L1/L2 Super DX3 Build

[burritoman1]

Hello!

After some issues with my last L1 build I've decided to start from scratch with a Super DX3. In the interest of saving money, I decided I would build my rocket so that it could later be used for my L2. Before I post some build pics, I'd like to ask a few general questions.

1. I have a fiberglass altimeter bay with a Raven 4 and backup altimeter, so I'm absolutely capable of doing dual deploy for my L1. However, I'm wondering if its smarter to instead do motor ejection or some combination thereof (ex: motor ejection for drogue, electronic deployment for main). I was also curious how I might build my rocket for the L1 so that I would be able to later add dual deployment for the L2.

2.I have some MR-1 Retention clips from a LOC-IV kit, I was wondering if that would be sufficient for L2. If not, I can DIY something more robust like the Madcow Retainer.

3.I have plenty of Rocketpoxy, I'm not sure if that would be overkill compared to JB Weld. My current plan is to JB Weld the internals and use Rocketpoxy for the fin fillets.

In addition, if you have any tips for strengthening my rocket for the L2 that aren't mentioned in the DX3 instructions I would love to hear them.

Thanks in advance!

 

[Titan II]

In addition, if you have any tips for strengthening my rocket for the L2 that aren't mentioned in the DX3 instructions I would love to hear them.

Not necessary at all.

 

[Handeman]

Are you doing the cardboard Super DX3, or the fiberglass version? It doesn't really matter much, but if you are doing the heavier fiberglass, I would recommend the 54mm MMT instead of the 38mm, especially if you intend to fly many L2 motors in it.

Since you say you want to save money, would I be correct in assuming you want to fly this rocket with more and larger L1 and later with a variety of L2 motors?

In either case, I would seriously consider building it with dual deploy, even with one altimeter. I don't think an L1 and small L2 really need dual altimeters since the reliability of todays altimeters are so good. In either case, I would fly with DD on the cert flight in the configuration you intend to use for all future L1 and L2 flights. I don't like the idea of switching configurations for cert vs. post-cert flights. Just seems like asking for trouble on the cert or the first post-cert flight.

As for the retainer, the retention clips should work fine. The force on the retainer is the surface area of the motor times the pressure of the ejection charge. Since this is a 4" rocket, the force on the top of a 38mm or 54mm motor is not near the force on the 4" av-bay so I don't think you will have any problems.

Good luck on the cert flight. Don't overthink it.

 

[burritoman1]

Are you doing the cardboard Super DX3, or the fiberglass version? It doesn't really matter much, but if you are doing the heavier fiberglass, I would recommend the 54mm MMT instead of the 38mm, especially if you intend to fly many L2 motors in it.

Since you say you want to save money, would I be correct in assuming you want to fly this rocket with more and larger L1 and later with a variety of L2 motors?

In either case, I would seriously consider building it with dual deploy, even with one altimeter. I don't think an L1 and small L2 really need dual altimeters since the reliability of todays altimeters are so good. In either case, I would fly with DD on the cert flight in the configuration you intend to use for all future L1 and L2 flights. I don't like the idea of switching configurations for cert vs. post-cert flights. Just seems like asking for trouble on the cert or the first post-cert flight.

As for the retainer, the retention clips should work fine. The force on the retainer is the surface area of the motor times the pressure of the ejection charge. Since this is a 4" rocket, the force on the top of a 38mm or 54mm motor is not near the force on the 4" av-bay so I don't think you will have any problems.

Good luck on the cert flight. Don't overthink it.

This is the cardboard kit, with the 38mm. I figured that the larger 38mm motors would get it as high as I would reasonably want it to go. I think I will go the dual deploy route, but in that case I'm wondering if I should do motor ejection for the drogue and electronic for the main or just electronic deployment for both chutes. Both would probably work, but I'd ideally like to play it safe.

 

[NTP2]

This is the cardboard kit, with the 38mm. I figured that the larger 38mm motors would get it as high as I would reasonably want it to go. I think I will go the dual deploy route, but in that case I'm wondering if I should do motor ejection for the drogue and electronic for the main or just electronic deployment for both chutes. Both would probably work, but I'd ideally like to play it safe.

Go with electronic deployment on main only so you have 1 less way to have a unplanned disassembly.

 

[Hobie1dog]

Go with electronic deployment on main only so you have 1 less way to have a unplanned disassembly.

