My quest for an O motor launch.

[Bat-mite]

Can't at work

You can also see them lying on the ground in the parts picture.

 

[neil_w]

 

[Nytrunner]

I must admit the thought of giant STOP sign halves as fins (fiberglass of course) does amuse me

They'd even blend in to the color scheme

 

[boatgeek]

You might consider painting the entire fin area black from the leading edge of the fins to the aft end. My thinking is that it's nice to have the aft bulkhead itself painted black since it gets sooted up anyway. If you do that, there's a lot of fiddly masking to get the red stripe and black fins, which could all be saved by going all black. I'm in the same camp as you on finishing, though I usually use real primer followed by top coat. On the other hand, go ahead if you want to do the masking.

 

[Bat-mite]

Thanks, Neil. I think that looks pretty nice.

That red part at the aft end is actually going to be a red aluminum thrust plate, which I am cannibalizing from my Formula 200. In the OR file, I just combined the thrust plate with the motor retainer to keep it simple. I also probablywon't paint the aluminum tip of the NC, either.

 

[neil_w]

I must admit the thought of giant STOP sign halves as fins (fiberglass of course) does amuse me

For anyone interested, see it here.

 

[Bat-mite]

Cool. But I don't want to stop. I want to GO, GO, GO!

 

[Bat-mite]

Baby steps. Had a short work day, so I got a little done.

I washed up the AV coupler, switchband, and bulkheads, then marked where I want the switchband. Will be shorter in the booster end to help make room for the drogue.



Sanded between the lines and inside the switchband.



And washed up the rest of the parts, minus the payload tube with the stuck 12" coupler. Still need to work on getting that thing unstuck.



RocketPoxy will arrive tomorrow, so I can't put the band on yet.

 

[Bat-mite]

Thoughts?

 

[neil_w]

Is that more of a magenta than a pure red? I like it.

It looks very nice as is, but to my eyes there's something not quite right about the roll pattern. I can't put my finger on it. Maybe needs something else near the nose cone to balance it. If I can come up with anything more specific I'll let you know.

But again, if you built that as shown it would be very nice.

 

[boatgeek]

Nice! Are the black stripes on the roll pattern wider than the silver stripes? If so, that might be what Neil was seeing.

That's a heck of a long nose cone. Can you stash a body in there?

 

[pondman]

Awesome! The O motor will do it proud.

 

[Bat-mite]

Is that more of a magenta than a pure red? I like it.

It looks very nice as is, but to my eyes there's something not quite right about the roll pattern. I can't put my finger on it. Maybe needs something else near the nose cone to balance it. If I can come up with anything more specific I'll let you know.

But again, if you built that as shown it would be very nice.

The actual color will be Colonial Red, which can be seen in its exactitude in the Radial Flyer photo here. The roll pattern is greatly affected by my OpenRocket skills, and is really just kind of like thinking out loud, so to speak.

A quick calc of pi * d gives me 25.14 of circumference. If I did 12 stripes (6 black, six silver), they would be about 2.1" each. Still thinking, and open to ideas.

 

[Bat-mite]

Nice! Are the black stripes on the roll pattern wider than the silver stripes? If so, that might be what Neil was seeing.

Probably. I was not being meticulous, but see above for the actual plan.

That's a heck of a long nose cone. Can you stash a body in there?

Maybe not a human body. Mwah-ha-ha-ha-ha!

 

[Bat-mite]

Awesome! The O motor will do it proud.

If I don't destroy with the M motor shakedown flight first. Wouldn't that be a hoot?

Thanks!

 

[Bat-mite]

BTW, 2 quarts of RocketPoxy, four 8g Rocket Junkies charge wells, some Doghouse wiring, and two Aerocon key switches have arrived. Time to get down to business.

 

[Bat-mite]

Hmm, even after all these years, I still get over-excited and do dumb things. I bought four (expenses) aluminum charge wells with 8g capacity; however, I had not actually calculated the charge size for the booster.

