Finishing touches on a Madcow DX-3 4" cardboard for L2

[Off Grid Gecko]

K guys, sorry didn't do a build thread, just jumping back on the wagon and what better way than building a rocket for my L2 cert?
Still need to lay down some clear coat and might do another layer of sparkles as well but focusing on my internals and have a few points that I think need some more consideration.

Can't promise I'll use all the ideas you guys present, but definitely looking for some advice/support on how to finish her out.
Here's a pic I took of her on the floor (she didn't like being down there one bit but it was for the greater good).

...
I found these little derlin plastic rivets to hold the payload bay to the e-bay up top. Figured they would do the job and they're nice and small and non-obtrusive, and hopefully not too draggy.


Instead of adding weight to the cone, I got the idea from a member here to bolt it into the base of the nosecone. On the sim with one of my L2 motor options, the CG/CP distance was coming in at .83D, so I extended it. Now showing between 1-2 for any motor I think she'll fly on, with some happy wiggle room on both ends of the spectrum, and I didn't have to mess around pouring stuff into the tip. I cut a hole in the side and used fender washers and a bolt to make a heavy little stack...



Loctite included of course.

Pretty sure all of that is fine, and to keep this broken up I'll get into the meat and potatoes with another post below this one. Incomming shortly.

 

[Off Grid Gecko]

Okay, so a couple things I'm really concerned about as this will be a dual deploy setup are the electronics bay sturdiness, and the potential use of shear pins. Here are some closeups and I'll describe below.







All the hardware is threaded 1/4-20 and the nuts (locking and regular) are grade-8. The washers were whatever I could find, stamped UAB,, I think they're zinc but not the best at hardware stuff and codes.

The derlin spacers on the bottom of the sled were set with 5-min JB ClearWeld and much to my surprise I needed zero sanding to get everything to screw together tightly without undue stress. The wood is Luon (sp?) (it's a phillipino ply, 3 thin layers sandwiching the semi-exotic wood between used for backings and other stuff like that, works great for a fin material so I have extra laying around).
Those are lock-nuts on the eye-bolts and yes I intent to check that they are tight as part of every pre-flight prep. I don't want to glue them in case I need to replace one later.

Seem strong enough? I'm looking at around 3000-3500 ft on a J, but will be launching it on an H or I with just single deploy to test and make sure everything looks good on the electronics and have a "dry run" or two before attempting my L2 with her.

As you can see, I also put some beer-can tabs at the front of the payload bay in case I decide shear pins then I already have reinforcement and just need to drill holes. I would be totally comfortable doing this at the launch site, so I figured don't run. Pins are coming soon and they are 20# break nylon screws. Open to opinions on this. If not I'll stuff that NC in there nice and tight, but with all the weight in it now I think prolly better to use the pins for the dual deploy setup.

I have brass 45ACP cases lying all over the place, thinking about epoxying some on the ebay endplates for charge wells (JB clear weld or JB weld will be the glue of choice). I have my little yellow rocket that will test this idea with clear weld on a mid-power motor as well. It will be that or cpvc. I can also knock out a primer pocket or drill a hole and add a screw for a more secure hold,, or maybe a tiny bolt? Ideas?

Overall just looking for like... not being embarrased, lol. Want some sanity checking as I'm in the woods by myself and there's not a lot of dialogue anyway, especially not about rockets.

Nother thing. My bottom t-nut (rail lug, brian not working, for the 1010 rail) went in a little crooked. Directly along the line, but angled back toward the motor maybe 10deg. It's in solid and from past experience I wouldn't expect that to be an issue but wondering if I should remove it, smush wood glue into the hole then redrill and reset or just leave it. I don't have a pic of that one sorry.

I plan on attaching a 9v battery in the bay by drilling 6 holes and wrapping it with the 1/4" wide tie wraps. EZ-mini will be mounted with derlin mounting screws, switch will just depend on what switch I end up getting.

Seem solid? Hoping to have it done soon and maybe even get the motors and at least do my test launches next month. Body needs another coat of sparkle (or 2) and some clear. Finished scuffing it with 600 grit yesterday, that's why it might look a bit dull.

 

[GalantVR41062]

I flew a MC DX3 4" cardboard kit for my L2 a handful of years ago. Here is a link to my build thread: https://www.rocketryforum.com/threa...and-plywood-kit-38mm-mmt.147205/#post-1826103

I have flown mine on a AT H242 up to a CTI J530IMAX.

