Orbital Transport

Time to start my next rocket!  This is one I wanted to build for about 38 years now: The Orbital Transport.  I bought the Estes kit as a kid, and since it was a fairly complex rocket, I waited to build it until I had a bit more experience with some other kits.  I was in the process of building an Estes Andromeda back then, but never finished it until about 35 years later as a BAR.

Fortunately, all that rocket stuff was safely stored in my parent's basement. I re-acquired all my older rockets and restored most of them to flying condition.  The Andromeda, which was not finished then, was finished recently and also flown.  There was this one final kit I had which was this Estes Orbital Transport. Unfortunately I couldn't find it to save my life. With the original kits going for about $100 on eBay, I wasn't about to buy another Estes kit!

Luckily, Semroc makes an Orbital Transport clone.  I of course bought it.  That was back in 2011. As one might have expected, it sat for a long time while I finished other kits, but finally I thought enough is enough. This will be my next kit even though I have at least a dozen or two other kits I want to build immediately, some of them acquired even before the Semroc's Orbital Transport in 2011.

My first impression when I opened the kit up was that this was smaller than I thought it was. I guess in my head I imagined it to be a much bigger kit, since I had this concept that it was the pinnacle of Estes kits. I suppose it was in - like - 1971, which I think was the year it was on the catalog's cover.

So here we go. I'm going to let you watch the entire build process. I'm building this roughly in the order of the instructions, but not really. My building process involves waiting for all the critical glue joints to dry, so they won't be disturbed while working on another part of the rocket. Meanwhile I skip ahead and do whatever else I can get away with, and make plenty of modifications on the way. I don't get a kit done in a few hours, but more like a few months to a year depending on how ambitious I am about sanding and painting.

First, we have the two main wings that are made in two balsa sheets. The trailing edges were glued on to the main wings, and the parts were sandwiched between wax paper and weighted down with books.  No, I didn't think you'd want to see a picture of a pile of books.

I cut out the balsa pieces very carefully. This is usually the time when I change to a brand-new blade.  New, sharp blades are critical for precise, effort free cutting and shaping. Not just with X-acto blades, but hacksaws, circular saws, kitchen knives, you name it.

Interestingly, the laser cut balsa included light markings for assembling the under-wing engine tubes.  That's helpful, but if you follow the directions and sand the sheets before assembly you sand off the markings.  I sanded very lightly.

Next, we are instructed to glue in the outer sides of the ramjet tube box.  Since this was the sacred Orbital Transport, I wanted to make sure to have everything trued up well. I used a pair of carpenter triangles to make sure the parts were at exact 90-degree angles.

After putting the parts together, I used a small sculpting tool to scrape away the excess glue that oozes out uncontrollably. I can add clean fillets afterwards, but I didn't want odd, lumpy fillets here.  The goal was to simply attach the pieces now and fillet them for strength and then appearance later.  Then I held them against the squares until they set.

The next step was to attach the previously glued jet tubes onto the wings.  I also was able to add the small center divider between the intakes.  These pieces were sanded before I attached them, since they will be difficult to sand when assembled.  In this picture you can see one of the stainless steel sculpting tools I use to clean off the excess glue.

While those pieces were drying I skipped ahead and did some work on the motor tube. In the picture below I dry-fitted the motor clip, but after staring at it I decided I wanted the newer, better clips with the EZ-grab hook end. The motor clip in the picture below was not used and thrown into my spare parts box.

This is where I ran into my first problem. The bottom piece of wood was a bit too narrow to fit perfectly across the two sides of the engine boxes.  If I put them snugly together, the one inboard side would be at an angle.  After some time I decided the best thing to do was to carefully leave a small gap in the glued edges that I can fill in later.  Since the bottoms are glued to the sides and the center piece and the tubes themselves, the bottoms didn't need to have a very good glue joint here.  Mostly I didn't want to have boxes that were not square when viewed closely.

When I began to glue up the motor tube and centering rings and motor clip, I noticed that the kit and instructions didn't include a motor block.  Instead, it appears Semroc expects the little steel tab to hold the motor securely.  No way.  My rocket was going to have a motor block no matter what the weight penalty was going to be.

Rather than fish around my boxes for an extra block which I'm sure I had somewhere, I grabbed the nearest empty motor casing and cut a 1/4" end off of it using a small hobby miter box and X-acto saw.  Dang if it didn't fit perfectly!  Here it is when still being test-fit without glue.

Back to the wings, the next step was to attach the outboard wing tips.  These are vertical and serve as both style features and vertical fins (rudders).  Again I needed these to be square, and there wasn't enough room for those big heavy carpenter squares, so instead I found some small aluminum angle pieces that did the job perfectly.  I pressed the two pieces against the inside corners and held them tight with clothes pins.

