Saturday, July 31, 2010

The EGE talks about what you're interested in.

Aside from the questions, there are clearly some thing you want to know about. I'll do my best to deliver:

July 10th: "Aerotech G71 vs G77":

The G71 and G77 are fairly similar motors. Both are Redline motors, with the awesome laser-red flame.

The G71 is a reload for the 29/40-120 hobby case. Its impulse is 107 Ns, at it contains 56.9 grams of propellant. It comes with delays of 4, 7, and 10 seconds.

The G77 actually comes in 2 slightly different styles. One is a reload for the 29/120 case (different from the 29/40-120). It is 105 Ns, with 58 grams of propellant and available delays of S (6 seconds) and M (10).

The other is a single-use motor, available in preassembled and loadable (different from reloadable) varieties. It contains 58.1 grams of propellant which generate 102.9 Ns of total impulse; available delays are 4, 7, and 10.

The bottom line: If you have the 29/40-120 hobby case, use the G71R reload.
If you have the 29/120 case, use the G77R reload.
If you have neither, use the G77R single-use motor. Choose the loadable variety if you want to save money and don't mind spending a few minutes building the motor.

July 12th: "best glue for ttw fin fillets mid power high power hpr rocketry":

Are you using fiberglass? If so, use epoxy.
Are you using carbon fiber? If so, use special high-temperature epoxy for carbon fiber.

If not, it depends on the application. For most uses, wood glue is excellent. It bonds excellently to paper / cardboard and all varieties of wood. It's incredibly strong, safe, and easy to use. It's cheap, sands well, and you can spread it into fillets with your fingers. It's slow to dry, though.

For attaching plastic, fiberglass, carbon fiber, metal, Blue Tube, or Quantum tube, epoxy will work better. It dries quickly and attaches almost everything. But, it'll stick to you, and it can cause allergies, so use *nitrile* (not latex) gloves.

A good compromise for larger rockets that need a lot of strength may be epoxy clay. It sets up rock hard, gives you plenty of time to precisely shape your fillets, and attaches anything. But it's expensive, and too much will be heavy.

July 12th: "blue thunder propellant formula":

Blue Thunder is a high-solids blend that burns very efficiently, with little smoke or colored flame. This indicates that it's almost pure ammonium perchlorate / aluminium blend, with few additives. I know very little about motor making; this site may be of help.

UPDATE: Thanks to Ken Kzak:

Blue Thunder is a high-solids blend that's mostly ammonium perchlorate and binders (PBAN and HTPB). Wikipedia gives one common recipe for high-performance, low-smoke motors as around 80% AP, 18% binder, and 2% metal. For Blue Thunder, that metal might be aluminium, magnesium, or copper.

July 13th: "rocksim file for madcow 2.6 patriot high powered rocket":

Madcow are awesome folk; I highly recommend their kits. On their page for the 2.6" fiberglass Patriot is a convenient link to the Rocksim file.

July 29th: "wisdom is knowing that you'll be an idiot in the future which qc comic":

Number Nine Hundred Seventy-six.

For the future, Ohnorobot is extremely useful, and searches over 100,000 panels of over 1700 comics.


Laura said...

But I'm NOT interested! Can't you talk about Firefly or Doctor Who or how amazing your friend Laura is?

KenKzak said...

Re; Blue Thunder recipes.
They do use high solids loading but mostly AP and binders, with minor percentages of copper compounds and chlorine donors to produce the blue coloring, little or no Aluminum at all.
Aluminum raises the combustion temp AND brightens [whitens] the flame, typically consuming or paling any color production.

RE; Epoxies for large jobs. Rather than epoxy putties, which are IMO not the best at bonding, and hard to feather like at the edge of a fillet, it's better to start with a medium to long cure structural epoxy, then add a sandable lightweight filler to thicken it to suit each particular job. I mention longer cure times because there is extra mixing time required and once the filler is added the epoxy seems to have more trouble shedding byproduct heat, therfore cures noticably faster.

KenKzak said...

I agree with Laura, let's hear more about Laura.
Do you think she would be a good Spunky Lab Assistant?


The EGE said...

RE: lab assistant: Prolly not. All the sciencey parts aren't so good. Laura's awesome and all, but the only science she's got much interest in is forensics.

RE: Blue Thunder: Never knew that. Will add that to the post.

RE: epoxy clay: The clay I got from Apogee bonds well and is easy to fillet. What kind did you use?

RE: Laura: Eventually. There's maybe a post about Firefly coming. And I'm not interested in Doctor Who.

KenKzak said...

After plowing through a dozen or so BT recipes I found only one with 2% Alum, one other with similar Mg. Aerotech BT recipes may differ though.

I don't remember the epoxy putty I had, but it wasn't a hobby brand, so was probably lumpier stuff.

Forensics is good. Figuring out why a rocket or other project went wrong is often more interesting than getting it right the first time.
"Sifting the clues."

I used to watch a lot of Dr Who 20+ years ago, haven't seen the newest Doctor. Haven't seen Firefly either, but I'm curious.


The EGE said...

I've done a lot of analysis on what went wrong. On ver few occasions have I been unable to figure out what the problem was.

If you've never seen Firefly, what have you been doing with your life?

KenKzak said...

Living a life without cable TV, or a cell phone for 7 years or so.
It allows more time for music, motorcycles, and womens. Epoxy and power tools too.
I still watch plenty of CSI and NCIS type programs plus movies on VHS/DVD.