INS Vikrant News and Discussion

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Re: INS Vikrant News and Discussion

Postby vina » 24 Jun 2015 12:50

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.

Ah, that is true when you are running before the wind and use either a square sail like the Roman ships of old , or the more modern way of sailing by opening out the main sail fully to a side and unfurling a spinnaker. But the question was how do you sail upwind ?

The answer to that is by tacking. So how exactly do you zig-zag upwind ? Basically, the it is like this. You obviously can't sail directly upwind. So point the bow slightly off dead ahead , then given that, you have an apparent wind (i.e., vector add the wind blow straight head towards you and the boat velocity at a certain heading , the resultant will be the apparent wind blowing from somewhere between ahead to the beam). So, now the sail is an airfoil (just imagine a cross section), and you position it in the apparent wind,it will generate a lift and a drag. Resolve those along the length of the boat and perpendicular to it, and you get a force driving the boat forward in the given heading and a force dragging the boat perpendicular to it. Now, sail boats have huge keels precisely for this reason,to counteract that force dragging it perpendicular to that heading. As you are going diagonally upwind, to go straight ahead, you have to zig-zag.
Google around there will be articles with pictures

sankum wrote:Just read the paper below.

If I can summarise that paper in one sentence, it is this.
As the plane leaves the ski jump it is below take off speed!It is thrown up in the air ballistically like a bullet

So, in Inglees the paper says.
The plane is not flying as it leaves the ramp, but it sinks back vertically like anything thrown up and the design point is for it to start flying at the deck level as it sinks!

In Yindee I said
As you are thrown up ballistically, what you get is enough time, so that the engine can get the plane up to flying speed before you hit the water!


So with that, all this "Angle of Attack" business is moot. So yeah, while the plane might have an angle of attack as it leaves a moving ship (with a stationary ship, the angle of attack is zero , just like it is for a plane zooming up vertically) due to the apparent wind, the plane is not flying yet and the predominant thing working here is like a pure ballistic thing, with the engine working during the time to get it up to flying speed as it fall slowly back.

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Re: INS Vikrant News and Discussion

Postby geeth » 24 Jun 2015 14:14

You obviously can't sail directly upwind


You can.


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Re: INS Vikrant News and Discussion

Postby shiv » 24 Jun 2015 16:16

OK - sailboat into wind. take 2

  • Assume wind is blowing exactly from north to south
  • Arrange the sail so that it forms a very small angle of attack against the wind. That will produce "lift" and push the sail at right angles to the wind direction. Assume that the sail is angled such that the "lift" is to the west (left) and the sail tends to move west
  • The sail is attached to a boat by a mast. The mast tries to push the boat west, at right angles to north south wind direction
  • If the boat is oriented north-south, it will move sideways
  • Orient the bow (nose) of the boat to the north-west direction (tilted to the "left", -towards the west)
  • The mast still tries to push the boat to the west, but the orientation of the boat creates two forces. The sideways moving boat now has an "angle attack" against the water (ie water is moving relative to boat) that creates two forces, one trying to resist the motion of the boat to the west and the other pushing the boat "forwards" towards the north.
  • The boat will then move in a north-west direction - obliquely against the wind

ooops just saw vina's answer - will check if I was right :D :oops:

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Re: INS Vikrant News and Discussion

Postby vina » 24 Jun 2015 18:14

geeth wrote:You can.

Of course, you can, but you wont go anywhere ! This is the first thing in Point of Sail.
Last edited by vina on 24 Jun 2015 19:05, edited 1 time in total.

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Re: INS Vikrant News and Discussion

Postby vina » 24 Jun 2015 18:29


Thanks. Basically fully confirms the two points I made.

1. It is a ballistic flight as it leaves the ramp, giving time for the engines to get it to winged flight before it hits the water
2. The ship motion sets up the apparent wind (as if flowing from below the ship) when the plane is on the ramp increasing the angle of attack.

Yeah, this is basically it. The rest is all just fleshing out the details.

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Re: INS Vikrant News and Discussion

Postby Aditya G » 24 Jun 2015 19:08

Ski jump capable MiG-27!

Image

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Re: INS Vikrant News and Discussion

Postby NRao » 24 Jun 2015 19:34

How about a Gnat on a ski jump?

