Wednesday, July 20, 2016

3-D printed Saturn V build notes, part 3

Well, it is all together but still naked:

P1350025The final weight went up as I didn't account for the epoxy in the nose, the shock tether, or the screw that holds the motor retainer/launch lug. I'm not used to worrying about 0.09 oz. It now weighs in at 4.3 oz. I actually did the arithmetic and think this is close enough for a steely-eyed missile man.

Hopefully, I can score a C6-3 and fly next week. It may or may not have any black sections at that time.

Tuesday, July 19, 2016

3-D printed Saturn V build notes, part 2

This is the "well, crap, that ain't supposed to happen" edition.  I proceeded to dry stack the parts, put in a motor, and fill the nose section with 0.8 ounces of lead.  I checked the CG and it is almost as specified in the instructions. It is less than 1/8" of the goal. Well, that's not too bad.

Then I raise one eyebrow as I look at those tiny fins. True scale, no (not 'bo' as originally posted) clear stuff.

Then I weigh it and find it comes in at 4.21 oz.  I check the charts and Estes launch weight specs and find this doesn't leave the proper thrust-to-weight ratio and exceeds Estes' recommendation. hence, the "well crap" status.

What's an extra 0.21 ounces anyway? Where are my B14s?

3-D printed Saturn V build notes, part 1

I started by dry fitting all the parts. The fit of all the ABS-on-ABS joints is a bit rough due to the surface finish but are not too snug. I may sand the nose cone shoulder to make it smoother. The motor retainer required some Dremeling to allow a C6 to fit well. I also had to grind the inside of the motor mount near the motor block.

I was worried about the thick motor mount but, barring cutting the entire middle section out, I can't see that I could save that much weight. I drilled one big hole in the middle and discovered what I should have realized - that the structure is basically hollow. So, it is now attached with 5-minute epoxy.

My next worry is how the ABS will handle ejection gasses. I could ask on TRF but decided to put a cardboard buffer in the lower body. The ID is almost 29mm so I cut a short piece from a thin wall tube, sectioned it, and slipped it in.

BUT, what is really scaring me is the prospects of painting this thing. Even if the smooth body sections were sanded smooth, much of the painting is on ribbed sections. These will be hard to mask.

Monday, July 18, 2016

Next build: Boyce 1:312 Saturn V

For quite a while I've been wanting a 3-D printed rocket. I have generally thought they are too expensive and a couple of attempts to get economical parts fell through. Last week, however, I learned that Boyce Aerospace Hobbies is back in business. And they are offering 3-D printed scale rockets! What interested me is their line of 'mini' kits. These range in price from $11.59 to $23.00 and seemed like a good way to experience a 3-D printed kit first hand. I opted for the big expensive one - a 1:312 scale Saturn V that is just over a foot tall and flies on a C6-5's.

The kit consists of nine printed parts, including a nozzle unit for display. The escape tower is merely a section of wooden dowel. You have to add a Kevlar shock tether and a parachute.


Assorted musings:

The kit includes a motor retainer with an integral launch lug. That's both useful and it keeps a launch lug off your nice scale model.

As is typical for these things, the surface is rough. I don't think I'll try to sand it smooth. But will make sure everything fits well.

They say to use CA on it - I'm thinking 5-min epoxy, applied very lightly.

The motor mount is very thick. My first thought is that I could drill some holes to lighten it up.

It will require nose weight. They don't say how much, but do tell you where the CG needs to be.

Sunday, July 17, 2016

Rocket launch fix ups in progress

Chesapeake Sea Monster - I cleaned up the torn paper left behind when the rear wing snapped off and filled the exposed areas with Fill'n'Finish. I decided not to re-paper these areas but rather just to fill the grain and hit it with white primer. I am gluing the wing back on with the same Titebond no-drip wood glue that I used the first time. I first thought about beefing up that joint with epoxy or glue rivets or whatever. Then I realized that, if the joint is too strong, it is likely that the wood itself would break. A frangible joint isn't always bad. Glue fillets are drying. Primer tomorrow or the next day.

Big Brute - There was a small ding on the tip of one fin and a big chunk of paint chipped off the cone. The fin is cleaned up and will be touch painted. I waited too long before the two coats of paint on the cone and it crazed. That has been re-sanded and will be repainted in a couple of days.

Jayhawk - Most of the fin joints on the body had some cracks. I treated these with thin CA, did a little filling, and touch-primed them. I will also touch up the color coat with a brush. I'd have to mask a bunch of decals to spray this one. The nose cone is another animal. The two canards are held in place with two dowels that run through the nose cone. One of these snapped off.  I decided to cut the dowels out of the canards and replace them. What a mess I made of them. I contacted Mike Stoop at Madcow and he will send me replacements for only the cost of shipping. What a class act!

Saturday, July 16, 2016

Launch Report 2016-7 (MDRA)

Location: Central Sod Farm, Centreville, MD
Weather: mid to high 80s, humid, mostly overcast, wind 0+
Total flights: Today - 5; YTD - 57
Total motors: Today - 15; YTD - 70
Motors by class YTD: MMX-1, 1/2A-2, A-12, B-2, C-27, D-6, E-8, F-5, G-7

I can't believe it was nine months since I made it to MDRA, and they ordered up great weather for this momentous event. It was too hot but that's what you expect in July!


My Photos

My Flights
  1. Chesapeake Sea Monster on three D12s and eight C6s - Ignitions duties were handle by three soldered igniter assemblies using the old Q2G2's and the club's Cluster Buck. The ground level wind was still and the boost was arrow straight. All eleven motors ignited. Ejection occurred around apogee and it landed very close by. The large rear fin set popped surprise here. There was a little soot here and there, but baby wipes took care of that. I got Peter to shoot video it so that should show up within a few weeks.
  2. Fett Boy on a G74-6  -  Excellent flight with the Chute Release set to @200'.
  3. Big Brute on a G106-7 - Another good flight, with the Chute Release moved up to 300'.
  4. Madcow Jayhawk on a F59-5 - Straight boost, very slow spin (only a few rotations on the way up). The down wasn't so good. It didn't look like the chute had deployed but it was there. Unfortunately when the CR let it go, it tried to open momentarily and then totally collapsed. One cannard broke off and mose fin joints cracked. Thin CA is my friend. I have to think on that cannard.
  5. Hat of Death on a G74 - A crowd pleaser, as usual.

Friday, July 08, 2016

Holy water and the Sacred Wrench of Baikonur

As astra, Kate!

Expedition 48 Blessing (NHQ201607070024)

(Yeah, I know it's not a wrench, but that's what it initially looked like when a small version was viewed.)