LCA News and Discussions

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Kartik
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Re: LCA News and Discussions

Postby Kartik » 22 May 2012 09:09

shiv wrote:
Kartik wrote:
read this thread as well if you like. the Tornado, Harrier, Hawk, etc. all have explosive cord over the pilot's head. On the Tornado, it does seem to be adhesively attached to the canopy

http://webarchive.nationalarchives.gov. ... 135_f3.jpg


I am not disputing that this is done. I am disputing the idea that the incomplete strip above the NLCA pilots head is the same as this complete strip seen in the photo you have linked.


As the picture posted by Indranil shows, this seems to be there on other Tejas' as well. There is absolutely no other fathomable reason why they'd put anything on the canopy. As long as the canopy shatters when the explosives go off, the job is done.

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Re: LCA News and Discussions

Postby shiv » 22 May 2012 09:12

Kartik wrote:As the picture posted by Indranil shows, this seems to be there on other Tejas' as well. There is absolutely no other fathomable reason why they'd put anything on the canopy. As long as the canopy shatters when the explosives go off, the job is done.


Kartik, canopies are not supposed to shatter and they don't shatter when hit by birds/bullets/shrapnel. They break but do not shatter. If they are cut they need to be cut fully. Not partially.

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Re: LCA News and Discussions

Postby Kartik » 22 May 2012 09:19

shiv wrote:
Kartik wrote:As the picture posted by Indranil shows, this seems to be there on other Tejas' as well. There is absolutely no other fathomable reason why they'd put anything on the canopy. As long as the canopy shatters when the explosives go off, the job is done.


Kartik, canopies are not supposed to shatter and they don't shatter when hit by birds/bullets/shrapnel. They break but do not shatter. If they are cut they need to be cut fully. Not partially.


not true Shivji. This document that I'd posted earlier clearly talks about TTC (Through The Canopy) escape capability being a design requirement for canopies.

What you've stated is actually a fact that is stated in the document itself- that resisting bird strike and allowing through canopy escape are contradictory requirements as one requires strengthening (should not be brittle and a sandwich composite type design works best) and the other requires that it should shatter when required.

The forward canopy poses a most difficult general problem of integrating thru-the-canopy (TTC) ejection system with improved bird strike resistance while maintaining present optical and durability characteristics. Combining efficient bird strike protection and TTC ejection are
novel and contradictory requirements since the tough materials which resist bird penetrations also resist "punch through" ejection.

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Re: LCA News and Discussions

Postby SaiK » 22 May 2012 09:32

sounds like the canopy must be built to withstand bird strike, but not the explosive charge. contradicting only within the strengths limits of taking bird hits.

but then if it shatters on bird strike, we still need make sure a safe ejection happens on impact detection or air flow sensor or pressure sensor based. worst case, pilots pulls the strings if he/she is still conscious.

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Re: LCA News and Discussions

Postby Rahul M » 22 May 2012 09:36

shiv wrote:Folks I am no expert, but I seriously doubt if a strip of explosive will be pasted right above the pilot's head.

if you remember older hawks, they had the explosive strip in a zigzag line on the canopy right above the pilot's head.

Image

A BAE Hawk showing the explosive cord in the canopy


re : holding against bird strike. I assume the explosive cord would blast from inside to outwards and the strength of the canopy would work as in an egg shell. *much* easier to break from within than outside.

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Re: LCA News and Discussions

Postby Kartik » 22 May 2012 09:41

Rahul, I looked at IAF Hawks and they too have the explosive cord..and since HAL should be building the canopies for the Hawk, the knowhow for how to build such a canopy would already exist at HAL.

Image

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Re: LCA News and Discussions

Postby SaiK » 22 May 2012 09:42

And a design like pak-fa, where the canopy slides backwards perhaps does not require any explosives for their canopy... as long as they push buttons and engage it to slide back.

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Re: LCA News and Discussions

Postby Rahul M » 22 May 2012 09:45

^^ psyche, I would expect the whole canopy to be blown away by explosives placed on the hinge and a couple of other places.

kartik, thx, I didn't have a IAF hawk close-up handy.

