Scramjets

[Mobius]

Hey people, you're mostly semi-geeky, so you'll be aware of the recent Scramjet test, and the scramjet experiments atop a pegasus rocket in 2005.

It's really starting to bug me that every news report I read keeps on saying \"This is the future of air travel\", and \"This will lead to airliners which can reach MACH 7 and cross the _____ in _____ minutes. (Fill in blanks).

Why am I bugged? Because it is so completely obvious that no civilian will EVER ride in a plane powered by scramjets. More to the point no civilian CAN ever ride in a scramjet powered aircraft.

Think about it: you have to achieve at least MACH 5 before a scramjet will work correctly, and how do you propose to get to that speed? Regardless of the answer, the ascent has to be very steep in order to get out of the thick part of the atmosphere. That means G forces, at least 1 of 'em, and more likely 2 of 'em!

Then, when you engage the scramjets, you'll get at least 2Gs acceleration, for about 2 minutes, and then the engines will cut off as the plane literally skips out of the atmosphere. About 2 minutes later, the craft will have sunk back down into air thick enough to drive the scramjet again.

So, you get 1-2 Gs at take off, then 2+ Gs of scramjet for 2 minutes. Then 2 minutes of free fall. The only time anyone can go to the toilet is on the glide into landing. So it's out of reach for 50% of the time, and out of order for the other 50%.

Look, most people can barely handle a bit of turbulence in a 747 - let alone the gut-wrenching forces of between freefall and 2+ Gs. 99% of people would be throwing up violently within 2 minutes of takeoff - and if not, then within 30 seconds of going into the first freefall.

It is patently stupid to think that ANY company can create a commercial service from a craft which behaves like this. Maybe you could sedate your passengers, but sedation takes time to wear off, and by the time it's worn off, you could have flown on a 747...

The only things which are EVER going to use scramjets are missiles, and possibly (although unlikely is my guess) a fly-back booster for some kind of space launch system.

[dissent]

Look, most people can barely handle a bit of turbulence in a 747 - let alone the gut-wrenching forces of between freefall and 2+ Gs. 99% of people would be throwing up violently within 2 minutes of takeoff - and if not, then within 30 seconds of going into the first freefall.

So I should forget about the in-flight meal then?

[Iceman]

So I should forget about the in-flight meal then?

Maybe so but the Mile High Club would sure be fun as he||.

[Duper]

This really is no big deal. the SR-71 would cruise at Mach 7 at higher altitudes. Those were \"normal\" ram jets.

[Ferno]

give em all five point harnesses.

[fliptw]

airplanes != rockets. Planes don't need to be at mach5+ from take off to landing.

Taking an hour to get to mach 5 and another hour to slow down will still reduce travel times greatly.

[Duper]

Taking an hour really isn't necessary to accelerate safely. The Blackbird could get from NewYork to London in under an hour. Mach 5 flight would really be advantagious in trans-Pacific flights which can take up to 14 hours. (That's real time) So ,yeah, it WOULD help. Even it was only to cut that time in half and even if it they did take an hour up and down.... 4 hours instead of 14? You Betcha!

btw, why is this in the E&C forum?

[fliptw]

btw, why is this in the E&C forum?

Its mobius.

[Lothar]

This really is no big deal. the SR-71 would cruise at Mach 7 at higher altitudes.

Source?

The unclassified top speed of the blackbird is just under 2500 mph, which is pretty close to mach 4 at 100,000 feet. I've heard the airspeed indicator tops out at mach 6. (Unfortunately, it's not set up like a car speedometer; you can't see the top speed unless the plane is actually moving that fast, so I can't verify that from the blackbird I sat in.)

why is this in the E&C forum?

Because I've been busy for a few days. No longer...

[Paul]

Taking an hour really isn't necessary to accelerate safely. The Blackbird could get from NewYork to London in under an hour. Mach 5 flight would really be advantagious in trans-Pacific flights which can take up to 14 hours. (That's real time) So ,yeah, it WOULD help. Even it was only to cut that time in half and even if it they did take an hour up and down.... 4 hours instead of 14? You Betcha!

And don't forget relativistic effects

[Lothar]

Doing a little more research on the blackbird... seems its pilots all got \"mach 3\" badges. Not mach 4, but mach 3. Also seems the shockwaves formed by the nose would cause engine problems just shy of mach 4, and the heat would stress the glass in the cockpit about that same speed.

Overall, it's doubtful that the blackbird was anywhere close to mach 7, though it may have been a little faster than the mach 3.5 generally quoted. The X43, though, can really haul.

[Duper]

This really is no big deal. the SR-71 would cruise at Mach 7 at higher altitudes.

Source?

Classified documents while I was in the USAF. As I recall it was upper altitutdes.

[Richard Cranium]

Classified documents while I was in the USAF. As I recall it was upper altitutdes.

Hey, I just found a leak for military secrets.

[Dedman]

Why am I bugged?

Because your sheep cut you off?

[TechPro]

The X43, though, can really haul.

So... why was the X43 discontinued after it's third (and fastest) flight?

So, you get 1-2 Gs at take off, then 2+ Gs of scramjet for 2 minutes. Then 2 minutes of free fall. The only time anyone can go to the toilet is on the glide into landing. So it's out of reach for 50% of the time, and out of order for the other 50%.

Oh yeah, trying to squeeze one out just in time to get all those Gs... but then maybe it'd all come out easier that way.

[Lothar]

This really is no big deal. the SR-71 would cruise at Mach 7 at higher altitudes.

Source?

Classified documents while I was in the USAF. :mrgreen: As I recall it was upper altitutdes.

Call me a disbeliever. You don't generally go through the process to get that level of clearance and then leak secrets on an internet bulletin board.

But we'll see when it becomes declassified in 20+ years I guess...