INS Vikrant: News and Discussion

SNaik · Post by **SNaik** » 25 Jun 2015 12:20

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

Exactly.

vina · Post by **vina** » 25 Jun 2015 13:06

sankum wrote: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.

Let us put the conceptual thing here. First, we can put in the numerical later.

1. The engine works and puts out thrust. This at the end of the run, at the top of the ski jump has two things.
a. The speed of the plane, i.e. kinetic energy
b. The potential energy of the plane , since it has risen a height h above the deck.

So from stand still to top of the ski jump, the Thrust*distance (work done) = kinetic energy + potential energy.
It follows that the speed at the top of the ramp will be less than what you have calculated (you haven't factored in the height increase, some work is done against gravity, you have assumed a level surface)

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.

Forget about all this. The plane is not flying at all, but rather is ballistic. Assume that the plane is launched at an angle of 14deg or whatever the ramp angle is to the horizontal. Now break the thrust into two complaints, along the vertical, and horizontal.

The vertical component of thrust works against gravity, so the plane sinks at a rate less than g . It will be (g - x). The horizontal component accelerates the plane parallel to the water, until it reaches flight speed when it starts "flying", at that point you can drop the nose and start flying as normal. The vertical component of thrust keeps the plane in the air far longer than if it was a pure dumb ballistic path like that of a bullet , giving it more time to get to flight speed before hitting the water.

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

The angle of attack business comes in for this reason. Though the plane as it leaves the ramp is like a rock flung upwards, the pitch angle at which it exits has to be maintained at the designed level for the control surfaces have to be active. Yaw and pitch controls will be very problematic and that is what will get investigated at a maximum in both theoretical studies and in wind tunnel models.
The trouble is, the moment the plane leaves the deck, nose instantaneously tends to drop (the plane is free of the contact with the carrier and it is flying in free air like a normal plane climbing) and the tail and elevators /elevons may not be effective anymore and the control system /pilot has to pull the stick back and keep the nose up and fly at an angle of attack sufficient for the control surfaces to be effective,even if the main wing is not generating enough lift to fly the plane (this is far less of a problem for the harrier as it has active controls). And this is what the papers Sankum and others posted as well said about pilot response needed for each kind of plane.

So there will be a minimum speed at which the plane need to be at the end of the ramp for the control surfaces to be effective. So for a plane with a given T:W ratio, that will decide the length of the run.

srai · Post by **srai** » 25 Jun 2015 13:34

Some images to put words into visual diagrams:

maitya · Post by **maitya** » 25 Jun 2015 14:53

vina wrote:
sankum wrote:It is a semi ballistic lift off aided by aerodynamic lift for transition to free flight.
The angle of attack business comes in for this reason. Though the plane as it leaves the ramp is like a rock flung upwards, the pitch angle at which it exits has to be maintained at the designed level for the control surfaces have to be active.
...
and the tail and elevators /elevons may not be effective anymore and the control system /pilot has to pull the stick back and keep the nose up and fly at an angle of attack sufficient for the control surfaces to be effective,even if the main wing is not generating enough lift to fly the plane (this is far less of a problem for the harrier as it has active controls)
...

But, but this is exactly the reason why I's not able to agree, fully, neither with your earlier posts nor Shalavji's earlier posts ... as it was appearing to me, in pure layman pov, while there are 2 contributing factors (ballistic tarjectory due to ski-jump and angle-of-attack induced lift), each of you are talking about only 1 factor while completely blanking out the other contributing factor.

And sankumji (to which Ramanji agreed) was trying to bring in both.

From a layman pov, if there's an angle of attack, there will be a lift (and drag of course), however in-sufficient may it be and this ballistic profile aided with this insufficient lift provides the platform enough time to build up enough speed (and thus lift) to fly normally.

Isn't it - but then where is the dis-agreement?

vina · Post by **vina** » 25 Jun 2015 20:33

maitya wrote:From a layman pov, ....

