INS Vikrant News and Discussion

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Re: INS Vikrant News and Discussion

Postby NRao » 22 Jun 2015 05:54

That "DTTI" that the Centcom loves to hate, while the Pacom loves?

The "DTTI" has expectations - like any other acronym.

I have a feeling that the IN understands it very, very well. Which is why the IN is sitting down to share thoughts - how often does that happen? It is serious enough for the PM and Prez of two nations to talk about.

The Vikrant, just like the LCA, is the best thing since sliced bread. Both are indispensable (even at 30 years and going)

But there is a dimension that the IN cannot afford to let go. Ordering another Vikrant is not the issue. The issue is about the other dimension that DTTI offers. And, the fact that the IN and teh GoI have decided to get involved with the DTTI says a lot - something that has been neglected in discussions.

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Re: INS Vikrant News and Discussion

Postby NRao » 22 Jun 2015 05:56

- self deleted -
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Re: INS Vikrant News and Discussion

Postby Bade » 22 Jun 2015 06:19

I do my part of reading and between the lines of open source that I can find, CSL is pushing hard on the dry dock. The outcome on that will tell to some extent what GoI is thinking as well as the Navy, though not entirely as it is not carrier specific but has other uses too.

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Re: INS Vikrant News and Discussion

Postby NRao » 22 Jun 2015 06:40

DTTI, another dimension:

Margolis believes it could be used in any future confrontation to overwhelm Pakistan’s aging navy. He further notes, “Pakistan could not fight for longer than a week in the face of an Indian naval blockade – unless the U.S. Navy challenged it.”

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Re: INS Vikrant News and Discussion

Postby amit » 22 Jun 2015 07:05

Cain Marko wrote:Whether they go with a large super carrier, cats etc., is not so much my concern currently. ...more important to order another Vikrant class right away. Also, I don't see Indian ACs playing a similar role to the USN - pulverizING enemy defenses and imposing nfz across the globe or controlling the skies in the Pacific. More like sea denial and fleet defense for which a modded AEW platform should do. What exactly is the need for super heavies taking off from the carriers? A 29K with all its payload of about 5500kg is more than enough for such roles...


The undying love for Russian maal is one of the signature features of this forum. :D

Sea denial is the No1 priority for the Indian Navy and this will probably remain so over the next several decades. India is, after all, a status quo power.

However, the question to ask is: Will the 29K with about 5500kg of stores be adequate for this job in say 2040-2050 time frame? If the answer is a resounding No, then the next questions is: What planes (remember the weight restrictions which STOBAR brings) will replace them? Are their any designs around? Our own AMCA is likely to be in the medium weight category and heavier than the 29Ks.

The point of confusion on this thread IMHO is that the distinction between fact that the Vishal is meant to be an aircraft carrier designed for our needs several decades in the future as opposed to Vikrant which is a carrier designed for our immediate needs is being lost.

I too want the Navy to go for another Vikrant, particularly since CSL has said it can deliver one within 4-5 years. However, if the Navy does not go for the offer, it means that it thinks that the two carriers that we will have once Vikrant enters services is adequate for our present needs.

By exploring the options of EMAL, nuclear power, flat top etc for Vishal, the Navy is showing strategic foresight in designing a ship which will serve us well into 2060-2070 time frame.

IMO, I would think its obvious that the strategic calculus which defines India's military posture today will not apply in that period when we will likely have the world's largest GDP or in a worst case the world's second largest.

JMT

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Re: INS Vikrant News and Discussion

Postby Hobbes » 22 Jun 2015 07:48

Interestingly, Wikipedia says the Vikrant is the first of two such carriers:
The Vikrant class (Sanskrit: विक्रान्त) (formerly Project 71 Air Defence Ship (ADS) or Indigenous Aircraft Carrier (IAC)) is a class of two aircraft carriers being built for the Indian Navy. The two vessels are the largest warships and the first aircraft carriers to be designed and built in India. They are being built by Cochin Shipyard.

