Scratch Build Project Deux, Building a "Fantasy"

This project evolved out of a thread started by modeltrains on April 23rd in the Watering Hole and can be found here:https://www.rocketryforum.com/showthread.php?53052-Rockets-from-album-and-45-single-covers

After some discussion by the participants, I put together this design in RockSim 9 that comes pretty close to the shape of the rocket found on the cover the single.


I realize that there are accomplished scratch builders here, but I thought I might do this as a step by step for those who are starting out that might find some of my methods useful.

I began by ordering the stock parts I needed through BRS Hobbies https://www.brshobbies.com/ (My apologies to them, I think I have referred to them in other posts as BSR) and a custom turned nose cone and transition from Excelsior Rocketry https://www.excelsiorrocketry.com/ The lower primary tube is based on a BT-60 with a four inch balsa transition into a BT-50.


The BT-60 needs to be cut to a 10 inch length so what I do, is make tick marks around the tube and then use label making tape also as marking guide and a backstop for the X-Acto blade.


Using the tube marking guide as a cradle I slowly rotate the tube as I allow the blade tip to scribe and gently cut the tube. After several revolutions you end up with a clean and even cut.


After you remove the label tape you will notice that it has stripped-off the glassine surface. That's okay, I ll be sanding most of this off later when filling tube seams. Plus it gives the primer better surface to adhere to later as well.


Repeat the cutting process for the BT-50. You will need a 3 inch section of this and when finished, you will have the two main tubes. We still have five more tubes to cut for the powered outboards and the motor mounts so if you decide to build this rocket you will have plenty of practice.


Now you can dry -fit the nose cone and transition and admire what you have so far. In this state, the rocket is a little over 24 inches in length. The addition of the fins later will give it an additional 2 inches to its overall height.


More to come.
Steve

I'm in!!

Krusty

OOOOOHHHHHHHH........A FAT-Bottomed Rocket, COOL!!!!!!

The roll of thunder and flashes of lightning provided the backdrop for more work on the Fantasy Rocket tonight.

I cut the BT-50 tubes for the powered outboards and the core motor mount and the BT-20s for the 18mm mounts.


The powered outboard are four inches and length and the nose cone shoulders were 1 and 1/8 inches in length and this posed a clearance problem for the shoulder bottom and the top of the 18mm mount. Using a razor saw, I cut the shoulder back to 3/8ths of an inch and now have plenty of room between the two and will be able to add a venting port to the outboards.


After about three hours of tube cutting the major components are complete and it is time to move on to the fins and strakes.


More later.
Steve

Cut out the lower fins (1/8 inch) and upper fins (3/32 inch) All that remains is to cut out the transition strakes and the fin extensions that run along the body and I can begin the assembly process.

Very nice looking work; I appreciate descriptions that focus on tools and technique.

JohnCoker said:

Very nice looking work; I appreciate descriptions that focus on tools and technique.

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Thank you John, but now that you said that I feel sort of bad. Last night's post was abbreviated and I omitted a lot of stuff because the more I thought about it, the more I convinced myself that anyone reading this thread were more than likely accomplished enough that they would find the information a little too basic and thus a tedious read.

Thanks again John.

Steve

I appreciate seeing just exactly how others do things. I may be able to do the same things through different techniques, in which case I enjoy learning the technique you use. Or I may pick up an ability I didn't have before. Carry on with detail, please.

A favorite quote: The smart mouse has more than one hole.

SteveA said:

Cut out the lower fins (1/8 inch) and upper fins (3/32 inch) All that remains is to cut out the transition strakes and the fin extensions that run along the body and I can begin the assembly process.
View attachment 128747

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Why is the grain of the wood not parallel to the leading edge of the fins? I would think you'd be losing some streangth with the way the fins are cut.

bradycros said:

Why is the grain of the wood not parallel to the leading edge of the fins? I would think you'd be losing some streangth with the way the fins are cut.

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Actually, and this is embarrassing, I did have to re-cut the main fins for that very reason. Speed kills.

SteveA said:

Actually, and this is embarrassing, I did have to re-cut the main fins for that very reason. Speed kills.

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Good thing ya caught it before you glued them up. Carry on.

It's a bit annoying how life can get in the way of good build momentum and even suck the desire to finish anything right out of you. Regardless, we're back to the build. I should note, that in an earlier post Brady correctly pointed out that my grain was not running along my leading edge. I had noticed that as well and hadn't paid attention how I'd laid out my templates and my grain was running away from the leading edge rather than with it. As a result I had to cut a new set of fins in the correct direction shortly after I posted the photo of the first set. These are the correct fins So, tonight I began shaping the airfoil along the leading edge and I also laid-out the booster fin to get an idea what it would look like. Initially, I thought I wanted the bottom of the booster touching the ground, but I think I'll do the opposite and have only the fin-tip supporting the rocket. Now that we have everything cut out (correctly) and I finish shaping them, we'll start on the assembly.
Stay Tuned.
Steve

Cool build---watching

Disclaimer: I am simultaneously posting this build thread on a rocketry Facebook page I own and it is geared for those who are not into rocketry at the depth that we are and for the kids I run through my programs. The posts are very basic in its information regarding the techniques I use. I realize that most everyone who visits these threads are accomplished builders. I just copy and paste he text so I don't have to re-write it. And hope that someone will find something useful.

