L1 Build - Madcow Super DX3

[SandiaMan]

Hi folks,

I'm a BAR, back after a 2 decades away caused in large part by an CATO on an Estes rocket. Back because all that time I really wanted to do HPR and now I can afford it and am technically capable (at least I believe so). I've been stalking forums and building MPRs for about 6months now and ready to give an L1 a shot.

After quite a bit of deliberation I settled on a Madcow Super DX3. The main qualities for me were:

• Rugged parts
• slotted airframe
• Payload bay
• Missile-like aesthetic
• 4" BT
• 38mm MMT

Im a big fan of this kit's construction and instructions, and this definitely gives me a lot of respect for MCR.

 

[mikec]

Great choice. Best of luck with your build. See https://www.rocketreviews.com/madcow-rocketry-super-dx3-by-mike-caplinger.html for some thoughts on mine.

 

[SandiaMan]

The biggest challenge was deciding how to bevel the fins. The fins are 5 layer 1/4" plywood. While the instructions don't call for beveling/airfoiling, it would be odd not to I think. Hand sanding the 6 fins on my NCR Cluster Duck got pretty old, and also a bit uneven, so I decided I needed a new approach. After reading through John Coker's excellent overview I decided to give it a try on my table saw, but using a normal blade rather than a sanding disc since I'm using plywood not fiberglass. I wasn't even going to start until I made that decision. So having made that decision I started on the Motor Mount. Based on Mike Caplinger's review on Rocket Reviews I decided to leave off the aft centering ring to do internal fillets. I have it held on with painters tape so that I can use keep it even when epoxying it in.

 

[SandiaMan]

Hi @mikec your review as instrumental in my decision. A few things I noticed since your review was posted is that the newer nose cone seems to be much longer, giving the rocket an overall height that's ~66". It also comes in 54mm or 38mm. I went for 38mm based on the reviews on the Madcow site, which suggested going for 38mm for cost of operations.

 

[SandiaMan]

Once I actually got the MMT epoxyed up, I beveled the fins. This was a multistep process.

First I cut a blank 1/4 block of wood from some scrap so I could work out the kinks of beveling before touching my kit's fins. This proved to be a very good idea. With a blank cute, I banked the blade at 15 deg and ran the blank over it using just the fence at just under 1/8th of an inch from the throat. This was the first learning opportunity. The throat of the table saw was opened up by beveling the blade and without having horizontal stability of the working piece, it tended to drift into the throat and let to an uneven bevel. However, the bevel looked great, even if it was uneven. I could fix the unevenness. So I clamped a real fin to a big block of wood, using the table bed to align the bottom of the fin with the block, and then ran it through (with fence adjustments). I had to reclamp 4 times for each fin. 1 for each side for the leading edge and the outside edge. That did the trick! Afterwards I used 60 grit to round the trailing edges, then sanded the whole thing with 220.

WIth the fins cut in the early afternoon, in the evening I worked on epoxying the MMT in to the booster and then the fins to it. The motor mount went in pretty smoothly with taped on aft ring. I made sure to line it up so that I could epoxy the aft ring to the tangs when after they were all attached to the MMT. The fin tangs needed some sanding on the bottom to allow the root to fully lay flat on the BT, but not much. 5min epoxy on the bottom of the tang, and the root. Once that all set up, I looked at the epoxy on the tang/MMT mounts. I really lathered it on, so it looked pretty solid. Instead of doing fillets there, I made a new batch of epoxy and added small fillets where the fin tang meets the inside of the body tube. The instructions called for epoxy fillets on the outside of the BT to the fins, but i just haven't had good luck with epoxy putty and fillets, and I really want these to be smooth and even. I tried couple times with epoxy putty, but it wouldn't smooth down nicely, or it started coming off. I roughed up the surface with sandpaper too. no help. So instead I added fillets using CWF. They'll work well I believe, and I feel confident that the fins are adequately attached.

To finish it and seal it in, I added a ring of epoxy around the BT and on the tangs and slid the aft ring over the MMT and in to place.

