LCA news and discussion

[shiv]

Right, I see it on the Typhoon. Surely it is an intake of some sort but I would guess that most computers on the aircraft will be near the nose and the cockpit and not so much near the tail and the typhoon cutaway kinda supports that theory.

There is no rule that cooling ducts or electronics have to be in a particular place. Cooling air intakes can be used for electronics as well as for cooling other hot items - such as liquid coolants/oil.

Also it surely wasnt an original design feature on the first 2 manufactured Tejas and was added later, so should I presume that overheating of ?avionics and computers was an identified problem?

You can presume whatever you feel you need to presume, but the earlier aircraft not have the all the planned equipment in place, because they were initially testing only the flying characteristics. More and more equipment was added with later builds.

[geeth]

>>>There seems to be a ?secondary inlet of some sort just where the tail meets the fuselage on some tejas like KH 2012 while missing in older ones like KH 2002...any idea about what it may be? I have not seen any such thing in other aircrafts.

Isn't it the air intake for the auxiliary turbine for restarting the main jet engine in mid-air?(developed by HAL, forgot the exact name for it)

[Natt]

Dear Shiv and Kartik,
If you see, my original post about this topic is in form of a question. Clearly, I admit I did not know what the particular structure was. I was offered an explanation and I was trying to understand the whole thing. Suddenly comes the whole treatment thing.. have you seen cars with ejection seats , comparing apples and oranges, presume what you like, i this and that... wow what was that all about.
When someone asks a question that clearly means he/she doesnt know it. Try helping out and not ridiculing.

[Kartik]

Dear Shiv and Kartik,
If you see, my original post about this topic is in form of a question. Clearly, I admit I did not know what the particular structure was. I was offered an explanation and I was trying to understand the whole thing. Suddenly comes the whole treatment thing.. have you seen cars with ejection seats , comparing apples and oranges, presume what you like, i this and that... wow what was that all about.
When someone asks a question that clearly means he/she doesnt know it. Try helping out and not ridiculing.

don't play the victim here. you first said you'd not seen it on any other fighter. I pointed out the Typhoon. Then you said you guessed that avionics or computers are not kept that far from the cockpit or radome, which is also false and I pointed out the Gripen, where the FCS computer and air data probes are near the tail root. all this was done in a civil manner so I don't get why you're upset.

then you made that statement about air-cooling saying that even cars today have better solutions. That indicates that you don't understand what drives designs in aircraft. I simply pointed out that its not a valid comparison at all to say that something exists in cars so implying that aircraft designers are behind the curve by use air-cooling. So, to show the fallacy of your line of argument I pointed out a few aircraft technologies that production cars don't have because each has its own requirements and those requirements drive the design..does that mean that car designers are not up to date ? no it doesn't.

Then you said something about the first 2 prototypes not having this ram-air scoop so it was an afterthought..well many things in all kinds of products are afterthoughts- when testing starts you realize something was missed. In the case of the Tejas, my guess was that the TD's didn't need the ram-air scoop because they lacked certain instruments and avionics that were added later on on the production variants. is that clear now ?

If you don't know what you're talking about as you say, then please desist from making claims without having researched them first a bit. At least thats what I do. As I've pointed out above, your statements were all inaccurate and I merely pointed that out. If you feel that you're being treated badly because you're new here, well that's got nothing to do with it. and what is all this cribbing about "this or that" or ridiculing you? no one did that, so don't make a fuss over it.

[vcsekhar]

Questions for experts..
There seems to be a ?secondary inlet of some sort just where the tail meets the fuselage on some tejas like KH 2012 while missing in older ones like KH 2002...any idea about what it may be? I have not seen any such thing in other aircrafts.
If you see in the formation picture..the lead the rear two aircraft have it and the middle 2 do not.

Right, I see it on the Typhoon. Surely it is an intake of some sort but I would guess that most computers on the aircraft will be near the nose and the cockpit and not so much near the tail and the typhoon cutaway kinda supports that theory. Also it surely wasnt an original design feature on the first 2 manufactured Tejas and was added later, so should I presume that overheating of ?avionics and computers was an identified problem? also was it solved by letting it be air cooled? I mean even Cars are doing better than that.
Could it be a gauge inlet of some sort for air speed, temp..?

