Aero India 2013 !

My attention instinctively turns towards anything or anyone whenever i hear the word "jet" or a "plane". So, how could i possibly miss attending the Aero India 2013 this year !

We saw an SUV heading towards the air base as we were on our way, and the SUV driver was too enthusiastic that morning. He seemed to drive his SUV beating all others on the road. I couldn't do anything but smile, since it was obvious that all aviation enthusiasts would be more impressed with a jet flying low at breath taking speeds. I know a lot of people really love cars that have enormous engines and accelerate fast,but you know what, I like something with a little more power !

Sukhoi Su-30 MKI of the IAF

Traffic is not a new issue in Bangalore. We managed to reach there on time though and were greeted by dust covered skies and the Sukhoi-30 doing a majestic aerobatic display.However, we decided to head towards the business stalls. MOdels, there were lots of models. Sukhoi had their new Pak 50 model on display. So was BAE Hawk, LCA, Sukhoi 30 and most of the USAF jets and bombers. I still don't understand why the major aviation manufacturers do not sell any of their merchandise at the air shows. My eyes were on the models and my ears were on the roaring sounds of those jet engines out there doing manoeuvres.

B-2 Bomber of the USAF

Luckily met a PCB manufacturer who had designed a 28 layer PCB for the SUkhoi-30 MKI ! Imagine a 28 layer circuit board !

28 layer PCB of the Sukhoi-Su-30 MKI

Tiger Moth

Afternoon was all for the air display. Army was the first with their paratroopers hanging down a rope.  Tiger moth was the first aircraft though. Loved the sound of the old engine. As tiger moth flew, the mighty Sukhoi was taxiing for the runway !! 

Sukhoi Su-30 Taxiing for a display

The acceleration of the aircraft is amazing. It covered more than a thousand feet on the ground in a matter of 2 seconds and the pilots took off  right in front of us as he banked left to show the blue lit after-burners amd climbed into the skies and circled the runway and came around for another pass. He then pulled up, for a vertical climb, did a big 360 loop and levelled himself, made a 360 degree yaw, and performed a controlled fall. Seeing the Su-30MKI in action with its thrust-verctor control is more thrilling than describing them through words.

Sukhoi- Su-30 MKI - Isn't that a beauty?

Rudra

HAL Rudra was next. The aerobatics by the helicopter was quite good. The red Bull team was amazing as they always are.The French Rafale was eager to display all of its mighty power. I guess it was because the Indian Air Force selected Rafale through the MMRCA deal. The pilot was too enthusiastic to do all manouveres and really pushed the aircraft. It was a really good display.Our LCA was not behind either. The aircraft is getting better as time passes by. It was certainly more impressive than it was in the Aero India 2011.

Red Bull team with their amazing display

The Italian AWACS did a display too. ALH was really good with its display as it did a 360 degree loop.But what i missed the most was the display by the Russian Knights! Weather problems delayed their arrival to Bangalore.One Su-30 can dampen all others at the base, i wonder how 4 Su-27 jets would make one feel.





Though the IAF has a squadron of Mirage-2000, MIG-29,many IL-76 heavy lift aircrafts,An-32, i cannot fathom why the air force is reluctant to display them at the airshow.

Rafale getting ready for a vertical climb

Italian AWACS

In the end, though i loved watching all the planes flying under the scorching sun making us dehydrate, it was generally disappointing since no one at the air show was eager to display their aircrafts to the audience as MMRCA deal was done. I guess it's all about money everywhere!!

The Roaring Jet Engines !

Who doesn’t love the sounds made by the roaring jet engine of a military air craft and hate the humming sound in the commercial counterpart? Having said so many things about the planes, let’s have a look at what is the source of power/energy for these machines that help them fly.

The answer is obviously the jet engine (as it is commonly called). The principle on which it works is similar to the 4stroke engine – which has 4 stages of fuel combustion.

