Caught on video: an RNoAF F-16 ingests a bird during take off.
Birds ingested in aircraft engines can have devastating effects. The video below, shared on Twitter by Stephen Trimble, Aviation reporter and editor for Flightglobal’s Americas bureau (@FG_STrim), was reportedly filmed on May 7 at Kjeller airport. It shows a Royal Norwegian Air Force F-16 taking off for a test flight following maintenance activity.
At 00:19 you can clearly see the aircraft’s engine emanating flames (generating a loud bang) in what seems to be the typical behaviour of a compressor stall. Without retracting the landing gear, the F-16 continues to climb to perform an emergency landing a few minutes later at Oslo Gardemoen.
We have often commented videos of photographs of jets suffering compressor stalls. Here’s the explanation we published last time:
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”.
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.
According to the reports issued later by the RoNAF, the aircraft suffered a “birdstrike”: the bird(s) got sucked into the F-16’s air intake causing the compressor stall and the consequent distinct long flame.
Here’s the May 7 incident, filmed from distance at two different locations:
We have received an email from Pierric Joseph, an associated professor in a engineer school) that provides more accurate explanation of what a compressor surge is. Here’s an excerpt from PJ’s message:
“You state that compressor surge is a particular case when engine ingests hot vapour generated by launch catapult, this is not totally true.
The general phenomenon is compressor stall. It can be divided into two categories:
– Compressor surge : all the rotor blade blades “lose” (i.e. the airfoil stalls like an airplane wing) the airflow at the same time, then get it again, then lose it again, etc. Due to this particular motion, we call it “pumping” in my language.
– Rotating stall : only a few blades on the annulus “lose” the airflow, and you get some kind of stalled pockets (you can have several of them) which rotates with a different velocity than the rotor (and in the opposite direction).
Usually, you go to rotating stall then to full stall (or surge). So the actual challenge is to detect early warning of the rotating stall and to take the appropriate measures.
Another cause of compressor stall, if you want to be more exhaustive: you can add smoke ingestion due to missile shot (some particular engines go to special mode when firing missile – not a secret thing, it is even written on some wikipedia page for some particular engine).”
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”.
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.
A quite embarrassing episode marked the end of MAKS 2011 air show on Aug. 21, at Ramenskoye air base, near Moscow. The Sukhoi PAK-FA/T-50, Russia’s 5th generation fighter plane, was forced to abort take off after suffering a flameout in the right-hand Saturn engine.
As below footage shows, the T-50-2, the second prototype of the stealth fighter (52 Blue), aborts its take off roll after bursts of flames erupted from the engine.
Deploying the airbrakes and the two drag chutes after reaching a speed of around 60 MPH, Sukhoi’s test pilot was able to halt the aircraft well before the end of the runway.
If the PAK-FA flameout in front of some 200.000 spectators had only a negative impact on Sukhoi’s reputation, similar engine failures can be quite thrilling if they occur to fully loaded planes in dangerous phases of a flight: departure, initial climb, landing.
I took the top picture in the Indian Ocean aboard USS Nimitz (CVN-68) on Oct. 19, 2009. An F-18C (BuNo 165205 Modex 405) belonging to the VFA-86 “Sidewinders” experiences a compressor stall during the catapult launch from CAT number 4. The aircraft is fully loaded with fuel and weapons, and it is taking off to perform an on-call CAS in support of Operation Enduring Freedom in Afghanistan.
Fortunately, the aircraft took off in spite of the loud bang and flames coming out from the port engine exhaust that in the second image seems to be operating without the afterburner.
Here’s the entire sequence of the launch showing the single engine departure.
The compressor surge is a particular kind of compressor stall 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”.
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.
Compressor surges are frequent on U.S. aircraft carriers. Unlike the T-50, that could precautionally abort its take off, carrier air wing airplanes can’t stop their run once it’s started. Fortunately, F-18s are used to take off even if an engine is temporarily unserviceable: this shows once again how rusty Legacy Hornet are sometime tougher than some 4+ or 5th generation “colleagues”.
When, last year, I visited the USS Nimitz and had the opportunity to take the following picture (Part 1 and Part 2)
I didn’t think that compressor stalls during “cat shots” (catapult lauches) were frequent events. However, a quick look at US Navy website let me realize that compressor stalls or compressor surges are common (most probably?) because the hot vapour generated by the catapult is ingested by the aircraft 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”.
The following pictures are all US Navy images taken from the official website: http://www.navy.mil
In the previous post “Compressor stall…in the worst case scenario” I explained what a compressor stall (or surge) basing on a picture I took aboard USS Nimitz. I uploaded an image within that post that I created by merging two pictures I took one after the other. Since that picture provided a view of the last few seconds of the catapult launch by a VFA-86 F-18C, I thought it could be interesting to publish the whole take off sequence that you can find here below.
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