Military

Why Were The SR-71 Engines’ So Far Apart From Each Other?

Published

2 years ago

19/10/2021

The SR-71 was a marvel, a super plane that marked an era. The technology it had on it is still unmatched. One of the most impressive things about the jet was its engines. Not only the sheer power of them but their placement of them. Two Pratt & Whitney J58 axial-flow turbojet engines powered the SR-71. The J58 was a significant technological advancement at the time, capable of delivering a static thrust of 32,500 IBF (145 kN). Around Mach 3.2, the Blackbird’s average cruising speed, the engine was most efficient. Normally, fighter jets have a single or dual engine that is mounted closely together. But the engines mounted on the SR-71 were quite far apart. The SR-71’s primary concept is that when it speeds up, it switches from turbojet to primarily ramjet operation. The engine’s inlet must be extremely efficient for the ramjet-like function to work. That is to say, it does more than simply slow the flow of air from supersonic to subsonic. That could be done with a simple shock.

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Instead, the SR-71 intake tries to create as little entropy as possible by sending Mach 3.4 air through a series of oblique shocks that progressively slow it down to subsonic speed while compressing it to 40 times its ambient pressure. The turbojet can’t burn much fuel at this temperature, so it provides more drag than thrust. However, the majority of that pressure remains at the afterburner’s end, which is sufficient to considerably expand the exhaust through the nozzle and efficiently generate a lot of thrusts. Kelly Johnson was a pragmatist when it came to engineering. He’d already created a Mach 2 interceptor, the F-104 Starfighter. That plane has a fixed-geometry intake that is almost radially symmetrical. At most speeds, it was wasteful, and it wouldn’t function at all for a Mach 3.4 plane.

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The oblique shock waves from the inlet spike, in particular, do not behave properly at the surface against the fuselage. A variable geometry intake would be used on the next plane. To get the geometry appropriate, the entrance spike that generates the oblique shocks that accomplish efficient compression would have to migrate aft at higher speeds. Because the shocks must be well behaved, the inlet must be totally radially symmetrical and have minimal interaction with the fuselage. At low Mach values, however, the shock from the aircraft’s nose is not strongly angled. Putting the engine inlet at the nose, like on the MiG-21 or Lightning, is one technique to avoid the engine interfering with the shock. Kelly, on the other hand, would require an intake that was larger than the fuselage for the high-speed, high-altitude Blackbird. There was no way the nose could be big enough. Furthermore, if he placed the intake there, the body would be mostly duct, leaving no room for fuel. As a result, the SR-71 engine intakes reside behind the shock wave produced by the plane’s nose but have no additional interaction with the fuselage. Because the nose oblique shock wave redirects the airflow outward a little, the cones actually point together a little bit if you look closely. Because the fuselage works as a lifting body in cruise and has a short angle of attack, the cones also point down.

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As a result, the location of the engine intakes is confined twice. It must be far enough away from the fuselage to avoid interfering with the fuselage’s disrupted airflow. It must avoid the vortex that emerges from the fuselage chine and travels across the top of the wing. It must, however, be near enough to the fuselage to remain under the nose shock even when traveling at maximum speed. If they were any further out, the nose shock would speedily cross the inlet, resulting in an inlet unstart and an engine flameout.

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The image above depicts a shock simulation at Mach 1.25. I couldn’t find a picture showing the shocks at higher speeds. The shock angle pulls more back as the Mach number climbs until the nose shock is just in front of the engine inlet cones at Mach 3.4.

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Related Topics:avgeeks Aviation blackbird fighterjet Jets MACH shockwaves SR-71 subsonic supersonic

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Military

The B-17 Flying Fortress: A Legendary Bomber Aircraft of World War II

Published

6 months ago

29/03/2023

VISHNU

Let’s first listen to how the machine sounds. Enjoy!

Daleflying

The B-17 Flying Fortress was a critical component of the Allied forces during World War II. With its powerful engines, advanced weaponry, and remarkable durability, this bomber aircraft became an icon of American air power. Its contributions to the war effort are still felt to this day, and its legacy continues to inspire people around the world.

Aircraft Design

The B-17 Flying Fortress was designed and built by Boeing. It was a four-engine heavy bomber aircraft that first entered service in 1938. The bomber was named the “Flying Fortress” due to its powerful armament, which included multiple machine guns and cannon turrets. The aircraft could carry a heavy payload and fly at high altitudes, which made it a valuable asset for strategic bombing missions over enemy territory.

Role of B17 fortress during the war

During World War II, aircraft played a critical role in the Allied victory. It was used extensively in bombing raids over Europe, targeting strategic military and industrial targets and occupied territories. Despite the dangers of flying over enemy territory and facing intense anti-aircraft fire and enemy fighter planes, B-17 crews were determined to complete their missions. The bravery and dedication of these crews, often comprised of young men in their late teens or early twenties, helped turn the tide of the war in favor of the Allies.

How it shaped modern Warfare

The B-17 Flying Fortress was also instrumental in the development of modern air warfare tactics and technology. The lessons learned from its use in World War II helped shape the future of strategic bombing and air power and paved the way for the development of modern bomber aircraft. The bomber’s success paved the way for further advancements in aviation, and it remains an important part of aviation history today.