 

[DMehalko]

Looking good!

 

[SandiaMan]

@mikec how did you set up your ebay on yours? I thought I recalled seeing a dual deployment pic. I'm not doing dual deployment on my L1, but I'd like to be able to on my L2.

 

[Handeman]

Looks like it's going to be a great L1 rocket.
I would recommend adding the av-bay and get used to DD. It's not really that hard and you might find you prefer flying with DD rather than motor ejection.
Have you decided on which motor you are going to cert on? You could adapt down to 29 and use a baby H like a H128W or a mid H like a 38mm H123W. After you cert and start exploring the range of L1 motors you will find there is a huge difference between a small H and large I and you really won't appreciate that difference until you actually fly them. That's some of the fun of L1.

BTW, search through some of the build threads here for tips on doing fillets. There are guys on here that are true artists when it comes to fillets.

 

[mikec]

I initially built mine with the coupler just glued into the payload section and I flew my L1 and L2 with motor ejection only (extra nose weight required for the L2). Then I bought another section of tubing and an ebay kit so I can fly it either way (mine just barely squeezes under the Class 1 weight limit in its original configuration, but the ebay pushes it over.)

 

[SandiaMan]

@Handeman thanks for stopping by! I will definitely be doing DD for my L2, but everything I've heard says to KISS for a cert flight. I'm doing my first RMS flight for my L1, which is already a little complex, so I'm holding off for now.

@mikec this is pretty much what I was thinking, so glad to hear it's working out for you. What Gs do you fly with? All the ones I simmed I couldn'tuld get enough velocity off the rail?

 

[mikec]

What Gs do you fly with?

Aerotech G79-4 and G64-4, CTI G60 and G69. Mostly the G64. It's not terribly fast off the rail but in low wind it's always been fine, gets 500 feet or a little less. Nice demo flights.

 

[SandiaMan]

@Handeman I'm flying on a 38mm H130W for my L1. RockSim says 1700 AGL and 49mph off the rail. I'm looking forward to trying bigger stuff for sure. The big I pic from mikec definitely has me excited: https://www.rocketreviews.com/file-842463/sdx3.jpg

 

[SandiaMan]

So with single deploy as the method for target launch, I went ahead and continued on with the assembly per the normal instructions (break in half). I epoxied the bulkhead in to the connector and connector in to the payload tube. I friction fit the nose cone for now with painters tape. I'm not sure how I'm going to attach it in general. Since this is likely only going up to <2500 ft on single deploy, I'm wondering if friction fit is enough? I definitely do not want debris falling, so I'm considering pins, rivets, etc. Open to thoughts.

@mikec we have a fairly steady breeze here, so I'm not sure I could get away with that. I test flew my Cluster Duck on a questionably powerful engine and had a rather unfortunate weathercocking experience. My intention was to simply test the airframe, and thankfully it turns out that it very strong.

@Handeman Thanks for the suggestion to search on fillet techniques. After several unsatisfactory attempts freehanding it with CWF I searched and found the mask/scoop method as suggested by Ian on his badassrocketry website, and discussed on the Mach1 thread. I masked the top/bottom off the fillet with painters tape and used a large popsicle stick to spread it down the length of the fine joint. It is much more even and smoother. I will definitely be using this method in the future. I still need to find a better way to use the epoxy putty/clay, but for now this will work perfectly.

On the last fillet photo you can see new fillet on top, old style on bottom. Top fillet is wet and drying, so it will be sanded to blend with the BT and fin still.

 

[boatgeek]

So with single deploy as the method for target launch, I went ahead and continued on with the assembly per the normal instructions (break in half). I epoxied the bulkhead in to the connector and connector in to the payload tube. I friction fit the nose cone for now with painters tape. I'm not sure how I'm going to attach it in general. Since this is likely only going up to <2500 ft on single deploy, I'm wondering if friction fit is enough? I definitely do not want debris falling, so I'm considering pins, rivets, etc. Open to thoughts.

