Estes Ramjet Oversized!

thingiverse

Previously I'd release a "Fat Ramjet" model based on ellipticaloptician's designs but that rocket crashed. In inspecting the wreckage, I determined I could do better, so here is the redesign of the parts. There are two versions of the base and the mid parts, one sized for Estes Maxi Rods (3/16 inches in diameter) and one sized for regular launch rods. If you decide to do the double scale model, I strongly recommend you use the maxi rod size. To make the double scale version, you will need two BT-80 tubes at 10.5 inches long each, and one 20-inch BT-55 center tube. I had to use a coupler to make my center tube because the stock size for BT-55s is 18 inches. You will want to cut a section of the centering ring out of the top piece and the one side of the middle piece that lines up with the launch lugs, otherwise the rod will rub on the rings. I provided nose cones for both the double scale model and the fat short version. Both nose cones use the "Goblin" nosecone bases from here (https://www.thingiverse.com/thing:3073567). I used the "tight" base and put an eyebolt through the hole in the bottom. Epoxy a nut on the inside of the base to run the eyebolt to, and you can then add washers to the nose cone to get the proper stability level. Note that the "Fat Ramjet" version, being a short fat rocket, requires a lot of weight in the nose to be stable. I made it as a challenge, but I don't recommend it. It'll maybe get a hundred feet or so out of an C6-5, but should fly high enough on a 24mm C or D. Having said that, I've not flown mine yet. Ellipticaloptician's original designs, that these are based on, are sized for standard Estes D-sized motors. While these should fly on a D, I would recommend using this adapter (https://www.thingiverse.com/thing:3071923) to fly them on larger Aerotech engines. I will also be publishing an adapter to allow you to use an Estes E in these designs; it should be noted that this adapter will extend downward from the bottom of the rocket 25mm, moving the center of gravity backwards. This may result in a loss of stability. The Fat Ramjet required a lot of weight in the nose to reach stability in a swing test. I used five fender washers. I've not checked the double scale ramjet yet but in preliminary tests prior to painting, it seemed stable as is. Being such a large rocket, however, it's hard to be sure from a swing test. The double scale is actually lighter than the Fat Ramjet, however, due to the weight that needed to be added to the Fat Ramjet. This design should supercede my original Fat Ramjet design found here (https://www.thingiverse.com/thing:3062627), though that design can certainly still be used. 5/4/2019 Edit: I added a mid section that is also a coupler so you can just shorten two BT-55s from their original size to get it to fit. This coupler includes a loop to attach a shock cord to. I also added a version of the double scale fin rotated to the position I used when printing. This both fits on my printer better and aligns the "grain" of the print in a stronger position. 5/6/2019 Edit: The rotated fin for the 2x doesn't work, as it keeps falling over part way into the print. So I added a new one that has a cross piece. This is intended to be printed with supports with the idea that the supports will stabilize the fin as it prints. The supports and tab can then be removed. 5/8/2019 Edit: I redesigned ellipticaloptician's original motor can to accept E-motors instead of D motors and created a 2x Ramjet base to use this new can. This is part of my project to rebuild the rocket after the original's "Core Sample" last year. NOTE: You will have to scale the decals to fit. FLIGHT REPORT: Flew the Double Scale Ramjet on an E12-5 today using my E engine adapter. Everything looked good until the nose cone and chute separated at apogee. The body came down ballistically and made a nice loud "Thunk" upon hitting the earth, where it took a core sample. I know the rocket works, but sadly, mine is not reparable. Be sure you use good shock cord. The kevlar I used was apparently not up to the task.