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Re: INS Vikrant News and Discussion

Postby Hobbes » 22 Jun 2015 08:03

Newb question on GT vs. nuclear propulsion:

The LM-2500 G4 is reported to have a shaft power output of ~36 MW. The Vikrant class uses four GTs for a net shaft power of ~144 MW. The Arihant's reactor is rated for 83 MWt. Assuming a steam turbine efficiency of 35%, this translates to a shaft power availability of around 30 MW. Why cannot we have a Vikrant class derivative powered by four (or more) Arihant reactors?

JMT...

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Re: INS Vikrant News and Discussion

Postby Viv S » 22 Jun 2015 08:07

amit wrote:I too want the Navy to go for another Vikrant, particularly since CSL has said it can deliver one within 4-5 years. However, if the Navy does not go for the offer, it means that it thinks that the two carriers that we will have once Vikrant enters services is adequate for our present needs.

By exploring the options of EMAL, nuclear power, flat top etc for Vishal, the Navy is showing strategic foresight in designing a ship which will serve us well into 2060-2070 time frame.


1. That would certainly be the ideal solution. A nuclear powered CATOBAR ship is a necessity, but its also a technological challenge with the timelines therefore being unreliable, possibly extending past 2030 (though US consultancy will probably help move things along). Ideally, we should have a Vikrant follow-on (Viraat II) delivered before 2025. Use a V-22 based solution for AEW&C. The Vishal can then be commissioned post-2030 with a complement of N-AMCAs. Perhaps even scaled up to 75,000 ton+ displacement (wide beam capable of simultaneous launch and recovery).

2. The other issue here as you mentioned, is the MiG-29K. It suffices for now but it isn't even comparable to the best types of its own generation (like the Rafale). With stealth fighters set to proliferate in coming years (along with AEGIS-type destroyers), over the long term we need a supplement to the MiG, if not an outright replacement. The only viable option I can think off is the F-35B. Its capable of taking off with a full payload from a ski-jump, will allow for simultaneous launch-and-recovery, and should be a able to mesh splendidly with an AEW&C aircraft of US origin.

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Re: INS Vikrant News and Discussion

Postby amit » 22 Jun 2015 10:58

^^^^^^

Agree with your points.

Designing a 65-75 k CATOBAR will be a huge design challenge. For this reason I really like the Navy's approach. They have started planning for a ship now despite the requirement for it unlikely to occur before 2030 decade. (It will only occur when the Chinese are able to build a similar type of carrier).

A lots of challenges and slipped deadlines are to be expected. In this regard any design help from the US is always welcome. Once we get the Vishal out, maybe we will have a Vishal class similar to the Nimitz class for the US.

And I have a feeling the Navy has already decided that the next upgrade in terms of planes for the carriers will be a combination of F35 and the AMCA. The Navy is thinking long term and thinking big IMO. I only wish the other two branches had such strategic vision.

JMT

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Re: INS Vikrant News and Discussion

Postby Singha » 22 Jun 2015 11:31

I thinki n-reactor + shield vessel + heat exchanger + steam turbine will be less compact than a Lm2500 of equivalent power, albeit the space needed for the big bunker of fuel will be saved elsewhere in the ship...but in engine room terms the gas turbine will more compact.

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Re: INS Vikrant News and Discussion

Postby amit » 22 Jun 2015 11:47

Singha wrote:I thinki n-reactor + shield vessel + heat exchanger + steam turbine will be less compact than a Lm2500 of equivalent power, albeit the space needed for the big bunker of fuel will be saved elsewhere in the ship...but in engine room terms the gas turbine will more compact.


The fuel bunker, in terms of space will probably be able to house another 8-10 aircraft.

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Re: INS Vikrant News and Discussion

Postby NRao » 22 Jun 2015 12:10

Hobbes wrote:Interestingly, Wikipedia says the Vikrant is the first of two such carriers:
The Vikrant class (Sanskrit: विक्रान्त) (formerly Project 71 Air Defence Ship (ADS) or Indigenous Aircraft Carrier (IAC)) is a class of two aircraft carriers being built for the Indian Navy. The two vessels are the largest warships and the first aircraft carriers to be designed and built in India. They are being built by Cochin Shipyard.


