GTV Build Pictures

It all started with a conversation with Bob Yanacek about a rocket he has, and my newbie-ness in the world of rocketry.  He feels that its not a rocket unless it launches from a tower.  I have several models including this cluster that have launch lugs on them and Bob has given me a hard time about it for a while now.  I was over at his place one evening and he started giving me shit about having launch lugs on my rockets (again) and I realized that the fins on Bob's GTV were WAY to big.  He likes towers because the extra altitude you get without having a launch lug out in the breeze, so it doesn't really make sense that the fins on his rockets would be any bigger than absolutely necessary.  I pointed this out to him, and he dropped the challenge, why don't you build one?  So I am.  Bob lost his GTV  in Lowden at a WHIP launch during the weekend of May 24-25.  His is rebuilding at the same time I am building this one.  Here is the story of my adventure in rocket building.

Of course the first thing a guy must do is design the rocket.  RockSim to the rescue, I don't even want to begin the calculations required to come up with the stability factors etc.  Here is the design.  It doesn't include everything (missing a Pratt Hobbies microbeacon, glue, fillets, fiberglass reinforcing for the fins) but its close enough to get the idea.  The simulations of this rocket as configured below take it to 6700 ft on a G25-15 motor.  Gotta love it.  If I make a mile in its final configuration, I'll be satisfied.  It'll be a personal best at this point.

The name of this rocket (at this point) is GTV.  The name is not mine, credit goes to Bob Yanacek.  It stands for G (motor) Test Vehicle.  Bob has given the rocket a name...it's "According to BOB, baby, dinky, tiny, too small fins"

This is the body tube, it is 18 inches long.  Notice the channel for the fins, I machined them on a mill at work.  Click on the photo to view it full size.

These are the fins.  They are made from 0.060 in. G10 FR4.  Root cord: 2.5" Tip cord: 1" Semi-Span: 1.5" and swept angle: 38.8 degrees.  Note the notch in the back, its for motor retention.  The aerodynamic shape was machined at work on the mill.  It is at 3 degrees and 0.020 inches deep.

Sort of a preview of what the rocket will look like sans nose cone.  The clear plastic thingy is another of Bob's ideas, its a fin alignment tool (FAT).  I cut it and the fins for this rocket on a circuit board mill at work.  The circuit board mill is sort of an XY CNC type machine designed to make circuit boards quickly.  It doesn't have a Z axis control...so you set the depth with a little stop block that rides on the material.  Its pretty accurate, so it fits the bill here.

This shows the fins glued into place with Epoxy.

The fins are in place and the gray stuff is JB Weld, I used it to make the fillets for the fins.  This strengthens them and helps them to stay in place during the expected supersonic flights of this rocket.  There is a motor in the back of this rocket to demonstrate the motor retention system I am trying out.  To use it I cut 1/4 in. of a 29mm body tube off, I glue it to the motor with CA glue to make a thrust ring and then cut the notches out opposite each fin.  I put the motor in and line the slots up so the thrust ring is tight against the body tube then give the motor 1/6th of a turn to lock it in place...It has never launched, so I don't know how successful it will be.

First coat of spot putty.  Looks like a barber pole.  The second picture is after sanding and applying Fiberglass from midspan of one fin over the body tube and up midspan of the next fin.

First coat of primer, on to sanding and making it pretty.

Second coat of primer, getting pretty now.  Used a light grey primer for this coat, the white primer (Krylon) doesn't dry well and gums up the paper when I sand.  The second coat of primer is a filling type primer from Dupli-Color, it gets rid of all those minor imperfections I am so good at leaving behind.  This shot is before I did the final wet sanding.

This is a shot of the base coat I put on.  I experimented a bit with the paint.  The final color is Safety orange, but it seemed kind of dull over the white box I tried it on.  Playing around a bit I put orange on one side and this yellow on the other, then covered half of each side to see if the paint looked good together, I liked the way the orange looked over the yellow, so that's the way I painted the rocket.

This is the final color.  Smoothest, shiniest paint job I have done to date...I like it.  I *Hope* I can see it from the mile or so I expect it to fly.  You'll notice that there isn't a nose cone yet.  I ordered it from All Hobbies and should have it here by the Saturday SPARC launch.  There won't be time to paint it prior to flight, so it'll be a half finished bird for its first flights.

Well Ursula didn't show up, she injured her back and wasn't able to come.  So, no flights for ATBBDTTSF.  Bob flew his on a G35-7 and got a nice zipper for his troubles.  Thinking of a simple mod to allow the use of a timer, when I get the nose cone I'll post details.

Here's a sneak peek into another project.

My level one rocket