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Re: LCA News and Discussions

Postby shiv » 22 May 2012 09:49

Kartik your 160 page pdf has a lot of information. I will post some of that on here:

A lot depends on the actual material used to make the canopy
Starting page 52

Canopy Severance Patterns

Many variations of overhead patterns have been used for escape
systems.

A listing of the basic overhead patterns is given
below, but it should be noted that many variations of these
basic patterns have or could be implemented.

Single Overhead Centerline Cut

This pattern structurally degrades the canopy allowing
seat and pilot to be ejected through the remaining canopy structure.

The result of this pattern is primary fracturing
down the canopy centerline and secondary angular fracturing
emanating from the primary fracture ..

Overhead Panel Cutout

This pattern cuts a panel from canopy of sufficient size to
allow seat and pilot ejection without contacting the canopy
structure.


Full Perimeter Cut
This pattern utilizes a single loop of MDF running around the
fuel perimeter of the canopy.
The principle here is that the
entire canopy can be severred basically in one piece except

Overhead Sawtooth Cut
This pattern implements a loop of MDF incorporating sawtooth
shaped crack initiation points.


Starting page 67
Five basic techniques have been used to clear the canopy for
ejection.

Each technique is briefly described below.

Canopy Centerline Severance

The canopy is explosively cut along its centerline and
ejection through the canopy provides the required break-
out. This technique is incorporated on the A-7K Aircraft
which utilizes an acrylic transparency. This concept is
not feasible for the T-38 because the centerline cut will
not sufficiently degrade the polycarbonate transparency
to allow ejection without injury to the student pilot.

Seat Mounted Canopy Piercing

A seat mounted cutting blade is provided and during ejec-
tion the blade breaks the canopy as the seat and crew
member pass through. This technique is presently used as
a backup for the canopy jettison system on the T-38 air-
craft.
<snip>
The MAGNA analysis indicates that a seat mounted canopy
breaker might be capable of breaking through a .40 thick
polycarbonate canopy utilizing the force available with
the existing seat catapult. The analysis further states
that the biodynamic response of the student pilot body to
the resulting acceleration may be unacceptable

Total Canopy Fracture


The canopy is explosively fractured into small fragments
and the seat/crew member eject through the canopy plane.
This technique is utilized in conjunction with acrylic
canopy transparencies wherein the primary and interacting
The shock waves can reliably break up the canopy.
British Harrier and XTV Aircraft incorporate this technique
for clearing the canopy for ejection. This technique is
not possible with polycarbonate transparencies. The poly-
carbonate material is resistant to the cracking and crack
propogation characteristics required for success of the
total Canopy Fracture technique.

Canopy Jettison

A ballistic thruster is used to drive the canopy pivotting
mechanism up into the airstream and clear of the ejection
path. This technique is widely used and is presently
incorporated in the T-38 Aircraft. *The existing jettison
system will continue to be the primary mode of canopy re-
moval for the T-38 Aircraft. The new canopy system weight
is dependent primarily on the transparency design ulti-
mately chosen for bird proofing. This additional weight
varies from 15 to 45 pounds with the different transparency
designs. This additional weight will have a degrading
effect on the existing thrusters. Should the capabilities
of the thrusters be exceeded, they could be replaced with
more powerful thrusters.

Canopy Mounted Rocket Motor Jettison


Solid propellant rocket motors are mounted to the canopy
frame or side rails. When the canopy is released the roc-
ket motors thrust the canopy up and clear of the ejection
path. This technique is used on the F-16 and F-18 Aircraft
and performance is within system requirements for each
application. This concept could be utilized on the T-38
in conjunction with full perimeter severance for canopy
removal. Use of the F-16 or F-18 rocket motors would im-
prove canopy jettison performance because the T-38 canopy
is much smaller and lighter.
<snip>
The potential for student pilot burn hazard exists with
rocket motor exhaust blast unless attention is given to the
problem. This hazard can be eliminated in the manner dis-
cussed below.