Steve

Getting Ready for final assembly:

Before assembly, it's always a good idea to fill the seams of tube spirals. Sometimes it seems like the spirals are tight enough and you don't need to fill the seams. However, it's always a good rule to go ahead and fill them. Often, what will happen, is when you prime the body tube for painting the seams will show and will look as deep and wide as the Trench, on the Death Star. I use Elmer's Carpenter's Wood Filler. It's inexpensive and a large tub will last you for multiple projects and it's easily sanded. In addition, it does not add a lot of extra weight to your rocket. Just a dollop in a small container with a few drops of water and thin it to the consistency of ketchup and apply with a disposable sponge brush. Allow to dry overnight and sand smooth the next day.


No matter how complex or simple a rocket design, at its core is a standard design for motor mounts. If you have followed any other build of mine, you'll notice that these mounts for the 18mm outboards look exactly like all the other motor mounts from earlier builds. There are basic rules in everything. Once you have mastered them, you'll find that you can build just about anything. Complex designs are just basic designs with a new twist. Then, it opens up a whole new realm of possibilities and makes you want to push the envelope a little further each time. It truly becomes addictive.


One of the centering rings for the 24mm motor mount. I've cut a notch in this ring to thread 300# Kevlar cord through as part of the recovery system. I will address this further, but when using Kevlar, it's best to cut your cord so that when the mount is in place, the Kevlar does not extend above the edge of the body tube. Otherwise, when the chute ejects, and hits the slip stream, it will pull the Kevlar into the edge and slice your body tube like warm butter. When this occurs, it's called a zipper.

The completed motor mount.

Hey, she's getting there!
Going to have to look up that FB page.

modeltrains said:

Hey, she's getting there!
Going to have to look up that FB page.

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Big Creek Rocketry
https://www.facebook.com/pages/Big-Creek-Rocketry/146698285492655?ref=ts&fref=ts

Ah, thanks!

Scotty Dog said:

OOOOOHHHHHHHH........A FAT-Bottomed Rocket, COOL!!!!!!

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Fat bottomed rockets and fat bottomed girls!

After filling the tube seams and allowing them to dry, I sanded down the tubes to remove the excess filler and the glassine finish of the tube. When it's time to prime for painting, the removal of the glossy finish will allow the primer to adhere better, or in other words, it provides "tooth". The tube was then marked with positioning lines for the addition of the fins, strakes, and other surface details.


I began with the addition on the primary fins that will not carry the powered outboards as well as the secondary fins for the upper body tube


Once the secondary fins were in place I went ahead and dry assembled the rest to get a better idea how it would look.


In regards to the primary fins, these were merely "tacked-on" I did not want to permanently attach them until I could I check all four fin sets for proper alignment and stance of the rocket and it was a good thing that I did.




I attached the first outboard pod and it was here that I could see that there were issues. Once attached, the outboard canted slightly in and I became worried that once powered and in flight, the exhaust jet could interfere with a straight flight or cause damage to the lower body. I decided then to remove the tacked pieces and redesign the fins in the plan file and start over. I also decided that I did not like how far the body tube extended beyond the fin line have decided to reposition them in the plan file as well.

This design may not have been as easy I expected. It is a good learning experience though both in construction as well as design. I guess it's true that it always looks better on paper.:grin:

Aw, bummer abuto having to redo. Keeps the hobby from getting dull, though.

modeltrains said:

Aw, bummer abuto having to redo. Keeps the hobby from getting dull, though.

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Re-worked the design and printed out the templates for the powered fins. Let you know how it works out this time around.:wink:

Success!


Sometimes, it's a good idea to take your own advise. I always tell the kids (at ad nausea) who take my classes that speed and short cuts kill a project. When working on the powered fins last time, I didn't like the way the templates looked so I tried to extrapolate using one of the regular fins and the end result was a crappy looking fin and having to rip the fins back off the body tube and starting over. I scrapped the fins in the Rocksim design and started over from the beginning, literately going back to the drawing board. Using the regular fins, I checked and re-checked the dimensions and plotted them out again in Rocksim. This time the templates looked correct for what I was trying to achieve.

Using the templates I traced my patterns and cut them out of 1/8 balsa and was rewarded with a set of powered fins that looked just like those on the CAD 2D diagram.




I began attaching the sub assemblies to the fin and this process was fiddly to say the least. The extra weight of the pod continuously pulled the fin away from the body. However, after allowing the glue become much more tacky, the third attempt to attach it was successful.



Both powered fins attached.






It looks like the outboards are canted inward, but they're not. They are attached at 90 degrees. I think the sweep of the fin gives the impression that they are canted. This drove me nuts at first until I checked the angle several times to insure that they were indeed straight.

Next few steps are to fillet the fin roots, add the body fin extensions and the transition strakes. After that we seal the fins and putty fillets. after that, few steps are to fillet the fin roots, add the body fin extensions and the transition strakes and then prime. After that we seal the fins and putty fillets and then prime.

I'm happy with how this is turning out. After checking with the reference image, it appears to be staying true to the original rocket. I'm eager to see how it will look with the fin extensions and transition strakes.

Hope you like it too.

Steve

After revising the design and running a few sims, I noted that this rocket (in the sims) plows through the wind really well. Sim # 11 is in winds up to 20 mph and she will still fly straight. Obviously a design intended for Kansas.:grin: