Tinker Rocket Build Thread

[Iceman1979]

Ok, I said this was my wifes rocket and she has given it a name. She loves Disney's Tinkerbell and thus named it Tinker Rocket. So, I guess it's time to start the build thread.

About all I have done to the rocket thus far is to start making the fins. I have them all cut out and sanded to shape. I had to cut the TTW fin tabs and CA them to the fins seperately. All 3 fins are roughly the same size and shape. Some of the fins had some gouges in the wood so I filled them and sanded them. I'm surprised how well it tourned out.

I'm waiting on the fiberglass to get here so the fins are put aside for now. Next I think I'm goin to work on the logistics of glueing the MMT into the BT. I have some old posts to go back and re-read from my "A few questions" thread for some good suggestions on how to do that.

The only picture I have at the moment is the one of the parts I have so far. Hopefully I will be able post some more pictures tonight of the fin making process.

My puppy loves to chew on things and I happened to leave the cord to my camera plugged into the PC and dangling down to the floor and of course she found it. I have two computers though and one of them has memory card readers so here's hoping I have the right one.

Here is the one picture for now.

 

[Iceman1979]

Here are the pictures of the fins.

The first picture is right after I glued the TTW tab on. The second and third picture is one where when I flipped over the fin I saw this scrape that had to be filled in so I took some wood fill epoxy and filled it in and sanded it.

 

[Iceman1979]

Here are the rest of the fin pics. These pics are after I finished sanding them and trying to give them an airfoil shape.

 

[DaveCombs]

I'm glad you're going to glass the fins, because by adding the tabs onto the fins (rather than cutting the fins out with the tabs all in one piece), you've introduced a breaking point into the fin. You'll be relying on the glass for strength more than the TTW tabs.

Not that you'd want to try this, but if you had a fin that had the tab included, you could flex that thing all day long at the fin root and the tab wouldn't break off. But with the two-piece fins you made, there's a pretty good chance that the tab will break off. Leave yourself plenty of material to include the tabs; if this was a from a kit with pre-cut fins, use them as a pattern and get a plywood sheet to remake the whole fin set with the tabs on them.

You did a GREAT job with the airfoils, too.

 

[Iceman1979]

I'm glad you're going to glass the fins, because by adding the tabs onto the fins (rather than cutting the fins out with the tabs all in one piece), you've introduced a breaking point into the fin. You'll be relying on the glass for strength more than the TTW tabs.

Yeah, I figured that might be the case. The sheets of balsa that I got were to narrow to have the tabs as part of the fin so I ended up having to do it this way. I would have prefered to cut it as one piece but since I was going to glass it I figured it would be ok.

Once they are glassed to you think they will hold up or do you think I really need to go get some aircraft ply and redo the fins with the tabs? If I go with plywood do I need to forego the fiberglass?

I jotted down the measurements from a rocksim file and then replicated it on the balsa wood with a strait edge and a ruler. That is not to hard to replicate if I needed to.

I made some assumptions that lead me to the fiberglass/balsa route.
1. I thought the fiberglass skin would help protect the fins when they repeatedly hit the ground (i'm assuming here that my rocket will last more than one flight haha). With that in mind thats why I went with the balsa wood for the fins. I figured the plywood would be to heavy with the glass added an I also figured that a glassed balsa would be stronger than just bare plywood.
2. I figured glassed balsa would be easier to sand and paint.
3. I assumed that balsa/fiberglass would be stronger and lighter than just plain plywood.

I am always open to suggestions.
Thanks for the feedback thus far.

John

 

[DaveCombs]

OK. I went back and re-read the original post (like I should have the first time, to be honest). Here's what I gather:

3" airframe
29mm MMT
G motors

With this, you're into mid-power with a good amount of speed and a good amount of recovery weight (what the rocket weighs when it sets back down on the ground. If it's not too late in the build, my personal feeling is that you should take a page from most mid-power manufacturers and switch to plywood fins (like 1/8" 5-ply) instead of balsa - it's not strong enough. While you're going to be going faster than you would with BP motors, ply will be more than sufficient for low-drag (highly-swept) fins on a G motor. Plus, with the added stiffness of the plywood, with the proper chute selection your descent speed should be low enough that you won't have to worry about breaking fins on touchdown. Look at the other AT mid-power kits (like the Arreaux, Mustang, etc.) and LOC Precision kits (Onyx, Graduator, Lil' Nuke) - they all use TTW plywood fins and don't require glassing.

