Bharat Rakshak

THe pitch up or down depends on whether the airbrakes are on top or bottom rather than aft or front.

Then there was the problem of uncontrolled pitching problem even during the first taxi trials..they were trying to correct it. This is what my chaiwala classmate told. I am not in touch with any of them for clarification. Those in the loop may be able to clarify.

The flight control computer’s job is to know where the CG is at all times. Otherwise how will it apply corrective inputs via FBW and keep the aircraft flying. If the Flight Computer doesn’t know where the CG is, the aircraft won’t fly in the first place.

Why are you confusing such a simple thing ... If there is a component of force created by the airbrake which does notpass through the CG it will have a turning moment ... elementary class 11 physics. There is no aerodynamics or rocket science involved.

That is not a fact.
http://images3.jetphotos.net/img/1/5/7/ ... 740875.jpg

Boss, I didn't read your post before.

Now tell me, isn't that exactly what I said? i.e., if the airbrakes are on top, the turning moment created by drag will tend to lift the nose up, because the CG of a/c is below the airbrakes(drag force). If the airbrakes are at the bottom part, the turning moment created by drag will tend to lift the nose down, because the CG of a/c is above the airbrakes(drag force).

Am I confused?

Sarkarji, This is not completely true. There are Flight computers which work on feedback control loop which knows your desired orientation and direction. It just creates feedback based the observed deviation and the amplitude of the feedback is based on the amplitude of deviation.

IIRC it was something like a rocking motion during the high speed trials, which they were trying to analyse way back in 2002..Most probably an aerodynamic problem. As I said before, I don't know whether the same problem persists now (unlikely).

But tendency to pitch up or down when air brakes are applied is not a problem as such, as long as it is within the design limits. If not, they would redesign the air brake to suit the needs.

Boss, I didn't read your post before.

Now tell me, isn't that exactly what I said? i.e., if the airbrakes are on top, the turning moment created by drag will tend to lift the nose up, because the CG of a/c is below the airbrakes(drag force). If the airbrakes are at the bottom part, the turning moment created by drag will tend to lift the nose down, because the CG of a/c is above the airbrakes(drag force).

Am I confused?

THe pitch up or down depends on whether the airbrakes are on top or bottom rather than aft or front.

Indranil ji, I am writing my understanding below, please correct me wherever I am mistaken.

A fighter with negative static stability or relaxed static stability will need constant trimming of its control surfaces to help it fly. In the event the trimming stops when FCS fails, the plane will crash like the two out of three Su-30MKI crashes so far.

So to help fly the plane, Control Laws are written for the flight control computer. These Control Laws cover different flight regimes. The DFCC uses air data to understand the flight regime + pilot inputs, and thereafter passes control commands to the elevons, rudder and leading edge slats.

The CG is behind the center of lift. Now, the CG will move forward or back due to depletion of fuel (and external stores if carried). But the range of positions of the CG in different flight regimes and different external stores will be well defined so as to enable the control laws function to keep the aircraft in stable flight. So for a specific fighter, its range of CG locations depending on flight regimes and payload would be well known and defined in the DFCC for the control laws to work properly.

So the location of CG is not unknown in a NSS/RSS aircraft. This is my understanding, correct me if I am mistaken here.

The F-18 has oversized stabilators and flight control surfaces for adequate flight control. Hawk airbrake might create a downward pitch, but the aircraft is designed to be very stable, since it’s a trainer.

They were rejected for failing the technical evaluation, that included these very parameters. Your statement completely contradicts reality.

The F-16 was designed as a A2A fighter, and the bells and whistles added for A2G role ate away flight performance required for the A2A role.

Then why can’t the FCS correct the uncommanded pitch created by the original airbrakes.

Agreed, from what I have been told, the IAF considers the pitch effect a nuisance but definitely not a showstopper. It has no effect on the induction plans.

MIL-STD-1797A4 states: “The aircraft shall be…resistant to departure from controlled flight, post-stall gyrations and spins. Adequate warning of approach to departure shall be provided. The aircraft shall exhibit no uncommanded motion which cannot be arrested promptly by simple application of pilot control.”

Thank you for asking this question. It means assessing all the available means to achieve an end, and choosing the simplest and least riskiest means of achieving that end.

Like having airbrakes closer to CoG than having it elsewhere and having FCS mitigate any side effects. FWIW, using MLG door is reverting back to simpler design philosophy. Now, I am sure that the designers would have had some valid reason for not doing so in the first time itself, like avionics in the dorsal or fuel tanks in the ventral or wings, however, a simpler approach would have given precedence to placement of airbrakes.

Which BR member will volunteer his son or father or brother or husband to go to fight knowing fully well they cannot outturn the enemy in a sticky situation? I am sure your perspective of “IAF not supporting…” will do an Immelman turn when your own flesh and blood goes to a fight in a Mk1.

...

But tendency to pitch up or down when air brakes are applied is not a problem as such, as long as it is within the design limits. If not, they would redesign the air brake to suit the needs.

What is the WVR missile we are planning for Upg Mirage and Rafale. Don't tell its Matra's Magic 2.
...

