APRO Lander II Build Thread

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Really nice work...you definitely have excellent modeling skills!

Thanks. I'm a bit out of my comfort zone with some aspects of this build, but I seem to be plodding my way through successfully thus far. I think it takes me way longer than most (I work slowly and think about things a lot before doing them) but I enjoy approaching it that way.

When it comes to fin papering, though.... I bow to no man. :grin:
 
If's any consolation Neil, this design gave me hurdles too. Most of my builds come off the CAD program and run like clockwork. Both versions I did of APRO were different, and equally challenging.
 
SHAZAM! Somehow, I never saw the fin installation segment till now.Most impressive. And you'll have better fin fillets than I do for sure. Should I EVER have to or want to do another one of these, I'm stealing some of your ideas.
 
SHAZAM! Somehow, I never saw the fin installation segment till now.Most impressive. And you'll have better fin fillets than I do for sure. Should I EVER have to or want to do another one of these, I'm stealing some of your ideas.

I'm sincerely glad you like it. I figured that this build would be different enough from yours to be interesting.

I think I'm just about out of the woods with regard to the trickiest bits of construction. Still plenty of work to be done, but I'm pretty confident of success now.

More to come...
 
Although I'm still waiting for my 3D-printed rod catcher (argh) it's still a perfectly good time to cut the lug holes. I'll need one each in the large and rear transitions. What should be the position and shape of the holes?

Well, I could eyeball it, but that's no fun. I tried to think of an analytical solution but it eluded me. And so I created a generalized solution: a Perl script (available on request) that would generate a lug hole template, given the shroud parameters, lug diameter, and radial distance from the lug to the center. The output looked like this (click to get full sized version so you can actually see it):
lug and tube assembly - 6.jpg

The oval is the lug cutout, and the arc on the bottom aligns with the inner edge of the transition. After cutting out and wrapping it around the transition, it looks like this:
lug and tube assembly - 3.jpg

Trace the lug cutout onto the transition and cut it out (I didn't do it quite as precisely as I wanted to, but OK) and then test:
lug and tube assembly - 4.jpg

As it turned out, the hole in the rear transition was easier to just cut as a circular hole (I used a 1/4" drill) with a hand-marked location. Here is a nice long lug (extremely useful for this purpose) threaded through both holes and of course the big ring, to test fit and placement:
lug and tube assembly - 5.jpg

I love it when a plan comes together. :)

I chose not to simply use a single long lug in the build because I was concerned about rod binding, so instead I'll have shorter lugs front and back and the rod catcher in the middle. I can't glue the front lug or the big transition until the rod catcher is in place, so for now I just glued in the rear lug, which extends from the rear transition to the big ring:
lug and tube assembly - 7.jpg

And that's all for now!
 
I've been experimenting with fabricating the front transition. My initial efforts with the heavy posterboard were not so hot, so I thought I'd take another approach: one of Chris Michielssen's "super shrouds". But due to a personality defect I am unable to do it exactly as described, but instead must customize the procedure for myself. The fundamental principle is just to make two nested shrouds of a lighter material.

I started with standard 65 lb card stock. Jeez that stuff is *so* much easier to work with; my initial efforts at making single shrouds with it were already way better than my last ones. But when I nested them, the pressure of the inner shroud caused the glue tab on the outer shroud to become visible through the paper on the outside. So I made a modification: Instead of constructing a complete inner shroud, I'd cut the piece and then remove a bit off the end equal to the glue tab on the outer shroud. Then I'd glue it in position such that the gap corresponded with the outer glue tab. This seemed brilliant: this way there's be exactly two layers of cardstock everywhere. Here's what it looks like on the inside:
attachment.php


In reality it was quite hard to glue the inner shroud in its "loose" form, because it had a mind of its own and wanted to go everywhere but in the correct place. In the end I got it in *almost* the correct spot; you can see towards the small side the inner shroud overlaps the glue tab ever so slightly (curses! :mad:).

To keep it in the right shape while the glue was drying, I pushed it over a bottle of eyeglass cleaner that just so happens to be *slightly* larger than BT55, with a very smooth curved shoulder. So I pushed the part as far as it would comfortably go onto the shoulder and it indeed set into a perfect circle.

attachment.php


So the finished shroud is very nice and *very strong*, much more so than the large ones I made out of the posterboard. I am definitely going to use this approach from now on.

