Bharat Rakshak Forum Announcement

Hello Everyone,

A warm welcome back to the Bharat Rakshak Forum.

Important Notice: Due to a corruption in the BR forum database we regret to announce that data records relating to some of our registered users have been lost. We estimate approx. 500 user details are deleted.

To ease the process of recreating the user IDs we request members that have previously posted on the BR forums to recognise and identify their posts, once the posts are identified please contact the BRF moderator team by emailing BRF Mod Team with your post details.

The mod team will be able to update your username, email etc. so that the user history can be maintained.

Unfortunately for members that have never posted or have had all their posts deleted i.e. users that have 0 posts, we will be unable to recreate your account hence we request that you re-register again.

We apologise for any inconvenience caused and thank you for your understanding.

Regards,
Seetal

Naval LCA - News and Discussion

The Military Issues & History Forum is a venue to discuss issues relating to the military aspects of the Indian Armed Forces, whether the past, present or future. We request members to kindly stay within the mandate of this forum and keep their exchanges of views, on a civilised level, however vehemently any disagreement may be felt. All feedback regarding forum usage may be sent to the moderators using the Feedback Form or by clicking the Report Post Icon in any objectionable post for proper action. Please note that the views expressed by the Members and Moderators on these discussion boards are that of the individuals only and do not reflect the official policy or view of the Bharat-Rakshak.com Website. Copyright Violation is strictly prohibited and may result in revocation of your posting rights - please read the FAQ for full details. Users must also abide by the Forum Guidelines at all times.
NRao
BRF Oldie
Posts: 15355
Joined: 01 Jan 1970 05:30
Location: Illini Nation

Re: Naval LCA - News and Discussion

Postby NRao » 20 Apr 2017 16:36

The "problem" with a ski jump, when compared to a cat, is not just the reduced load a plane carries, but also the cat has a far better sortie rate (it is called something else that escapes me as I post). A cat allows more planes in the air (per unit of time) + the planes are far better equipped.

Then one has to account for recovering the assets AND moving them efficiently to allow other assets to take off or land or moved below deck.

These are the very things that have influenced the Vishal. And the USN offer for certifying the Vikrant.

A configurable ski jump WILL impact the ship's design in other areas and make it ineffective.

JTull
BRFite
Posts: 1868
Joined: 18 Jul 2001 11:31

Re: Naval LCA - News and Discussion

Postby JTull » 20 Apr 2017 18:51

Launch rate!

JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 20 Apr 2017 21:10

shiv wrote:^^Does no one in this world get credit for coming up with solutions where the problem does not exist? I'm outta here.


I know just the right use for this 45deg ramp. We should put it at Silk Board in Bangalore. Cars when driven fast enough can clear Silk Board in few seconds (well not all, Nano doesn't have enough T/W ratio, it has to be rejected only). And we can make is variable angle so depending on the queue length on the signal and incoming car type and where it wants to go, it will adjust the angle automatically (well given its BLR, the system will be manually run by Traffic cops. But what the hell..). At maximum 45deg angle it will let you land directly in Whitefield...!!

JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 20 Apr 2017 21:14

NRao wrote:The "problem" with a ski jump, when compared to a cat, is not just the reduced load a plane carries, but also the cat has a far better sortie rate (it is called something else that escapes me as I post). A cat allows more planes in the air (per unit of time) + the planes are far better equipped.

Then one has to account for recovering the assets AND moving them efficiently to allow other assets to take off or land or moved below deck.

These are the very things that have influenced the Vishal. And the USN offer for certifying the Vikrant.

A configurable ski jump WILL impact the ship's design in other areas and make it ineffective.


What is the baseline for your comparison..?? USN has 4 CATs on its Nimitz/Ford Class, and its huge in size. Where as Ramp AC are much smaller in size and have 2 points of launch. If you compare single CAT with single Ramp, I don't see how CAT should have significantly higher launch rate.

BTW USN was thinking of putting ramp in from of the CATs. I think EMALS on ramp is a good idea. EMALS can be fitted on Ramp I suppose.

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 20 Apr 2017 21:27

JayS wrote:
shiv wrote:^^Does no one in this world get credit for coming up with solutions where the problem does not exist? I'm outta here.


I know just the right use for this 45deg ramp. We should put it at Silk Board in Bangalore. Cars when driven fast enough can clear Silk Board in few seconds (well not all, Nano doesn't have enough T/W ratio, it has to be rejected only). And we can make is variable angle so depending on the queue length on the signal and incoming car type and where it wants to go, it will adjust the angle automatically (well given its BLR, the system will be manually run by Traffic cops. But what the hell..). At maximum 45deg angle it will let you land directly in Whitefield...!!

:D

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 20 Apr 2017 21:48

NRao wrote:The "problem" with a ski jump, when compared to a cat, is not just the reduced load a plane carries, but also the cat has a far better sortie rate (it is called something else that escapes me as I post). A cat allows more planes in the air (per unit of time) + the planes are far better equipped.

Where did you get this? Try doing this from a single CAT.

Mihir
BR Mainsite Crew
Posts: 798
Joined: 14 Nov 2004 21:26

Re: Naval LCA - News and Discussion

Postby Mihir » 21 Apr 2017 02:46

Marten wrote:
shiv wrote:The moving ramp could have self attuning PID controls with adaptive mechanisms depending on environment and sensed weight of plane and its velocity.

Not to forget, parallel synchronized sensor fusion from outboard conformal synaptic networks with dynamic holo haptic input for the operators.

We need a more contemporary reimagining of our four-dimensional transitional hardware. We need to rethink the aerial horizontal paradigm to integrate administrative time-phases, ambient asset hardware to enable holistic mobility management.