I would recommend you weld the eyelets on the ebay end caps or switch to 1/4" diameter U bolts. I would use 1/2" pvc caps screwed down for charge wells, cheap, strong, non conductive, short. I use 1gram for my apogee event and 1.4grams on the main event with 2 2-56 nylon screws holding the nose cone on, ground test until your sure it's good. I recommend you do a sold retention for the nose cone, depending on flight profile, wind at altitude, delay times, shock cord length, as the harness fully extends and the drogue inflates the nose cone could come out and deploy the main. I agree that 3000-3500' is possible, what J motor are you looking at? Make sure your motor and 9volt battery are very secure. I have 3 screws going into my ebay lid to hold my payload tube on.

Study for the test, have someone take some pictures and video, keep working on the simulation file and make changes after your H and I flights to better predict the J flight, use a check list, prep and disassemble the rocket a few times at home to get the process down, have fun.

~John

 

[Off Grid Gecko]

I flew a MC DX3 4" cardboard kit for my L2 a handful of years ago. Here is a link to my build thread: https://www.rocketryforum.com/threa...and-plywood-kit-38mm-mmt.147205/#post-1826103

I have flown mine on a AT H242 up to a CTI J530IMAX.

I would recommend you weld the eyelets on the ebay end caps or switch to 1/4" diameter U bolts. I would use 1/2" pvc caps screwed down for charge wells, cheap, strong, non conductive, short. I use 1gram for my apogee event and 1.4grams on the main event with 2 2-56 nylon screws holding the nose cone on, ground test until your sure it's good. I recommend you do a sold retention for the nose cone, depending on flight profile, wind at altitude, delay times, shock cord length, as the harness fully extends and the drogue inflates the nose cone could come out and deploy the main. I agree that 3000-3500' is possible, what J motor are you looking at? Make sure your motor and 9volt battery are very secure. I have 3 screws going into my ebay lid to hold my payload tube on.

Study for the test, have someone take some pictures and video, keep working on the simulation file and make changes after your H and I flights to better predict the J flight, use a check list, prep and disassemble the rocket a few times at home to get the process down, have fun.

~John

Thank you for that. I'll take a look at your build thread later today. Prfessor recommended welding the eyelets as well. Thing is, with everything already put together I won't be able to get to the one inside of the fin can. I can scratch them up maybe and add a touch of JB Weld. Surprised to learn that a 100lb hook can bend so easily but you are the second person to mention it to me. That might be a good reason for me to glue on the ebay lid as well on the main side I suppose, just lesson the stress from that side.

What about going with longer shock cords and z-folding them with some masking tape? I haven't ordered a new main chute yet so I'll prolly be picking up some shock cord with it and use the included one for the fin can side. I'm sure testing will tell.

1-1.4 grams is about what I was figuring (calculated 1.2 iirc) but have gotten varying opinions on that. Will try a couple ways for sure on the ground before test flights and see what happens. First test flight there won't be anything behind the nose but a shock cord, maybe a long streamer or something for effect or put the drogue in there. Don't want to rely on it just to see it pop open at 400-500 feet.

Thanks again for the thoughtful comments. Will check out your build thread for sure and see if I can hook up a friend with a mig welder to take care of the eye-bolts I can get to.

 

[Off Grid Gecko]

Someone had also mentioned to me about the vent hole for the altimeter needing to be sharp. All the holes on this build are cut nice and clean but I was wondering if anyone had insight into this. I would think the size of the hole would matter more than any fuzziness from the cardboard. I have a 1/4" hole (perhaps a size larger) in the little exterior band for the payload bay My vents are drilled about 1/8th of an inch. Haven't given much thought to this but also wondering if those sizes will be adequate.

 

[SILVERFOX]

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Someone had also mentioned to me about the vent hole for the altimeter needing to be sharp. All the holes on this build are cut nice and clean but I was wondering if anyone had insight into this. I would think the size of the hole would matter more than any fuzziness from the cardboard. I have a 1/4" hole (perhaps a size larger) in the little exterior band for the payload bay My vents are drilled about 1/8th of an inch. Haven't given much thought to this but also wondering if those sizes will be adequate.




1/8" vents should work fine. Superglue around the inside edges and re-drilling cleans up the holes, and it's great for getting the sheer pin holes from getting out of round. Looks like you are thoughtful, curious and meticulous enough that you will have success! Enjoy!!

 

[Off Grid Gecko]

Waiting on fedex to get my igniters here. Might drive back to NARAM tomorrow rocketless and enjoy the show, or take the lil one with me and launch it on a C.

