New 102mm project - Chimichunga-I

[jqavins]

Yeah, that could work.

 

[snrkl]

Update: the pvc jig I built didn’t work - the mosquito net needs to be HARD up against the surface to work, and needs to stay there for 15-20 minutes till the paint gels.

I ended up abandoning texture between the fins on the can, instead just painting it red.

A little of the texture is still visible through the respray - I’m not too worried about it.




All the masks removed at the 20min mark and I’m reasonably happy with the finish.

 

[snrkl]

Stacked up:

 

[snrkl]

Decals meeting me at the field on Sunday...

Tomorrow night, last checklists and tests...

Sunday, maiden flight...

 

[Andrew_ASC]

Beautiful.

 

[jqavins]

That is one pretty, pretty rocket.

Wishing you calm winds and clear skies. May she fly straight and true, and come down soft!

 

[OverTheTop]

Nice outcome snrkl. You must be happy with that. The decals should really make it sing!

Good luck with the maiden flight(s)

 

[snrkl]

Ah... final weigh in came out at 600g heavier than OR predicted. Not unusual but unexpected. I’ve been weighing as I went and unfortunately had the “with motor” figure in my head, so didn’t think anything was amiss.

Impact: 2100ft to 1600ft and a 5.41:1 thrust to weight ratio off the pad...

Low and slow she’ll be on the I175 tomorrow. Low and slow...

 

[snrkl]

 

[OverTheTop]

NICE!!! Don't those decals make it spectacular

Did you get it off the ground, other than on your foot?

 

[snrkl]

Much hassle - I discovered on the rail that my rotary switch was cactus.

3 attempts to troubleshoot - working fine on the table, re-install and not working on the rail.

Ended up replacing the functionality with a twist and tape made from an old igniter lead...

Three trips to the pad and finally got it up.

Long story short: we popped main at apogee.

Three possible causes:
1) I realised I didn’t ground test with nosecone electronics installed, so there was more mass in the fwd section.

2) I had trouble accurately measuring 0.93g of 4F black powder in the field - the high accuracy digital scales were wavering with the wind. I had to settle on an average one 1g

3) If the motor eject went early, it could have all gone bad.

My operating theory is - likely a combo of all of the above - the A3 track support motor eject going way too early:
View attachment 361311
View attachment 361312

Plan to refly the same motor with accurately measured 4F BP charges next time and removing to motor eject charge.

 

[snrkl]

Reattaching A3 pics as the forum seems to be marking them as access denied for some reason...

 

[snrkl]

DHBARR: did you see the “deadpool-esque” solution to the nose cone paint incident?

Just cover it with a “Maximum Effort” sticker...


#minimumEffort

 

[dhbarr]

Amazing choice, looks great!

 

[Steve Shannon]

I’m completely impressed!

 

[jlabrasca]

Learned more strine today. From context, "cactus" ="fubar"?

Very pretty. How did it look going up?

 

[jqavins]

When it doesn't go as planned, it's a learning experience. When the learning experience doesn't damage anything, it's a win. So congratulations.

How did the sims match up to the actual apogee with the measured full-up weight? Since it was over the anticipated weight, mightn't you want to have a fresh look at motor selection for next time? You could compare the predicted to achieved apogee with this motor and use that to adjust the Cd, then sim with some others.

I'm not saying the same motor is a bad choice - I really have no idea - but this does look like the time run more and updated sims before spending the money.

 

[Nytrunner]

I'm trying to parse cactus too.

Switch wouldn't work......switch betrayed you.....are cactuses known for betrayal in Australia?
Is it related to the feeling of sitting down on what looked like a reliable rock only it turns out to be a cactus?

 

[snrkl]

I looked it up:

https://english.stackexchange.com/q...ies-use-cactus-to-mean-dead-useless-or-broken

 

[boatgeek]

Nice flight! I just love the decals and the paint job.

