FlisKits Tumble Weed on a MicroMaxx II

[MarkII]

As an old timer in this hobby, I have a special place in my heart for the Estes Astron Sprite. It was my second ever model rocket, and despite its diminutive size, I really liked the way it was designed and the innovative way in which it recovered. Rather than deploy a device at apogee, it executed a weight shift, moving the CG rearward of the CP, making the rocket unstable and causing it to tumble back down. The tumbling motion produced a good deal of drag, which was enough to slow the descent to a safe rate.

Fast forward 35 years; I am now a BAR. While searching online, I come across the FlisKits web site. It had a multitude of interesting kits for sale, but one of them immediately caught my eye. It bore more than a passing resemblance to my beloved Sprite, but it was smaller, downsized to fly on a 13mm mini motor. I simply had to have it, and after building it I proceeded to fly the heck out of it. Somehow I managed not to lose it either, and even now it continues to be my most-flown rocket.

Although it was very cool, the Sprite was quite a small rocket, and the Tumble Weed is substantially smaller that even that classic. In fact, it is comparable in size to some of FlisKits' MTTM (MicroMaxx) kits. And so it came to pass that 3 years ago, a light bulb (figuratively) flashed on over my head. I had an idea! With parts purchased from FlisKits, I created a sliding motor mount for it that would allow it to fly on a MicroMaxx motor. I didn't want to make the conversion permanent, so I designed the mount to be completely removable for occasions when I wanted to launch the TW on 13mm motors. I also wanted to see if I could have it continue to recover via weight shift-induced tumbling. One other thing I wanted to do was to have the mount anchored to the rocket in some way so that if the hook failed to catch the mount as it slid rearward after the ejection charge fired, it would still remain with the rocket and not be lost.

[MarkII]

I built the sliding mount out of parts that I obtained from FlisKits. I assembled an EMK-6-5 motor mount around a BT-5 coupler, and then lengthened it with a short section of BT-4. I attached a short length of Kevlar thread to the upper section with Mylar tape, and tied a loop in the other end of the thread. I painted the upper BT-4 section with thin CA to harden it, and then sanded the outside of the mount so that it would slide more easily in and out of the rocket. The mount is 1.75" long, the same length as a 13mm motor.

[MarkII]

Launching the Tumble Weed on micro power is a hoot and a half. When I want to launch it on a mighty MicroMaxx II, I slide in the mount all the way in and then reach through one of the vent holes with tweezers to grab the loop of the thread and pull it out of the hole. It is sized to be just long enough to extend down the outside of the rocket and slip over the end of the motor hook. When the ejection charge fires, the mount is ejected out of the aft end. It is prevented from being completely ejected by a combination of the motor hook and the thread. The thread is stopped before it can be pulled entirely back in through the hole by the loop around the hook. Even though the mass of the motor mount is somewhat less than that of a spent 13mm motor, the weight transfer is still sufficient to cause the rocket to tumble. I found that even though the mount blocks the vent holes when it is in the forward position, the vents still allow too much pressure to escape before the mount can be forced down into the lower position. So I take some more Mylar tape and wrap it around the rocket to cover them up, and then poke a pair of small holes in the tape with a pencil tip.

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[MarkII]

How does the Tumble Weed fly on a MicroMaxx II? Well, that's when the hilarity begins. Don't worry, it does boost and recover safely. I use a clothespin to stand it off about halfway up on my 1/8" launch rod to cut down on the drag loss. At ignition it shoots up completely straight. For the 3 feet or so it goes fast, and then it looks as if someone is applying brakes that have worn down pads. It coasts to a stop about 30 feet up, traveling in a perfectly vertical trajectory all the way. It stops, and then just seems to hang there in mid-air for a second or so, as if to look around and take in the view. It is still pointing straight up and has made a dead stop in the air. The image that comes to mind is of Wile E. Coyote at the moment he realizes that he has run off the edge of a cliff. Then it hits Reverse and comes straight back down to terra firma, firing the ejection charge and starting to tumble about 5 feet into the return trip. It usually bounces off the blast deflector on the pad before hitting the ground. If I can stop giggling long enough, I'll pick it up, pop a fresh motor in and do it again.

