Intercontinental Transport

[reddrock]

Things are not working as I hoped with mainstream media so I thought I would try TRF. I see some great information on various forums and threads, so I'm optimistic, and like the interactive aspect. On to rockets!

Some time ago I came across a concept design for a supersonic passenger plane that I really liked. It was on NASA APOD (Astronomy Picture Of the Day - a cool site). Since the photo is probably copyrighted or otherwise protected, I'll just post the link ( https://apod.nasa.gov/apod/ap171001.html ). Hopefully that doesn't get me in trouble.

This is sleek and futuristic design without unrealistic appendages that don’t make sense in an atmosphere. With modifications it would make a very cool rocket. One of the things that is enticing is the fuselage (or main BT) is not round, but oval or elliptical. It also has a long tapered nose, swept back wings, canards, and a kind of swept tail ring-fin. By adding these same components in mirror image to make it symmetrical, it could be turned into a rocket.

The first decisions were how big to make it overall, what size MT, and then on to fun stuff like material selection, construction techniques and all those other things that make scratch building rewarding. I have lots of parts laying around from years of scratch building and wanted to use some of them. One item is a long conical 3" diameter NC that will work well for the nose of what I decided to call the Intercontinental Transport (IT). A PML phenolic 3" tube (O.D. = 3.12") that I have works with the NC and is a good basis for the center of the rocket with an elliptical tube over it. With that in mind I rejected a 29mm MT because H or even I power seems too low for what is going to be a draggy rocket. Thus I decided on a 38mm MT, which works well with a 38mm Slimline retainer I have. Also in my box of parts is a cut-off PNC which will work for a tail cone when I cut the tip off.

That's it for now. I'll come back later with more (with photos).

 

[reddrock]

Ok, obviously had an issue with trying to post too many characters, but photos with that text still posted. So here's some explanation to go with the photos.

Elliptical Tube

Previous composite lamination projects have made me aware that a 1 or 2 layer fiberglass (FG) tube has a lot of flexibility. I can use a larger tube as a mandrel to make a 2 layer FG tube and squeeze it into an elliptical shape to fit over the 3" Center Tube (CT). I decided on a 5.5" diameter tube as the mandrel. I tightly covered a 5.5" diameter tube in mylar and painted 2 coats of PVA on the mylar, letting the first coat dry before applying the second coat in the perpendicular direction. When this was dry, I laminated 2 layers of 6 oz loose plain weave FG over the mandrel. Since I am after flexibility, not strength, I used polyester resin. Of course with poly resin there was no oven curing or vacuum bagging. When cured, the FG tube was easily removed from the cardboard tube and mylar. With two layers of PVA, it was thick enough to just peel off the inside of the FG tube, no need for scrubbing with water to remove the PVA.

Centering Ellipses
It's easy enough to measure the circumference of a standard 5.5" tube. Most equations for the circumference of ellipses I found were approximate. , I played around with some math to try and figure out how to draw the ellipse accurately. The string method with pins at the 2 foci didn’t seem reliable. I Goggled “how to print an ellipse” and found the site https://www.blocklayer.com/oval-templateseng.aspx . Life just got a whole lot easier!

I need 1/8” on the narrow side of CE next to the CT tso the CE won't break, and that’s assuming a ½” thick Baltic Birch plate to make it from. Thus, the minor axis of ellipse is 3.12" + 2*0.125" = 3.37”. I squeezed the FG tube to this dimension and measured the major axis at 4.28”. I entered the major and minor axes and downloaded a PDF of the ellipse. Then I printed this at full scale, carefully cut it out, traced it on ½” Baltic Birch stock, and cut that out with a band saw. Finally, I lightly sanded the edges to remove saw marks and round the edges. It fit great inside the 5.5" FG tube. The last step will be to cut a hole in the center for the 3” CT.

 

[reddrock]

Unfortunately I didn't take any photos of making the 5.5" diameter FG tube.

My designs are modeled on RockSim, which I've been using since version 3. RockSim continues to get more sophisticated, but so do my designs, and I find I have to make simplifications in the modeling. An engineer once told me "All models are wrong, but some models are useful." The primary simplification I made was to model the 2-part swept ring fin as a simple non-swept single ring fin. If anybody knows how to directly model a 2-part swept ring fin in RockSim please tell me. I'm not too old to learn some new tricks.


Between the modeling and trying to get proportions close to the original concept, I came up with a 12.25" diameter ring fin. I happened to have a piece of Quick tube that is 12-5/8" diameter and decided that was close enough to use as a mandrel to make the tub fin. The process used on the 5.5" FG tube was also used to make the ring fin tube, except I used 6 oz Carbon Fiber (CF) instead of FG for better strength with less weight. Here's a shot of the CF ring fin tube on the mandrel and off the mandrel before the mylar was removed.