MICA IMO is an overkill for a WVR dogfight for its price/range. It is more of a replacement for Super 530.

With announcement of Rafale as the Indian Air Force’s (IAF) next generation fighter, the “dogfight” among six of the world’s leading aircraft seems to have ended. However, those unfamiliar with weaponization strategies might wonder how countries decide upon any weapon system. Is it simply a matter of the best? If so, what is best?

The answer isn’t straightforward. The choice of a weapon system has less to do with specifics of its technical capabilities and more with imperatives of strategic doctrine. To understand this better, let’s start the journey from a lowly assault rifle rather than a sophisticated aerial platform such as a fighter jet.

An assault rifle is the mainstay of infantry, i.e. bulk of the fighting force of any country, and has over 10 design parameters which are often contradictory. For instance, a rifle should be accurate, have long range, be easy to maintain, sturdy enough to survive the rigours of battlefield, have a rapid rate of fire, and easy to handle with one hand for urban combat. In addition, the weapon must be light, have compact ammunition of the same calibre as other weapons so that supply chain logistics are manageable. It must have the capability to be used in different versions, for instance, paratroopers need shorter rifles and infantry support groups need longer ranges. Each of these requirements contradicts many others.

For example, accuracy over long ranges means the barrel will have to be long and the rate of fire cannot be high. This in turn makes the rifle unwieldy and suboptimal in a fierce firefight. If the rifle has to be sturdy with heavy munitions then it can’t be light and soldiers will tire before they enter battle.

Such complications exacerbate as weapon platforms get more complex. For instance, let’s consider the battle tank. The North Atlantic Treaty Organization (Nato) designers were compelled to build heavier tanks because their theatres are limited in space and their tanks had to be heavily armoured to hold ground without ceding position. A lesson reinforced by the German blitzkrieg when France was overrun in a matter of days. Also, Nato countries have comparatively low manpower though they are better skilled and educated. Hence, tanks such as the British Chieftain and French Leclerc were designed upward of 55 tonnes, have high crew comfort and the crew is “dual traded”, i.e. each member of the crew is expected to know more than just his own job, necessitating higher investments in training and retention.

The Soviets, however, relied on a much lighter and cheaper tank of the T54/55 series, because they could trade “time for space”. The Soviet strategy was to let invaders enter deep into the Russian hinterland—a situation they could afford, primarily because of their strategic depth—and then hit the supply chains through encirclement and, of course, the assistance of “General” Winter. The “Warsaw” doctrine, therefore, catered to Russia’s strengths which are plentiful supply of conscripted manpower, manoeuvring space and the severe weather where sophisticated equipment had more chances of failure. These strategies are consistent with their assault rifles as well. While the West has relied on relatively sophisticated weapons such as the American M16, British FAL and the French Famas, the Soviets developed the cheap but reliable AK47 series.

The key to understanding these strategies is to appreciate that in combat, a weapon is never pitted against another weapon in purely technical terms. It is, instead, a combination of the technical prowess, soldier’s capabilities, terrain and the national doctrine which decides the optimum arraignment of weapon platforms. So, while a sophisticated Heckler and Koch rifle could be an ideal weapon for highly-trained special forces, a much cheaper and rugged AK47 is better suited for mass infantry attacks, though on a purely technical comparison, the Heckler would outgun the AK.

Fighter aircraft are sophisticated weapon platforms and, hence, their inter-linkage is far more complicated. Modern fighters are expected to perform “omniroles”. They have to be highly manoeuvrable for “air-to-air” dogfights, possess heavy lift capability for tactical and strategic bombing, have long radius of action, be capable of operations from land and sea, etc. Their supply chain is even more complicated, especially for India, which has a wide and diverse area of geographical interest. Fighters need air refuelling, naval carriers, multi-weapon capability, an intricate web of radars, airborne warning and control system, sophisticated maintenance, repair and overhaul facilities and indigenous manufacturing to minimize external dependence.

They also need synchronization with other arms such as the army and navy. For, while IAF may pummel the enemy and establish air superiority, it is of little use unless armoured formations can rapidly exploit this hole and pour into enemy territory. And the latter’s ability to do that is contingent on their own modernization programme which depends on the country’s threat perceptions and mitigation strategy over the coming decades.

Viewed from this perspective, it is rarely the technical superiority of any single weapon system that matters. Instead, it is the complex “organization for battle” derived from strategic doctrine which serves as credible deterrence. And deterrence is what it must be—because as any soldier will affirm, war is an ironic game. The only winning move—is not to play.

MICA IMO is an overkill for a WVR dogfight for its price/range. It is more of a replacement for Super 530.

...
Breaking away from established doctrines, the very high technical standards set by MICA are the result of an innovative operational concept. These evolved from the global understanding of the air-to-air battlespace and the appreciation of the need for a weapon system that would ensure asymmetry to win in aerial combat.

MICA stands for “Missile d’Interception, de Combat et d’Autodéfense”. A clear statement that this single missile system had to cover all facets of the air-to-air battle - BVR (Beyond Visual Range) interception, dogfight and self-defence.