Ok. I will explain everything again such that a layman can understand,
Assume that you are the guy at ADA who is tasked with responding to the query from the Navy on suitability of the LCA for the carrier. Let us go step by step, even "algorithmically" like the IT/Vity boys.

Step 1) The Navy has done what !!! They have gone and bought that Russian Kakkoose ! The brass are retarded beyond belief! Now they want check if we can fly the LCA from that ?
Step 2) The Russian rust bucket has a take off run of X m (say) and a 14 deg ski ramp (say) , the end of the ramp is h meters above deck,and turns into the wind and makes 25 knots (ie roughly 45 kmph) for launching aircraft.
Step 3) Okay.. Lets see. My take off speed is 150 knots (Say) indicated speed , thankfully because of the ship moving, I am starting at 25 knots.
Step 4) Lets find the speed at the end of the ramp, with my total all up weight W and Thrust T.
So my intial KE of 25 knots + work done by my engine during take off run = KE at top of ramp + PE at top of the ramp.
Step 5) Okay, did the math and found out that my speed V at the top of the ramp is 85 knots (say).. Holy Kakkoose,that is below my take off speed! This thing is going to fall like a turd!
Step 6) Emergency call to the aero model /wind tunnel guy on the intercom. Dude! I am in deep doo-doo and need your help super fast. I know I need to fill the form in triplicate and laminate and send it to the Baboon in the office, I don't have the time for that now, I promise to do that at the earliest. Can you do this please ?
Step 7) Phew thanks.. I owe you one for this. See, I have to fly this thing off a ramp which launches it at 14 deg pitch angle (nose up & musharraf down at 14) at a speed below take off speed and is therefore stalled. I can only pray that I hold this 14 deg pitch angle and hope to gain speed and fly off before I hit the water. I just need to find out if it can be controlled. So, please, with the take off flap and positions settings, can you run the model in the wind tunnel at the 14 deg pitch angle to find the minimum speed at which this can be controlled (pitch, yaw ,roll) ? (Minimum stall speed)
Step 8 ) That speed is 75 knots you say ,phew what a relief.
Step 9) Okay, let me check the sink rate I will have with the Nose Up and Mushraff down at 14 deg position.. Okay, it is (g-x) by resolving the thrust vertically and horizontally. I am accelerating at Y horizontally and will take t secs to reach flight speed and start climbing.. Okay, with the given sink rate, I will stay in the air far longer than t secs before I hit the water.. Thank god. So it can be done
Step 10) Write out the report, put in Govt of India Baboo Inglees in i, have it triplicated, laminated and have it sent in the mail, registered post, ack due onree, thank you.

There.. Very simple, all i Inglees, no confusion, no need to add pesky things like vector quantities, all easy peasy very easy to understand.

TSJones · Post by **TSJones** » 25 Jun 2015 21:05

I'll bet an airplane doesn't take off as fast on a ski jump as it does on a flat surface.

I would also humbly point out that the good doctor's model airplane does not have flaps and ailerons which might help just a teensy bit for an airplane to take off....like point the nose up, grab a bigger cut of air, etc.

don't mind me....continue to march.

geeth · Post by **geeth** » 25 Jun 2015 21:30

I don't see anything about airflow from "beneath the wing" etc here either? 'll bet an airplane doesn't take off as fast on a ski jump as it does on a flat surface.

Loss in speed will get converted to gain in height...?

NRao · Post by **NRao** » 25 Jun 2015 21:41

There are vids where a plane, using a CAT, sinks, while most others do not sink. I just took it mean that the planes that did sink just did not have enough factors to get them air borne before they left the carrier. Or, those that did not sink had sufficient "lift" JUST prior to departing the carrier. The contribution to this "lift" I assumed from various factor - it could not be just because of the CAT (which I think is a near constant factor).

Picklu · Post by **Picklu** » 25 Jun 2015 21:45

Well, let me open my stupid mouth as well.

Stunt bikers and stunt riders use an angled ramp like sky jump to remain airbourn during the period of stunt. They could have used a high but flat ramp (like a diver) but that is not really efficient or economic from the energy point of the view and hence they do not do so. It has nothing to do with AoA since bike or car is not really aerodynamic. So are the case with skateboarders, it is really mechanical force not aerodynamic.