@mikec we have a fairly steady breeze here, so I'm not sure I could get away with that. I test flew my Cluster Duck on a questionably powerful engine and had a rather unfortunate weathercocking experience. My intention was to simply test the airframe, and thankfully it turns out that it very strong.

@Handeman Thanks for the suggestion to search on fillet techniques. After several unsatisfactory attempts freehanding it with CWF I searched and found the mask/scoop method as suggested by Ian on his badassrocketry website, and discussed on the Mach1 thread. I masked the top/bottom off the fillet with painters tape and used a large popsicle stick to spread it down the length of the fine joint. It is much more even and smoother. I will definitely be using this method in the future. I still need to find a better way to use the epoxy putty/clay, but for now this will work perfectly.

On the last fillet photo you can see new fillet on top, old style on bottom. Top fillet is wet and drying, so it will be sanded to blend with the BT and fin still.

A tight friction fit will be fine, though I would put another layer of tape closer to the bottom of the nose cone shoulder so that the shoulder still has some friction even if it comes a little bit loose. If you want to go belt and suspenders, you can drill a couple of small holes in the bulkhead, thread a small piece of 550 paracord (or something else light) and then tie that to the nose cone. That way, even if it comes off, it stays attached to everything else.

My personal opinion is that the best technique for using epoxy clay is to toss it in the garbage and get something that self-levels and/or is easier to sand. There are many excellent options at a variety of price points. I grant that opinion isn't universal, but this is the Internet so I'm going to broadcast it far and wide!

 

[SandiaMan]

Right now I just have the top taped to keep things in place when working, but the NC conveniently has two ridges that are there to help friction fit. If I do use it with a friction fit I'll do a second wrap over that ridge, and maybe use a single layer of electrical tape over the paint tape.

So far my only success with the clay has been using it as lug reinforcement on MPR rockets. the last batch I mixed (squished) together ended up in the trash. Two part epoxy and CWF seem much more workable. The epoxy is just god awful expensive to use that much, but uh... probably cheaper than losing a rocket, so... still refining technique.

 

[mikec]

Friction fit is very iffy IMHO. I used plastic pop rivets on mine. If you go with friction fit, the backup cord is a good idea.

For cardboard rockets I use two-part epoxy wood paste for fillets. Search for "PC-Woody". It's super thick and won't run, you can do the whole rocket in one mix.

 

[Handeman]

I would just use a wrap of 3/4 electrical tape on the outside, 1/2 on the nose cone and 1/2 on the BT. Kind of like you do for LPR/MPR motor retention. If you want to be extra careful, tie a piece of shock cord between the nose cone and the payload bay. Then if it does come loose, you won't lose it.

 

[SandiaMan]

Thanks everyone for the tips and suggestions. I still haven't resolved the nose cone issue. Right now it's a real beast to get on and off with all the painting tape I have a round it from painting. And that's a lot of what I've been doing. I did a layer of flat gray primer to see how the finish looked with a base coat. The answer was... not nearly as nice as I want. I mixed up some watered down CWF and filled the grooves and went over all the rougher spots on the fillets, then sanded it down with 150 grit sandpaper. After that I sprayed on a second primer coat and sanded with 220 and 600. I originally was going to do a color scheme similar to the HOT SHOT sounding rocket, but I bought this beautiful satin ink blue on a whim and it was too alluring not to at least try. When it was on the nose cone though, it just didn't work for me. I'll save it for my daughter's mean machine where we're going Red, White, and Blue. I repainted over it back to white to get back to the sounding rocket color scheme. I'm still working on the fin outlines, but here we go.

Still to do: epoxy retainer to MMT (may do tonight), mount rail buttons, final install of recovery system components

 

[ridnharley]

I just earned my Cert Level 1 with the Madcow Super DX3. I used 4 #6 screws to attach the nosecone to the body tube.
I then used 4 removable body pins from Apogee to secure the coupler to the upper body tube. I used 4 rivets to attach the coupler to the lower body tube.
That worked well for motor deployment. I flew an H283 DMS with a 7 second delay. Gave me an 800 foot apogee, 36" chute came out and came down no problems. Cert earned.

