LCA: News & Discussions - October 2016

Neshant · Post by **Neshant** » 05 Mar 2017 15:17

If there is a requirement for high speed data transmission on board an aircraft, fiber optic cabling can be used for that specific requirement. e.g. very high res video data transfer.
But for the most part, wires are more than adequate for telemetry data transfers. The amount of data transferred for that purpose is quite small.

Beyond that, i guess fiber optic lines are immune to electronic RF jamming.

Maybe it weighs a little less (or maybe not) as metal jackets are needed around fiber lines to ensure they don't bend at acute angles and ruin the fiber.

I don't think I see any other benefits to so called "fly-by-light" beyond the above.

Singha · Post by **Singha** » 05 Mar 2017 16:37

I have heard that fiber is cheaper than copper cable these days. the claim was made by a next-door RWA who are installing a fiber backbone in their complex for 100s of cctv cameras, intercom, and internet traffic from individual flats serving multiple vendors. they are not letting all providers run wild and install a unruly mass of cables in the utility shafts.

I suppose such centralized shared fiber bones are ok for aviation applications too these days as the focus is on not getting hit, rather than sustaining any battle damage and then being glued together by ground crew with rough patches to fight again. todays high composite a.c are simply not rugged as the WW2 kit with their mechanical control rods and pulleys and analog electrical control systems.

Neshant · Post by **Neshant** » 05 Mar 2017 16:56

NRao wrote:Very few things carry over as is, including skills. May be riveters, harness assemblers, etc. But even they have to be retrained. The F-35 has ridiculous tolerances, forcing machines to oversee the work of humans and other machines.

WRT the AMCA, it was supposed to be FBL, not FBW. If that is still the game plane, then pretty much everything changes. Nothing in common with the LCA as far as the nerve center is concerned. The AMCA will have no wires to seriously talk about. (On that matter, Dr. A. K. Ghosh has been at it for about 10 years now.)

My feel is that they will need another facility for the AMCA. And it will be a parallel effort.

FBW or FBL has zero to do with a new facility.
The electronics for FBL based avionics will be developed at the sub-system level (hopefully at the private sector level) and merely integrated into the aircraft at the facility.
Also what specifically do you mean by very few things carry over?
A great deal of the LCA will carry over into the AMCA. I don't believe the AMCA will be anything more than a twin engine LCA for the most part.

shiv · Post by **shiv** » 05 Mar 2017 17:07

Singha wrote: todays high composite a.c are simply not rugged as the WW2 kit with their mechanical control rods and pulleys and analog electrical control systems.

The only comparison I can make is that I have used and bought cars from my father's era 1960s to today. When it comes to bumps - today's bumpers are far better than the chromed stuff we used to have. Collisions just bounce off. Bigger bumps cause buckling but not a mass of crumpled metal. The parts that need to be strong are strong and redundant parts like top of roof are thinner - so my father's car was arguably better at withstanding coconut hits from above. But that has not happened yet.

So I doubt if today's aircraft are that bad. That is my guesspinion

Karan M · Post by **Karan M** » 05 Mar 2017 18:19

Check the senior officers comment.

http://m.indiatoday.in/story/light-comb ... 97119.html

Karan M · Post by **Karan M** » 05 Mar 2017 18:20

Pilots aircraft.

Singha · Post by **Singha** » 05 Mar 2017 19:08

Unlike a car hitting something the aircraft after hit does need to fly back.

shiv · Post by **shiv** » 05 Mar 2017 19:58

Singha wrote:Unlike a car hitting something the aircraft after hit does need to fly back.

Naturally - but it is the behaviour of the material and where it is that counts and not some vague feeling that "metal is strong" - non metal is not.

Unfortunately I have not been able to find references to behaviour of composites under battle conditions, but I take the attitude that if a lay person who has nothing to do with aircraft design can express concerns about battle damage it is unlikely that actual aircraft designers would have somehow "forgotten" about that aspect as in "Oops. Somehow we never thought of that while we were building this fighter aircraft"

There are two or three separate considerations
1. Actual shrapnel/bullet holes - high velocity projectiles In this case I don't think composites and metal will behave very differently - but this is guesswork. In fact at higher angles of incidence composites may be superior to metal. After all "bullet proof" and "lightweight" is by definition composite
2. Deformation from a nearby explosion: here I think composites are better.
3. Fire: I don't know - but there is some online information about fire resistant composites used in aircraft structures
http://www.atsb.gov.au/publications/200 ... 40046.aspx

Fire resistant and self sealing tanks are usually composites and not metal. Aluminium of course burns well and is used in Diwali crackers also

So my general impression is that composites stand up well against metal parts in aircraft

JayS · Post by **JayS** » 05 Mar 2017 20:07

From FB.

srai · Post by **srai** » 05 Mar 2017 20:25

Karan M wrote:Check the senior officers comment.

http://m.indiatoday.in/story/light-comb ... 97119.html

Marketing is key! Unlike the private sector that spends good amount of money on marketing and advertising, public sector does it as an afterthought. A product won't sell unless a good marketing campaign promotes it. Look at how that journalist's perception changed after taking that flight and the glowing article about the LCA he ended up writing. More is needed.

