2016/07/26

Keep away from jet engine

"In thrust, we trust!"
Jet engines are powerful parts of aircraft that shall be always approached with care, based on their enormous thrust creating capability, which is the result of acceleration of gas (air) flowing through the propulsion system (engine, or engine + propeller). Actually, why jet engines are so dangerous?

Hazard warning decals on a CFM56 engine nacelle
As a civil traveler, turbofan engines are the ones you are most likely to come across at an airport (turboprops too, but let's leave them for another talk). If you look carefully, you may notice a red warning sticker on the side of the engine nacelles. If you've ever been wondering what does it mean, and never had the chance to observe it carefully, then here it is:
Speaking of turbofans engines, those are the ones with transonic velocity regime (Mach numbers from 0.75 to 0.9). Looking into the front core of the engine, the large fan can be seen, so the air entering the core first passes through the fan and is partially compressed by it. Most of the air, however, bypasses the core and goes directly to an exhaust nozzle. This is why these engines are also called as bypass engines. The remaining air inside, called the core stream, proceeds directly to its own exhaust nozzle, through a series of compressor blades (high- and low-pressure), to the combustion chamber and leavers the nozzle after the turbine stage.
Schematic illustration of major components on an engine (Trent XWB engine on Airbus A350-941, F-WWCF)
A key parameter for classifying the turbofan is its bypass ratio, defined as the ratio of the mass flow rate of the bypass stream to the mass flow rate of the core stream. Having very high bypass ratio involves the use of fans with very large diameters, even up to 3 meters. The bigger the diameter, the more efficient the engine will be. Those huge fans, rotating with large rotational speed can cause a huge suction in front of the engine. The core stream that is leaving the engine has temperature of 300-500°C, as they mix with the bypass air. Hot and strong stream of air leaving the engine can have very powerful blowing effects, as presented in the videos below. This is the reason why the one should avoid a running engine. (even a standing one can cause burning injuries if it's after operation)

Another major issue is the engine inlet and its risk of ingestion. The working principle of jet engines is based on simple physics. An operating engine will introduce low air pressure in the inlet. As a result of this low pressure, the air will move towards the engine core. As the air flows into the engine, the amount of air near the inlet will have higher velocity that the rest, further away from it. The suction is the strongest at the inlet. (Think about a similar example in a bathtub full of water. If you unplug the tub, the water will start flowing out. At the outlet, which could be our engine inlet, huge suction is present.) Due to this huge suction effect of an engine, it is dangerous for any ground personnel to stay in the vicinity of a jet engine.
CFM56 engine hazard area

The clearance distance for high-bypass engines, with 2-3 meters fan diameter, is usually about 10 m to the front and 50 m to the rare. The picture shows the hazard areas for CFM56 engine, which has fan diameter of only 1.55 meter. This area however can vary with different engine power settings.


The following collection of videos are intended to show how dangerous the blast, or exhaust of a running jet engine can be.
Starting with a van that is being destroyed by the jet blast:

Following with a famous car vs. Boeing 747 example in Top Gear TV series:

Lastly, humans can be blown away too, which occurs usually at St. Maarten:

Another topic involved with jet engines is: F.O.D.  (Foreign Object Debris/Detection/Damage), which now should be obvious why it is dangerous for the engines and rotating elements. Foreign object damage is a result of any foreign debris or object that is sucked by the inflow. The debris can come from any ground vehicle, wind, ground personnel or even from other aircraft. The importance of a clear ground and runways is therefore crucial at areas where airplanes are taxiing and flying. Not only it is a threat on the ground, as flying birds can be sucked too - known as 'bird strike' incidents. Coming back to the damage that they can cause are very varying. Engines are designed to withstand major damage that could be caused by small metal objects. Special tests have to be passed in order to give certificates to any engine. Usually a frozen chicken is shot to the engine, which has to keep all of its damaged parts inside the nacelles. They can not cause any further damage to the rest of the aircraft. The following video is presenting this testing.
The major issue here is however the functionality of the engine later on. The foreign objects could break off blades, those metal parts will cause further damage to other parts, which all will result in a reduction of thrust, or even an engine shut-down. This is very crucial when approaching the ground or during takeoff. Bird feather and bones are the most unwanted "by-products" of a bird strike, which can seriously damage the turbine blades by clogging its cooling holes.