Same wiki:

INS Vishal (Sanskrit: Vishal "giant"[5]) (IAC-II) is the second Vikrant-class aircraft carrier currently in its design phase, which will be built by Cochin Shipyard Limited for the Indian Navy and the second aircraft carrier built in India.

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Re: INS Vikrant News and Discussion

Postby Singha » 22 Jun 2015 18:48

soothing video of the QE2 class.... https://www.youtube.com/watch?v=GwAERRMw6QU

due to vertical landing, she can park a lot of aircraft at the back. there is no need for a clear landing strip.

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Re: INS Vikrant News and Discussion

Postby brar_w » 22 Jun 2015 19:18

Singha wrote:soothing video of the QE2 class.... https://www.youtube.com/watch?v=GwAERRMw6QU

due to vertical landing, she can park a lot of aircraft at the back. there is no need for a clear landing strip.



Not all landings will be vertical, in fact during high tempo ops quite a few may well be rolling and that seems to be what the brits are doing at PAX at the moment as far as develping tactics and protocols since the Marines only plan on doing rolling landings on land.


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Re: INS Vikrant News and Discussion

Postby Singha » 22 Jun 2015 19:23

That's a harrier style vertical landing!
They fly parallel to the carrier and sideslip in to land.
The stern can have a full arc of aircraft

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Re: INS Vikrant News and Discussion

Postby brar_w » 22 Jun 2015 19:29

The video above is not a regular vertical landing as is done on ships by the Harrier or the F-35B. Here the aircraft is approaching much like a conventional aircraft but at a much slower pace. The Marines do it at 40 Knots but the Brits will go even slower to shorten runway length requirements. They are called rolling vertical landings (RVL). RVL's up the bring back weights and this is critically important for heavy bombing type missions. You approach the runway like a carrier aircraft and land at a very low speed utilizing the entire length of the runway.

Harrier RVL - https://www.youtube.com/watch?v=yu0TJ9NMDgA

F-35 RVL is as done in the video in my previous post. Vertical landing is done as you said, lining up parallel to the ship and then using the yaw to get back .

https://www.youtube.com/watch?v=1Ocbu7dQnIE

The Marines practice RVL's on land and have been doing them from Forward Base's in Afghanistan and Iraq in both Gulf Wars etc (I had posted a post regarding all that earlier in the turkey thread). The Marines do it off of make shift runways using the Matting so they can afford a faster approach speed. The Brits need to come in slower so they are developing their own tactics and syllabi at the moment and hope to be done by the end of this summer. BAE systems has been doing RVL sim work out of the UK in support of the F-35B for a few years now.
Last edited by brar_w on 22 Jun 2015 20:10, edited 3 times in total.

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Re: INS Vikrant News and Discussion

Postby Shalav » 22 Jun 2015 19:52

amit wrote:The fuel bunker, in terms of space will probably be able to house another 8-10 aircraft.


Fuel and other liquid consumables are stored in the double hulls of carriers.

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Re: INS Vikrant News and Discussion

Postby Eric Leiderman » 22 Jun 2015 21:36

The footprint for a gas turbine might be smaller than a n=plant, However when you factor in the 4 exhaust manifolds and the fresh air maniolds
A lot of prime real estate will be used up on multiple decks These will have a dia of approx 24 inches each x 8 (withlagging maybe 36 inches)
Also with such huge deck penetrations as required for clean and exhaust air, the fire control plans get quite complicated.

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Re: INS Vikrant News and Discussion

Postby srin » 22 Jun 2015 22:05

For pros and cons of the nuclear powered carrier, refer to this: https://www.youtube.com/watch?v=PuFr8R6Vofs#t=37m

Takeaways:
A conventional carrier will need to be refuelled-at-sea every 3 days or so (2million litres of fuel). They are talking about 81000 ton USS Forrestal - should be double for our 45000 ton carriers.
Installing reactors requires strengthened keel
But space that was previously taken by fuel can now be used for aircraft fuel and ammunition.

