Bunny Rabbit Goonie build - Part 2: How lucky are four paws?
The Thrifty Rocketeer continues...
Welcome back to the build session for the Bunny Rabbit "Goonie" (thank you, Peter Alway!) that we started some days ago.
This is my second such Rabbit Rocket, and I've learned a thing or two along the way. I've mixed in the use of some tools and techniques, and taken a few side trips to show you how I approach some tasks.... but we're back on track in the build thread.
When last we talked, I had shown how to lay out the templates, cut out the balsa fins, and began sealing them with a wood glue slurry. We did only 3 of the five fins for time. Let me assure you that while you were away, I have also done the two large hind leg fins, as well as finished 3 coats on the tail fin and at least two more on the front paws. By my count, that should make this rabbit four times as lucky as his real life counter-part. (Just a little joke...)
I'd like to point out that each successive coat of wood glue slurry tends to tint the balsa fins more and more yellow. That's not bad, but remember the glue is adding weight that must be overcome or lifted by the rocket motor eventually. I would recommend after an initial coat and sanding, that you limit the number of successive coats to one or two...until you get a smooth surface.
Note also that I feathered the leading edge of the fins, if only for principle. This led me to a problem.
In my initial Rabbit Rocket construction, it wasn't clear to me if the front paws/fins were supposed to face forward, or trail backwards. I choose to feather the ends of the front paws, but then reversed myself and glued them on backwards, trailing in the air-stream. In the current build, I have decided to mount the new fins facing forward, which is counter intuitive. As a result, I have had to feather three sides of these fins, and further re-coat them with the sealant slurry.
In the meantime, I have begun attaching the larger fins to the rear of the body tube. I took a measure of the circumference of the body tube at 13 cm and divided that by 3 fins. The result is a spacing of 4.33 cm between each fin. I laid this out on the edge of a small sheet of scratch paper and marked the points 120 degrees around the tube.
I then used the straight edge of the side of a Great Planes EZ Touch hand sander and marked in pencil about 3 inches along the body tube. In fact, I should have continued two of those lines all the way up to the top, as we shall see... but I did that later.
The gluing of such oddly shaped hind legs is awkward, to say the least. So I started with the prepared tail fin, making sure the root edge was sanded, flat and straight. I squeezed a small bead of wood glue on the root edge and positioned it with the bottom edge just at the end of the body tube. This meant it hangs over the back edge, but not as much as the hind leg fins will.
***NOTE: Traditional build instructions from Estes for the Baby Bertha has you build and insert the motor mount BEFORE attaching the fins. If you do that now, you can push the motor mount up inside by setting it on a table top until the tail pipe is flush with the body tube. IF you attach the fins NOW, you won't be able to use that technique. Think about this before proceeding.
NOTE: After marking the fin lines up the body tube, I took a bit of sand paper and roughed up the line, breaking the shinny surface of the body tube and allowing a better grip of the glue. The tail fin is not hard to do, but how to hold it for the glue to dry?
I use an old empty inverted egg carton to hold small rockets stationary while the fins dry. By careful positioning, I get the fin to stand vertical while the glue dries. At least 15 minutes goes by until the glue starts to set up, and I watch carefully to assure the fin doesn't fall over.
After a half hour or so, I can rotate the body tube, and with careful positioning, a hind leg fin is then glued in the same manner. Note that the awkward weight of this leg and body tube requires absolute stillness to dry and not tip over. Don't walk away from this process until you are SURE that the fin is standing straight up and balanced.
The last fin, another hind leg fin, is the hardest to do because you already have one hind leg on, and it may not want to sit in the correct position for you to hold leg two vertical to dry. I'm getting pretty good at it after much practice. I recommend this to the new rocketeer as an easy way to hold or position fins. (You may prefer a fin jig, guillotine, or similar fancy guide. But remember, this blog is called "The THRIFTY Rocketeer" and I'm doing it on the cheap. I'm certain the other jigs are fine and work well. More power to them!)
So, now, after re-feathering my front paws, I have re-coated them again, and I await them to dry. I should have extended the fin lines all the way up the tube, but I find it no problem to extend them after the hind leg fins are dry. I again sand off the mark as I roughen the surface. Note the plans do not tell you where to position the front paws, except that they are critical to be in alignment with the two rear leg fins. I am positioning mine so the front paws do not extend behind the top of the body tube. We'll see how that works out.
Finally, I have to add the launch lug, which I will position between the hind legs. It would have been easier to have marked this line before attaching the legs, but I can do this by eye. The plans tell you to cut the launch lug to 2 3/4" but I'm not sure how critical it will be. I'd follow the instructions in the Baby Bertha kit to be sure.
Now, you may have noticed that I totally skipped the prep of the motor mount and gluing the centering rings, engine block, retainer spring, etc. I must confess that I have done so many of these that I'm not really sure there's any point in belaboring it by detailing it here.
