Little Deuce Coupe

[scsager]

I've gotten way behind in the build queue, so I've been putting in a lot of hours in the man cave lately.

I usually watch old movies or listen to classic old music when I build rockets. A Beach Boys song got me thinking about a build that I've been wanting to do for a long time.


This first post is just sort of a teaser.




I scoured the interweb to bring you the best quality youtube video I could find for this tune. This is from March 14, 1964… forty eight years ago… man, am I feeling old.


http://www.youtube.com/watch?v=oAfkUJ6zS04


Additional video of the Lost Beach Boys concert Here - for those of you who are fans.


Build thread continues… tomorrow.

[Doggonewild]

I like clusters and the Beach Boys. I'll be watchin'.

[CarVac]

Gonna be on the very bleeding edge of mid-power, huh?

[Handeman]

I don't know the details, but I guess the members of the BBs didn't get along so well. BUT, I just heard the other day that they a getting together for a 50th anniversary tour.

[Scotty Dog]

I don't know the details, but I guess the members of the BBs didn't get along so well. BUT, I just heard the other day that they a getting together for a 50th anniversary tour.

Geeze,thats to bad. I would rather listen to a brain worm munching on my gray matter than listen to the Beach Boys.
Sho-Saw-Wee, me no like.

[scsager]

I saw these nice centering rings on the Balsa Machining Service web site. BMS does a great job with laser cut rings of all kinds. These caught my attention because they fit in a BT80. Two 29mm motor tubes will just barely fit a BT80. It's a tight fit, with just a few millimeters to spare.



Like most BMS parts, they require just a bit of sanding for a perfect fit.
-That's when the first issue cropped up. They way these are cut, the tubes touch in the middle. That’s not a problem with low power BP motors, but Reloads or AT single use motors have a rear thrust ring that gets in the way.



No problem, I'll just enlarge/elongate the holes with the Dremel tool.

*Easier said than done.*

I placed another order with BMS for an extra dozen rings... just to be on the safe side.

With practice, I got real good at finessing these rings to make a 2mm gap between the motor tubes.






Now for power considerations. On the NAR web site I saw this chart for Model rocket Site dimensions.
The entry for "Two Gs" intrigued me. As it turns out a 2xG80 cluster is the bleeding edge of "Model" rocketry.
Anyone can fly 2xG80 power without any certification, or waiver needed. That's cool because even though I am L1 - anyone can copy my build or make a comparable design.

*Note - some of the NFPA regulations are changing this year. There will be some updates to the safety code, etc. As far as I can tell, the average thrust and total propellant weight rules are not changing.

Check out Doug79 for the current power metric.


Two G80's produce a lot of power. At 137ns each, the combined total thrust is 274ns. That’s 85% of a full H motor.

Aerotech makes 14 different High Power "H" motors. Only one, the H268R produces more total thrust than the two G80 cluster used in this build.


This build starts with the design in OpenRocket. After a lot of "what-if" simulations, I started narrowing down what I wanted this rocket to be. Should I sacrifice altitude for bullet-proof construction, or go lean and mean, testing the speed of paper tubes and wood glue?

Lean and mean is both less expensive and more gutsy.

Open rocket has great Optimization tools. I spent lots of time on the simulator - hours really - learning a lot. I have it to the point now where I can dial-in the altitude I want. I was surprised that I couldn't get it to hit a mile in altitude. I think this has to do with the things I couldn't/wouldn't change… motor, nose cone and body diameter. I could only top out at about 4500 feet with the high thrust short burn G80s in the BT80.




I decided to "dial in" 1200 meters, or 3/4 of a mile for altitude. The end result is a 25 inch rocket that weighs 23 oz.
If OpenRocket is accurate, It should see 29Gs and hit Mach 0.9. Good thing I rounded those fins.

I'm not sure the build weight will match the sim, but I'll try to make adjustments as I go.


Mach 0.9 (670mph) What was I thinking...

[CarVac]

If you're level 1 already, then fly two G138's. Much more awesome, since they're 157 Ns apiece, and have progressive burns. Plus, the blue flame is much more visible from the 'New Blue' propellant than the older varieties (though I'm not sure what's in the G80 single-use motors).

[Rex R]

Q did you remember that Bong is approx 900' above sealevel ? it do make a difference.
rex

[chadrog]

Ahhhh, because it's still under 125g, I stand corrected.