The 4 stroke internal combustion engine uses – Intake, Compression, Ignition and power, and exhaust strokes to deliver power to the wheels. The turbojet/turbofan engines (as they are technically called) works along the same principle. The text book definition for a jet engine says that it is a reaction engine that discharges fast moving air which generates thrust by Jet Propulsion. A jet engine loosely refers to Turbofans, Turbojets, Rockets, Ram jets and Pulse jets.

Early air crafts used piston based engines to deliver power to the rotating blades. But as the speeds of air crafts increased, propeller blades approached the speeds of sound and the piston engines were not energy efficient at those speeds. A radical method for power delivery was needed, which led to the development of Jet Engines.

“Suck –Squeeze- Bang –Blow” is the typical flow of the fuel combustion. Atmospheric air is taken in and the speed is reduced (Intake) and is compressed in multiple stages (called Squeeze) and ignited with the fuel in the combustion chamber (called Bang) and then the hot exhaust gases are sent out (called Blow) that provide the thrust.

Turbo Jets

This is the simplest form of an air breathing engine. The intake consists of several huge blades that basically reduce the speed of air that enters the engine. The output of the intake section is fed to the compressor section, where a set of blades compress the air in ratios of 15:1 or more, which in turn increases the pressure and hence the temperature of the air. This highly compressed air is typically used in modern commercial air crafts to cool the turbines / air-conditioning / cabin pressurization or anti- icing for engine inlets.

The air that enters the combustion chamber is now lacking only the fuel to ignite. Once the fuel is sprayed, the mixture ignites to generate the energy needed to provide the thrust. The burning process is a bit different when compared to piston engines. Air temperature and pressure increases dramatically in a piston engine while air temperature increases while pressure decreases in case of jet engines. Only a small portion of the compressed air is actually used for combustion with the fuel. The rest of the air is used to absorb the tremendous amounts of heat generated in the combustion chamber. The engine section is so designed that there is a layer of unburned air between the engine core and the outer walls. This unburned air when mixed with the burning air fuel mixture brings down the temperature of the mixture to levels that the turbine can handle.

The air-fuel mixture is kept to a minimum to ensure that all the fuel is burnt completely providing the maximum amount of thrust as the flame of burning fuel exits the rear of the engine producing opposite force in the forward direction.

Another method that is generally used to provide additional thrust to the aircraft is to use after-burners where fuel is sprayed directly onto the hot exhaust gases to boost the thrust significantly. The only disadvantage is that the efficiency of these after-burners is too low and an F15 fighter aircraft with full fuel load can empty itself in 10 minutes of after-burner flight!!!

Turbo Fans

Turbofans are almost similar to the turbojets. Turbofans have a turbojet core and a big fan preceding the intake stage of the turbojet. There are two variants of the turbofans. Before they are discussed, Bypass Ratio has to be understood. The ratio of the amount of air that bypasses the engine core to the amount of air that passes through the core is known as the Bypass Ratio.

Depending on the ratio, turbo fans are classified into Low bypass turbo fans and high bypass turbofans.

Low Bypass Turbofans

A Low bypass turbofan typically has a multistage compressor instead of a single compressor as seen in turbojets. Since the core is huge and heavier, the airflow into the core needs to be larger and the engine needs to produce more thrust to drive the fans at the front to operate them at their designed limits of air flow and pressure ratios. Evidently, these type of turbofans produce more thrust as the core occupies a larger volume of the engine and is mainly used in modern military jets as speed and agility are advantageous than efficiency of operation.

After burner stages exist for the low bypass turbofans which facilitate the fighter jets to fly at supersonic speeds. Since fighter jets operate at all speeds (if not all, at least supersonic and subsonic flights), an afterburner duct followed by a variable geometry exit nozzle is used. When the after burners are not used, the nozzle is at its lowest opening diameter and the exhaust gases flow out to produce enough thrust. When fuel is sprayed to the exhaust gases in the afterburner duct, the temperature of the gases increases by a large degree and the exit nozzle must be at its widest to allow large volumes of gases to flow out which have higher exhaust velocity. This can be seen in the picture of a Sukhoi Su-35 shown above with a small exhaust opening for normal operations and wider opening to the right for after burner operations.

