes del Fuego

[Oliver Arend]

Due to "popular demand" in my rocket statistics thread, here is a bit of information and a couple pictures of my newly nearly-finished "Heroes del Fuego".

After a couple of years spent abroad, without building rockets, I finally got to finish a rocket whose construction I started before I left to France -- well, about one afternoon of work is still missing.

The original idea was based on a discussion with Swiss rocketeer Andi Wirth, whether it was possible to build a rocket whose burnout would be at apogee, using Held 1000 engines (these are German engines relating to a C2-0, with the usual black powder peak early in the burn). After a couple of simulations I found: a 300 g rocket using nine Held 1000 ignited in three groups -- first 4 of them, followed by 3, and finally 2 more Helds -- would have about 16 s of burntime and reach apogee at 230 m, maxing out at 21,6 m/s (yes, ~70 ft/s). Concerns relating to safety (extreme burntime, very low speed) and weight -- 300 g given the size is very low and tough to obtain, 9 Helds need about 70 mm of body tube diameter -- made me change the rocket into a simple one with all 9 engines igniting at the same time and electronic recovery using a MAD device.

The name is a mix of the rocket engine's name ("Held" means "hero") and the Spanish rock group "Heroes del Silencio".

A Catia model looks like this:
[attch1]

You can recognize the ogive nosecone up front, a very long and empty tube, containing the parachute and plenty of hot air, a bulkhead, the electronics board and the transition from small to large diameter. The e-board and the forward bulkhead will be glued to the transition, whereas the long tube will be slid onto these and connected to the transition with screws. The parachute will eject at the nosecone.

The aft part holds the three fins and the motor mount. The latter consists of four bulkheads in total: the most forward (in direction of flight) is solid and serves as thrust bulkhead. The one right next to is has 9 holes for the engines, and the last but one also has these 9 holes. These three are glued into the rocket; the last bulkhead has smaller holes that only allow the exhaust gases to escape, serves as motor retention and is connected to the 3rd bulkhead by two screws.

[attch2]

Oliver

View attachment h9_1.JPG

View attachment h9_2.JPG

 

[Oliver Arend]

The completed rocket looks like this:
[attch1]

The fins didn't get the sweet beveling shown in the Catia model, but are simple 3 mm balsa boards with 50 g/m^2 glass on each side. The body tubes are 0.8 mm balsa boards on 75 resp. 50 mm PVC tubes reinforced with 50 g glass on the outside. The grains run lengthwise. In hindsight, using spirally wound balsa and glass on both sides could significantly increase strength and etch a bit off the weight.

[attch2]

The transition and thse nosecone were turned by Paul Stania and received a layer of 25 g glass to protect the balsa from dents and scratches on exposed surfaces. The shock cord has not been attached yet and runs between two eyebolts, one epoxied into the NC, the other glassed to the inside of the transition. I didn't find any smaller bolts at the hardware store.

[attch3]

A view of the business end, you can recognize the motor retention bulkhead and the two M3 screws. The last but one bulkhead is recessed pretty far into the BT, otherwise you wouldn't get the engines in or out properly. The whole system still works. Railguides were screwed and glued into the fixed bulkheads.

The fins are attached with 5 min-epoxy on the inside, the fillets are made of 40 min-epoxy with cotton flox. The fin attachments seem a lot stronger than the body tube.

The motor mount in detail:
[attch4]

The guts of the rocket are made of a 3x1 mm balsa sandwich board with four 25 g-glass layers and a 2x3 mm balsa bulkhead with 50 g-glass on each side. The nut on the left is used to attach the forward BT to the rest of the rocket. The board provides space for balsa block holding the control LED and the arming switch for the MAD. The female connector is attached to the rocket (via the wires), whereas the MAD is sitting on brass threaded rods. The four holes in front will be used to attach a 9V battery with cable ties. If the rocket should come in ballistic, the heavy battery won't destroy the electronics. The cable ties would also permit to use a board with a 12V-battery and a 9V connector.

