Estes AMRAAM AIM-120 Downscale, Build, Part 4, Making The Conduit

Blowing up the Alway drawing in Corel Draw - I came up with the dimensions for the long conduit tunnel.

Tunnel dimensions:

11.75" long

.130” high x x .40 wide

I used the online picture to get a better idea of the shape.

The tunnel is wide and won't have a good fit over the round tube.

I rolled some 320 grit sandpaper around the tube.

Using straight back and forth movements, a curvature was sanded into the bottom.

Here's a better fit.

Any gap will be filled with a glue fillet.

Estes AMRAAM AIM-120 Downscale, Build, Part 3, Cutting Out The Fins

This is a spare parts build.

The scrap 3/32" balsa sheet edge was a bit banged up.

Before cutting out the fins, 

The soon to be leading edges were sanded square using a sanding block.

Old school:

Tracing around a cardstock template using a pencil.

I don't like using a pen. Unless the ink is sanded off, it will bleed through the final paint.

On hand cut fins, gang sand them.

Stack and square them up using a sanding block with 220 grit.

On the left is the upper fins,

On the right are the lower fins.

Estes AMRAAM AIM-120 Downscale, Build, Part 2, Semi-Scale "Cheat"

 

After a few searches, I found a clean copy of the Peter Alway drawing.

To view it: CLICK HERE

Note there is a boat tail on the real missile.

I did run the numbers to get the tube lengths. See the first "background" post. 

But, to get the fin patterns - 

I dropped the Alway drawings into Corel Draw and enlarged it until the body was 1" diameter. The BT-50H tubes I'll be using are .990" in diameter.

With the drawing enlarged I simply traced the fins.

Because the rocket body is tall, I had to draw the fins on two different pages.

Estes AMRAAM AIM-120 Downscale, Build, Part 1, Parts

I decided to go with one long tube, 16.40" long

Heat shrink tubing is now added to most all my new builds. Slide over the Kevlar line down to the engine mount and hit with a hear gun.

Odd'l Rockets 12" parachute

Forward fins can make a rocket unstable - .50 oz. of clay weight will be pressed into the nose cone.

The 1/8" diameter launch lug will be cut in half.

Apogee plastic nose cone is PNC-24D at 2.75" long. It's a close match to the AMRAAM scale length and shape.

3/32" thick balsa for the fins.

The water slide decals have been redrawn, the original kit had stickers.

I thought about a boat tail but decided against it. The boat tail wouldn't allow for an engine hook and would require friction fitting. The original Estes kit didn't have a boat tail.

Estes AMRAAM AIM-120 Downscale, Build Background

This is going to be a slight downscale based on the Estes AMRAAM kit.

Research is often part of a build - 

Here's some scattered specs I found online:

AMRAAM AIM-120 

Boxed kit, #2153. Part of the Estes BETA series 

Scale: 1:5

Produced 1996-2001

Original kit had stickers, not water slide decals.

Skill Level 1

Recommended Engines: B4-2, B6-2, C5-3, C6-3, C6-5

Maximum Estimated Altitude: 400 ft

My build will be a downscale from original kit BT-55 tubes to BT-50H (heavy wall tubing)

Downscale info:

Original kit tubes

#2153 AIM 120 AMRAAM   031191   BT-55   (2)   11.00" 030326   BT-20J   2.75"

Downscale tubes (2)

Two 8.20" long BT-50H tubes or single tube, 16.40" long

To downsize - 

BT-55 is 1.325" diam. / BT-50H (heavy wall) is .990" diam. = Scale Factor of 1.338 or 1.34

Divide the original (two) BT-55 11" length tubes by 1.34  =   (two) 8.20" long BT-50H tubes or one long  BT-50H tube at 16.40"

To see the original kit instructions, from the Rocketry Forum: CLICK HERE 

and scroll down to post #6.

If the PDF image comes up upside down, look for the "square/arrow icon at the top bar. Hovering over it brings up "Rotate counter clockwise" Click on it twice and the image will flip. 

BMS School Rocket, Build, Finished

A sharp, well designed rocket for school programs looking for something other than a snap together build. Thru-the-wall fins, Kevlar shock cord and a Mylar streamer.

The instructions only suggest an A8-3 motor, but it would certainly be stable with a B6 or C6 engine. 

You might not get it back with the C6-5 motor.

Taller than an Estes Alpha, with the extra length it should be easier to pack the wadding and streamer.

R.O..C.K. Monthly Launch, June 7, 2025

I had hoped to get in two more test flights of the Odd'l Rockets ROBOT today.

Boost was stable with a B6-4 motor, but at ejection the head popped off! The rear ejection worked fine, and the main body found.

But, the head was lost. No C6-5 second launch today.

Second up was the downscaled Centuri UFO INVADER. 

It performed as advertised, turning over at apogee and landing on the spring wire legs. 

Space X has nothing on this 1976s kit!

Boost was labored but straight up with a C6-3 in the tail.

The New Way LETTER GO yielded the best launch picture of the day.

An older Chinese Quest B6-4 had a noisy boost with an altitude guess at 325 feet.

The 12" parachute was large enough for recovery on the newly mowed field.

You can see how small the ASP Micro HAWK next to the BT-55 diameter model.

I like to add a Micro-Maxx launch for some variety. Boost is always fast. Altitude was an estimated 75 feet.

I asked for extra eyes to follow the descent but with the shiny streamer it was easy to track.

Only launched four rockets today. It was very hot and might be my last launch until Florida cools off next October.