If you don't have a Ph.D in Technology Strategy already, this is your chance! :P

Mihir
BR Mainsite Crew
Posts: 798
Joined: 14 Nov 2004 21:26

Re: Naval LCA - News and Discussion

Postby Mihir » 21 Apr 2017 03:08

Neshant wrote:Draw bridges are not new.

The technology is hundreds of years old.

Never mind planes, trains literally go over them.


... when they're lowered. Not when they're raised!

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 03:42

I don't like to lecture people on how to behave but most of us don't have the humility to ask questions as student realizing that they probably don't know the answer, and others don't have the patience a knowledgeable person should bear.

Neshant, yesterday night, I had thought of answering your questions in detail, but I think I have to explain a lot. Instead, I will point you to pertinent directions. Please do some reading before asking more questions even if you feel you already know the answer. There is no harm.

There is no denying that generating lift through wings is much more efficient than generating lift through thrust. For fighter planes, in typical take off regimes, the former is about 7-8 times more efficient than the latter. For STOL take-offs, conventional planes with thrust vectoring don't vector thrust till just before TO. At that moment, they actually vector thrust up. Why? What governs that moment of time? Yet, for very short take-offs, VTOL aircrafts like F-35 and Harrier, try to keep the thrust as horizontal as possible (governed by nozzle redirection latency), and just prior to TO vector their thrust down. Why? What governs this moment of time? As an aside, I can say with some level of certainty that an F-35C will have greater weapon carrying capability off a skijump than a F-35B. Brar probably has the numbers.

Regarding, a movable skijump. Even a fixed skijump moves as it pitches and rolls with the ship. They already figure this out in the "margins". hey will calculate the configurations with which a plane can take off that skijump. The more margins you want to build in for variations, the more extra thrust you will require. This is what Cmde Balaji was complaining about, that IN's wind over deck requirements for new aircrafts are more relaxed than that desired of LCA-Navy. As for 45 degrees ramp, I told you before that the plane won't fly at that attitude after it leaves the ship.

Okay, I now I want to turn my focus to the rest of the members.
In a related question: is it worth discussing whether thrust vectoring could help LCA Navy Mk2 to carry higher payloads off a ski jump or not? I don't know the answers. Can somebody educate me?

Kartik
BRF Oldie
Posts: 3300
Joined: 04 Feb 2004 12:31

Re: Naval LCA - News and Discussion

Postby Kartik » 21 Apr 2017 04:56

MMR with Datalink demonstrated on NP2. From ADA's Annual report. Is the Navy's Datalink similar to the ODL that was being developed for the IAF?

Advance features like MMR - Air to Sea mode and Data Link functionalities has been demonstrated both with Sea Harrier and Ground
Station (Simulating the Aircraft carrier scenario).


and

Multi Mode Radar (MMR), codeveloped with M/s.ELTA, Israel, has been successfully integrated on LCA Navy Fighter (NP2). The LCA Navy has data link as additional feature in MMR.
Last edited by Kartik on 21 Apr 2017 05:31, edited 2 times in total.

Kartik
BRF Oldie
Posts: 3300
Joined: 04 Feb 2004 12:31

Re: Naval LCA - News and Discussion

Postby Kartik » 21 Apr 2017 05:25

Expect NP-5 Naval LCA twin seater to fly soon.

From ADA's annual report

Additional LCA Navy Trainer (NP5):

Second LCA Naval Trainer (NP5) deemed to be a production standard trainer aircraft, is an improved version of NP1. Presently aircraft is in build stage and all major modules are under assembly. The Rear fuselage assembly, Radome assembly and Fin & Rudder are successfully completed. 90% of Front Fuselage Assembly is completed. Centre Fuselage Assembly build under progress. Major LRUs are available and procurement of remaining LRUs is under progress . Installation drawings are released and kit preparations are under progress for equipping. The Maiden flight of NP5 aircraft is being planned by first quarter of 2017.



Improvements in NP-5 over NP1

The second Trainer aircraft (NP5) is being built close to production standard incorporating modification and additional functionalities compare to NP1 aircraft as follows:

Modifications:
1. Modified cockpit with 19deg Field of View HUD
2. Ni-Cd Battery in place of Ag-Zn battery in NP1
3. V/UHF Radio in place of INCOM
4. Implementation of three Auxiliary Air Intake Door(AAID)

Additional LRUs :
1. SPJ POD integration
2. Laser Designator Pod
3. Air to Air Refueling probe (as retro mod)
4. HMDS
5. CMDS
6. TACAN
7. VOR/ILS
8. SLB

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 21 Apr 2017 07:09

Indranil wrote:In a related question: is it worth discussing whether thrust vectoring could help LCA Navy Mk2 to carry higher payloads off a ski jump or not? I don't know the answers. Can somebody educate me?

When I read between my broken teeth I get the idea that movement is always 180 degrees away from thrust. For a mass to move in any direction the thrust, the center of mass and the desired direction of movement must form a straight line.

In the LCA the thrust, the center of mass and the pointy nose are in a straight line. The LCA's thrust acts on its center of mass to make the pointy nose move forward. Conveniently this is the direction needed for maximum lift from the wings. If the thrust is directed away (say partially downwards/earthwards) it will merely tilt the musharraf upwards as the aircraft will rotate tail up-nose down around the center of mass. This is not lift. It is pitch down. Not only is part of the thrust now directed away, the pitch down also reduces wing lift by altering the direction of movement adversely.

Causing a pitch up by vectoring the thrust upwards only aggravates the pitch up caused by the ramp. Continued unchecked thrust "vectoring" in this direction will change the angle of attack beyond Kulbit, into somersault followed by Davy Jones manoeuvre.

Unless lift can be made to act symmetrically on the center of mass there will be no net improvement in take off distance or mass. I would say than an unqualified "Hmm slow day today - whatcha say we use thrust vectoring on LCA?" means nothing without planning to superimpose the direction of thrust vectoring on the direction of movement required for most efficient lift. Fitting Geisha fans around the musharraf cannot work.

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 08:51

Hakeem, it is obvious that TVC will create a moment: that is its purpose! Those moments can be used to provide control when the traditional control surfaces are not effective enough. Can that be used when to lower the ramp exit velocity. Do you know which of the two velocity is higher :

1. V-1: minimum velocity at which you have pitch authority to maintain most favoured AoA for climbout.
2. V-2: minimum velocity from which V-climbout can be achieved within sufficient time.

My guess is V-1 > V-2, which is the minimum ramp exit velocity. And if, I am right. Then by using control augmentation through TVC, V-2 can be lowered. This translates to greater payload carrying capability for the same amount of thrust. Let me elaborate further.

Your sequence of the use of TVC is off. There will be no thrust vectoring till the plane exits the ramp. Therefore, there is no difference in ramp exit speed vis-a-vis a plane without TVC. Right after the moment the plane leaves the ramp, the TVC kicks in to assist the elevons to keep the nose pointed at the right attitude. As soon as the velocity is reached wherein the elevons can provide adequate authority, the thrust is redirected along the longitudinal axis for fastest acceleration to climb out speed.

The above is not very different from what you see when a thrust vectored aircraft takes off from a runway. The vector control is used to lower the V-r (or speed at which the aircraft can "rotate" on the runway) enabling shorter take off runs.


JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 21 Apr 2017 09:12

shiv wrote:
Indranil wrote:In a related question: is it worth discussing whether thrust vectoring could help LCA Navy Mk2 to carry higher payloads off a ski jump or not? I don't know the answers. Can somebody educate me?

When I read between my broken teeth I get the idea that movement is always 180 degrees away from thrust. For a mass to move in any direction the thrust, the center of mass and the desired direction of movement must form a straight line.

In the LCA the thrust, the center of mass and the pointy nose are in a straight line. The LCA's thrust acts on its center of mass to make the pointy nose move forward. Conveniently this is the direction needed for maximum lift from the wings. If the thrust is directed away (say partially downwards/earthwards) it will merely tilt the musharraf upwards as the aircraft will rotate tail up-nose down around the center of mass. This is not lift. It is pitch down. Not only is part of the thrust now directed away, the pitch down also reduces wing lift by altering the direction of movement adversely.

Causing a pitch up by vectoring the thrust upwards only aggravates the pitch up caused by the ramp. Continued unchecked thrust "vectoring" in this direction will change the angle of attack beyond Kulbit, into somersault followed by Davy Jones manoeuvre.

Unless lift can be made to act symmetrically on the center of mass there will be no net improvement in take off distance or mass. I would say than an unqualified "Hmm slow day today - whatcha say we use thrust vectoring on LCA?" means nothing without planning to superimpose the direction of thrust vectoring on the direction of movement required for most efficient lift. Fitting Geisha fans around the musharraf cannot work.


Very good explanations. Its a dead end. Time for the question whether NLCA could use TV was in early 1990's. Its too late to incorporate it even if it was useful or even practically possible.

JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 21 Apr 2017 09:34

Indranil wrote:Hakeem, it is obvious that TVC will create a moment: that is its purpose! Those moments can be used to provide control when the traditional control surfaces are not effective enough. Can that be used when to lower the ramp exit velocity. Do you know which of the two velocity is higher :

1. V-1: minimum velocity at which you have pitch authority to maintain most favoured AoA for climbout.
2. V-2: minimum velocity from which V-climbout can be achieved within sufficient time.


Where did you get this from that there is no pitch authority for NLCA at ramp exit..? I can wager 100bucks all the aircrafts TOing of the ramp are sized for pitch autority right after the ramp exit in worst condition. Having no pitch authority means certain death for the pilot if anything goes wrong on the deck during launch or just at the ramp exit. There chances of ejection would depend on keeping attitude. If you see specifically NLCA, they have modified FCS (hands off launch) to reduce AoA immediately after ramp exit as any jet has natural tendency to have rapid pitch up after ramp exit. In fact in the first flight the switch to recognise ramp exit event failed, NP1 pitched up rapidly and Pilot had to manually reduce pitch. This delayed second flight by 3months or so. FCS is designed to reduce AoA after ramp exit. The americans did the same with FA18A when they tested it off the ramp. This means there is sufficient pitch authority available at ramp exit Velocity.

Even if we say its not there, why TV for just this small reason?? Why not just upsize elevators..? LCA doesnt have an issue of blocked elevator. Simple upsizing should increase pitch authority. (But they already have huge elevators anyway.)

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 09:52

That's not what I said. I said any aircraft needs to have pitch authority as soon as it leaves the ramp. If pitch authority provided by the elevons is augmented by the thrust vectoring, then ramp exit speed can be lowered.

I remember watching the video. Let me watch it again. IIRC it is not because the plane naturally wants to pitch-up. The control laws has to switch modes when the aircraft leaves the ramp because pilot controls have different effects between the modes. Due to the delayed detection of ramp exit, the control laws provided inputs corresponding to the plane being on the ramp when it was actually in the air. This lead to the pitch up. I will confirm after watching the video again.

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 21 Apr 2017 10:10

Indranil wrote:There will be no thrust vectoring till the plane exits the ramp. Therefore, there is no difference in ramp exit speed vis-a-vis a plane without TVC. Right after the moment the plane leaves the ramp, the TVC kicks in to assist the elevons to keep the nose pointed at the right attitude. As soon as the velocity is reached wherein the elevons can provide adequate authority, the thrust is redirected along the longitudinal axis for fastest acceleration to climb out speed.


One thing that has not been mentioned at all in all the posts so far (Except an indirect reference by Mihir i think) is that a conventional (No thrust vectoring) ramp take off is not just about velocity. It is about acceleration - i.e. continuous increase of velocity and therefore continuous increase in lift and control surface authority before the ramp, on the ramp and beyond the ramp.

When the plane is forced to go up a ramp - I do not have the data - but the sudden change of direction only results in a slowing of acceleration, but not a decrease in velocity. The fact that the plane has reached velocity to stay in the air when it exits the ramp means that there is enough lift to hold the plane at that height and angle of attack as it exits the ramp i.e. it is just above stalling speed. That means the control surfaces have control authority at this point.

However at the point of going off the ramp the velocity is just above stalling speed and acceleration is required. Acceleration requires continued thrust. If the thrust is deflected downwards at this point, acceleration will drop. If the engine has vast excess power (not true for LCA) then the drop in acceleration may be insignificant. But the LCA may simply slow down below stalling speed if the forward thrust is decreased. If velocity drops below stalling then the control surfaces will not have authority. What is the point in reducing forward thrust and when what is needed is a continuous increase in velocity?

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 21 Apr 2017 10:14

Indranil wrote:That's not what I said. I said any aircraft needs to have pitch authority as soon as it leaves the ramp. If pitch authority provided by the elevons is augmented by the thrust vectoring, then ramp exit speed can be lowered.

With respect Indranil - any "authority" that the elevons have is totally dependent on airspeed. The authority fails as the plane approaches stalling speed. The velocity must ALWAYS remain above stalling speed to maintain elevon authority. What is the exact speed on ramp exit? What is the stalling speed? What is the forward thrust required to keep the plane above stalling speed. Would directing the forward thrust elsewhere retain enough forward component to keep the velocity above stalling speed? I don't have this data

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 10:51

The ramp exit speed is much lower than stall speed. Mig-29s exit ramps at 70 knots.

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 21 Apr 2017 10:55

Indranil wrote:The ramp exit speed is much lower than stall speed. Mig-29s exit ramps at 70 knots.

Would control surface authority be augmented by reducing forward thrust at this stage?

Wiki says:
A MiG-29 launching over the ski-jump ramp on a Kuznetsov-class aircraft carrier can takeoff at a speed of about 70 kn (81 mph; 130 km/h) instead of the usual 140 kn (160 mph; 260 km/h) (depending on many factors such as gross weight)


The vast excess power that a MiG 29 can generate especially if lightly loaded, in addition to a healthy 30 plus knot headwind from the ship sailing full speed into the wind makes this believable, but probably not routine or desirable.

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 11:02

Boeing actually patented a method to decrease ramp exit speeds using a concept very similar to what I was discussing.

Referring now to Figure 14, the takeoff sequence of events is summarized:

In step 1 the engine is throttled up to maximum power and the brakes are released.
In step 2 the aircraft accelerates to takeoff speed. The thrust vector angle is zero for maximum acceleration.
In step 3 the nose gear contacts the ski jump ramp and the nose of the aircraft begins to rotate up. The velocity vector is still parallel to the runway.
In step 4 the main gear contacts the ski jump ramp. The nose continues to rotate up, but now the entire aircraft is lifted up, also. So the velocity vector has been rotated up. With the main gear lifted above the runway, the aircraft is free to rotate to a higher angle of attack than its normal tailscrape angle.
In step 5 the aircraft has cleared the ski jump ramp and its nose continues to rotate up to the maximum angle of attack, which is between the aircraft's normal angle of attack and 70°. The thrust is vectored down to stop the rotation and to generate additional lift. The aircraft continues to accelerate to its normal climb speed.
Image

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 11:09

shiv wrote:
Indranil wrote:The ramp exit speed is much lower than stall speed. Mig-29s exit ramps at 70 knots.

Would control surface authority be augmented by reducing forward thrust at this stage?

I don't think that you are understanding what I am asking or suggesting. Please read what I have written again. There is no TVC before ramp exit, so TVC or non-TVC doesn't matter. However, if you could augment control surfaces using TVC after ramp exit, you could have exited the ramp at a lower speed. Hence for the same thrust, you could take off with more payload.

If LCA had the excess thrust of the Mig-29, I would not be discussing this. This discussion is meaningful because LCA doesn't enjoy the same levels of TWR.

vina
BRF Oldie
Posts: 5829
Joined: 11 May 2005 06:56
Location: Doing Nijikaran, Udharikaran and Baazarikaran to Commies and Assorted Leftists

Re: Naval LCA - News and Discussion

Postby vina » 21 Apr 2017 11:16

Indranil wrote:Hakeem, it is obvious that TVC will create a moment: that is its purpose! Those moments can be used to provide control when the traditional control surfaces are not effective enough. Can that be used when to lower the ramp exit velocity. Do you know which of the two velocity is higher :

1. V-1: minimum velocity at which you have pitch authority to maintain most favoured AoA for climbout.
2. V-2: minimum velocity from which V-climbout can be achieved within sufficient time.

JayS wrote:Where did you get this from that there is no pitch authority for NLCA at ramp exit..? I can wager 100bucks all the aircrafts TOing of the ramp are sized for pitch autority right after the ramp exit in worst condition.


Like a bad dream (or a good dream?) the same questions keep coming up again and again. We have been through all this earlier as well, under "INS Vikrant News and Discussion" thread long long ago.

So let me copy paste a few things from that thread (long archived) so that we get the basics right.

It is just high school vector algebra and physics
1. Ski Jump launches you ballistically. At the moment the plane exits the ramp, it is NOT flying (i.e., lift NOT= wt) . What it does is, it gives it time for the plane to pick up speed (as it is launched ballistically) to start flying before it hits water
2. If the ship is stationary, the AoA at launch is ZERO . If the ship is moving (it will move INTO a wind , why?), there is a relative wind and the AoA is HIGHER than the 14 deg or whatever the ramp angle at the moment it leaves the ramp . The relative wind comes from a direction below (do the vector algebra). Check this out if you want to see "papers".

Well, what is this thing called relative wind There is No Such Thing
Don't believe me ? Read this post
So what is this Relative Wind business ? Ok, answer a question with a question Can a Sailboat sail Upwind ? How?
Were the "Savage "Polynesians with their triangular and rigged sails, more technologically advanced than the Romans and their squad rigged galleys ? Check here Polynesians vs Romans

So lets do Math and see how it works

Lets foggedabout all this and put it in Simple English with step by step cook book on how this works . Step 1 and Step 5 , 6 , 7, 8 & 9 are extremely important .

So how does all this work for a plane with Thrust vectoring Like the Harrier

What does thrust vectoring do to the Sink rate as in Step 9 ?
Last edited by vina on 21 Apr 2017 11:26, edited 3 times in total.

vina
BRF Oldie
Posts: 5829
Joined: 11 May 2005 06:56
Location: Doing Nijikaran, Udharikaran and Baazarikaran to Commies and Assorted Leftists

Re: Naval LCA - News and Discussion

Postby vina » 21 Apr 2017 11:20

Indranil wrote:The ramp exit speed is much lower than stall speed. Mig-29s exit ramps at 70 knots.

Just read through what I just posted before this.
And ah, we are back to high school physics of relative motion. The ramp speed wrt 70 Knots wrt to the SHIP. The ship itself is doing something like 25kts and ideally you want a 5 to 10 knot wind and you steam INTO the wind. So the Wind On Deck is something like 30 to 35 knots ! You have to add that to the 70 knots and the Mig 29 is actually leaving the ramp at something like 100 knots which is below the flying speed by 40 knots ! So what gives and how does it fly and not crash ? That is in the previous post I made summarising what we discussed much earlier in another thread.

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 21 Apr 2017 11:21

Indranil wrote:.
In step 5 the aircraft has cleared the ski jump ramp and its nose continues to rotate up to the maximum angle of attack, which is between the aircraft's normal angle of attack and 70°. The thrust is vectored down to stop the rotation and to generate additional lift. The aircraft continues to accelerate to its normal climb speed.

There is no reason for the nose to continue to rotate by itself up to maximum angle of attack as long as there is no control input.

In fact the LCA shows elevons in a position that causes nose-up before and after it exits the ramp.
Watch from here: https://youtu.be/dB73FdERNBA?t=63

As long as takeoff speed off the ramp is above stalling and the plane is accelerating, a pitch up is desirable to gain altitude and speed which are the two most crucial parameters in the immediate post take off period for safety. The LCA appears to do exactly that - i.e. increase its angle of attack after exiting the ramp.

vina
BRF Oldie
Posts: 5829
Joined: 11 May 2005 06:56
Location: Doing Nijikaran, Udharikaran and Baazarikaran to Commies and Assorted Leftists

Re: Naval LCA - News and Discussion

Postby vina » 21 Apr 2017 11:29

shiv wrote:its angle of attack after exiting the ramp.

Please check your own experiment and answer to that in earlier thread on WHY that happens and why the "Savage" Polynesians were in fact more advanced than the "civilised" Romans

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 21 Apr 2017 11:30

Indranil wrote:I don't think that you are understanding what I am asking or suggesting. Please read what I have written again. There is no TVC before ramp exit, so TVC or non-TVC doesn't matter. However, if you could augment control surfaces using TVC after ramp exit, you could have exited the ramp at a lower speed. Hence for the same thrust, you could take off with more payload.

You are saying "augmentation" of control surfaces but are only speaking of control in pitch, not yaw or roll

My awareness in this area can me measured by the gaps in my teeth - but this is what I think:

1. A plane coming off a ramp must crash if it does not accelerate above stalling speed before it hits the water.
2. Control surface authority is marginal or non existent below stalling speed
3. Control surface authority is pitch, roll and yaw.

If engine thrust is directed to pitch alone it will assist in a change of attitude. (more pitch/less pitch etc). A change of attitude is loss of energy and loss of airspeed and further degradation in yaw and roll controls in a flight regime that is at or marginally above stall speed.

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 11:45

Hakeem, all I can request you is to read our discussion again and try to understand what I am saying. Right now your teeth look quite intact.

LCA does not use elevons before ramp exit. On hitting the ramp, its pitch up increases rapidly which the classical CLAW would see as an anomaly and try to fight. Hence, a special case for the ramp has been created which clips the feedback and hence, the CLAW does not provide any control inputs till ramp exit is detected. They have watched the videos many times to make sure that this is the exact behavior of the aircraft on the ramp.

However, in the first test there was a delay of 1.3 seconds in detecting ramp exit. During this time, the CLAW control inputs were damped (thinking that the aircraft was still on the ramp). Because LCA is a statically unstable aircraft, it continued to pitch up in the absence of CLAW control inputs.

Jay, as you can imagine, I revisited the video. The details above are from the video. I also read the first NACA paper on ski jumps. On a statically stable plane, there no natural tendency to continue to pitch up after ramp exit.

Vina, I will read your links tomorrow and answer.

Atmavik
BRFite
Posts: 282
Joined: 24 Aug 2016 04:43

Re: Naval LCA - News and Discussion

Postby Atmavik » 21 Apr 2017 11:59

Image

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 12:02

ACtually Vina, I cursorily went over your links. I agree. But, I am not asking the question that you had answered before. My question is different: Will the addition of TVC allow aircrafts to lave lower ramp exit speeds, thus allowing them to have lower TWR?

JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 21 Apr 2017 12:05

Indranil wrote:That's not what I said. I said any aircraft needs to have pitch authority as soon as it leaves the ramp. If pitch authority provided by the elevons is augmented by the thrust vectoring, then ramp exit speed can be lowered.

I remember watching the video. Let me watch it again. IIRC it is not because the plane naturally wants to pitch-up. The control laws has to switch modes when the aircraft leaves the ramp because pilot controls have different effects between the modes. Due to the delayed detection of ramp exit, the control laws provided inputs corresponding to the plane being on the ramp when it was actually in the air. This lead to the pitch up. I will confirm after watching the video again.


My bad, I assumed you are talking specifically for NLCA.

Indranil, imagine throwing a big flat plate at an angle at high speed in air, it will tend to pitch up. LCA is like that plate at ramp exit since its at very low speed and comparatively very high AoA. In case of NLCA also, the pitch up is natural tendency and the FCS tries to control it (NLCA (just like any other unstable fighter) is unstable aircraft and it will pitch up at slightest of disturbance and diverge rapidly unless you control it). On the ramp they clipped this pitch rate feedback to let the pitch rate rise naturally without the FCS trying to fight it, since it concludes its uncommented pitch rate. (14deg ramp is cross in about 1sec giving 14deg/sec pitch rate approximately speaking). This meant that they reduced the artificial stability of the Jet. This special mode had to be removed the moment it leaves the ramp. Which didn't happen due to incorrect determination of ramp-exit event. Thus the pitch up which was partially controlled by FCS and partially by pilot stick input. Dr. Saraf makes the exact comment in the video that NLCA was flying at reduced stability for 1.3sec..!!

Also, I don't think pilot is suppose to give any inputs on the ramp, its hands-off take-off. FCS does it all - all it has to do is keep the jet dead straight and on a trajectory with smooth AoA rise at desired rate and till a desired max level and hold it there until it reaches Nz=1G where its flying on its own. (I don't know if this is just some mish-mashed memory in my mind, I tend to have that kind of stuff a lot, but I think I read/saw somewhere that F/A18 pilots count to 3 or 4 after CAT exit before touching the stick. By that time the jet is airborne. Similar thing should be there for NLCA in its final avatar.)

PS: Too many new posts while I was typing.

JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 21 Apr 2017 12:11

Indranil wrote:Boeing actually patented a method to decrease ramp exit speeds using a concept very similar to what I was discussing.

Referring now to Figure 14, the takeoff sequence of events is summarized:

In step 1 the engine is throttled up to maximum power and the brakes are released.
In step 2 the aircraft accelerates to takeoff speed. The thrust vector angle is zero for maximum acceleration.
In step 3 the nose gear contacts the ski jump ramp and the nose of the aircraft begins to rotate up. The velocity vector is still parallel to the runway.
In step 4 the main gear contacts the ski jump ramp. The nose continues to rotate up, but now the entire aircraft is lifted up, also. So the velocity vector has been rotated up. With the main gear lifted above the runway, the aircraft is free to rotate to a higher angle of attack than its normal tailscrape angle.
In step 5 the aircraft has cleared the ski jump ramp and its nose continues to rotate up to the maximum angle of attack, which is between the aircraft's normal angle of attack and 70°. The thrust is vectored down to stop the rotation and to generate additional lift. The aircraft continues to accelerate to its normal climb speed.


That's X-31. There is probably videos of the Extremely short Landing they tried with it. Can't remember about take off, but few other jets can do it in air shows, usual suspects from Russia and F22 for example. But this thing could work only when the jet is lightly loaded or have very high excess thrust right off the deck even at MTOW.

It has a canard to command pitch up even when TV is downwards pushing the nose down. And it augments lift too. Wonder if this will work for aircraft without canard.

JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 21 Apr 2017 13:02

shiv wrote:There is no reason for the nose to continue to rotate by itself up to maximum angle of attack as long as there is no control input.

In fact the LCA shows elevons in a position that causes nose-up before and after it exits the ramp.
Watch from here: https://youtu.be/dB73FdERNBA?t=63

As long as takeoff speed off the ramp is above stalling and the plane is accelerating, a pitch up is desirable to gain altitude and speed which are the two most crucial parameters in the immediate post take off period for safety. The LCA appears to do exactly that - i.e. increase its angle of attack after exiting the ramp.


An unstable aircraft will pitch up unless you control it. If you configure FCS such that it does not try to control this, then without any control input the aircraft will pitch. And indeed that's what happened in NCLA's first flight.

You can check out Elevon deflection angle in the Aero Seminar video here: https://youtu.be/le4-iucZRVE. It starts negative, goes to zero, comes down and then tapers off to near-zero. Blue line is unmodified CLAW which would fight the perceived un-commanded pitch up thus as high as +10deg (downward) elevon deflection. But in modified CLAW they clipped this response thus you see flat portion in red line there on the ramp.

Also Shiv, the speed need not be more than Stall speed at ramp exit. In fact it is not. If you check the Nz graph in shows in the AI Seminar (https://youtu.be/le4-iucZRVE) above, after ramp exit Nz immediately drops to ZERO. Which means its more or less in free flight. Very less life. You can call it pre-stall regime since its not even started flying in first place to stall. Then Nz value slowly rises to 1 where it starts generating enough life to support its own weight. The aircraft is basically a flying stone (exaggeration of coarse) at the ram exit. The trajectory is thus referred to as Semi-ballistic in that seminar.

JayS
BRFite
Posts: 1798
Joined: 11 Aug 2016 06:14

Re: Naval LCA - News and Discussion

Postby JayS » 21 Apr 2017 13:16

JayS wrote:
Indranil wrote:Hakeem, it is obvious that TVC will create a moment: that is its purpose! Those moments can be used to provide control when the traditional control surfaces are not effective enough. Can that be used when to lower the ramp exit velocity. Do you know which of the two velocity is higher :

1. V-1: minimum velocity at which you have pitch authority to maintain most favoured AoA for climbout.
2. V-2: minimum velocity from which V-climbout can be achieved within sufficient time.


Where did you get this from that there is no pitch authority for NLCA at ramp exit..? I can wager 100bucks all the aircrafts TOing of the ramp are sized for pitch autority right after the ramp exit in worst condition. Having no pitch authority means certain death for the pilot if anything goes wrong on the deck during launch or just at the ramp exit.

Just realised a fallacy in my thinking. Right after the ramp may not be exactly o.oo1sec after the ramp but could be 1sec after the ramp exit. The whole point of ramp is to give enough time and distance.

vina
BRF Oldie
Posts: 5829
Joined: 11 May 2005 06:56
Location: Doing Nijikaran, Udharikaran and Baazarikaran to Commies and Assorted Leftists

Re: Naval LCA - News and Discussion

Postby vina » 21 Apr 2017 13:33

Indranil wrote:ACtually Vina, I cursorily went over your links. I agree. But, I am not asking the question that you had answered before. My question is different: Will the addition of TVC allow aircrafts to lave lower ramp exit speeds, thus allowing them to have lower TWR?

Read it in entirety . The answers to you questions are there. Specifically in these parts . I talked about the Harrier as well and the control problem of LCA /Mig 29 etc wrt Harrier.

So lets do Math and see how it works

Lets foggedabout all this and put it in Simple LAYMAN English with step by step cook book on how this works . Step 1 and Step 5 , 6 , 7, 8 & 9 are extremely important .

So how does all this work for a plane with Thrust vectoring Like the Harrier

What does thrust vectoring do to the Sink rate as in Step 9 ?


The thing you need to remember with "thrust vectoring" (like in Harrier of F35B and NOT like in the F22 and SU30MKI) , is that the Harrier and F35B have active GAS powered controls for pitch , yaw and roll (with louvres opening out for each of those posts), because they have to control it in hover condition. Those planes are a different ball game altogether and can launch off a ramp at LOWER speed than an equivalent weight conventional plane (assume TOW of Harrier = TOW LCA) because it can be controlled far better at lower speed. If you decrease the ramp exit speed, you decrease the required T:W ratio required for a given take off run length.

The ramp speed needed at exit will be higher for a conventional plane (mig 29, LCA and so hypothetically a SU -33 MKI or F22 even with thrust vectoring) for the same take off run length and will need higher T:W ratio , to accelerate to that speed.

So fundamentally it is a control problem in stalled condition. The answer to your question is will thrust vectoring help , is that it depends on what KIND of active control you are talking about. If Harrier /F35B type (all of pitch , yaw and roll with active stabilisation), yes. If you are talking of SU-30MKI or F22 type , NO, you will not be able to lower T:W requirement.

And oh, for perspective, the rumoured payload of the J-15 Ding-Dong flying out of the Liaoning is JUST 4000lbs (ie. LESS Than 2 TONS) . I am willing to bet that the overweight NLCA MK1 has similar or BETTER payload. The J15 Ding-Dong also is a far heavier plane and carries more momentum when it lands. It will take some pretty serious amount of effort to stop it, just as it will take the engines a huge amount of thrust to get it up to take off speed in a limited take off run on the Varyag /Liaoning.

And some obviously semi-literate in these matters Iyer-Mitra types will set off random dhoti shivers about how the LCA MK1 is a "failure" , while the J-15 ding-dong is super duper successful ! Pays to keep perspective as always

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 21 Apr 2017 16:31

JayS wrote:An unstable aircraft will pitch up unless you control it. If you configure FCS such that it does not try to control this, then without any control input the aircraft will pitch. And indeed that's what happened in NCLA's first flight.

That is not what the narration in the video says. Oh OK - you are saying the same thing in a different way..

The basic CLAW had software to command elevons to oppose uncontrolled pitch as you say, but the CLAW interpreted the ski-ramp itself as uncontrolled pitch and would compensate to control that. So before the first flight they turned off the pitch control commands as the plane entered the ramp with the idea that the pitch control software would kick in as soon as ramp exit was detected by a switch in the landing gear.

But in the first take-off the plane went into uncontrolled pitch with rise in AoA that was manually damped by the pilot.

This sudden uncontrolled rise in AoA was because there was a 1.3 second delay in the landing gear switch that detected ramp exit and during this 1.3 seconds the pitch control software had not kicked in by design. They figured out why there was a 1.3 second delay and rewrote the software to do a better detection of ramp exit after which the software ignored only the pitch that was caused by climbing the ramp but kicked in immediately after ramp exit.

