Well, Bohica got me thinking about a ring fin rocket that would be pretty cool when he announced his Reaver..It came about actually with me thinking of a silly name for his rocket before he chose 'Reaver' and kind of morphed..I had been mulling over the design in my head for quite a while and ordered the parts from Semroc a couple weeks ago..Main body tube is 18" length of BT-50, a conical nose cone, and the ring fin is BT-100..

I made it 'convertable' from 24mm to 18mm..Built an 18mm motor mount that is secure with a hook I attached to the BT-50 and engine block in the main tube..

Here is a picture of the parts:



Tubes are already marked..The BT-100 is marked with preliminary locations for where to cut it..It will not remain 'straight' for long

__________________
Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

Well, not really a build thread..lol..Anyway, I glued the inner fins on and then found that I had done a basic math error in the size of the fins! No biggy really...4 spacer strips cut and CA'd to the fin tips and problem solved..Next up was the cut design for the BT-100..I thought some flowing lines would look best..Thought hard for it as I watched the NASCAR race..Then an idea hit me..I grabbed a quarter, made some half circles in the appropriate places, drew some lines to connect the curves and got my 'wave' pattern! Cut it out, then followed with the dremel and a grinding wheel to smooth the curves..Glued the BT-100 to the fins, stuck in an elastic shock cord and a Hartle streamer and done!

Here in it's nakedness, I present to you;

DAS HOOPTY



Took it out after the race and launched it on a B4-4..And a beautiful, straight flight to about 150'! Streamer slowed it perfectly and the ring help some too..Landed in the middle of the road in front of my house, no damage! I was almost jumping up and down in excitement!...lol..My very own creation, AND IT WORKED! Can't wait to see what it does on a C or even a D..

__________________
Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

You should be able to sim that one with a bit of trickery...

Measure the MAC of that ring -- how far down from the top edge is that line for the bottom cut? That gives you a more accurate area and mass value for the ring. Create a ring of that width and center it where yours is on the prototype, then add your pylons. The rest of the model is easy.

This should allow you to test that D12 and that C6 for balance.

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
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SAM 0044
AMA 352635

Am going to download a trial of rocksim and see about doing that Tried RS once before and couldn't make heads or tails out of it..lol...Hopefully it will be different now..I hope so, cause I really want to learn how to use that software as I want to start doing some of those scrounged up designs

__________________
Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

OK, got RockSim running...Had to purchase the license..lol..Should have aske: What do you mean by the MAC of the ring? This is my first serious attempt at designing a rocket..Anyways, I threw together the rocket in RockSim and it shows the stability as 0.74 or marginal..But the flight profile isn't at all close to what I experienced when I actually launched it..It shows it not going as high as I saw and ejection way past apogee..I am sure I got a couple things wrong in the sim..How do I show the motor mount?(18mm for BT-50)

Look over the rkt file and see if you can make it better...lol..Because it isn't showing what I actually achieved

Attached Files

Das Hoopty.rkt (31.9 KB, 63 views)

__________________
Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

Jon,

You're running into the same roadblock we've all been hitting -- RockSim doesn't handle ringtails correctly. It calculates more drag for the simulations than the actual flight prototype encounters in flight.

I just took a guess at the actual width of the ring. It should be measured from the leading edge at the crest of a wave to the trailing edge of the ring directly in line. The true width of that ring is not 3.3", but closer to 2.3"; it just fills a 3.3" area. I moved the ring forward 0.50" to compensate.

Attached is a revised RKT file.

Attached Files

Das Hoopty v2.rkt (43.6 KB, 61 views)

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
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BARCLONE Forum -- BARCLONE Forum

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SAM 0044
AMA 352635

Thanks Craig! I appreciate it! I was playing around with it this morning just before going to work..I added 1/2 oz of nose weight and ditched the 18mm motor mount..Loaded as many different motors ..Went all the way up to putting in an Ellis Mountain G37! STABLE with a 1.04 margin..

G37-6 1311 ft max altitude but 62.2 f/ps at DV

Here is the rkt file with all the different motors I threw into it Not that I would put a G37 in it...but.....snicker...

Attached Files

Das Hoopty v2 bunch of motors.rkt (193.0 KB, 61 views)

__________________
Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

(In a mock huff) Oh yes you would!!!

Is it any wonder why I constantly describe this place as an asylum???

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
BARCLONE Forum -- BARCLONE Forum

BARs helping BARs

SAM 0044
AMA 352635

Yeah, a true nut house Craig!

Anyways, been thinking of a paint scheme for Das Hoopty(and a name change as Das Hoopty is a silly name and the rocket turned out not looking 'silly') as I wait for a break in the humidity levels..I am thinking of going with a 2 tone green scheme, and changing the name to Green Wave..I have the 2 colors picked and am still undecided on the arrangement..The colors are Krylon: Hunter Green Gloss and Ivy Leaf(a new color)..Ring Ivy Green and body Hunter Green, or vice versa?

Conditions are almost ideal this morning to shoot some paint and I was going to primer it..But I just found out I am out of Krylon primer!Curses! Ah well, looks like a Tuesday project(my day off)..

__________________
Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

Break up the color arrangement, Jon. Don't use just one color for the ring and one for the body...

Ivy Green for the nose cone, hunter green for the body tube and pylons. Give the ring a base of ivy, but mask out a narrow stripe between the valleys and paint that hunter.

I like the name change.

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
BARCLONE Forum -- BARCLONE Forum

BARs helping BARs

SAM 0044
AMA 352635