 

[reddrock]

Wing Fins

There are three pairs of fins in addition to the ring fin. The biggest are what I will call the wing fins. These need to be strong and lightweight. I decided to draw on my limited composites experience and make them with a Nomex honeycomb core skinned with CF.

Disclaimer: I am not a composites expert, I am a novice using composites in my hobby. It is clear there are others on TRF that know far more about composites than I ever will. This is just what I did and I don't claim it is the best, most efficient, strongest, or anything else.

Using RockSim, I printed out a fin template, then traced around it adding half to three-quarters of an inch all around. The larger template was used to plot out 8 pieces of 6 oz CF. That's two pieces per side of both wing fins. In this case I used masking tape around the template and cut the CF on the tape.

The template straight from RockSim was used to cut out the Nomex honeycomb. I put down masking tape on the honeycomb and mark it where to cut using the template. A 4-1/2" circular saw with a plywood blade is what I use to cut the honeycomb.


For the layup I started with a piece of melamine faced particle board. The layup will be on one side and I will vacuum bag the layup and oven cure the parts under vacuum. First clean the melamine and ensure there are no bumps or gouges. Then I clean again with acetone (wearing non-porous gloves) and paper towels, turning the paper towels often. Next I apply 2" wide masking tape all around the edges of the melamine board. This is where I will later apply the vacuum sealant tape. Now I waxes the board three times with mold wax, allowing each coat to dry before applying the next coat. Each coat is applied in a different direction from the previous coat. Then I applied two coats of PVA, letting the first coat dry before applying the second coat in the perpendicular direction. The form is now ready.

All parts of the layup, CF, Nomex honeycomb, release film, bleeder/breather cloth, and vacuum bag were cut to the appropriate size and laid out ready to use. You don't want to be cutting these things out while mixed epoxy is burning through its working time. I will use epoxy resin and hardener on the fins which will be stronger with an oven cure.

On a separate surface I applied epoxy to one of the pieces of fin CF, then transferred it to the melamine form. A second piece of CF was laid on top of it and more epoxy applied with a brush. The Nomex honeycomb core was laid on top of the two layers of CF. A third piece of CF was saturated with epoxy on the separate surface and transferred to the top of the honeycomb. And a fourth piece of CF was prepared and applied in the same manner. This was repeated for the second wing fin.

Pink perforated release film cut slightly bigger then the layups was applied over the parts. This was then covered with bleeder/breather cloth. Before applying the vacuum bag I needed to first get sealant tape down. The 2" wide masking tape was removed, revealing a clean border of melamine. I put down yellow vacuum sealant tape all around the form, being careful to apply it in a "rolling" manner to avoid any air bubbles trapped in the sealant tape. There are fancy vacuum bagging connections one can use to attach the vacuum hose to the bag. I just apply sealant tape all the way around my vacuum hose about 4-6" from one end, and press the hose tape into the form tape with the end of the hose inside the area with the parts. I'm always careful to ensure the hose does not lay on top of the parts and I wrap a piece of bleeder/breather cloth around the end of the hose. Next I start in one corner and press the vacuum bag, which is a flat piece of 4 to 6 mil plastic, into the form sealant tape. Again I am careful to ensure there are no air bubbles between the sealant tape and the bag.

 

[reddrock]

I have bought bags specifically for vacuum bagging, but 4 to 6 mil thick plastic from a home improvement store works very well and is much cheaper. But I do purchase vacuum hose that is capable of oven curing temperatures.


Next I connect the vacuum hose to my vacuum system and slowly pull a vacuum. Usually I stop and work any bag wrinkles to the side of any parts so I don't end up with ridges of hardened epoxy on my finished parts. Reduces the post cure work. When I have a full vacuum pulled I put the form and parts in my curing oven and cure at about 170 degrees F for two hours. Let the assembly cool slowly in the oven with heat off.

When cured and cooled, I remove the assembly from the oven, remove the vacuum bag, bleeder/breather cloth, and release film. The part lift off easily from the form and are ready for trimming. Here's a photo of the assembly just removed from the oven. It includes the other ring fin support fins made the same way. More on them later.

 

[reddrock]

Time to add more to this build.
Ring fin support fins
The vacuum bagging photos show the core of the fins that call the ring fin supports. Per the concept these fins are thick, almost the width of the BT at the base, and taper to normal fin width where they intersect the ring fin.