I think that shiv and Kartik took an issue with this post... and I can totally understand why.
The first post was an innocent question, however the second one after a simple explanatory post was not. When you say things like
"so should I presume that overheating of avionics and computers was an identified problem? also was it solved by letting it be air cooled? I mean even Cars are doing better than that."
is bound to upset the more experienced members who took the time to explain the issue in the first place. Also don't presume that basic things have not been taken care of by the LCA designers, when they have developed a modern fighter with extensive use of composites and a full digital FBW system from scratch, they have the brains and the engineering know how. which btw has only been done by a handful of countries till now USA, RUS, UK, FR, I dont think that China, Brazil counts as yet. etc. Dont insult them like this.

So again if a beginner has a basic question that has been discussed many times in the past search the archives and then post.

chandrasekhar

[shiv]

When someone asks a question that clearly means he/she doesnt know it. Try helping out and not ridiculing.

Ridiculing? Excuse me? Was there something about my reply to you that you construed as "ridiculing"? May I point out that my post was entirely factual and heartfelt, and carried the same tone and tenor that your post did. If there was something you did not like about my reply, maybe you can understand that there was something not particularly likable about the way you phrase your innocent questions that made more than one person give you replies that you don't seem to like.

[Natt]

I rest my case. I am here to share my enthusiasm of military and not to argue, specially, about things I dont know. Never intended to offend anyone.

[Satyendra]

pranam to guru log, this is my first ever post on BR and i am excited
natt - first things first let me congratulate you for raking up the topic of "ram air scoop"
you identified the change which means you are curious and closely following the LCA discussion thread
i also thank "shiv and karthik" for their beautiful posts and find nothing offensive in the content,
infact i see a lot of restraint in their post of not to hurt you

[karan_mc]

its seems to be Air intake for Auxiliary power supply

[jaladipc]

Most of the electronic parts including mission computer and others were placed behind the seat.

And that intake infront of the vertical stab is for ramming the additional power supply units and also for cooling the electronics.

[neerajb]

Now my question is if the aircraft goes out of control in 250 ms than how come the actuator cycle of 500 ms controls the Tejas?

As far as Mechanical Control System goes, it does not really make sense to make correction very quickly, remember that the control system are made up of devices like Motors, actuators. These have their own response time, i.e. if you give a input to motor at t=0 sec , it will take some finite amount of time for the motor to respond and reach the steady state value(position wise or speed wise). So if you give a different input before the motor reached previous steady state value , the effect of previous input does not take place.

So usually the update for mechanical control system even in bodies moving with very high speed like Missiles takes place at less than 10Hz.

Shubham, the low refresh rate of physical actuators is obvious. I guess you didn't get my question right. The author wrote that an unstable configuration can't be flown by a human because of slow reation time of 500 ms. Further he says that aircraft would go out of control in a quarter of a second i.e. 250ms unless a correction in control surfaces (actuators) is applied before that. So for Tejas a refresh rate of atleast 4 cycles per second or 4 Hz is required whereas the actuators are moved every 500ms or at a frequency of 2 Hz.

Cheers....

[Shubham]

Shubham, the low refresh rate of physical actuators is obvious. I guess you didn't get my question right. The author wrote that an unstable configuration can't be flown by a human because of slow reaction time of 500 ms. Further he says that aircraft would go out of control in a quarter of a second i.e. 250ms unless a correction in control surfaces (actuators) is applied before that. So for Tejas a refresh rate of atleast 4 cycles per second or 4 Hz is required whereas the actuators are moved every 500ms or at a frequency of 2 Hz.

Cheers....

My explanation would be that(assuming what is said in the book is correct ) , We know that we have a constraint that we can't provide new input to the actuators before 500ms (according to the book), and also the sensor and computers are continuously running their computation and say one iteration of that computation takes 100ms.

So after end of every 100ms I have a new values of various errors and also new input values for the actuators. But I don't give this new input value to the actuators and keep on adding the calculated errors.
At the end of 5th iteration (ie 500ms) I have a value of error which is cumulative sum of the error derived from 5 previous iterations and based on this cumulative value, I find out the corresponding input value for the actuators.


The whole point being that with DFCC, we can hold back the input to the actuators till a certain time and calculate the input corresponding to the cumulative error.

In case of human, it would not work because he can't make sure of the "cumulative" part of error calculation, the moment you give a correcting input, the actual value of correcting input required has changed and this lag will make the flight uncontrollable.