Conclusion

The aircraft was a remarkable aircraft that helped turn the tide of World War II in favor of the Allies. Its advanced design and powerful armament made it an icon of American air power, and its contributions to the war effort were critical. The legacy of the B-17 Flying Fortress serves as a reminder of the bravery and sacrifice of the men who flew and maintained these remarkable aircraft, and of the critical role they played in the defeat of tyranny and the defense of freedom.

If you enjoyed reading this short article, don’t forget to share it with your avgeeks!

Military

Unveiling of the B-21 Raider: A Look at the Next-Generation Stealth Bomber

Published

7 months ago

09/03/2023

Mina Maher

On December 2, 2022, the U.S. Air Force unveiled the B-21 Raider, its next-generation stealth bomber, during a roll-out ceremony at Northrop Grumman’s facility in Palmdale, California. While certain angles of the aircraft were off-limits, the front view provided some interesting details about the highly secretive aircraft set to replace the B-1 and B-2 fleets.

The overall shape of the B-21 Raider:

The overall shape is similar to that of the B-2, though it is likely smaller in size than previously anticipated. The leading edge of the aircraft shows a different design concept from that of the B-2. The “hawk’s-beak” profile appears to be similar to the one shown in the latest renderings and less pronounced than that of the B-2. The Raider also features a different inlet configuration, and blended conformal engine nacelles cannot be seen from the front angle. A splitter plate is visible in the inlet of the Raider.

Landing Gear and Nose Doors:

The B-21 Raider has a two-wheel main landing gear (MLG), and its MLG doors have serrated edges. The nose gear door is serrated and is not attached to the gear leg but on the right side of the bay.

Windscreen:

The Raider’s new four-piece windscreen, similar to that of the B-2 Spirit, has a different shape for the two lateral windows. The side windows appear to be arched and narrower than the ones in the front, which are about half their height.

Color and Logo:

The color of the B-21 Raider appears to be a light gray, similar to that of the RQ-180. A small Northrop Grumman Flight test badge appears in front of the nose gear wheel bay and on the upper surface of the right-hand side wing, close to the tip. The U.S. Air Force roundel appears on the left wing.

Two new photos, taken on November 28, 2022, were released shortly after the official roll-out. One provides an elevated view of the aircraft, showing that the planform is probably not a cranked arrow wing, as some shadows in the first official images seemed to suggest. The other photo is a close-up of the B-21’s nose, showing the “hawk’s-beak” profile of the new bomber from a 3/4 point of view, which appears quite similar to that of the B-2.

The B-21 Raider’s unveiling has provided some valuable insights into the aircraft’s design, though much of it remains shrouded in secrecy. The new bomber is set to be a game-changer in the U.S. Air Force’s arsenal, with advanced stealth capabilities and a range of state-of-the-art features.

Sources:

Source: theaviationist

Featured Image by: Northrop Grumman

Informative

Life-Saving Technology: The F-35B’s Automatic Ejection System

Published

9 months ago

01/01/2023

Osman Jamil

The Lockheed Martin F-35 Lightning II is arguably the most advanced jet ever. With countless systems to sensors onboard, the F-35 is alone at the top and usually gets lonely at the top. The F-35B variant is the most advanced of the F-35 lineup. The F-35B type, explicitly built for the Marine Corps, could break the speed of sound while in flight and perform vertical landings on the tiniest of landing pads, much like a helicopter. As advanced as the jet is, a chance for error resulting in a crash still looms.

Read Also: A Battle Of Stealth: F-22 vs F-35

The jet contains an auto-eject capability system, where the jet senses the situation automatically and decides to eject the pilot itself without the pilot having to think about whether or not it is safe to do so. The seat installed is a Martin-Baker US16E type seat which delivers a previously unseen level of well-balanced optimization across critical performance factors such as safe terrain clearance limits, physiological loading limits, pilot boarding mass, and anthropometric accommodation ranges to completely satisfy the F-35 Escape System criteria.

All versions of the F-35 aircraft will share the US16E. The sole Joint Strike Fighter model with this technology is the F-35B, which is also the first American aircraft of any sort to have this capacity.

It is unclear exactly how or by what criteria the auto-eject system judges that the aircraft is not within the pilot’s control and initiates the ejection procedure. Its precise condition on the F-35B fleet is also unknown. It is well known that the US16E seats on every F-35 type are connected to the flying systems in some other way to prevent the pilot from ejecting in dangerous circumstances. It’s interesting to note that the Cold War-era Soviet Yak-38 and Yak-141 jump planes had engine configurations more akin to the F-35B.

However, both featured vertically mounted jet engines rather than lift fans and auto-eject systems. The F-35B’s inclusion of auto-eject is directly related to how challenging the aircraft’s vertical takeoff and landing is. In the hover mode, the jet’s Pratt & Whitney F135 engine’s power is directed downward through an articulating exhaust nozzle, and a large fan is mounted vertically in the center of the fuselage to create lift. The engine directly powers the lift fan through a big drive shaft connected to a carbon clutch.

The B version of the F-35 is significantly distinct from the other two primary variants. It differs from them all in so many ways that it has affected every aspect of its essential construction.