Not the most authoritative source, but ...............

The Problem with Ski-Jump Aircraft Carriers

For example, the J-15 when launched from the Liaoning can only carry 4,000 pounds of ordnance before it reaches its minimum airspeed requirement, conversely, the FA-18E/F Super Hornet can carry over 12,000 pounds of ordnance on a catapult aircraft carrier. The large differences between the two aircraft carriers can certainly have impacts to tactical considerations for mission planning and sortie generation rates.


Is there a land-to-ski_jump-to-cat ratio for the amount of ordnance?

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Re: INS Vikrant News and Discussion

Postby shiv » 24 Jun 2015 20:22

3-4 years ago I was trying to find out/demonstrate how a ski jump helps and made a video. I did not remember it or bother putting it online until today. It's not a world changing video - but its something :)
https://www.youtube.com/watch?v=Nn_Yb1mySvo

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Re: INS Vikrant News and Discussion

Postby sudeepj » 24 Jun 2015 20:59

I wonder if large H2O2 steam rockets can be used as RATO boosters for carrier aviation. These rockets dont produce toxic gases and H2O2 should not be much more hazardous than aviation gas to store.

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Re: INS Vikrant News and Discussion

Postby geeth » 24 Jun 2015 21:11

Of course, you can, but you wont go anywhere


You can move forward (if not race ahead) into the wind with a solid wing sail having an unsymmetric airfoil cross section..just wanted to highlight the force generated by airfoil section...google around for details :D

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 21:17




Looks like you read only the paragraph headers

on page 4 of doc2 we have some details

http://www.icas.org/ICAS_ARCHIVE/ICAS20 ... RS/167.PDF

In the ski-jump, the wind increases the speed and the angle of attack, as shown in Fig. 2.

The increase in angle of attack is:


(Equation)


Consequently, the aerodynamic lift rises up to:

(Equation)

And the lift increment will be:

(Equation)

At the end of the ski-jump, corresponding to

(Equation)


The work there talks about increased AoA creating more lift.

Ironically your own proof only proves my point. All your talk about airflow from the bottom of the wing etc... is nonsense and have no support in both the documents.

The facts are

1. increasing AoA provides greater lift
2. the ski-jump allows for increased AoA without stalling the wing

If you disagree with this show us actual proof that increased AoA does not increase lift.

Perhaps it is not I who has been "mouthing off"? hmmmm?

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 21:22

Moving on from blather, my main point still stands.

If an EMALS can be added to a ski-jump, you can get the required velocity and AoA from a shorter take-off run leaving the landing strip free for another waist located EMALS and a pocket sized USN type carrier - amongst other options.

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Re: INS Vikrant News and Discussion

Postby srin » 24 Jun 2015 21:32

Shalav wrote:Moving on from blather, my main point still stands.

If an EMALS can be added to a ski-jump, you can get the required velocity and AoA from a shorter take-off run leaving the landing strip free for another waist located EMALS and a pocket sized USN type carrier - amongst other options.


Would the non-fighters have problems with the AoA ? A 14-degree slope (of Vikky) seems pretty steep for non-fighters ...
Say we want to have an E2-D tomorrow operating off this EMALS-ski-jump, would it have enough speed to not stall ?

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 21:34

BTW these points from doc2

And the lift increment will be:

(Equation)

At the end of the ski-jump, corresponding to

(Equation)


are saying exactly what I initially stated on the previous page.

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.

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 21:51

srin

No idea - don't even know if an EMALS can be be made to work efficiently on a ski-ramp. Theoretically it should be possible. Everything else will have to be tested once (if) the EMALS on ski-jump ever becomes reality.

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Re: INS Vikrant News and Discussion

Postby NRao » 24 Jun 2015 21:52

a pocket sized USN type carrier - amongst other options.


I am betting that EMALS and pocket sized will not go together. EMALS , for a good ROI should need a decent sized air wing, for which you will need something fairly large (ship).

They should be meeting within the week and one of the topics is the number of planes. 30, I bet will not do.

