SpaceJet 4 inch upscale

RocketTree · Nov 25, 2023

SpaceJet is a scratch build, influenced by the Estes Jetliner BT60 kit. I have previously built the BT60 kit (heavily modified), then a BT80 29mm version. Here is the lightweight 4 inch upscale designed to fly on 29mm G motors to around 1250’ at 350km/h.

Some parts to get the build started...

Fins upscaled on OpenRocket from the original, and cut on the bandsaw.

Fin wraps printed on OpenRocket. Angle aluminum and a sharp pencil to layout the tube.

Cutting slots with a Mastercraft blade knife.

Main wings are glued together with plywood reinforcement strips.

Epoxy layer over reinforcement strips and fin tabs where they will be subjected to ejection blasts.

Install 1500lb kevlar loop, heat shrink, knot and epoxy to underside of ring.

Wing support can slotted and ready for fins.

Assemble wing can with BSI 15 min epoxy.

Wing installed with multiple internal fillets.

RocketTree · Nov 25, 2023

Motor mount assembly.

Install wing can to lower body tube with epoxy.

Motor mount ready to install.

Rear fins installed with CA, then internal fillets with BSI 15min epoxy.

RocketTree · Nov 25, 2023

Building the nose cone. I cut the shoulder off an Aerotech 4" thin wall cone.

Nose cone epoxied to inner centering ring and JB welded forward end of 1/4" threaded rod mount.

Thick wall coupler epoxied into nose cone and inner ring.

Two piece lid glued together and hardware installed.

Removable AV bay lid.

Nose cone assembled.

Most of the rocket assembled at this point. Upper body tube, jet pods, internal fillets, rear centering ring and retainer next.

MarsLander · Nov 25, 2023

Wow! Some nice work. Rock on!

RocketTree · Dec 3, 2023

Change of plans. The LOC 4" nose cone at 12.8" is much closer to scale with the original, so I will use this instead.
The previous 16" Aerotech nose cone will be used for a different project.

I started by cutting off the base with Mastercraft razor knife, using a small section of 4" tubing as a guide.

Cut rings for the AV bay. Two edges of the inner ring are notched to fit around plastic casting in the NC.

Install 54mm coupler guide with a jig to keep it centered.

Print template, drill holes for T nuts and install.

T Nuts installed, ready for epoxy. Holes drilled in end cap. I used M4 hardware for this.

Installed welded eye bolt and assembled the sled and bay with BSI 15 min epoxy.

Most of the rocket is ready for final assembly.

Rear internal fin fillets with BSI 15 min epoxy.

RocketTree · Dec 10, 2023

After some thought and calculation of fin flutter this weekend, I decided it was best to add a fiberboard veneer to the wings.

I used the original fin templates, cut four wings from fiberboard (0.029").

The fiberboard wings are epoxied to the plywood 3ply wing with BSI 15 min epoxy.

Weigh down while epoxy sets up and get the next one ready.

Epoxy has set overnight and the wings are now much stiffer. Internal rear fin fillets are done.

I sanded the fins to original shape and coated both of the new layers with extra thin CA. Final sanding with 320 grit in a few hours.

RocketTree · Jan 7, 2024

Not much progress over the holidays, but I got the wing "engine" pods built and installed, internal fin fillets, and upper body tube epoxied to the lower airframe. Next will be external fillets, launch lugs and its ready for finishing.

I had a limited amount of 1.9" tubing for the jet pods, so re-used some from an old rocket that was decommissioned. Plywood standoffs will be epoxied to the wing.