 

[GalantVR41062]

Congratulations and welcome to high power.

 

[SandiaMan]

Did you use the breakable rivets between the coupler/booster? My fit is so tight between the booster and the coupler/bay (epoxied couoler per directions) that I'm having to sand it to be confident it will even separate. I'm still debating on the NC because I'd like to leave it in a state that's ready for dual deploy, which would probably use the breakable pins.

Congratulations on your flight! I'm surprised it didn't fly higher on an H283, but I haven't simmed that engine. I'm flying an H130W RMS, it's simmed to 1700ft. I'd prefer 800 for a nice easy flight. I'm regretting a bit choosing an RMS for my first flight, but I'm not super worried, just a tad nervous (first RMS flight). If things are looking good tomorrow I may get to fly it.

I got the recovery system and retainer installed yesterday and one more fin striped. Just have to install the rail buttons to be able to fly. I picked up a nice piece of right angled aluminum to use as a guide for the upper button placement.

 

[Dan Griffing]

The biggest challenge was deciding how to bevel the fins. The fins are 5 layer 1/4" plywood. While the instructions don't call for beveling/airfoiling, it would be odd not to I think. Hand sanding the 6 fins on my NCR Cluster Duck got pretty old, and also a bit uneven, so I decided I needed a new approach. After reading through John Coker's excellent overview I decided to give it a try on my table saw, but using a normal blade rather than a sanding disc since I'm using plywood not fiberglass. I wasn't even going to start until I made that decision. So having made that decision I started on the Motor Mount. Based on Mike Caplinger's review on Rocket Reviews I decided to leave off the aft centering ring to do internal fillets. I have it held on with painters tape so that I can use keep it even when epoxying it in.

If you have access to a router table and either a 1/4“ or a 3/8” roundover bit, you can make a really neat ogive fin edge profile.

It’s best to practice on 1/4” stock to get the router depth and fence set right before working on your fins, and you need to go away from the grain on the surface layer of the fin plywood to avoid tear-out.

Using a router saves a lot of time, produces beautiful fin edge profiles, and only needs a little sanding as a final touch-up.

 

[SandiaMan]

Well I didn't get to fly today because I didn't have my motor assembled ahead of time and it just didn't seem doable on-site (wind + dust). We flew my daughter's Estes Executioner a couple of times. I made 7-engine clip whips for my NCR Cluster Duck but realized during flight prep that one of the motor mount rings seemed loose, so no flight there. Should have done a better triage after it's hard landing. Got to see some great flights though, and the Executioner has been a really nice MPR flyer, so all good.

 

[SandiaMan]

@Dan Griffing is that a DX3 in your avatar? Good tips on router, I have a handheld not a table, so I'll have to think about whether I can make it work. I did a pretty similar process with the table saw but the blade kerf is a bit unwieldy.

 

[Five]

I’m just finished my Super DX3. This is the biggest rocket I ever assembled. It costs me $35 for paint, clear coat, and JB weld alone. Not including 36” parachute, 12x12” chute protector, and 38mm retainer. Just waiting for the final finishing touch, a DX3 decal from amazon. Man! It sure does get expensive!
It pays off though. I plan to use her(DX3) for my L1 cert.
Isn’t she beautiful?

 

[SandiaMan]

Nice build! It does get expensive, but you can always use parts on other rockets. I use a 36" chute on a couple rockets and have it on a steel link to swap between them easily. Too bad the retainers aren't swappable...

 

[Five]

I was Contemplating on using a 38mm retainer from my HI-Tech because it’s out commission but that would total ruin the rocket when all’s it needs is a little cosmetic work done.

 

[pferg]

Just finished up a DX3 as well. Hoping to get my L1 soon!

 

[Five]

Just finished up a DX3 as well. Hoping to get my L1 soon!

Just finished up a DX3 as well. Hoping to get my L1 soon!

Badass! Where did you get the decals from?

 

[pferg]

Badass! Where did you get the decals from?

The red I masked and painted. The silver “Super DX3” came from stickershock23.com