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[JAL3]

How does the Tumble Weed fly on a MicroMaxx II? Well, that's when the hilarity begins. Don't worry, it does boost and recover safely. I use a clothespin to stand it off about halfway up on my 1/8" launch rod to cut down on the drag loss. At ignition it shoots up completely straight. For the 3 feet or so it goes fast, and then it looks as if someone is applying brakes that have worn down pads. It coasts to a stop about 30 feet up, traveling in a perfectly vertical trajectory all the way. It stops, and then just seems to hang there in mid-air for a second or so, as if to look around and take in the view. It is still pointing straight up and has made a dead stop in the air. The image that comes to mind is of Wile E. Coyote at the moment he realizes that he has run off the edge of a cliff. Then it hits Reverse and comes straight back down to terra firma, firing the ejection charge and starting to tumble about 5 feet into the return trip. It usually bounces off the blast deflector on the pad before hitting the ground. If you can stop giggling long enough, you can just pick it up, pop a fresh motor in and do it again.

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You realize, don't you, that this belongs in the Sprite gallery.

May I?

[MarkII]

You realize, don't you, that this belongs in the Sprite gallery.

May I?

Sprite or Tumble Weed? I do have a Sprite clone, but I haven't finished painting it yet.

[MarkII]

Yes! Wherever you think it fits.

[JAL3]

Sprite or Tumble Weed? I do have a Sprite clone, but I haven't finished painting it yet.

I guess I need guidance from you and Jim Flis on this. I thought that the Tumble Weed was a variant of the old Astron Sprite. Is that incorrect? I dunno.

[MarkII]

I guess I need guidance from you and Jim Flis on this. I thought that the Tumble Weed was a variant of the old Astron Sprite. Is that incorrect? I dunno.

It's obviously inspired by the Sprite, but it isn't a straight downscale (I don't think...). It is very nearly one, but it seems to me that there are a few subtle differences. I'd like to hear Jim's views on this. I could go either way and I would be honored to have my posts and pictures placed in any gallery.

[JAL3]

It's obviously inspired by the Sprite, but it isn't a straight downscale (I don't think...). It is very nearly one, but it seems to me that there are a few subtle differences. I'd like to hear Jim's views on this. I could go either way and I would be honored to have my posts and pictures placed in any gallery.

Your description pretty much fits with my prior conception. This is probably the most difficult thing about the gallery section. The galleries are for "archetypes" and all variations on the theme. The original design is the archetype and derivatives are all fair game.

I'd like to hear what Jim has to say as well.

[BEC]

This may get me to actually build the Tumbleweed kit I have from one of my first BAR orders - because, like you, Mark, the Sprite was one of my first rockets (if not THE first - I don't remember for sure).

Completely different scales but I had a go up (not far) - stop - wait then come down (on a 'chute in my case) flying a Maxi-Alpha 3 on a C11-3. A flight like that does make one giggle, indeed. Thanks for this thread.

[jflis]

It's obviously inspired by the Sprite, but it isn't a straight downscale (I don't think...). It is very nearly one, but it seems to me that there are a few subtle differences. I'd like to hear Jim's views on this. I could go either way and I would be honored to have my posts and pictures placed in any gallery.

You are correct that the Tumbleweed was inspired by the Sprite (who'da'thunk it ) but it is it's own beast so would be best served with its own thread in the GALLERY.

Love what you've done with it, by the way Very cool mod on one of our very early kits! And I love the flight profile you describe LOL

[mjennings]

Just built a TW with my Niece over Christmas, and was wondering how it would fair on MMX power. What kind of altitudes do you see on her using 13mm? From what you say she seems much more recoverable than a mosquito.

[plano-doug]

Just built a TW with my Niece over Christmas, and was wondering how it would fair on MMX power. What kind of altitudes do you see on her using 13mm? From what you say she seems much more recoverable than a mosquito.

My experience with the TW - 1 flight - was that we lost it on the way up, on a ½A motor (½A3-4T, IIRC). There were two of us tracking it - both quite experienced at this sort of thing - and we both lost it.

So I conclude it is just as "lose-able" as a Mosquito I think the MicroMaxx adaptor is a good idea. For sure, if you fly 13mm, try a ¼A3-3T on the first few flights.

Doug

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[MarkII]

Just built a TW with my Niece over Christmas, and was wondering how it would fair on MMX power. What kind of altitudes do you see on her using 13mm? From what you say she seems much more recoverable than a mosquito.

According to RockSim:

Motor............Alt......Max Veloc..........Time to
................(ft.).....(ft/sec)............apogee
1/4A3-2T.........207........172................3.04
1/2A3-2T.........385........304.4..............3.93
A3-4T............469........369.5..............4.11
A10-3T...........422........377.4..............2.90
1/8A.5-1.........109.........92.4..............1.80

The 1/8A.5-1 (MicroMaxx II) altitude estimate seems kind of high to me, based on my flight experience. But I didn't add the weight of the mount into the design. My altitudes were above half of that, or even a little less. Be sure to paint it a bright color or pattern if you are going to launch it on 1/2A or A.

