BSD 38 Special DD build thread

[Pantherjon]

L2 attempt on sat cross your fingers.

Good luck! What motor are you going to use? Single deploy again?

 

[ttabbal]

The battery I used was actually a 12v battery...I am thinking I did not use nearly as much BP as I needed to use..I kind of backed myself into a corner with my wanting to do this on Saturday..I hadn't gotten around to getting the BP til Friday so I didn't have an opportunity to do any ground tests..The e-matches were given to me and for the life of me I can't recall who he said made them..I used cut sections of a drinking straw to hold the BP(about 1.5" long)..And in hindsight, I should have gone ahead and put the motor ejection charge in as a backup-had the delay grain in for the tracking smoke..

Was a good lesson, expensive one, but a good one nonetheless..

Did you test your ematches with that battery? Those little 12V batteries don't pack much punch. I always use standard 9V batteries. They have less voltage, but last I checked they can deliver more amperage than those 12V batteries. Try using the vacuum test when you ground test. Load up the rocket as you would for a flight, then use a vacuum on the altimeter port to simulate a flight for the pressure sensor. That should allow you to test the whole system.

Oh, and try more BP. I also subscribe to the "blow it apart or blow it up" school of thought. Never blown one up. It takes less pressure to break it apart. And if I do blow one up, at least it doesn't come in ballistic.

 

[hazegry]

no single deploy that was just luck that it was that calm. I am using a RRC2 alt Jim at Missile works says it should be here today. I am crazy its going up an a loki J528 I am hoping for around 4000ft+ I got to get rocksim still so we will see.

 

[Pantherjon]

no single deploy that was just luck that it was that calm. I am using a RRC2 alt Jim at Missile works says it should be here today. I am crazy its going up an a loki J528 I am hoping for around 4000ft+ I got to get rocksim still so we will see.

I plugged the J528 into my RS file..And WOW! Almost 7400'!!:surprised:

Then again mine weighed in at 48oz, yours weighs a little more then mine did..Post the weight and CG location and I can plug your numbers in my RS file and re-run the sim...

 

[Roman]

Don't use those 12V ones for an altimeter, go for a 9V... I've used quite a few different 12V batteries with M.A.Ds and didnt really have good success. And a MAD dfntly needs less power than an alt.

 

[hazegry]

its 4lbs without the motor I was going to figure cg at the field so I am not sure about that with the motor installed

 

[Pantherjon]

its 4lbs without the motor I was going to figure cg at the field so I am not sure about that with the motor installed

The without motor CG is all I need..RS has the weights for the motors pretty accurate ...I will use my CG location and your weight and see what happens...

Just ran a sim at 4lbs empty weight...with the motor in it it weighs 5.6lbs..Got the sim saying predicted altitude of 6914 feet!

 

[hazegry]

no L2 yet thanks to the test change gonna try to take the test this week then drive 5 hours to launch Sat after I pull a 36 hour shift.

 

[BayouRat]

Test change? What did they change? Is that Tripoli or NAR?

 

[hazegry]

Nar changed them normally I wouldnt have cared but it really screwed with my timeframe since we didnt get the test in time for the last launch.

 

[Pantherjon]

no L2 yet thanks to the test change gonna try to take the test this week then drive 5 hours to launch Sat after I pull a 36 hour shift.

36hr shift! I hope some of that time is 'rest' time! Good luck!

 

[BayouRat]

Nar changed them normally I wouldnt have cared but it really screwed with my timeframe since we didnt get the test in time for the last launch.

Oh NAR, well that would explain why I did not know about a test change. What did they change?

 

[hazegry]

there is a sticky at the top of this page that explains all of the changes to the test its not that bad I took the test today and got a 100. I never know if I am going to get any sleep or not just have to see what happens but if I dont I will sleep on the way down and let the wife drive.

 

[Pantherjon]

Time to dig this old thread back up!...

Hazegry did you get your L2? I presume so, don't recall you posting it, or if you did, I missed it..:lol:

Anyways, I had a 'eureka moment' last night..Actually more like a "DOH' moment..I was re-reading thru the AiAlt45k User's Manual to make sure I get the ground testing right when I noticed a sentence on the last page that caught my eye:

"Make sure that at least 1/32" clearance is provided between the mounting plate and the face of the pressure sensor to allow for the proper pressure sensor operation."

I had been looking at my altimeter/sled earlier and after reading this I looked even closer and saw that there was just a sliver of space between the sensor and the sled..Just enough space that 110lb card stock barely squeezed thru the gap..This I think is what doomed my 38 Special cert attempt flight..No space between the sled and sensor, it couldn't detect anything and that's why neither of the charges went off..

I have now modified the mounting of my altimeter with a couple of washers and there is about a 1/4" gap there now!

A trip to Lowes is planned tomorrow to grab some hose and a suction cup and do some ground tests!Video(s) will be taken!

 

[hazegry]

I havent gotten it yet. I did have a cool flight to 6596 feet on a j528 but the chute tangled. I have a J712 for my second attempt but its hard to meet up with 2 L2 guys in my club. I am going to attempt it again in may since everybody else is up in MD for red glare.