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 21:59

In Doc2 pg 6

When an airplane takes-off from a curved- deck it suddenly jumps into free air. The objective is to approximately reach the suitable speed and angle of attack, at the end of the ski- jump, without exactly respecting the airplane lift to weight equilibrium


I don't see anything about airflow from "beneath the wing" etc here either?

I am guessing you just read the paragraph header "Semi-ballistic flight and launching compatibility" and jumped to a conclusion without bothering to read the rest of the paragraph, WHICH DOES NOT MENTION "ballistic" EVEN ONCE in the rest of the paragraph.

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Re: INS Vikrant News and Discussion

Postby geeth » 24 Jun 2015 22:26

I don't see anything about airflow from "beneath the wing" etc here either?


The "airflow" is the headwind (either due to the movement of ship or natural wind blowing or both), flowing horizontally; when the a/c takes off, this wind hits the bottom of the wing surface. Because of this, apart from the normal lift, the wing produces additional lift like that of a kite (or a flat plate at an angle in a laminar flow). This additional lift gives the feeling of an apparant increase in AoA (when you draw the resultant of vectors of wind and a/c movement). That is why the ship almost always head into the wind before a/c takes off. Also flying operations are restricted to 2-3 degree roll of ship.

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 22:34

Err...That is what an increased AoA is supposed to do. Which according to Vina is not applicable and I am "mouthing off", as per him it is really airflow beneath the wing!

Oh BTW you do realise this ski-jump principle works on land too right? See videos of N-LCA test or the latest F35 ski-jump tests. No headwind required at all!

ACs head into the wind because it allows for more airflow over wings. An additional 20-30 knots is good, that means the aircraft engines don't have to strain so much.

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 22:44

geeth wrote:
The "airflow" is the headwind (either due to the movement of ship or natural wind blowing or both), flowing horizontally; when the a/c takes off, this wind hits the bottom of the wing surface. Because of this, apart from the normal lift, the wing produces additional lift like that of a kite (or a flat plate at an angle in a laminar flow). This additional lift gives the feeling of an apparant increase in AoA (when you draw the resultant of vectors of wind and a/c movement). That is why the ship almost always head into the wind before a/c takes off. Also flying operations are restricted to 2-3 degree roll of ship.



Completely incorrect sirji. there is no such thing as normal lift and additional lift over the airfoils. Its all lift. The increase in AoA provides increased lift at the expense of increased drag. (see my previous description on last page).

Also as mentioned previously you don't need ship movement to use a ski-jump. It works just as well on land too. See N-LCA test and F35 ski-jump test.

Also google NATO research on land based ski-jumps in case of runway denial by Warsaw Pact forces. You will see a lot of studies on ski-jumps and they didn't even need headwinds.

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Re: INS Vikrant News and Discussion

Postby Cosmo_R » 24 Jun 2015 22:49

"a pocket sized USN type carrier - amongst other options"

I think we should have learned from the 'world's smallest combat aircraft' that we need to think big and move beyond the Folland Gnat box.

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Re: INS Vikrant News and Discussion

Postby srin » 24 Jun 2015 23:06

geeth wrote:
I don't see anything about airflow from "beneath the wing" etc here either?


The "airflow" is the headwind (either due to the movement of ship or natural wind blowing or both), flowing horizontally; when the a/c takes off, this wind hits the bottom of the wing surface. Because of this, apart from the normal lift, the wing produces additional lift like that of a kite (or a flat plate at an angle in a laminar flow). This additional lift gives the feeling of an apparant increase in AoA (when you draw the resultant of vectors of wind and a/c movement). That is why the ship almost always head into the wind before a/c takes off. Also flying operations are restricted to 2-3 degree roll of ship.


That's the airflow on a flat deck, rt ? On a ski-jump, would the take-off part of the deck have smooth head-wind ?

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Re: INS Vikrant News and Discussion

Postby Shalav » 24 Jun 2015 23:16

Cosmo - the IN is impressively frugal, jugadu and innovative. They tend to get the best from their machines Indian or phoren.

I'm betting the Vikrant will be used for a long time. so one could scrap it as bigger carriers are built, but it it more likely the IN will use it in some capacity till EoL. If you are going to be using it, a pocket USN carrier is an option. There will be other options too. I am just presenting one of them.

