good design?

Purki · Post by **Purki** » Fri Nov 02, 2007 8:10 pm

Alright, while I wait for my pulse-jet to be ready, I am thinking of building a cheap ramjet (O.K. quality), I sketched something while looking at my purple pen at school :oops: , some of the features that I have in mind are the following, (they might be stupid, and if so, please post on how to make it better)

1. Two fuel injectors, opposite sides.
2. Two spark plugs , opposite sides, about 1 inch from the injectors.
3. To keep Running constant, use a EDF electric fan to keep it running (this is my least concern, I would like to get the engine running first :P )
4. I tried making it curve-less so manufacturing would be easier.

Here are some NOT TO SCALE pictures:

Zippiot · Post by **Zippiot** » Mon Nov 05, 2007 4:14 am

Looks good to me, what are you gonna make the insides out of?

I've been playing around with carbon and dolomite, just gotta get it to stick together better......

Purki · Post by **Purki** » Tue Nov 06, 2007 1:42 am

Bah.. that design was too hard to make, well I did not try it, I just figured it was, so, I will make an XXXL (extra extra extra large) "Maggie Mug" ramjet, it will consist of two smaller Heineken kegs with a strainer as a flame holder, what i will do is cut both ends off the kegs, fit the strainer in the middle, and Tig Weld all around it, both sides, after it cools check for any leaks by placing it in a tub of water and pushing down on it while pouring water on the top or until it reaches where the flame holder is and check for leaks, after that i will TRY to make a cone for the front of the engine, meanwhile getting help or/and researching on where to place the spark plug and fuel injectors (hoping to run on propane) and after all, again, i will TRY to make a nozzle for the exhaust, i will see as i progress, and i will post as much progress as i can, here is the firs piece of progress, getting everything together (still need another keg, hopefully this weekend :twisted: )

PLEASE FEED-BACK!

larry cottrill · Post by **larry cottrill** » Wed Nov 07, 2007 1:00 pm

Purki -

This is too large, unless you can test it on a full-size airplane OR you have access to a HUGE high-speed fan! Here's the reason we hobbyists can't build and test big ramjets:

For the inlet and diffuser to work, you need FULL WIDTH laminar flow at high speed over AT LEAST the entire width of your jet inlet. That's the only way your diffuser section will behave like a true diffuser. Period.

Of course, that doesn't mean you can't have fun with something that size. It's just that when you test it with a sub-diameter blower your diffuser won't work properly, and you'll end up with basically a thrustless burner (probably good and noisy, though ;-).

Let's see what others have to say. Maybe I'm being too skeptical. But, I don't think so ...

L Cottrill

Zippiot · Post by **Zippiot** » Wed Nov 07, 2007 9:10 pm

I agree with larry, you need a massive blower for that. I use a shop vac nozzled down to 1.5-2 inches, blows about 200mph winds at 3 inches so the nozzle speeds things up.
General rule of thumb for a ramjet is that at 250mph inlet speed each square inch of intake can yeild 3.5 pounds of thrust.....I think..............

If you can keep 200mph winds over your intake you are set to jet, pun totally intended!