[scsager]

If you're level 1 already, then fly two G138's. Much more awesome, since they're 157 Ns apiece, and have progressive burns. Plus, the blue flame is much more visible from the 'New Blue' propellant than the older varieties (though I'm not sure what's in the G80 single-use motors).

Ha Ha - Great minds do think alike.... The sim does not show much difference in total altitude, but it goes seriously supersonic at 380 meters/sec (850mph). I even have 2 hobbyline cases. I'm just not sure I have the guts to try this... at least not on the first flight.

[scsager]

Q did you remember that Bong is approx 900' above sealevel ? it do make a difference.
rex

Yes - you're right... I set up Bong on the OpenRocket "Launch Conditions" screen using 42.62n, -88.16e, 245m altitude, and 1524mm launch rod length (5ft of effective length on a 6ft rail)




*** I just thought of a great feature request for OpenRocket. You should be able to set up a "Launch Site" with Lon, Lat, alt etc. and have it remember your entries. Maybe it could remember six different sites - that would be a time saver!

[scsager]

More design considerations.

I decided to go with normal Estes/Shurfire BT80, rather than the heavy wall stuff. I have both in the parts bin. The Thin wall tube is a way for me to challenge myself. For the rocket to withstand the forces involved will require good construction techniques.

The Tube dictated which nose cone I used (again from the parts bin)

Wood glue works well with paper tube, and produces joints stronger than the materials themselves.

The design rules of thumb were used as a starting point.
Length = > 10D
Rocket length no shorter than ten times the diameter. I started with 660mm which is 10x BT80 diameter of 66mm. Open Rocket gave better altitude with a much shorter rocket. Too short to pack the chute really. I compromised at 9.5D or about 630mm total length.

Fin Size root and chord = 1.5D
Again smaller fins give more altitude due to less drag at high speed. I settled on a root of 1.3D and chord of 0.9D for less drag at speed. There are trade offs here based on stability, weight, and drag.





Stability.
. > 1.0D
OpenRocket predicts this rocket will come off the 6ft rail at 130mph. Most of the time I will shoot for 1.5 caliber stability or more, but that's not needed here. The motors weigh almost as much as the empty rocket. Nose weight is needed to obtain 1.0 caliber. But as it burns propellant, the tail end gets lighter. At apogee the rocket will be 1.75 calibers.

Again several factors come into play. Optimal mass for the amount of thrust. Liftoff stability vs. apogee stability . Ballistic recovery Risk Management is also a factor. I have had a few recovery "issues" in the past. I'm all about safety, and less nose weight is usually less dangerous as long as a the stability margin is near 1.0. The configuration I'm going for should only require 3.5 oz of lead, and have more room for the recovery gear.







What I have on hand.
Just so happens that I have 4 G80-10 motors in my stash. I can tweak the build to go higher with the 13 second delay, but why blow another $40 bucks on new motors. This less aggressive design should go as high as possible with a 10 second delay.

Where will I fly this.
There really isn't much room for dual deploy in this short little rocket. Streamer recovery is out of the question. It would come down too hot with the heavy motors. The empty motors still weigh <130g or more than 4.5 oz.

Our usual launch site, Bong, isn't entirely out of the question, If I use a tracker. But then I have to design in a tracker… which I don't have. The club has one or two for member use. That's one possibility.




A bigger launch site such as the QCRS Princeton location might be better. It's not going all that high, but it's pretty high for it's size and visibility. Even at a larger site, a tracker might be a good idea. The projected altitude is 1200m = 3936ft = 0.75 mile. The rocket is 2.6" x 25" in size.

[scsager]

Time to get started building.




I have already cut some of the tubes to length, and I have sanded the rings to fit.

The bottom or lowest centering ring will use T-nuts for motor retention. So I have glued two rings together to make it stronger.

The build starts with the motor tube. The top most ring goes on the end of the tubes. Remember that the tubes have to have 2mm separation. They can't touch or the motors won't seat properly. A sanded down popsicle stick works to keep the tubes apart while the glue sets up. The first round of glue is just to get the ring tacked in place. Filets will come next.

[scsager]

To mount the mid centering I could just refer to the measurements in OR. The problem is the real rocket might not be exactly the same as the simulation… even though I'm building as designed.
I want the mid centering ring to be flush with the top of the fin slots. That way the fins have one more surface to glue onto - giving extra strength.

That means I need to cut the fin slots. I always like to have the fins in hand before I cut the slots…

So - in order to get the mid centering ring in the right place, I have to cut out the fins first… That makes sense doesn't it?