Same thing, this below is a view of the other side.  You may be able to see the small gap of the engine box filled with glue. I can fix that, but I wouldn't be easily able to fix a side that wasn't 90-degrees. I'll add more filler and sand for a round, smooth appearance later.  You may also notice in some cases I pre-rounded the leading edges.  Some edges will have to wait until this thing is all assembled.  Sanding won't be easy.

So with the main wing assemblies almost done, I went back to work on the motor mount.  Here we see the better Estes style motor clip, and the unused one supplied in the Semroc kit. It is all glued up and ready for install in the body tube. The Kevlar shock cord was added (something Estes doesn't do).  I wasn't too keen on adding the Kevlar here, since I think someday it will fail and will be hard to replace.  In the end I figured what the heck, use it while I can, and when it fails I'll attach a short Kevlar loop at the top of the body tube where Estes has you put that silly folded cardboard shock cord mount.

There's still much more to do, but this project isn't going to be a night's work. I do want to get it done soon, because the outside spray-painting season is ending a bit too soon.  Wouldn't want to wait until the first warm day of spring to get this finished.

Next It was time to add the launch lugs. Often a kit has you glue them directly to the side of the rocket. I noticed though that better results are had when a short stand-off is added to keep the rail away from the rocket side a bit.  Sometimes grimy, rusty stuff gets on the rocket.  I also imagine there could be more friction on the rod depending on how it bends during liftoff.
This kit was different. It used a small, round dowel instead of the usual strip of balsa. OK, I'll try it.  I did, it is all on ok, but next time I'll stick with a square piece of stand-off.  Square strips are easier because they remain flat when gluing. These round dowels let the lug roll, and its harder to keep them straight when gluing.

Here (above) is how I do this. Split lugs need to be aligned, so I use a bit of a steel rod to keep them pointed in the right direction. Since these dowels tended to roll, I attached two alligator clips to the rod.

 

The rod was then held in a frame that kept it in place.  I applied the glue and slowly lowered it into place along the marked line and let it dry.  Lucky I had this frame gizmo (for electronic soldering) that was useful for this step in the construction.

Cool to have it, but it would be easier just to stick with squared standoffs for the launch lugs from now on.
Did I mention that I am including a payload section to this rocket? I'm not changing the length, but I cut 3" off of the top of the body tube and I am adding a bulkhead.  Inside the bulkhead and the top 3 inches will be an altimeter compartment with padding.  I made this from a tube coupler and a small rounded piece of plywood.


That doesn't hold a screw eye very well, so instead I am using a small loop of Kevlar.

The Kevlar is knotted on the other side and is glued into place. I've done this now for I don't know how many rockets, and it has worked well so far.


I could probably trust the knot which is larger than the hole, but glue seems more reliable.  My method of gluing Kevlar is the same as when I use it as a shock cord mount.  I fray the ends of the Kevlar, and that provides a lot of gluing surface.


Is that any better?  Well, consider that pretty much all the glue joints would have to fail before the Kevlar rips free.  In the following picture you can see the frayed Kevlar after I smeared a thin layer of glue to the plywood.

Another area of glue that could stand a bit more strength is the fins.  I wish I could remember who I read this from so I could give them credit, but I can't remember. The idea is to give the glue a lot of small 'fingers' so it can grip better. I think he called them "rivets".

Using a small pin-point tool, I poke a lot of small holes along the line where the fins are attached. This allows small fingers of glue to penetrate into the body tube, but not enough to flow into the tube.

I do the same to the root edge of the balsa fins as seen here. Small enough to not weaken or crack the fins, but many of them to be effective.  The dried glue becomes a hardened blob that reaches into all those little holes in the fin and the body tube, making it next to impossible to fail at that glue joint.


It's true that I don't break or loose many fins, and I've only done this for maybe four or six rockets so far, but I haven't had any troubles with this method.

Stay tuned. It's soon time to move into final assembly and attach the built-up wings to the body tube, and then start on the glider...Now it is time to attach the wing assemblies to the body tube.  To make this job easy I pull out and dusted off my homemade fin jig.

There seems to be a lot of emphasis from what I read about rocket construction that discusses making sure the fins are properly aligned. That I agree with. Most of the tips emphasize making sure the fins project straight away from the body tube (radially), and making sure that they are evenly spaced around the body tube.  While I agree that it is aesthetically pleasing to do that, it is not very important to the performance of the rocket.

How can I say that?  I challenge you to flip through your catalog, or maybe online and look at a lot of kits for sale.  You'll find plenty of examples of rockets that have staggered wings and fins, and you'll see them attached at all angles (when seen end-on from the front or rear).  The examples I would show is this very Orbital Transport, or one of the Estes Interceptors.  Aerodynamically, there is no wrong radial angle to attach a fin (or wing) to a rocket. (Radial: as in seen from the end.) What only matters is the position on the rocket (how far back), and the surface area of the fin.  They don't even need to be balanced sizes, as many "wing-styled" kits will show you.