[nikhil_p]

To understand why actuators have a higher time delay, you need to understand how they work. Almost all actuators are driven by hydraulic pressure. A hydraulic system has various parts. E.g: liquid container, flow lines, valves, pump, crossover valve, etc. The fluid has a certain coeff of stress, which if exceeded can lead to rapid degenration of the fluid. Also, it takes some time (in ms) for the flow pressure to transfer. Also the actuators have a cylinder which depends upon flow pressure. The hoses are developed keeping a certain fow pressure max level in mind (500-5000 psi for example). However they will generally work between 45-75% capacity to maintain cost efficieny. All this adds to the time delay in the actuator actuation.

[Neshant]

how about using two actuators timed to be offset from one another by exactly half the reaction time of each. onboard electronic sensors can surely calculate the next position of the aircraft ahead of time and feed it to the second actuator to get it going before the first actuator is relinquished. As soon as the second actuator kicks in the first actuator begins to set itself up for the next calculated position and then engages immediately when its turn comes.

that could also act as redundancy but i guess weight is an issue. actually i don't like this design as its needlessly complicated.

perhaps some device other than hydraulic actuators are needed faster reaction, better precision and control. maybe electromagnets !? surely YINdia can design an electro-mechanical device that's light weight and operates faster than a slow actuator.

[shiv]

An aircraft is constantly being buffeted by high winds. Some of those winds may cause a sensor to sense that sense that the aircraft is going to go nose up - but that "nose up" push may itself last for just a few milliseconds as that gust passes, with the next gust causing nose down. So a sensor that triggers a reaction in an actuator 10 times a second may be too sensitive cause too many needless actuator movements.

Human reaction time is 0.2 seconds for visual cues, but longer for cues felt in the body like rolling or pitching, and there is an additional lag between human movement and actuator movement and a further time lag between actuator/control surface movement and response of the aircraft to that control surface movement. In a complex scenario with multiple sensor inputs from buffeting as well as pilot hand/body movement from physical jerking and G forces a plane could go out of control (or may be less easy to control), but the FBW will read inputs several times a second and feed just the right input required to react to changes twice a second which is adequate to help the pilot fly the aircraft without uncontrollable jerks. This gets all the more important in a situation of tight maneuvering where the pilot is overloaded with sensory cues and the FBW stays online to prevent needless actuator movement retaining controlled flight within pre-defined limits.

[shiv]

To understand why actuators have a higher time delay, you need to understand how they work. Almost all actuators are driven by hydraulic pressure. A hydraulic system has various parts. E.g: liquid container, flow lines, valves, pump, crossover valve, etc. The fluid has a certain coeff of stress, which if exceeded can lead to rapid degenration of the fluid. Also, it takes some time (in ms) for the flow pressure to transfer. Also the actuators have a cylinder which depends upon flow pressure. The hoses are developed keeping a certain fow pressure max level in mind (500-5000 psi for example). However they will generally work between 45-75% capacity to maintain cost efficieny. All this adds to the time delay in the actuator actuation.

Nikhil aren't FBW actuators motors, not hydraulic?

[rad]

The Ram air scoop at the base of the fin is for cooling the space between the engine and the airframe, I had asked the guy near the LCA model at aero india 2007 and this was his answer, especialy during after burner engagement there seems to be a lot of heat generated which was concerning . As far as i know there is no oil cooler or avionics cooling apparatus there. All a/c have scoops around so it is not new .

rad

[SRay]

From prior reading, I believe one of the main purposes of the rear dorsal inlet is to cool bleed air. This bleed air, taken from the engine after it has passed the compressors, is used for [many purposes](http://en.wikipedia.org/wiki/Bleed_air) from de-icing to pressurizing the cabin. However, if the engine gets too hot, the bleed air must be cooled by new air brought in by the inlet.

[rakall]

From prior reading, I believe one of the main purposes of the rear dorsal inlet is to cool bleed air. This bleed air, taken from the engine after it has passed the compressors, is used for [many purposes](http://en.wikipedia.org/wiki/Bleed_air) from de-icing to pressurizing the cabin. However, if the engine gets too hot, the bleed air must be cooled by new air brought in by the inlet.

That is true for civilian transport aircraft where the engine (and hence the compressor) on the wings (deicing application)..
In LCA the engine compressor is nearly at the tail end.. for the scooped air to be used to cool avionics or cabin the air has to bend 180deg and travel forward towards the avionics bay..

The scooped air in case of LCA is most likely to cool something related to the engine itself.. and rad's post seems most reasonable...

[a_kumar]

Photos : LCA Navy first flight target: End 2010

[Rahul M]

oh yeah !

