Brief:

For the 2009 Design This Spaceship contest, I chose the Rockedyne VTHL concept.  I could find very little information on this spacecraft except that it is a Vertical Take-off, Horizontal Landing Single-Stage-To-Orbit proposal that Rockedyne designed as a ramjet powered vehicle.
I imagine it as an unmanned transport (after all – there are no apparent windows) that uses the entire fuselage as an engine.  The circular fin acts as both intake and exhaust with a nose-spike and tail cone built right in.

Construction:

Parts list:

• BT-20: 10” long
• BT-70: 2” long
• BT-70 Coupler: 2pcs ¼” long
• BT-80: 2” long
• BT-20 to BT70 centering rings (2)
• BT-20 Engine Block
• Engine hook
• Mylar ring
• 2” Launch Lug 1/8” dia.
• Fishing weight
• BT-20 coupler ¼” long
• 2 ft. of Kevlar cord
• Balsa Machining BNC20R nose cone
• 3/32 balsa sheet
• ¼” square balsa strips (or similar scrap stock)
• Stiff paper for shrouds

Assembly (How to build one in 21 relatively painless steps):

1. Mark 4 lines at 90 degrees on the BT-20 and a line at 2 ½”, 3 1/8” and 4 7/8” from one end of tube. 
2. Install engine block 2 ½” in tube, from the marked end.
3. Cut 1/8 slit for engine hook at 2 ½” mark and install.
4. Glue Mylar ring at halfway point on engine hook – When done, you should have something that looks like this.

• Mark the BT-70 at four locations 90 degrees apart.
• Glue a centering ring 1/8” into BT-70, and then Glue coupler in place with 1/8” exposed.  Repeat on opposite end.
• Glue body tube assembly onto BT-20 aligning it on the marks.

• Form forward shroud into a cone and glue in place.

• Cut all the fins from 3/32 balsa.  I formed the wings in two pieces and glued them together, but you can make them of one piece if you have wide enough balsa, just make sure you follow the grain direction shown on the pattern.  Seal fins and nosecone with sanding sealer.  (I use three coats of Elmer’s  carpenter’s wood filler, thinned with water, but, whichever method you chose, I would recommend you seal the wood before assembling the model.)

• Notch wings for Mylar ring and coupler. Glue to body.

• Add some wood strips between center section and tail along wings to support rear shrouds, tapering the back end so that shroud will lay flat.

• Form rear shrouds to shape and test fit. Add top and bottom shrouds to rear,
• Glue launch lug on center section.

• Test fit BT-80 in between wings.  It should touch both wings and the launch lug without distorting.  Adjust the gap between the wings if necessary.
• Glue BT-80 to launch lug and inside of wings using thin CA wicked into joints.

• Bevel the wing tips so that they will cant outward about 15 degrees.  The exact angle is not critical, just that they are all equal.  Glue tips to wings.
• Fillet all joints
• This model requires as much nose weight as you can manage to fit.  The Balsa machining nose cone comes predrilled for a dowel and eye hook.  Cut dowel in half and add lead shot or fishing weights inside hole in nose cone.  Glue remaining half of the supplied dowel in behind it.  Add eye hook.

• Using a small piece of BT-20 coupler material, or a thrust block, tie one end of Kevlar cord to ring.  Cyno the knot.
• Apply a ring of glue 2” inside body. Using an engine spacer or engine, push the ring into the glue.

• Tie other end of the Kevlar to the nose cone.

Finishing:

Since I had pre-sealed all the balsa parts before assembly, just some light finish sanding at the joints was all that was needed to be ready for paint.

I first primered the rocket with grey sandable Rustoleum paint, and then wet sanded with 400 grit paper.

After a coating of white paint, I masked off all but ¼” of the leading edges of the wings, tails and center ring and painted them black.

After removing the masking, the basic colors were in place.

The NASA logos and lettering were images I downloaded off the internet and printed on self-adhesive paper.

With the logos in place, I felt the model was a pretty close replica of the painting.  The real question in my mind was: would it fly?

Flight:

The largest chute I could fit in the model was an 8.”  In balancing the model I felt the balance point was too far aft, so I added clay around the nose hook until the nosecone weighed 1 oz.  (The balance point - with engine in place - should be as far forward on the center ring-fin as you can manage.  Mine balances approximately ¾” back from the front of the intake.)  I tied a loop in the Kevlar about 4” back from the nosecone and attached the chute there.  After adding a few sheets of recovery wadding, and packing the chute, I was ready to try to fly it.

The finished weight of the rocket (without motor) was 2.5 oz, with almost half of that in the nose.  I wanted a calm day, but was running out of time, so I had to try it in 5 to 10 mph winds. I loaded a B4-2 engine and set it out on the pad. It lit on the first try and was surprisingly fast on takeoff.  Much to my amazement it flew very straight up and did not have trouble with the wind.  It arced over and ejected at apogee.  The chute opened, and it came down fairly quickly, popping off two of the tails on landing.  I was very impressed by its’ speed and stability in the wind.

After a few drops of superglue the fins were back on, and I loaded it with a B6-4. Again, it was fast off the pad, and went up several hundred feet.  Ejection was just past apogee, but not bad, but this time, the chute did not unfurl.  To my surprise, without the chute to drag the nose, the model fell in a slow, flat spin pivoting around the nosecone.  It this configuration, it actually fell slower than when the chute opened, and was undamaged on landing. Post-flight examination revealed that the chute had been burned on ejection and stuck together, but I was able to unfurl it and repack it.

For the final flight of the day (The wind was really picking up now and was a steady 10mph) I chose a C6-3 engine.  It lit on the first try, but only rose 25 feet or so before it started tumbling.  I suspect it was just too much tail weight to be stable, but it may have been the wind.  At any rate, it spun in the air, end over end, and ejected before hitting the ground.  It parawadded again, and did the same flat-spin landing without damage. 

Overall, I am happy with how well it flies on B motors and am very interested in its flat-spin recovery.  It is still in good flying shape and I want to experiment with using no chute and a streamer for recovery.  I just think C engines are too much for it.
If I were to start over, I might try to build a larger forward chute area in the nose (Perhaps a BT-50?) and would add clay under the forward shroud before attaching it to the body, to increase the nose weight. 

Summary:

Overall I think it is a very different looking rocket, and flies surprisingly well on small engines.  I look forward to more flights from it.