High Bypass Turbofans

The other variant of the turbo fans are the high bypass turbofans. They evolved from the low bypass turbo fans as commercial airliners wanted efficiency more than thrust.

As the name implies, the core is rather smaller comparatively, and produces lesser thrust. There is only one large fan at the input rather than a multistage fan as seen in low bypass engines.

The amount of noise produced by the engine mainly depends upon the difference between the exit velocity of the hot gases and that of the air surrounding it. Since high bypass turbofans mix the large amounts of low velocity bypassed air into the hot air stream at high velocities, the engine noise is considerably reduced when compared to pure turbojet engines. Needless to say, high bypass engines make your journey quieter than before.

Another interesting fact to be noted is the flight of heavy transport air crafts. The concept of thrust lapse rate comes into play. As altitude increases, the density of air decreases and the thrust produced by any engine depends upon the mass of air that enters into it. Hence high bypass ratio engines need to be bigger to produce enough thrust when climbing or in cruise at high altitudes. This means that because of the high thrust lapse rates, engines are bigger and the static thrust these engines produce are very high providing huge acceleration. This lone fact is responsible for the short take-offs performed by wide bodied heavy lifters!!

Turboprop

This is another form of air breathing engine where the core is a turbojet. However, the operation is a bit different. A propeller fan precedes the turbojet core. The operation of the turbojet remains the same, where compressor feeds the combustor that produces hot gases which drive the turbine. Some amount of power generated by the turbines is used to power the compressor section. The rest of the power is fed to the propeller blades through reduction gears. A propelling nozzle that exists at the rear of the engine expands the gases which are let out to the atmosphere. The nozzle relatively provides a small portion of the actual thrust generated by the engine. The propeller blades are huge and they produce most of the required thrust for the flight. Since propeller engines are costlier, these engines are mainly used for Short take off and landing (STOL) air crafts. Shown below is a comparison of all the three types of engines.

The concept of Ramjets, which is another type of engine, has been explained in the earlier post related to SR 71. Rockets on the other hand are simpler. It is not an air breathing engine. It does not take any atmospheric air to burn fuel. Air and fuel are both carried in tanks for the operation. Both the fuel and the oxidizer are mixed and burnt in a combustion chamber and the exhaust gases are propelled through a nozzle to produce tremendous amounts of thrust.

Scramjet

A Scramjet (Supersonic Combustion Ramjet) is an extension of the Ramjet. They both use the convergent input stage to “ram” the air into the engine for combustion and hence the name. Ramjet decelerates the air to subsonic speeds for its operation as the compressors do not work in the supersonic region. Scramjets on the other hand operate totally in the supersonic region. Though the speed of the air is reduced at the compressor stages, it would still be at supersonic velocities.

The Scramjets do not have any rotating mechanical components as seen in turbojets or turbofans. The engine has three stages: A converging inlet, where air is decelerated to lower supersonic speeds. A Combustor unit, which mixes air with the fuel to produce hot expanding gases and the last stage, is a convergent-divergent nozzle for the hot gases to flow out providing the huge thrust. This engine uses the energy in the air at transonic and supersonic speeds to compress and use for combustion. As they do not have any mechanical moving parts that help in compression, these engines cannot do a standing start and do not achieve any compression until supersonic flight. This means that there is a need for alternate methods of propulsion until the vehicle using a scramjet reaches supersonic speeds. Typically, rockets are used. Another way is to carry the vehicle under a heavy lift aircraft. Shown here is an experimental aircraft of NASA using Scramjet engine.

Pulse Jet engines and Pulse Detonation engines are some other types of jet engines where combustion occurs in pulses. They have been around in the design stages from a long time, but no major developments have been seen though.