[MarkII]

My Tumble Weed kit must have been one of the last few to have "cut your own" fins. A day or two after I placed the order, Jim announced that the kit would now feature laser-cut fins. I normally don't have any problem with a kit that requires me to cut out the fins myself; when I started in model rocketry, all kits were like that. But with the Tumble Weed, the template for the fin caps was so small that when I tried to hold it down and trace around it, my fingertip covered up nearly the entire template! I ended up using the sheet that I had cut the pattern out of as sort of a "reverse template." Once I got them traced out, I could not get three clean, accurate pieces cut out of balsa, even after many attempts. I ended up using 1/64 plywood for the caps, because I could make more precise cuts in it. After gluing them on, I used Carpenter's Wood Filler to build them up to the correct thickness.

[MarkII]

John -- you can put this thread in a "FlisKits Tumble Weed" gallery.

Don't worry -- I'll post photos for an Astron Sprite Gallery before too long. I've got a base coat on it, and I just need to add an accent color.

[MarkII]

From what you say she seems much more recoverable than a mosquito.

If you don't count the motor hook, which extends below the ring fin, the TW is actually a smidgen shorter than the Mosquito. (If you count the hook, it is exactly the same length.) The ring fin adds drag and mass, which probably keeps the altitude lower. It also helps it be more visible in flight. But you can definitely lose it if you don't carefully watch for it. Unlike the Mosquito, it won't simply vanish as soon as the motor ignites; if you have sharp eyesight and good lighting conditions, you can track it's flight. The most important thing, though, is to carefully note where it lands. If you launch it on MicroMaxx motors, you won't have any problem at all seeing it's entire flight and recovery.

[mjennings]

awesome thanks for the info. We did a red and yellow paint scheme, so that should help. I'll just have to remember to dig this thread up when I see her in the summer.

[plano-doug]

But with the Tumble Weed, the template for the fin caps was so small that when I tried to hold it down and trace around it, my fingertip covered up nearly the entire template! I ended up using the sheet that I had cut the pattern out of as sort of a "reverse template." Once I got them traced out, I could not get three clean, accurate pieces cut out of balsa, even after many attempts.

Several years ago, when I did my Sprite clone, I printed a sheet with many of the caps and fins on it, all spaced close together, and simply glued the sheet to the balsa rather than cutting them out and tracing. That made it much easier to get accurate outlines on the balsa. Given how important the accuracy of the fins are in these kits (to ensure proper mating with the ring), that eliminated one of the key error-introducing steps.

Of course, laser cut parts are the ultimate solution.

Doug

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[jflis]

When we upgraded the Tumbleweed to laser cut parts we also went with basswood (1/32") as we discovered that with balsa, even laser cut created problems as the tips were so small that they were subject to damage during handling... Not fun...

When I would build the earlier versions I would print the fin patterns up on label paper for the same reason you glued the patterns to the balsa. Not only did it make cutting them out much easier, but also provided added strength from the paper laminate...

[MarkII]

At the time, I didn't have a good way to make copies of the template or I would have done that too. Before trying plywood I did try to trace it out on basswood but I still couldn't get a good clean outline. They were better than the outlines on the balsa, but still not really usable. I realized that the most significant issue involved trying to cut out parts from material that was thicker than the part itself. I was able to cut the template out without too much difficulty from the thin cardstock sheet, so I reasoned that if I used thin material, I might have an easier time. I finally succeeded and was able to make much more accurate cuts when I switched to using 1/64" plywood. I cut out the general outline of the fin caps, and then gradually trimmed them down to their final shape. If the plywood hadn't worked, I was going to try thin styrene sheet next. And if that failed I would have turned to building up 3D parts from layers of cardstock. The fin caps were so small that I wondered whether it had even been a good idea to use wood for them in the first place. I thought at the time that getting them laser-cut from fiberboard might have been a better approach.

But that's all water under the bridge now. I keep meaning to add one to my next MicroMaxx order so that I can experience the difference, as well as to start building up my collection of TWs. During a subsequent build of an Intergalactic Man of Space (an even smaller and somewhat more complicated kit) I finally saw the wisdom of using laser-cut basswood for nanoscale parts.

As for the template itself, I found that using the hole that was left in the cardstock sheet after I cut out the template, rather than the template itself, worked much better at the time. I taped it down with removable tape each time and then traced around the inside edge.

[bradycros]

Nice!

[Micromeister]

Very nifty conversion Mark!
The Sprite is on my downscale list also. always liked the design, hadn't even looked at the tumbleweed.
really good stuff.