Two new projects

[geof]

My son and I finally made it to a club launch this winter. We had some great flights, and some not-so-great ones. But we came back energized to start some new projects (aside from my Mega-Snooper which is nearly done).

He's working on a 2x24mm fairly large rocket with some transitions and a clear payload. I'm working on a 29mm F-bomb made from one of those cool tubes that you get when ordering large prints from the Winkflash photo website.

First, we'll take a look at his project. Many of the parts are in the photo: a standard tube (BT60 I think), an old nose cone, 4 fins cut from the wings of "Flying Banana" (our huge Edmonds glider), a longer Winkflash tube, and a clear payload segment (I think from a Fliskits kit). There are two transitions (one shown). One we sanded down from a solid balsa bulkhead. The other (not shown) is another old nose cone where I took the pointy end and sanded it down to make an appropriate shoulder.

He made the motor mount from a variety of remants and spares; it is off drying somewhere. I'll mention a funny part of MMT construction when his next photos arrive.

Geof

PS. I've been gone for a while...what happened to my first thousand posts?

 

[geof]

The second build is one of those distracting projects that takes place when I'm not focused on my "real" rocket project (the Mega Snooper and some scratch gliders).

The Winkflash tube used here is 2in diam with extra thick phenolic walls, and 13.25in long. It comes with a shiny paper coating which is partially sanded away in the first photo.

I began with the yellow nosecone, which was (I think) a BT80 version of a Big Bertha cone. (The photo shows it after reshaping it and slicing off its tip.)

The cone shoulder had been bigger than the tube, so I originally sanded down the shoulder and then tapered the bottom part of the cone in an attempt to mimic the bulbous Honest John style. Well, when I did that and left the top round, my wife almost fell over laughing because the rocket was a dead ringer for a 13.25in phallus. She wouldn't let me keep it.

So, I dug up another nose cone. I sliced off the top of the yellow cone and carved out a hole. The black cone will fit in there, and I'll make some sort of smooth transition to meld the two cones into one.

 

[geof]

On with the winkflash project. I had some old 29mm motor mount tube sitting around so I used that. I simmed up to a H180W in this thing to ensure stability, but really even a G will yield rather dubious recovery chances. So I kept the motor tube fairly short.

The CRs and fins came from 0.11in ply. I'll use ttw fin tabs, mostly for the fun of it.

Space is rather cramped at the rear of the rocket, so I used a skinny retention strategy. Those small bolts pass through the aft CR and are epoxied into place. For retention, small clips will slide over the bolts and be held in place by nuts. The clips fit very nicely into the slots in the 29mm hobbyline case, or around the rim of the 29-180 case.

Next up: fins and kevlar rope!

 

[geof]

More winkflash progress.

In this photo the fins have been installed and filleted with epoxy. I decided to use brass launch lugs on this. I pushed them into the fillet while it was still pliable. Then, later, I used 2-part epoxy putty to shape a smooth sheath for the lug. What you see here will be smoothed up with a little sanding and filler.

 

[geof]

Another winkflash update. For small F-G rockets I hate to use an overkill shock cord. However, my kevlar string is a little too thin. I worry about zippers and burn-through.

So I have begun to make kevlar rope. Plus, it's just darn fun to do it.

There are a few rope-making websites around, but I haven't found any very clear. For the simplest form, you tie a circle of string and fix both ends to steady objects such as poles. I put one end on a pole for my wife to hold, and the other end passed through a dremel bit for quick spinning. Then, by hand (or by dremel) you rotate until everything is very tightly twisted. It should want to twist itself up in a tangle if you were to loosen the tension between poles. (Don't loosen the tension because if tangles you've got to start over!). If you turn it so tightly that it does twist into a tangle or it snaps and nearly takes out your wife's eye, then you made it too tight. I especially advise against the last one.

Now, retaining tension, have a third person (or yourself if you have long enough arms) grab the string right in the middle and slowly pull to form a V, and finally an I. Keep tension the whole time. Now this third person can gently start to release tension on her end, maybe by pinching the string a few inches down from the end and gently letting the very tip slide toward the pinch and lose its tension, then sliding the pinch down toward the partner(s), gradually letting the whole assembly go loose.

If you've done it right, the string will now tangle upon itself, in the opposite direction to the original twist. Amazingly, the tangle/twist will sort itself out into a rope. The end with the V-tip doesn't even need to be tied or anything. If you do it imperfectly, there may be a few knotty tangles in the rope. These can usually be straightened by running your thumbnail along the rope.

Tie off the other end. You're done! It's a nice, thicker rope with much more elasticity than the original string. I recommend it for fun and for rockets.

There's a fancier 3-strand version where you start with a loop and a half. After the twisting, you get two more people to pull the string into a Z, and then onwards to an I. I tried this a few times here, but could not get it to work.

Anyways, I'm done with it. This rope went into the forward centering ring and stretches out as the shock cord.

