Thursday, July 24, 2014

NASA provides 3-D printable models

Via io9, I see NASA has released 3-D printable models of several satellites, a couple of asteroids, and section of the Moon's surface: 3D Models - 3D printable. They have a disclaimer about some of these requiring tweaking by the user and the longest dimension is about 4".  I immediately hoped for models of rockets and rocket-related parts. On their main 3-D Models page, they have various rockets including Shuttles and Shuttle parts. While they eventually make them printable, at 4 inches these would only be suitable for desktop display. I wonder if CAD-enabled rocketeers could take these, scale them, cut them into parts that fit on their printer bases, and add the required motor and parachute holes? In any event, the Mercury capsules might be nice at 4" high:

Wednesday, July 23, 2014

"Terror in the Sky" Airfest (updated with a discussion of tolerances in design)

Braving the 100 degree humiture, I traipsed out this afternoon to a local park to fly a couple of low tech water rockets and my Blade 180-QX Quadcopter. My drone piloting skills suck...hence the name of the 'launch'.

Things started poorly when I realized I hadn't reloaded the battery in my camera. And I had gotten all fancy by bringing out the tripod. Rats!

Water rocket-wise, I mainly wanted to see if the 1980's vintage hand held water rocket, which I adapted to the Quest launcher, would be suitable for the grand rocketeers.

As expected, this small volume pressurized fast with my electric pump.  Faster than I had hoped for. 50 psi was the lowest I could get it and I ran up to 100 psi.  The performance was unimpressive and I am a little scared to run those pressures around kids. So, this will be retired.  At least the old rockets are tough. My kids bounced this one off the pavement more than once before the pump gave out. The new models are not nearly as least not the $2 variety. This was a CATO, not a lawn dart:


I also brought a 1L rocket with the Quest fins and bumper. This is where things went down hill.

I had recently bought some replacement nozzles knowing I was going to chop one up for the rocket shown earlier.  Well, something was up with the nozzle/launcher.  I flew several times at 80 and 100 psi. Most of the time, it wouldn't release without some nudging from my thumb. Not good for seeing the flight or staying dry. Glad I brought safety glasses. Once it launched spontaneously at 100 psi. Then it needed nudging again. I'm going to measure the nozzle and maybe lube it lightly?

At that point, the heat got to me and I scrubbed the quadcopter practice. Probably was a little too windy for this novice anyway.

UPDATE:  Well, I investigated the Quest nozzle issue further. This is all qualitative since I couldn't detect any differences with my calipers. Variations were beyond what I could reliably measure.

  • Original nozzle that came with the kit and is now on the red rocket above.  This is clearly the loosest fit.
  • The one that was on the other rocket that I flew. This was much tighter as it was full seated in the launcher. It slides in and out much better once it was lubed.  Is it loose enough?
  • The second new nozzle that I tried slides in and out easily. Very close if not the same as the original.
  • The third new nozzle was the tightest of all! I removed the O-ring and is was still just as tight. Enter the Dremel. Now that it is ground and lubed it its loose. Loose enough?
It appears there are variations in the molding process, possibly in the thousandths of an inch. My next solo outing will include testing all three of the new nozzles.

Tuesday, July 22, 2014

Cohete Gigante (a.k.a. Son of The Dude)

A while back I bought one of these for the grand rocketeers - $1.50 at Michael's. It is a rocket shaped Mylar balloon. The fins are held on with 2-sided tape. I glides pretty well and is indoor safe (i.e. light). On the drive home the gears spun up to speed and I decided I wanted one for my own devices.

When I got mine, it was on sale half off. I fashioned a card stock and foam board mount with a 24mm motor hole. This slides on the back end and holds the fins. The thing is so light that this extra weight brings the CG to almost the middle of said motor mount assembly. Per Rocksim, I needed about 2.5 oz to get it stable. To this end, I poured lead shot along strips of duct tape, folded them over and taped them to the front. The resulting 42" long, 4.5" diameter rocket comes in at about 5 oz unloaded.

This real time build is not iffy. I wanted to fly this on a mild D5 but it it a tad heavy and draggy. I'm worried the the Mylar body will buckle under even a D12. Then it is now nose heavy enough to lawn dart. I may yet try the D5 and see what happens. It will fly off a high power pad.

Local Nike Ajax display

The attached photo is the upper stage of a Nike Ajax, which is on display at a local high school. They are the "Rockets', due to a Nike Ajax battery that was located nearby. When the school was rebuilt, the missile was removed and refurbished. A shop class painted it the school colors vs. its natural scheme. I don't know if the missing fins are due to vandalism or just to make mount it easier. I don't remember how it was mounted before it was relocated.

Wednesday, July 16, 2014

Estes Mega Mosquito, Steam Punk, Forward Mounted Canted Cluster build thread, part 5

Spent yesterday cutting cardstock, placing stick on rivets, and add other missile-aneous trim. I could add more but I want to have it ready for the next MDRA launch and want to take advantage of today's sun for painting. Hope to get it all primered up today. I'm mostly happy with what I did but there is one tube that looks kinda funky. Oh well, it is what it is and that's all it is.

It weighs 12.6 oz w/o motors and with E9's and a 24" chute the CG is at the leading edge of the fins...pretty much where the unloaded CG of my 29mm version is.

To take a rough stab at delay selection, I totaled the thrust, avg and total, for 3xD12 and 3xE9, derated it for the cant angle, and picked a motor that was close to the resulting pseudo-motor. This was loaded in the 29mm Skeeter's Rocksim, the mass was adjusted for the actual rocket weight and the difference in motor weighs. D12-5's and E9-6's should be close enough.

I will decide depending on the wind on launch day.

On the first coat of primer, I was happy with the overall trim job (although it doesn't hold up to Fatboy's Spitfires). However, there are lots of bumps that will never be removed. Hope the Krylon hammered paint looks really hammered!

Today in history, a roar and a boom

Apollo 11 launch, July 16, 1969

Trinity Test, July 16, 1945 (via Wikipedia)

Tuesday, July 15, 2014

Estes Mega Mosquito, Steam Punk, Forward Mounted Canted Cluster build thread, part 4

Well, here are the major pieces dry fit. I reviewed the ongoing steampunk build threads including those by TRF members FayBoy and bill2654 and am doubting my resolve to stempunkify this thing. Their work has blown my mind, man!

PS - IMO the retainers and mounts look fine now that the fins are on...