Hence, my understanding is that the change of AoA due to sky jump provides less effect compared to ballistic effect of the speed of the aircraft on the sky jump. Else, that much AoA could have been obtained by simply deflecting the control surface that much at the end of the sky jump. The plane would not have stalled as it does not stall immediately after leaving the sky jump when it has the same speed but increased AoA.

Picklu · Post by **Picklu** » 25 Jun 2015 21:53

The forward airspeed due to the AC running into wind does play a role but even i do not think that launch are put on hold if there is no/negligible wind or due to some engine room problem the AC is operating with reduced speed (like Vikad's busted boiler). So, this forward airspeed does provide a boost or additional margin but most likely not absolutely necessary for launch.

NRao · Post by **NRao** » 25 Jun 2015 22:41

1) Watch the F-18 and the F-35 take off from a runway using EMALS, no wind, etc
2) Around 11 min the shooter mentions he is aided by others who provide wind info

TSJones · Post by **TSJones** » 26 Jun 2015 02:07

^^^^^^

did you see where the flaps in back of the wing are down during launch but at release from the deck to air the flaps are brought back up? also notice there is a foward slat in front of the wing that is extended forward then retracted when in flight.

muy importante....

Lalmohan · Post by **Lalmohan** » 26 Jun 2015 02:16

forward speed of carrier plus wind speed (carrier sails directly into wind) provides anywhere from 30 to 40 kts of flow over the aircraft wings before it even revs up. every kt of that wind is helpful. the ski jump allows the use of brute thrust to throw the aircraft into the sky quickly under its own steam (without a catapult) and at some stage when the thrust and lift vectors are producing more force than the drag and weight vectors the aircraft starts to fly

TSJones · Post by **TSJones** » 26 Jun 2015 02:21

according to US NAVAIR intro to aviation class which all aviation support enlisted ranks must attend both Navy and Marines: an airplane can fly because once the proper speed is attained, a vortex is created over the TOP of the wing lifting the airplane up. How is this vortex created? The top of the wing has a curvature built into it creating the vortex on top of the wing. Not all planes have the same curvature. A piper cub has a very large curvature. That plane wants to float in the air, man.

jet a/c, especially fighters have a very small curvature in comparison and thus are very difficult to fly, they do this because they want to go fast not slow like the piper cub. I have heard pilots call jet a/c "slick" because the jet a/c slice through the air

I laugh when I hear "you are the air BENEATH my wings".

Abhay_S · Post by **Abhay_S** » 26 Jun 2015 04:29

Tarmak shared this link.

NRao · Post by **NRao** » 26 Jun 2015 04:46

That is F-35B. Not fair. It could probably fly backwards of that ski jump.

shiv · Post by **shiv** » 26 Jun 2015 06:02

First 20 seconds - all the aircraft lose altitude after launch
https://www.youtube.com/watch?v=Mj30oQuTBDU

shiv · Post by **shiv** » 26 Jun 2015 06:12

TSJones wrote:^^^^^^

did you see where the flaps in back of the wing are down during launch but at release from the deck to air the flaps are brought back up? also notice there is a foward slat in front of the wing that is extended forward then retracted when in flight.

muy importante....

In every case the elevator is briefly operated to get the nose up just before the catapult launch is completed. The pilot just starts to get nose up and then returns the elevator to neutral. In other words there is some "angle of attack" thing going on here - the pilot pushes the tail down (pulls the nose up) to increase AOA just before the end of the catapult launch.

shiv · Post by **shiv** » 26 Jun 2015 06:16

TSJones wrote:according to US NAVAIR intro to aviation class which all aviation support enlisted ranks must attend both Navy and Marines: an airplane can fly because once the proper speed is attained, a vortex is created over the TOP of the wing lifting the airplane up. How is this vortex created? The top of the wing has a curvature built into it creating the vortex on top of the wing. Not all planes have the same curvature. A piper cub has a very large curvature. That plane wants to float in the air, man.

jet a/c, especially fighters have a very small curvature in comparison and thus are very difficult to fly, they do this because they want to go fast not slow like the piper cub. I have heard pilots call jet a/c "slick" because the jet a/c slice through the air

I laugh when I hear "you are the air BENEATH my wings".

I think the vortex creates a low pressure - which means that the wind beneath the wings exerts an upward pressure on the wings - so that little romantic love byte is true.

vina · Post by **vina** » 26 Jun 2015 09:42

TSJones wrote:I'll bet an airplane doesn't take off as fast on a ski jump as it does on a flat surface.

Yes . The good doctor's experiment proved that it does indeed need a slower speed to "take off" . Truth be said, off a ski jump, the plane is just thrown up into the air, and it really starts flying a good distance away from the point it leaves the ramp. On the ground, the plane is taken up to flight speed and rotated and starts flying up from there. Not a really apple to apple comparison in the strict sense.

How about if you had bet this way hypothetically?

TSJones wrote: Hypothetically -

1. I'll bet an airplane doesn't take off as fast on ski jump from a moving ship as it does on an exactly similar ski jump on a test facility ashore (assuming in both cases there is no prevailing wind)

2 . I'll bet an airplane taking off from a ski jump on a moving ship has a shorter take off distance than the same airplane from the ski jump on a shore based test facility (assuming in both cases there is no prevailing wind) .

Whaddya think ?

Singha · Post by **Singha** » 26 Jun 2015 13:14

even a catapult is just throwing off the plane by definition. any rotation will result in the nosewheel and strut being left behind on the carrier. but the throwing speed seems to be higher in catapult than solely under own engines on ski jump. and ofcourse shorter takeoff run, always a advantage on deck.

geeth · Post by **geeth** » 26 Jun 2015 16:38

I think the vortex creates a low pressure - which means that the wind beneath the wings exerts an upward pressure on the wings - so that little romantic love byte is true.

vortices are formed towards the trailing edge of the wing due to flow separation and is detrimental to lift. Another instance is the vortices generated deliberately by vortex generators. These act like fences to prevent sideward flow (due to sweep back).

The flow over the wings have more velocity than that under the wing and according to Bernoulli's principle, more velocity means less pressure. So the flow over wing has less pressure than that under wing thus creating a suction effect (lift).

I think many minds have been poisoned after reading last few pages of this thread and needs repair. Shivji used to be closer to target in matters of aerodynamics...dont know what happened.

TSJones · Post by **TSJones** » 26 Jun 2015 17:24

yes, less pressure is created. I called it it a vortex. my bad. Shiv got it right.

As usual somebody always wants to argue semantics.

NRao · Post by **NRao** » 26 Jun 2015 17:38

I think with either the CAT or EMALS, the basic idea is to toss the plane with enough speed and expect it to fly after the toss. IF it does actually fly prior to that expected point in time - great. Some do start flying early (leaving the flat top), some don't and yet a few others never fly and take a dunk.

shiv · Post by **shiv** » 26 Jun 2015 18:09

geeth wrote:
I think many minds have been poisoned after reading last few pages of this thread and needs repair. Shivji used to be closer to target in matters of aerodynamics...dont know what happened.

The best way to appear wise is to shut up - which I should have done a few years ago

Too late now

If I am not mistaken, airflow over the wing should stick to the wing - or else. But vortices forming over the wing or near the leading edge means stall coming soon

Manish_P · Post by **Manish_P** » 26 Jun 2015 18:57

Can't resist doing the unwise thing of butting in with my layman understanding (well reading actually)

http://www.pprune.org/archive/index.php/t-111712.html

Check out the comments from poster 'John Farley' (posted belowin quotes if external URLs are not welcome)

Cron and chaps:

There several ways to get your head round why the ski-jump improves a Harrier STO performance without getting into the maths. But some may not be familiar with the basics of the VTO and STO so forgive me for tidying those away first.