I would like to finish with a funny but at the same time memorable example of a FOD case. It happened to a Delta Airline's plane, when during taxiing, another aircraft's jet blast blew the empty cargo container away, which was then sucked by the inlet of another taxiing airplane. All the topics of this article is covered on one photo.
Delta Air Lines cargo container in engine, Febuary 1999
Have you noticed too that the warning decals are missing from the side of the engine?


_________________

References:
  • http://www.boeing.com/commercial/aeromagazine: Fred Zimmer - Preventing Engine Ingestion Injuries When Working Near Airplanes
  • http://www.cargolaw.com/1999nightmare.html
Cover picture: Engine Alliance GP7000 engine

Video's URL, in order of appearance:

  • https://www.youtube.com/watch?v=Q6AKVMtj5Kc
  • https://www.youtube.com/watch?v=ZJ9uWsvR1l0
  • https://www.youtube.com/watch?v=eV21f1MZ5iU
  • https://www.youtube.com/watch?v=_jfXX7qppbc

2016/03/17

What is Aerospace Engineering really about?

Probably many of you (colleges) have came across the situation of telling someone about your studies like:
"-I study Aerospace Engineering..." 
"-Oh, Space Engineering? Cool!"
"-NO, It's not only about space..."

And this is the end of the conversation. (Ok, some people may be more interested and they want to know what is this about.)

"The primary focus of the aerospace engineer is the design, construction, testing, and evaluation of craft that move through the atmosphere or outer space. This broad focus includes vehicle as simple as sled, bicycle, or automobile and as complex as high performance fighter aircraft such as the F-22 Raptor, or spacecraft such as the Space Shuttle or SpaceShipOne.
Falcon-9 Rocket lands on droneship, SpaceX


Most aerospace engineers specialize in one of the four major disciplines that must be understood to design a successful vehicle or enable it to safely operate: aerodynamicsavionicsmaterials science, and propulsion."[1]

According to 'definition' it is;
"Aerospace engineers design aircraft, spacecraft, satellites and missiles. In addition, these engineers test prototypes to make sure that they function according to plans. These professionals also design components and subassemblies for these craft; those parts include engines, airframes, wings, landing gear, control systems and instruments. Additionally, engineers may perform or write the specifications for destructive and nondestructive testing for strength, functionality, reliability, and long-term durability of aircraft and parts."[2]

As I usually define it to people; it is Aircraft / Aeronautical Engineer + Astronautical engineer.

In practice, we are the so-called "rocket-engineers" or the "top engineers", which is true on one hand. We study everything from all other engineering fields, no matter what you are specializing in in the future.

I would like to summarize the graduate course in a bit deeper way, focusing on the subjects and on the knowledge they can give us. (Here, I would like to note that many universities offering this course might have different syllabus, I am presenting what I have studied during my 3,5 years.) Many future or present students may find this collection useful for their studies.
just for fun

1st year:
This is the nightmare of all freshmen students. Your previous life changes from a normal human into a totally weird/nerd/unsocial one. You will be forced to study every day, no weekends guaranteed, daily attendance+studying time a day can be even up to 16 hours. If you are from a high-school that didn't teach you the basics properly, you'll suffer more.
  • You learn calculation tools like; Algebra, Calculus 1-2,
  • You spend endless hours of redrawing your Engineering drawings,
  • You start learning a programming language; this in most cases is C (the hardest one) to help with the crazy computations that you'll meet during your studies,
  • Mechanics 1-2, Materials, Physics, Mechanics of structures, Thermodynamics, Electronics are all part of this lovely year, just to make your life harder with those other subjects that you are already failing and struggling to pass. But these basic subjects are just to be an introduction for the upcoming years.
  • If all these wasn't enough, you learn additional, irrelevant subjects, just to have an even wider knowledge on all other fields of science; Philosophy, Environment, Economics, or a foreign language. (That last one is actually important.)