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Re: INS Vikrant News and Discussion

Postby Shalav » 22 Jun 2015 22:05

It makes no sense. The cat has enough power to get any aircraft up to flight speed, and you dont need the ski jump. The ski jump takes up parking space. You cant park any aircraft on the curved surface of the deck at the bow. If you have a cat , you dont need a ski jump for any reason. Even if you do add one, it contributes nothing, but takes away space and the size of your air wing.


I'll start my reasoning by getting back to basics - the reason for a cat. or a ski jump is because an aircraft carrier does not have the runway length required for a conventional take off run.

Aircraft can only fly if there is enough airflow over their wings to generate lift. Lift is generated by velocity and/or angle of attack of the airfoil. Hence if the aircraft can get fast enough it will fly or if it can change the AoA of the wings without stalling them it will fly.

To overcome this AC's use two methods

1) the catapult and
2) the ski jump.

The catapult is simple to understand - if you dont have enough runway length you use other means to accelerate the aircraft till it has reached its calculated t/o speed. Hence during the t/o run you augment the aircrafts engines with a catapult such that at the end of the AC runway the engines and catapult together put the aircraft at its designed t/o velocity.

Ski jumps work because they combine to use the principle of AoA and velocity. However the AoA is peculiar you cannot change the AoA without effecting the airflow over the wing.

At a 0' AoA airflow over the wing is "laminar" ie. the airflow is sticking to the surface of the wing on both sides from the leading edge to the trailing edge. This is an ideal airflow situation providing the best lift and turn rates. As you increase the angle of attack while maintaining the same speed, the airflow starts to "peel-away" from the surface of the wing starting from the trailing edge. As the AoA of the wing increases the point where the airflow "peels-away" moves away from the trailing edge towards the leading edge of the wing. This non-laminar airflow means loss of lift. Eventually if you keep increasing the AoA the non-laminar airflow will move so close to the leading edge that it will result in a situation where the generated lift is not enough to keep the aircraft flying. To keep laminar airflow you have to increase the airflow over the wing as you increase the AoA. This is done by speeding up.

Hence you will always find a calculated V(r) for any aircraft and given weight. This is the velocity at which the aircraft can be safely rotated for climb during its take-off run. Rotation before reaching this velocity will stall the wing and the the aircraft will have to pick up speed again to reach V(r). In most circumstances distance required to reach V(r) is more than the length of an AC itself.

So before ski jumps on ACs became a common sight, there existed an option to use aircraft from shorter carriers without catapults. However the laws of physics prevented the actual use of this principle. You could not rotate without enough velocity and you did not have the the runway length in smaller carriers to get that velocity without catapults. Therefore as long as you had the catapult technology you really did not need to even think about the AoA option. But if you did not have it or did did not want to research it you were definitely thinking about it.

The RN was the first to make it work, they figured out that they could change the angle of attack during t/o by using the ski-jump for their Harriers. However it was a precise calculation of the AoA hence the slope of the ski-jump combined with the minimum velocity the Harrier HAD TO BE AT when departing the ramp. In other words they calculated a t/o velocity required for a certain AoA and then build their ski-jump to this calculation. So when an aircraft departed the ski-jump t was at the desired AoA and velocity. This made it workable.

So why this long ramble? Because on the Vikrant one can use this combination of ski jump and ability to use an EMALS to make the t/o run shorter. Which in turn means you do not need a long t/o run over the landing stip.

Which means

a) you have the space to move your aircraft around and park on the aft surface of the deck and an increased airwing
b) More importantly - you can add another EMALS at the waist position and launch 2 aircraft simultaneously - this would means more airframes in the air at greater frequencies.
c) OR put two in the bow ahead of the landing strip and you've got yourself a US style carrier.

Any one of these are good enough reasons if the EMALS could be made to work on a curved form-factor of a ski-jump.