If you feel compelled to glass, you colud do a tip-to-tip glassing on the fins, but glassing the airframe is unneccessary on mid-power. You usually don't start glassing airframes until you're up into J impulse and above.

 

[Iceman1979]

The plan was to glass the entire fin using the balsa as a shape former. I was planning on cutting 2 sqaures of fiberglass big enough to lay the fin inside of, kind of like a sandwich. Then I was going to sandwich that with some peelply and breather and then vacuum bag it. Once it had hardened I was going to trim off the excess just beyond the edges of the fin and then sand it to shape. Basically the fin would be incased in fiberglass.

Sure I'm partial to doing it this way. I've put alot of planning into how I'm going to do it. But... If the end product is not going to be strong enough then that defeats the purpose of doing it this way.

I have not glued the fins onto the MMT yet. Infact I just got done glueing two of the CR's to the MMT last night (i'll post pics tonight). I still have to glue the fins to the MMT, Add the eye bolt to the forward most CR, Slot the BT, Slide the assembled MMT into the BT and then glue on the last CR at the end. So there is still room to change the fins if I need to.

If I go with the plywood fins I probably won't glass them. They'll be heavy enough as it is. Maybe I'll just wick some CA into the edges of the fins to give it some extra regidity.

Well, now is the time to decide what I'm going to do. Hmm... Lets see here... I can wait for the fiberglass to get here on thursday or I can go to the hobby shop tonight and pick up a sheet of plywood and be working on a new set of fins tonight. Ha, I guess I'm just over complicating this thing. Cutting and sanding a set of plywood fins would be so much less work then what I'm doing now.

Dern, I wanted to vacuum bag something lol. I guess I could glass the blasa fins for the practice.

 

[Iceman1979]

I foresee a couple of problems with the MMT and CR's.

1. The forward most CR is just under 18" from the bottom of the BT which puts it at/around 18" from the top of the BT. Without cutting the BT, attaching a shock cord is going to be fun.

2. I wanted to flush mount the aft most CR to the to BT with the MMT sticking out 3/8" but thinking about how to get ample glue inside the tube prior to inserting the ring will be a little tricky. And once I push in the CR, if I accidentally push it in to far than getting it back flush will also be a problem.

My possible solution to number 2.
I could probably scrape off the epoxy just on the inside of the BT building up a ring of epoxy all around the inside of the tube right at the bottom edge and then do the same to the edge of the CR just before inserting it into the BT. Once it is in there I could place the BT upright and allow the epoxy to puddle up around the inside edge of the BT. For the second half of the problem I could get some small screws and screw into the CR to grab onto and then just fill the holes in prior to sanding and painting. Another option would be to lightly tap the edge of the BT on the edge of a counter all they way around tapping the CR back to the bottom of the BT.

I'm not sure what I'm going to do on the shock cord issue just yet as I really don't want to cut the BT.

 

[new2hpr]

I'd recommend the plywood route.

As is, even with the fiberglass, the grain on your balsa fins is going the wrong way. It should be parallel to the leading edge of the fin. With it parallel to the body tube, the fin will be very weak and vulnerable to cracking or splitting on a grain line.

Just my $0.02.
Ken

 

[BsSmith]

What is the real problem with the balsa? I have seen high power rockets with glassed FOAM work! A few more layers of glass may be needed than a normal plywood fin, but these will probably turn out stronger than plywood.

 

[geof]

I'd recommend the plywood route.

As is, even with the fiberglass, the grain on your balsa fins is going the wrong way. It should be parallel to the leading edge of the fin. With it parallel to the body tube, the fin will be very weak and vulnerable to cracking or splitting on a grain line.