That said, while this piece is *almost* perfect, it could be improved, so I'm going to make one more and use whichever one comes out better.

Oh, I forgot to mention one other change I made to Chris's method: he calls for trimming the large end off the inner shroud after assembly, to line it up with outer shroud. I did what I thought would be easier: I cut the inner shroud about 1/16" shorter on the larger end, which was enough to ensure that it stays hidden inside the outer shroud. You can see it in the first picture. That was a good choice; there's no particular need for the two shrouds to be perfectly lined up, and it's super-easy to just adjust the size when cutting the paper in the first place, rather than trimming afterwards.
 

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That's right! Just you keep weighing this thing down with all your hot dawg modifications and such. By the time you get done with it, you'll need a G80 just to get it off the pad! :rofl: jk

That's bound to be a sturdy shroud. Can't imagine why you felt it necessary to make it that durable though. There's no real stress associated with that shroud. A bit of a wind breaker of sorts.
 
Whatever works, right? I was thinking about "card stock" and was wondering, is a manila folder too heavy for this use?
 
That's right! Just you keep weighing this thing down with all your hot dawg modifications and such. By the time you get done with it, you'll need a G80 just to get it off the pad! :rofl: jk

That is not necessarily far from the truth. :eyepop: This thing will not be setting any altitude records, that's for sure. I expect a composite E15 will be the ideal motor for it, although it should do "OK" on a D12.

That's bound to be a sturdy shroud. Can't imagine why you felt it necessary to make it that durable though. There's no real stress associated with that shroud. A bit of a wind breaker of sorts.

You might be right; maybe I'll just go with a nice simple single layer. I just made one and it seems to be my best one yet. I think my thinking was that everywhere I look people are making either double layer shrouds, or using 110 lb stock, or soaking them in CA, or filling them with foam (ahem) or all kinds of things to make them stronger than plain old 65 lb stock. Maybe I don't need it here. I think my biggest fear by far is sanding the primer and buckling the thing (I still worry about that with the larger transitions).

In fact, I was originally planning to put support fins under it... with the double shroud it would absolutely not be necessary; with the single... dunno, might feel better with them there.

My lack of experience with these things is showing I suppose.

Whatever works, right? I was thinking about "card stock" and was wondering, is a manila folder too heavy for this use?

That's really heavy, I suspect it'd be very difficult to get it to bend cleanly.
 
Neil, there's a lot of overkill commandos in this bunch. It's easy to get caught up is some of those rattlings too. At one point, I started questioning my own applications with regards to fillets, TTW fins, motor retention, you name it. FWIW, this is a LPR rocket. Your average card stock weight is plenty sufficient for the design unless you plan to shove something big in there. I'd be scratching my head about using an F motor or something. Then, you might need that extra reinforcement. And you are correct about altitude. It's gotta lotta drag. High speeds are not likely with this one.
65# for the top shroud is fine. 110# for the lower is fine also. These thicknesses of paper are pretty durable once they're formed and glued. More so than you might think.
 
OK, you've kind of talked me into just going with the single layer shroud... although I'm not really convinced that the double shroud is bad overkill per se. It is shockingly strong and really not so heavy (I will weight it when I get home, just to see how much difference it makes.)

It should look good no matter which way I go; these all came out pretty nice.
 
That's really heavy, I suspect it'd be very difficult to get it to bend cleanly.

Hmm... Perhaps then the card stock used by Estes for their face cards?

Also, if you're concerned that a single layer would need underlying support, aren't you then adding weight?
 
Hmm... Perhaps then the card stock used by Estes for their face cards?

That stuff is actually not that far off the posterboard I'm using, although I think my posterboard is a bit heavier. [edit: in fact I think the face card stock is *quite* a bit lighter... possibly even lighter than the 65 lb card stock I'm using]

Also, if you're concerned that a single layer would need underlying support, aren't you then adding weight?