Tailcone, Motor Mount and Shock Cord attachment
I fed a Kevlar leader leader between the MT and fwd center ring and glued it to the MT. The rest of the motor mount is a second center ring, a short coupler, and tailcone.



Last step is to glue the slimline retainer to the MT with JB Weld.

Visible in this photo is a smaller CE used on both fwd and aft ends of the 3" center tube. These were sized and placed to get a taper on the outside elliptical tube that closely matches the NC and tailcone.

More Wing Fin work
Even after vacuum bagging the wing fins are not smooth due to the 6oz cloth weave pushing into the honeycomb. I experimented with two fillers: epoxy resin mixed with phenolic microballoons (brown) on one side, and resin mixed with Q-cells (white) on the other side.


In the end I didn't find much difference in the sanding. I also glued 1/4" dowel to the leading and trailing edges of the wing fins.

Fin attachment
With the CEs glued in place on the 3" center tube and motor mount/tailcone assembly installed, it's time to attach the fins. I use cardboard fin alignment guides and for some reason really like this part of the build.


Subassembly showing fins and centering ellipses.


Fins are first tacked in place and cured, the alignment guide removed, then1/8" dowel glued into the fillet against fin and tube.


Next time I'll get into constructing the elliptical BT with tapered ends.

 

[neil_w]

Fun project! Paging @mbeels….

BTW posting a link will never get you in trouble, and if you had copied and pasted the image here no one would have cared either.

 

[reddrock]

In reviewing this thread I noticed I posted a photo of just the large CEs, not the small CEs that help form the taper of the elliptical tube. So here it is.


Elliptical BT
Remember I started with a 2 layer of 3.2 oz FG tube formed on a 5.5" tube so I can squeeze it into an elliptical shape. I ended up with two of these tubes that will meet on a CE. Each one will get narrow long V shaped cuts in one end to make the tapers. The aft piece is harder because it must fit over the 4 fins in the taper section. Here's a photo of the FG piece with the cuts for the fins, but it's hard to see due to its transparency.


And here it is placed over the aft end for a dry fit.


And here I have glued the piece in place and taped the tapered end to hold it against the wing fins.


This was repeated for the forward end, but it was simpler without fins to work around.

At this point I have an assembly of 4 flat fins, tailcone/motor mount, central 3" tube, and outside elliptical tube tapered at both aft and forward ends. However, the elliptical tube is weak, so I applied a layer of 6oz CF over the elliptical tube to stiffen it up.

Now the assembly is stronger but I have some dimples and pin holes to clean up. Break out the Bondo and apply a thin layer all over to fill the pin holes. Then sand and add some more to fill in low spots and the transition between the elliptical tube and tailcone. When it looks good, I mask the fins and apply a coat of primer. The primer always brings out more imperfections that are usually minor. I use red Bondo Glazing and Spot Putty with appropriate sanding to fix these missed pin holes and divits. Another coat of primer is applied and the result checked to ensure I like the smoothness and overall curves.

The elliptical body is essentially done except for final paint. Back to the ring fin support fins.

 

[jqavins]

One of the things that is enticing is the fuselage (or main BT) is not round, but oval or elliptical.

Hey! Welcome, friend! Mine is (well, was) the only rocket I've ever encountered with an elliptical body tube. Probably others have done it, but yours is only the second that I know of.

That is one sleek beauty. I shall read on with interest.

[F]or some reason really like this part of the build.

It's because this is where it really starts to look like a rocket.

 

[reddrock]

More Ring Fin Support Fins
Looking back at the concept, it has a fuselage that sweeps up as a kind of vertical stabilizer and intersects with the half ring fin. On the rocket I will make this and a mirror image for symmetry. Normally we want our fins thin, but here the fin base will be nearly the width of the BT and narrowing to a normal fin width at the fin tip.

I decided to apply the elliptical concept here too. A series of ellipses were designed with the online tool, printed, and cut out. The major axis of each ellipse matches the chord length at its position on the fin. The minor axis of each ellipse is determined by the slope from the lowest ellipse to the fin tip. Then I cut out the width of the Nomex/CF core on the major axis to get templates to for cutting out plywood partial ellipses. These plywood partial ellipses were glued to in steps to each side of the two ring fin support fins.
Here's a shot of the base fin ellipse:

And here's a shot of the fin with all the ellipses glued on:

Looking aft from the front of the wing fin, here's a shot of the two support fins with ellipses glued on:


Next step is to skin the support fins.
DISCLOSURE: I have never built an RC plane or glider from scratch or even a kit. No dlubt there are folks out there that know how to do this better. I won't shy away from constructive criticism.

