MK82 High Drag bomb rocket

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Here are a couple more pictures of the rocket. This is the front end where the outer body tube will slide on the coupler tube.

IMG_2252.JPG

IMG_2253.JPG


I drilled holes through the MMT for the kevlar shock cords to pass through. I lined them with brass tubing to keep the cords from getting scorched.

IMG_2251.JPG
 
I glued the shock cord mounts to the petals. I also added a 1/8" x 3/8" balsa rib to each petal to add strength and give it a little more military look.

IMG_2254.jpg

IMG_2255.jpg


Next up is ejection charge testing. Muhahahahahahaa.
 
Really nice...

I do have a question... have you simmed this thing out and determined if it'll be stable?? Where is your CG and CP??

Reason I ask is, the fins look awfully small... the strakes should help, but MOST of the stability effects of a fin are span-wise (perpendicular dimension from the body tube) not lengthwise (parallel to the body tube long axis). The fact that the strakes are SO long may actually work against you, IOW the strakes may not contribute much of anything to stability due to their length. The fin span looks pretty small too, ie the fins don't stick out very far from the tube...

Just wondering because you don't want it to part your hair as soon as it leaves the rod or rail... The design looks great otherwise. I assume you want to keep the weight as low as possible to minimize descent speed... makes good sense. I just wonder though with the small fins and the weight of the hinges, motor, and other parts tending to be concentrated toward the back (other than the slider part where the body sections part out into petals for descent) how the CG/CP relationship looks...

Best of luck and kudos on a great project! KUTGW!! OL JR :)
 
Here's an ejection charge test with a stock .5g charge. I taped the bottom of the nose cone shut. I'm going to try it again with the tape removed.

[YOUTUBE]uSSxYVFTbw8[/YOUTUBE]


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Yes, it's motor only ejection. And yes I have simulated it in Openrocket and it will probably need some nose weight. I'm going to do a swing test before I fly it.


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Well I tried again with the tape removed and a couple stops on the forward body tube. The tube stopped but the cone kept going. I think I need to try a different method to stop the cone and tube and cut the charge down.

[YOUTUBE]S6MhPOjrwQk[/YOUTUBE]



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I think getting the right size ejection charge should do it. Way to energetic now. I know you want to keep it as light as possible but I think a bulkhead in the upper body tube right above the stuffer tube would get the gasses exiting your coupler rather than pressurizing the whole upper body tube. After you get that right all you have to worry about next is the timing of the charge!! You do not want it moving too fast at ejection. Again VERY NICE project.
 
SUCCESS!!!!

I drilled two 3/16" holes in the bottom of the nose cone and tied a loop of 1/8" Kevlar though it and the brass tubes that protect the shock cords. It is just long enough that the body tube will clear the petals by about 1/4". I reduced the charge to .3g. The body tube moved just enough to clear 3 of the 4 petals. I'm going to try again with .4g but I'm sure that it will work.


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I added 1mil plastic panels between the petals. I attached them with double sided tape.

ImageUploadedByRocketry Forum1409627393.515339.jpg


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Great progress on this project. Looking forward to seeing it fly.
 
Dude, you put that nose cone in the bushes! Nice.....


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I posted a video of the test I did with my 7.5" Door Knob and my neighbor told me I should point all future tests in the other direction. Now I'm starting to agree with her. :D

Lowpuller said:
Dude, you put that nose cone in the bushes! Nice.....


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Click to expand...
 
Thanks to everyone that has contributed to this thread. It's been a fun project.
 
This is such a cool project! What are you planning to fly it on? My thought is that you really would not want it too high, because the fun will be to see the deployment.

I like all the ground testing. It looks fun. I don't actually do any kind of deployment using electronics, but now I'm thinking I might still want to spend some time "testing" in my backyard. Boom! That ought to get the neighbor's dogs excited!
 
My thoughts exactly Thirsty. It will fly on a D12 or E15. I'll shoot for 500' or so.

I bought 10 of the non-regulated ematches last week. I burned through 5-6 this weekend. The 2g charge in my Door Knob was more fun though. :wink:
 
evvo, I've had a couple people express interest in the drawings, but I think that *IF* it works out I might offer a it as a kit or semi-kit through my web store. It would be cheaper for everyone to get the parts cut in batches.

I've never built any skill level 4 or 5 kits, but I'd say this rocket would fall along those lines.
 
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A semi-kit would be great!
I've got no shortage of tubing, rings, nosecones.
It's the specialty parts that are worth it!
It reminds me of the Estes Skywinder, one of my favorite kits. A nice easy to build helicopter (just have to reinforce the center tube!)
 
I bought some D15T-4 reloads yesterday for the test flight(s). Hopefully I can use all of them. It should get about 440' on that motor. OpenRocket is calling for a 3.95 second delay so that's about as close as I can hope for.

When I got home I attempted a string flight test. Stock it flew sideways, with one ounce taped to the nose it started to fly a little straighter, and with 2 ounces it seemed pretty happy. RTF it will weigh 9-10 oz. I need to stop by Michael's to get some clay today.

The only things left to do are install the clay and add some silicon sealant to the shock cords so they stay centered on the motor mount. The heat shrink tubing I added keeps moving around.
 
I flew the rocket this morning. It flew straight and the ejection charge went off just after apogee. Unfortunately the ejection charge sounded weak and only one of the petals opened. The rocket fell flat so there was little damage. I decided that maybe since I added weight to the nose cone that the ejection charge wasn't strong enough to kick it off. I was also under the assumption that the stock charge was .5g like I had read so I measured out a .6g charge and flew the rocket again. It arced over and was heading for the ground when the charge went off. The charge was so strong that it tore out the bottom of the nose cone and blew out the side of the upper body tube. :facepalm:

I went home and measured the final ejection charge in the package and it was only .2g. So, I should have used a .4g charge like I thought in the first place. Thankfully I have another nose cone and tube, so I'll repair it and try again later today.
 
The third flight was almost a success. The ejection charge was probably still a bit too strong, but three of the petals deployed and it came down safely. The motor ejected out of the rocket though. I'd like to put some bigger springs on the petals if I can find some.

[YOUTUBE]FfLNd7FWuuc[/YOUTUBE]


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You're on to something for sure here Chris! Your hinge assembly could end up inspiring a lot of creative designs, I have a few ideas that are beyond my abilities right now!
 
Thanks again for the comments. I uploaded a HD version of the video. In it you can clearly see that the deployment was successful but the rocket immediately did a full flip and closed one of the petals. So, I have proof that I need stronger springs on the petals. It's pretty obvious that I can cut down the gores between the petals too, since it came down at a reasonable speed even with only 2 gores deployed.
 
Thanks!

I ordered some stronger springs for the petals from McMaster Carr yesterday. I also made a template to remove about 1/2 of the material from the plastic sheeting I added between the petals. I also need to reglue the brass tubes that the shock cords pass through. Apparently the .6g ejection charge broke both of them loose. :facepalm:

I'm planning to fly it again this weekend at LUNAR's Moffett Field launch. Wish me luck.


Chris
 

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