2nd year (3rd semester):
Let's assume, you have passed somehow that first year and still want to continue your Aerospace course. You hear it from others that "oh, second year will be easier". Definitely, but not on this major. It may feel slightly easier, because you are adapted to such a lifestyle that doesn't involve friends, you gave up all your hobbies and you are not freaking out if you have not a single weekend in half a year. You eat breakfast at 7, lunch at 19-21pm, dinner at midnight. The 2nd year is when the fun begins. This is when you actually see airplanes on the slides and are so excited about the new subjects.
Programming a CNC machine for milling
  • Calculus 3 is giving you more nightmares, but it is now making a lot of sense.
  • Engineering graphics is turning into Computer Aided Design (CAD),
  • Fluid mechanics and Basics of Control and Automation requires you to use all your Calculus skills, even the ones you have not yet studied. (Catch 22)
  • Machine Design begins, offering all nice and practical theory and calculations related to metal fatigue, calculations for those elements that you had to draw all the time on Graphics in the last year, you learn mainly about their design,
  • Manufacturing technology will teach you how things are made.
  • Mechanics of structures 2 seems like a piece of cake and you start to enjoy solid mechanics, as long as it's easier to understand than fluids.
  • Aeronautical systems 1. is you favorite subject this semester, which you enjoy following as an aviation addict, and you want to correct the teacher about ILS. But you may not knew the operation mechanism of the HSI.
  • Finally you have other introductory subject into Aerospace, Materials in Aerospace (now a more specific one as before),

still 2nd year (4th semester):
Now you start feeling something neutral. If you have passed everything so far, you start to meet your old friends or the new ones that also passed everything, if not, you are still determined and ready to retake some subject with the new 12 others. Here is when everything gets messed up. But it is also the turning point.
  • Aerodynamics, the long awaited subject, that is as cruel as Fluid Mechanics was, but you study the air more deeply, not those pumps, dams or Hagen–Poiseuille flow, for instance. Your favorite equation is Navier-Stokes, but you still have no idea how to solve it.
    Fluid Mechanics consultation with prof.
  • Astronautics, just in case to learn something at last about the space,
  • more Electronics, labs, and Electric circuits,
  • more Machine Design (now gears, clutches, and many more fun mechanism)
  • As for other laboratories are concerned, you will have them too. Machine Design, Mechanics of structures, Thermodynamics or even Aerodynamics labs. They are really amazing and you can't wait to attend the next class, apart from the fact that you have to prepare tonnes of reports and study for entry tests. This is where you either way have to work in a team, if so far you haven't gained this skill.
  • Mechanics of Flight, together with its lovely projects. Got to choose your aircraft, but pick wisely, you will spend your next one year working on it every week. Calculations of all kinds of graphs within Mechanics of aircraft. Pretty nice subject.
  • Propulsion systems, to know how piston engines and jet engines, etc. work,
  • Last but not least, Computer science continues, or i should rather call it Numerical methods. Yeah, those Runge-Kutta ODE-s and writing C programs to calculate Gauss-Elimination and the rest.
After successfully finishing the 2nd year, you came to a point where you can take a huge breath. You are able to survive whatever comes after, and you can start thinking of going for a beer or a date.


3rd year (5th semester):

This semester is a continuation of previous subject together with additional more.
  • Aeronautical systems 2.,
  • Aircraft Design 1. your favorite subject finally has come. Theory of everything on an aircraft, structures of fuselage, wing, empennage. Nice and time consuming projects where you can start the design of you own aircraft.
  • Aircraft Engine Design 1. if you like propulsion more, here you have it.
Did I mention propulsion?
Hinge system on a UAV rotorcraft
  • Chemistry of combustion, just to hate Chemistry even more.
  • Machine Design 3, to know a bit about metal contact, and elastohydrodynamic lubrication,
  • Mechanics of flight 2., now you completely hate that chosen aircraft, but still please calculate 5 more projects about its dynamical behaviors.
  • Rotorcraft Aeromechanics, 'cos you have to answer your friend's question about helicopters too, and you had Mechanics 2. too early, so in case not to forget all the knowledge,
  • Spacecraft design, so that now people can really say that you're a "rocket-scientist",
  • Aircraft Engines Maintenance, to get familiarized about GE, Rolls-Royce or PW engines.
  • Selected Applications of CAD/CAM/CAE Systems - to learn some CAD modelling using professional software like; Unigraphics NX, or Solidworks, or AutoCAD, etc.