G

 

[jj94]

Thanks for the rope tutorial. I think it's really cool. But to me, it seems like a lot of kevlar is being used for a small piece of rope.

 

[hcmbanjo]

You might get a few ideas from this tool, available from model expo.

https://www.modelexpo-online.com/product.asp?ITEMNO=MS110

It's really meant for model ship rigging, but it might get the creative juices flowing.

Also, they're running a special on #11 X-Acto style blades - 100 blades for $4.99!
Best price I've ever seen!
The blade part number is MT8001, you have to let them know the offer code is W364 when ordering.
They always have lots of modeler's tools for sale, some are better than others. But, the blades I've bought in bulk before have always been as good as the X-Acto brand.

Hans "Chris" Michielssen
Old/New NAR # 19086 SR

 

[geof]

Update on the winkflash project. The body is done. That is a lot easier than the nose.

G

 

[geof]

Back to my son's project. We got the fins on and loosely dryfit the pieces to see what we have.

This is a 2 x E9-6 cluster.

After some fiddling in rocksim and matching measurements to rocksim specifications, here's what we've got, approx. The rocket is 45.5in tall, 2.125in max diam. Simmed to 1300ft on the cluster. Empty weight: 12oz including 1oz of noseweight. This was weird. With no nose weight we got a stability margin of 4, which is clearly sensible because it is a very long rocket. Yet when we took it outside to spin it, we needed 2.5oz to get a good result. Well, the spin test is conservative and my string wan't as long as it should be. So I was sure we could use no weight, but decided to add 1oz anyway.

Next will we glue it together and fill up any blemishes.

 

[geof]

Back to the winkflash project. The goals for this rocket are: short 29mm and fly it on a G33 (or G53 if I can't find the old G33) without losing it.

With a G33, I get stability margins of 2.1 with 3oz of nose weight and 2.8 with 6oz and 3.3 with 9oz. The altitudes with G33 for these choices were 2700ft, 2300, and 1900. With a G64 I get 3450, 3100, and 2800. Just for fun a H180 with 3oz (which fits and is stable) yields 5300ft!

Well, I don't want to lose it. Also, I decided to make an adjustable noseweight system, whose construction added a bit of weight where normally there would be a small eyebolt. With that and some nose weight, I got a total addition of 5 5/8 oz. Pretty close to a compromise.

My preferred method of adding large amounts of nose weight is to melt lead. Aside from being a clean and fun way to do it (as compared to epoxy and fishing weights), I like this method because it completely fills the nose space from the very tip. This gets the most effectiveness for the least weight.

The phot shows the result. I've also got the bottom half of the nose in the photo, to remind you how the two parts fit together.

G

 

[geof]

Now to finalize the full nose cone. I've made two radical nose cones (e.g. with concavities) previously using this method. This current attempt is less ambitious.

First I glued the two parts together. Then I used CA to glue some balsa blocks around the seam where the biggest break in the smooth profile was. The first photo shows this. Then I sanded down those blocks and added two more rings of balsa--this time much thinner than the 1/4in thickness I used before. The second photo shows this at the stage when I have nearly completed the bottom ring. The top ring was not yet begun. Again I sanded everything down.

Of course there are large gaps between the various blocks, even after sanding. Also, the shape is not quite what I want. So next I fill the entire region with wood putty, smearing on lots of excess to give me some sanding room. That's shown in the third photo. Now I'm just about to go outside and sand the thing to shape. There will probably be some unevenness which will require another iteration of filling and sanding.

Geof

 

[BsSmith]

Does the launch rod go through the nose? In the picture it doesn't seem like the lugs are on standoffs.

 

[geof]

Ooh. I forgot about that. I'll have to think of something. Let me see how bad it is. That's kind of ironic. Usually I don't put the lugs on until the last minute. To avoid forgetting them, I put them on early.

 

[geof]

Okay, this will work. When the glue dries I'll clean up and contour the "standoffs" and fix it up with some epoxy putty for a smooth look, good as new! Thanks for preventing disaster.

G

 

[geof]

All done!

My son's rocket is below. "Military Maurader". Notice that it has an army man pilot in the payload section. My son wants me to show you an "up close" view of the army man, but I think you get the idea.

This was made from all scrap parts, as described above. As usual, we forgot the launch lugs, but we'll be sure to attach them before launching!

G

 

[geof]

For my rocket made from the Winkflash photo tube, we left of in post #11 with the progress on the nose cone. Below, after lots more filling, shaping, and sanding, here is the final result.

I've also attached a picture of the rocket fully primed and ready for paint.

G

 

[geof]

And here is the final paint job. The second photo shows the stand-off launch lugs.

This has been a fun project, and represents my first chance to fire a G33 motor!

The first launch, however, is planned to be a F52-8T. Unfortunately, I could only find the 11sec delay, so I'll drill it down to the right delay time.

Once I've flown it, I'll post it on EMRR with a full report and vital stats including final weight.

G

 

[jj94]

Wow, nice job with the nose cone. It looks so smooth.