I modified the fin template slightly from the OR print out. These (possibly trans sonic) fins are cut from my supply of BMS 1/8" 3 ply Lite plywood. The big sheets this comes in are a little bendy due to the grain running in the same direction on the outer layers. Once they are cut down to size they seem very stiff and exceptionally light weight. When I make these kind of fins, I just round the leading/trailing edges. I could spend the time and effort to make these more aerodynamic. I have no doubt it would improve performance. If /when I build the next one of these I might do that.



Fin slots are cut next using a nice piece of angle aluminum. See Kit, I was paying attention! I always make these a touch on the small side so I can sand them to fit. (that's why I needed the finished fins first.)

Now that I have fin slots, I can be sure to get the mid ring in just the right spot via test fitting.




The TTW fins will also need to be custom fit/sanded to mount to the motor tube. The OR fin templates don't really "auto-size" the fin tabs correctly with a cluster mount.

Finally, the mid ring gets glued on to the motor tubes in the right spot.



A spacer is also made and glued in place between the tubes to keep them separated at the required 2mm distance.

[Handeman]

Ha Ha - Great minds do think alike.... The sim does not show much difference in total altitude, but it goes seriously supersonic at 380 meters/sec (850mph). I even have 2 hobbyline cases. I'm just not sure I have the guts to try this... at least not on the first flight.

Why not, it's just a rocket. Give it a shot!


No Guts, No Glory!

[scsager]

OpenRocket does not auto-adjust the TTW tabs for clusters. That's O.K. I got it covered. I was planning for this. After the motor mount glue has fully set up. The fins tabs are custom cut and sanded to fit.




Then One fin at a time is glued in place using the trusty old fin jig built-in to the end of the Estes tube marking guide.





This is a pretty long boring drawn out process. I'll skip all the little details, and just mention the main steps.

After all fins are attached, a quick check with some old motors to make sure everything still fits. Then six fillets per fin (four inside, two outside) make sure everything is rock solid.





Time to mount the T-nut retainers. These were "adjusted using the course sanding drum on the Dremel. Yup, sanding drum (not grinding wheel) seems to work best. All three spikes still engage the centering ring for a solid mount.




Fin can is all sealed up at the rear. This is a solid fin can . I doubt that aerodynamic stress will be a problem for this part of the rocket. (famous last words)



Tomorrow I start work on the baffle.

[qquake2k]

This is looking really good!

[jeffgeraci]

This rocket will last you forever, can't wait to see what happens next!

[scsager]

This is looking really good!

Thanks Jim, coming from you that's a real complement. I've admired your builds for a long time.

[scsager]

This rocket will last you forever, can't wait to see what happens next!

I don't know if it will last forever, but I seems like it is taking forever to finish. If I can get it done on time, I am thinking about a first flight at the clubs next high power launch May 19 & 20.

[scsager]

I escaped from work at the regular time for once and the weather was nice for a change. Perfect time to get some primer on of couple of other builds. (so another late start getting back to the build)

The baffle is cut to size from a longer length of BT80 coupler material. It will seat all the way down to the centering ring, and stick out the top 66mm - or 1x the body diameter.






The baffle will use 3 pieces of ply bulk head. One mid plate drilled with about 20 small holes in the center. The top plate is made from 2 bulkheads glued together for extra strength. The top plate is also the shock cord attachment point with a #10 wire eyebolt. The #10 eyebolt is the next sixe up from the #8 that I usually use. I wanted a little extra weight, and a little extra strength. A one piece forged eyebolt would be best , but my assembly technique *might* add a little extra failure resistance.





With no nut on the top, the open end of the eyebolt is drawn tight against top washer. Then some carefully placed JB weld may give a tiny bit more failure resistance.

[qquake2k]

"How do you know Rosie O'Donnel hasn't eaten her children? Have you seen them lately?"

[qquake2k]

Thanks Jim, coming from you that's a real complement. I've admired your builds for a long time.

I'm prolific, but I don't consider myself a craftsman. You're really doing it right.

[scsager]

Attachment 83158

The interior of the coupler is flooded with thin CA to help minimize charring.




At the top, the bulk plate is recessed about 5mm (1/4") to make room for a reinforcing fillet ring made from a scrap of coupler tube. This is trimmed flush after the glue dries.





Don't really know if the JB weld will help stop the eyebolt from opening under extreme load, but It can't hurt anything .