(6th semester):
Now you can say, you've done something. Let's say you are over half of it. Keep working on!
Business Jet wing loads calculated with AVL
  • Aircraft Design 2, still airplanes, still projects, calculations, but it is getting more fun with Xfoil, AVL for aerodynamic computations, or even XFLR for airfoil design. Your programming skills are just about to pay-off.
  • Aircraft Maintenance, to get familiarized, how maintenance of Boeing or Airbus planes are done.
  • Finite element Method (FEM), is a lovely subject after those Mechanics of Structures classes. Now you learn the same as before but applied through FEM theory and FEAnalysis. Using a software like, ANSYS, you perform some calculations during labs. (Now the word lab is always about computer aided calculations or design.)
  • Machine Design continues but this is time for your own design. Design a shaft, control system or a gearbox, up to your requirements. Calculation from scratch, hand drawings, computer drawings, 3D models and calculations, documentations and huge printout drawings.
  • let's have a bit more Physics; Quantum mechanics and Quantum Physics,
  • Simulations of Aeronautical Systems, on which you perform simulation using MATLAB software, calculate dynamic motion equation, and present your ides. Flap, rudder, aileron or similar motion systems.
  • Structure and Assembly of airframes is also an integral part of aircraft manufacturing, learning about technologies used in production, design your own jig or tooling dock.

That'd be all? No!

  • Intermediate Project, or let's say, a pre-engineering thesis. You need to choose this on your own, get a supervisor and do something 'fun' to prepare you for your actual thesis. In some cases it is also a thesis but a bit less time consuming.


You've completed 3rd year, congratulations! You can proudly pass your printed A1 size drawings to your father, show your mid-thesis that you've made but you are still not an engineer with it.

4th year (7th semester):
Now that you have completed the most of it, you will have the same amount in one semester. Just kidding, you can sit back, relax and DO YOUR THESIS! Start immediately, because you will end up making it in the next semester. Don't forget about your still ongoing subject, such as:
Static Pressure plot of a flow in a T-connection, FLUENT
  • Computational Fluid Dynamics (CFD), the lovely Navier-Stokes equation is finally about to be solved, but unfortunately for compressible flow. Don't give up yet, FLUENT is only a user-friendly version for basic flows. Imagine what people with CFD doctor degree do, they code their own calculations for turbulent flow. Aw... too hard to even thing of it. So no reason to panic about your simple PDE and ODE problems. The only reason to panic is if you have forgotten Fluid Mechanics, Aerodynamics or Calculus 1-3, and Numerical Methods. So basically all the "best" subjects.
  • FEM 2. is just a continuation of the previous, more applications, and more colorful images in ANSYS Mechanical program,
  • Simulators, it can be flight or any other. No not flying, rather theory about the design principles, operations and computer network and algorithm used.
  • Vibrations and Aeroelasticity is another integral subject of any Aerospace Engineer, so here you get familiarized about vibration phenomena, the famous flutter, but all of it's types, computation of spring supported models and many more.
  • Aeronautical Regulations is needed in case you will once design your own aircraft, so to know how the certification process is.

PZL-106 BT aircraft, CAD model of empannage
Now it's time for your final Thesis. It is not a descriptive 30 pages long, study about airplanes. No, it is engineering so do it as it supposed to be done. Design, create, calculate, model, analyse something that hasn't been done before! Something that can improve Aerospace technology in any way. This is your whole summary of learned few things. You choose your specialization based on this work. If you lack any knowledge, well, time to study on your own. When finishing it finally, you only need to worry about your final defense exam, where you just need to know all about 100 topics, related to all the subject that you've completed. (I hope you still remember what the layout of rockets are or what is the extensometry method in solid mechanics.)