Could you have had an apogee charge and the motor eject going off at the same moment? That could definitely have blown your main out. The altitude curve at the ejection time was pretty flat, so it could have been both. What was the nominal delay on the motor?

 

[jlabrasca]

I looked it up:

https://english.stackexchange.com/q...ies-use-cactus-to-mean-dead-useless-or-broken

Of course! The Royal Australian Air Force says "cactused" because that suggests "prickly pear" which is reminiscent of the RAF expression "Its all gone a bit pear shaped" which means a plan that has gone badly (after the shape of the path traced by a flier during a poorly executed aerobatic maneuver). Its so obvious, now that I think about it. <smile>

Do they have chicken fried steak in Australia?

Seriously, I am learning a lot from you. Popsicles are called paddle pops, Clue is called Cluedo. If I ever make it to Australia, I won't need a phrasebook.

 

[snrkl]

Of course! The Royal Australian Air Force says "cactused" because that suggests "prickly pear" which is reminiscent of the RAF expression "Its all gone a bit pear shaped" which means a plan that has gone badly (after the shape of the path traced by a flier during a poorly executed aerobatic maneuver). Its so obvious, now that I think about it. <smile>

Do they have chicken fried steak in Australia?

Seriously, I am learning a lot from you. Popsicles are called paddle pops, Clue is called Cluedo. If I ever make it to Australia, I won't need a phrasebook.

And “Waldo” is “Wally”...

 

[snrkl]

Flight video finally up:



[Edit reason: had to tweak the video slightly and re-upload, so I replaced with the new youtube URL...]

 

[Andrew_ASC]

Nice.

 

[jlabrasca]

And “Waldo” is “Wally”...

Is this likely to come up?

Seriously, how did the flight look. Any issues attributable to the slightly warped fins?

EDIT: NEVER MIND -- you were posting video while I was being a smart-ass.

 

[snrkl]

Two flights planned for the 14th October public launch... ambitious, but I won’t have kids this time, so easier to get in and get it done...

Flight 1: LRV is out of stock of the motor I used for the maiden, so instead I’ll be flying a CTI 413I236-17A Blue Streak

Flight 2: if flight one is successful (and I don’t break something) I’ll be flying a CTI 700J400-16A Smokey Sam..

Haven’t got the sims handy (I’m mobile atm) but flight one should do about 2000ft and flight two around 3000ft from memory.

Both these flights, being higher, mean I need to increase the drogue from 18” to 30”.. need to figure out if I use my existing 30” or if I get a 30” with a spill hole.

 

[boatgeek]

Nice flight and video writeup. At least you didn't have too far to walk. It's funny how you don't think about how silly "getting all the laundry out" is until you hear someone say that you've gotten all the washing out. Also, now I understand why you had a ladder on your checklist. I like the higher loading height of the launch rail, but it's up pretty high for turning on electronics.

You should be able to use the same drogue for any apogee altitude. The J400 should be a really fun flight.

 

[snrkl]

Nice flight and video writeup. At least you didn't have too far to walk. It's funny how you don't think about how silly "getting all the laundry out" is until you hear someone say that you've gotten all the washing out. Also, now I understand why you had a ladder on your checklist. I like the higher loading height of the launch rail, but it's up pretty high for turning on electronics.

You should be able to use the same drogue for any apogee altitude. The J400 should be a really fun flight.

With the bigger motors, OR is complaining about high speed recovery when deploying main, I assume, due to the longer fall time... a larger drogue fixes that...

 

[jqavins]

With the bigger motors, OR is complaining about high speed recovery when deploying main, I assume, due to the longer fall time... a larger drogue fixes that...

That strikes me as... odd. The rocket under drogue should easily come down to its terminal velocity very fast, so it should be going at that speed no matter how high the drogue deployment was. I won't say it's wrong, but it really is odd.

 

[boatgeek]

Maybe the extra weight of the burned out motor is just enough to push the descent rate over OR's line in the sand? Might be worth looking at the two descent rates with the same chutes and see how different they are.