The Great Ramjet Challenge!!!

[redneck]

ok gotcha... that makes sence. but here is another question, why not make the spike in the intake divergent, convergent, picks up air at a high speed then sloing it down the the max that the difuser exit diameter will allow? or can you do that so long as you have the required air speed?

[redneck]

a quick question to help improve my understanding. why is it that the exhaust exit must be larger than the intake difuser? does this have to do with pressures? seems to me that a smaller hole makes for higher velocity gasses. i know that there is a limit to that, but somebody please break it down barney style for me?????

[thecheat]

STILL trying to get everything put together... lots of interruptions so I really haven't gotten anything done... still must deepen the slits to fit the tail cone in.

Congrats redneck! It seems your jet is getting better all the time!

Irvine, any improvements on yours?

[Jim Berquist]

Yes intake pressure and velocities.

Since your so good at this , Give me some Ideas for a 50 mph engine that will work.

Not Really , Yea Really,,,, You hit it ,,,,,,,,,small front for high volume.

Large for small volume...........

Just do your thing and you will be all right!!!

I am still working on the little ram for the Can - Man Project....


Jim

[redneck]

Since your so good at this , Give me some Ideas for a 50 mph engine that will work.

sarcasm?

[Zippiot]

Anyone know how to calculate the airspeed and cfm of the air blown by a valveless pj?
Just wondering if you could make a tiny valveless flightworthy by adding the thrust from the ramjet.

[Eric]

Calculations only work well once you have measurements and extrapolated patterns for a specific design otherwise its basically a lot of guessing and assumptions. The fact that the velocity and flow rate change 200 times a second doesnt help any...

Best thing to do is put a long tube the size of the ramjet opening behind the engine and use some kind of device to measure the average air speed, the long tube helps dampen the individual pulses and smooth the flow.

Pulsejets beat just about any blower you can find/afford in both flow and speed.

You could get a 50 mph ramjet but its not going to generate enough power to continue pushing itself forward at that speed. Just stick one to the roof of your car for testing, and hope it helps you outrun the cops.

Actually thinking back to the first episode of myth busters where they put the JATO's on the car and got it to go 300, jatos and ramjet would work quite nicely. Get it up to operating speed and kick on the ramjets and accelerate to a cool mach 2.5 :D

Eric

[Zippiot]

I remember seeing a picture of a ramjet strapped to a big truck, said it made like 200 pounds of thrust...
I'll look for it

[heada]

200 pounds of thrust on a 5000 pound truck.....take a long time to get going at any kind of speed.

I'm working on a rocket launched ramjet. The rocket will get the ramjet to transonic speeds (600 mph to 800 mph) The ramjet I'm designing should work in the 500 mph to 1000 mph range (I hope)

Once I have anything worth posting, I'll post it.

-Aaron

[Zippiot]

5000 pound, I musta said it was a big rig right? Closer to 5 tons minimum!

How big of a booster stage are you using, I wanted to make a ramrocket but to get it up to speed the booster had to be huge!

[heada]

4 54mm J motors(J1299), Each one producing just under 1300 Ns for 0.65 seconds or a total of 3388N. I should be able to lift about 75 pounds to 5000 feet and reach 600 mph at 1000 feet.

First flight will be the rocket and motors with dead weight to simulate the ramjet. Second flight will be with a ramjet and fuel but not running. Third flight will be a 5 second burn on the ramjet. Fourth flight will be a 30 second burn on the ramjet (which I expect to reach at or near 50,000 feet) After that, I should add a 3rd stage which will be a long burning(9+ seconds) K motor (K250). That motor alone holds an altitude record of over 30,000 feet.

This will be a multi-year project and not something that I expect to run flawlessly. By the time I'm ready for the full 3 stage flight I should have my level 3 certification.

If you're interested in the rocketry part of it, I highly suggest that you join one of the rocketry groups (NAR or TRA in the states) and get your certifications. I have my level 2 certification so I can use motors up to L (or a total of 5120 N)

[Zippiot]

On some gov't site I remember reading that no civilian ramrocket can burn for more than 40 seconds...maybe that was just in cali?

What rocket and ramjet configuration are you using, 4 boosters around 1 central ramjet?

[heada]

Easiest answer first. 4 J motors in a strap on fastion (like the GEM motors on the Delta-II) They would fall off after burn out. I've also been thinking of trying out a new motor I saw the other day. The J1999. For $20 more each motor, the difference in thrust is HUGE. The J1299 will produce about 350 pounds of thrust (each) on ignition while the J1999 will produce about 520 pounds of thrust (each) For the additional thrust, I only gain about 3 pounds in motor weight and it would still be under the 5120 N limit for my Level 2 certification (barely). I'm not quite sure how I'd attach the 3rd stage rocket...so thats still up in the air (no pun intended)

Now, about the limitations on a rocket...

total impulse < 200,000 lb-sec
total burn time < 15 seconds
sectional density < 12 lb/sq in.

The only limit I would exceed is the burn time but I don't know if it applies to this configuration or not. The ramjet is an air-breathing motor, not a rocket motor. Its no different than the many jet engines in airplanes today. If I ask the AST (a branch of the FAA) if it does apply, then I would have to apply for a USLV (Unguided Suborbital Launch Vehicle) permit and fly it from an approved space port (there are a few of them around the country)

http://www.faa.gov/about/office_org/hea ... pdated.pdf

Testing the rocket for flight 1 and 2 I can do locally (I have a monthly waiver to 8000 feet and L motors) The 30 second flight would have to be somewhere like Blackrock, NV where they have a 100,000 feet waiver once a year. A full flight would have to be at one of the approved space ports because I think it could break the 100,000 limit (if I ignite the K250 going 600 mph at 60,000 feet, it would easily go over 150,000 feet)

Then again, the hard part is getting a ramjet that works in the 500 mph to 1000 mph range. And then after you build it, how do you test it? I think I need a book called "So you want to be an aeronautical engineer..." :)

-Aaron

[Zippiot]

I interned at my local nasa and got a "maybe" as to whether or not I could test my ramrocket there. The guy had to say maybe b/c he doesnt "offcially" have all access to the air above the base, but they all wanted to see what I had come up with.

Plus it is a military base and small airports are only a few miles away...


I was going to have a very long motor centered in a ramjet, the motor was one time use and the case would be something that can burn. At launch the fuel to the ramjet would be turned on and the hot rocket exhaust would ignite it, once the ramejt could overtake the rocket (burnout msot likely) it would start burning through the case of the rocket, kinda like adding a little extra fuel. I planned on a 3 second rocket burn time and a 20 second ramjet burn time. With how fast the rocket would be moving at the end of the ramjets burn I would need a huge amount of time before the parachute ejected.


I have it all drawn up but lack the desire to send a rocket well past what I think I could safely launch...


Plus if it tipped towards the ground right after launch it would make a giant fireball near a bunch of people not to mention cato the motor, all kinds of dangerous!


One day.....

[Eric]

Here is a pic of the all stainless final version of the TP-180-70 ramjet. Increased the diameter to 7" and adjusted the other dims.

Length: 19"
Diameter: 7"
Intake dia: 3.5"
Exhaust dia: 4"
Diffuser length: 5"
Nozzle: 4"

With all the extras in place the engine comes to 4.9 pounds. Later in testing I may decide to convert it to a CD nozzle or just add a SR71 style nozzle to the end. Might post some video tomorrow.

The cat and dynajet are for size reference. :)

Eric