This is all in a nut-shell about how to become an Aerospace Engineer graduate student!
just another day at your desk
Well, did I mention that all these years worth something if you do your Master studies too? As others often say; "this is not as hard a rocket science". I say, this is, so study it accordingly. Be a Master in it, if you want to make something out of it.

I would like to finish this summary with my favorite quotation that my cousin told be before university:
"When it gets really hard, remember that it will always be harder!"


Reference:
[1] - Aerospace Engineering: From the Ground Up, Ben Senson, Jasen Ritter, pp.4.,2011
[2] - http://www.livescience.com/47702-aerospace-engineering.html

2016/02/26

SpaceX SES-9 Mission Overview

26th February 2016 at 11:29pm UTC,

Space Launch Complex 40, Cape Canaveral, Florida, Earth

It is the second launch of the upgraded Falcon-9 rocket, Falcon-9’s first GTO mission, first attempt to try to land on a droneship and I will be writing about the special challenges of that landing. I will also be writing about the SES-9 Spacecraft and about the upgrades that were made to the pad in order to launch this more powerful rocket.

Let’s do a brief walk-through of what we’re looking at:
  • Firstly, the upgraded rocket itself and the Space Launching Complex.

  • Rocket first stage (bottom part): Carries the satellite up to the edge of space, about a 100km high, moving at about 2,5 kilometers/seconds (at the time of separation). (Usually it’s lower of that about 2 km/s for some lower Earth orbit.)

  • Interstage (second stage): Going to carry the satellite, speed it up, and carry it further towards to geostationary orbit, which is its final position that is going to.

  • Payload (top): The fairing, or the nose cone, which is made of a carbon composite structure that actually holds the satellite inside of it.
  • Just next to it, there is the transporter erector or the strong backThis is what actually carries the Falcon-9 out from the hangar to the launch pad, and then raises it up to its current position.

  • There are several lightning towers surrounding it. Florida is one of the lightning capitals of the world, and these safely direct that energy to the ground, instead of affecting some of the sensitive electronics there that are actually on the vehicle.


The launch will be a potential autonomous space-board droneship landing. After the first stage, the second stage separates, the first stage will be continuing on a ballistic trajectory towards the “Of Course I Still Love You” droneship.

About the SES-9 Satellite:
SES-9 is the 9th telecommunication satellite in the SES family, and the second SES satellite that SpaceX is putting into orbit. They will be delivering SES-9 to GTO (Geostationary Transfer Orbit) at about 38000km high (or even higher). After they drop off the spacecraft, it will use it's on board thrusters to adjust its position and to transfer from GTO into its final Geostationary Orbit.
Geostationary Orbit is so high up that it orbits the planet at about the same speed that the Earth rotates, and this makes the satellite appear like a star in the star. So it is going to be a fixed point in the sky, whenever you look up.

Let's compare this to the ISS (International Space Station) which is in low-Earth orbit, at about 300km, which is much closer to the Earth, therefore it means that the GTO orbits much faster, this is why you can see that star moving, when you look up at the sky, and you can actually see the Station transmitting across the sky. They will be dropping SES-9 over a 100 times as higher as the ISS is. To get that high, a lot of propellant is needed. They are not going to have a tonne of it left over in the first stage, they're flying back down to the droneship. In given the needs, use every single last drop of that remaining propellant to burn the Falcon-9 engines to slow it down and orient it onto the droneship, this landing attempt is going to be one of the most challenging one.
The launch window for the launch day is 96 minutes long, and the reason for that is because as the Earth rotates, the final orbit of the target that they're trying to drop the satellites up to, isn't a fixed distance from the launch-pad, which means that there is a certain window where you can get to the same destination easier than others. If they had to try the launch outside of that 96 minute window, they'd run the risks of not having enough propellant to get them to a desired orbit. Within that window, SpaceX can make as many attempts as necessary.
If they have to hold the countdown between the time of liquid oxygen loading and T-0, they'll scrub for the day, and will try again on another day. It takes probably more than the time they have in the window to offload the cold liquid oxygen and load a new batch on board.