A Harrier will only VTO if its weight is less than some 96 percent of the thrust available. (Not 100% as you need a tad to spare to accelerate the thing upwards as well as carrying the weight)

So, at max AUW you will typically be short of three or four tons of lift (actual amount depends on the mark of motor and airframe) This calls for an STO where you need to go fast enough on the surface for the wing to carry the excess weight plus some margin to stop it staggering, then when you bang the nozzles down the thing will get airborne on a mix of engine and wing lift.

Now imagine doing this from a flat deck. Life is better than from a runway as the deck height above the water is free and so you can delete the margin needed to stop the runway stagger. You shoot off into the air regardless and can also rotate the aircraft to the optimum AOA – which you cannot do ON the runway because of the bicycle main gear being well aft of the CG.

But all of this ship advantage vanishes (and then some) in rough water. If the ship is pitching you may get to the end of the deck when the bow is down and finish up diving towards the sea. Pulling out from this dive requires the ability to pull g, which means a considerable margin of lift is needed. So, once you are using all the deck to accelerate to as high an 'end' speed as possible you have no option but to reduce STO weight. And this weight reduction can be very large so quickly negating the benefit of the STO in the first place. So you become a fair weather only toy.

Now stick a ramp on the end where the exit angle is greater than any conceivable bow down tendency and you make every launch start with a climb courtesy of the ramp and the gear. End of ship motion problem Now consider a ramp angle much greater than that needed for the above and you really start to win. Your question is Why?

The secret is the ramp gives you TIME in the air even if you have zero lift.(I trust you can accept that even your bike or car would fly for quite a few moments before it gradually fell back towards the sea if you shot up a ramp at seventy or so kts)

If your bike or car is now a Harrier - where the engine can carry say 70 percent of the weight - then even without ANY wing lift you will only sink back towards the sea at 30% of gravity. If you arrange that the wing lift actually carries half of that 30% lift deficit then gravity only sucks you down at 15% of its normal rate. Which means you curve upwards for many seconds before you get level, let alone sink. You use this TIME to accelerate the wing to a higher airspeed (through the proper use of nozzle angle) to get more aerodynamic lift and so fly happily away. Even though you started at a weight that could NEVER have flown off a flat deck in a calm sea – because then you would not have had enough acceleration time before you got to the water.

There are many other advantages to the ski-jump in terms of handling and safety but your question was about performance.

and

Smoke too much

Your observations are correct. With the Harrier II wing (GR7, AV-8B etc) the flaps are so large they could not be put down beyond about 30 deg when the nozzles are aft (as in the STO ground roll) without being blown off. So their selection is armed by the pilot during TO checks after which they travel automatically with the nozzles.
As for a down ramp at the start of the deck roll, I agree that would have to help performance. I think its downside (sorry) is the further reduction in space usable by marching bands. You could also use a large hamster wheel as well, then after N revs to build up speed FLYCO (or any of the old guys who used to fire the catapults) could open a flap and let you loose.

Tinstaafl

Too right. 45 deg IS the optimum angle if you are only considering performance (those early brown jobs knew a thing or two). But we stopped our trials at 20 deg because the law of diminishing returns was rearing its ugly head plus a whole host of adverse ship related issues were appearing on the scene. 15 deg is the practical man’s choice as it provides real benefits to the Harrier with negligible disadvantages to the ship.

The ski-jump has been described as the 'runway in the sky' as it just gives you time to accelerate to flying speed. The Russians use it for flying Su-27 and MiG-29s from ships rather than bother with catapults. But not all aircraft can benefit from a sk-jump. You need a high thrust weight ratio to make the most of the time provided and you need to have aerodynamics that provide adequate control of attitude at well below normal flying speed.
Like the Russians above.

