Bharat Rakshak

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Background articles on HAL Tejas (LCA)

1.http://en.wikipedia.org/wiki/HAL_Tejas

2.Remembrance of Aeronautical Matters Past (Brief history of India's Aerospace Industry)
http://vayuaerospace.in/Selected_articl ... brance.htm

3.All the articles at BR page on LCA.
http://www.bharat-rakshak.com/IAF/Aircr ... Links.html

4.http://www.acig.org/exclusives/LCA/ACIG ... Tejas.html

5.http://www.lca-tejas.org/

6.Good background on project, a bit dated.
http://www.geocities.com/spacetransport ... t-lca.html

7. Harry's Radiance of the Tejas article
http://www.bharat-rakshak.com/IAF/downl ... diance.pdf

8. ADA overview on LCA, including interviews of test pilots, a peak inside the R&D labs and rare footage.



Newbies beware ! If you make ignorant remarks, you could be grilled by gurus
to test your LCA knowledge from these pages !
And, if you come out deficient..............(you would do better not to find out !)

Please stay on topic.

That means :
a> No comparison with aircraft A,B or C.
b> No half-baked suggestions to improve LCA like "add a laser gun"/"merge DRDO with ISRO " etc etc.
c> NO whining.
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Last page of old incarnation, here

X-post..

Tejas to be based at IAF's first fighter air base in the peninsular region at Sulur in Tamil Nadu..



http://www.asianage.com/india/first-iaf ... ase-tn-573

This provides some clarity on Mid-air refuelling capability of Tejas.. The existence of the same was being discussed earlier in the thread.

I have read it a thousand times before, but yesterday I was watching episode of The Big Bang Theory and I could totally relate it to the episode.
Leonard: We are trying to reflect the laser off the moon
Big Dorky Guy: How can you be sure that won't blow up the moon?
Leonard: Don't worry, we have set it to "stun" mode

Sorry for going OT

add *2* laser guns

Noob questions from the old thread
*deleted*
I am new to this forum but have keen interest in airforce, aircrafts and rockets. I have one question on LCA testing. My concern is that how much of this testing is valid when even the engine of aircraft is not finalized. Will all parameters like Weight, balance etc not change rendering most of current testing as invalid?

many thanks for your ideas.

No object on earth. LCA included, will fail to lose altitude instantly if the forces holding it up are reduced or removed. In the case of the LCA, if the engine is switched off. thrust comes down to zero instantly, and air resistance instantly slows the aircraft down and the aircraft instantly loses lift from the wings. Consequently it begins to descend immediately.

I think engine relight is more difficult and complex than kitchen gas burner relight as the tragic crash of the Saras proved, so shutting off an engine deliberately is not to be done lightly. Better to let off flares, try evasive action and take one's chances with the IR missile.

At a high altitude the LCA is likely to be able to glide some distance with the engine turned off, descending all the time. An attempt to point the nose up in this condition will slow the aircraft down so much that wing lift reduces to near zero and that will result in a spin as the plane starts to fall out of the sky. If the plane has altitude, it may be possible to recover from the spin. If not it's a crash.

Shiv, I will look at this slightly differently

establishing a baseline, LCA can fly at tree top level at a minimum speed using x thrust overcoming y drag so if x is removed the plane loses altitude immediately

at a high speed, hx thrust overcomes hy drag

the moment engine is shut off hx goes to zero but there is enough forward momentum that is helped by hy -> y transition in drag reduction as well

This KE can be bled by increasing AOA atleast for say 60 secs and the FBW will ensure that the altitude variation band remains around 20 meters, that 60 secs should be good enough to lose a IR missile lock

the other way is how much altitude can it gain at zero power but sheer momentum before stall occurs, climb AOA is optimized for max. glide time

assume auxiliary power is available and candle flame in a hurricane technology is there

Could anybody clarify about the Range? Flying Range of 500 km / Extended range of 1000 km does not seem right.(Wikipedia lists it as 3000 km for LCA Tejas)

Regardless of speed, thrust is always equal to drag in level flight. Otherwise, you must be accelerating, climbing, etc.



