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Hybrid ram/scram/rocket?


Arugela

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Stupid question...

I'm working on my ssto design again. I came up against the reality that it's only running at a small fraction of the designed cargo space I set it too. I could obviously just step back the cargo space, or ....

Is it possible to have a combo ram/scram jet with the igniter being the rocket engines. And does a mass ammount of rocket engines lighting it help reduce the problem with lower ignition conditions.

So, the idea is a ram/scramjet with the rocket igniters running at the same time instead of seperately. The normal variance of airflow happen and at low speed you just run off of the rockets until you get higher and it naturally goes faster(keeping both active or, if possible, lower the thurst of the rockets to lower fuel flow.). This from what I can tell doesn't give massive thrust from the scramjet side but would it give higher ISP effectively to the rocket engines allowing them great fuel efficiency over the run? Would you have to lower the airflow/fuelflow of the rockets to do this? or could you do this full blast. The other possibility is that it would simply use more fuel overall. Or would it massively increase the thrust added to it? I haven't had any luck getting through the pressure in out equations to do the math on this yet.

Example:(very overblown example)

I have a ship with absolute maximum mass of 108k tons. It has a normal flight takeoff of 71,280-86,400 tons. It has 144 raptor engines(300 thrust each, I think 312.5 lbs fuel per second, 360 chamber pressure? Over the real specs.) This gives 10 minutes of flight at 144 engines and 43,200tons thrust. If I added a bypass for airflow and a giant inlet the size of the entire array or engines and had a large area in the back for it to expand from could Increase the thrust/efficiency of the rocket engines? Has this been tried before? The ship has a Drag coefficient of 0 .5 because it's big and blocky.

Is it possible the massive amount of engines flamed on would keep a ram/scramjet ignited regardless of conditions and that it could slowly enhance the rocket engines as it goes up? The idea would be to potentially maintain the same fuel use while enhancing the thrust or ISP or both.

Would this help get better overall ISP and hence range?

FYI cargo space is 17,280 tons with 432,000 ft3 at 80 tons /ft3. Body weight would be aiming for 4320tons for 21600 tons non fuel weight. This leaves a formula of 9.81*ISP*ln(4-5~). I was aiming for 918 ISP average if possible. I'm assuming this may be very unrealistic though.

Alternatively I could up the engines to 216(50% increase) for 64800 tons thrust and 7.5 minutes of flight time at full burn. Not sure which would be needed. Assuming either works with the bodies bad aerdynamics. (Still haven't gotten through that foruma fully either.)

 

TLDR:

Ship mass: 108,000 tons(hypothetical max/absolute max)

Normal takeoff weight: 71,280-86,400 tons

Engines: 144-216 raptor engines (300 thrust each, I think 312.5 lbs fuel per second, 360 chamber pressure? Over the real specs.)

Thrust: 43,200-64,800 tons thrust

Fuel: 13500 tons lch4 / 51,300 tons lox / air ? (from intakes)

Estimate flight/burn time: 10-7.5 minutes(144-216 engines.) with just rockets.

Cargo weight: 17,280 tons (432,000 ft3 @ 80tons / ft3)

Body mass: 4,320 tons

Non fuel mass: 21,600 tons

Assumed Drag Coefficient: 0.5 (assuming this is realistic.)

 

Could using a ram/scram jet constantly opened with the rocket, using the rockets as the igniters, start out on rocket mode and relatively normal ISP then increase the thrust or ISP as the rocket goes up and gains more speed/pressure difference for the rocket thrust from the ram/scramjet intakes.

The rockets are inbedded within a large chamber in the back of the ram/scramjet, as the igniters, presumably in the final back chamber or similar. Wherever is appropriate. would this help keep it ignited if they are both constantly on and still guzzing massive fuel.

The idea would be a hybridized version where they are both enhancing each other instead of a bypass where one is active then the other. Or something similar to that.

And would you need the nozzles. Or could you chop them off and use the back chamber as a giant nozzle for both? Or for the chamber and nozzle.

Edited by Arugela
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  • 2 weeks later...

A more likely configuration would be a compressor fan with bypass doors that close as the engine transitions to supersonic / ramjet speeds. Then later transitions to scramjet and then rocket. There are research documents proposing this. Having it also be a rocket engine might not be realistic or feasible, but I wrote up a config that does turn one of the OPT parts into a hybrid scramjet / rocket engine using the data from the research document for the Mach curve data. I'll post it later today.

Edit: Ooops, I kind of skimmed over parts of your question because it was early and I had to go make breakfast, so I'm looking at it now and I'm not really sure what you were asking here... I could still post my config but I'm not sure it's what you're looking for?

Edited by Starwaster
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