Harrier Ski Jump Farnborough 1978

vina · Post by **vina** » 26 Jun 2015 20:31

Manish_P wrote:Can't resist doing the unwise thing of butting in with my layman understanding (well reading actually)
http://www.pprune.org/archive/index.php/t-111712.html

.. The secret is the ramp gives you TIME in the air even if you have zero lift.(I trust you can accept that even your bike or car would fly for quite a few moments before it gradually fell back towards the sea if you shot up a ramp at seventy or so kts)

... If your bike or car is now a Harrier - where the engine can carry say 70 percent of the weight - then even without ANY wing lift you will only sink back towards the sea at 30% of gravity. If you arrange that the wing lift actually carries half of that 30% lift deficit then gravity only sucks you down at 15% of its normal rate. Which means you curve upwards for many seconds before you get level, let alone sink. You use this TIME to accelerate the wing to a higher airspeed (through the proper use of nozzle angle) to get more aerodynamic lift and so fly happily away. Even though you started at a weight that could NEVER have flown off a flat deck in a calm sea – because then you would not have had enough acceleration time before you got to the water.

The ski-jump has been described as the 'runway in the sky' as it just gives you time to accelerate to flying speed. The Russians use it for flying Su-27 and MiG-29s from ships rather than bother with catapults. But not all aircraft can benefit from a sk-jump. You need a high thrust weight ratio to make the most of the time provided and you need to have aerodynamics that provide adequate control of attitude at well below normal flying speed.
Like the Russians above.

Yup, Exactly how it works. As I explained earlier, for a ski jump launch off a carrier, the control problem is far more difficult for a conventional plane like he Mig 29/ LCA etc because the are below flight speed, but still need control authority in the stalled condition, than it is for the Harrier which has active controls in pitch, yaw and roll.

Check out the video of one of the Harrier's designers explaining all the controls and how the Harrier works.

This entire discussion began with having a ski jump AND emals. Like I said, it doesnt make sense to do both.The EMal can easily generate the indicated air speed at which the aircraft nearly starts to fly before throwing it out over the bow and in addition , just watch the old WWII type videos of tail dragger aircraft taking on their own power from carriers Zeroes, Hellcats, Bearcats, etc.. They just fly off over the bow without the tail coming up and the wing at an angle of attack to the flow. They have low take off speeds anyways and can do it. You can do a similar thing with the Cats/Emals by just putting a longer nose landing gear and get the nose up and musharraf down and fire the cat/email and shoot it out over the bow. That is exactly what is done for the Rafale M! That will actually be flying at a higher lift angle of attack config and probably wont need too much time to get to flight speed and wont sink much at all before climbing.

brar_w · Post by **brar_w** » 26 Jun 2015 20:56

C-130 and U-2 taking off without a ramp or a CAT

https://www.youtube.com/watch?v=uM5AI3YSV3M

https://www.youtube.com/watch?v=L8HMPMYL19E

TSJones · Post by **TSJones** » 26 Jun 2015 21:50

^^^^

Yup, that c-130 pilot probably has balls of steel. They clank when he walks.

Philip · Post by **Philip** » 26 Jun 2015 23:06

The ski-jump/Sea Harrier partnership had the unique advantage over other types due to the SH's "VIFF" ing capability (vectoring in forward flight),the ability to rotate the exhaust nozzles while taking off and in flight,giving the aircraft extra lift,etc.,why not a single SH has been shot down in aerial combat. The beauty of the ski-jump is that when the carrier pitches in a trough,the aircraft is still launched at an angle elevated to the sea/horizon,preventing the aircraft from ditching.It was also found to have improved significantly the sea keeping ability of the carriers,esp. in rough weather.

sankum · Post by **sankum** » 26 Jun 2015 23:36

Automated Take-Off From Aircraft Carriers For India's Naval Light Combat Aircraft [LCA-Navy]

See video after 24 min for next 3 minutes.

shiv · Post by **shiv** » 27 Jun 2015 05:13

vina wrote:
Manish_P wrote:You can do a similar thing with the Cats/Emals by just putting a longer nose landing gear and get the nose up and musharraf down and fire the cat/email and shoot it out over the bow. That is exactly what is done for the Rafale M! That will actually be flying at a higher lift angle of attack config and probably wont need too much time to get to flight speed and wont sink much at all before climbing.