Let’s learn a bit about the satellite technology:
SES is one of the world’s largest satellites communication companies and with over 50 satellites in orbit. They are based at Luxemburg, in Europe. SES-9 is the latest satellite in their fleet and they have planned to launch 7 more satellites between now and 2017. SES-satellites offer all kinds of service, internet coverage, date services for mobile phones, airplane wifi, SES also broadcasts 7000 TV channels, more than any other media broadcasting in the world. They have satellites that they can mobilize in just 24 hours to help with disaster communications, with satellites that enable internet access in rural areas all around the world.
For today's launch, Falcon-9 is going to put SES-9 satellite at the highest possible orbit as it can, currently targeted for around 38000km or even higher. Then after it is separated from Falcon-9, SES will use its on board, liquid propellant thrusters to perform any major launch maneuvers or adjustments. A little it will use its electrical propulsion system to help finding its final position in GTO.

About the launching process:
SpaceX team monitors the temperature of liquid oxygen. It is important to keep the liquid oxygen cold enough under the rocket, especially in the second stage. When the team has the go/no go poll, they verify that everybody is ready to enter the launch out of sequence and begin propellant loading. Next step is a precision timing sequence between the ground computers and the Flacon-9 flight computers. They want to test as much as they can, as close to launch as possible, to make sure  that everything is working. So if that ends, the're moving the throttle valves on the engines. These set the power of the engines, so they are moving them to arrange the motion, to make sure if they are working. They're also setting the gimballing of the engines, making sure the actuators and the sensors are all connected and that the engines are able to steer the rocket throughout the flight.
In accordingly about T-10 minutes, the pre-valves will be opened and began chilling in the first stage engines. Getting the Merlin turbo pumps ready for the cold temperatures at ignition, just a couple of seconds before T0 (liftoff time).
When the Falcon-9 goes from ground power to internal power, it is possible to see the clamp arms, opening up on the second stage. The erector will then start to move always from the vehicle, that happens at T-4.5 minutes. Liquid oxygen loading is going to finish loading on the Falcon-9, between T-3 and T-2 minutes.

Upgrades made to the launch-pad system:

These upgrades allows the team to further improve the reliability at once with better processing time than ever before. One of the upgrades they have made are to the hold-down system, the hold clamps that physically hold the rocket to the ground while the engine comes up to full power. Right next to those hold-downs are the quick disconnects, these hold the electrical lines and the fuel plumbing that connects to the vehicle. They have made adjustments to those quick disconnects, changing the type of springs that they were using there so that they are not susceptible to a particular failure modes. 
The second big upgrade they have made is a much bigger increase of surge of liquid oxygen. As you know the rocket runs on liquid oxygen and RP-1 kerosene fuel and both of these fuels need to be as cold as possible before they are loaded into the rocket. The whole point of adding all of these capacity is to shorten the recycle time, which is the time it takes to completely empty and reload the rocket. Previously they just had one sphere that held the whole liquid oxygen (on Apollo testing). Now they have two much longer cylinders that keep that RP-1 at super cold temperature, and they have the ability to fill the first stage in 30 minutes.
They have also made upgrades to the transponder erector because the Falcon-9 is longer and heavier, and has a more powerful engine, they had to add blast place to the bottom, so that the transporter erector does not melt at the base.
They have also added more counter weights and more powerful lift cylinders, so they can have heavier payload on top of the Falcon-9 and still raise it to launch position without any problems. 

About the Mission Timeline:
On the spacecraft site, the SES spacecraft is gone on internal power. The range is good, the upper altitude winds are good.
At T-5 minutes accounting, everything seemed good.

At T-01:41, the SpaxeX team had to call for “hold-hold-hold” that stopped the count-down.

They were in the middle of propellant load, they were just loading up liquid oxygen on first and second stage. Falcon-9 was not in any significant concerns, static fires were revealed and lit down the engines and in additionally shut them down and then drained propellants.
The rocket then come back and the launch  was postponed for couple days later. 

Wish to see a successful launch in the near future.


