by Ihor Cap

I loved aircraft ever since I first laid my hands on a model airplane when I was just knee high to a beer bottle. What kid doesn’t? My favorite ones were the fighter aircraft planes, probably because they were the fastest, and coolest looking planes, unlike the typical and plain looking civilian aircraft. They still are, I think. It is these same criteria that also helped define my search for the coolest flying military aircraft around: they are the fastest and the sleekest looking aircraft; they are also the most awesome aircraft in their class. There are many military aircraft that meet these criteria but only three are super cool in my book. The first aircraft to be described here is the B-2 Spirit, a subsonic aircraft that approaches the speed of sound. The second aircraft is the supersonic SR-71 Blackbird and it flies three times faster than the speed of sound. The third aircraft described herein is the hypersonic X-43A Scramjet which is totally cool because it rips through the sound barrier at 9.25 Mach speed. Civilians could easily mistake these aircraft for UFOs. Finally, this article also includes some must see photos and video clips of these and other related military aircraft that are helpful to my story here.

Speed of Sound and Mach Speed Defined

There is no one standard to define the speed of sound, but a few definitions will help you understand the phenomenon better. The reason for this is because the speed of sound is not a stable factor. It fluctuates as a function of altitude. Wikipedia defines the speed of sound as an audible or inaudible sound wave that penetrates an elastic medium. The medium undergoes some sort of stress and then returns to its original shape.

In “dry air at 20 °C (68 °F), the speed of sound is 343 meters per second (1,125 ft/s). This equates to 1,236 kilometers per hour (768 mph), or about one kilometer in three seconds and about one mile in five seconds.” Elsewhere Wikipedia states that the “….speed of sound in air is referred to as Mach 1 by aerospace physics”. The US Department of Defense Dictionary of Military and Associated Words specify that “the speed of sound at sea level in the International Standard Atmosphere is 1,108 feet per second (or 658 knots, or 1,215 kilometers per hour)”. NATO uses the same standard.  Aircraft flying below the speed of sound are typically called subsonic. Aircraft flying at the speed of sound and up to around Mach 5 speed are dubbed supersonic. Any aircraft flying at high supersonic speeds or beyond Mach 5 speed are called hypersonic. (See Wikipedia for a discussion of these)

Exploring the Speed of Sound and Mach Speed Further

Like Wikipedia, the Handy Science Answer Book, compiled by the Science and Technology Department of the Carnegie Library of Pittsburgh, also tells us that it takes five seconds for sound to travel one mile or about 1.61 km by air.  Yet, it takes only one second for sound to travel the same distance underwater.  It travels faster still in iron and steel. So, hypothetically speaking, if an aircraft traveling beyond the speed of sound is underwater, will it be able to fly out? I’m not sure but that is what it looks like in one of many You Tube videos I found on the internet covering the same event. One video claims that this aircraft flies out from under the water. Another video of the same F15 military aircraft claims that it was launched from underwater, a third claims that the video is actually shown in reverse and that the plane crashed into the water. Finally, the last video of the same event claims that it is not a plane at all but a rocket launched from a submarine. In any case the video clip itself is pretty awesome.  What do I think? To me it looks like an F15 Eagle aircraft of the USAF launched from underwater.  Readers should know that this jet aircraft is capable of vertical acceleration and creates a powerful after burn from its two engines which you can see in the video. It flies at Mach 2.5 speed. Compare the picture of the F15 Eagle Aircraft with that of the one in the video. Look the same? I thought so too.

F-15E Strike Eagle with Underside View

What is Sonic Boom?

The incredible thing about supersonic flight is that “…it not only produces an audible effect, but also a visible one” says a You Tube video by sciencemadefun. It’s an audible sound that generates a sonic wave known as sonic boom.  The sound is much like the one associated with the crack of a bullet or thunder passing overhead. A person will hear the sonic boom of the passing aircraft only when the cone shaped shock wave crosses the observer’s location at the edge of the cone’s mouth. The pictures below illustrate fighter aircraft breaking through the sound barrier leaving a cone shaped vapor cloud behind that is visible to the naked eye.

 

Sonic Boom Cloud from Supersonic Flyby

The Three Coolest Military Aircraft

Subsonic Class Aircraft: B-2 Spirit Stealth Bomber

Subsonic Class Aircraft:  B-2 Spirit

What is Cool About It: The B-2 Spirit first rolled out in 1988. It is also referred to as the Stealth Bomber.  It is a bat-like shaped aircraft that has lower acoustic and infra red signatures from previous planes. It cruises at a speed of about 870 km/h, 541 mph or Mach 0.85 speed, but can reach sonic boom speeds of up to 972 km/h, 604 mph or Mach 0.95. Designed in response to the Soviet Russian threat, it could easily carry nuclear bombs around the globe within a few hours.  

 Supersonic Class Aircraft: SR-71 Blackbird

Supersonic Class Aircraft:  SR-71 Blackbird

What is Cool About It:  The SR-71 Blackbird is a U.S. Air Force strategic reconnaissance jet plane reaches a maximum speed of about 3,530 km/h, 2,200 mph or roughly three times the speed of sound (Mach 3.2). It can fly at altitudes of 85,000 feet. The aircraft materials are mostly made up of titanium (85%) and the rest of the frame is composed of composite materials so it can easily withstand high temperature cruising speeds.  This was precedent setting in the American aircraft industry. It is the first time that any American aircraft used titanium to fabricate a high-speed aircraft. Its first flight took place in 1964.  This aircraft was decommissioned in the year 1990.

Hypersonic Class Aircraft: X-43A Scramjet

Hypersonic Class Aircraft:  X-43A Scramjet

What is Cool About It: NASA’s X-43A Scramjet is not like the other aircraft reviewed here. It was designed as a one-time use experimental vehicle without recovery. It has no pilot and believe it or not, instead of relying on its flying wings to lift it into the air, the aircraft mostly depends on its lifting body design to provide that lift for flight. This hydrogen-powered vehicle does not rely on oxygen to fuel the engine and its design requires it to fly at speeds greater than Mach 7 at the start.  Initially, a modified B-52 bomber aircraft drops it from the sky and then a Pegasus rocket provides further acceleration to bring it to Mach 7 speed. The X-43A then automatically kicks in at this speed and separates from the rocket to fly on its own. The first flight test happened in 2001 and went horribly wrong. It crashed into the ocean after spinning out of control. Its greatest success was experienced the third time around. Wikipedia describes this record breaking experience in these words.

“The third flight of the X-43A set a new speed record of 12,144 km/h (7,546 mph), or Mach 9.8, on November 16, 2004. It was boosted by a modified Pegasus rocket which was launched from a Boeing B-52 at 13,157 meters (43,166 ft). After a free flight where the scramjet operated for about ten seconds, the craft made a planned crash into the Pacific Ocean off the coast of southern California.”

The X-43A project retired soon after. It was replaced by a new generation scramjet, dubbed the X-51 in late 2005. The X-51 recorded its maiden captive flight in December of 2009 and its first free flight on May 26, 2010.  It travels at Mach 6 speed but holds the record for the longest scramjet flight burn time ever. The X-51 flew for 140 seconds compared to the 12 second flight time of the X-43.  The future hope of hypersonic flight is to not only demonstrate improved acceleration but continued flight stability.

Author Information:

Ihor Cap, Ph.D.

Ihor Cap is a web author at http://articlesandblogs.ezreklama.com.