MYSTERIOUS OBJECTS on Planes – Nacelle Strakes by Captain Joe


Dear friends and followers, welcome back to my channel. Today: clarifying another mysterious object on airplanes, which I’m very sure many of you have seen before sitting in a window seat next to the jet engine. What is this and more importantly, what is it good for, and what’s that got to do with NASCAR racing? So let’s get started. [Intro] Now let’s imagine you looking out of an airplane window close to the jet engine, and you spot this little spoiler mounted on the upper inboard part of the engine cowling. It doesn’t move, it’s not retractable, and on most of them there’s a placard stating “no step.” What you see here is a so-called Nacelle chine or a Strake. Now to understand what it’s good for, we’re gonna have to look at this chart right here. What you see here is the lift coefficient relative to the angle of attack. And we need to interpret this chart to understand what the strike is good for. So what is the angle of attack? Now let’s say this Boeing 777 is in a climb, so the artificial horizon would show a positive pitch up attitude. Relative to the horizon, that’s the pitch angle. If we quickly look at this artificial horizon it’s little easy to understand. So the line is separating the blue part, or the sky, from the brown part, the earth. That’s the zero degrees pitch line. Now the lines above and below show the respective degrees of pitch. So here, the plane is in a climb with 7.5 degrees up, and here it’s in a descent with 5 degrees down pitch angle. Now another important angle is the flight path angle, or vector. The flight path angle can clearly be seen during takeoff and landing. You often see planes take off and their pitch angle is high, but they don’t climb as good as they pitch upwards, so it looks as if the plane is dragging through the air, which it looks very similar to this. This kind of movement So the path it’s actually climbing is the flight path vector, and relative to the ground is the flight path angle. Now similar when a plane comes in for landing, it has a pitch up attitude, but it’s actually descending, and in modern planes you can add the flight path vector to your display to see how well your plane is really climbing or descending. Now if you subtract the flight path angle from the pitch angle you have your angle of attack. The other axis in our diagram is the lift coefficient. It’s a little more to explain, but for today’s topic it’s important to know that the higher the angle of attack, the higher the lift coefficient but to a certain point, where the aircraft would then stall, resulting in a descent. This little video right here shows a perfect example of the angle of attack in regards to the lift coefficient and finally a stall. At the front You can see the angle of attack indicator. The higher it goes, the more the plane creates lift and climbs. On top of the wing you see these strips of wool. Now once the angle of attack is too high, the wool strips start flapping about, meaning the airflow is separating from the wing surface, becoming turbulent, reducing the lift and forcing the plane to stall. Now you might ask, “Joe, this is all great to know, but what’s that going to do with the strake on the side of the engine?” when an aircraft lands or takes off, its wings has to have sufficient lift at low speeds, as it is flying at a higher angle of attack. Therefore, slats and flaps are used to create further lift during these slower flight phases, but slats and flaps are less efficient if the air flow separates before even reaching the high-lift devices, and because most commercial jet airliners have their engines mounted below the wing, the engine shape itself creates an unwanted air flow separation on the upper part of the wing with increasing angle of attack. Comparable to the slipstream race car drivers profit from to get closer to their opponent. The car in front creates a wind shadow, so does the engine for the wing. Therefore, air is less likely to flow laminar over the wing, so to counteract the air flow separation, engineers came up with a Nacelle Strake, which more or less guides the air upward to the wing, and to maintain a good airflow over the slats, wing and flaps which you can clearly see here in this video. You can also call this a vortex generator as it creates an energized flow of air or a stable vortex over the wing, and due to this little strake, the plane could fly at a higher angle of attack resulting in more lift, and reducing the stall speed. You’ll be surprised to see that nearly all jet airliners have the nacelle strakes Installed. Just a few to mention, which you could look out for, is the Airbus A320, the Boeing 737, clearly under Boeing 777 and 787. Some models even have two strakes on both sides of the engines, such as the good, old [McDonnell Douglas] MD-11, and the Boeing Globemaster, and newer models such as the Airbus A350 1000 and the Airbus A320-NEO. Also, Engineers are testing retractable strakes, as today’s strakes do create unnecessary drag during cruise, increasing the fuel consumption. So make sure to get a window seat close to the engine the next time you book your flight because if you’re lucky and the temperature is low and if humidity is high, you can virtually see the vortex due to adiabatic cooling, which just looks absolutely amazing. That’s it for today. Thank you very much for your time. Don’t forget: a good pilot is always learning. Wishing you all the best. See you next week, Your Captain, Joe. [Outro]

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