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Re: INS Vikrant News and Discussion

Postby sankum » 23 Jun 2015 04:56

Mig 29k with 18T thrust and 24.5 MTOW needs 195m @ full afterburner for 14.3 degree ski jump take off say @50m/sec velocity. The vertical component is 50 sin 14.3=12.3m/sec and horizontal velocity is 50cos 14.3degree=48.5m/sec.

Thus for 1.5m/sec loss in horizontal velocity the aircraft is thrown up @ 12.3m/sec.

I have taken ball park 10 % as friction/ drag losses.

To get to say 65m/sec estimated take off velocity the 12.3m/sec vertical velocity is enough to give say 5 sec+ time to let the aircraft accelerate to 65m/sec @ optimal AoA i.e the best aerodynamic profile (@ sub optimal take of speed possible) which normally would have required 400m plus run on a normal runway.

For future naval pakfa and naval amca with 0.9 thrust to MTOW ratio will require say 155m estimated ski jump take off for same aerodynamic profile.

If EMALS is used for curved ski jump say catapult length reduces to say 50m for same g acceleration limit.

You require EMALS to launch Hawk eye AEW and UCAV which does not have the required trust to weight ratio to execute the ski jump launch from 50m catapult and you will have to go for higher g acceleration limits and thus we will have to revert back to 90m length.

Thus no apparent use to ski jump EMALS launch.

Even INS Vishal with complement of est. 36 fighters, 4AEW and 8 Helo will have only 2 EMALS catapult.

So no ski jump EMALS launch is practically feasible.

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Re: INS Vikrant News and Discussion

Postby Prem » 23 Jun 2015 09:03

About US new Carrier. Much Power production required for Laser weapons

This is America's new $13 billion warship
http://finance.yahoo.com/news/americas- ... 31205.html

The ship will feature a host of changes over the current Nimitz-class carrier. Ford-class carriers will be capable of generating three times more electrical power than the older carrier classes, for example.This increased electrical power supply allows the Ford to use the newly designed Electro-Magnetic Aircraft Launch System (EMALS), which will allow the vessel to launch 25% more aircraft a day than the previous steam-powered launch systems. The amount of electricity onboard also makes the Ford-class carriers ideal candidates to field laser and directed-energy weapons in the future, like rail guns and missile interceptors.This size will allow the carrier to house about 4,400 staff and personnel while also carrying more than 75 aircraft.

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Re: INS Vikrant News and Discussion

Postby rkhanna » 23 Jun 2015 09:53

^^ so a carrier such as this will eventually evolve to have Missile Interceptors and EM Rail guns (which can build up a decent rage) as well as a 75AC integral Fleet. Thats a whole new form of Battleship.

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Re: INS Vikrant News and Discussion

Postby Shalav » 23 Jun 2015 11:50

Sankum

50m/sec = 180 kph = ~98 knots
65m/sec = 235 kph = ~120 knots

- is that what you say are the rotation velocity for a fully loaded MiG29? Where did you get these numbers from?

Vertical velocity in a ski jump has no meaning - AoA and horizontal velocity is what allows for aircraft to t/o from a ski jump.

/// for PAK-FA or N-LCA - where are you getting the numbers from?

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Re: INS Vikrant News and Discussion

Postby sankum » 23 Jun 2015 12:06

50m/sec is simple physics for 0.73 thrust ratio for a mig 29k accelerating for a 195m run.

125kts was take of speed for mig 29 data from a magazine 25years back data . It may very well be 70-75m/sec. I will go with 75m/sec for fully loaded mig 29k.

Well I am not a aerodynamics guy and you may be right in your analysis for take off theory from a ski jump and I found no material for that from internet.

Naval pakfa and naval amca thrust take off ratio is based on open source and just estimated.

Anyway cost of developing curved Emals will be high and Russian super carriers proposed will carry skijump for simplicity and naval pakfa with internal load should be able to take off from 110m forward runway and catapults will be used for AEW.

Well I did not do energy calculations for ski jump take off which I realized later my flaw in approach, my bad.

I have stopped doing this for last 15 years, Just did simple physics.