Reference used:
  • SpaceX.com
  • SES-9 Full Webcast, narrated by: Lauren Lyons - Mission Integration Engineer, Michael Hammersley - Materials & Process Engineer, John Insprucker - Falcon 9 Product Director, Tom Praderio - Firmware Engineer

2016/01/07

How to make airfoil profile with deflected flat, using XFOIL

The following post is intended to describe, how to generate a flap deflection on a given airfoil, using XFOIL software. The need for this kind of technique might be useful when modeling a wing profile together with a deflected trailing edge and you would like to have them as an integral part. It is easier therefore to create only one wing in your CAD model, based on the airfoil nodes that already contains the flap, for instance.

Application example: Vertical tail section with deflected rudder

(Please note, the part after the double slash symbol was used for comments only!)


Start opening XFOIL:

XFOIL c> naca0012 //This will load a typical airfoil from the XFOIL library.

It will display the following information about the loaded airfoil:
Max thickeess, Max camber, Buffer airfoil points (e.g.331points)
Panel parameters used...etc.

XFOIL c> gdes //Opens Geometry Design, to work with the buffer airfoil,

.GDES c> f //type "f" for flap definition,

Enter flap hinge x location  r> 0.6   //in this case 60% of chord,

Enter flap hinge y location (or 999 to specify y/t)  r> 999
//Here 999 is used to give y location in percentage of the total thickness,

Then it asks for that value:
Enter flap hinge relative y/t location  r> 0.5

Enter flap deflection in degrees (+ down) r> 10


After setting the deflection angle, you may look into PltLib window, where the airfoil with deflected flat is shown.
white: original airfoil, pink: deflected airfoil with 10 deg
Next command will be to execute it.
.GDES c> x

Current airfoil nodes set from buffer airfoil nodes (335)  //This tells the total number of the newly created nodes.

.GDES c> (hit enter to exit from GDES)

XFOIL c> save

Enter output filename s> naca0012_flap.dat (type a file name with or without extension)

Enter --> you may find the created *.dat file in your XFOIL working directory.

2015/11/18

When it comes to disaster

During your engineering career you will probably experience the burden of responsibility. Especially when working in the field of aviation, the world of safety regulations, you may have the fear, what if “my aircraft” fails in some way. Have I done those calculations correctly and precisely? Regardless of what you are doing, you must always do your job with full care and attention and make sure that none of the things will cause any incident, failure or worse. An aircraft has many “back-up” systems and lots of redundancy is involved but still there could be human factors, technical malfunctions or sabotage that could lead to disaster.

Recently there has been a Metrojet accident over Egypt, where an Airbus A321-200 aircraft was crashed. The final report of the investigation will most probably determine the causes of this crash therefore we have no right to state anything about it.

What I know so far, is that I was working on that specific aircraft the year before the accident. EI-ETJ is the aircraft registration code, and looking back my notes and photos, I have realized, this is the same aircraft. The aircraft had a complete C-check a year ago and a right engine replacement. Just like all the other planes, it was safely sent back to service from the maintenance hangar for further flights.

There is this strange feeling about the situation, as you feel involved in that plane’s life. Those old seats that were replaced, the old smell from that deck, the cockpit, the engines, the vibration of the whole plane that you felt during its engine test, it’s all a memory. Let’s remember for those who have lost their lives on this aircraft and hope to find out as quickly as possible the causes of this catastrophe.




Reference:

This blog has nothing to do with the airline or any nationality. The pictures are NOT for any further use or for any downloading purposes. The blog is only an engineering point of view into the aircraft industry. Any discussion related to the accident that may be insulting will be removed.

2015/11/08

Boeing 787-8, the Dreamliner


The Dreamliner for me is still a wonder, and engineering masterpiece. I’ve recently came across the following picture posted by LOT – Polish Airline’s facebook site, which just caught my attention. (this is not an advert)


Have a look at how this 'beauty' is made up or what structural elements an aviation aficionado sees.
for large size, click on the image

Thank you for the photo permission and credit to Marek Kwasowski.

2015/10/19

Weather forecasting with the help of CFD

In this blog, I am intending to present a basic equation of Fluid Mechanics, then give some related views on weather forecasting science with a help of a useful and versatile website. Finally give some hints about METAR, the meteorological "code" used by pilots.

For the sake of simplicity, let's introduce the following equation to lose 90% of the readers of this blog.

