Mega der Red Max kit questions

Hi all, I'm new to the forums. Well, sort of. I've been reading a lot and checking out build threads for awhile.

I've been into rocketry since cub scouts(a long time ago) and have built quite a few including some scratch builts I wish I still had. I'm getting back into it because my girlfriend and her sister have daughters, and I would like to kind of push them towards a more "science" type of career/interest. We need more female scientists. That is just my personal opinion.

Anyways.... I've built/launched/lost the Der Red Max rocket numerous times over the years. It is definitely a favorite. I saw the various upscales people did. Then I saw that Estes had released an official upscale a couple weeks ago(yeah, I know it wasn't just released, it was just the first time I had heard about it) and I ordered one immediately. During that couple weeks I have looked at some of the threads in my spare time.

The kit arrived today. Good grief. I'm kind of in shock that Estes would actually make a kit this BIG. Maybe I should build this thing for my level 1 certification.

I've read that some people have thought about putting 38mm motor mounts in them, but haven't seen the results or if they did it. What would be the pros and cons of doing that?

I haven't attempted a build like this before. I've always used extra thick CA glue to build my rockets. I'm going to assume thick CA will be of absolutely no use on this build other than to glue/laminate the fins together and maybe "tack weld" the middle centering ring in place inside the body tube with a drop or three before actually securing it with something stronger. Has anyone tried that expanding gorilla glue as a motor mount adhesive? I'm thinking because it expands somewhat it would provide a wider thrust transfer area from the motor mount to the body tube/fin assembly. I don't plan on filling the cavity with expanding glue, just running a bead around the seams and joints inside the body tube.

I want extra thick fillets on the outside where the fins meet the body tube. Partly(well, mostly) for looks. Would water putty over a glue fillet suffice? I bought one of those giant containers of durhams rock hard water putty because I was briefly considering building sugar motors, but the risk of a cato on something I am putting this much effort into kind of scares me. I think I will find some sort of reloadable motor and commercially available reloads for it. That kind of goes back to the 29mm or 38mm motor mount debate.

Another thing that worries me is the thought of zippering.. Could I glue a 1"-2" piece of 4" body tube around the outside of the nosecone end of the body tube to reinforce it in the event of a pre-apogee deployment? I don't think I want to fiberglass the whole thing. Or wait.... Maybe a 1" ring of fiberglass at the very end of the tube might look good if it were done carefully and aesthetically. A band sculpted so it looks like it is supposed to be there. I just don't want to add too much weight. I'd like it to be able to actually fly and recover on non level 1 motors, even if it doesn't go very high.

I gather that this may be your first experience with mid power and through-the-wall fins, and you may find yourself tempted to 'overbuild'...resist the temptation. ordinary wood glue works quite well for most things on that model. there are only one item that needs epoxy (that I know of) and that is the motor retainer. epoxy is my choice for doing tube couplers in that size, for all other wood/wood and wood/paper joints wood glue is better. build it stock, and follow the instructions for the most part. if you don't plan on using BP motors, omit the motor block, hold off gluing the aft centering ring in place until after you do the internal fillets. problem with the putty is, it is heavy and will add weight where you don't want/need it. tite bond no-drip makes very nice external fillets .
38mm
38mm is nice if you want to run 'H' (or higher) motors...but Aerotech only makes 2(I think) non-high power 'G's in 38mm, while a 29/40-120 case gives you a bigger selection for other rockets that you may acquire in the future. I would suggest that you build the MDRM with a 29mm mount and save the 38mm conversion idea until you have a bit more experience with fin tabs...they can be a challenge shortening them to match a different size motor tube.
Rex

I used epoxy to laminate the fins together. I've heard of a number of complaints of the fins warping because of the water in the glue. Plus the drying time of wood glue under pressure and very little air exposure is LOOOOONNNNG. I also used epoxy for the whole thing. I know there's a debate about glue vs. epoxy for paper and wood rockets. I just prefer epoxy because it sets much faster.

To that end, I used automotive epoxy and cooking flour for my fillets around the fins. made them look real nice. I also kept the elastic shock cord but had another piece of it lying around and added that so I had a nice long extension for recovery.

I fly H's in mine all the time. Looks cool on an H123 Skidmark.

I would recommend building it stock as well. I, too, had heard about the possibility of warped fins. I used wood glue and layers of plastic between each fin, placed them on a flat surface (my garage floor) and applied lots of weight evenly. You have to be careful when you place the weight so as not to move the fins out of place. Let dry for a day, remove, and sand. They didn't dry evenly, so I stacked them together, screwd them together and sanded them so they would all be even. I used epoxy to glue them in and for the fillets. I did modify mine for 38mm, but again I recommend just going with the 29mm. It is a beautiful kit and a great flier. You will not be disappointed. One other suggestion: Get an eye bolt and attach it to the top centering ring. Epoxy in place. Find some tubular nylon (1/2" or 5/8" will work) and attach about 3 to 4x's the length of the rocket to the eyebolt (do this BEFORE glueing inside the BT). This is now your shock cord. Attach 'chute and nose cone. Post pictures when you're finished.