Not too long ago a friend exited the hobby (how can/do you do that?) and left me some Fliteskin. I decided to check out this material for skinning the support fins. First I cut a piece of heavy paper big enough to wrap around the aft side of a fin. Some rough calculations gave me a first cut template for cutting a piece of Fliteskin. I held the Fliteskin in place against the fin and marked it to trim the fit.


Glue was applied to the rear of the fin plate and edges of the elliptical ribs, then the Fliteskin was wrapped around the trailing edge of the fin. Notice the Fliteskin does not wrap all the way around and meet in the front of the fin. Tape and small clamps were used to hold the Fliteskin in place while the glue dried.

Here's what it looks like when the tape and clamps are removed:


The process is repeated for applying Fliteskin to the leading edge of the fin.
Paper template and Fliteskin:

There's a cut in the Fliteskin to within 1/4" of the centerline to allow better conformance to the rocket shape.

JB Weld applied the the leading edge and side of aft Fliteskin in prep for gluing the leading edge piece.

Here's the leading edge Fliteskin piece taped in place during curing. Note I have now glued the "flap" at the forward fin base down the the BT.

And here's a shot of both support fins in final Fliteskin curing:

 

[reddrock]

Well that was a nice holiday break. Hope yours was good too.

More on Support Fins
After the glue cured on the Fliteskin, I peeled off all the tape holding it in place. The Fliteskin gave me a good surface to work with but it is not structurally strong. I decided to apply two layers of CF using the same process and templates I used on the Fliteskin. However I did use epoxy for the CF. Here's a support fin with the first layer of CF all cured.

And here's a shot that captures both support fins with two layers of CF applied and cured:

Now I have pinholes, divits and rough area on the trailing edge to fill on the support fins. I started filling with Bondo, sanding after filling, and came back with light filling using Bondo putty.



After filling and sanding the support fins several times I applied primer to get a better feel for the overall shape and where finish filling needs to be done. Here's a shot with some of the last filling ready for final priming. At this point it looks as much like a fish as it does a rocket. That will change when I get the ring fin and NC on.



That's it for the wing and support fins. Ready now to move on to the ring fin.

Ring Fin
Earlier I showed a picture of making a CF tube using a 12 Quick tube as a mandrel. This 12" CF tube turned out real nice when pulled off the Quick tube and the mylar was removed from the inside of the CF tube. It is such a nice smooth finish on the inside I decided to use the inside as is.The ring fin will be round, not squeezed into an ellipse. But It will be cut into a swept shape with the forward ends at the wing fins and the aft end of the sweeps at the aft end of the support fins.

Marking the CF tube to make the cuts for the sweep shape is a bit of a challenge, I have used white, silver, and yellow markers of various types with some success. But here I applied wide masking tape over the entire outside surface of the CF tube and made the marks on the masking tape. Then I cut the tube with a Dremel freehand. Following the concept my plan was to have the trailing edge of the forward part of the ring fin even with the trailing edge of the wing fin. But somewhere I miscalculated. Now I had a ring fin that intersected the middle of the wing fin when lined up with the aft end of the support fins. There was no way to notch the ring fin on one edge and make it fit. To verify this I tried a dry fit. The dry fit would also tell me more precisely where the ring fin would intersect the sing fins. Problem is it takes two hands to hold the ring fin steady and one to mark the intersection points. I solved this by clamping chopsticks to the support fin tips parallel with the BT. Then I could hold the ring fin steady with one hand and mark with the other.

Notice the masking tape is still on the outside of the ring fin and the inside shows the CF. Here's a view that better shows the ring fin sweep.

I used carpenter squares to mark the lines of where the ring fin could intersect the wing fin.

Looks like that is my attachment limit for this post. I'll pick it up next time with the ring fin attachment.

 

[reddrock]

Ring Fin Attachment
With the wing fins marked for where the outside of the ring fin can intersect, I measured the distance from the aft end of the ring fin to the aft end of the support fins. This measurement was applied to the wing fins to determine where the intersection of the ring fin. The ring fin was cut in half and tabs cut on the forward ends where they intersect the wing fins. Corresponding slots were cut with a Dremel into the wing fins and cleaned up with a small square file. The primer around the slots was sanded off for better glue adhesion.
Here's a photo of a wing fin slot and ring fin tab:

And here is a photo of the joint dry fit:

Notice the nice finish on the inside of the ring fin. I originally planned to paint the entire ring fin but decided to leave the inside naked to show off the CF.
And here is the wing fin slots all sanded and ready for gluing the ring fin in place on the first side.


