Bharat Rakshak

indranilroy,

First, In all wings, flow over the upper surface is much more critical than the lower surface. This is the reason why you can suspend pylons, weapons, fuel tanks, engine mounts, etc. on the bottom of the wings and yet not affect the essential lift capability of the wing. The wing-body blending on the upper surface essentially creates a larger upper wing surface for lift to act. This is not critical on the lower surface.

Second, while blending in the lower surface may marginally reduce interference drag it will either (a) increase the cross-sectional area in the fuselage section where cross sectional area is very critical (i.e., wing-fuselage junction) thereby increasing wave drag and hampering trans/supersonic performance, or (b) if the fuselage is tapered to maintain the same cross sectional area, reduce the volume available in the fuselage, which is a critical commodity in a small aircraft.

My guess is that the designers concluded that the tradeoff wasn't worth it.

I like your answer . My answers inline (in blue).


Anyways, it is nice discussion. As an aerodynamics enthusiast, I would love to know why certain choices were made. Probably that would not happen in public space. Will have to befriend some LCA guys or get employed there! Problem is why would they hire me

Flight test update

LCA-Tejas has completed 1778 Test Flights successfully. (14-Feb-2012).
(TD1-233,TD2-305,PV1-242,PV2-212,PV3-330,LSP1-67,LSP2-198,PV5-36,LSP3-46,LSP4-44,LSP5-65)

from

LCA-Tejas has completed 1777 Test Flights successfully. (10-Feb-2012).
(TD1-233,TD2-305,PV1-242,PV2-212,PV3-330,LSP1-67,LSP2-198,PV5-36,LSP3-46,LSP4-44,LSP5-64)

indranilroy,



I think you are talking about different things in the same breath.

First: Does "smoothening" the lower surface affect lift coefficient? Yes, anything that affects the airfoil profile will affect the lift coefficient. Second: Does it *adversely* affect lift coefficient? Probably. You are essentially tending towards a symmetric airfoil, which have lower lift coefficients than cambered airfoils for a given angle-of-attack.
Third: LCA wing has a huge "twist" at the root. Yes. This is for two reasons: first to ensure that the entire wing doesn't stall at once. Second, a lot of that "twist" at the root is to control the oblique shocks for the inlet to operate at supersonic speeds.

The issue I was trying to highlight in my first statement is that there are good reasons to wing-body blend the upper surface; not so for the lower surface.



I was not referring to critical mach at all. The point is blending the lower surface will increase the cross sectional area of the airplane. Increasing/decreasing the cross sectional area smoothly is not enough. I think this is the point you are missing. The CS area distribution must match the Sears-Haack distribution closely to minimize wave drag. Just blending without paying attention to the Sears-Haack distribution will increase wave drag unless the fuselage volume is correspondingly reduced, which we cannot do for reasons of packaging/estate management.

Raman sir, probably you are right!

You are right ... if we have to retain the sharp edge of the leading edge of the wing and trailing edge of the supersonic wing, then the smoothening will be a bulge and that will lower the camber and hence the CL. That is a good point.

I remember the wonderful discussion of the LCA wing a couple of years back. So I do understand the basics and reasons behinds its shape. I was very interested to know ... I thought some of the posts there should have been made sticky .

Coming now to the tradeoff between the wave drag and the interference drag. I will try to dig up the area curve of LCA Tejas (Kartik could you help me find the pdf which discussed the planned refinements in LCA) ... may be we can do some back of the envelop calculations for increase in wave drag ... Alas we can't do anything to find the approximate decrease in interference drag.

Once again it was a good discussion for me

Okay found the paper which had the area curve: http://www.drdo.gov.in/drdo/pub/dss/200 ... EMILAC.pdf (pg. 9).

Question is whether it is acceptable to increase the area between stations 6 to 11 or so?

Most probably they would have done CFD analysis and found that it is not! Ah, but the itch to know ...

Hi All,
This is my first post although I have been lurking on BR for almost 11 years.
Am SDRE IT guy from Bangalore.

Yesterday around 2 pm show LCA with IFR probe. Are there any of them LSP or PV flying with IFR attached? Or was it LSP 6/7

Flight Test News


LCA-Tejas has completed 1779 Test Flights successfully. (16-Feb-2012).

(TD1-233,TD2-305,PV1-242,PV2-212,PV3-330,LSP1-67,LSP2-198,PV5-36,LSP3-46,LSP4-45,LSP5-65)


LCA-Tejas has completed 1778 Test Flights successfully. (14-Feb-2012).

(TD1-233,TD2-305,PV1-242,PV2-212,PV3-330,LSP1-67,LSP2-198,PV5-36,LSP3-46,LSP4-44,LSP5-65)

Based on ADA website no LSP6/7 in the Air, only 1 flight in the last 2 days.

AV, would be nicer for the sake of continuity to use suryag's last post. His update was for Feb 14?

Ok, Sorry copy posted from ADA website. Corrected my post, continuing from Suryag's post

Very, very interesting Ketan, welcome to the board - you come bearing good/interesting news. Can any jingos with inside clearances to sensitive areas such as golf courses or roof tops confirm this development?

CM

[wetdreams] was it PV2?, it seems to have flown after a long time (after two months)[/wetdreams]

Are you sure it was an LCA? Some fighter jets are difficult to distinguish from afar. A M2000 for e.g. can easily be confused with an LCA if you catch only a quick glimpse or if it's too far away. A M2000 would be a rare sight in BLR though.

in 7 yrs the only time I have never seen M2K in HAL. did see MKI few times flying into HAL for events like AI09.

So lets see what is the sequence of events for an LCA new bird to fly

1. Fabrication
2. Roll out
3. SCT, vibration and other tests
4. Engine Ground Run (EGR)
5. Nose wheel checks (at 70 kmph per above report)
6. Low speed taxi trials (at 140 kmph per above report)
7. High speed taxi trials (at 200-220 kmph per above report)
8. Rotation tests?
9. First flight

"They" don't fly, they are for some sort of "research purposes" onlee.

Had earlier posted about seeing a pilot from Sq 1 (Tigers) during AI. Don't recollect seeing M2Ks flying then tho.

Flight test update

LCA-Tejas has completed 1780 Test Flights successfully. (17-Feb-2012).
(TD1-233,TD2-305,PV1-242,PV2-212,PV3-330,LSP1-68,LSP2-198,PV5-36,LSP3-46,LSP4-45,LSP5-65)

from

LCA-Tejas has completed 1779 Test Flights successfully. (16-Feb-2012).
(TD1-233,TD2-305,PV1-242,PV2-212,PV3-330,LSP1-67,LSP2-198,PV5-36,LSP3-46,LSP4-45,LSP5-65)

Someday i would like to know what group of aircraft was used for what kind of flight testing

So Boeing is planning to make about 10 Dreamliners a month by Q4 2013, scaling up from its current 2.5 a month . Meanwhile, HAL is going to make about 10 a year ramping up from Zero all of last year.... just saying.

http://online.wsj.com/article/BT-CO-201 ... 01263.html

you shouldn't have

Thanks CM



I don't think it was M2000, thought i could only get a gimps of it while riding. I ride home for the lunch as it is just about a KM from working place.

As for the LCA? or what i show was coming in to landing from Marthahalli end. May be they have upgraded one of the LSP which are flying.

CM

Kakarat's photo of a scan of tejas booklet from AEROINDIA 2011 did show the IFR probe. i won't doubt if it has been carried to it's logical conclusion. so what ketan is saying may actually be true!!

FWIW take a look at this -

http://www.bharat-rakshak.com/media/Aer ... 1.jpg.html

It was an M2K and not an IFR equipped LCA, the M2Ks are overhauled in HAL overhaul division, so finding one shouldn't be problem at all.

An easy way to distinguish an M2K from an LCA is the massive size of the LCA wing compared to its fuselage. M2K's wing does not look as oversized.

Just saying what? Any idea how many firm orders Boeing has for the 787 as compared to the LCA? If Boeing didn't make that many a month, they'd lose a whole bunch of new customers to Airbus' A350, since those customers will not be willing to wait till they get their 787s after 10+ years or so. Boeing replaced the anaemic 767 line with the 787 line since there were almost no orders for the 767 anymore..and then set up another one at its Everett plant just because it has so many orders for the 787..and then it went on to set up another entire 787 factory in South Carolina because even that wasn't enough.

Why would HAL set up a larger assembly line unless they can get firm orders from their one and only customer? If IAF only intends to place orders for 40 Tejas Mk1, HAL will only set up an assembly line for 10.

Orders cannot be given until the design meets basic performance parameters.

In DRDO's own words http://www.drdo.gov.in/drdo/pub/dss/200 ... EMILAC.pdf




Tejas airbrakes http://www.bharat-rakshak.com/media/Aer ... e.jpg.html Sukhoi airbrakes http://www.flickr.com/photos/vishwak/5436297107/ mounted close to CoG, so no such moment arm acting on the aircraft. Mirage 2000 airbrakes are mounted on wing http://rafaleair.free.fr/photo2/mirage%202000-5%20F.jpg close to CoG.

Common sense dictates such parts be close to CoG to minimize uncommanded movements. However, for reasons best known to designers, they didn’t. Simulation/Testing should have revealed this during design, but again, this went ahead.

F-16 has rear brakes, but they split open equalizing the force unlike the upward-only Tejas http://pafwallpapers.com/blog/wp-conten ... arrows.jpg

Solution So we’ll see a plane that’ll keep opening its MLG doors in flight.

Solution In Mk2

Now this is interesting. Many BR members on seeing the abrupt training edge had commented that it would be draggy. http://imageshack.us/photo/my-images/88 ... 01is2.jpg/
Common Sense that airflow split at wing root leading edge should be enabled to rejoin at the wing root trailing edge.

Again, why didn’t this come up during initial design/testing.

Atleast until 2009, there was no solution in place.

IAF has valid reasons to describe Tejas as a deformed Cheetah. Despite that 40 planes have been ordered, that is 5.5% of its authorized fighter force. FWIW, I doubt IAF will ever deploy Mk 1 in air to air combat, risking the lives of the pilot without performance requirements being met. Also, with further design changes, manufacturing will be impacted.