[attch5]

The igniter wires are led through two holes in the bulkhead to a terminal strip. The ejection charge will be installed together with the igniter, there is not enough space for a canister anyway. The whole thing is not 100% gas tight, but an MAD device is less sensitive than a barometric altimeter.

The shock cord will run below the board (eye bolt not visible).

With the forward BT attached it looks like this:
[attch6]

On the bottom the arming switch, the control LED port on top, and the screw connecting BT and the rest of the rocket on the left. A countersunk screw doesn't really make sense in a 1 mm wall, and since my finishing leaves a lot to be desired, the cD doesn't matter either.

Oliver

 

[Oliver Arend]

one more attachment

 

[Oliver Arend]

What's missing to make this a ready-to-fly rocket is the shock cord with parachute. I will be using a Rocketman drogue from my yet-to-be-built DD MiniBBX.

I'll also have to figure out the ejection charge size. I will play with NC powder a bit, if it doesn't work I'll have to use black powder.

A flashpan has already been made, but I don't have any pictures right now. It's basically 9 wells holding black powder for each engine and small channels connecting the wells. An e-match will be put into the central well, and a board with a hole for each engine will be attached to the block with a gap of about 2 mm, for any excess pressure to build off.

I've already learned a bit from the construction:
1. The engine mount without tubes or similar guides doesn't really make sense.
2. "Slide tube on, screw it tight" is simple (installing the battery, the igniter and the ejection charge), but more complex electronics and especially those requiring gastight installation, will make me rethink this. But most rockets using this kind of electronics will be bigger.
3. Balsa-glass-sandwiches can be made stronger and even lighter.
4. I'm afraid of zippers in the fwd BT, but one or two layers of 25 g-glass should do it.
5. I should put more though into the installation of electronics and switches before construction.

A couple of numbers:

Length: 1.47 m
Diameter: 77/52 mm
Mass (like on the pictures, that's without shock cord, chute, engines or battery): 338 g
Estimated launch mass: 600-650 g

The wRASP simulation uses 420 g empty, thats 618 g at launch:

Max. accel.: 11.2 G
Velocity after 2 m of rail: 17.3 m/s
Max. velocity: 58.3 m/s
Apogee: 323 m
Time to apogee: 9.8 s

Oliver

 

[cls]

Oliver, interesting project and very nicely built! thanks for sharing, we enjoyed your photos. Those C2 motors sound, umm, a little bit interesting, but ultimately difficult to use.

 

[Oliver Arend]

The Heroes del Fuego flew this weekend at ALRS in Switzerland. Using a flashpan-like contraption I was able to ignite all the engines, but it seems the small distance between the rail guides increased friction on the rail so the already low thrust peak was completely lost on the rail. The rest of the flight -- five seconds! -- was low and slow. The Dentamag electronics ignited the ejection charge right at burnout when the rocket started to go horizontally. Damage is a few mm of zipper on the top end of the body tube and a totally charred retention bulkhead. I will have to replace the latter by a metal one.

I attached two pictures taken by Olivier Timper right after ignition and just off the rail -- notice the difference in flame (and thus thrust...).

Oliver

 

[Balltip]

That looks fun! I have been looking at those Held motors but have yet to order any. Would be really nice to get a rocket glider for those.

Did you have great time at ALRS? We did not go, but plans have already been made to go next year! We're planning on driving down, and combine ALRS with a trip to Italy!

 

[Oliver Arend]

> Did you have great time at ALRS? We did not go, but plans have already been made to go next year! We're planning on driving down, and combine ALRS with a trip to Italy!

ALRS was awesome this year, great people, great flights and perfect weather. Except the hotel still sucks -- they only have six beer mugs, that were usually occupied by Ze Germans, and are outrageously expensive.

If you're going, talk to Rolf Örell; he may appreciate having a car down there for once ;-)

Oliver

 

[jj94]

Cool, I love the idea of a C2...SAUCER!!! The bodytubes you used are very interesting. I've never seen them made from wood.