Watch from: https://youtu.be/le4-iucZRVE?t=714

Indranil
Forum Moderator
Posts: 5195
Joined: 02 Apr 2010 01:21

Re: Naval LCA - News and Discussion

Postby Indranil » 21 Apr 2017 20:47

Hakeem, good to see you back on track. The teeth are again starting to show the gaps :D. Now make them move with the understanding that the 70 degree AoA take off on the Boeing patent is not possible without TVC.

Jay, I thought they were talking of the X-31, but could not join the Rockwell-Boeing connection. You are definitely right that the kind of maneuvers described in that patent is for a very lightly loaded plane. But what I am saying is can we use TVC to exit the ramp and maintain a 15 degree AoA at ramp exit at speeds lower than what could be possible with control surfaces alone? By the way, the AoA of the plane leaving a ramp is much more variable than a flat plate tossed in the air. The aircraft pitches down when the nose wheel leaves the ramp but the main gear is still supported by the ramp. Right after the main gear exits the ramp, the AoA increases sharply because the aircraft encounters air which is being forced up by the leading edge of the ramp (they actually have to make sure that the AoA does not go beyond the critical angle). Thereafter, the aircraft completely looses the ground effect and experiences a pitch down due to loss of lift.

Vina, it is easy to see why you missed the beginning of the discussion with all the back and forth. I started by saying that Harrier/F-35B use TVC in a completely different manner because of their VTOL capabilities than planes like Su-30/F-22. And from your linked posts it is clear that we both understand the basics of the difference. What is surprising you dismiss that TVC can be used to control the plane in stalled regimes. That's what all those post stall maneuvers (barring the cobra) are. Albeit, we cannot use the 2D-vectoring nozzles in the canted fashion as on the Su-30 to also get yaw control, but a 3D vectoring system like the ones on the Mig-29 OVT engines can easily provide us even that. Even if I go, with 2D thrust vectoring, as you know: for most airplanes, the minimum speed required for yaw control is lower than minimum speed for roll control is lower than the minimum speed required for pitch control using conventional surfaces. So, if I use thrust vectoring to augment the pitch control only at ramp exit, can we now lower the exit to the speed required to have roll control using conventional surfaces?

vina
BRF Oldie
Posts: 5829
Joined: 11 May 2005 06:56
Location: Doing Nijikaran, Udharikaran and Baazarikaran to Commies and Assorted Leftists

Re: Naval LCA - News and Discussion

Postby vina » 22 Apr 2017 06:57

Indranil wrote: What is surprising you dismiss that TVC can be used to control the plane in stalled regimes. That's what all those post stall maneuvers (barring the cobra) are. Albeit, we cannot use the 2D-vectoring nozzles in the canted fashion as on the Su-30 to also get yaw control, but a 3D vectoring system like the ones on the Mig-29 OVT engines can easily provide us even that.

There are differences. All the nice videos of Flankers being thrown about in the air like juggler's balls and downing flat spins and Kulbits and tail slides all that is fine. However, if you notice, the recovery from ALL of them is by dropping the nose and gaining airspeed. Why the plane falls a couple of 100 feet even when doing those routines (like flat spin) . What they are doing is trading height for speed in recovery .That kind of thing is not an option from a ski jump.

So, if I use thrust vectoring to augment the pitch control only at ramp exit, can we now lower the exit to the speed required to have roll control using conventional surfaces?


Show me a routine where a flanker is stalled in level flight , then with nose is kept high and fully controlled,doesnt drop height, picks up speed and then climbs away and I will buy that.

What TVC (like flanker) will do however is reduce the sink rate (on of the points in the Layman Simple English cook book) I posted and i asked about and that gives you more time and more payload and you can relax one more constraint a bit (time the ballistic flight can last and hence amount of time the engine can work to accelerate you). But whether that can affect the take off t:w , I don't think so.

vina
BRF Oldie
Posts: 5829
Joined: 11 May 2005 06:56
Location: Doing Nijikaran, Udharikaran and Baazarikaran to Commies and Assorted Leftists

Re: Naval LCA - News and Discussion

Postby vina » 22 Apr 2017 07:13

Just saw the presentation by Dr Saraf & Capt Dahiya you folks had kindly posted. A couple of quick observations.

1. Our cameramen are so used to covering Politicos and Actors and other kinds they have simply no idea that they should point the camera at the presentation screen and NOT the face.

2. From what I can see presented.
a. The CAS of the LCA as it hits the ramp is about 100 to 110 knots, the end of the ski jump to when it starts "flying" is around 150 knots
b. The angle of attack as it leaves the ramp instantaneously shoots up the moment it exits the ramp (can see why, the plane is pitched up and the velocity vector doesnt match the pitch angle)
c. Amazing simply how INEFFICIENT and lack of margins there is, when you are launching a conventional plane from a ski jump. Stuff like bleed air shut off, ECS shutdown, cooling down etc , just shows it.
d. This entire STOBAR with conventional aircraft is so sub optimal. In a hot day , with no sea breeze and if you have mechanical problems /battle damage and the carrier can't put out the required speed , the planes can't take off . This kind of stuff is best left to VSTOL aircraft.

3. I really think this "Russian" idea of force fitting a square peg into a round hole is simply too much.
4. Catapults are the way to go. You have far higher margins, don't have to do grapple with the difficult take off control problems and far safer.

shiv
BRF Oldie
Posts: 31538
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: Naval LCA - News and Discussion

Postby shiv » 22 Apr 2017 07:19

Naaah. Fuggedabahtit
Last edited by shiv on 22 Apr 2017 08:06, edited 1 time in total.


Return to “Military Issues & History Forum”

Who is online

Users browsing this forum: achoudhury, dkhare, Google Feedfetcher, rnareddy, RohitAM and 17 guests