Maybe that explains why the Dassault Etendard has an extra-long nosegear

Singha · Post by **Singha** » 27 Jun 2015 20:53

I propose the entire wing itself be able to turn up and down like a huge canard. using it as airbrakes the plane could also lose speed very swiftly in a emergency and use them as airbrakes after landing.

Abhay_S · Post by **Abhay_S** » 27 Jun 2015 22:01

where are our Aero Experts Indranil and Yak Hearder ji ? we need them to settle this debate.

Shreeman · Post by **Shreeman** » 28 Jun 2015 01:41

Here is a practical little experiment for all you budding jet pilots. You know those flappy things that have one or more settings? That you cant retract until you reach a certain height? Go ahead and retract them any way, right after wheels are off the ground. Also, dont extend them when coming back down. Best demonstration of lift. No one responsible for any pranging that may occur. Also, if you dont reply with a report from hospital bed then we will understand you tried and succeeded!

vina · Post by **vina** » 28 Jun 2015 06:10

Singha wrote:I propose the entire wing itself be able to turn up and down like a huge canard. using it as airbrakes the plane could also lose speed very swiftly in a emergency and use them as airbrakes after landing.

Check out the Vought F8 Crusader with it's Variable Incidece Wing

shiv · Post by **shiv** » 28 Jun 2015 06:19

Shreeman wrote:Here is a practical little experiment for all you budding jet pilots. You know those flappy things that have one or more settings? That you cant retract until you reach a certain height? Go ahead and retract them any way, right after wheels are off the ground. Also, dont extend them when coming back down. Best demonstration of lift. No one responsible for any pranging that may occur. Also, if you dont reply with a report from hospital bed then we will understand you tried and succeeded!

Heck Shreeman you are tempting me. Guess what? I had made a video 3-4 years ago as part of my "aerodynamics research"

. I will upload soon.

shiv · Post by **shiv** » 28 Jun 2015 06:22

Looks like the SeaHawk also has a nose-up attitude with a "tall" nose-gear for the increased angle of attack on take-off

shiv · Post by **shiv** » 28 Jun 2015 06:31

Singha wrote:I propose the entire wing itself be able to turn up and down like a huge canard. using it as airbrakes the plane could also lose speed very swiftly in a emergency and use them as airbrakes after landing.

As Shreeman pointed out - - here is the C-17 with gi-normous flaps that do the same job
https://www.youtube.com/watch?v=quOwa58NeHE

Shreeman · Post by **Shreeman** » 28 Jun 2015 07:18

Never easy to put this stuff in lay language:
1. The ski jump is there to increase all up load. Catapults break down. Even under best of circumstances. Given the general state of things, best to stick with them for another generation. This is probably the reason over all else.
2. You could theoretically make a downward facing ski slope and launch into the sea from a high enough pedestal. Make an elevator to raise the craft to the slope and down it goes!
3. The geometry/algebra has been beaten to death. It is dead, I checked.
4. The 14 degrees is curious, 12 degrees suited the take off speed of the harrier. Both LCA/29k use 14 degrees. What all up was required to deviate from the 12?
5. Parachutes will outlive the utility of any other air brake. But even they are useless on the short tarmak surrounded by dip.
6. Air brake are useless below a certain speed, impractical/impossible above a certain speed.
7. For all wing geometry, this flying business is tricky. Trivial to go from "here I am riding the wind" to "uhoh, what do we do now?". A simple gust of wind at the wrong time can upset all those computations your mighty powerful computer is making. And this is most likely at take off or landing.
8. In particular, for this transition business. Not worth the mechanical complexity. If you just want to stop, attach a hook to your tail. If you are on land, unfurl. No air brake is going to shorten anything. They help with minir adjustments. and this is also why many engines reverse thrust.
9. Wing forms vary, during phases of flight, and they are sufficient to let you know the dynamic nature of your endeavor. Next time in commercial travel, feel for when a. flaps retract, b. flaps extend, c. landing gear comes out, d. air brakes/thrust devices deploy. All very interesting.

I know nothing, and will deny everything.