The Legendary SR-71, Blackbird

For 24 years, from 1966 through the 1980s, US leaders from field commanders to the President of the United States relied on data gathered by SR 71 Blackbird reconnaissance aircraft. Flying missions around the globe at speeds above Mach 3 and altitudes of 85,000 feet (26,000 m) or more, Blackbirds were a vital tool of strategic military decisions as their advanced photographic and electronic sensor systems collected intelligence for the Air Force and other federal agencies.

The whole program of the SR 71 started as soon as the Lockheed U2 started to become vulnerable for the Soviet missiles. The U2 was more of a glider based design which flew at normal operating speeds and at heights up to 70,000 feet which were easy for enemy aircrafts to attack. This was an easy target for missiles too as the speeds of U2 was less too. Hence,a new aircraft was needed, that would fly faster and higher and would outrun every surface-to-air missile. This led to the birth of SR-71 Program. The SR-71 is a delta wing, twin engined, and high altitude reconnaissance aircraft with a maximum operating ceiling of 85000 feet at 3.2 Mach!

The aircraft remains a technological marvel. Practically every area of design required new approaches or breakthroughs in technology. To withstand high temperatures generated by friction in the upper atmosphere during sustained Mach 3 flight, the Blackbird required an array of specially developed materials including high temperature fuel, sealants, lubricants, wiring and other components. Ninety-three percent of the Blackbird's airframe consists of titanium alloy that allows the aircraft to operate in a regime where temperatures range from 230 degrees Celsius at its midsection to 510 degrees Celsius near the engine exhaust. The cockpit canopy, made of special heat resistant glass, must withstand surface temperatures as high as 340 degrees Celsius.

A new engine design was needed too. Turbo jet engines are in-efficient at very high speeds and Ramjet engines are not efficient at low speeds. So, both of these technologies were combined to allow for a "Variable Cycle" engine that works in all the three speed ranges. Two Pratt & Whitney J58 turbojet engines with afterburners, each supplying more than 35,000 pounds of thrust, are housed in wing with diameters larger than the fuselage itself. Virtually every part of these complex power plants had to be fabricated from special materials to meet the demands of triple-sonic flight.

A moveable spike in each inlet controls airflow, retracting at speeds above Mach 1.6 to capture more air for the engines. At sub-sonic speeds and below 30,000 feet, the spikes would be in locked position and the air needed for the turbines are fed through the bleed openings. Above the speeds of 1.6 Mach, the spikes open up and are in forward position and open up 1-5/8 inches per 0.1 Mach number. The air which is let in will be compressed by the compressors and then they split two ways. One stream is fed to the core, which is the turbine; the other stream is bypassed for the after burners. The excess air is dropped out of the system through the bleed outlets. As the speeds increase and it reaches speeds nearing 3.0 Mach, the acceleration of the aircraft itself would heat up the air too much and then compression of the air and another round of compression within the turbine would increase the air temperature tremendously. To compensate the high temperature of the air flowing through the turbines, the air: fuel mixture that is fed to the turbine is reduced to prevent the turbine blades from melting. Thus the SR-71's turbojet components produce far less thrust and the Blackbird flies most of the times with more than 80% of the thrust generated by the bypassed stream of air that is ignited in the afterburner stage and generating huge thrust as it expands through the nozzle.

This meant that the jet needed a new fuel too. The fuel not only was needed to act as a source of energy for the turbines, but also as a coolant/heat sink for the engine and aircraft accessories, air conditioning systems and TEB (Tri Ethyl Borane) tanks and control lines that actuated the afterburners. Engine oil is cooled by the main engine fuel through a heat exchanger and cooling pipes. The fuel was also used in most of the engine hydraulics too. This meant that the fuel needed to possess properties such as high thermal stability and should not break down at high temperatures and form coke deposits or damage the fuel tanks.