Huh?




The bottom line is this: the engine is the sole source of power. If you lose thrust, you will rapidly lose energy in terms of airspeed, altitude or both. Energy is life itself for a fighter pilot. He is loathe to lose it, especially when he needs it most: missile evasion. What happens when a second missile is fired? Furthermore, a gas turbine is not something you can stop or start like a lamp. It takes several seconds to spool them up or down, and a relight drill is stressful enough when there isn't a missile being shot at you. Furthermore, modern IR missiles are IIR and are not attracted solely by engine heat. Switching off the engine does little more than making it easier for the missile to hit you.

What do you have against DIRCM?

msdogra, that is the combat radius, to and fro and probably includes a not insignificant time over target as well.

if the IR missile sensor is looking at these IR sources due to release of flares

x x x X x x x

it probably knows to lock onto X which is the aircraft engine

and if we change it to by turning off the engine

X X X x X X X

it will lock onto any of the false IR source X

i would imagine missiles with camera based optics are rather difficult to evade.

In a combat situation it is unwise to assume that just one IR missile will be fired. No missile has a 100% hit capability and the chances of getting into an ideal missile launching situation are not that high. So a mix of one IR and one radar homing missile may be fired. In there is no guarantee that the missile firing pilot is under such stress that he is trying to escape the scene, he may well be waiting for his missile to hit or miss, or for you to shut off your engine after which he can take his time and watch you fall to the ground or use guns or another missile.

I am way waaay away from the following and any errors are mine. Please feel free to point out errors

Total energy of aircraft=Potential Energy(PE) + Kinetic Energy(KE)
KE=(mv^2)/2
PE is proportional to altitude

Total energy of the aircraft can be increased by increasing altitude (more thrust required), or by increasing velocity (more thrust required, but trim used to prevent increase in altitude)

The engine provides force (thrust). Unless Newton can be proved wrong a force will always and invariably cause acceleration. A constant force cannot result in constant velocity in the absence of some factor that counteracts that force exactly. In the case of an aircraft that is drag.

v(velocity) is dependent on thrust from the engine. If thrust falls to zero, then velocity falls and KE falls. The only way for the aircraft to then increase its KE would be to convert some of ite PE into KE by losing altitude. The commonest word for losing altitude is "falling"

That is why the bolded part in the following sentence can occur only with djinn physics


PS- an OT rant. The real complaint I have about education in India is that a few weeks spent playing with toy aeroplanes will teach one the basic principles of aerodynamics far better than a year of rote learning. The formulae and principles become so easy to follow if that play experience is there. Sadly the Indian education system is killing the play (practical) part for madrassa like rote.

Good logic, but, if it was that easy a solution I would imagine it would exist in all manuals and the relight sequencing would be mature, robust and very, very reliable.

It's been several decades since IR missiles worked that way.

Modern IR missiles like Python V and AIM-9X are IIR missiles. They don't just see heat spots, they see full images in infrared. They can see a hot aircraft body against the cooler sky regardless of whether the engine is off or not. They don't need to see the aircraft engine at all --- the hot skin of the aircraft will do (cf. all aspect vs rear aspect missiles). They can detect (and reject) flares that fall as opposed to an aircraft that flies. They can detect (and reject) flares since they have a different temperature profile compared to what they expect to see from an engine or airframe. They can pull 50+ Gs and out turn anything an aircraft can do.

Flares only work against older generation IR missiles. These missiles can be fooled by flares regardless of whether the engine is off or on.

In either case, turning off the engine is completely useless and only increases the chances of getting yourself killed: high energy is life itself for a pilot.

I don't want to appear brusque, but it's always a good idea to research a little before proposing random pet theories, which, IMO are a dime a dozen. Even a simple wikipedia search would have given you the answers. E.g., I can see that you did not look up DIRCM, which I had mentioned in my earlier post.

So heres a hypothetical question for all of you guys here ...


If you were to design a PERFECT Tejas MK2 what features would you want / add ? ( assume reasonable resource and time constraints )

Hmm, let us see.. What is the difference in IR profile when the engine is just killed, and just throttled to 'idle'?