Well a open floating mind leads to new creative ideas and thanks for proposing such a solution.

" The beauty of technological applications lies in the way the practical limitations are bypassed"

This was my quote when I was doing my engineering degree.

Well your idea prompted me to do some mind exercise. Thanks for that.
Last edited by sankum on 23 Jun 2015 14:17, edited 3 times in total.

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Re: INS Vikrant News and Discussion

Postby jcrocks » 23 Jun 2015 12:18

Shalav wrote:So why this long ramble? Because on the Vikrant one can use this combination of ski jump and ability to use an EMALS to make the t/o run shorter. Which in turn means you do not need a long t/o run over the landing stip.

Which means

a) you have the space to move your aircraft around and park on the aft surface of the deck and an increased airwing
b) More importantly - you can add another EMALS at the waist position and launch 2 aircraft simultaneously - this would means more airframes in the air at greater frequencies.
c) OR put two in the bow ahead of the landing strip and you've got yourself a US style carrier.

Any one of these are good enough reasons if the EMALS could be made to work on a curved form-factor of a ski-jump.


Thank you sir, for taking time to dissect the differences and the fundas behind cat and skijump take off/landing. Good learnings..thanks again..
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Reason: fixed formatting

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Re: INS Vikrant News and Discussion

Postby brar_w » 23 Jun 2015 13:47

rkhanna wrote:^^ so a carrier such as this will eventually evolve to have Missile Interceptors and EM Rail guns (which can build up a decent rage) as well as a 75AC integral Fleet. Thats a whole new form of Battleship.


In reality, no..Those will be reserved for support ships and not the carrier itself.

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Re: INS Vikrant News and Discussion

Postby Aditya G » 24 Jun 2015 01:48

newbie pooch: can SHARs operate from Vikramaditya? The ski jump here has a different angle compared to Viraat.

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Re: INS Vikrant News and Discussion

Postby vina » 24 Jun 2015 05:44

The RN was the first to make it work, they figured out that they could change the angle of attack during t/o by using the ski-jump for their Harriers. However it was a precise calculation of the AoA hence the slope of the ski-jump combined with the minimum velocity the Harrier HAD TO BE AT when departing the ramp


Forget about anything more "high flying" beyond high school physics and vector algebra. The physics of this is pretty simple. There are two things at work.

1. The ski jump is exactly that, a ski jump, which launches you in the air in a ballistic trajectory and since you spend more time in the air, the horizontal distance you travel will be higher before you hit the sea surface if you just went straight off the end of the bow. Of course, in the meantime, the engine keeps working and you get up to flight speed before you hit the water.

2. If the carrier was stationary, like in a ski jump in Switzerland, then that is all there is to it. The angle of attack in this case is zero ! However, the carrier will be moving into the wind while launching aircraft, and so there is a relative wind. Now since the carrier is moving into the wind, there will be an angle of attack. It is easy to calculate that from 10th grade vector algebra, assuming the carrier is going at 25 knots, the aircraft is launched at 175 knots at a 15deg angle (the apparent wind will look like it is coming from below the carrier on to the wings of the plane, the angle at which it comes AoA is the angle between the flight vector and apparent wind vector).

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 06:01

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 06:10

vina wrote:1. The ski jump is exactly that, a ski jump, which launches you in the air in a ballistic trajectory and since you spend more time in the air, the horizontal distance you travel will be higher before you hit the sea surface if you just went straight off the end of the bow. Of course, in the meantime, the engine keeps working and you get up to flight speed before you hit the water.


Nonsense Vina - you don't need a ski jump to get a higher distance off the ground. You could just build a ship with a taller hull. There's your "more distance before you hit the ground" right there! Why bother with a ski jump in the first place? hmmmm?

2. If the carrier was stationary, like in a ski jump in Switzerland, then that is all there is to it. The angle of attack in this case is zero ! However, the carrier will be moving into the wind while launching aircraft, and so there is a relative wind. Now since the carrier is moving into the wind, there will be an angle of attack. It is easy to calculate that from 10th grade vector algebra, assuming the carrier is going at 25 knots, the aircraft is launched at 175 knots at a 15deg angle (the apparent wind will look like it is coming from below the carrier on to the wings of the plane, the angle at which it comes AoA is the angle between the flight vector and apparent wind vector).