 

[Off Grid Gecko]

First test fitting shear pins... I hate the plastic nosecone on this thing, it's so,,, not right, ,but it's workable. I'm firmly convinced that three of these pins is too much. I'm yanking on the thing and it isn't budging. Pretty sure air pressure at 3000 feet isn't going to work it out, nor is a little pop from the deployment charge. Might try one or two. One seems like a no-go I just can't trust the inner nose diameter. Will prolly do 2/3 for the first test.

Got my stuff today but don't have time to make 80 igniters so gonna push that off. Plenty of time.

AeroPack is fitted to the motor tube and JB weld needs to cure so not much else. I grabbed 3/4 cpvc caps instead of half inch,, annoying, but went ahead and glued them on. If nothing else I'll put a smaller charge cap inside of it if I need to make it smaller. Secured with JB clear and a #8 machine screw/nut. Even if the nut manages to back off I'm sure the epoxy will hold it.

I don't have a big kevlar ribbon but I do have some kevlar 1500 lb test line. Was thinking about securing that to the shock cord end but not sure yet on that either. All these decisions, lol. I won't order the motors till she's flight ready so that I can't talk myself into coming up with a quick fix and flying it.

 

[Off Grid Gecko]

Side question: You guys every bang and yank on your rocket components just to make sure they are solid. Caught myself slapping the piss out of my electronics bay after the CPVC epoxy hardened. I just don't want something to snap off in flight cause there was a week spot that could have easily been "stress tested" on the ground.

With my L1 I remember standing it upside down on the fin-can/motor-tube section. Put a tin pellet can over the motor mount, and stacked several bricks on top to simulate the thrust of a heavy I motor, being careful that I didn't let it tip. When I removed the blocks, the pellet tin was smushed and all the pellets inside were out of round. Didn't hurt the rocket one bit.

 

[dr wogz]

As we tell some of our students: "the recovery event / process is likely the most violent aspect of the flight.."

what 'not right' with the nose cone?

 

[Off Grid Gecko]

As we tell some of our students: "the recovery event / process is likely the most violent aspect of the flight.."

what 'not right' with the nose cone?

sorry for the late reply been busy.
It's too small, it's out of round, and even after sitting in the sun all day at naram there are two places on it where the top of the cardboard from the payload bay is pretty well exposed.

I called MadCow, no answer. Sent them an email asking if a FG nosecone would fit the tube and told them what was going on and that I'd prolly need a replacement... no answer. Thinking about getting some chutes from Apogee so I might just order a cone from them. Maybe pay a lil more but when I call them they answer the phone, so I'm sure I can get some guidance on a cone that will fit properly. I'll just leave it unpainted, maybe sand it or clean up flashing or something. I just want things to be right.

Have a couple reservations about these rivets too, so she might not fly this month. Maybe Oct. at least get a maiden on her but my buisness in crypto-dev is slowing so I'm going back to mostly savings mode. Gonna make a couple smaller rockets too that need minimal prep and still try to get to the local group launches.

 

[Off Grid Gecko]

New nose cone arrived from MadCow the other day. They finally got back to me. Spent my Sunday doing some rocket stuff. Got a test lined up. Staged 2 old tires with the front end of the rocket resting on one while using the other for a stop at the back in case of recoil, lol.

Re-ran my calcs and decided to test with 15gn(1 gram) of FFFF. Seemed like a good overall place to start. I tested the altimiter in flight on a mid-power rocket so I'm happy with its performance, rand a direct wire through the breathing hole and connected to the altimeter and fired electrically from the altos-ui software.

3 of those #2 pins and the new NC popped off with some authority, gave a little bit of a tug to the rocket body (no motor weight installed) and pulled it onto the prop tire when the cord extended fully... I dunno. Haven't done this before. But I would call that a successful test.

I'm running the charge in a cpvc tube, then drop in the match with the little red hood aiming it into the powder, then pack with dog barf and secure with a piece of masking tape, just like I did on the little rocket. It looks like I'm getting a pretty clean burn.

Pins all 3 sheared cleanly, with a bit left in the nose and the screw still installed on the airframe. No damage to my beercan tabs, no visible stressing of the eyebolts. The shock cord got a little soot on it but didn't get burned at all.

When I did up the weight on the new NC I replaced the 3/8 bolt with a 3/8 steel eyebolt also. The more I look at that plastic loop the less I trust it. So essentially, the heavy part of the nose is all one chunk of steel with a nosecone mounted to it.

I think I earned a bear. Thanks to everyone who chimed in here and on my other posts. Gonna look at ordering some motors. Maiden on a strong H or an I, then L2 attempt on a J. Both of them likely in the 300N range for thrust.