Ans: Essentially the same, at least for the first few minutes.

DIRCM if available is fine, stealth is even better

if vector thruster cone is pointing away from the missile sensor with the engine either at idle thrust or killed would it not affect the IR profile

I don't think it matters if you are looking into the exhaust directly. You won't 'see' the combustor directly, and the high-temp turbine which is visible will be hot for some time.

Any idea what was it today morning around 9:10
Sounded like quite a few fighters taking off within a min or so

I think it was Ben Rich who who once famously said, "General, that's why they call them 'miss-iles' instead of 'hit-iles'!!". Quite a few missiles don't actually hit the target, but they explode close enough to it to cause damage.

Standard SOP to avoid a missile is to twist and turn the aircraft and pull some high G maneuvers. One of the myths spread by TV and movies is that missiles burn all the way to the target. In real life, most missiles have a rocket motor that burns for a few seconds and then they cruise the rest of the way to the target. This means if the plane twists and turns, the missile will try to twist and turn as well to follow it and these maneuvers will cause it to lose speed. Since a missile doesn't have a rocket motor powering it continuously, any speed loss caused to it is permanent. Missiles also can't turn as fast as planes can because they have higher speed and smaller control surfaces (newer missiles attempt to rectify this with some thrust vectoring).

So with this in mind, the LCA pilot needs max. thrust available on the jet to perform the evasive turns. Turning off the engine is just a bad idea.

I counted 5 of them taking off back to back. They have not returned yet. I am not expert however they didnt looked like LCA to me, they sounded like it though.

at 7.50am today a lone dark grey C130 took off to the west. It had a white patch on the tail .
could either be manufacturer owned bird sent to train indic pilots for C130J or just a routine
refueling stop.

singaporean AF en route to france ? anyway, not this thread please.

Sorry, OT but even a F-16 was spotted yesterday near HAL. SO, must be the SAF onlee...

Again my apologies for going OT, please let me know if I should shift this to appropriate thread
I quote this from Wikipedia:


So, I guess, the future missiles are going to burn all the way to the target.

Try this small experiment at home. Very simple...
heat a pan, spoon and an aluminum foil piece on the same flame for exactly the same time (say 2 minutes). Then wait for 1 minute and test the temperature of each. ( use a cake thermometer or you can carefully just touch). You will see what cools down and what doesn't. vary the cooling times and plot a temp/time graph. You will see HOW long it takes for the metals to cool down. The fry pan will possibly be a stainless steel or iron made thing. The spoon is definitely stainless steel and the Al foil is well Al.

This will give you a fair idea whether your hypothesis will work.

like mentioned earlier, most IR missiles will make out the temperature differential. Also, remember that most IR missiles are in the WVR range, if the pilot shuts off the engine, he loses maneuverability and also an aircraft engine has a decent turn on time requirement before it reaches full power. All the enemy has to do is come closer and use his guns for target practice.

Anyways OT for this thread. Mods please move to app thread.

some points to ponder

a) if we take an IR picture of a commercial jet engine from the exhaust side and again when the reverse thrusters are engaged but at idle thrust, they will be different

b) people loath the idea of a coasting fighter while its natural for a missile while both are managed by FCS

about the need for high energy state for the pilot to out maneuver a missile, people are discovering value in subsonic stealth, not being able to obtain a lock on a fighter is the future and the idea of suppressing IR signature is on the same lines and whether this succeeds or not is the question

doesn't succeed due to newer generation IR missiles doesn't negate
points a (altering IR profile) and b (coasting on idle thrust)

its raining self-styled gurus these days, maybe it helps that I am no newbie on BR either

^ Fwiw modern AAM missiles have IIR sensors I wonder how effective such last minute desperate measures like shutting the engine or somehow pointing the nozzle away are gonna help. Check the following video showing actual target image as visible to the IIR seeker (around 45 seconds onwards).