The Navier-Stokes equation for compressible fluid
It this form, the body force f has been decomposed, but the mass conservation, equation of state and equation for the conservation of energy is needed.

To write it in an even more general form:
Which written in an expanded form:
where: 









To solve the above equation, one needs to know initial conditions, such as pressure – p(r,t) , temperature – T(r,t) and velocity – V(r,t), which are usually provided.


(more about the equation in another blog: Navier-Stokes 3D fully expanded form)

Weather forecasting is basically the simulation of time-dependent phenomena, the solution of the N-S equation with the help of the known initial conditions. The initial conditions can be density, temperature, (wind) velocity and pressure. With the help of atmospheric models, one can compute meteorological information for future times at given locations and altitudes. The measures are taken from the meteorological ground stations, weather balloons and satellites as well.
Wind forecasting at surface level (Source: www.windyty.com)
Many websites provide such weather information but probably one of the best looking and advantageous is: windyty.com


The site allows you to display the streamlines of wind, temperature profiles, clouds, waves, snow and pressure information about given altitudes. Even more, by clicking to any location, the one can find detailed forecast for that location. Many more info is displayed, as the site is connected to the latest METAR-s measured at certain airports.





What exactly is METAR and how it is used in aviation?
The first thing which might be new on the above picture, under the 'Warsaw' text, is: 'EPWA', which is the ICAO code for Chopin Airport. (Each airport has such identification code but this may be the topic of another blog.) Coming back to the METAR, which is a line of code, made at each meteorological stations on some airports. This is the code that pilots are receiving and this is set into the flight instruments. Looking at EPWA's METAR code:


EPWA 182130Z 23003KT 200V270 6000 -RA BKN049 08/07 Q1017 NOSIG

  1. EPWA
    It starts with the already defines ICAO code of the airport.
  2. 182130Z
    Then follows the day and time: 18th of the month, at 21:30, Z - "zulu", meaning the local time when the measurement was made.
  3. 23003KT 200V270
    This is the average of the surface winds in 10 minute intervals.
    The first three digits are showing the direction of the wind, which in this case is 230° and the next two digits are the velocity, that is 4 knots (KT). MPS - if given in m/s, KMH - if given in km/h-s. (If the wind velocity is greater than 100 knots, it'll be 3-digits long.)
    If during the 10 minutes interval the direction of the wind has changed 60° or more and the wind's velocity is greater than 6 km/h (3kt), then the two boundary directions has to be displayed, in clockwise direction. The letter V (varied) is used to separate these directions. In our case; the wind has changed direction between 200°and 270°.
  4. 6000
    Horizontal visibility given in meters.
  5. -RA
    This section is for the actual weather conditions, given in codes. RA - rain, the negative sign means light rain.
  6. BKN049
    This field is dedicated to the clouds. The first part is the quantity of clouds, given by the numbering system following it. So 08/07 belongs to the BKN - Broken clouds category. The next three digits: 049 is the cloud base altitude in feet: at 4900feet. (
  7. 08/07
    The first two digits are the temperature, the next two are the dew point 
    in degrees.
  8. Q1017
    QNH - 
    barometric pressure adjusted to sea level, given in hectopascals: 1017hPa.
    (1013 mbar = 29.92 inHg = 760 Hgmm = 14.69 PSI)
  9. NOSIG
    Meaning no significant change is expected.
METARs for a given location (Source: windyty.com)

This code can of course change in any conditions, can have more terms, more information, depending on the weather itself. In this blog, I only wanted to present the idea behind it, of course this simple code "METAR" could be a whole course on how to write, interpret it and so on. The website has the feature that it encodes this METAR into a user friendly code, making it available to read by anyone.



I hope this blog helped to understand the compressible N-S equation and gave a useful link to weather forecasting in a fun way. Start exploring for such beautiful and colorful maps.
Pressure at 10km altitude (Source: windity.com)

Resources:
  • John D. Anderson Jr. - Fundamentals of Aerodynamics, Fourth edition, Chapter 15. pp., 2007
  • https://en.wikipedia.org/wiki/Atmospheric_model
  • https://www.windyty.com
  • CFD lectures - dr Jacek Rokicki