Marketing Campaign -> outsource to PR firm; buy adverting, write ups, design promotional marketing materials, sleek posters and videos, pictures of LCA loaded with AAMs and ASMs etc. Counter false news.
Win the hearts and minds -> Continue to demo fly with junior and senior IAF/IN officers as well as Indian "defense" journalists. Also, potential customers. Run tours of production facilities. Distribute high quality LCA brochures and magazines. Every officers' mess should have a stack of these along with school libraries.
International MII Pride -> demo LCA at major international air shows. Include demo flights with passengers (encourage write up in major aviation journals).
National promotion -> Do something like Nat Geo Mission Udaan but with the lucky winners getting to fly the LCA at the end. Promotion and Application centers at every major Indian cities.
Movies -> Bollywood Top Gun featuring the LCA

Marten · Post by **Marten** » 05 Mar 2017 21:22

Srai, superb suggestions. Jingos will line up for that chance. Make it a list of ten folks and you will have a serial on your hands!!!

Dileep · Post by **Dileep** » 05 Mar 2017 21:27

The "Fly-By-Wire" literally means the movement of the control surfaces are done by signals over a wire, ie not by cables pulled by levers or hydraulic fluid pushing on a piston. The figurative meaning is, the pilot input is not directly coupled to the control movement. Rather, a computer takes the input, does its own calculations and does the movements.

The "Flying" I mentioned is that one. It will take decades before the control surface movements are put on glass. It will be the last one to convert IMO.

Fiber is indeed cheaper than copper by all parameters, even by the raw cost of cable. The only problem is, you can't strip the insulation and twist the copper to repair a connection. You need a splicing machine to do that. But most of the copper applications (like Gig Ethernet) too will fail if you do that kind of repair.

>>actual aircraft designers would have somehow "forgotten" about that aspect as in "Oops. Somehow we never thought of that while we were building this fighter aircraft"

That is what EXACTLY happened with LCA unfortunately. I was surprised to notice that the best they have progressed upto is the admission that "technicians will have to maintain it at the airbases" Combat damage is still out of belief zone. As I see it, a few shrapnels can put it out of commission for the rest of the conflict. I specifically asked about the combat damage issue in the context of fiber being difficult to repair, the answer I got is that copper is also similar onlee. You can't repair it at the base onlee. Maybe it is like that for ALL new gen aircrafts. I don't know. I don't know if the indomitable Rambha can be patched up and put back to flight either.

It is possible to just replace the copper with fiber, by changing the interface cards. But why do that, when you can really leverage the capabilities of fiber. Whether one card or the whole system, you need to go through the same stringent process of design and qualification. So, why not leverage the capabilities and build the best? Those who kept their eyes and ears open at the AI show would have definitely got a feeling of things to come.

Ref to the concept of 'slow signals' can go over copper anyway, ever heard of 'multiplexing'? Why pull hundred cables when you can do the same with just one fiber? OK, a few fibers routed through separate paths for redundancy onlee.

NRao · Post by **NRao** » 05 Mar 2017 22:18

FBL:

viewtopic.php?f=3&t=5739&p=2124177#p2124177

ashishvikas · Post by **ashishvikas** » 05 Mar 2017 22:26

What is this sticking out of Tejas SP4 ? Gun ?

https://ibb.co/j3VqFa

https://m.facebook.com/tejas.lca/photos ... 17/?type=3

shiv · Post by **shiv** » 05 Mar 2017 22:35

Dileep wrote:Combat damage is still out of belief zone. As I see it, a few shrapnels can put it out of commission for the rest of the conflict.

Of course even service with IAF was out of belief zone till recently

, but why do you say that about a few shrapnel holes? Typically no aircraft goes out of commission for a few bullet holes unless something vital inside is damaged.

More relevant is whether it can fly back with damage and to what extent damage can be tolerated. For example - if part of the wingtip is blown off, or if an aileron is blown off will it fly? What are the fallback controls when FBW stops working - I think AM Rajkumar has said something about this in his book.