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Re: INS Vikrant News and Discussion

Postby Mihir » 25 Jun 2015 02:57

Shalav wrote: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.


Nitpick. What you are referring to "laminar" flow, is actually called attached flow. "Laminar" flow occurs when the air moves in 'smooth' layers without any irregular fluctuations. Whether the flow over a wing is laminar or not does not depend on the angle of attack.

Also, you and vina are both right. The ski jump increases the angle of attack and also throws the plane in the air so that it can gain speed while it sinks back to the level of the deck. In essence, it adds a virtual deck of sorts ahead of the physical deck that increases the aircraft's take-off run.

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Re: INS Vikrant News and Discussion

Postby Shalav » 25 Jun 2015 04:17

Nitpick accepted.


Moving on


Vina is incorrect. There is no such thing as airflow parallel to the wing in an angled takeoff. All airflow is always parallel to the ground. Airflow does not magically change direction to be parallel to the wing when AoA is changed for a climb rotation, then change directions again to be parallel to the ground when the aircraft has departed the ramp or even a flat deck and into a climb or when it has reached level flight. Increased AoA is what provides increased lift - not some magical airflow beneath the wing after ramp departure.

vina wrote:
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!


This is rubbish.

1. It does not matter if the carrier is stationary or moving, the airflow is ALWAYS parallel to the ground.

2. You don't have to be on a carrier to use a ski-jump. The question is - when used on land and there is no carrier, what happens to all these magical changes of airflow?

3. This made me LoL - "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" - REALLY - the airflow magically changes direction to be parallel to the ground when the carrier is moving and when it is stationary airflow mysteriously flows parallel to the ramp? - "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!"

4. Sinking back to surface level has mostly been observed on flat-deck and/or catapult assisted takeoffs. Angled deck takeoffs almost never exhibit this property - the reason is that at the point of departure from the angled ramp the aircraft is supposed to be at the velocity to maintain its AoA and which in turn means it can maintain its climb rate. Velocity only keeps increasing after this - which in turn leads to more altitude. Only if it's velocity decreases will the aircraft sink. Hence if all aircraft systems function normally and it is within the correct weight range one almost never sees a sink from an angled deck take off.

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Re: INS Vikrant News and Discussion

Postby Shreeman » 25 Jun 2015 05:22

Alright, you all know a lot. So,

1. why the 14 degrees?
2. why the varying total lengths if still 14 degrees?
3. how much was/is gained from 12 to 14 degrees?
4. There has been a bit of traffic re. one engine aspect. Did two engines figure into either the 14 degree computation or the wire placement?
5. Landing is a controlled crash, and flying slower if you first got up there somehow is usually not the problem. So is it the one engine take off that is the issue or the one engine landing?
6. will the single engine bird qualify for no engine landing then?

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Re: INS Vikrant News and Discussion

Postby amit » 25 Jun 2015 05:28

Shalav wrote:Moving on from blather, my main point still stands.

If an EMALS can be added to a ski-jump, you can get the required velocity and AoA from a shorter take-off run leaving the landing strip free for another waist located EMALS and a pocket sized USN type carrier - amongst other options.


Shalav,

The physics discussion on Ski-jump has been fascinating. However, I still don't understand why you'd need both EMALS AND a Ski-jump (let's leave aside for the moment the technical feasibility of having a curved catapult system)?

The steam catapult systems on Nimitz class carriers are around 95 meters long. I don't know the actual length Vikrant's ski jump but considering that it's 262 meters long I would reckon its probably longer. Add to this fact that the Nimitiz class is around 310 meters long, being more than twice the weight of the Vikrant.

When you consider that Vishal will be in the 65K-75K class then its quite likely the boat will be at least 300 meters long and (this is important) around 75-80 meters wide. It will be quite possible to have three catapults on the ship, two on the foredeck like the Nimitz and one at the waist. With that you can have either simultaneous launches from the foredeck and waist or a simultaneous launch and recovery.

From an operational perspective, again what added benefit will a Ski-jump bring to the table? The planes that will be using the Vishal's (and its successors') landing deck would most probably be a combination of F35s (the Navy has long made it known that it's interested in this aircraft) and either the naval AMCA or the naval version of the FGFA. Both the later are yet to be built and hence can be built from ground up to be catapult launched. That leaves the naval Tejas. I think it's front wheels can be strengthened to withstand the force of a catapult.

