SR-71 Blackbird / Aurora, page 5
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reply posted on 17-9-2004 @ 02:03 PM by VW Devotee
Ok, I'm going to try to address a bunch of things in this one post, so here goes.

1. The SR-71, A-12, M-21 are all based on the same airframe, much the same way a Dodge Stealth is just a rebadged Mitsubishi 3000GT.

2. In order for an aircraft to rotate and climb absolutely vertically, the engine must be able to produce thrust equal to the weight of the aircraft plus the total aerodynamic drag of the fuselage.

3. As far as a ram jet engine being used at mach twenty, the airflow into could not be slowed down sufficiently without creating an ungodly long intake tract. Ram jet engines must have a subsonic flow within the engine in order to function, beyond that and a scram jet engine is needed.

4. Sustained flight at mach twenty would result in so much heat that no material could withstand it for any length of time. As I recall someone in the string suggested tiles like those used in the space shuttle, these would not work for a normal aircraft for several reasons. The tiles are too rough to provide good subsonic lift needed for takeoff and landing. More importantly the tiles are designed to be ablative. That is, the tiles disintegrate in the heat to disperse the energy, it takes a while but when you consider that the space shuttle only experiences the temperatures for a few minutes at a time and an aircraft flying at mach twenty would experience those temperature for (probably) hours on end.

5. To whoever said that the raptor could fly backward at 70 degrees, I say "WHAAAAAAAT?!?!?" I assume that you meant that it can climb at 70 degrees while inverted, is that what you meant?

6. The top speed of the SR-71 is limited by the fact that the mach cone must end up on the inlet spikes or the engines will "unstart" from the supersonic flow into them. using a little bit of geometry and trigonometry (and looking up the equation on the internet, email me if you want the address) the maximum speed for the SR-71 is about mach 3.8, anything beyond that and the mach cone comes to the inside of the engines and they "unstart".

7. In the picture of the SR-71 in flight the things someone was asking about (in reference to the "donuts on a rope" post) what you are seeing in the afterburner exhaust are called mach diamonds, they are present in the exhaust of all afterburners and rocket engines and have nothing to do with unusual exhaust contrails.

I hope that all of that helps with tangents of this thread. Having said that, if anyone disagrees with any of my conclusions I encourage irate responses and look forward to defending my positions.


reply posted on 17-9-2004 @ 03:55 PM by E_T
Originally posted by VW Devotee
6. The top speed of the SR-71 is limited by the fact that the mach cone must end up on the inlet spikes or the engines will "unstart" from the supersonic flow into them. using a little bit of geometry and trigonometry (and looking up the equation on the internet, email me if you want the address) the maximum speed for the SR-71 is about mach 3.8, anything beyond that and the mach cone comes to the inside of the engines and they "unstart".


The fastest published speed of the SR is Mach 3.5. There are several factors that limit the speed of the SR. One is the shock waves generated by various parts of the plane, at around Mach 3.6-3.8 the shock wave off the nose of the aircraft narrows enough to go into the engine, while there is the inlet spike (which slows the air to subsonic before it enters the engine), the shock wave bypasses the spike and causes the engine to unstart.

Second, the heat generated by the plane moving through the atmosphere. Even titanium has it's limits, and the heat generated by the SR brings the fuselage to the brink. It was discovered during a Lockheed Skunk Works study to see how much money and development it would take to get the SR to go faster than it's designed top speed (mach 3.2-3.5) that the metal divider between the windshield was heating up so much above mach 3.5 that it was affecting the integrity of the windshield, and at that point they had stretched the glass technology to the maximum.

www.neworegontrail.com...


Originally posted by waynos
No, I think that picture just shows the afterburner shock cones of the Blackbirds J-58 (?) engines, I've seen the same effect on many photo's of jets with afterburners on so it can't really be the same effect.


7. In the picture of the SR-71 in flight the things someone was asking about (in reference to the "donuts on a rope" post) what you are seeing in the afterburner exhaust are called mach diamonds, they are present in the exhaust of all afterburners and rocket engines and have nothing to do with unusual exhaust contrails.

Correct term is shock diamonds.

www.wvi.com...



Something running hot?

Here's bigger image for those who want nice dekstop background image:
www.mobiledyne.com...
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