building a ramjet

I'm thinking how utterly cool it would be to build a working ramjet and fly a rocket using it. Even cooler would be if it could go supersonic, but I doubt I have the knowledge to play around in that area. Does anyone know any people that have tried this? Were they succesful? Just how much work would be involved in designing an amatur ramjet?

If this idea's realistic, I'd plan to get some people in my aerospace department together and start working on a practical design. Could make a sweet undergrad research project...

 

Log in or Sign up to hide all adverts.

Guy, you are aware, are you not, that there is a LOT of prior art here, and at the hobbyist level? Please look it up and gain a perspective so that you will have a better idea what you want this project to do and where to go with it.

Ramjets need to be moving at a certain minimum speed to work at all, so a working model is going to have to go on a vehicle that can accelerate it to its operating speed. You are not only going to have to build a ramjet, you are going to have to build a vehicle and engines to take it up to speed.

The whole point of the exercise is to acquire knowledge, so have fun.

 

Log in or Sign up to hide all adverts.

A working ramjet? Not really something you can easily build since to test it you'll need to get air moving past it faster than 0.5 Mach. Not a realistic undergrad project unless you just model the thing using computational fluid dynamics - that could be an interesting project.

 

Log in or Sign up to hide all adverts.

They are said to be very,very loud. Maybe not an ideal garage project. Unless you live in Montana.

 

A quick google finds this;

http://www.cottrillcyclodyne.com/Maggie_Muggs/Maggie.html#TOP

looks like fun, ....!

 

Hell, wear earplugs and call it techno.

 

after looking on various websites I figured putting the thing on a rocket (to give it the initial boost) would be the way to go. and flunch, now that I think about it, that would be pretty cool way to do it, do the design with fluid dynamics in account and consider construction later. I was wondering if just making a rough design and building that would be more realistic, even if it's not as efficient. but spending the time to make a high-quality ramjet design does seem to make more sense as a "research" project.

loud, I'll bet, probably sound exactly like a jet engine WOULD sound if you put it in your garage, lol. but launched a mile or so into the air... probably not too bad. thanks for the link

 

Ah, problems here are;

Ramjets are typically made out of a metal tube, to withstand the combustion temperatures. Metal tubes are fairly heavy.

Model Rockets tend to use high impulse, short burn engines (10-100 Newton seconds of impulse, ten second burn, for a hobby rocket engine) and are made of of lightweight cardboard tubes.

So you'd need to cluster lots and lots of high power solid rocket motors to accelerate that large ish mass of metal tube, get your ramjet up to speed, and them ignite it while it's in the air.

Getting the timing right will be quite tricky.

You'll have a solid rocket burn time of maybe ten seconds, in which time you'll have to get up to speed, and then start pumping fuel into your engine, and ignite it, before the solid propellant burns out (model rockets reach apogee in a coast phase, you need to get your ramjet lit well before that).

I'd suggest as a starting platform, to use a 'ramrocket' configuration, ie, a duct around your engine, that sucks in cool air, which is mixed with the rocket exhaust, and which expands, extracting heat from your exhaust, and providing more thrust;

Please Register or Log in to view the hidden image!

(from http://www.ukrocketman.com/digital/pulsejets.shtml)

This is very simple, basically a thin metal tube that is larger than your rocket body, and extends beyond the end of your engine for six inches or more.

You could then try using a timer, and a valve, to release pre-pressurised fuel into the exhaust, to ignite that, and provide more thrust. Only issue here, is that ramjets use a diffuser, to mix the fuel and air, and keep the combustion from blowing out. Not quite sure how this would work with a ramrocket config, as you need a straight exit for your rocket thrust, that can't pass through a diffuser. I guess you could make a fairly long duct compared to it's width, and inject the fuel a fair way away from the solid engine, so the combustion does't set the tail of yoru rocket alight (or just use aluminium tube for your rocket body I guess!).

Without a diffuser you may suffer flame out once the solid engine has burned out though, as there will be too much airflow in the duct to hold a flame (the diffuser slows the air enough so it has time to mix the fuel and combust, and ignite the incoming fuel).

You could perhaps use the forward charge of a shorter burn time engine (you know this this works right? A typical hobby solid rocket engine burns for say 10 seconds,, then a fuse burns away inside the rocket from between zero (instantaneous) to five seconds, before igniting a _forward_ charge which is enough to blow off the nosecone of your rocket to release the 'chute'. You could perhaps use this forward charge to engage a diffuser or sorts (and operate your fuel valve), anything that can be made to slow the airflow in the duct once the other solid engines are nearly spent. Some perforated flap arrangement, sections springing down, released by a latch.