Iirc there is a better quality video for Python-4/5.

http://www.youtube.com/watch?v=4g4_jzqBJnA

You are no newbie to self serving rhetoric when what you wrote was complete rubbish, claiming that an aircraft could increase its AoA and coast without power AND without losing more than 20 meters altitude for a full 60 seconds. You have to first accept that in your non-newbieness you were bringing in djinn physics.

Now you are saying a missile can coast without power and that people are against you when you say that a plane can also coast without power. A missile (within the atmosphere) that is coasting without power is exactly like a bullet. It is losing velocity and energy all the time. If it attempts to increase its altitude or maneuver, it loses energy faster and slows down more quickly and its range will decrease. If it tries to maintain altitude it can never do that because it is losing energy all the time. It can only describe a parabolic path towards the center of the earth.

That is why the missile must hit an aircraft within seconds of its losing power. Fortunately a missile at Mach 3 will be doing about 1000 meters per second and can hit an aircraft that is nearly 1 km away in a second. (technically any bullet can do that) In this 1 second, if it tries to fly level, it will inevitably lose 10 meters of altitude because of gravity. If it maneuvers, it slows down faster.

I would like to see you come up with any links that can disprove physics. The only expertise required is high school physics in this case which I presume most people on here have acquired. We can worry about ideas and expertise after that. I am sure you can calculate exactly how far any object will fall in 60 seconds and what is necessary to prevent it from falling using 10th std physics knowledge alone.

Admins,

Would it be possible to move the djinn physics discussion to the newb thread? The current discussion has absolutely nothing to do with LCA.

(I will delete this post later.)

Engine relight is being talked off here like relighting your gas stove or switching on your fan. It seems people are not reading enough before posting here. One needs to read the Saras crash report ( it's been posted somewhere in BR) in order to understand the complexity/prerequisites of a relight. Under the stressful environment of aerial combat, it is impractical to expect the pilot to go through shutdown/relight and add to that the altitude and speed constraints for a relight. He may/may not evade the missile but surely be doomed to death if he goes for a shutdown.



Very true, can't agree more.

Cheers....

True from what I understand modern IIR sensors looks at a photographic image of a target which is to say target as a whole , rather then specific hot areas of the target.

So it really does not matter if you shut of the engine , change the direction of exhaust/nozzle or AB , you cant spoof the missile with those tricks.

The only way to spoof ( near foolproof ) the modern IIR missile is to temporary blind the missile using DIRCM , kinetically out maneuver it or damage the seeker head of the missile using some sort of laser shots

people, LCA thread.

For the LCA
http://upload.wikimedia.org/wikipedia/c ... osites.jpg

how stealth it can become if the engine is recessed like this
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by making the wings curve back as shown at 27 secs into this video
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The LCA's intakes are Y-shaped (twin-S if you like) as in the image below and are perfectly stealthy


Image is a video grab from 35 secs in the following video
http://www.youtube.com/cybersurg#p/u/30/755G4aqQ9mk

JMT.... It will be the shape of aircraft that will determine most of its stealth , LCA having composite ,RAM coating,being small or having Y duct will not make it stealthy but will definitely lower its overall RCS in clean config , but once you hang those external fuel tanks and A2A and A2G missile on those pylons and in the field conditions they operate it would be any body guess what effect it would have on RCS of aircraft

It is quite fascinating when Eurofighter , Rafale PR tom toms about its low RCS( ~ 0.5 m2 ) in clean config , I wonder how much of those figures are valid with weapons/fuel tank load and in actual field condition.

this is an interesting topic.
There are a lot of advantages to having a small low RCS plane in an A2A fight.
I had spoken to a IAF pilot who had flown Mig 21's and I had asked him about this very point and he came up with something interesting.
He said that as soon as they get a signal on their RWR's that someone is tracking them they get the direction of the emitter from the HADF, they will change direction or orientation of the aircraft (or any other combination of the various options) to break radar lock, he actually did not seem too worried about being locked on radar (I was surprised, BVR and all), obviously i did not ask and he did not tell me the details but having an aircraft with good RCS is always good even if you are loaded with weapons and tanks as you can show your best side to the enemy when needed

So the LCA having a small RCS would give a good advantage to the pilots when they need it.
Just my 2cents anyways.