Good ramjet?

[1fastneonrt]

Hello everyone, I am new to the forum and very surprised of the vast information that is on this site. I am interested in making a ramjet but am confused. I have looked at the Maggie-mugs ramjet but am not sure if that’s really a ramjet. I basically know how a ramjet works in general. A ramjet takes supersonic air and slows it down to a subsonic speed (means of diffusion) and compresses the air slightly before being heated by a flame. The heated air (or super heated air) moves and exits the rear at a greater velocity than the incoming air at the intake, thus creating a forward thrust. I have a design in mind but am not sure if this would be a correctly designed ramjet. Please correct me if I am wrong, I'm still learning the ropes here. I have no dimensions for it yet; it's still a general design. Let me know what you guys think. Thanks

[larry cottrill]

1fast, that looks really good. Yes, that WILL be a ramjet - IF you can move enough air into it. The diffuser cone is really nice, but that area ratio means you'll need some really fast air to get full power out of it. You have a fairly high speed design there, because the exhaust area is so much larger than the intake area. That means you will need to get pretty fast air going in to achieve real pressure in the chamber, and thence, good usable thrust. Adequately testing this will be the tough part.

The problem always seems to be that it's not easy to get that large a cross-section of very fast air, clear across the intake. If you use too narrow a stream, so there's some edge turbulence inside the engine's intake rim, you won't get good diffuser action - you MUST have an airstream somewhat larger across than the front rim of the diffuser cone.

It would help to put a SLIGHT intake flare on the front rim - you don't want too much, because whatever you provide will reduce the effective area ratio of the diffuser.

I like this one very much. Intuitively, the flameholder looks about right to me.

L Cottrill

[1fastneonrt]

Well I am relieved that it's a good design. I will be crunching some numbers over here shortly after the new year. I kind of figured that I would need some really fast moving air with this design but I will see what the numbers tell me. I would like to keep the design around the maggie-mug concept but I don't think it's going to give me the length I need. If I need to I will eliminate the intake cone to change the speed of the jet. I will let everyone know the final design and dimensions and will take pictures of the assembly steps. Thanks larry for your reply.