This criterion led to the development of JP-7(Jet Propellant 7) grade fuel. It had a huge thermal stability and a high flash point. The fuel was so stable at normal temperatures that, if you drop a lit match into a can of JP-7 fuel, the match would go off; but would not ignite the fuel. This led to another problem. The engines do not work without the fuel. This new fuel does not ignite at normal temperatures. Adding a servo motor to assist in air compression to ignite the mixture also would not solve the problem. Thus a new compound, Tri Ethyl Borane (TEB) was used. This chemical ignites at the first contact with air and it proved to be a good starter for the SR-71's advanced engines. Hence, every aircraft has a small tank of TEB containing up to 600cc to start the engines. This is the only limiting factor for the aircraft for long range operations because the SR71 has to turn off the after burners to refuel and the small size of the TEB tank limited its range as TEB was used for igniting the after burners too would last for 16 ignitions/re-ignitions.

Overall, the entire design of the plane was too far ahead in its technological achievement at that time and even new factories had to be built to manufacture them since normal tools could not be used with titanium based structures. Every aircraft that was built till this date was hand made and each aircraft had a unique response of its own. All this meant that the SR 71 which would be spying on an enemy had to just push its throttles full forward as soon as it sees a SAM alert.

Though the Blackbird was decommissioned from service in the 1990's, researchers are looking into using the SR-71 design along with aero spike engines to use this as an Reusable Launch Vehicle for space programs.

All these things remind me about the quote at the entrance to the SR-71 Hangar at Kadena Air Base in Japan.

"Though I fly through the valley of death, I shall fear no evil for I am at 80,000 feet and climbing"

Sukhoi- The Emperor of the Skies !!

Military information from the Soviet Union was subject to the most stringent secrecy until the Paris Air Show in 1989. The Sukhoi Design Bureau displayed their Su-27 to the public and it instantly became a sensation! The public display not only amused the experts, but also baffledthe enthusiasts with its stunning display of aerobatic maneuvers.

The “Cobra” is the most popular among them. The Sukhoi could fly in level and pitch up its nose by 120 degrees and return back to the same leveled flight and still be in the control of the pilot. The manoeuvre gets its name because a cobra does the same with its hood.

I’d say that the Sukhoi Su-27 completely redefined the meaning of maneuverability.

The prototypes built in 1980’s came with the FBW control system and backed up with a manual control too. Though the Russians didn’t like to use much of electronics in their jets, the Su-27 surprisingly came with electronic displays and HUDs. Hands on Throttle and Stick (HOTAS) principle was used where all critical operating elements and controls are available on the thrust control lever and the control column (joystick).

Notice that the Su-27 has a hanging nose and a rolling front fuselage. Many pilots still call the Su series as the CRANE. No doubt, the Sukhoi looks elegant. But there are more aerodynamic reasons to its beauty rather than the aesthetic ones. The drooping nose for instance gave the pilot a near to 360 degree view of the environment he was around. Of course there are electronic displays that can give you all the information you need, but the pilot’s capability to understand the environment around him is higher if he can see through his eyes!

The Sukhoi also came with a revolutionary wing design, which makes it unbeatable. It is called as the “Strake Wing”.

The striking features are its variable sweeps within a wing. Closer to the Fuselage is a steep sweep, which makes it more efficient when flying at supersonic speeds, preventing the appearance of rhythmic shock waves. It is then followed by a gentle slope which is a common practice in wing design. Thus the steep sweep improves stability at high speeds; while the gentle sweep along with the fuselage provide a good lift to the massive fighter at low speeds.

Even, the cockpit is elevated from the fuselage as seen from the figure. This not only allows for a good view around, but also has some aerodynamic importance. The air flowing over the cockpit creates a natural low pressure region right behind the cockpit thus providing a good lift without the use of any thrust vectoring principles.