I read about the fin warping issue, which is why I was thinking about using the thick CA. it doesn't have any moisture in it as far as I know.

I had great luck using a laminating epoxy (aeropoxy) and letting it cure for 36 hrs between two granite tiles with some weight on top. Those fins are straight as a light beam.


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Welcome Gatlas15,

Building Der Mega Max completely stock is perfectly OK.

Many folks use Titebond wood glue (I get mine at the Ace Hardware) for rockets like this.

5 Minute, or even 15 minute epoxy from the hobby store and some Microballoons, can be used to make nice external fillets. Realize though these are more for looks, as they provide little real reinforcement.

Zippering - I hear you!!! You have a good idea with a single wrap of lightweight fiberglass around the top few inches of the body tube. Done correctly and filled in nicely, no one would even know its there... There are other ways of preventing zippers - which you can find searching the forum.

29mm vs 38mm... I think it's best to build stock 29mm. Plenty of motor options, cheaper, lighter, and you can still L1 if you want to with 29mm.

Good luck!

For the MDRM fins, there's a case to be made for each adhesive. On my MDRM, I used thick CA on two of them, and wood glue on the other. Epoxy would've been good as well. All the fins turned out fine, no warping. Twenty+ years ago I used the same method on my MegaAlpha (5.5" upscale of Alpha -- and I mean everything was upscaled, even the fin thickness). I made the fins of 3/16" birch plywood, with large lightening holes, and laminated it with 3/16" balsa on both sides using epoxy. After shaping the balsa for airfoils, I wraped them with a single layer of 1/2 oz. fiberglass.

Water putty can definitely be heavy. I would use epoxy with microballoons. However, my experience is that you want longer curing epoxy; the microballoons with speed up the curing, sometimes too fast. Also, don't put too much microballoons in the mix, or they will crack when slightly flexed, and then you'll have to convince the RSO that the cracks are just cosmetic and don't mean your fin's about to fall off (again, I speak from experience!)

I have one stock and one highly modified (3x29mm canted cluster). Both are great rockets. I looked at doing a 38mm Max a while ago and concluded that it wasn't really worth the trouble, but your mileage may vary.

The only change I would recommend to the stock max would be to improve the shock cord mount with a proper eyebolt, shock cord, and nosecone attachment (I don't trust the molded-in plastic ones). Also rail buttons if you have a rail to launch from.

3 29mm motors? Holy cow... Why not 4 in a y pattern? I just looked at the bottom and there IS room.. At that point the possibility of losing it increases exponentially, as well as cost per launch. But boy.... that would be an awesome launch. find 4 of the longest burn, lowest impulse 29mm motors. The ones that put out the black smoke. Great. Now I have to do it. I need 3 more motor tubes.

Thick CA worked beautifully on laminating the fins together. No warping whatsoever and I had a second or so to realign the balsa slightly before it grabbed hold. I didn't bother trying the thin stuff. It would probably wick away and dry too quickly.

on second thought... I don't want to throw a hundred dollars away every time I want to put that thing in the air. I think it will stay stock.

gatlas15 said:

3 29mm motors? Holy cow... Why not 4 in a y pattern? I just looked at the bottom and there IS room.. At that point the possibility of losing it increases exponentially, as well as cost per launch. But boy.... that would be an awesome launch. find 4 of the longest burn, lowest impulse 29mm motors. The ones that put out the black smoke. Great. Now I have to do it. I need 3 more motor tubes.

Thick CA worked beautifully on laminating the fins together. No warping whatsoever and I had a second or so to realign the balsa slightly before it grabbed hold. I didn't bother trying the thin stuff. It would probably wick away and dry too quickly.

Click to expand...

Ha! It's expensive to launch to be sure, but it is by far the coolest rocket in my (admittedly small so far) collection. UpscaleCNC can make you a mount...

I thought about the central motor tube, but there are issues with making room for motor retention, and the CG moves even further aft so you get more weight in the nose and not a lot of actual gain, and the build gets a little more complicated in other ways because you have to put in another centering ring and really only have room for a 1- or 2-grain in the middle. Plus the central motor would interfere with the triple-plume smoke trail I was looking for.



That last shot is courtesy of Mark Emerson.

https://www.youtube.com/watch?v=n18pGPtzVj8

https://www.youtube.com/watch?v=7-oyq6TAxJ4

https://www.youtube.com/watch?v=YKTAEXL1JYM

https://www.youtube.com/watch?v=D-WcUq-YOYo

As the designer of this kit for Estes all I can say about your three motor version is, COOL!

John Boren

wfcook said:

Ha! It's expensive to launch to be sure, but it is by far the coolest rocket in my (admittedly small so far) collection. UpscaleCNC can make you a mount...

I thought about the central motor tube, but there are issues with making room for motor retention, and the CG moves even further aft so you get more weight in the nose and not a lot of actual gain, and the build gets a little more complicated in other ways because you have to put in another centering ring and really only have room for a 1- or 2-grain in the middle. Plus the central motor would interfere with the triple-plume smoke trail I was looking for.