Just my $0.02.
Ken

Ken is totally right on both counts. Plywood is more sensible, without glass. And the grain is the wrong way (although I'm not sure if that matters after glassing).

Also, I would quibble with some previous comments about the tabs. I would not have glued on the tabs, just out of habit. But since you did, let me say that a good wood-to-wood bond with yellow wood glue is stronger than the wood itself, regardless if whether it is balsa or plywood or, for that matter, 1in pine. The possible problem you have with your approach is that you used CA rather than wood glue. If you glass all the way down the tab, I guess you're back to my original uncertainty: whether glass sufficiently strengthens balsa.

You've only used a bit of cheap balsa. My suggestion is still to toss out the fins and restart with ply. Wood glue for fin-to-body and -to-MMT. Or epoxy if you want. No glass.

 

[Iceman1979]

I picked up some 1/8" lite ply from the hobby store today so i'm working on the new fins now. It's a good thing too as I messed up the balsa fins anyway. I re-drew the fins on a sheet of paper and I noticed that the design was slightly differant than my balsa fins. After checking my measurements I realized that the balsa fins were cut wrong.

I took the coordinates from rocksim and drew the fin out on paper with a ruler and pen. I don't have a printer at my apartment at the moment so I'm having to transfer it from rocksim to paper manually.

I'll get some pics posted as soon as I can get the new fins cut out.

 

[Iceman1979]

Alright, here are some more pictures of the progress thus far.

This first picture is where I sealed the ends of the BT with some CA glue. The last three are where I glued the CR's to the MMT.

 

[Iceman1979]

Ok, more pictures...

First pictures are the new fins! It was fun cutting them out with and xacto knife. The next picture is of my wife working on her rocket. and the next two are the MMT with the fins attached.

 

[Iceman1979]

It's really amazing what a huge difference the wood grain direction makes when you cut the fins. These fins are pretty stout.

 

[rokitflite]

Whew... When I read the original title I thought it was going to be Tinker from Speed Buggy! I could not imagine how you were gonna tie him into a flight/rocket theme.

 

[Iceman1979]

haha, no, nothing like that.

I am curious to see how she paints this rocket though. I'm sure Tinkerbell will be on the rocket in some form or another.

 

[Pippen]

haha, no, nothing like that.

I am curious to see how she paints this rocket though. I'm sure Tinkerbell will be on the rocket in some form or another.

Well, if it were my house, she'd be needing LOTS and LOTS of hot pink and lime green paint plus a big Tinkerbell sticker. This one's my daughter's from a few year's back--she was going to do a name on the side in green but the plan fell through.

Thanks for doing the build thread--it's always fun to see a project come together.

 

[DaveCombs]

And the grain is the wrong way (although I'm not sure if that matters after glassing).

It's really amazing what a huge difference the wood grain direction makes when you cut the fins. These fins are pretty stout.

What Geof said was applicable to balsa. Plywood layers are actually laid down perpendicular to each other (alternating -- this way and | that way) and that's what gives it the strength (as well as the number of layers). For those reasons, grain direction really isn't important on plywood.

Now, since it appears that you haven't yet put the motor mount into the body tube, take the time now to drill a hole in the upper CR and put in your eyebolt for the shock cord. Then get a quick link, tie the shock cord to it, attach the quick link to the eyebolt, and then pass the free end of the shock cord down through the MMT so you can push the motor mount into the airframe. (I really need to post pics when I tell people to do these things!)

 

[Iceman1979]

Yeah, I'm sure. We have a trip to Michaels planned so we'll see what colors she picks out. She said something about doing a cross spiral paint job on the body. Not sure yet how she plans to tie that all into tinkerbell. Well, I won't worry about it to much, after all this is her rocket.

So far I've been doing most of the work on it. I've come up with a design (that she Ok'd) and put it in rocksim. I've done all the research and planning, all the measuring and cutting so I naturally assumed I was building it too.

I'm sitting at the table working on the rocket and I aske her to come over and give me a hand. After she is done she asks me "is there is anything else I could do, after all it is my rocket". Needless to say the rest of the rocket buildig for the night was done by her. At that point I was just there to hold rocket parts for her.