Further improvements over the initial Sukhoi design was done over the years and each of those fighters and bombers are brilliant in their own way! Thrust Vectoring, Canards instead of steep slope to provide additional maneuverability at low speeds was introduced in Su-30. A long range bomber version was also developed. It was so massive that the Su-34 could fly from Moscow to Paris with only a full load of fuel in its internal tanks!!

All these improvements over the years have earned Sukhoi a great deal of respect in the fighter jet community. Most of the manoeuvres that the fifth generation fighter jets do today, the Sukhoi was able to do the same back in 1990s!!! It is evident that the Sukhoi did designs that were more practical and simple.

It was estimated that the design was future proof for at least 20 years. But, that design is still in use and is evolving into more advanced fighter jets. All these make the Sukhoi an EMPEROR of the skies.

The Air Show Experience !

"Why are you here at office today??" , " Will it be good this time?" , "Are you attending the air show?" , "Where is it? update me with the details?" , "I may not attend. I'm not as enthusiastic as you are!" ,"I'm sure you're not going to miss it" These are the reactions that i got from people around me about the Aero India 2011 which was held at Yelahanka Air Force Base in Bangalore.

On the inagural day, my cousin kept pinging me about what was going on at the Air Force Base(AFB).I was at office and couldn't stop thinking about how much fun it'll be tomorrow seeing the flying birds. I barely slept that night. I was so excited about attending my FIRST ! Air show tomorrow.

The D-day came and there we were, me, my brothers and a few friends. While driving to the AFB, we were greeted by the LCA doing some manoeuvres, a few kilometres from where we were parking the vehicle. Had to take a bus from the parking lot to the base and the F 16 and F 18s that flew during that time made the structure of the whole bus vibrate !!

We enter the gates and there's a long queue to put me into a sad state. Luckily, we got in soon.The first plane i saw from a very close distance was the GA8-TC Airvan from Mahindra Aerospace. It was quite good, but my eyes were searching for a special one ! I was looking for the Sukhoi Su 30 MKI. I've always been awe struck by the amazing manoeuvres it can do. I couldn't find it ! But there were all the planes that i wanted to see though. A whole bunch of private jets, heavy lift transport aircrafts, mid-air refuell tankers, attack helicopters,fighter jets, turbines and a lot more !! I then decided to take it slowly and see all of them one by one.Luckily, got a chance to talk to a french guy from Eurocopter who was kind enough to let me into their Fennec helicopter and feel the controls of the machine. Loved the whole experience with the helicopter. Asked a few questions about it and then took a few pics and headed into the business stalls at the large hangars.

I'd say i have a small collection of tiny model planes and its definitely hard to find good ones here. But, as soon as i entered the hangars, i was overwhelmed to see a lot of detailed large scale models. I have no idea if such big models are available for purchase; but,if it is, I so badly want a lot of them! Went through most of the stalls staring at all those pretty models and saw some cool hardware and test equipments used in the field of Avionics. It was lunch time by then and the weather was hot as hell, added to that was the open areas at the base,and we all were totally exhausted and needed some energy to keep going for the whole noon.

The first display again after lunch was by the Light Combat Aircraft and yes it did fly well, but wasn't that impressive when compared to other jets. I think the test pilots did not want to push the aircraft to its limits as the testing of that aircraft has just begun.And then there was the Intermediate Jet Trainer, it didn't fly fast or do any stunts in the air, but then its a trainer aircraft right?

The next display was by the Russian made Sukhoi Su 30 MKI of the Indian Air Force. Needless to say, its the emperor of the skies and it flew like one. Didn't do the breath taking stunts like the Cobra or the Kulbit, but that was the first aircraft on which i saw the afterburners on. The light blue colored flame from the exhaust nozzles looked great while the whole base was vibrating with its noise. I must say, roaring jet engines is an understatement !