The dry fit resulted in a slight gap between the support fin and the ring fin. I cut down a popsicle stick that fit just right as a shim. I had to be careful to fill the honeycomb voids in the wing fin slots, but leave the slot open for the other ring fin half.
Here's the first half of the ring fin with glue curing (note the rough surface of the outside of the ring fin):

With a closeup of the support fin to ring fin junction:


Now I flipped the rocket over and repeated the process on the other side to complete the ring fin attachment. Then I made ring fin fillets using JB Weld. Fillets were applied at all ring fin attachment points. I like to tape off both sides of a fillet, apply the glue, smooth it with a stick then a finger dipped in alcohol, and remove the tape before the glue sets.

With all the fillets cured I removed all the masking tape. The outside of the ring fin was filled with epoxy mixed with Q cells. This gave a nice contrast of inside and outside surfaces of the ring fin in photos. Here's some different views that show off the different shapes as the basic rocket is coming together.





Next time I'll pick up with the wing pods which turned out to be the biggest PITA of the whole build, mostly due to my poor choice in materials.

 

[GlenP]

Very cool. It does look somewhat bio-inspired almost like a living creature ship out of Farscape or something.

 

[reddrock]

Wing Pods
Like most of this build I utilized parts I had laying around to make the rocket. I have this box of old low power parts, tubes, NCs, transitions, etc that I used to cobble together the wing pods. The pod tail cones and nose cones are plastic, the transition is balsa, and the tubes cardboard (of course).

Knowing the rocket is going to land on the aft end of the pods, I drilled the tail cones, ran a metal rod down the center, and filled the cones with JB Weld. The long small diameter tube was slotted so the wing fin extends through the tube to the outboard side. That makes the small tubes strong with the fin through the center. I assumed the forward end of the pod would not see much stress so I didn't reinforce this end. But you know what they say about "assume"! More on that later. Here's a shot of the forward end of the pods with a first coat of primer and some filling sanded and ready for another coat of primer.


And here's the aft end of the rocket with the pods assembled on the wing fins ready for primer.




It was about this time that the forward end of the small tube failed while handling the rocket after priming. I had to cut the tube off while glued to the wing fin and figure out how to reinforce and reattach the pod forward end. My solution was to slot a dowel of the diameter to fit inside the tube with the wing fin inside the slot. Best understood with some photos.




Copious amounts of glue around this "clothespin" fix and the forward pod section resulted in a fix I assumed would work. But there's that word again. We will come back to that.

Nose Cone
I already had a long conical NC, so really all I needed to do was design and attach some canard fins. Elliptical fins were designed with RockSim, templates printed, and then fins cut from Baltic Birch plywood. My simulations showed I might need a bit of nose weight and I was considering how to attach the canard fins. My solution was to glue a piece of 54mm tube inside the NC and use a centering ring on the aft end of the NC shoulder to keep it centered. First I marked slots for the fins and cut the slots with a Dremel. The centering ring was dry fit while I glued the 54mm tube and canard fins in place. Then I glued the CR in place. Here's a shot of the NC with fins after a layer of primer, some sanded fill, and ready for final coat of primer.


At this point all the assembly is done and I'm ready for the final priming followed by taping and painting the finish coats. That will be the next post.

 

[reddrock]

Like the rest of the rocket, the paint scheme was inspired by the concept supersonic plane. Instead of green over white with blue accent stripes, I chose fluorescent orange over white with cherry red accent stripes. The front end of the BT and most of the NC will be orange fading out to white on the NC tip and aft two thirds of the BT. The front half of the wing fins, wing pods, and the front half of the outside of the ring fin will be orange. Cherry red accent stripes will be painted behind the orange on the wing fins and ring fin. Two red stripes will be painted along the length of the BT above and below each wing fin.

First I painted the entire rocket white. No photo of this as it really isn't that interesting. Then I taped off the sections of wing fins and ring fin to remain white. I also covered the aft half of the BT to prevent orange overspray. Fluorescent paint needs a white undercoat to really pop the color. But I find fluorescent paint is thin, runs easy, and it takes multiple light coats to get good results. Next I painted the front third of the BT and all but the tip of the NC orange.

After the orange paint dried I removed all the tape and paper over the areas where the red stripes will go. I used a flexible ruler to scribe pencil lines down the length of the BT, along the wing fins, and over the curve of the ring fin. Here's a couple of shots of the process.




With initial lines in place it is easy to mark the width of the stripes and draw the other edge of the stripes. Stripe width was tapered toward the nose and the tailcone.