Also regarding your point about pocket sized carriers, EMALs is a full electric system and I reckon a ship with three EMALs will need to produce around 200 MW of power. Assuming we will go for the nuclear option why would want to fit a 200 MW nuclear plant on a 30k-40k ship? Building cost wise how much would you save by building a ship half the size of Vishal's proposed sized, particularly considering the fact that all future carriers would be built using modular construction.

IMO we need to start thinking big and not in terms of smallest, lightest, cheapest etc. More so since we are a talking about systems that we will use in the timeframe beyond 2030 when we will be one of the biggest economies in the world with a lot of money to spare.
Last edited by amit on 25 Jun 2015 05:45, edited 2 times in total.

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Re: INS Vikrant News and Discussion

Postby TSJones » 25 Jun 2015 05:42

shiv wrote:3-4 years ago I was trying to find out/demonstrate how a ski jump helps and made a video. I did not remember it or bother putting it online until today. It's not a world changing video - but its something :)
https://www.youtube.com/watch?v=Nn_Yb1mySvo


I'll be darn. A flying carpet. The legend is true! :)

It is true that you get a bigger cut of air with a ski jump. you may sink some immediately there after, but you are gaining momentum by then and forcing more air over over the wing providing lift.

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Re: INS Vikrant News and Discussion

Postby shiv » 25 Jun 2015 06:36

About this animated discussion re AOA and ballistic toss up etc - I scanned through the pdf linked by sankum

Let me pose some moron questions that would help me understand

1. Aircraft coming off a flat deck sink a bit (9 feet, the paper says) before getting into level flight
2. A ski jump can be designed and used to neutralise this sinking - the idea being that take-offs can be achieved from a shorter take-off run

I assume that a plane sinks after leaving the edge of the deck because it's lifting surfaces are not generating enough lift for level flight, let alone climbing.

Why should sinking make level flight possible? I guess that as the plane sinks, it is accelerating both because of max engine thrust and gravity and that acceleration eventually gives it enough speed for the lifting surfaces to generate the lift required for level flight.

Why should take off from an angled deck prevent this sinking if the launch velocity of the aircraft is the same? At that same launch velocity, the lift generated cannot be sufficient for level flight whether the take off is from a flat deck or an angled one. Why doesn't the plane simply stall?

The only explanation I can think of is that the plane has a tendency to "sink" even when it is launched from an angled deck. But that sinking is neutralised by the upward momentum that the plane has acquired - so that it does not rise but simply settles into level flight after ski-jump launch rather than sinking first and then settling into level flight.

To my eyes, that is what appears to be happening in this video
https://www.youtube.com/watch?v=L2fZubfxjnQ


I guess that for all this to happen a whole lot of conditions have to be met in terms of velocity at launch, weight, power available, headwind and angle of launch.

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Re: INS Vikrant News and Discussion

Postby NRao » 25 Jun 2015 06:49

why you'd need both EMALS AND a Ski-jump


I too do not see a need for such an overkill. Which plane would the IN have that the EMALS or even the CAT cannot handle. Max on the ordnance and refuel in flight.

For a ship that will play itself into the 2070s no need to get cute. That too when the one with all the experience is willing to provide advice. Design a Vishal that best fits the IN and the political posture.

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Re: INS Vikrant News and Discussion

Postby RoyG » 25 Jun 2015 07:03

Shiv,

You clearly had too much time on your hands :lol:

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Re: INS Vikrant News and Discussion

Postby Abhay_S » 25 Jun 2015 07:07

[quote="Shreeman"]Alright, you all know a lot. So,

With Risk of opening my mouth and clearing all doubt :lol: i will try to answer one of your questions.

5. Landing is a controlled crash, and flying slower if you first got up there somehow is usually not the problem. So is it the one engine take off that is the issue or the one engine landing?

the One Engine can be an issue if the arrestor hook does not catch one of the wires while landing. in this case the aircraft may not have enough power to take of again for a second attempt. it all depends on T/W ratio.

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Re: INS Vikrant News and Discussion

Postby Shreeman » 25 Jun 2015 07:39

^^^
Single engine lightweight fyter => engine fail => ditch => SAR.