View attachment 169427 View attachment 169428 View attachment 169429 View attachment 169430 View attachment 169431 View attachment 169426

That last shot is courtesy of Mark Emerson.

https://www.youtube.com/watch?v=n18pGPtzVj8

https://www.youtube.com/watch?v=7-oyq6TAxJ4

https://www.youtube.com/watch?v=YKTAEXL1JYM

https://www.youtube.com/watch?v=D-WcUq-YOYo

Click to expand...

Dude, that is pretty cool! Well done!

Very high praise, Thanks! I'm going to get a swelled head...

I really do recommend building one, as it was really a lot of fun, but first build the stock Mega Max. It's a great kit and it flies wonderfully. Build it complete with the thick, square (not rounded) fins to get the full effect. This rocket isn't about setting altitude or speed records. It's just supposed to look great as it powers it's way off the pad!

wfcook said:

Ha! It's expensive to launch to be sure, but it is by far the coolest rocket in my (admittedly small so far) collection. UpscaleCNC can make you a mount...

I thought about the central motor tube, but there are issues with making room for motor retention, and the CG moves even further aft so you get more weight in the nose and not a lot of actual gain, and the build gets a little more complicated in other ways because you have to put in another centering ring and really only have room for a 1- or 2-grain in the middle. Plus the central motor would interfere with the triple-plume smoke trail I was looking for.

View attachment 169427 View attachment 169428 View attachment 169429 View attachment 169430 View attachment 169431 View attachment 169426

That last shot is courtesy of Mark Emerson.

https://www.youtube.com/watch?v=n18pGPtzVj8

https://www.youtube.com/watch?v=7-oyq6TAxJ4

https://www.youtube.com/watch?v=YKTAEXL1JYM

https://www.youtube.com/watch?v=D-WcUq-YOYo

Click to expand...

By far, the most impressive liftoff I have ever seen on motors that aren't M and above.

Nicely done!!!


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I have a question about angled cluster motors. I believe you angle the motors to get their thrust to pass through the center of gravity of the model. So what would happen in the case of the Mega Max above if you only installed one motor of sufficient impulse to fly the model on. Would it in fact fly straight?

John Boren

wfcook said:

Ha! It's expensive to launch to be sure, but it is by far the coolest rocket in my (admittedly small so far) collection. UpscaleCNC can make you a mount...

I thought about the central motor tube, but there are issues with making room for motor retention, and the CG moves even further aft so you get more weight in the nose and not a lot of actual gain, and the build gets a little more complicated in other ways because you have to put in another centering ring and really only have room for a 1- or 2-grain in the middle. Plus the central motor would interfere with the triple-plume smoke trail I was looking for.

View attachment 169427 View attachment 169428 View attachment 169429 View attachment 169430 View attachment 169431 View attachment 169426

That last shot is courtesy of Mark Emerson.

https://www.youtube.com/watch?v=n18pGPtzVj8

https://www.youtube.com/watch?v=7-oyq6TAxJ4

https://www.youtube.com/watch?v=YKTAEXL1JYM

https://www.youtube.com/watch?v=D-WcUq-YOYo

Click to expand...

DUDE!! That last shot is beyond awesome! Awesome... Just Awesome!!!:headbang:

think it would tend to fly diagonally...think one would have to research the 'Deuces Wild' rocket....
Rex

JumpJet said:

I have a question about angled cluster motors. I believe you angle the motors to get their thrust to pass through the center of gravity of the model. So what would happen in the case of the Mega Max above if you only installed one motor of sufficient impulse to fly the model on. Would it in fact fly straight?

John Boren

Click to expand...

John, apologies for this response which is more terse than I would like. I am in the middle of nowhere with only 3G service on my phone.

If you look at the latest Peak of Flight newsletter (#363) from Apogee I have a detailed discussion of the design procedure.

A couple of people have looked into canted/focused clusters in detail and found that you actually want the focus of the cluster about halfway between the CG and the CP. What SHOULD happen if they don't all light is that the rocket should go up at some equilibrium yaw angle, with the moment from the motors being balanced by the moment of the forces on the fins and body tube. High drag, but stable. I have not had this happen yet, and I'm not brave enough to try it on purpose on this bird, but I have heard of it happening and Jim Flis has posted that he has seen it happen many times with the Deuce and Tres. I figure it's only a matter of time before I get to post a first-hand report of such a failure.

My rocket is built very conservatively, with 1/4" centering rings and solid 1/4" fins, plus ample weight in the nose. I now suspect I could get by with a rocket that is significantly lighter.

When I get a chance (a better connection) I will post my spreadsheet for these geometric calculations if you are interested. As another thread has indicated, much of this can be done with a good CAD package, and I did it both ways. I found some shortcomings with the CAD approach and was glad to have both methods to use as verification.




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Apologies to the OP for sort of hijacking the thread...


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One thing I would be really curious to find out is what happens if I out three different motors in the thing, e.g. One red, one white, one blue. On a normal cluster that's a Bad Idea but in this thing I am not sure...


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