[steve]

Photos : LCA Navy first flight target: End 2010

Thank you for posting LCA navy version pictures . This is the very first time I am seeing the navy version of LCA . Great pics .

[nikhil_p]

To understand why actuators have a higher time delay, you need to understand how they work. Almost all actuators are driven by hydraulic pressure. A hydraulic system has various parts. E.g: liquid container, flow lines, valves, pump, crossover valve, etc. The fluid has a certain coeff of stress, which if exceeded can lead to rapid degenration of the fluid. Also, it takes some time (in ms) for the flow pressure to transfer. Also the actuators have a cylinder which depends upon flow pressure. The hoses are developed keeping a certain fow pressure max level in mind (500-5000 psi for example). However they will generally work between 45-75% capacity to maintain cost efficieny. All this adds to the time delay in the actuator actuation.

Nikhil aren't FBW actuators motors, not hydraulic?

In a hydraulic system Motors my be electrical...they drive pumps which then transmit the energy. Ideally a hydraulic system has more cyclic efficiency vis a vis cost and maintenance. Also electro actuators need gearing to work which can mean in case there is a gear tooth failure, it can damage the entire sytem. Also the tolerances will be very high, the metal will have to be fatigue tested all the time and you are talking gears which are smaller than the little finger nail in some cases. This will mean more cost. Electro actuator systems are used as backup systems.
Also hydraulic sytems tend to be more efficient as only one pump can maintain a specific fluid pressure in the master cylinder. This is then transmitted to the entire assembly, including vane control, flaperon/aileron control sytems, fuel pump etc. The combination valves in the specific location can then reduce the pressure based on the system that it is supposed to control.Overall this will increase the efficiency. Also backup is easier as the channels will ideally be split working out of two tandem cylinders for op-fail-opsafe performance. .
Hope that answers it...guru log may add more!

[Abhibhushan]

Shiv said

Nikhil aren't FBW actuators motors, not hydraulic?

In fly by wire concept Instructions to actuators are sent electronically while the actuator movements are generally by hydraulic pressure. In aircraft that have powered control systems but are not FBW, the instructions to the actuators are mecanical whereafter the actuators are worked by hydraulic pressure.

Nikhil has already explained why hydraulic actuation is preferred over electric or mechanical actuation. Hydraulic/mechanical screw-jack actuation has been experimented with, in the Gnat and the Javelin for instance, but the practice has not caught on. To the best of my knowledge, no one has attempted to move a primary actuator electrically. Electric actuation is however used for secondary purposes such as moving a trim-tab or for supplimentory movement of the tailplane (as in the Hunter)

[vcsekhar]

There is a lot of work going on in the US and EU countries for electrically driven actuators for the movement of the primary flight control surfaces.
We are a supplier to a company in the UK that designs some electrical controls for the motors that are used in this and they told me that their systems are being used currently in the Boeing 787 and the Airbus A400M. The horizontal stabilizer trim control and the main braking actuators are electric on the 787 and both used to be hydraulic in earlier planes.
So don't count out the use of full electrical control actuation in the near future. The aerospace companies would love to remove the hydraulic systems from the planes as they are heavy and a constant source of leaks due to the high pressure of operation and wear and tear of seals. One statistic i got was that 1 lb saved from the airframe weight was equal to 1000's of $ over the life of the plane in fuel costs alone.

In a presentation on the subject they threw out statistics about how much weight they could remove from a plane compared to a hydraulic system and the advantages to the TWR, Reliability in MTBF etc...

[tsarkar]

The effort to reduce hydraulics in aircraft is called “More Electric Aircraft”.

Most aircraft have hydraulic actuation, with each successive generation gradually replacing with electrical systems.

The A-380 and JSF both are supposed to have higher usage of electric actuation, and this has contributed to severe delays in both programs.

Both production models will have hybrid systems, rather than full electric actuation, since it is deemed as too technologically risky to do away with all hydraulics. More here on the hybrid system proposed for the A-380

http://www.aviationtoday.com/av/categor ... 12874.html

An F-16 demonstrator has flown with all-electric flight controls. Lockheed engineers call the concept power-by-wire.

http://www.nationalmuseum.af.mil/factsh ... asp?id=612

[putnanja]

LiveFist has the photos of Naval LCA. Why does the naval LCA have a hump like the trainer version? The trainer version will have the 2nd pilot in there. What will the naval version have?

[sohamn]

That's because the pilot in the naval LCA need better forward visibility while landing and take off from an aircraft carrier.