Quarter inch wide blue vinyl 3M tape was laid down along the pencil lines. Paper cut to size and paper tape was used to cover the entire rocket except where the red stripes were painted. Ready to break out the cherry red paint!





All that taping for just a bit of paint! Now to remove all the paper and tape to apply a final clear coat. That is except for the inside of the ring fin and the motor retainer which will both be black.

It was in the process of doing this that one of the pod tips broke off. Damn! So close. I hate doing repairs before I even get to fly. It was the Balsa transition that broke. Looking close it appears that the transition was cut about halfway through at some point. This piece came to me from someone leaving the hobby. It was probably already cut and I just didn't notice before I used it. My bad.


My repair is to drill out the center of both the small pod tube and the transition so I can glue in a length of all thread.



This last photo also shows some of the bleed through I got at the edges of the vinyl tape. In addition to the pod repair I will be fixing the paint job to look better. I launch in the desert where there are no power lines or trees to worry about. But rocks abound and scratches come with every launch. Still, I like to start with a nice paint job, even if it's not the quality I see in some magazines.
More later.

 

[boomtube-mk2]

Amazing what you can accomplish with a little Bondo and elbow grease.

So, what do you plan to fly it on?

 

[KenRico]

looks good Paul !

 

[jqavins]

I'd love to see this little fishy up close and personal, and watch it fly. Alas, that's not to be. Please post finished glamor shots and launch video.

 

[GlenP]

Very cool rocket and cool linked photo of the transport that inspired it. Kind of reminds me of another rocket with a futuristic space transport theme that has a non circular, kind of elliptical cross section, it was on the cover of the Centuri Design Manual, and @rosko_racer built one called The Phoenix. The thread is so old that many of the pictures have been lost, but he posted his working templates in this post
https://www.rocketryforum.com/threads/centuris-early-concept-rocket.96328/page-5#post-1713994Screen shot if the cover and his line drawings from one of his PDFs


http://www.ninfinger.org/rockets/catalogs/centuridesign/cendesign.html
This is the hollowed balsa rocket on this page of a later revision:
http://www.spacemodeling.org/jimz/manuals/cmrdm28.tif

 

[Sandy H.]

Like the rest of the rocket, the paint scheme was inspired by the concept supersonic plane. Instead of green over white with blue accent stripes, I chose fluorescent orange over white with cherry red accent stripes. The front end of the BT and most of the NC will be orange fading out to white on the NC tip and aft two thirds of the BT. The front half of the wing fins, wing pods, and the front half of the outside of the ring fin will be orange. Cherry red accent stripes will be painted behind the orange on the wing fins and ring fin. Two red stripes will be painted along the length of the BT above and below each wing fin.

First I painted the entire rocket white. No photo of this as it really isn't that interesting. Then I taped off the sections of wing fins and ring fin to remain white. I also covered the aft half of the BT to prevent orange overspray. Fluorescent paint needs a white undercoat to really pop the color. But I find fluorescent paint is thin, runs easy, and it takes multiple light coats to get good results. Next I painted the front third of the BT and all but the tip of the NC orange.

After the orange paint dried I removed all the tape and paper over the areas where the red stripes will go. I used a flexible ruler to scribe pencil lines down the length of the BT, along the wing fins, and over the curve of the ring fin. Here's a couple of shots of the process.
View attachment 499652
View attachment 499653
View attachment 499655

With initial lines in place it is easy to mark the width of the stripes and draw the other edge of the stripes. Stripe width was tapered toward the nose and the tailcone.

Quarter inch wide blue vinyl 3M tape was laid down along the pencil lines. Paper cut to size and paper tape was used to cover the entire rocket except where the red stripes were painted. Ready to break out the cherry red paint!
View attachment 499658
View attachment 499659
View attachment 499660
View attachment 499661

All that taping for just a bit of paint! Now to remove all the paper and tape to apply a final clear coat. That is except for the inside of the ring fin and the motor retainer which will both be black.

It was in the process of doing this that one of the pod tips broke off. Damn! So close. I hate doing repairs before I even get to fly. It was the Balsa transition that broke. Looking close it appears that the transition was cut about halfway through at some point. This piece came to me from someone leaving the hobby. It was probably already cut and I just didn't notice before I used it. My bad.
View attachment 499666

My repair is to drill out the center of both the small pod tube and the transition so I can glue in a length of all thread.
View attachment 499667
View attachment 499668

This last photo also shows some of the bleed through I got at the edges of the vinyl tape. In addition to the pod repair I will be fixing the paint job to look better. I launch in the desert where there are no power lines or trees to worry about. But rocks abound and scratches come with every launch. Still, I like to start with a nice paint job, even if it's not the quality I see in some magazines.
More later.

