Joe Turners L2 Build Thread

Discussions on mid/high powered model rockets using F powered motors and above.

Moderator: Moderators

User avatar
OverTheTop
It's only money...
It's only money...
Posts: 2412
Joined: Sat Jul 21, 2007 2:20 pm
Location: Melbourne, Australia

Re: Joe Turners L2 Build Thread

Postby OverTheTop » Mon Oct 09, 2017 10:48 am

NOTE: The formula is exactly same one that OTT provided about a year ago. OTT recommended 0.06, so I can see where this comes in. All starting to make some sense.

Careful. The constant in the calculation I use is 0.006, not 0.06. You could get some enthusiastic separations with the larger number :shock: .
TRA #13430
L3
"Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

User avatar
RainierWolfcastle
Parachute Packer
Parachute Packer
Posts: 34
Joined: Wed Sep 02, 2015 11:29 am

Re: Joe Turners L2 Build Thread

Postby RainierWolfcastle » Mon Oct 09, 2017 11:37 am

OverTheTop wrote:
NOTE: The formula is exactly same one that OTT provided about a year ago. OTT recommended 0.06, so I can see where this comes in. All starting to make some sense.

Careful. The constant in the calculation I use is 0.006, not 0.06. You could get some enthusiastic separations with the larger number :shock: .



But it could get a decent altitude boost!*







*For whichever remaining pieces of the rocket are lucky enough to travel upward.
- Ben

 "If I have seen further, it is by standing on the shoulders of giants." - Sir Isaac Newton, 1675

joeman
Rocket Crew
Rocket Crew
Posts: 215
Joined: Fri Mar 06, 2015 9:05 am

Re: Joe Turners L2 Build Thread

Postby joeman » Mon Oct 09, 2017 11:55 am

oh goodness me!

Yes - I was 0.006 or (1/167)

Thanks guys.

mmm I need to work out how to edit a post. Last thing I want is to give someone else the wrong idea later...when they read it.
L1 - Callisto (H133) - 11-Jan-2016

User avatar
SpaceManMat
Astronaut
Astronaut
Posts: 1838
Joined: Mon Dec 15, 2008 9:56 pm
Location: Brisbane

Re: Joe Turners L2 Build Thread

Postby SpaceManMat » Mon Oct 09, 2017 5:52 pm

I think your over doing it. I would not go with the assumption that it won't vent. I this is causing to over do the pins and then to over compensate with bigger BP charges. End result high energy deployment. You'll then need to make sure that you use extra long recovery harness. With a reasonable sized vent your main concern should be drag separation. Anyway that's just my view, willing for someone with a bit more experience to say otherwise.

FYI, when it comes to BP sizing always ground test. There's far too many variables to get it right first time.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 10,849 feet
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

joeman
Rocket Crew
Rocket Crew
Posts: 215
Joined: Fri Mar 06, 2015 9:05 am

Re: Joe Turners L2 Build Thread

Postby joeman » Tue Oct 10, 2017 8:18 am

Yes. Perhaps it is.
I'll think about it a bit more.

Re: number of shear pins
I know having just One shear pin is a no no. I could imagine two shear pins exhibiting problems in some occasions too.... though probably not as easily/often.

That I guess was some of my reasoning for going 3 instead of 2. Perhaps I am being over cautious.

Yes, I need to do some tests. Start off with less BP and see how effective it is.

Yes, I should consider the implications in recovery harness before drilling.

Thanks Mat
L1 - Callisto (H133) - 11-Jan-2016

User avatar
OverTheTop
It's only money...
It's only money...
Posts: 2412
Joined: Sat Jul 21, 2007 2:20 pm
Location: Melbourne, Australia

Re: Joe Turners L2 Build Thread

Postby OverTheTop » Tue Oct 10, 2017 8:39 am

I have heard it said that three shear pins will stop the separation point rocking, potentially causing problems.

I use two shear pins as a matter of course. Zero problems experienced so far.
TRA #13430
L3
"Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

joeman
Rocket Crew
Rocket Crew
Posts: 215
Joined: Fri Mar 06, 2015 9:05 am

Re: Joe Turners L2 Build Thread

Postby joeman » Wed Oct 11, 2017 9:36 am

ok
After some reflection, I think as Mat says, equalisation can probably occur sufficiently quickly (so long as I drill sufficiently sized venting holes). On one of the more powerful motors, burnout is ~750metres. Apogee (3300metres) is ~22 seconds later. I am sure this is adequate time for significant equalisation to occur. This means a reduced separation force.

SO...I've decided to go for two shear pins. I figured that so long as I do not use "borderline quantity" amount of BP, even if there is a little bit of seepage, it should produce sufficient pressure to shear the two pins (2/56). Also, rhe coupler/tube fits is not sloppy...Sloppy fits I think could lead to increased chance of it cocking. I'll of course do a number of tests to ensure I'm comfortable with the separation/ejection; and to determine suitable size BP charge.