There are some rocketeers who will tell you not to use the Estes rubber shock cord, but instead to fashion your own 10 inch Kevlar string shock cord, and to attach some duct tape to the point where it would emerge from the body tube up top. I'm not going to get into that debate, except to say that I have no Kevlar string, and I've always used the rubber shock cord and T-bag securing method. But we'll leave that for the next entry in this blog thread.
Until that time, keep your glue capped, and save all your balsa wood scraps! (You never know when you'll need them!)
Welcome back to the build session for the Bunny Rabbit "Goonie" (thank you, Peter Alway!) that we started some days ago.
This is my second such Rabbit Rocket, and I've learned a thing or two along the way. I've mixed in the use of some tools and techniques, and taken a few side trips to show you how I approach some tasks.... but we're back on track in the build thread.
When last we talked, I had shown how to lay out the templates, cut out the balsa fins, and began sealing them with a wood glue slurry. We did only 3 of the five fins for time. Let me assure you that while you were away, I have also done the two large hind leg fins, as well as finished 3 coats on the tail fin and at least two more on the front paws. By my count, that should make this rabbit four times as lucky as his real life counter-part. (Just a little joke...)
Note also that I feathered the leading edge of the fins, if only for principle. This led me to a problem.
In my initial Rabbit Rocket construction, it wasn't clear to me if the front paws/fins were supposed to face forward, or trail backwards. I choose to feather the ends of the front paws, but then reversed myself and glued them on backwards, trailing in the air-stream. In the current build, I have decided to mount the new fins facing forward, which is counter intuitive. As a result, I have had to feather three sides of these fins, and further re-coat them with the sealant slurry.
In the meantime, I have begun attaching the larger fins to the rear of the body tube. I took a measure of the circumference of the body tube at 13 cm and divided that by 3 fins. The result is a spacing of 4.33 cm between each fin. I laid this out on the edge of a small sheet of scratch paper and marked the points 120 degrees around the tube.I then used the straight edge of the side of a Great Planes EZ Touch hand sander and marked in pencil about 3 inches along the body tube. In fact, I should have continued two of those lines all the way up to the top, as we shall see... but I did that later.
The gluing of such oddly shaped hind legs is awkward, to say the least. So I started with the prepared tail fin, making sure the root edge was sanded, flat and straight. I squeezed a small bead of wood glue on the root edge and positioned it with the bottom edge just at the end of the body tube. This meant it hangs over the back edge, but not as much as the hind leg fins will.
NOTE: After marking the fin lines up the body tube, I took a bit of sand paper and roughed up the line, breaking the shinny surface of the body tube and allowing a better grip of the glue. The tail fin is not hard to do, but how to hold it for the glue to dry?
I use an old empty inverted egg carton to hold small rockets stationary while the fins dry. By careful positioning, I get the fin to stand vertical while the glue dries. At least 15 minutes goes by until the glue starts to set up, and I watch carefully to assure the fin doesn't fall over.
After a half hour or so, I can rotate the body tube, and with careful positioning, a hind leg fin is then glued in the same manner. Note that the awkward weight of this leg and body tube requires absolute stillness to dry and not tip over. Don't walk away from this process until you are SURE that the fin is standing straight up and balanced.
The last fin, another hind leg fin, is the hardest to do because you already have one hind leg on, and it may not want to sit in the correct position for you to hold leg two vertical to dry. I'm getting pretty good at it after much practice. I recommend this to the new rocketeer as an easy way to hold or position fins. (You may prefer a fin jig, guillotine, or similar fancy guide. But remember, this blog is called "The THRIFTY Rocketeer" and I'm doing it on the cheap. I'm certain the other jigs are fine and work well. More power to them!)
So, now, after re-feathering my front paws, I have re-coated them again, and I await them to dry. I should have extended the fin lines all the way up the tube, but I find it no problem to extend them after the hind leg fins are dry. I again sand off the mark as I roughen the surface. Note the plans do not tell you where to position the front paws, except that they are critical to be in alignment with the two rear leg fins. I am positioning mine so the front paws do not extend behind the top of the body tube. We'll see how that works out.
Finally, I have to add the launch lug, which I will position between the hind legs. It would have been easier to have marked this line before attaching the legs, but I can do this by eye. The plans tell you to cut the launch lug to 2 3/4" but I'm not sure how critical it will be. I'd follow the instructions in the Baby Bertha kit to be sure.
Footnote: I realized after snapping this photo, that it looks rather rude. That's the only thing I'll say about this Easter bunny and his desire for the egg cartoon. This is a family blog, after all!
Now, you may have noticed that I totally skipped the prep of the motor mount and gluing the centering rings, engine block, retainer spring, etc. I must confess that I have done so many of these that I'm not really sure there's any point in belaboring it by detailing it here.
There are some rocketeers who will tell you not to use the Estes rubber shock cord, but instead to fashion your own 10 inch Kevlar string shock cord, and to attach some duct tape to the point where it would emerge from the body tube up top. I'm not going to get into that debate, except to say that I have no Kevlar string, and I've always used the rubber shock cord and T-bag securing method. But we'll leave that for the next entry in this blog thread.
Until that time, keep your glue capped, and save all your balsa wood scraps! (You never know when you'll need them!)
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