+1 sounds ideal

 

[86mustang408w]

Good luck man. I thought about using the same rocket for L1/L2 but I'm just going to split them up.

 

[Titan II]

I think I will go the dual deploy route, but in that case I'm wondering if I should do motor ejection for the drogue and electronic for the main or just electronic deployment for both chutes. Both would probably work, but I'd ideally like to play it safe.

If you do electronic, use it for both and keep the motor ejection as a secondary for the drogue.

 

[thzero]

1. I have a fiberglass altimeter bay with a Raven 4 and backup altimeter, so I'm absolutely capable of doing dual deploy for my L1. However, I'm wondering if its smarter to instead do motor ejection or some combination thereof (ex: motor ejection for drogue, electronic deployment for main). I was also curious how I might build my rocket for the L1 so that I would be able to later add dual deployment for the L2.

You don't have to wait until you are L2 to do dual deploy... you can do dual deploy even with mid power rockets. Most people recommend don't do your L1 or L2 with dual deploy, but do what you want.

Build a separate rocket for L2 and learn something new.

I have plenty of Rocketpoxy, I'm not sure if that would be overkill compared to JB Weld. My current plan is to JB Weld the internals and use Rocketpoxy for the fin fillets.

JBWeld is good for the fin root to motor case and the motor retainer. Use rocket poxy for everything else.

In addition, if you have any tips for strengthening my rocket for the L2 that aren't mentioned in the DX3 instructions I would love to hear them.

Not necessary unless you are doing something odd, or if you are learning new techniques.

 

[bad_idea]

I'm wondering if I should do motor ejection for the drogue and electronic for the main or just electronic deployment for both chutes. Both would probably work, but I'd ideally like to play it safe.

Use electronic deployment for both. If you have experience with dual deploy, ditch the motor ejection charge entirely if you're flying a motor that might chuff or if the longest available delay is relatively close to the projected apogee.

 

[burritoman1]

I've started the build, epoxying both centering rings to the MMT as level as I could make them. However I noticed that when I screwed the eyebolt into the forward bulkhead that it sinks into the hole a bit, causing it to be at a bit of angle. Is it supposed to look like that? I'm considering just putting another washer on the other side of the centering ring to fix it.

 

[thzero]

I've started the build, epoxying both centering rings to the MMT as level as I could make them. However I noticed that when I screwed the eyebolt into the forward bulkhead that it sinks into the hole a bit, causing it to be at a bit of angle. Is it supposed to look like that? I'm considering just putting another washer on the other side of the centering ring to fix it.

I do... But I also use forged eyebolts.

 

[boatgeek]

This is the cardboard kit, with the 38mm. I figured that the larger 38mm motors would get it as high as I would reasonably want it to go. I think I will go the dual deploy route, but in that case I'm wondering if I should do motor ejection for the drogue and electronic for the main or just electronic deployment for both chutes. Both would probably work, but I'd ideally like to play it safe.

I would go electronic for both main and drogue and either drill the motor delay a few seconds long or just leave it undrilled. That way the motor can be a backup for the drogue. You won’t have a backup for the main but landing on drogue alone is rarely catastrophic.

 

[GalantVR41062]

I have a MC 4" super dx-3 cardboard and plywood, build thread and journey to level 2 here: https://www.rocketryforum.com/threads/madcow-super-dx3-cardboard-and-plywood-kit-38mm-mmt.147205/

You can dual deploy this rocket, you could motor eject and longer walk it pending motor choice and field size/weather, you could motor eject with a Jolly logic chute release, many options.

I would watch the center of gravity, the back end of mine ended up a little heavy so with the larger 38mm J motors maintaining the 1cal of stability is tricky.

I would use a forged eyebolt or weld the ones you have so the eyelet does not pull open, and make sure you use locktite, locking nut or epoxy to prevent it loosing over its service life.

I am a big fan of capturing the fins with centering rings, but is probably over kill for a rocket like this, unless your flying something like the Loki J1000/J1026 motors.

I have flown mine on the Loki H160b motor to the CTI J530 IMAX. I used titebind 2 wood glue, rocketpoxy fillets, nothing fancy.

Have fun and learn along the way.

 

[burritoman1]

I would go electronic for both main and drogue and either drill the motor delay a few seconds long or just leave it undrilled. That way the motor can be a backup for the drogue. You won’t have a backup for the main but landing on drogue alone is rarely catastrophic.

I think this is the route I will end up going thanks!