RE: Vent hole sizing
I can see that there are are MANY resources on the Internet and on this forum regarding the vent sizing. The following seems like a very trusted resource.

http://www.vernk.com/AltimeterPortSizing.htm

I've calculated the hole sizing. NOTE: For the Booster Air-frame, It recommends ~9mm size holes. This seems quite large. I've thought about using 1/4 (6.35mm holes). I've placed them in places where there should be minimal/no turbulence.

Does any of this reasoning seem way off? Any concerns?

IMG_3859_edited_sml.jpg


Thanks for your frank and fearless advise. Much appreciated.

Cheers!

Joe
L1 - Callisto (H133) - 11-Jan-2016

joeman
Rocket Crew
Rocket Crew
Posts: 215
Joined: Fri Mar 06, 2015 9:05 am

Re: Joe Turners L2 Build Thread

Postby joeman » Wed Oct 11, 2017 9:51 am

oh yes, at bottom... 4 holes - 90 degrees apart.

Measure twice, cut/drill once.
L1 - Callisto (H133) - 11-Jan-2016

User avatar
OverTheTop
It's only money...
It's only money...
Posts: 2412
Joined: Sat Jul 21, 2007 2:20 pm
Location: Melbourne, Australia

Re: Joe Turners L2 Build Thread

Postby OverTheTop » Wed Oct 11, 2017 12:38 pm

Vent holes for the airframe seem to be a bit larger than I would use, particularly the lower section. If it were me I would probably use 3 x 1/8" holes for the top section.

Avionics bay is about right for vents IMHO. If you are using one RBF pin and one switch, have you considered just two RBF pins? That is what I have gravitated to over the years. Nice and simple. Not easy to forget. YMMV.

Remember for the lower airframe that unless your motor is an airtight fit there is plenty of breathing room around it and out the tail. This depends on your retention system. I normally mount at the front end, so that gives me a good vent to the rear. Your rear appears to be relatively well sealed, and assuming you have no chute in the rear section I would think about 3 x 1/8" holes there would suffice. I would probably use the same even if you put a chute in there.
TRA #13430
L3
"Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

Stewart
Rocket Crew
Rocket Crew
Posts: 253
Joined: Sat Jul 31, 2010 10:15 pm
Location: OAKEY,Qld

Re: Joe Turners L2 Build Thread

Postby Stewart » Wed Oct 11, 2017 5:38 pm

Altimeter bay vents have a different requirement to airframe vents-- alt bay require zero pressure differential to get accurate readings, wereas airframe just needs to bleed out pressure at sufficient rate so as the pressure differential isn't enough to cause separation of the airframe components.
That said ive had no problems with a single 3/16" vent on a 4"airframe to 10,000ft
QRS#85
TRA#13049 L2

User avatar
OverTheTop
It's only money...
It's only money...
Posts: 2412
Joined: Sat Jul 21, 2007 2:20 pm
Location: Melbourne, Australia

Re: Joe Turners L2 Build Thread

Postby OverTheTop » Wed Oct 11, 2017 5:54 pm

Altimeter bay vents have a different requirement to airframe vents-- alt bay require zero pressure differential to get accurate readings, wereas airframe just needs to bleed out pressure at sufficient rate so as the pressure differential isn't enough to cause separation of the airframe components.

Mostly. Deployment is not usually affected. The vertical rate at apogee is zero, so the internal pressure gets a chance to catch up with the real pressure as the bird finishes coasting to apogee. If you want more accurate baro altitude data on the way up, particularly during the fast part of the ascent, then the larger holes become more important. Small holes effectively provide a low-pass filter. The smaller bay volume usually helps to keep the time-constant of this filter down too.
TRA #13430
L3
"Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

joeman
Rocket Crew
Rocket Crew
Posts: 215
Joined: Fri Mar 06, 2015 9:05 am

Re: Joe Turners L2 Build Thread

Postby joeman » Fri Oct 13, 2017 1:52 pm

G'day
After a little more looking around, most likely will go for 3 x 1/8" holes in upper and lower as suggested by OTT. Will probably position a bit closer to the top of air-frame tubes, so that have less chance of Chute getting in the way. Something to do on Sunday - my day off.

I found a very interesting link , someone attempting to model the flow of air out.

http://home.earthlink.net/~david.schult ... chute.html


RE: Avionics
Still like the idea of 3 for the Avionics bay though, need to make sure it gets accurate readings, but will check instructions on Altimeter incase they have any other suggestions. I know they often mention something important.

RE: RBF pins
I didn't think of that. Might be an idea. I do like the idea of some positive feedback, e.g. LED, or Buzzer (sound) that indicates that it is on and working... I should have a check list...tick off - help make sure I don't forget anything.


Need to start working out what components to get for the recovery system.

Thanks Guys!

Cheers!