Crazy cool design.

Multiple places here and on the internet in general give tips on reducing the bleed-through in the paint. I think I first saw it on an RC plane forum, but its everywhere by now if you know to ask the question. Some say clearcoat after adding the tape, others say spray the previous color. Either way, the goal is to 'seal' the tape with a coat of clear or base color so that when it seeps under (and it does) you don't have a color problem, you have a texture problem at most. I think this was recently posted in an HPR thread, so it is apparently a technique that is super important, but not common knowledge. Give it a try sometime and see if you like the results.

I usually spray water based paint from an HVLP or airbrush and the added benefit of a coat of clear after basecoat and then again after masking but before painting is that if you really butcher hand-fades with the airbrush or similar, you can wash the paint off while still wet pretty easily. With spray cans, you might not have that same option, as things will react, but I have done it with water based paint and you can clean off the bad problem when you realize you messed up and since the previous layer was sealed, you don't screw it up.

Again, very cool design and I look forward to the completion of the build and the first flight!

Sandy.

 

[reddrock]

Some say clearcoat after adding the tape, others say spray the previous color. Either way, the goal is to 'seal' the tape with a coat of clear or base color so that when it seeps under (and it does) you don't have a color problem, you have a texture problem at most.

I was able to scrape most of the bleed through off with an Xacto knife, but I wouldn't want to repeat the process. Still, I will need to do some touch up. I then applied a coat of clear. The plan is to tape off the red stripes, take your hint and apply another coat of clear, then white and orange as needed. I'll score at the tape edge before removing the tape so it doesn't pull up the paint I just applied.

 

[reddrock]

I got the pod repaired and smoothed out with Bondo putty and light sanding.



GPS
I mentioned I launch in the desert. Unfortunately, it is not a dry lake bed or even flat with sparse vegetation everywhere. There are plenty of small hills, gullies, and lots of scrub (bush I think they call it down under). We have found that even if you are not pushing the waiver it is easy to lose a rocket if it lands more than 1000' away. Over the years I have played around with several different GPS systems. Lately I have settled on the Missile Works RTx with navigation option. I like to put the Tx in the nose cone to keep it away from other electronics and usually it will fit. I have even installed it in a 38mm plastic NC by cutting off the base and using the following method.

I make a sled that mounts on a bulkhead to keep the main chute from entangling in the NC electronics. Three in-line holes for #2 screws are drilled and countersunk in the NC shoulder. Three #2 T-nuts are glued to the frontside of the sled and nylon spacers are glued to the backside. These spacers are just long enough to hold the sled/bulkhead in the right position. Three #2 flathead screws hold the sled in place and the countersunk heads clear the BT so the NC fits. Here's some pictures to make the text clear.




Oh yeah, I painted the NC with white and orange but still have stripes to do. Before I do that I need to determine if I need any nose weight. If so, I will put a metal pin (piece of clothes hanger?) through the NC before pouring in lead shot mixed with epoxy. Of course I will then have to patch up the paint job. Hmmm... should have done this first. Anyway, back to RockSim for some stability analysis.

RockSim update
There are multiple simplifications I had to make to the model due to limitations of RockSim (not that other rocket simulations do these any better).

BTs are assumed to be cylinders with a round cross-section, but I have an elliptical BT. So I calculated the area of my ellipse and used a circle with the same area.

RockSim also assumes that fins are planer with options for the edges. But my support fins are almost as thick as the minor axis of the BT ellipse at the fin root, and taper to a normal fin width at the tip. I used the average thickness with rounded edges in RockSim. But then I had to play around with materials on the support fins to get an appropriate weight. I didn't see a way to designate hollow fins.

Ring fins are simple cylinders in RockSim with no sweep. It was easy enough to model the ringfin as a cylinder since it is round in cross-section. But I had to average the forward and aft locations to get something that makes sense.

RockSim diagrams:



This shows a static margin of 2.07 without a motor. An 11" x 38mm motor (say an AT I366 Redline) fills the MT right up to the Cp. That brings the static margin down to 1.47. Normally I would be happy with that, or even something less. But I really don't know how good my model simplifications will play out. So I'm thinking of adding some nose weight. There's about 5" in the very narrow NC tip above the GPS that should be enough to add some weight.

 

[jqavins]

But then I had to play around with materials on the support fins to get an appropriate weight.

There is a mass override feature that is a bunch easier than searching for a material that happens to come out at the correct weight.

