Scramjets

I read through a few scramjet threads from way back whenever. There were some interesting links pointing the to Australian scramjet tests and the successful flight of the NASA X-43A. It seemed people were getting pretty excited by the idea. Rest assured you won't be flying on a Northwest Scramjet to your favorite vacation spot any time soon.

The biggest problem lies in that they just aren't economical at all. They don't even function well below a certain speed (~mach5 I have read). First you need a regular jet engine craft to take you to a certain altitude before rockets (or something of the like) take you even higher (over 100,000 ft) altitude and functional speed (mach 5?) before the scramjet becomes useful. Also the X-43A was unmanned, only 12 ft long, and crashed into the ocean after the "successful flight."

I'm assuming part of the Aurora project might be testing these exotic engines as a useful replacement to the SR-71. Since the SR-71 debuted in the 1960s I would assume they are beyond mere testing of its replacement. I have heard of the rumored SR-75 but I'm not certain of the authenticity of these claims. What do you all think? Do black projects really see a future in Scramjet technology? Or is it already a reality in "hush hush circles" as related to recon, bombing etc?

I imagine that scramjets are already being tested by the Skunkworks division (not just of Lockheed, but of the combat aircraft manufacturers in general), but not yet in use. Because scramjets are so anti-economical commercial jets don't need them. But since faster=better in military jet circles, I'm fairly sure that they're at least exploring and testing the idea.

Originally posted by Scramjet76
They don't even function well below a certain speed (~mach5 I have read). First you need a regular jet engine craft to take you to a certain altitude before rockets (or something of the like) take you even higher (over 100,000 ft) altitude and functional speed (mach 5?) before the scramjet becomes useful.

A pure "scramjet" is just as you describe, a system that needs a boost to get up to a speed where it's airflow becomes effective for propulsion.
However, nearly all of the development currently ongoing with scramjets has included dual mode engine capability. Here are some explanations for those not familiar with the subject.

Ramjet
Ramjets have no moving parts, they consist of an air intake, a diffusor, a combustion chamber and a nozzle, (The flow in the combustion chamber is subsonic). Adequate pressurization is created only by the high speed of the engine. Traditionally Ramjets work only at speeds above Mach 1.5 or 2. This means a booster engine is needed for initial acceleration.

Scramjet
The concept is identical to the ramjet, but with supersonic internal flow. The scramjet becomes more efficient than the ramjet above Mach 6.

Dual-Mode Ramjet
Ramjet that uses subsonic combustion initially, but changes to supersonic combustion in order to accelerate to speeds between Mach 2 and Mach 10.



It is generally considered that a standard but potent turbojet could get the aircraft to the point where a ramjet can operate. Once the ramjet gets the vehicle up to Mach 4 to Mach 6, the scramjet mode kicks in and off you go to Mach 10+.

Originally posted by Scramjet76
Also the X-43A was unmanned, only 12 ft long, and crashed into the ocean after the "successful flight."

The X-43 did as it was supposed to do, and that is fall harmlessly in the ocean. It would have been needlessly expensive to make retractable landing gear for the X-43, given the size of craft they had to work with.

Originally posted by Scramjet76
What do you all think? Do black projects really see a future in Scramjet technology? Or is it already a reality in "hush hush circles" as related to recon, bombing etc?

There certainly may be scramjet work going on that is more advanced than what the public is made aware of, I know some guys who swear they saw a formation of 3 waveriders flying over Nellis airspace - but heatwaves out there can do strange things to what you think you see.

There is an alternative to the turbofan/ramjet/scramjet stages. That alternative may have had extensive development by DARPA, NASA and a defense contractor or two... is called the Air Core Enhanced Turbo Ramjet. If I was "Aurora" hunting, I might be looking at that research as well as PDE's. Just a thought...

Sources:
Conceptual design of a Mach 10, global reach reconnaissance aircraft: NASA, Langley Research Center, Hampton, VA

Ramjet/Scramjet Technology, an Introduction: ONERA.FR

Nice post intelgurl... complete with drawings even !

The main point being that even military fighter planes (which fly at supersonic speeds) slow the incoming air to subsonic speeds before it mixes with the fuel. This is where the scramjet differs from the jet engine.

I would be shocked it there wasn't a black project that didn't use scramjet tech.

With a turbojet/ram/scramjet, you have a plane that can takeoff on a normal runway, using normal jet engines (so it wont sound odd to somebody who might here it a ways away), they once it get high enough crank up the speed. I believe the "theoretical" limit for scramjets is mach 15...so you would also need a small rocket if you needed to reach Low Earth Orbit...but by itself could easily achieve a high sub-orbit.

PDE's can take-off conventionally, but there loud. I believe there theoretical limit is around mach 10.

It's time for an update on scramjets. Actually I found this cool figure showing the propulsion efficiency of a rocket engine, rocket-based combined cycle (RBCC) engine, and turbine-based combined cycle (TBCC) engine. This research is valuable for determining the future space/earth hybrid vehicle.


source

Other links- Related article from NASA