RoyG · Post by **RoyG** » 05 Mar 2017 22:46

ashishvikas wrote:What is this sticking out of Tejas SP4 ? Gun ?

https://ibb.co/j3VqFa

https://m.facebook.com/tejas.lca/photos ... 17/?type=3

gsh-23.

ashishvikas · Post by **ashishvikas** » 05 Mar 2017 22:58

RoyG wrote:
ashishvikas wrote:What is this sticking out of Tejas SP4 ? Gun ?

https://ibb.co/j3VqFa

https://m.facebook.com/tejas.lca/photos ... 17/?type=3
gsh-23.

Is this position of GSH-23 OK ? It's hanging outside, haven't seen something like this in earlier SP1-SP3.

Moreover, Isn't GSH-23 was planned for only FOC aircrafts ? good to see they added it in IOC-2 aircraft as well

JayS · Post by **JayS** » 05 Mar 2017 23:52

ashishvikas wrote:
RoyG wrote:
gsh-23.
Is this position of GSH-23 OK ? It's hanging outside, haven't seen something like this in earlier SP1-SP3.

Moreover, Isn't GSH-23 was planned for only FOC aircrafts ? good to see they added it in IOC-2 aircraft as well

Its there on other SP's as well. Also on some LSP's (later models I suppose), NPs. What we see it gun housing. Gun need not be in there.

Karan M · Post by **Karan M** » 06 Mar 2017 00:23

With all these electric jets heavy battle damage is a question of placement. For Su-30 too, its full of gizmos and the engine bays and cockpit apart, rest is super vulnerable to heavy missile warheads.

svinayak · Post by **svinayak** » 06 Mar 2017 06:32

jamwal wrote:https://www.youtube.com/watch?v=pfk5lfh9Z0c

The Amazing Fighter Jet Race | Documentary On India's Single Engine Fighter Jet Procurement Program
Bharat Karnad is one of speakers.

Good propaganda video
Public discussion has to increase on why IAF does not choose Indian products. Why IAF does not have a design Dir and who it did not advance Indian design for the last 50 years.

Dileep · Post by **Dileep** » 06 Mar 2017 07:04

Shiv, a shrapnel may just puncture the skin, or it may sever a cable, or damage an LRU. Problem No 1 is, will it fly back? Problem No 2 is can it get back into the fight? Currently, I don't think option 2 is there.

With the systemic redundancies in place, it sure should fly back. My concern is that at least the avionics people seemed to NOT consider combat damage as a possibility. They worry about systemic failure onlee. If the redundant systems and paths are not spread out properly and carefully, single point failures can occur. Remember crash of UA-232?. I prefer to believe that the integration designers took care of this. But the attitude of the avionics folk is going to stay with me for long.

In the current avionics suite, there is a full backup system, with 'fly back home' displays. The small square screen above the main MFDs are for this purpose. If the flight control is working, this can take you home.

Neshant · Post by **Neshant** » 06 Mar 2017 07:28

The IAF threatening to import foreign single engine fighters had one good outcome - it lit a fire under the buttocks of the LCA development team.

Only now are they rushing to meet deadlines & milestones on the LCA project - working overtime & stuff.

But years were wasted in foot dragging to the point that the project is near cancellation (or failure).

Failure being defined as only a handful of planes being produced prior to termination of the project in favor of imported planes.

I suspect the rapid attempts at getting the AMCA going is to preserve the LCA team in case the project fails and gets cancelled. Hence the reason claims are being made that the AMCA design is all set to go even though there has been zero discussion about its design (other than vague concepts).

If the LCA is cancelled before the AMCA starts up, there will a very strong public cynicism of all claims of ADA, DRDO, HAL of producing a next generation plane when they produced nothing after 3 decades on the LCA. There will be such a strong backlash that many heads of these govt organization will have to be fired.

This is literally the last chance the LCA has to succeed. One more f-up, major deadline overrun or falling asleep on the job and the program will be cancelled. I see the IAF's threat to import F-16s and Gripens in that light. I hope I'm wrong.

svinayak · Post by **svinayak** » 06 Mar 2017 07:55

IAF should have been supporting a Indian aircraft design bureau 40 years ago. IJT, Hawk copy should have come out in the 70s/80s.

After that giveing LCA/AMCA team a chance to reach the deadline before the imports come in sounds more realistic.

Cybaru · Post by **Cybaru** » 06 Mar 2017 07:58

I think thats where it helps having clauses like US has on importing defense equipment. They foster the local industry and USAF has to buy local and not some superior European offering.

shiv · Post by **shiv** » 06 Mar 2017 08:03

Dileep wrote:Shiv, a shrapnel may just puncture the skin, or it may sever a cable, or damage an LRU. Problem No 1 is, will it fly back? Problem No 2 is can it get back into the fight? Currently, I don't think option 2 is there.
.

This is equally true for 3rd gen metal skinned aircraft with rods and cables. Holes without internal damage can simply be patched up. Stories about such events are numerous. If it flies back it is capable of flight and what repair is possible depends on the damage.