Yes, although it is very very little. And to be honest I'm still not really decided on how much I should even care about that weight, given that the rest of this thing is not, shall we say, "performance optimized". ;)

I'll weigh the various parts in the name of science and we'll see what it all means.
 
OK, you've kind of talked me into just going with the single layer shroud... although I'm not really convinced that the double shroud is bad overkill per se. It is shockingly strong and really not so heavy (I will weight it when I get home, just to see how much difference it makes.)

Hey, if you think the weight is negligible, tell me to go jump in a lake. Far be it from me to dictate how you should build this bird. You're already doing a better job than I did.
 
Hey, if you think the weight is negligible, tell me to go jump in a lake. Far be it from me to dictate how you should build this bird. You're already doing a better job than I did.

Eh, no worries. Overbuilding is easy, hitting the right balance of strength and weight is harder. I'm still learning, and I value the input.
 
My handy-dandy AWS scale says:
  • Single layer shroud weighs 1.3g
  • Double layer shroud weighs 2.7g (not too surprising)
  • Support fins weigh a total of 0.6g (balsa is light :))

Therefore, single layer shroud + support fins is lighter by a whopping 0.8g (or 0.03 oz). This weight difference is in the noise for most any rocket flying on something larger than an A, and so I would not hesitate to use the supershroud method in the future for all but the smallest rockets. For this one I'm still undecided, will make my final decision when the time comes. I still have a few other things still to do first, and things are slowing down due to assorted other real-life activities taking priority right now.

In the meantime, I've noticed that the large ends of my shrouds are not quite large enough to fit over the aft centering ring, which means I cut the paper a bit too tight on the outer circumference. That means.... yessiree, I'm gonna make some more. Fortunately these are cheap and easy and rather enjoyable to make, so I don't mind. Also I'm learning and getting better at it with each new one I make, I think.

One last opinion to solicit on this matter: if I were to use the support fins (which are just simple triangles to fit under the shroud), should I put them directly under the strakes, so the shroud will be tightly sandwiched between them, or offset them by 45 degrees from the strakes, so they'll provide support in between? I can think of reasons to do it either way. Ultimately it's probably six of one, half a dozen of the other, but I'm still trying to reason out whether one way would be superior to the other (and all will be moot if I end up going with a double shroud, which is still a good possibility). My objective as always is provided good support so I can safely sand the primer without ruining it.

Thank you all for playing along at home.
 
My handy-dandy AWS scale says:
  • Single layer shroud weighs 1.3g
  • Double layer shroud weighs 2.7g (not too surprising)
  • Support fins weigh a total of 0.6g (balsa is light :))
One last opinion to solicit on this matter: if I were to use the support fins (which are just simple triangles to fit under the shroud), should I put them directly under the strakes, so the shroud will be tightly sandwiched between them, or offset them by 45 degrees from the strakes, so they'll provide support in between? I can think of reasons to do it either way. Ultimately it's probably six of one, half a dozen of the other, but I'm still trying to reason out whether one way would be superior to the other (and all will be moot if I end up going with a double shroud, which is still a good possibility). My objective as always is provided good support so I can safely sand the primer without ruining it.

Thank you all for playing along at home.

DOOD! There you go again. You're putting way too much paranoid thought into this construction. Since you seem convinced that a double shroud is the way to go, then there's absolutely no need for further support. Forget the name APRO anymore. Just call it Ft. Knox.
 
In other news, finally got this today:
ImageUploadedByRocketry Forum1479222454.616836.jpg
Look forward to testing fit and getting this glued in, which will then allow me to glue the big transition.

(weighs in at 1.3 g, in case anyone is interested)
 
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Not trying to play "Devil's Advocate" here, but consider the weight of the glue required to glue in all those balsa wood supports also. :wink:
 
Not trying to play "Devil's Advocate" here, but consider the weight of the glue required to glue in all those balsa wood supports also. :wink:
In fact I've been generally curious about the contribution of glue to the weight of the finished model. When my builds come out heavier than anticipated (which is basically always, I'm sure you're surprised to hear that ;)), I have to assume that unaccounted glue weight has to be the most significant factor. Fillets are presumably the biggest culprit, but all glue must be contributing to some extent. I'd like to get a better handle on it, if for no other reason than to be able to improve the accuracy of my OR models.