Twin,one fails => eject stores => minimal fuel (recall fuel dumping is on even the single engine fyter) => one attempt => ditch on failure => SAR.

Twins with both engines seem to take a salty drink every now and then on youtube. You can ruin a twin by going full fast when tail is caught up. And a hundred other ways. Why is this *unlikely* scenario worth the arguments going on? Just bad mouthing another tin can?

Availability of engine? All engines will have this issue. The 404 and 414 when time comes. But I dont get this mental gymnastics. If you are where there is no diversion and cant stay up then you ditch and wait for a passing helicopter. Isnt that what everyone does?

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Re: INS Vikrant News and Discussion

Postby shiv » 25 Jun 2015 08:08

RoyG wrote:Shiv,

You clearly had too much time on your hands :lol:

Whaddaya mean? that is serious aerodynamics research!! :D

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Re: INS Vikrant News and Discussion

Postby member_28108 » 25 Jun 2015 08:26

Sailing against the wind - from the old Ya perlman's book which we used to read as children- a classic
http://site-children.com/perelman2-161.htm

vina
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Re: INS Vikrant News and Discussion

Postby vina » 25 Jun 2015 09:08

shiv wrote:3-4 years ago I was trying to find out/demonstrate how a ski jump helps and made a video. I did not remember it or bother putting it online until today. It's not a world changing video - but its something :)
https://www.youtube.com/watch?v=Nn_Yb1mySvo


Perfect! This is the kind of "Aerodynamic Research " that warms the cockles of one's heart. Yeah. Very simple to see it yourself. All you need is a wind up rubber band motor model airplane, a book and a sheet of cardboard (a thin one that bends under it's own weight) and can see things for yourself!

This kind of practical hands on stuff is how engineering progressed over the millennia.

See, it is like this. The "savages" in the south seas (aka the Polynesians ) explored the frontiers of the world to the widest before. The feats of voyage and navigation by them was simply brilliant mindbogglingly amazing. All trial and error and using grey matter between their ears only. Note, they probably didn't know vector addition or some rubbish called airfoil or "lift"/"drag" and definitely some kakkoose that was tossed around here as laminar flow or whatever, but they DISCOVERED that you could sail against the wind by having a fore and aft mast and using the sail as they could feel the wind coming from a different direction on their faces when the pointed the boat on a different heading and presto, you could go against the wind. Compare that with the "civilised" Roman galleys with their square sails that just runs ahead of the wind and can't do Pakistan against the wind and you had to have an army of slaves in the galleys rowing!

Also, the Polynesians did some amazing feats of long distance sailing. They settled tiny specks of islands in the middle of the vast pacific,all the way from Hawaii to New Zealand to the tiny islands in-between! Something the white guys couldn't do until they invented something called a "Chronometer" (i.e. reliable time piece) . How did the Polynesians do it, without a compass and time piece and hit microscopically tiny islands in the vast Pacific separated by thousands of miles.

And think of this. The Polynesians and the brown skinned natives in our coasts had multi hulled vessels (called Kattumaram in the Coramandal coast now fancily called Catamarans, and the Polynesians had their out rigger canoes).. So what is the difference between those vessels and the (traditional) mono hull vessels ? (hint .. the multi hull vessels are geometry stabilised, while the mono hulls are gravity stabilised, fundamentally different, not what google warriors here will think these are two mono hulls tied together to increase deck area or some such kakkoose)

Coming to the point, I posted this question about how a sailing boat can sail against the wind to show a fundamental point, which is, there is a something called an "apparent wind" (which is the vector addition of the velocity of your boat in a certain heading, and the direction of the prevailing wind , which gives the resultant vector and that is commonly known as apparent wind) and that is what the sail will feel and you can use it to move against.