A blast deflector for the rocket motors can be designed
which will direct the hot gas output away from the student
pilot during ejection. Test results for the F-18 aircraft
(reference MDAC Report Number MDCA7T27) verifies that the
eleapsed time between rocket motor ignition and canopy sep-
aration from aircraft is only 0.083 seconds. Canopy separ-
ation from the F-18 occurs after the canopy has rotated up
and back in a 450 arc.
The short time duration of rocket motor blast (0.083 second)
combined with blast deflectors for the T-38 will negate the
possibility of injury due rocket gas output. This rationale
justifies the rocket motors for consideration as a possible
candidate for T-38 canopy removal.

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Re: LCA News and Discussions

Postby shiv » 22 May 2012 09:52

Rahul M wrote:
shiv wrote:Folks I am no expert, but I seriously doubt if a strip of explosive will be pasted right above the pilot's head.

if you remember older hawks, they had the explosive strip in a zigzag line on the canopy right above the pilot's head.


Rahul are you absolutely sure that zigzag is NOT the defogging wiring. A separate white strip is clearly visible on the canopy perimeter. :D In any case Google confirms that you are right...

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Re: LCA News and Discussions

Postby Indranil » 22 May 2012 09:58

Shivji,

as Kartik pointed out, the strip on top of the pilots head is not the only severance point. There are explosive chrages on the periphery where the canopy meets the cockpit. The explosive strip on the top of the canopy is used for extra protection. You can imagine if the cockpit is only severed from the edges, it might still be largely intact. If that mass hits the pilot, he would definitely perish. So the top is also cracked up for additional safety.

In the pic of the LCA that I had posted, please notice the "shell tooth" on the right hand side of the head rest. That shell tooth design is also a common practise. The tooth is designed like the safety hammer used to break the windows and windscreens of auotmobiles. The tooth breaks the canopy if there is any contact at all, not the head of the pilot. This is the exact system as in the A-10 Thunderbolt. Notice the line charge on its cockpit. It is also not complete.

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Re: LCA News and Discussions

Postby SaiK » 22 May 2012 10:13


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Re: LCA News and Discussions

Postby akimalik » 22 May 2012 10:28

One quick question that I wanted to ask regarding the ejection procedure....
Q. Is the pressure of the gas generated by the rocket motors of the Ejection Seat also used/useful in pushing out the canopy (due to +ve pressure buildup within the cockpit as a result of the rocket exhaust)?

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Re: LCA News and Discussions

Postby Kartik » 22 May 2012 10:58

And an old B/W video that shows through-canopy ejection trials. as is plainly visible, the canopy shatters before the pilot actually begins to emerge through the canopy itself. At 0:13 of the video, the canopy opens up almost like a clamshell, as described in the other document I'd posted.

Youtube video

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Re: LCA News and Discussions

Postby vina » 22 May 2012 11:18

Kartik wrote:And an old B/W video that shows through-canopy ejection trials. as is plainly visible, the canopy shatters before the pilot actually begins to emerge through the canopy itself. At 0:13 of the video, the canopy opens up almost like a clamshell, as described in the other document I'd posted.

Youtube video


The only problem with thru the canopy ejection is that when the canopy shatters, it should be absolutely ensured that the flying shards are not razor sharp jagged daggers that you would get when a window pane disintegrates or a mirror disintegrates. Or else the pilot will get skewered, defeating the point of ejection in the first place.

It is for that reason that they have safety glass mandatory in automobiles, which is basically two tempered glass sheets sandwiched together on a thin film material, so that when it fractures in an accident, it sort of holds together
and even if shatters, it shatters into small pieces with rounded edges and dont kill the passengers inside when they are showered.

Maybe the plastic material used in the canopies dont produce that kind of knife like shards that glass does.

But between jettisoning the canopy and punching through the canopy, the latter is definitely faster , while the former will take a few tenths of a second for the canopy to get clear of the plane safely before the seat can come out and the through the canopy system is probably safer as well because there is no canopy flying around that can impact the pilot(s) ejecting.

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Re: LCA News and Discussions

Postby Kartik » 22 May 2012 11:37

vina wrote:The only problem with thru the canopy ejection is that when the canopy shatters, it should be absolutely ensured that the flying shards are not razor sharp jagged daggers that you would get when a window pane disintegrates or a mirror disintegrates. Or else the pilot will get skewered, defeating the point of ejection in the first place.