Apparent wind coming from below the carrier?

AoA effects can be experimented by anyone in a moving vehicle. Stick your hand out with your palm parallel to the ground - your hand will lift with the moving wind. Change the angle of your thumb and raise it a little bit, your palm will feel great force. simple sirji.

I leave it to you to figure out the rest.

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Re: INS Vikrant News and Discussion

Postby vina » 24 Jun 2015 08:58

Shalav wrote:Nonsense Vina - you don't need a ski jump to get a higher distance off the ground. You could just build a ship with a taller hull. There's your "more distance before you hit the ground" right there! Why bother with a ski jump in the first place? hmmmm?


Well, I remember basic high school physics about why you fire a gun at an angle to the horizontal and not simply parallel to the ground and max distance achieved at 45deg angle and the range is symmetric above and below 45 deg, i.e. gun firing at 30deg will have same range as 60 deg etc.. I must be dreaming of course. So for a Bofors gun, instead of shooting at 45 deg to get 30 km range, you should actually build a 30,000 foot pedestal (some of the shells reach that height) , mount the gun on top of it and fire horizontally instead!

Apparent wind coming from below the carrier?

Funny, isnt it ? Did you actually add the relative wind vector over the carrier and the vector of the plane as it is taking off from the ski jump and see the resultant and see which direction to the plane it is ? Of course not . Why add or actually do logical thinking at all when you actually already "know" or "feel" or "think"?

AoA effects can be experimented by anyone in a moving vehicle. Stick your hand out with your palm parallel to the ground - your hand will lift with the moving wind. Change the angle of your thumb and raise it a little bit, your palm will feel great force. simple sirji


Problem is , before mouthing off words like angle of attack, you should know what it really is! . It is the angle between the relative wind and the longitudinal axis of the plane (i.e., line joining nose to tail). So if you see a plane in an airshow doing a low speed, high angle of attack pass, you will notice that the plane is flying parallel to the ground, but the nose is pointed up with it's Musharraf down!

Right.. When your palm is parallel to the ground (assuming that the car is traveling on a level ground), the angle of attack is ZERO! A symmetrical airfoil will experience ZERO lift. The reason why your palm is lifted,because it is NOT symmetric, and generates lift at zero angle of attack!

Similarly, when the carrier is stationary , and the plane is taking off at an angle, to the ground, the plane is flying with orientation parallel to the airflow and angle of attack is zero again!.

However, when the carrier is moving , there is a wind over deck and the relative wind will result in an angle of attack on the plane on the take off ramp, because the airflow is not coming parallel to the ramp (like in a stationary ski slope), but the plane's wings will see it coming from below the carrier!

I leave it to you to figure out the rest.

Indeed. Have a nice day.

vina
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Re: INS Vikrant News and Discussion

Postby vina » 24 Jun 2015 09:08

Ok. Since this is a boat thread after all , and some basic physics are shot, , let us have quick quiz.

REMEMBER NO GOOGLING and answers have to be substantiated by mathematics (high school level only required) , no "feeling","thinking" etc.

Question is this.
Can a sail boat sail AGAINSTthe wind ? If yes, how and if no, why not?


Hint
Consider direction of motion of boat, the direction of wind, do vector algebra , and then a further hint.. there is a wing out there somewhere which generates lift and drag

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Re: INS Vikrant News and Discussion

Postby shiv » 24 Jun 2015 09:25

vina wrote:Ok. Since this is a boat thread after all , and some basic physics are shot, , let us have quick quiz.

REMEMBER NO GOOGLING and answers have to be substantiated by mathematics (high school level only required) , no "feeling","thinking" etc.

Question is this.
Can a sail boat sail AGAINSTthe wind ? If yes, how and if no, why not?