I have a MC 4" super dx-3 cardboard and plywood, build thread and journey to level 2 here: https://www.rocketryforum.com/threads/madcow-super-dx3-cardboard-and-plywood-kit-38mm-mmt.147205/

You can dual deploy this rocket, you could motor eject and longer walk it pending motor choice and field size/weather, you could motor eject with a Jolly logic chute release, many options.

I would watch the center of gravity, the back end of mine ended up a little heavy so with the larger 38mm J motors maintaining the 1cal of stability is tricky.

I would use a forged eyebolt or weld the ones you have so the eyelet does not pull open, and make sure you use locktite, locking nut or epoxy to prevent it loosing over its service life.

I am a big fan of capturing the fins with centering rings, but is probably over kill for a rocket like this, unless your flying something like the Loki J1000/J1026 motors.

I have flown mine on the Loki H160b motor to the CTI J530 IMAX. I used titebind 2 wood glue, rocketpoxy fillets, nothing fancy.

Have fun and learn along the way.

I looked through that thread, a lot of valuable information in there. Capturing the fins probably would have been a great idea, too bad I already glued the aft centering ring on. I do have a laser cutter available to me though, so I can probably cut a third ring into two halves that I can assemble around the motor tube. I'm also considering injecting internal fillets through a hole drilled through the aft ring.

 

[Handeman]

This is the cardboard kit, with the 38mm. I figured that the larger 38mm motors would get it as high as I would reasonably want it to go. I think I will go the dual deploy route, but in that case I'm wondering if I should do motor ejection for the drogue and electronic for the main or just electronic deployment for both chutes. Both would probably work, but I'd ideally like to play it safe.

I've never used motor ejection with DD for the last 16 years.

I'm not convinced using motor ejection backup on a DD flight isn't a higher risk of failure than just using the electronics. In 16 years, I've only had two apogee charges fail on DD flights. I've had 3 motors ejections go off at motor burnout which zippered the rockets and shredded chutes.
Motor eject could have helped those 2 apogee charge failures, but I fly so many more DD flights than motor ejection flights that I would expect, at the failure rates I experienced, instead of the 2 DD apogee failures, I would have had 4 - 6 motor ejection failures instead if I had used motor ejection backup on all of those DD flights.

If you are really worried about a DD failure, add a backup altimeter. I don't think that really gives you that much more safety margin, but it could add to peace of mind, especially on large projects where weight and expense of redundant altimeters isn't much of a consideration in the overall project.

If you do fly with motor ejection as a DD backup, make sure it's set about 2 seconds after apogee. You don't want it going off early and if you do have a DD failure, a very late motor ejection could still zipper the rocket. Also make sure the motor ejection charge is sized right. Not too small that it doesn't open the rocket, but not so large that if it goes off a little before the apogee charge, it doesn't cause excessive shock on the system and cause a main deploy at apogee.

 

[burritoman1]

Capturing the fins probably would have been a great idea, too bad I already glued the aft centering ring on. I do have a laser cutter available to me though, so I can probably cut a third ring into two halves that I can assemble around the motor tube. I'm also considering injecting internal fillets through a hole drilled through the aft ring.

Ok so i'm considering opening up the fin slots to the end of the BT so that i can put a third centering ring on the MMT and some thorough internal fillets on the fin can. It would then be as simple as just sliding the whole assembly into the BT. I just want to make sure im not going to significantly weaken the BT by doing so. As for patching up the hole, I have fiberglass sheets I can use but perhaps duct tape would be easier.

 

[jackiboi_11]

That’s what loc does on their LNR systems. Not completely sure how it will work for your DX3 but if you mean making a slit so the fin can can be inserted already assembled it won’t cause any weakness when you epoxy the can in

 

[ridnharley]

I used a Super DX3 cardboard for my cert 1.
To get my cert I kept things very simple.
After that I changed things up.
I used a 3rd centering ring on the motor tube for extra strength.
I attached the nosecone with sheet metal screws.
Plastic rivets held the bay in the upper tube.
Shear pins held the upper and lower airframes together.
I flew on an H283 and used the chute that came with the kit.
I used a parachute protector cloth.
Very simple up, motor ejection charge, descent and a Cert 1.

 

[burritoman1]

Hello everyone! I know it's been a while but I've made a lot of progress since my last build. I'll start by listing what I've done so far.


I opened up the fin slots to the end of the body tube so that I could assemble the fin can externally.