88" total - 29" from top CR - 8" AV bay intrusion = 51"

51" X 7.75" ID @ 12 psi would require a charge size of a whopping 14.9 grams!

Now, I know the motor will consume a good bit of space, and 12 psi might be too much. My Formula 200 has 18" of volume in the booster, not including motor displacement, and I am good with a charge force of 6.4 psi. That would bring the Performer 200 booster charge back to a measly 7.95 grams.

I guess I will ground test with 8g and see where it goes. If I need more than that, I guess I may have a couple of nice 8g aluminum charge wells to sell on the cheap.

 

[Nytrunner]

What's the diameter of your charge wells? You could JB weld some copper pipe extensions to them if necessary, although 10 psi on your airframe cross section is a lot of force and you could probably get away with smaller charges

 

[Bat-mite]

What's the diameter of your charge wells? You could JB weld some copper pipe extensions to them if necessary, although 10 psi on your airframe cross section is a lot of force and you could probably get away with smaller charges

They're about an inch, details here; https://rocketjunkies.com/product/8-gram-aluminum-charge-wells/

I don't know if the 1" is ID or OD.

 

[mccordmw]

14 g? That seems like a lot. My 8" diameter L3 had long sections and needed something like 5 g.

At 10 psi, an 8" diameter surface has an area of 50 sq in. That would take about 500 lbs of force. Even with 3 x 80 lb shear pins, you are 2x more than needed.

Or am I miscalculating? I'm at a bar on Blue Moon number 2.

 

[mccordmw]

Here's what I had frim my L3 documentation.

Charge calculation
https://www.rimworld.com/nassarocketry/indextools.html


Lower airframe: 8" x 28"

Desired pressure: 5.7 psi (250 lb force on bulkhead)

FFFFg BP: 4.1g

Shear pins (4-40): 3 (@ 50-76 lb shear strength = 225 lb max)


Upper airframe: 8" x 28"

Desired pressure: 5.7psi (250 lb force on nosecone base)

FFFFg BP: 4.1g

Shear pins (4-40): 3 (@ 50-76 lb shear strength = 225 lb max)

 

[Bat-mite]

I need to pressurize 8" X 51". That's almost double your volume.

 

[LawnDart2020]

I recently launched a 4" FWF rocket that had good ground tests, shear pins sheared, nose cone went 20 feet, and kevlar extended. When I launched it, the main charge and redundant charge failed to separate the nose from the payload and it came down under drogue only (about 60 fps). I asked someone and they didn't seem surprised that it didn't work, because "on the ground isn't the same as in the air". They said that they use a gram per inch of diameter in FWF, and more for long sections. You're not going to hurt the airframe within reason, so better safe than sorry.

 

[Nathan]

15g of BP is probably too much. The enclosed payload tube of my Frenzy XXL is 8" x 44". I use 5.5g for primary charge and 6.5g for backup charge. Have flown it 3 times so far with no problems.

 

[Bat-mite]

15g of BP is probably too much. The enclosed payload tube of my Frenzy XXL is 8" x 44". I use 5.5g for primary charge and 6.5g for backup charge. Have flown it 3 times so far with no problems.

Thanks. Like I said, I'll start at 8g to test, and hopefully work down from there.

 

[Bat-mite]

neil_w was kind enough to try out a whole bunch of roll pattern designs for me, and I think I am going with this.

Thanks, Neil!

 

[neil_w]

Happy to help! Let me know if you need anymore fiddling.

 

[G_T]

You can pick up charge wells for larger rockets in the plumbing section of a hardware store. Your choice - copper pipe end caps or PVC ones. Bolt through the cap to a solid bulkhead, and run a wire through the side.

Gerald

 

[Bat-mite]

Got the switchband epoxied onto the AV coupler, and two 3/4" switch holes drilled, as well as three 1/2" vent holes. Taped her up for painting, but then a thunderstorm came in. No paint tonight.

Sadly, due to stupidity, my switch holes aren't even. Sigh.

 

[Bat-mite]

Ready for paint.