Hint
Consider direction of motion of boat, the direction of wind, do vector algebra , and then a further hint.. there is a wing out there somewhere which generates lift and drag

LOLOLOLOL!! This is for me because I am zero math and even Googling won't help!!!

I used to wonder about this , and I simply guessed that if the sail is 90 degrees to long axis of boat, the boat will move back

If sail is turned to so that it is almost parallel to axis - but off by say 10 degrees - it is offering a "wing like" angle of attack to the wind that should cause the boat to move sideways. If a second sail, acting like a flaperon is placed behind this sail to catch the slipstream I am simply guessing that it would be possible to create a net forward, against the wind movement. I think the boat could move obliquely against the wind with low pressure on the same side of both sails/aerofoils. I guess a rudder would be essential here.

I suppose reversing the sail orientation every few minutes would allow a zig-zag net movement against the wind. Guesswork. Zero math. If I'm wrong I'm wrong.

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Re: INS Vikrant News and Discussion

Postby Singha » 24 Jun 2015 09:32

yes I dont think you can sail straight against the wind but zig zag (called tacking?) your way up.

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Re: INS Vikrant News and Discussion

Postby vina » 24 Jun 2015 09:47

Singha wrote:yes I dont think you can sail straight against the wind but zig zag (called tacking?) your way up.

Indeed. However ,even when you are tacking, you are sailing against the direction of the wind. How does that happen ?

Hint : Remember , vector algebra is your friend. And yes, Shiv is on the right path, the sail is an airfoil!

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 10:04

vina wrote:...

blah...
blah...

Have a nice day.


err no - when a plane takes off at an angle the AoA is NOT zero. The airflow is STILL parallel to the ground.

That sirji is why millions of planes land every year with a nose up attitude - hope you realise it is to increase the AoA to airflow for greater lift when landing.

Airflow does not magically move parallel to the wing during angled take off, forward velocity ensures the airflow is parallel to ground AND at an angle to the wing. Which creates the AoA without stalling it. Simple concept really. But apparently something you can't imagine, since you've spoken otherwise already.

Oh BTW - let me point you to one link

https://en.wikipedia.org/wiki/Angle_of_attack

Relation between angle of attack and lift

The lift coefficient of a fixed-wing aircraft varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases.[6]

As the angle of attack of a fixed-wing aircraft increases, separation of the airflow from the upper surface of the wing becomes more pronounced, leading to a reduction in the rate of increase of the lift coefficient. The figure shows a typical curve for a cambered straight wing. A symmetrical wing has zero lift at 0 degrees angle of attack. The lift curve is also influenced by wing planform. A swept wing has a lower, flatter curve with a higher critical angle.




PS: Here's a google link for your reading only

https://encrypted.google.com/search?q=w ... +increased

You really should try to use it.

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Re: INS Vikrant News and Discussion

Postby geeth » 24 Jun 2015 10:07

Depending on how you hoist the sail, one can also.say that the sails capture energy from the flow like a impulse/reaction turbine vane.

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Re: INS Vikrant News and Discussion

Postby geeth » 24 Jun 2015 10:36

^^A Skijump helps an a/c in :

1. Gaining height in a short span of time which is crucial while taking off
2. Increase in angle of attack particularly when flying into headwind, which helps in increased lift and increase in stall AoA
3. While taking off at an angle, engine thrust has a vertical as well as horizontal component. The vertical component assist lift.
4. Due to the circular motion IIRC there is a slight gain in velocity..I am not so sure..will have to check.
5. The lifting devices like flaps need not be put at max angle- so less drag and a gain in speed

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Re: INS Vikrant News and Discussion

Postby sankum » 24 Jun 2015 11:19

Vertical velocity is indeed imparted by the ski jump to allow the aircraft to take off.

I did a numerical analysis 15 years back based on simple physics that showed that take off weight is roughly cube root function of the take off distance in case of ski jump launch and was quite embrassed to think that it was all wrong. Now I think I was right though several other factors are also in play.

Just read the paper below.

http://www.dtic.mil/dtic/tr/fulltext/u2/a237265.pdf


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