After securing the fins to the motor tube with JB weld, I've begun to do internal fillets with West Systems 105/206 epoxy. I also put a third centering ring on top of the fin tabs to make them more secure. Since the aft centering ring was already glued on, I just cut the third ring in half and assembled it around the motor tube.





Unfortunately, without the colloidal silica the epoxy was very runny. I had to leave the fincan upright to dry, so I can only do 1 pair at a time (every 24 hours). In fact, the epoxy was so runny that it seeped through a gap in the centering ring and dripped down to the table, gluing the bottom fin to it VERY securely. I was able to separate it by blasting it with a heat gun, but it ended up taking a chunk of the table with it. After sanding it down with a dremel (and ruining the bevel edge I took ages making ) it looks more or less good as new.




I also created two very simple charge wells by putting a 1/4-20 bolt through a 1/2 in PVC end cap. With these done I should be ready to put together my e-bay.




I have also secured my L1 motor (H219-T). I'll post the exact info from OpenRocket later, but the numbers seemed to work out pretty well: 1500 ft apogee, peak acceleration of 20Gs, 70mph off the launch rail.

Anyways, with a month left until the expected launch date there's still quite a few things left to do.

TO-DO LIST

• Finish internal fillets
• Secure fin assembly to lower BT
• Add external fillets to fins
• Construct e-bay and test electronics and BP charges.
• Install and test recovery hardware
• Sanding, painting, polishing, and decals

As always, if you have any comments/tips/critiques add them below!

 

[thzero]

West systems that you were using is a laminating epoxy. For fillets you need to use some type of filler, or something like Rocketpoxy thats basically already prefilled. Most guides, etc. say to have a peanut butter consistency.

Unless you are experienced with electronic ejection, I'd avoid it for the certs

 

[burritoman1]

West systems that you were using is a laminating epoxy. For fillets you need to use some type of filler, or something like Rocketpoxy thats basically already prefilled. Most guides, etc. say to have a peanut butter consistency.

Unless you are experienced with electronic ejection, I'd avoid it for the certs

I've been using 404 high density filler. I'm probably going to purchase the 406 silica for the external fillets but I figured the 404 would suffice for the internal fillets.

 

[Flare]

DX3 is a nice kit. I fiberglassed mine and got an L2. It'll fly nicely low and slow for an L1, I know several people who have used that kit unmodified for theirs. That thing is beefy and I would feel comfortable flying it on a K. (I've got the 54mm mount.) You might need to add some noseweight - it's not usually stable right out of the box in my experience building my own and helping others build theirs.

 

[burritoman1]

DX3 is a nice kit. I fiberglassed mine and got an L2. It'll fly nicely low and slow for an L1, I know several people who have used that kit unmodified for theirs. That thing is beefy and I would feel comfortable flying it on a K. (I've got the 54mm mount.) You might need to add some noseweight - it's not usually stable right out of the box in my experience building my own and helping others build theirs.

I have modified it quite a bit, including doubling up the bulkheads and adding internal fillets and beefier recovery hardware. I ended up not fiberglassing the inside (although I plan to for my next build), but since I'm limited to 38mm J motors I am confident it should hold up. These modifications have added a lot of weight to the aft end of the rocket (current sim estimates a stability of 0.8 cal) so I will carefully measure the CoM and add epoxy to the nose cone until its stable again.

 

[burritoman1]

Here's how the first pair of fillets turned out. Not pretty, but functional. Next time I'll try to mix the epoxy to peanut butter consistency instead of applesauce. I'll also use a popsicle stick to smooth out it more even.

 

[Five]

Its not absolutely necessary you use DD for your L2. I would pass the L1 and L2 with single deployment then configure it after. It would take a lot of stress off you.

 

[thzero]

Its not absolutely necessary you use DD for your L2. I would pass the L1 and L2 with single deployment then configure it after. It would take a lot of stress off you.

True enough re: level 2 and DD. Certainly if you aren't well versed with DD from mid-power and level 1 work it's probably less ideal to use it for your cert flight

 

[Approx]

Don’t over think it. I did 4” cardboard super dx3 for both level 1 and 2. No dual deploy and just followed the directions plus a few handy tricks from John Coker’s videos like removing the back bulkhead to do internal fillets and also plywood and t-nuts for the rail buttons. No special reinforcement anywhere. It flew fine on an h100 and a j250.