The FlisKits Tumbleweed is a great little rocket that sort of resembles a downscaled Astron Sprite. Instead of using the long-discontinued Estes Series III "shorty" motors, though, it flies their modern-day successors, Estes 13 mm "T" motors. The Tumbleweed really gets great performance from these motors, too; sometimes, a little too much performance, if you know what I mean. When I took my TW out for its first few flights on a very large, well-manicured series of athletic fields, it took me up to an hour to locate it lying on the field after each flight. Partly inspired by that experience, but mostly just to see if I could do it, I decided to try to make an adapter that would allow my Tumbleweed to fly on Micromaxx motors. The model is small enough and light enough to make such a conversion feasible. I did not want to make the mount permanent, though. I still wanted to be able to fly the model on 13 mm motors (like 1/4A's), so I wanted to make a mount that was removable. I also wanted to design it so that it would eject rearward and cause the Tumbleweed to tumble during recovery, just like the model was designed to do. In the following few posts, I'll describe how I did just that.

Mark \\.

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SAM # 0011

I built the adapter mount using a FlisKits BT-2.5-5 motor mount and a combination of a BT-5 coupler and a short length of BT-4. I sanded the coupler down until it was able to slide easily in and out of the body tube. when the motor's ejection charge fires, the entire mount kicks back and is stopped by a combination of the motor hook and a lightweight Kevlar leash attached to the forward end of the mount. I made the leash out of 10 lb. Kevlar and put a loop in the free end of it.

When I install the mount, I insert the leash first. When it reaches the vent holes, I push the free end of the leash out the hole that is on the side closest to the motor hook with a small stick.

Mark \\.

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SAM # 0011

When the mount is fully inserted, the leash is just long enough for the loop on the end of it to just fit over the end of the motor hook when I pull it down along the outside of the body tube. With it looped over the end of the hook, the leash slides up the hook and tightens against the body tube when the motor mount is pulled out, and it is just long enough to stop the mount when it reaches the end of the hook.

During installation, after I slip the loop over the end of the motor hook, I pull the mount down to tighten the leash against the side of the body tube. Then I put one wrap of 1/2-inch wide Mylar tape around the vent holes to cover them. This keeps the leash held against the body, so that it doesn't flap around after I push the mount back up into the body. But the main reason that I cover up the vent holes is because they are too large for the Micromaxx motor's tiny ejection charge. I poke a small hole in the Mylar tape over each vent hole to allow the ejection charge to vent.

I built the mount out of a combination of a BT-5 coupler and a length of BT-4, in order to make it long enough to reach the base of the nose cone when the mount is fully inserted. A combination of two couplers glued together could also be used. The mount has to be long enough to reach up past the vent holes, yet be light enough to keep the rocket from exceeding the maximum liftoff weight for the Micromaxx-II motor (around 18 - 20 grams).

I constructed the Micromaxx adapter so that I could install in and remove it easily, to allow me to switch between flying the model on 6 mm and 13 mm motors.

Mark \\.

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SAM # 0011

I use my standard low-power launcher to launch my Tumbleweed on Micro power. I stand it off at least half-way up my 36" x 1/8" rod, though, and I give the rod a quick sanding with extra-fine sandpaper to make sure that it is really clean and smooth. (It is important to do this in any case, but it makes a particularly big difference in this case.)

The Tumbleweed starts off fast but slows down quickly, coasting to a dead stop in mid-air, about 30 feet up, after a perfectly vertical flight. It just kind of hangs there for a couple of heartbeats, as if to take in the view, and then it drops, firing the ejection charge about halfway down. It really helps if you launch the rocket in dead still air, but launching mine in a very slight breeze a couple of times didn't hurt its flights.

Be aware that the Tumbleweed might hit the blast deflector on the pad on the way down. Also be careful that you don't hurt yourself as you fall to the ground, laughing your klister off.

Mark \\.

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Kewl!

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Jon
SAM #0396
BAR 02/07
NAR 86940
KF4GUL
Aim high, fly straight!

Nice write up, Mark. Good job.

Doug

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YORF member #11

What a hoot! I love a good kit mod and this one is great

Does it actually tumble? I was wondering is there was enough mass in the spent MMX motor casing...

Hey, this could be the only tumble recovery model that you could actually have a chance of catching after launching... LOL

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I know! I wasn't really sure that it would have any kind of actual flight on a Micromaxx-II, but I have been delighted with the flights that it has turned in. They are really something to see, but in a comical way, rather than being impressive. It's neat to watch the TW really zip upwards for about 10 feet, and then put on the brakes and coast to a dead stop in mid-air, pause for a split second, and then just drop. Like something you would see in a Road Runner/Wile E. Coyote cartoon.

But to get this kind of flight, the launch rod has to be really clean. I found that any residue on the rod will create more drag than the little Micromaxx motor can overcome. Replacing the 1/8" rod with a length of music wire that is just a little bit smaller in diameter, like 0.080" or 0.095", may help, too, but I haven't tried that yet. It also helps to launch it in very still air, with the launch rod pointing straight up.


Yes!! Well, sort of... First of all, you have to realize that the TW doesn't have very far to fall when you launch it with this motor. When it starts to drop, aft end first, it will naturally start to somersault anyway. The ejection charge fires late, after the TW has already started to fall, but yes, it does seem to alter the rocket's orientation at that point. The rearward ejection appears to cause the TW to rapidly spin around its CG, but it doesn't get to do very much of that before it hits the ground. One thing it doesn't do is lawn dart, so I guess that in itself is evidence that the Tumbleweed was actually tumbling during its return to Earth.

What may help it to tumble is the fact that the ejecting motor mount, which doesn't have all that much mass by itself, is anchored to the rocket by a leash running almost to the top of the rocket and then down the outside to its anchor point near the aft end of the motor tube. When it ejects and extends that leash to its limit, it gives the rocket a little off-center lateral jerk on the aft end of the airframe, right below the rocket's CG. I think that action might play a role in causing the rocket to tumble.


Absolutely! You will never have to walk far or search very hard for it after it recovers, either. Did you ever think that you would be able to launch your Tumbleweed over and over right in your own backyard?

Mark \\.

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SAM # 0011