It is for that reason that they have safety glass mandatory in automobiles, which is basically two tempered glass sheets sandwiched together on a thin film material, so that when it fractures in an accident, it sort of holds together
and even if shatters, it shatters into small pieces with rounded edges and dont kill the passengers inside when they are showered.

Maybe the plastic material used in the canopies dont produce that kind of knife like shards that glass does.

But between jettisoning the canopy and punching through the canopy, the latter is definitely faster , while the former will take a few tenths of a second for the canopy to get clear of the plane safely before the seat can come out and the through the canopy system is probably safer as well because there is no canopy flying around that can impact the pilot(s) ejecting.


yes, it shouldn't cause grievous injury to a pilot. But the canopies nowadays are built as laminates due to the bird strike protection requirements. The F-16's canopy is built from 3 layers, the first being polycarbonate, then another thinner layer of polyurethane to bond the polycarbonate to the last layer of acrylic. The canopy won't (at least in theory) shatter like glass and send sharp pieces flying around inside the cockpit.

added later: One more benefit of the canopy fracturing mechanism using explosive cords is that its a lot less complicated and weighs less as well also being less likely to fail. Canopy jettisoning schemes require latches with release devices and pyrotechnic rockets that can jettison the canopy in flight or on the ground. The explosive cord design is simpler and considered safer too since there are fewer systems that can fail in the event of an ejection.

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Re: LCA News and Discussions

Postby Lalmohan » 22 May 2012 12:13

in some planes, the front hinged canopy was meant to separate with the ejection seat, shielding the pilot from the oncoming blast of the airstream. this was for high speed ejection scenarios. i think they since established that most ejections happen at lower speeds and there is very little time for the pilot to get out and have enough safety height. zero zero seats (0 airspeed, 0 height) therefore rely on the shattering model to ensure that the pilot gets out fast enough and has enough time/height for his chute to deploy

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Re: LCA News and Discussions

Postby shiv » 22 May 2012 16:20

vina wrote:
Maybe the plastic material used in the canopies dont produce that kind of knife like shards that glass does.


Kartik's 160 page pdf says that acrylic, used in Harriers and Hawk will shatter and can be used for punch through ejection. But polycarbonate as in F-16 does not shatter. There seems to be a lot of intricate detail in the choices that are made.

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Re: LCA News and Discussions

Postby Singha » 22 May 2012 16:53

I was reading somewhere the 1-piece F22/JSF/F16/EF type bubble caponies are very complex to make and only advanced nations allowed to make it.

have we mastered this esoteric branch of plastics ? apparently not going by the LCA canopy.

another psyops stick used to beat is the narrow FOV framed HUD vs the wide FOV frameless HUD

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Re: LCA News and Discussions

Postby SaiK » 22 May 2012 17:08

http://kedar.smugmug.com/Miscellanous/S ... fZ2Y-M.jpg

on the ergo, is it too tight for our pilot here ? say, he is ejecting out. will his knees hit anything else?
--

on the polycarbonate, is it a better design to have not a single piece canopy, but multiple pieces that when charged would split into predetermined shape pieces?

I still think the slide back is a better system.

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Re: LCA News and Discussions

Postby Lalmohan » 22 May 2012 17:45

ejection seats have straps that pull the pilots legs into the seat as it shoots up, to try to keep everything together
but ejection remains a dangerous process, with fractures and lumbar compression as distinct possibilities

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Re: LCA News and Discussions

Postby Surya » 22 May 2012 17:51

on the ergo, is it too tight for our pilot here ? say, he is ejecting out. will his knees hit anything else?


yes and in the past limbs have been left behind

but nowadays when ejection is activated I believe there are straps that pull the legs in tucking it clear of the obstructions (my friends Migs had it)


Its still nervewracking
Last edited by Surya on 22 May 2012 18:35, edited 1 time in total.

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Re: LCA News and Discussions

Postby shiv » 22 May 2012 18:20

SaiK wrote:http://kedar.smugmug.com/Miscellanous/Stuff/cockpitkedarkDSC1059/498514415_DfZ2Y-M.jpg

on the ergo, is it too tight for our pilot here ? say, he is ejecting out. will his knees hit anything else?
--


Well that photo is via one of Kedar's superschlong lenses so it's all foreshortened.