Joe
L1 - Callisto (H133) - 11-Jan-2016

Stewart
Rocket Crew
Rocket Crew
Posts: 253
Joined: Sat Jul 31, 2010 10:15 pm
Location: OAKEY,Qld

Re: Joe Turners L2 Build Thread

Postby Stewart » Fri Oct 13, 2017 11:53 pm

Joe,
dl and read the Wildman darkstar instructions :- http://www.wildmanrocketry.com/pdf/Kits ... rkStar.pdf a very similar rocket and look at the airframe vent size recommendations these rockets built as designed are tried and tested,
re avbay vents my preference is to use 4 vents
QRS#85
TRA#13049 L2

User avatar
Crazy Jim
CrAzY 'Tiger Terror' Jim
CrAzY 'Tiger Terror' Jim
Posts: 248
Joined: Mon Oct 04, 2010 4:39 pm
Location: Savannah GA, USA

Re: Joe Turners L2 Build Thread

Postby Crazy Jim » Mon Oct 16, 2017 5:07 pm

G'day Joe!

FYI: I'm the guy in photo holding DarkStar Xtreme in the instruction link above. I built & fly the prototype & wrote the instructions for this and 31 other Wildman kits. Just a few helpful [I hope] hints to help you finish this ...so far wonderful...build of yours. Great job so far, BUT you are overthinking all this a bit.

Mine has flown to 16,600 ft. no issues, built as described.

1 vent per airframe section is all that's needed. 1/8 hole in payload and 1/8 in fincan. If it makes you sleep better... up it to 5/32. Anymore is overkill! Yeah you can fiddle all day with calculations, but I assure mine are based on years of flying experience with airframes of this size. Flying all types of motors with various thrust curves, especially high thrust motors where you need to vent fast, due to speeds.

Vent band holes [for altimeter reading] were determined by discussion with Jim Amos of missleworks. Hole sizes for various altimeter bays can be found on his site under RRC3 manual. 2 years of testing, on top of usual calculators determined actual sizes. Recommended to use odd # of holes when ever possible. That reason is cause for a whole 'nother thread. Suffice to say it has to do with airflow around a tube and the negative pressure on downwind side of tube equalizing with positive side. This comes into play with wind shears you may pass through on the way up & gusts on the pad over 20mph that can drop pressure on negative side quickly triggering a false apogee detect.
This can fire a charge on pad. Well that issue has been corrected, but some altimeters will still do it.
3 holes 3/16 or 1/4 can be used.
I use 2.25 grams bp on main.

Often overlooked is apogee charge. IT SHOULD VARY, depending on size of motor flown.
A 2.5 g charge is perfect for a mid to long 54 motor, but when flying a long 75mm M - motor there is very little space left between top of motor with 25ft of shock cord/nomex/chute stuffed on top. Then only a 1.5 g charge is needed, you're only pressurizing a 10 in space.
Most flyers over look this item and just use same size charge no matter what motor is flown. As always ground testing is recommended, due to variance in build technique and tightness of parts fit. Mine are based on a nice snug fit.

As stated in manual I use 3 pins 2-256 nylon, which have a shear break of 24lbs @ on average.

I use a Topflight 84 or 96inch chute depending on wind conditions. What ever Blake sells in a similar size, I'm sure, will suffice.
When finished & painted The DarkStar & your OZZ version [virtually identical by the way] make for one sexy looking rocket & great sport flier! My favorite motor pick is any of the CTI 2-grain 75mm loads. Little known fact.....they sell for less than their 54mm counterparts and are a better value. Over here in US prices they are 30-45 dollars cheaper than a 6xl 54mm!
Mine flies 8600-9200ft on those 2-grain loads. I love the L-910 C star, it's tailor made for this rocket.

Have fun and good luck finishing your project.

Semper Fly,

Crazy Jim

PS when you get tired of flying this..... just change DarkStar vinyl to Katana, it will look fantastic
100_7164.jpg




I can have Blake send you parts to build a bigger one....LOL
100_6181.jpg


PPSS: Rocket Trivia..... by the way at the top of this page, flying sideways, is the "Drama Queen" flying on a sparky "O" motor. 7.5in diameter 14ft tall .
I built that in 3 days and delivered it to Blake at BlackRock.....Lol
Jim Hendricksen
"Crazy Jim's Gone Bananas"
L-3 Tripoli 9396
ICBM, Orangeburg, SC USA
Quad Cities, Princeton, Illinois
MDRA Price Maryland
"Made" Member Chicago Rocket Mafia

Rocketry..........an exact science......but not exactly!

User avatar
SpaceManMat
Astronaut
Astronaut
Posts: 1838
Joined: Mon Dec 15, 2008 9:56 pm
Location: Brisbane

Re: Joe Turners L2 Build Thread

Postby SpaceManMat » Mon Oct 16, 2017 9:07 pm

Crazy Jim wrote:PPSS: Rocket Trivia..... by the way at the top of this page, flying sideways, is the "Drama Queen" flying on a sparky "O" motor. 7.5in diameter 14ft tall .
I built that in 3 days and delivered it to Blake at BlackRock.....Lol


I've always wondered who Blake named that rocket after :mrgreen:
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 10,849 feet
Largest Motor: CTI 1115J530 IM
Current Project: X Wing


Return to “Mid/High Powered Rocketry”

Who is online

Users browsing this forum: No registered users and 1 guest