Now, an unlettered savage in the south seas who probably went head hunting knows for 4000 years the apparent wind business , while now the folks who managed to clear high school math and went on to higher technical courses, can't get it into their to put pen on paper , draw the motion of the plane, the direction of the wind and add two together to get the resultant wind and keep insisting that launching off a stationary ski jump (like on land in the test facility at say Goa or a guy taking off from an alpine ski jump in Switzerland ) is exactly the same as off a moving ship ! They will have to quote "formulas" from some technical paper (how are the formulas derived?) that was googled around, or some "software" (like the Mongolian Yakherder says, I worked in the (ef) FLUENT effect, instead of actually using the grey cells between the ears) and someone even googles up what he read as a child on how sailboats work, instead of actually putting pen on paper and adding two vectors like he was taught in 10th grade using his own grey matter ! Ask them to add vector a + vector b , pat will come the answer however!

And on top of it, when you realise that the main effect of it all is that is just like a bullet shot off from a gun at an angle, and this is airflow business just a secondary effect which probably doesn't matter, you get an answer, that they will build a taller ship and not a ski jump, thrown in with mangled nonsense about angle of attack and laminar flow and what have you .

You have to wonder at the idiocy of it all.Sigh!

Shalav
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Re: INS Vikrant News and Discussion

Postby Shalav » 25 Jun 2015 11:07

vina wrote:
shiv wrote:3-4 years ago I was trying to find out/demonstrate how a ski jump helps and made a video. I did not remember it or bother putting it online until today. It's not a world changing video - but its something :)
https://www.youtube.com/watch?v=Nn_Yb1mySvo


Perfect! This is the kind of "Aerodynamic Research " that warms the cockles of one's heart. Yeah. Very simple to see it yourself. All you need is a wind up rubber band motor model airplane, a book and a sheet of cardboard (a thin one that bends under it's own weight) and can see things for yourself!

This kind of practical hands on stuff is how engineering progressed over the millennia.

See, it is like this. The "savages" in the south seas (aka the Polynesians ) explored the frontiers of the world to the widest before. The feats of voyage and navigation by them was simply brilliant mindbogglingly amazing. All trial and error and using grey matter between their ears only. Note, they probably didn't know vector addition or some rubbish called airfoil or "lift"/"drag" and definitely some kakkoose that was tossed around here as laminar flow or whatever, but they DISCOVERED that you could sail against the wind by having a fore and aft mast and using the sail as they could feel the wind coming from a different direction on their faces when the pointed the boat on a different heading and presto, you could go against the wind. Compare that with the "civilised" Roman galleys with their square sails that just runs ahead of the wind and can't do Pakistan against the wind and you had to have an army of slaves in the galleys rowing!

Also, the Polynesians did some amazing feats of long distance sailing. They settled tiny specks of islands in the middle of the vast pacific,all the way from Hawaii to New Zealand to the tiny islands in-between! Something the white guys couldn't do until they invented something called a "Chronometer" (i.e. reliable time piece) . How did the Polynesians do it, without a compass and time piece and hit microscopically tiny islands in the vast Pacific separated by thousands of miles.

And think of this. The Polynesians and the brown skinned natives in our coasts had multi hulled vessels (called Kattumaram in the Coramandal coast now fancily called Catamarans, and the Polynesians had their out rigger canoes).. So what is the difference between those vessels and the (traditional) mono hull vessels ? (hint .. the multi hull vessels are geometry stabilised, while the mono hulls are gravity stabilised, fundamentally different, not what google warriors here will think these are two mono hulls tied together to increase deck area or some such kakkoose)

Coming to the point, I posted this question about how a sailing boat can sail against the wind to show a fundamental point, which is, there is a something called an "apparent wind" (which is the vector addition of the velocity of your boat in a certain heading, and the direction of the prevailing wind , which gives the resultant vector and that is commonly known as apparent wind) and that is what the sail will feel and you can use it to move against.

Now, an unlettered savage in the south seas who probably went head hunting knows for 4000 years the apparent wind business , while now the folks who managed to clear high school math and went on to higher technical courses, can't get it into their to put pen on paper , draw the motion of the plane, the direction of the wind and add two together to get the resultant wind and keep insisting that launching off a stationary ski jump (like on land in the test facility at say Goa or a guy taking off from an alpine ski jump in Switzerland ) is exactly the same as off a moving ship ! They will have to quote "formulas" from some technical paper (how are the formulas derived?) that was googled around, or some "software" (like the Mongolian Yakherder says, I worked in the (ef) FLUENT effect, instead of actually using the grey cells between the ears) and someone even googles up what he read as a child on how sailboats work, instead of actually putting pen on paper and adding two vectors like he was taught in 10th grade using his own grey matter ! Ask them to add vector a + vector b , pat will come the answer however!