Tsarkarji we have done this so many times. Supporters of the forces insist everything should be fine before they are inducted, supporters of the tejas say, the forces inducted far inferior equipment in the past. I am not even an aviation noob, but high landing speed of MIG21 was/is considered hazardous, so why didnt the famed MIG bureau consider this while designing ? This aspect of MIG21 is taken as a characteristic of the aircraft and tactics built around it. Similarly there was something with the JAG

In similar vein cant the IAF accept it and make it better rather than coming up with newtonian statements like "it is a deformed cheetah" ? Why wasnt the IAF involved in providing design inputs during the 1990-93 timeframe ? I am sure they have a wealth of experience in operating aircraft a simple thing(the CoG thing) that could strike you(no offence intended) would have struck any iaf pilot Why didnt they communicate it then? Both sides are to be blamed hope AMCA charts a different course

Tsarkarji, thank you for the informative post.

The linked DRDO article was very interesting. By any chance, if you have more links to any other similar articles on LCA/HJT-36/Dhurv could you please share them? I would like to go through them.

Thanks.

I was talking about if from HAL's point of view. They won't be able to set up a larger assembly line without a larger order. As for whether or not the IAF can or cannot place a larger order for the Tejas, I don't subscribe to the theory that a few teething troubles should mean that they show dampened enthusiasm for the aircraft itself.

The pitch up issue is not a make or break type issue. The Typhoon had a major transonic pitch-up issue as late as 2002 that was solved with a major FCS update. Typhoon transonic pitch-up issue. And yet, did that mean that the Eurofighter nations said, hey lets just order a token 40 odd Eurofighter's each?




Yes, why deploy a Tejas Mk1, when you have MiG-21s with even worse aerodynamic flaws that an inattentive pilot would push over the limit in the blink of an eye.

Kartik, I was juxtaposing HAL manufacturing speeds vis-a-vis other companies ( making a much larger and complex plane). HAL bosses claimed they would be rolling out one fighter a month starting September 2010. So far all we have had is missed deadlines. You can all jump in and tell me that IAF has not given firm orders , but as the poster above mentioned, it's more of a chicken and egg story. IAF has committed to higher numbers, but ASRs are still not met and delivery deadlines have slipped to a point that not a single new plane flew in 2011.

Vikram W ji you havent visited the raffy thread i suppose(link posted by kartik ji)
rafale flight test

From the above link

so either rafale is not as complex as tejas or Dassault is as inept as HAL

Regardless of how the IAF characterizes the LCA, if India pursues her own strategic goals - not in consonance with the hyper power blocks, the deformed Cheetah may be the only cat in Indian service with any claws and fangs! Others may simply be grounded!

Relying on french technology against russian one, does not lead to independence rather only transferring dependence to another country. The problem is DRDO's failure and GoI support to all indigenous efforts for Kaveri, which is core for any dependency relationship. No matter, how successful LCA is, if Kaveri-snecma is all it gets, then we are totally dependent on french for executions. All it takes is sarkozy or a future fr president making a statement.

Kaveri++ standing by itself.. charting its own life time and establishing for our services is vital for LCA's long term goals. This $2b deal with fr needs to be reviewed by strategists, and work with already dependent nations to reduce dependency on long term basis. The short term dependency is manageable, for us, but not long term. Fr is our next gen russia!

Even the Hawk had a single airbrake that was located in front of its ventral fins. Lack of common sense on the part of Hawker Siddeley perhaps?





Even the Tornado's airbrakes are located right at the end, just under the fin



And look at where the F/A-18's airbrakes are located..

I am no aero expert.
Is the problem with uncommanded pitch-up in LCA is because of delta wing?
I ask because, all other aircraft examples Kartik took can compensate for pitch up by the elevators. Since LCA's air-breaks appear to be dang on delta wing Aileron are they more of a problem?

IIRC, even the Gnat used the MLG doors as airbrakes. I always thought it was a very clever idea and wonder why more aircraft don't use this technique - probably saves weight as well.

That is exactly my thought!

The only reason I could think of is that while coming in to land the aircraft has lower decelerating power without dedicated airbrakes.

No it is just simple physics ... if you apply a force not passing through CG, it would provide a moment, delta wing or not.

the gear box of India’s Light Combat Aircraft (LCA), Tejas, was tested in the CATH chambers.The building contains Combined Altitude, Temperature and Humidity (CATH) chambers, thermal shock chambers, dust chambers, corrosion chambers, and so on, where the various parts of radars are tested thoroughly before the systems are deployed in the field. The thermal shock chamber has three compartments. In the “cold” compartment, the temperature ranges from -700 Celsius to +800 C and in the hot cell, it ranges from 00 C to 2000 C. The third compartment has ambient temperature. The airborne radar systems are tested in these temperatures because when an aircraft climbs to an altitude of 40,000 feet (12,000 metres), the transition time from the ambient temperature to freezing cold is only 10 minutes. The airborne radar systems should withstand these thermal shocks.
Combined Altitude, Temperature and Humidity (CATH) chambers