Then was the display by the Eurofighter Typhoon. It's a very small aircraft designed for medium range operations but the capabilities it has are many.I had under estimated that its flying would be not that great and the typhoon took me by surprise.Then came the famous F 16 Falcon and the F 18 Super Hornets. Both the planes performed well and the F 16 pilot did a continuous vertical climb for more than 1500 feet over us and it was a delight to watch it. Low Fly-by, steep turnings, low fly-by with afterburners, steep vertical climbs and a whole lot of other manoeuvres kept the audience wanting to see more.The Sukhoi Superjet and a Saab private jet also did some stunts in the air and we simply hadn't expected such manoeuvres from them.

The red bull aerobatics team were really amazing. They were led by a lady ! Not many women pilots get to lead a stunt team and the stunts which the team performed were wonderful.Then was the turn of the MI 26 choppers and the Saarang team. They did quite well.At last was that of the Suryakirans, our aerobatics stunt team from the Indian Air Force. Used the tricolor of our flag for the trail on their flight path, flew overhead at high speeds, made some close encounter stunts and at last drew a heart with a pierced arrow in the air !

All those planes did so many stunts that are simply hard to explain. Added to that, in between those flight displays, the test pilots who flew the jets used to walk around and make the crowd envy them ! I'm not sure of the crowd, bit i did envy those pilots for sure.

It was just me and the planes all through the day. I realised that day how much more there is to learn about these machines.They still continue to impress me ! I have no clue how time flew so fast that day and towards the end of it, i had about 5 kilos of brochures, around 800 pictures of planes and helicopters, atleast 15,000 crores worth of planes behind me,a tired body but a very happy and satisfied me.

Wonders of FBW

Now that the FBW system related to Commercial aircrafts is clear, lets look at the more exiting part of this technology. That's the FBW Control system of military aircrafts !

Though the whole architecture remains the same,the way its tuned by software to operate for much more extreme conditions is what makes this architecture more interesting. The number of control computers and control surfaces will increase for sure as fighters and other military aircrafts are more agile and powerful than their commercial counterparts. Though the control
systems are customised with each and every aircraft, I'll be looking into a few popular aircrafts and their control systems.


For example, consider the Boeing B2 Stealth Bomber. Just at the first look, the plane seems to look too flat or thin for its size. Notice that the plane does not have a tail too !! It's a known that the tail of a plane is responisble for a large percentage of the Radar Cross Section (RCA) So,Boeing just decided to remove the tail itself ! But they are still managing to fly the plane by continuous control of two control surfaces on either sides of the wing which require frequent adjustments to be made, which can only be done through a computer.




So is the case with an F 117 Stealth Bomber. Its unique shape comes because Radar signals are completely reflected in some other direction instead of bouncing back to the transmitter.This is what makes it a stealth aircraft. The bad shape gives the plane bad aerodynamic efficiency and control ! This can obviously be managed by a computer alone.





Similarly, the V22 Osprey has a unique deisgn. It can operate both as a helicopter and a plane. It works as a helicopter during landings and take-offs. This dual functionality is a part of the design because this feature makes it a utility flying machine and does not need a runway and that makes it very mobile. It operates like an aircraft when its cruising as the efficiency of a plane is more than a helicopter. However, the transistion from the rotors being upright while landing and take offs, to tilting by 90 degrees while in cruise is very crucial and requires a lot of precision and is done by computers rather than pilots. This is one of the reasons why the Harrier Jump jets used to crash a lot during take offs while the F 35 on the other hand can operate smoothly without any considerable risk when compared to the harrier jet.



Artificial Stability is another advantage of the FBW. Instability is deliberately fed into the system and is then controlled by computers for better performance. Consider the Eurofighter Typhoon. While it is taxiing on ground or parked, the nose of the plane always pitches up. This means that the center of gravity for the plane is far from the center and this gives us an advantage! The plane has a tendency to pitch up very easily. The climb rate for such an aircraft is higher than a normal plane. However the plane operates as usual without pitching up all the time as it is controlled by a computer rather than direct control of the pilot. We induce instability into the system and then create stability artificially using computers,hence the name.

