During the display at the Zeltweg airshow in Austria, the Belgian Air Force F-16 suffered a compressor stall that caused a loud bang and an impressive backfire.

On Sept. 3, during its display at the AIRPOWER 2016 airshow in Zeltweg, the “Viper” of the Belgian Air Force F-16 Solo Display Team suffered an apparent compressor stall that forced the pilot to perform a precautionary landing.

Take a look at the footage below. If you jump to 03:20 you will see the aircraft’s engine emanating flames (generating a loud bang you can’t hear) in what seems to be the typical behaviour of a compressor stall.

Compressor stalls (sometimes referred to as afterburner stalls in aircraft with reheat) are not too rare among military aircraft. They can be caused by several factors, including birdstrikes, FOD (Foreign Object Damage), ingestion of turbulent or hot airflow into the air intake etc.

A compressor stall is a local disruption of the airflow in the compressor whose severity may vary from a momentary power drop to a complete loss of compression.

A particular kind of compressor stall is the compression surge that occurs when the hot vapour generated by the aircraft carrier’s catapult is ingested by the aircraft air intake thus creating a breakdown in compression resulting in a the compressor’s inability to absorb the momentary disturbance and to continue pushing the air against the already-compressed air behind it. As a consequence, there’s a momentary reversal of air flow and a violent expulsion of previously compressed air out through the engine intake producing some loud bangs from the engine and “back fires”.

You can find several images of aircraft suffering compressor surges while taking off from airbases or being launched from the flight deck of an aircraft carrier.

As already explained on The Aviationist in the past, in most of the cases even after suffering a “surge” the compressor will usually recover to normal flow once the engine pressure ratio reduces to a level at which the compressor is capable of sustaining stable airflow.

Some engines have automatic recover functions even if pilots experiencing the surge can be compelled to act on the throttle or, in some cases, relight the engine.

Image Credit: Flight Video & Photo. H/T our friends at From The Skies for sending this over to us.

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The A-10 Thunderbolt II is still one of the toughest planes around.

On Jul. 16, two U.S. Air Force A-10s belonging to the 75th Fighter Squadron, from Moody Air Force Base, performed austere landing operations at the National Training Center at Fort Irwin, California.

This event marked the very first time Warthog pilots in a Green Flag-West training exercise landed at the NTC and to meet face-to-face with an Army ground commander: after the two aircraft landed sending up clouds of dirt, the two pilots met with the combat controllers who called them in. Then, according the Air Force, they got into separate Humvees and left the site to meet with an Army brigade commander and his staff in another location on the range.

“This meeting established rapport with the brigade and reassured them that the Air Force will be there for them when they call. By meeting with the commander and his staff and seeing the battlefield from the ground, the pilots gained an appreciation for what our ground forces go through during a Green Flag rotation,” the Air Force said in an official release.

The A-10s proved their unique capability to perform their Close Air Support, Combat Search And Rescue and Forward Air Control mission, then land in an unprepared field, to refuel and take off again to continue the fight.

Even though an airborne tanker would support real operations, the landing capability allows the “Hogs” to land to refuel on the ground if necessary: in a contested environment, the threat could be too high to have aerial refuelers support the attack planes.

Landing close to the battlefield provides additional on-station time for the A-10s.

The A-10 was built to land on an unprepared runway: the dirt won’t negatively affect the engine or tires. Thunderbolts deployed in Europe as part on an Air Force Theater Security Package have demonstrated austere landing capability at an abandoned Cold War-era airfield in Poland.

Image credit: U.S. Air Force

 

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During a media briefing held at Farnborough, Irkut‘s vice-president Konstantin Popovich recounted a funny episode that had occurred during the Yakovlev Yak-130 combat trainer first flight at the Airshow 2012.

The Russian aircraft is equipped with shields that close the air intakes for FOD (Foreign Object Damage) prevention. The system is intented to enable the Irkut-built Yak-130 to operate from unpaved/unprepared runways.

“You can not taxi because the air intakes are closed” Farnborough ATC controllers told the Yak-130 aircrew. Even after explaining that the engine-shields were a normal feature of the plane, the Tower asked if they were sure to be able to take off with the closed intakes.

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The following pictures show the Pratt & Whitney’s Boeing 747SP flying test bed at the company’s Mirabel Aerospace Centre, in Mirabel, Quebec, Canada, with a PW1217G engine flying on a specially designed stub wing.

The “fuselage’s engine” is a PW127G, designed for the Mitsubishi Regional Jet (MRJ) aircraft, that was attached to the mini-Jumbo to perform flight testing needed to complement the PurePower Geared Turbofan engine family’s sea level data collected during ground engine testing and to validate performance, operability and in-flight starting.

Not only the somehow weird test bed platform is interesting. The PurePower engine itself is worth a mention. This kind of new generation engine family uses an advanced gear system allowing the engine’s fan to operate at a different speed than the low-pressure compressor and turbine in such a way to improve engine’s efficiency, environmental emissions and noise.

However, along with the reduced environmental impact, the new geared turbofans provide a better FOD (Foreign Object Damage) resistance: as pointed out by a recent AOL Defense article, since they have a much higher “bypass ratio” (meaning that a higher amount of air sucked by the engine bypasses the core of the engine where air is mixed with fuel and ingnited), there’s a higher chance that anything sucked by the engine bypasses the most delicate part of the engine.

Furthermore, the intake fans don’t run as fast as previous generation engines and so they don’t behave as eager vacuum cleaners and the shape of the new engine is such that it can be mounted higher (on the wing) than traditional engines, increasing the distance from the ground and from all those objects that could damage it.

Although these engines are being developed for the civilian airliners, they could be much useful for all those military planes called to operate from dirty and unpaved airstrips.

Larger geared turbofans for wide-bodies could be equip future and current cargo planes, tankers, AWACS, JSTARS, and maybe the future Air Force One too (the Presidential VC-25A is equipped with General Electric engine, though).

As already explained in a previous post,  in NASA, Pratt & Whitney and U.S. Air Force have parternered to develop and test technology for improved sensors that can detect changes in vibration, speed, temperature and emissions which are symptomatic of engine problems. Such sensors should be able to alert pilots of destructive volcanic ash particles as well, before the engine is damaged.

Image credit: Pratt & Whitney

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I’m pretty sure many of this weblog’s readers have already seen this phenomenon generated at the air intake of an F-16. There is also a quite famous image of a C-17 engine, generating this tornado-like spinning vortex. However, the following picture is the first I’ve seen so far showing the vortex generated by an Italian Eurofighter Typhoon (F-2000A according to the Mission Design Series).

The picture was taken in May 2011, by Nicola Ruffino and shows a Typhoon of the 36° Stormo, based at Gioia del Colle, generating a vortex on the apron before taxiing for night sortie.

The principle is quite simple: the air is sucked into the intake generating a depression. As the pressure lowers, the air cools and the water vapor contained in it condesates and becomes visible. The process is the same I’ve explained when I discussed sonic booms and condensation clouds) and it is frequent in high humidity or wet weather conditions.

Noteworthy, if temperature is particularly low the water vapor contained in the air changes directly to ice (without first becoming a liquid). Known as “deposition”, this phase transition can cause some problem to the aircraft, in the form of engine Ice FOD (Foreign Object Damage) and intake ice build-up.