I was so excited to see her work on the rocket that I had to get a picture. Of course I got in trouble for taking the picture and when she sees it on here I'm going to be in more trouble

We're going to be working on the slotting the BT tonight and hopefully be able to put it all together, YAY!

 

[DaveCombs]

After she is done she asks me "is there is anything else I could do, after all it is my rocket". Needless to say the rest of the rocket buildig for the night was done by her. At that point I was just there to hold rocket parts for her.

...We're going to be working on the slotting the BT tonight and hopefully be able to put it all together, YAY!

She has the right attitude!

Do you have a Dremel? They're GREAT for slotting tubes. You can stack a couple of cutoff wheels together to make the slot the right width. I've done that on all my MPR/HPR builds. Just take your time and make plenty of guide lines to follow and you'll be fine.

 

[Iceman1979]

Yeah I do have a dremel! I would have never thought of that for cutting the slots. I have a quick link (like the one in the pic) that I'll use to attach to the eye bolt like you suggested.

Ok, I didn't think I would be this far this quick so I don't have shock cord or chute yet. The chute I'll probably make out of a broken umbrella. I was hoping to be able to pick up something from home depot or Michaels that would work. Any ideas on something that I could find locvally like walmart, or any of the other store I mentioned?

 

[DaveCombs]

For the shock cord, see if there is a GOOD sporting goods store near you that carries climbing gear. You can get 1/2" tubular nylon (it's the flat ribbon-looking stuff), or you can even get 1/4" accessory cord which will do the job just fine. GET A LOT, like 25 or 30 feet; you won't use all of it, but you'll have plenty to work with. While you're there, have them show you how to tie a double figure-8 knot (or figure-8 with follow) to attach it to the quick link (if you don't know how).

 

[Iceman1979]

Cool, I'm on a quest to find a local sports store. Thanks for the advice.

 

[Iceman1979]

There are some sports athority stores around here and only one dedicated to outdoors sports.

I'm going to see what I can find. so far I'm not seeing anything like what you described. Would nylon rope like what is depicted in the double figure 8 tutorial work?

 

[DaveCombs]

https://blastzone.com/pml/

On the left-hand gutter, click on "Recovery". That's the tubular nylon you're looking for. Alternately, here's an example of accessory cord:

https://www.bdel.com/gear/accessory_cord.php

 

[Iceman1979]

Well, I get home and the Rouse-Tech motor tube and retension set has arrived. To my surprise there is another package in the box with a thank you note. They gave me a free plastic parachute. I guess parachute problem is solved

While I was at work I had my wife work on her rocket. She drew and cut the fin slots in the BT and test fitted everything. After some verry minor trimming it fit perfectly.

Here are some more pictures of the progress so far.

 

[DaveCombs]

GOOD JOB! That's an interesting back end on the 29-40/120; looks bigger than the AT version but it shouldn't matter.

Hack: I get it now; that's an AeroPack on the back end. DUH. I have one of those and didn't even recognize it!

 

[Iceman1979]

Yeah I forgot to take it off from when I test fitting everything and thats the pic I snapped. I should have taken it off to sho the idividual parts.


Update: My wife and I worked untill about midnight getting most everything glued up. The forward most CR still needs some glue, the parachute still needs it's shroud lines cut to lenght and attached, the nose cone needs to be sanded, Need to attach the nose cone and parachute to the shock cord, and add some filits to the fin/BT joints. I'm waiting on skylighter to process my order which has my cab-o-sil and some other chemicals in it. Once that gets here I can do the fillits and then start the painting process. My wife still is un-sure of how she wants it painted so we'll probably do a lite coat of primer and then wait untill she knows what she wants.

On the shock cord, how long do I need to cut it? I've seen some photos of the Initiator on its way down and it looked like it had an extremely long shock cord.

 

[Iceman1979]

Oh, Dave,

My MMT is about 1/4" longer than it need to be. According to the AeroPack instuctions longer is ok, What's your thoughts on that? Should I cut it down or just leave it as is?

Thanks
John