The MICA system comprises 2 versions: MICA (EM) RF with an active radio frequency seeker and MICA IR with a passive dual waveband imaging infrared seeker. Both missiles are fully qualified and in mass production, being currently flown by numerous air forces worldwide.

A “full MICA” configuration on an aircraft such as Rafale gives a very flexible and high BVR fire power for Air Superiority during all kind of missions: combat air patrol, sweep, deep strike, recce, maritime operations. MICA missile in BVR mode introduces a new way of waging air combat by offering multi-target capability at extended ranges with the two interoperable guidance systems to hamper enemy counter measures. All carried (EM) RF or IR MICA missiles are fully BVR, being operable with or without data link target designation updating.

In short range (SR) combat, a MICA configuration on an aircraft offers a full "new generation" capability thanks to the outstanding performance of the missile (extreme agility and manoeuvrability). An additional advantage lies in the possibility of launching MICA with its seeker (namely IR) either locked-on to the target or not, while still featuring all BVR qualities.
...

question is -
(1) is MicaIR having a better IIR seeker than python5?
(2) is passive BVR shooting using spectra + micaIR a proven concept?
(3) is MicaIR more manouverable than python5 or less?

we are certainly getting python5 to replace the old R73 stocks for sure....with K74 nowhere in the horizon....

whether or not we get MicaIR on rafale or settle for python5 depends on above questions.

there is no doubt we will get MicaEM (and Astra) and wont bother with amraam.

You are basically confused about the difference between mechanics and aerodynamics.

The flight control computer’s job is to know where the CG is at all times. Otherwise how will it apply corrective inputs via FBW and keep the aircraft flying. If the Flight Computer doesn’t know where the CG is, the aircraft won’t fly in the first place.

From those I spoke to, the FBW is not able to detect and actuate the elevons well in time to correct. FWIW, the services do not consider this as a showstopper, and this is not considered either for IOC or FOC.

This was just an example of the complex FBW development process that could have been avoided using a proven technology for getting the aircraft in the air, and zero base FBW development could have commenced as an enhancement.

What is the problem with the LCA airbrakes..? I really can't comprehend anything from the discussion going on here.

Can someone please elaborate ? TIA

The main problem with AAM, especially BVR, is that each uses a proprietary/encrypted channel between an aircraft's Radar and missile's receiver for target lock launch and mid-course guidance. The manufactures are reluctant to share these. As a result, you only see R-77 integrated with only Russian radars; MICA with French radars; Derby with Israeli radars; AMRAAM with American and EF radars. You see this effect with the indigenous Astra, which uses a Russian Agat seeker, is being integrated with Su-30MKI first, then MiG-29 and also the LCA (but could face integration challenges with its hybrid (Israeli/DRDO) MMR radar).

Why is it not possible to design the weapons in a manner that allows the customer to reflash the comsec gear on missile/radar with their own specific encryption codes?

There is no fundamental reason why this can't be done, is there? I mean other than to lock in weapon-radar-airframe combo by the OEM?

I shall try to explain briefly, since you must be knowing the basics.

Take the case of a twin engine a/c. Suppose the left engine fails-then the forces are unbalanced and the right engine will create a yaw moment and tend to turn the nose of the a/c to the left. It is a simple example of mechanics i.e., a force with an arm (lever) will create a moment. No aerodynamics involved here.

Now, how do you correct this yaw moment? by deflecting the rudder to the right, a counter yaw moment can be created and make the a/c fly straight. The force produced by the deflection of rudder is aerodynamic force.

Similarly, the air brakes are essentially spoilers (of speed). They use the aerodynamic force created (pressure drag) when a flat plate is placed perpendicular to the flow. If the plate is convex, then coefficient of drag is less and if concave, more (than a flat plate). This is the aerodynamic force created to decelerate the a/c.

If these air brakes are placed above or below the horizontal CG line, then an unintended moment is also produced - if above the CG line a nose-up moment and if below, a nose-down moment. This moment is largely countered by the mass of a/c ahead or behind the CG as the case may be.

Take another case of that of a commercial a/c in flight. At the beginning of the flight, it may be carrying about 100 Tons or more of fuel, but towards the end of the flight, most of it is consumed. But the aerodynamic shape of the a/c remains same for all practical purposes. What happens?

While in steady level flight, The Dynamic lift will compensate the weight - The CG and CL (centre of lift) are apart in all three X-Y-Z axis. As the fuel gets consumed (and as there is movement inside a/c) the CG constantly shifts (Mechanics). How do you correct it? By adjusting the position of the CL (Aerodynamics).

Position of CL can be adjusted in different ways, depending upon the control surfaces available. One way is by changing the attitude of the a/c (thereby the angle of attack) by deflecting the elevators. Another way is by deflecting the flaps on wings. Ultimately, when the most desired position is arrived, the a/c is supposed to be 'trimmed' - resulting in minimum fuel consumption. For commercial a/c, the most important factor is fuel consumption. Therefore they try to achieve it by deflecting the control surfaces as little as necessary, therby reducing the drag.

Lastly, Canards, elevators, ailerons, flaps and also spoilers (of lift), airbrakes etc are aerodynamic control surfaces and the forces produced by the devices follow the laws of mechanics.