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Re: LCA News and Discussions

Postby SaiK » 22 May 2012 20:32

http://www.bharat-rakshak.com/NEWS/newsrf.php?newsid=18626
As a Test pilot, Suneet along with other team members have given many valuable inputs to make Tejas a completely pilot-friendly fighter. He has contributed in bringing out many modifications to the Tejas' cockpit over the years,”

we need more of these.

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Re: LCA News and Discussions

Postby shiv » 22 May 2012 20:42

SaiK wrote:
http://www.bharat-rakshak.com/NEWS/newsrf.php?newsid=18626
As a Test pilot, Suneet along with other team members have given many valuable inputs to make Tejas a completely pilot-friendly fighter. He has contributed in bringing out many modifications to the Tejas' cockpit over the years,”

we need more of these.

The photo of the LCA canopy there has a white centerline strip, which, after all my thrashing about and struggling is beginning to look more and more like a strip of explosive canopy shattering tape even to my jaundiced eyes. I guess I have to let cognitive dissonance pass into history and accept that it is exactly as Kartik guessed it to be. Acrylic seems to shatter pretty cheerfully when subjected to the right stresses.

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Re: LCA News and Discussions

Postby SaiK » 22 May 2012 21:29

I think the prototype versions are acrylic ones, and the production variants are polycarbonate ones, per:
http://www.scribd.com/doc/38523381/Tejas-Radiance
scroll to page where it discusses about cockpit

so shivji, we still have the discussion point of shattering polycarbonate one.

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Re: LCA News and Discussions

Postby shiv » 23 May 2012 06:04

SaiK wrote:I think the prototype versions are acrylic ones, and the production variants are polycarbonate ones, per:
http://www.scribd.com/doc/38523381/Tejas-Radiance
scroll to page where it discusses about cockpit

so shivji, we still have the discussion point of shattering polycarbonate one.


In fact that photo of the LCA canopy having been cut and not shattered fit in with the idea that it may be polycarbonate. Acrylic apparently shatters well and creating cracks using explosive in a single centerline cut is OK for acrylic (in some instances at least). Polycarbonate canopies are flexible, do not shatter, and are inherently bird hit resistant.

There are two steps as per Kartiks 160 page pdf
1. Canopy severance
2. Removal of canopy from the ejection path

Regarding the second issue, quoting From page 67 of the pdf
3.5
Canopy Removal After Severance:
The question here is not cutting the transparency, but how can the canopy be removed from the ejection path?

One of the canopy severance candidates for the T-38 canopy is a full perimeter severance pattern. This pattern cuts the
entire transparency to provide an escape path.

Canopy Centerline Severance:
The canopy is explosively cut along its centerline and
ejection through the canopy provides the required break-
out. This technique is incorporated on the A-7K Aircraft
which utilizes an acrylic transparency. This concept is
not feasible for the T-38 because the centerline cut will
not sufficiently degrade the polycarbonate transparency
to allow ejection without injury to the student pilot.

Seat Mounted Canopy Piercing:
A seat mounted cutting blade is provided and during ejec-
tion the blade breaks the canopy as the seat and crew
member pass through.
<snip>...
The MAGNA analysis indicates that a seat mounted canopy
breaker might be capable of breaking through a .40 thick
polycarbonate canopy utilizing the force available with
the existing seat catapult. The analysis further states
that the biodynamic response of the student pilot body to
the resulting acceleration may be unacceptable when con-
sidering the acceleration and deceleration loads antici-
pated. The anlaysis is a nice piece of work, but the con-
clusion section ignores canopy breakout of the required
ejection envelope.

Ejection requires a clear path for the seat
and student pilot head and extremities.
The forces required to open up the seat - man envelope combined
with the sharp, ragged fracturing canopy would surely
cause severe injury as the student pilot passed through.
We consider through the canopy ejection to be a totally
unacceptable concept for the T-38 bird impact resistant
canopy.

As per the pdf neither a seat mounted blade nor a single centerline cut were suitable for the polycarbonate canopy of the T-38. This may or may not translate into reality for the LCA canopy even if it is polycarbonate.