It sounds like so much fun I want to make one myself!

 

Building a crude ramjet itself is not a problem, but it has to be moving >600km/h before it can be efficient. When stationary it's as good as a heater.

 

heres plans for a $60 ramjet made from coffee cups.

enjoy.

http://www.cottrillcyclodyne.com/Maggie_Muggs/Maggie.html

 

DUH! I linked that a few posts up you MORON! Nice on your planet, is it?

 

Efficiency does't matter a damn, this is about a hobby experiment.

 

You don't need to move the ramjet at >0.5 Mach. You DO have to figure out how to make the air move through it at several hundred miles per hour.....

Hard-mount it to something, and attach strain gauges to determine if it is making any thrust.

 

How do you plan to test it? Perhaps a motor driven rotating arm with it at the end?

 

not that I know what I'm doing or anything... but here's where the posts have lead me to think so far...

I was planning to test it in flight. either that or I could figure out who's ass I need to kiss for a test in the school's windtunnel. I havn't seriously looked into either of these, but I'm looking at the ramrocket idea phlogistician put up as candidate for a live launch, since it would essentially be a rocket up untill it's velocity is high enough. the configuration of the rocket nozzle - slash - ramjet fuel injector could at least be an interesting topic for a design study...

a forward charge setting off a diffuser, brilliant! either that or designing a very clever solid-state system involving no spring-loading or moving parts, but i havn't the slightest how such a diffuser would even look, which is why I thought it'd make a cool research project! still love the idea, might be a backup if we're not clever enough to make a breakthrough component, lol

The ramrocket could be in the form of a liquid-liquid engine (maybe NOS for an oxidizer) where oxygen injection is electronically/mechanically regulated such that initially, it's open-throttling the oxidizer to operate the ramrocket as a rocket, but once speed picks up it slowly thins out the amount of oxidizer being injected as it can now use external air as a ramjet. The testing would consist of repeated test launches (or burns in a wind tunnel) where the goal would be to tweak the rocket to the point where there is no internal oxidizer being used to supplement the ramrocket at higher speeds.

Such a rocket would be pretty freaking big, and would cost a lot to make and maintain since it'd probably be mostly metal and composites. That, plus whatever exotic fuel we decided to use might make high enough prices that it would never happen. Not to mention that such a rocket would be large enough as to go outside the designation of an amatur rocket, and thus alot more red tape and fees (so i understand). I'm starting to think more and more such a project would be a research project only, with no actual rocket construction, because no one in the school would be crazy enough to poor money on it

Please Register or Log in to view the hidden image!

.

 

For many decades a successful model aircraft engine has been produced and used, and a number of its clones. It is a pulse jet or flutter valve engine. It might be useful as a basis for adapting a ramjet head onto it.

Having just Googled "dynajet pulsejet", I know that you may be able to see a good amount of perhaps useful information.

 

You might think of adapting parts, techniques, and fuel cells from the model airplane shops and catalogs. They have some serious engines and fuels. A lot of the things you might need come pre-manufactured and tested.

Maybe you can use a charge of compressed air to start the engine. Think about making it a very small one, a couple of inches wide and a few inches high.

 

Dynajets and their clones, in their original flutter valve form, have usually been started by using compressed air, often coming from an ordinary tire pump. However, a ramjet transmutation is a no-mans-land of knowing how to start it.

And, no kidding, they are LOUD!

 

I'd start small, for many and various reasons. First, cost, you'll be able to find lots of widths of pipe in diameters in the scale of inches to play with, and solid fuel hobby rockets will provide enough thrust to get that sort of weight moving. So that part is off the shelf, and easily aquired.

Secondly, the jet part requires a rocket carrying a payload of pressurised fuel, so carrying the least possible during proving flights is safest. You have to think what would happen if all the fuel somehow caught light at the same time, and with rocketry, weird stuff does happen (say for instance your rocket 'groundsharks' and ploughs into a wall, kaboom!)

Oxidiser, ... oh dear, now we really are talking about a bomb! Sounds like an added complication, to deliver a short burst of oxidiser into your fuel mix.

Start simple, and get clever later. I think a minor triumph would be just seeing the ramjet fuel ignite, let alone providing any thrust!

 

there is alot of paperwork and burocracy that goes into flying your own airplane, you will need a lawyer. ever if you build it which I find hard to believe, you will have to get clearence from the government and an inspection to deam it safe to fly.