 

[stealthfixr]

Thanks to all of you, I've been bitten by the 38 Special bug. I just ordered my first real HPR today, and I cannot wait to get it and certify soon! I ordered the kit from Dennis at Rocketry Zone, and I am kicking myself because I just saw him at the Orangeburg launch two days ago. A little birdie told me how nice it would be to certify at the NSL in May, and I could not resist. I've wanted to to HPR for a long time, so this is exciting!

Speaking of, does anyone have a correct Rocksim file for the current BSD 38 Special? The one posted on EMRR is a 2.6" diameter, 47" length 38 Special. I think the new one is closer to 3" diameter and 57" in length. Thanks!

 

[Pantherjon]

stealthfixr,
Well here is the RS file I modified to match my 38 Special..I used the 'mass override' for the weight and CG location..This is an edited version of the one I downloaded off EMRR to show the correct length of 58"..You will probably need to change the 'mass override' when you finish yours to match your real world rocket..

BTW, this one is set for dual deploy..

View attachment MY bsd_38specialDD.rkt

 

[SpartaChris]

Speaking of, does anyone have a correct Rocksim file for the current BSD 38 Special? The one posted on EMRR is a 2.6" diameter, 47" length 38 Special. I think the new one is closer to 3" diameter and 57" in length. Thanks!

Why not create your own? Your sim will me more accurate that way anyway, especially if you make any modifications.

 

[stealthfixr]

Why not create your own? Your sim will me more accurate that way anyway, especially if you make any modifications.

Why have a RockSim library then? Why share files at all? :surprised:

Because there is no sense reinventing the wheel as far as using the basic template of the stock kit. I can then modify the stock file to my customizations, weight, CG, etc. I don't have the BSD components in my Rocksim database to build one from scratch, or a breakout of each and every part in this kit. Also, it would be nice to get an idea of how fast and how high it may go on different motors before building, testing different combinations, weights, & payloads. EMRR does not have the correct file loaded, and it might help others by uploading the accurate to current specs file.

 

[SpartaChris]

Why have a RockSim library then? Why share files at all? :surprised:

Because there is no sense reinventing the wheel as far as using the basic template of the stock kit. I can then modify the stock file to my customizations, weight, CG, etc. I don't have the BSD components in my Rocksim database to build one from scratch, or a breakout of each and every part in this kit. Also, it would be nice to get an idea of how fast and how high it may go on different motors before building, testing different combinations, weights, & payloads. EMRR does not have the correct file loaded, and it might help others by uploading the accurate to current specs file.

Whoa man, calm down now. Take a deep breath. Count to three. Now exhale. Good.

Using someone else's file doesn't mean your rocket will come out the same. You're going to have to weigh your individual components to get an accurate sim anyway, so you might as well create your own to begin with is all I was getting at. Might save you a bit more time in the long run.

 

[MarkM]

I'll have to agree with Stealth on this one. As long as he modifies the Rocksim file he acquires to match his own 38 Special (additional tubes, different recovery gear, whatever). I find it totally unnecessary (and way too time consuming for a minuscule gain in accuracy) to plug in the weights of the individual components. As long the rocket is weighed (loaded with recovery gear, but not motor) after completion (including paint) and the Mass Override feature is enabled with the weight of the rocket inputed. Additionally YOUR CG (not what Rocksim calculates) should be put into the Mass Override pane. Making those mods, a Rocksim acquired from someone else or the Rocksim database should be as accurate as it really needs be. Of course with the caveat that the rocket was correctly set-up in Rocksim the first time or is modified so is correct.

I think most, including me, use Rocksim simply as a guideline to get a rough estimate on altitude, speed and making sure the rocket will be stable with whatever maximum size motor the flies wishes to stuff in the thing.

 

[stealthfixr]

Compared to the file on EMRR, I believe the attached one is much closer to the current BSD 38 Special dimensions (3.0" dia) and weight (3.0 lbs), though I built it from LOC parts in my database. And, it has a Giant Leap Slimline retainer on the end--other than that, single-deploy, bone stock. The flight sims should be closer so others have more of an idea of what to expect before they buy & fly. It's not perfect, but it's a much better starting point to modify your own BSD 38 Special build with your particular weight and CG measurements. Enjoy!

PS: MY 38 Special is nearing completion--can't wait to fly it and hopefully L1 cert at the NSL later this month! While my CG has yet to be set, I am under weight at 2.8 lbs--used 3.0 lbs in the sim since that is the BSD reported dry weight.

View attachment BSD 38 Special Mine.rkt

 

[n5wd]

... It's not perfect, but it's a much better starting point to modify your own BSD 38 Special build with your particular weight and CG measurements.

s-f,

(hope you don't mind if we're informal, today... ) Thanks! I received my 38spcl last week and was just getting started on the Rocksim file. We've got a high power launch at McGregor in a couple of weeks, but all next weekend is dedicated to a trip to the TARC finals, so not sure if it's going to be ready to fly then. Good luck with yours!