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Re: LCA News and Discussions

Postby Ganesh_S » 23 May 2012 06:51

OT- An F-15 pilot narrates his experince on supersonic ejection.

http://www.youtube.com/watch?v=HecyxhXD ... re=related

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Re: LCA News and Discussions

Postby Cain Marko » 23 May 2012 07:54

^^ OK, I just gave up my lifelong ambition of becoming a fighter pilot! :eek: Scary. Dhoti shivering...

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Re: LCA News and Discussions

Postby Lalmohan » 23 May 2012 12:20

this discussion definitely illustrates why aircraft programmes require vast technological and scientific resources to be available to the developer...

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Re: LCA News and Discussions

Postby ArmenT » 23 May 2012 13:03

shiv wrote:
vina wrote:
Maybe the plastic material used in the canopies dont produce that kind of knife like shards that glass does.


Kartik's 160 page pdf says that acrylic, used in Harriers and Hawk will shatter and can be used for punch through ejection. But polycarbonate as in F-16 does not shatter. There seems to be a lot of intricate detail in the choices that are made.

Yep, neither the method of using explosive cord, nor the method of using a sharp cutting tooth on the top of the seat can be used if the canopy material is made of a flexible plastic like the F16's polycarbonate. In such cases, the entire canopy needs to be ditched before the ejection seat fires and this adds slightly more delay to the ejection process.

While explosive cord based systems are faster and simpler, explosive cord also creates a pressure wave inside the cockpit when it goes off and has a chance of sending high-velocity fragments in the direction of the pilot.

And speaking of canopies, before anyone asks why LCA doesn't have a bubble canopy like the F16 does, they aren't exactly all that advantageous as some people think. Sure they provide an unobstructed 360 degree view, but one fighter pilot said he preferred using his rear view mirror/cam, because he said that when pulling high-G maneuvers, only a superman can rotate his head back to see if someone is on his tail. Note that neither F-22 nor F-35 use a bubble canopy either.

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Re: LCA News and Discussions

Postby SaiK » 23 May 2012 21:34

How is the join (bonding) strength of Acrylic + polycarbonate is? If both qualify safety requriements for bird hits, we could design the joins such a way, that splits and shatters the acrcylic, and blows away the polycarbonate. Let us say, 1cm of arcylic join in the center line, or perhaps on the edges.. so that a single piece of PC blows away, after the thin acrylic lines shatters.

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Re: LCA News and Discussions

Postby negi » 23 May 2012 22:35

Armen by bubble canopy you mean one piece canopy or the shape ? Because the F-22 and F-35 do have one piece canopies , there is no separate frontal glass piece in front of the pilot which is the case with other ACs.


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Re: LCA News and Discussions

Postby manum » 24 May 2012 19:33

Acrylic is not the toughest of transparent material...while polycarbonate was considered so...since the introduction of guerilla glass...

Glass is not good for extreme moulding...and then it shatters into pieces...

I got this info when I was trying to get a moulded transparent furniture which shall withstand extreme uses...

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Re: LCA News and Discussions

Postby SaiK » 24 May 2012 19:40

then hind hinged canopy or slide back design is the safest bet for ejections. a pilot saved is worth more than billion $ plane.

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Re: LCA News and Discussions

Postby manum » 24 May 2012 19:55

Don't know...but I doubt acrylic polycarbonate needed to be joined in layers...because those canopies are made in moulds...and acrylic and polycarbonate follow different process of manufacturing...Its complicating the process...

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Re: LCA News and Discussions

Postby SaiK » 24 May 2012 20:11

right, and further we have already chosen poly for the production model.. so there is no question of shattering it., (seeing the reasoning from the discussions so far).

other option is to release the hinge and blow it away.

Lalmohan
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Re: LCA News and Discussions

Postby Lalmohan » 24 May 2012 20:11

SaiK wrote:then hind hinged canopy or slide back design is the safest bet for ejections. a pilot saved is worth more than billion $ plane.


the design was changed because these models do not give enough time for the pilot to get out alive

SaiK
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Re: LCA News and Discussions

Postby SaiK » 24 May 2012 20:19

^ you are saying the side hinged is better than hind hinged?


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