Shock Cord, upper air frame and nose cone are all that is left. That and I still have to think about a radio tracker (if any) , and a paint job - I think I'll start by Googling "Flame Job". Might as well challenge myself fully in all areas.

[scsager]

Another late niter. Raining this morning, but by late afternoon it became sunny, cool, but sunny - time to get a little more paint on some of the builds. Then my oldest daughter had a HS band concert this evening… well here I am at midnight updating the build.

The nose cone is going to take a little work. The design in OpenRocket calls for 100 grams in nose weight to give about 1 caliber of stability. I cut the 3 meter shock cord from my stash of 3mm braided Kevlar. (rocketry is my excuse to use the metric system) That's about 10ft of 1/8" Kevlar. I plan to use a TopFlight recovery 24" chute. So I stuffed that into the already cut upper airframe and taped on the nose cone to hold it in place.

Then I weighed out 100g of lead shot into a plastic "shot glass" (what would you use?) Then taped that to the nose.

OpenRocket shows the CP to be at 470mm back from the nose, so I marked that spot on the airframe. Then measured up 66mm and marked where I wanted the CG to be.

I put the rocket on the balance beam and bango (rocketry slang for bingo) it balanced at 1 caliber right away with no adjustment.

Extra bonus… I found one more use for the Super Multi-Functional Estes Tube Marking Guide.

[scsager]

The inside of the nose cone must be rough sanded to promote better epoxy adhesion. The puny molded nose cone eye is chopped off with a hobby knife, and the hole needs to be opened up a bit to allow the sanding dowel to fit. Step bit from Harbor freight is used to enlarge the hole.





Sanding dowel is used to rough up the inside of the nose cone.
Very important to give the epoxy a more mechanical bond.




In addition to sanding, pins are used to make sure the nose weight stays put. I drilled 2 sets of holes in the nose cone where the epoxy/lead shot will end up. A small hardwood dowel is inserted thru the holes. This helps anchor the nose weight after the epoxy cures .




I used a new technique this time. I used a dowel pin in one set of holes, and just tape over the other set of holes. The idea behind the tape is that the epoxy itself will fill the holes and make "epoxy rivets". After everything cures, I will just pull the tape off - and no sanding required. At least that's the idea, we'll see how that works out. The dowel pin will need to be sanded flush with the nose cone. This will be difficult to do without damaging the smooth surface of the nose cone.





I'm using Hobby store brand 30 minute epoxy for this. After mixing the epoxy, about half of it is pored into the nose cone. This is followed by about half of the lead shot. Then the rest of the epoxy is poured in, followed by the rest of the shot.

The epoxy may become hot while it cures, and I don't want it to damage the plastic nose. The nose is suspended in a cup of cold water to keep the epoxy cool while it cures.

[scsager]

Well this is a perfect excuse to bring another music video into the build while we wait for the epoxy to stay cool in that cup while it cures . Here's the backstory on this one…

I went to high school with a guy named Mike. After HS, Mike moved out to LA and became a big-time hot-shot movie director. Here's a shot of Mike (in the Santa Cruz T-shirt) and some of his crew setting up the final shot for a music video.






Now go Here to watch the music video - pay special attention to the very last shot in the video... notice the similarity to the photo. The people are different, but the ceiling is the same...

http://www.youtube.com/watch?v=BKZqGJONH68&ob=av2e

Tune in again tomorrow for more nonsense... and some rocket making.

[McKailas Dad]

Scott, looks like you are doing an awesome job! I am really looking forward to seeing you launch this. Maybe if you de-tuned it (F24 x2?), you could fly it at Johnson Creek?

Keep it comin', looks great. I knew somethin' called the Little Duece Coupe HAD to be great!

Any plans for Three Ducks on a Pond?

[Rex R]

then there is '409' & 'Drag City'( http://youtu.be/c2GwDGjiV4k )

[scsager]

Scott, looks like you are doing an awesome job! I am really looking forward to seeing you launch this. Maybe if you de-tuned it (F24 x2?), you could fly it at Johnson Creek?

Keep it comin', looks great. I knew somethin' called the Little Duece Coupe HAD to be great!

Any plans for Three Ducks on a Pond?

I have to do more simulations on 2xE and 2xF power to see what would really work ... and I have on my *MUST* do list to fly at JC and the Sod Farm this year. I've never flown at either location (hangs head in shame)

This Saturday I think we are headed up to Sheboygan to watch em fly the Rockets for Schools program.