On these, the rudders (dorsal or ventral) must be a minimum size, and larger wing surfaces don't affect stability in a very negative way (unless they are ridiculously over-sized.)  There can be three, four, five or even more fins on the rocket and it doesn't matter.  I've built all three of those types. I've even seen online a rocket that had ELEVEN fins - swear to God.

So while the angle from the rocket center isn't very important, the angle of the fin from front-to-rear is very important. If any fin is canted (so that the extended imaginary plane of the fin does not coincide with the front-to-back axis of the rocket), it will induce a roll in the rocket unless by dumb luck another fin is canted in exactly the opposite direction. In that case it will simply add drag on one side, slow the rocket, and may cause a curved flight.

You can design a rocket to have a strong spin for stability, but generally you want a rocket to fly straight without rolling a lot.  The rolling motion reduces the top speed and altitude of the rocket by taking energy away from the vertical.  Fins canted at an angle will generate more air resistance, where the kinetic energy of the rocket is transferred into the spin.  If you have a camera on the rocket, you will end up with a very disoriented video. If the fins are angled in the same direction, it could cause the whole rocket to turn in the opposite direction.

I got into all that because my jig is made to make sure the fins are aligned exactly front-to-back.  These fins are held tight in between two stiff and long aluminum angles.  These are attached to two wood pieces with a 90-degree corner that holds the tube of the rocket in the exact same longitudinal (front-to-back) direction as the fins, as seen below.  In this case, it was the Transport's right wing.  I had to accommodate the big "engine pods", but at least if I knew I drew the guide lines straight, I could carefully place them and have them at the right angle to the nose.

 

You can see that the body tube is held in snugly against the fins with some bungee cords.  That makes it easy to pull the tube away after it was all aligned and apply a line of glue. Then I slowly release the tube back into it's final glued position.  This following pix shows the top side of the rocket after gluing.

Since the fake engine pods interfere with the fin jig, the body tube had to be positioned away from the rear V-notch, so I wasn't exactly sure if the tube center was exactly in line with the plane of the wings, so I just eye-balled it.  Close enough.

But when it came time to attach the second wing/fin, I was worried about the flat-alignment of the two wings for aesthetic reasons.  I did the best I could, but then checked it with a cardboard cut-out jig that was included in the kit. The cardboard piece had an exact half circle for the body tube and two long ends for the fins.  Funny though it did not exactly fit the rocket.  It would have if the fins were infinitely thin, but the cardboard jig did not allow for the fin thickness, so when held to the fins/body tube, it didn't exactly align snug with the body tube.  It did however work as a straight-edge ruler with a big "bite" out of the center to clear the body tube, so it was useful to verify that the wings were flat to each other.  Below I just glued the left fin/wing assembly.

Here we see the underside of the left wing being attached.

The side view of the jig, showing the underside of both wings after being glued.  When I attach fins either with or without this jig, I run a somewhat thin line of glue down the root.  The goal is merely to attach the wing, with maybe just a little glue oozing out the root.  Later I add a line of glue as a fillet to the root edges to make sure that the glue has a good contact surface to both the fins and the body tube.  It doesn't always look pretty, it's there for structure.  I will then later fill in the fillet area with some Hobico filler material and sand it to a really nice rounded fillet.  This way I am sure there is plenty of tough-holding glue, and a smooth and aerodynamic fillet to the fins to hide the underlying glue fillet.

I made sure to not attach the other fins and rudder pieces so they wouldn't interfere with the main wings.  When those were done, I then attached the two ventral fins to the underside.  Here we see the first one attached.  These were small, and hard to use a jig on, so I did my best to align them with the pen line and hoped for the best.

I used the same eyeball method to glue in the two supports for the glider and the two air fences on the wing tops as seen below.

The last step for me was to glue the two top rudders.  Again I just did the best I could to align them front-to-back with my eye and the LASER-lines marked on the fins.  I used small pieces of aluminum angles to hold them at 90-degrees from the wing surface for aesthetic quality.  Clothes pins are awesome for this type of work.

You can easily see the large surface area of the wings that make a good fin to control the pitching of the rocket.  What you can't see so easily (and this is the clever part of these designs) is the two other fins that control the yaw of the rocket.  This is handled with the combined surface area of the two rudders, the lower rudders on the wing tips, the two ventral rudders, and to a lesser extent the glider supports, wing fences, and the sides of the engine pods.  You can't count the wings/rudder surfaces of the glider because they are loosely attached during liftoff, and any angle of the relative wind on the glider will simply cause the glider to shift, not push the rocket back onto the path of flight.


Next, I jump to the glider assembly, and work on the payload section of this rocket.  After that it will be pretty much done except for the laborious process of sanding and balsa filling and sanding and priming and sanding and painting etc.  Did I mention the sanding?






