Big Ugly Bug II (BUB2)

Big Ugly Bug II (BUB2) is my third scratch-built model rocket, and my second high-power model. After the Big Ugly Bug splattered itself all over the NDRA launch site at Ulland Park, I was a bit discouraged. I stuck with Estes model rocket kits and a few flights with a composite 24mm motor for a while. Eventually I got the bug again, and decided to build my largest high-power yet. Naturally, a scaled-up Mosquito isn't what you'd think of when you think high-power, so naturally that's what I decided to build.

This time I decided to go with commercial rocket parts, since they would be lighter than building my own, and make assembly go more quickly. I still have to fabricate a nose and fins though.

Update: March 3, 2002
BUB2 is now complete. For fin fabrication, I finally settled on using foamcore fins, which were laminated with fiberglass and polyester resin. These were sanded to shape, then the edges filled with auto body filler and sanded to round. Here is an image of the parts before the fins were fiberglassed:



I used through-the-wall mounting to attach the fins to both the body tube and to the 29mm motor mount. After the epoxy had cured I filled the space between the motor mount and the body tube with two-part expanding foam. This adds weight but strengthens the fin mount considerably.

I was planning on fabricating a nose cone for this rocket as well, but a friend in the Fargo rocket club sent me a link to ScotGlas, which makes (among other things) 4" diameter up-scale Mosquito nosecones! The $30 pricetag looked like a better bet than hours in the shop, sanding more fiberglass, so I bought one.

I was planning on painting the BUB2 blaze orange, like the BUB. Blaze orange looks a lot better with a bright yellow undercoat, so after applying grey auto primer and sanding, I put the yellow on. However, I decided I liked the yellow so much I skipped the orange. Here is the rocket after painting:



I left the nose unpainted, at the request of other club members. They want me to put a strobe light in it if/when we ever have a night launch.

In the photo you can see through the nose the dowel I epoxied in to have a place to put a screw-eye to attach the shock cord, and also the 8oz. of lead shot I had to add to move the center of gravity to the correct spot for flight stability. I added a 24" diameter nylon parachute, about 20' of shock cord, and a Nomex pad in place of wadding.

I used VCP to calculate the center of pressure on the rocket, and had to add the shot to achieve one-caliber stability. The completed rocket weighs 2 pounds, 8 oz., and a simulation on wRASP predicts a flight to just over 1000 feet using an Aerotech H128W. This will be the setup for my NAR Level 1 certification attempt, which I will try for this spring.

One more picture of the BUB2, as part of the "Rocket Garden" display by our club at a mall show in Moorhead, MN:




Success!!!

On Saturday, March 23, 2002 I made my NAR Level 1 certification attempt. I launched the BUB2 on an Aerotech H128W loaded in a Dr. Rocket 29mm 180 casing (had to borrow the 180 tube from another flier, thanks Mike!). The BUB2 was the first certification flight of the day. It launched with a nice, bright white flame and weathercocked only slightly. The medium delay was perfect, the 'chute deployed, and the rocket landed about 200' down range from the launcher. There was some slight damage to the paint and one fillet was cracked, but the rocket was still flightworthy so the certification group signed off on the flight.

Failure!!!



The BUB2 suffered a catastrophic fin failure flying on an Aerotech H180W. Here's the gist of what happened, cut and pasted from an email I sent a fellow HPR enthusiast: 

Date: Saturday, April 20, 2002
Subject: Big 'skeeter blues...

(snip)

        On launch, the BUB2 weathercocks slightly and heads to the
north-east, just like my H128W certification flight.  The bright yellow
rocket is roaring along, spouting a white flame as long as the body
tube, when suddenly, just before burnout and maximum velocity, something
goes catastrophically wrong.  In the blink of an eye, where there was
once a cool-looking rocket flying nicely, there is now a huge cloud of
bright yellow debris, fluttering slowly down towards the ground.  The
majority of the rocket looks to be still intact, the body tube and nose
still attached and the parachute deployed.  The black nomex pad has ripped
away and settles to the ground along with all the other shreds.

        What happened?  Theories are many, but here is what I think
occured:  On an earlier flight the BUB2 slightly damaged two of the
fins near their root edge.  I repaired this with CA adhesive, and it
may or may not have had a role in the failure.  A simulation of the
BUB2 on an H180W motor predicts a maximum speed of 257 mph.  Since the
failure occured close to burnout, I suspect that the long, relativly
flexible fins started to flutter at this speed.  This caused all three
fins to delaminate, shearing at the foam core (the autobody filler
caps didn't lend much strength, they were mostly for aerodynamics).  The
unsuppored fiberglass skins now underwent flutter and tore away from the
rocket body.  The sudden deceleration this caused made the ballasted nose
seperate from the rocket body, pulling out the recovery system which 
deployed at probably better than 150 mph.  That in turn caused the
non-stretchable nomex to tear away from the shock cord.  The cord and
parachute, being stretchable nylon, had enough give to absorb the 
sudden shock and stayed together, allowing all the 'expensive bits' to
come back to the ground relativly undamaged.  In fact, all that really
was destroyed was the fins.  Unfortunately, they were the only components
I designed and fabricated from scratch.  Oh well, lesson learned.  I'll
have some images of the shredded rocket on my website soon.


Oh well, some days you get the bear, some days the bear gets you.