And on top of it, when you realise that the main effect of it all is that is just like a bullet shot off from a gun at an angle, and this is airflow business just a secondary effect which probably doesn't matter, you get an answer, that they will build a taller ship and not a ski jump, thrown in with mangled nonsense about angle of attack and laminar flow and what have you .

You have to wonder at the idiocy of it all.Sigh!


LoL :D - well deflected sirji!

Lots of talk about sailing ships and 10th standard maths. Even some talk about drawings and using grey cells.

But at the end of a long ramble there is

1. no substantiation that AoA does not increase lift
2. no proof of magical changes in airflow depending on if carrier is stationary or in motion
3. no substantiation of airflow from beneath the wing
4. NOT EVEN a drawing by you.

You're pretty quick to ask others to do what you are not doing yourself.

How droll !!

sankum
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Re: INS Vikrant News and Discussion

Postby sankum » 25 Jun 2015 11:19

Let we explain in simple physics and simple math the launch of a fully loaded mig 29k with 24.5T MTOW with 18 T full afterburner thrust from a 14.3 degree skijump and a 195 m take off run. On a normal runway the take off speed is taken @75m/sec i.e, 145knots.

square velocity = 2* acceleration*distance=2*7.2*195=2808(acceleration= 18/24.5*9.8=7.2m/square sec)

Thus velocity at ski jump exit =53m/sec.

Now the vertical velocity imparted= 53 sin 14.3= 13m/sec.

Now the aircraft exits the ski jump @high AoA to maximize lift and I take drag decrement to acceleration @1.7m/square sec corresponding to L/D of 6 for MTOW lift

( L/D is actually 3 at ski jump exit as Lift is half of MTOW as velocity is 70% of required for take off and lift 50% as lift is function of square velocity)

So the aircraft accelerates @ 7.2-1.7=5.5m/square sec for next 4 sec to reach 75m/sec for free flight.

Because the lift is half of the MTOW the aircraft falls towards earth with a velocity decrement 5m/sec which gets subtracted from the vertical velocity of 13m/sec to have a still net upward velocity of 8m/sec after the first second but velocity meanwhile increase to 58.5m/sec increasing the lift and decreasing the upward velocity decrement.

I took this repeatedly for next 3 sec in one second interval(the calculation I did is for half second interval) for a total of 4.89+3.36+2.47+1.17=11.89 m/sec velocity decrement and you still get a positive upward velocity of 13-11.89= 1m /sec i.e, a safe flight to free flight transition in 4 sec.

The altitude gained will be 17m with respect to maximum altitude of ski jump and 270m distance from the ski jump. ( this you can see in how NLCA curves out from ski jump in video posted by shiv)

It is a semi ballistic lift off aided by aerodynamic lift for transition to free flight.

vina
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Re: INS Vikrant News and Discussion

Postby vina » 25 Jun 2015 11:48

Shalav wrote:1. no substantiation that AoA does not increase lift

Prove to me that you did not beat your wife yesterday!
You shovel some dung around, and you expect me to prove /disprove it ?

2. no proof of magical changes in airflow depending on if carrier is stationary or in motion
3. no substantiation of airflow from beneath the wing
4. NOT EVEN a drawing by you.


Why ? Didn't you pass high school math ? Cant you google around for a Vector A - Vector B diagram that I need to do it for you ? Wan't it there in the "PlaySchool Physics" book that was posted here , I assume it had some diagrams .

You're pretty quick to ask others to do what you are not doing yourself.

How droll !!

Droll, indeed, here. A langot wearing, probably illiterate SDRE in the Marina beach in Madras knows about relative wind. He is showing you. See the picture. Also he is showing you have a catamaran works. lf. He will not know your fancy lift and drag or angle of attack ,laminar flow rubbish, but he actually KNOWS how to use an airfoil and exploit relative wind, while you with your fancy terms can't even fathom such a thing exists. Wonder between the illiterate fisherman and you, who is actually more logical and scientific and who is a poseur.

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