With this, posts related to FBW ends.That puts us into thinking about one thing.

Who do you think is really flying the plane ?? Computers or Pilots??

Fly By Wire Architecture

I am somehow inclined towards Airbus than Boeing for many silly reasons. Not that i dont like Boeing, its a wonderful company.They have made some of the most innovative and amazing air crafts. Airbus on the other hand is an EADS company in European region where people speak a lot of languages i like, located in France - a place i want to visit. They have built the biggest commercial airliner till date and so on. Hence, I will be looking into how FBW is implemented in an Airbus aircraft.

Why do we need Fly by Wire? Is it just electronic control instead of conventional ways of controlling an aircraft and having flashy big screens and hundreds of buttons all over the cockpit?? Or is there something else??

There's certainly more.. Fly by wire has a lot of advantages. There is improved flight handling, operating within the flight envelope, reduced maintenance cost and weight. Safety improvements too.

So, how is it all done?

We know that there are both primary and secondary control surfaces to be managed. From the earlier post, its also known that they are controlled by a computer too. The advantage is that there is redundancy at all levels - control surfaces are redundant, computers are redundant, power supplies to these computers are redundant too. There is always a dissimilarity in the hardware and software used on the flight computers so that the common mode failures are eliminated.


The pilot's demands go to the computers. The word "Computer" is so generic here and it is actually a combination of multiple systems together.There are three units within it:



2 Elevator and Aileron Computers (ELAC)
3 Spoiler and Elevator Computers (SEC)
2 Flight Augmentation Computers (FAC)

These computers manage the electrical signaling. Two computers are dedicated to data handling from the control computers for indication, warnings, maintenance and recording purposes.

Thus we have 7 computers to handle the signaling with ELAC using Motorola 68000 IC, SEC using the first of X86 based processors, the 8086 and FAC using the 80286. Can't stop thinking how small and low performance devices these IC's are compared to the Gigahertz processors of today ! Even then,they manage such a huge aircraft !

Different software languages are used for each channel. Popular ones being C and Assembly level languages and usually another custom language developed by the aircraft manufacturer.

Each of this computer is capable of detecting errors in its operations, stop its control over the surface it manages and interrupt the other computer that he is not controlling the surface anymore. However, all the computers will be generating the control signals that are necessary while ONLY one of them is actually controlling it.

The architecture of the FBW System is as shown in the diagram. SFCC is the Slat and Flap Control Computer.



The architecture of each of the ELAC/SEC/FLCC is as shown.

There are two parts, Control and Monitor. Control unit is responsible for generating the electrical signals while the monitor is constantly reading the mechanical movements of the parts. Since all of us are pretty good with drawing and developing our own algorithms and architectures, I'm not going to talk of every single little detail.


At last, when you see both the pictures and try to put the structure of each computer into the FBW architecture and imagine the bigger system in mind, you can see how large and complex the whole of Fly-By-Wire System is :)


After going through all this architectures and all of the technical blah-blah, I'm sure there is a big mystery in your mind :)

What does this all mean to me when i fly ??? !!!


Well, the FBW System will not allow the plane to do manoeuvres which cross certain limits when considering a commercial aircraft. It WILL NOT allow the pilot to pitch more than 15 degrees while in flight and pitch only up to 30 degrees while landing, not bank more than 33 degrees at any point of time so that your drink that you paid for will not spill over you.
Even if the pilot tries to bank your plane to more than 33 degrees, the plane may bank for a while until it has processed that the banking angle is out of limits and the system automatically reduces the bank angle.There are a whole set of rules that are hard coded into the system so that your flight is as comfortable as possible.

This Architecture speaks of how to keep the plane within the operating limits to make sure the passengers enjoy their flight over the clouds. But, there is another much more interesting face to this.How can this be used to achieve the impossible ?? Any guesses of what i am talking about ?