That brings the static margin down to 1.47. Normally I would be happy with that, or even something less. But I really don't know how good my model simplifications will play out. So I'm thinking of adding some nose weight.

Why not swing test, and then decide about nose weight?

 

[reddrock]

Been almost a month since I last posted on this project. Life got in the way (house maintenance, wiring, plumbing, helping friends, car shopping, etc.), but now I've finally got back to it.

I decided to tape off the red stripes and the orange areas on the fins. Then I sprayed a coat of clear to seal the tape edges and let this dry overnight. I came back and sprayed white except where it transitions to orange at the forward end. Also, I did some cleanup around the repaired wing pod. Then painted the repair white.
Here's a shot of all but the NC with red stripes and orange on wings taped off in blue and green, ready for clear coat.


I'll have to bag almost the entire rocket to paint the pod repair orange. Then I plan to score the edge of all the tape before removing it. Finally, I will clear coat the entire rocket.

And there's the red strips to paint on the NC still.

While I was out I got to thinking about the RockSim model. I used a 5.5" diameter tube to model the center elliptical body because I used a 5.5" diameter tube as a mandrel for the fiberglass tube I squeezed into an ellipse. But this is wrong when using the "maximum frontal diameter" to determine static stability. I need to determine the area of the ellipse and use a round tube of the same area to model the ellipse. So I made another update to the RockSim file. I helped the stability just a bit. Likely I will add a few ounces of nose weight.

 

[jqavins]

Many people advocate using the CP-CG distance divided by the rocket's length instead of using the forward diameter. About 10 to 15 percent is good. That works out better, they say, for very long or very short models like a Mean Machine or a Fat Boy. There are good reasons for it. The inertia of habits being what it is, I have not switch my thinking over. In this case, though, it might be useful to think that way.

(For "normal" looking rockets, the L:W is usually in the ballpark of 10:1, give or take a fair amount, so 10 to 15 percent of length is about the same as 1.0 to 1.5 calibers.)

 

[lakeroadster]

What an amazing build, you've certainly got some mad skills!

Thank you so much for taking the time to document this for us.

In regard to stability.... will you be doing a swing test? That test always gives me a hands on actual feel for stability. Once you do a few swing tests, with various different rockets, you begin to get a feel for just how stable one rocket of your fleet is vs another.

 

[reddrock]

Well it's been another month. This time I got diverted by some other rocket projects, not home maintenance. I have now completed the build and painting.

I decided to permanently add some nose weight. First I measured out the lead shot and filled the tip of the NC to measure how far aft it would go. Then I poured the shot into a paper cup. I drilled a hole all the way through both sides of the NC forward of the aft point where the shot will reside. A piece of hanger wire was cut longer than the NC width at the holes and inserted all the way through the NC. I taped around the wire so epoxy will not bleed through. Then I mixed epoxy with the lead shot and poured it into the inverted NC using a funnel. A little more epoxy was required to completely cover the shot.

After the epoxy cured I removed the tape, carefully cut the excess wire off with a Dremel (love that tool), applied some Bondo putty, and sanded smooth when cured. Ready for paint.


There is no taping on the NC paint scheme, so it was easy to do. With all the colors applied to the entire rocket, I next gave it a coat of clear. The last of the tape was removed revealing the CF inside of the ring fin and the black Slimline retainer. The inside CF ring fin came out probably the best looking of everything. Too bad it is mostly hidden. There's no polish or clear coat on it, just the resin which turned out very smooth, and the CF fabric which I was able to avoid any wrinkles.

Here's photos of the completed rocket.





BTW, it's interesting that nobody asked about choice and placement of launch lugs and/or rail guides.

I personally prefer rail guides but do have some rockets that can only use launch lugs. In the last two photos above you can see the 1010 rail guides I ended up using. They are a bit forward of normal position due to the tapering and contours at the aft end of the rocket. I didn't want to break up that design flow with offset struts for mounting rail guides or launch lugs. I considered a wing fin to mount a rail guide, but it would then be perpendicular to the body tube where the second guide would go. The same problem exists using a support fin. I even considered the ring fin, but it projects too far away from the body where a second guide would go. In the end I settled for the guides on the non-tapered elliptical body more or less between the fins. I plan to launch on a long rail so I have good speed before the rocket leaves the rail.

Weather permitting, I plan the inaugural launch in just over 2 weeks. I'll try to get some photos and post them.

 

[OzHybrid]

Nice job doesn't seem like enough for this level of build. So... NICE job....
Norm

 

[jqavins]

Oooh, purdy!

 

[les]

FANTASTIC!!!!!!