...time passes...




OK, apparently the better part of a year has gone by, and I haven't finished it yet.  I did miss the summer painting season, but another summer is upon us and through the winter, little by little, I completed the construction and have recently finished the primer spray coats.  But that's jumping ahead. Let me fill you in with what I did over the winter.


According to the instructions, I started work on the glider.  The wings are simply glued together at an angle, and then the wings are glued onto the glider's body tube as seen below. Here I also glued the glider's rudder on.  Another step was to form the small exhaust nozzle from cardboard and glue it to a disk. That's what is seen in the background.

After that step, the elevons are glued into place, also at an angle. A cardboard template is used to set the angle, but then it dries on it's own, supported by the tip of a clothespin. I will later add a heavier glue fillet for strength, and try to shape it to be smooth...



.When I was gluing the glider's rudder, I found the plastic fin guide from Estes to work well for this task. It very effectively keeps the angle of the fin directly in line with the body tube as seen below.

When the wings, elevons, and rudder were dried I attached the small wood <?what's-it-called?> under the forward part of the tube.  This holds the glider onto the main rocket body during liftoff.  I don't recall if the instructions specified to round and streamline this part like I did, but of course I wanted to.  I also may have shortened it a bit so that it did not touch the nose cone.

The instructions say to glue the nosecone and tail cone to the rocket body, but I want to do 2 things with this that requires them not to be glued. One, I want to put an altimeter in the glider tube to record glider data separate from the booster's data.  Two, by adjusting the exact position of the altimeter, I will be able to make balance adjustments to the glider without adding any weight beyond the 6 or 7 grams of the altimeter.  These features are only possible by friction fitting the nose cone.

So while all that glider glue is drying, I turned my attention back to the main rocket.  I made a small loop in the Kevlar shock cord, and glued it secure in the body tube.  I think this picture was taken earlier, before the motor mount was glued in, because it was made just long enough to reach the end of the tube but not go past the edge.

That part of the shock cord will be rubber/elastic, so that the Kevlar will not be able to cut through the end of the body tube (Zipper damage).

Another assembly step was to make the tail cone of the glider.  Here it is after being tack-glued to a small disk of plywood and then a better glue applied to the inside of the cone.  Still not sure what color to make this.  Also I am not sure how to hide the overlap seam of the cardboard with some kind of filler, or if I want to.  I will soak-in some CA glue though, to make it stiffer and less prone to damage.

The glue dry, I go back to the main rocket body.  The rather weak glue joints I first applied are now being re-inforced with a much thicker glue fillet.  I try to make these as clean as possible, but they never come out perfect.  The Titebond III glue I use shrinks when dry, so it seems to suck-in, leaving a bit of a bead around the outer perimeter of the glue area.  This is done for strength, and I can add cosmetic filler later on.

There is yet another task to do to the main rocket, since I added the payload section for an altimeter.  Inside the bulkhead (made from a tube coupler), I placed and hot-glued some foam plastic padding to cradle the Altimeter Two.  I have to use hot glue here - but just a dab or two - because that seems to be the only glue that holds these padding pieces in place.

 

The altimeter fits snuggly in there, and is covered by the upper part of the body tube with holes in it to allow the altimeter to "breathe".  It is then held in place by the nose cone, and a small bit of more plastic foam to press it in a bit to keep it from rattling around in there.  I didn't use to glue these pieces, but learned to after a few light breezes blows these pieces away out at the launch site.

At this point I have all the major construction and glue dried, so it's time to balsa fillercoat and begin finishing. Normally I would paper cover all the balsa parts, but given the complexity of the balsa, I though I would go with the traditional method. I test fitted the rocket and glider and now I am starting to get excited about the model.

Here is a view from the underside of the Orbital Transport.

And here is a better view of the back end.  You will notice I decided to leave the trailing edges of the main wings square. Tapering them would look a bit awkward with all the intersecting planes. I did taper the upper and lower rudders though, and all leading edges are rounded, including the boxes for the fake engine tubes.

The above were taken after a bunch of fillercoat layers were completed. Next step is to prime the entire rocket. I used gray primer, and then sanded that thick, heavy coat down to almost nothing. This is to fill in all the tiny surface variations. My next coat of primer will be white.  This allows me to see when I have sanded down to the layer beneath, so I can stop before I sanded away all the primer.  The final goal is to have a thin, light layer of primer before adding all the white paint.

The current status is the rocket has been primed with white primer, and now I am waiting for that to dry and sand everything smooth again.  I hope to complete the primer sanding soon, so I still have some good weather to start the final white gloss paint.  Cold and humid are not good for spray painting, so I hope to complete this while still in August 2017.  (That's a little behind schedule since I bought this kit in 2011.)