In this case, I feel pretty confident that the glue weight for those little pieces would be darn close to zero, but next time I attach them or any other fins I'll see if I can measure out the glue weight.
 
Indeed Layne. And I get a kick out of watching someone build one of them in a build thread. Neil has made some mods that are sincerely impressive, that I had not considered. That being said, if I had it to do over again, I would definitely follow his lead on some of them. Keeping in mind though, that said modifications would be beneficial rather than overkill.

Neil, I apologize for sounding off at you earlier. But it was reasonable for me to point out an unnecessary application. Since I’ve already built two of these, you might think I’d know a thing or two about it. I used 110# cardstock for that forward shroud (having reviewed my own build thread) and didn’t experience any problems sanding the primer. Contrary to earlier comments, I used CA to strengthen the entire forward shroud up, and was quite pleased at how rigid it was. Plus, it made sanding the overlapped paper possible without any fuzz and such. I sorta get that layered shroud approach for something that might require it. And with the given card weight used here, I see no need for that. Internal bracing could present a problem if you thought about gluing them to the underside of the shroud. You could easily end up with ripples once the glue dries. Making something better is always a plus. But you’re not building a tank, are you?

Just food for thought.
 
Neil, I apologize for sounding off at you earlier. But it was reasonable for me to point out an unnecessary application. Since I’ve already built two of these, you might think I’d know a thing or two about it.
No problem, just keep in mind:
1) This is for fun and learning. I like to try out all the different techniques I've read about. Not all of them are necessary. I certainly want to steer clear of anything that's really over the cliff, but I don't think an extra gram's worth of shroud qualifies.
2) My #1 goal is to ensure that I can get this thing to the finish line successfully; I won't be building another one (enjoyable though it may be). That means I'm generally going to err in the direction of overbuilding, *especially* because I haven't worked with paper shrouds like this before. Not only have I not worked with them before, I've never touched one on someone else's rocket, so I have no idea how they should "feel". And it's even worse than that, because it's not fair to judge them before assembly, because they will undoubtedly get much sturdier once glued into place. And finally, I tend to be a bit, ah, "vigorous" when sanding filler/primer, so I need to take that into account as well.

So this is sort of a guinea pig build for me. At the end, I'll be able to judge how all the different transitions worked out, and refine my technique for the future.

I used 110# cardstock for that forward shroud (having reviewed my own build thread) and didn’t experience any problems sanding the primer. Contrary to earlier comments, I used CA to strengthen the entire forward shroud up, and was quite pleased at how rigid it was.
In that case it would seem to me (unless I'm reading this wrong) that a doubled 65 lb paper shroud is a reasonable equivalent to a CA'ed 110 lb paper shroud, no?

Internal bracing could present a problem if you thought about gluing them to the underside of the shroud. You could easily end up with ripples once the glue dries.

Originally I intended to glue them, but did eventually realize that it was a bad idea for that exact reason. The braces shall not be glued.
 
The glue itself is going to be a serious reinforcement for layered shrouds. I've never heard of doing this before. But then again, I get what I need from gauging my card stock weights. They don't call me the "Tranny King" for nothing you know. I probably didn't really need to CA it either. But since I wanted to sand the step-down on the overlap smooth, I knew I'd need to. So I just CA'd the whole thing. It's a totally negligible weight factor, so I didn't give it a second thought. But between the two approaches, 6 of one / 1/2 dozen of the other. They'd both be super strong. And for what it's worth, I forgive you for being an overkill commando. :grin:
 
And I forgive *you* for having built 10x as many rockets as I have. :)

Anyway, I'm having good results with my latest round of shrouds. Will report soon on that, along with other build updates.
HAHAHA! Man, somehow I can't design a rocket without sticking a transition on it somewhere. I do have a few, but they look ordinary. The Lander is by far, one for the books. Transitions from hell! But the more you make, the better you get at them. I love it when I nail the perfect fit. And that happens about 50% of the time. I can deal with a little overlapping or too snug to the tube. Those can be altered and fixed. It's the undersized fit that pisses in my cornflakes. That constitutes a re-do. Keep up the good work.
 
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