[sohamn]

The effort to reduce hydraulics in aircraft is called “More Electric Aircraft”.

Most aircraft have hydraulic actuation, with each successive generation gradually replacing with electrical systems.

The A-380 and JSF both are supposed to have higher usage of electric actuation, and this has contributed to severe delays in both programs.

Both production models will have hybrid systems, rather than full electric actuation, since it is deemed as too technologically risky to do away with all hydraulics. More here on the hybrid system proposed for the A-380

http://www.aviationtoday.com/av/categor ... 12874.html

An F-16 demonstrator has flown with all-electric flight controls. Lockheed engineers call the concept power-by-wire.

http://www.nationalmuseum.af.mil/factsh ... asp?id=612

During wwII, fw 190 had all electical actuators for the flight controls. Kurt tank had foreseen the flaw in hydralic controls and thus fw190 had become the best piston engined fighter of the war.

[mukul_chou]

Questions for experts..
There seems to be a ?secondary inlet of some sort just where the tail meets the fuselage on some tejas like KH 2012 while missing in older ones like KH 2002...any idea about what it may be? I have not seen any such thing in other aircrafts.
If you see in the formation picture..the lead the rear two aircraft have it and the middle 2 do not.

http://yfrog.com/htdsc1058lcarampj
http://yfrog.com/i31186470j
http://yfrog.com/11lcadiffj

that can not be an air intake... the hole is missing. This is clear from these pics

http://www.bharat-rakshak.com/IAF/Image ... 2.jpg.html
http://www.bharat-rakshak.com/IAF/Image ... 1.jpg.html
probably gurus can enlighten on this..

[Rahul M]

mukul, the LCA has "no" air intake in that configuration, I wonder how the engine works !

on a more serious note, the scoop is blocked, you won't want a little birdie to make it its home would you ?

[a_kumar]

Made my day!!!

LCA Navy targets first flight this year : Report

The first prototype of the LCA Navy (NP-1) will be a two-seat trainer variant of the naval fighter, and will be followed by the single-seat NP-2 (of the kind shown in the photos above). I met LCA Navy programme director Cmde CD Balaji (Retd) today at DefExpo and received a full update on the programme. Cmde Balaji says he is aiming for a full power-on of NP-1 in the next three months, a roll out of the aircraft from its final integration facility by mid-2010, and a first flight in the second half of this year.

[Carl_T]

Is this first flight of prototype? So that means a few years more before operational status?

[putnanja]

That's because the pilot in the naval LCA need better forward visibility while landing and take off from an aircraft carrier.

What will the additional space behind the pilot in N-LCA be used for? additional fuel? The image on Shiv Arror's blog has lot of space behind the pilot

[mukul_chou]

mukul, the LCA has "no" air intake in that configuration, I wonder how the engine works !

on a more serious note, the scoop is blocked, you won't want a little birdie to make it its home would you ?

Thanks for your info. I always believed that is not an air intake until I see this
http://i843.photobucket.com/albums/zz35 ... 751392.jpg

[Cain Marko]

^^^ Is that some kind of photochop or is the LCA carrying 3 EFTs under one wing? Or is it 2 X EFTs + some kind of A2G missile + Litening? Never did see that image before. Thanks mukul.

CM.

[Singha]

the green is a streamlined cover for a flat nosed dumb bomb(s).

[Srivastav]

^^^ Is that some kind of photochop or is the LCA carrying 3 EFTs under one wing? Or is it 2 X EFTs + some kind of A2G missile + Litening? Never did see that image before. Thanks mukul.

CM.

CM saar, i think its the 25lb practice dumb bomb carrier and a 500 lb practice dumb bomb

[Natt]

That's because the pilot in the naval LCA need better forward visibility while landing and take off from an aircraft carrier.

What will the additional space behind the pilot in N-LCA be used for? additional fuel? The image on Shiv Arror's blog has lot of space behind the pilot

The space will indeed be used for additional fuel and some avionics.
Here s an excerpt form ajai shukla's blog.
"The twin-seat Tejas is also important for the Indian Navy. The naval version of the Tejas, which will operate off aircraft carriers, will be based on the Tejas trainer; it’s higher cockpit allows the pilot a view of the carrier landing deck while descending steeply to land. In the naval Tejas there is no second cockpit; its place is taken by an extra fuel tank and some avionics."

http://ajaishukla.blogspot.com/2009/11/ ... ainer.html

[KrishG]

Antenna of MMR for LCA displayed at DEFEXPO