The Hunter had cables running up dorsally and could get away ventral battle damage. On the other hand -belly landings are not allowed on the Jaguar - presumably because there is something vital running underneath. The Su 7 was discovered to be good at flying back with damage but I am yet to see glossy brochures/ads advertising battle damage survival for any aircraft apart from the usual noises made about cables running in areas where they will not get hit first by ground fire.

But Googling for "modern developments" one finds references to damage assessments and standardized regimes for damage repair. But no references to combat damage. Not surprising because the number of aircraft suffering combat damage from 1980 to 2015 is far smaller than the number from 1940 to 1980. In fact only the A-10 and Su 25 (a reactive "me too" effort) and helicopters feature special armour for combat damage protection. Vietnam, 1971 Indo-Pak and the Arab Israeli wars were pretty much the last classic "WW 2 style" wars involving aircraft.

ramana · Post by **ramana** » 06 Mar 2017 08:11

Shiv, Look at pics of A10 which was designed with combat damage survival in mind.

ramana · Post by **ramana** » 06 Mar 2017 08:19

svinayak wrote:
jamwal wrote:https://www.youtube.com/watch?v=pfk5lfh9Z0c

The Amazing Fighter Jet Race | Documentary On India's Single Engine Fighter Jet Procurement Program
Bharat Karnad is one of speakers.
Good propaganda video
Public discussion has to increase on why IAF does not choose Indian products. Why IAF does not have a design Dir and who it did not advance Indian design for the last 50 years.

Not really. Before that let's discuss Congress party penchant for loot via IAF purchases since the 1950s.

So bringing in IAF is moot.

shiv · Post by **shiv** » 06 Mar 2017 08:28

ramana wrote:Shiv, Look at pics of A10 which was designed with combat damage survival in mind.

ramana that is what I said in my post.

In fact after diligently following aircraft specs and descriptions for decades in the (now defunct) Observers books series (I have a collection of about 20-25 of them) the only aircraft ever that had a claim from design stage to be resistant to battle damage was the A-10. No other aircraft among at least 100 different designs carried such a claim.

Rakesh · Post by **Rakesh** » 06 Mar 2017 08:38

Neshant: if you are reading this...I sent you a PM. please check.

JayS · Post by **JayS** » 06 Mar 2017 12:55

First: We have so far only one fighter developed and deployed in operational service, and the institutional knowledge from that program has been lost due to lack of any follow up programs until LCA came up. Until we go through the entire cycle of design-develop-manufacture-operationalize-maintain-upgrade for at least one program we will not build up the complete set up skills and knowledge that a fighter program needs. That's why it is more important to operationalize even half-baked fighter rather than waiting for the perfect fighter indefinitely. Until the learning from the field does not feedback to the designers and they try to deal with those problems, the design teams would never learn to take care of these things a priori. Considering all the factors during design is not a trivial thing. You can do it to only so much level without having little or no institutional knowledge. I always say, a great OEM/organisation is not the one which never screws up, but the one which know how to handle it when things get f*c*ed up real bad. It will be a while before our design teams can learn to anticipate majority of operational issues and try to take them into consideration. We are still building our institutional knowledge. Good thing is technology is on our side. We are learning things in one project what took US for example many projects. We are leaning from their experience too. But some things simply have to be experienced by you first hand.

Second: One can never anticipate all the possible things that the product might have to face in real life. There will always be things happening outside the expected envelop and designs would fail in those situations. Also one cannot design a product for every possible contingency even if its known. Simply because one has to prioritize the design objectives and have to take up only those many which are physically doable within given time and resources. Given infinite time and resources, any team can develop an invincible fighter which will fly back even on one wing. Battle damage is crucial factor and more likely to happen given its intended usage, for jets like A-10 and it makes sense to put efforts on making it battle damage proof. The probability of similar damage it simply too less for LCA. Remember the jets fly majority of their life in peace time and the resources to keep them flying are significantly more in the peacetime than in wars many a times. The design team and the user needs to figure out acceptable solution and choose which things are priorities and which can be dispensed with. I remember an incident that AM P Rajkumar quoted in his book on LCA. ADA was struggling to figure out how to test the redundancy of quad channel FCS, when 2 or 3 of the channels fail. When they got consultancy from BAE on this, BAE told ADA that they never even consider case of 3 channel failure out of 4. Simply because its so rare that if that happens something is really wrong and you would be bailing out anyway. That's institutional knowledge for you.

Its perfectly all right to have an fighter designed for fly back capacity only with significant battle damage, but not for getting back immediately in combat with that damage again, without significant repairs. Every aircraft has a class of damages/issues for which the aircraft is designed only to be able to land back somewhere safely under those conditions. There have been some operational aircrafts which had an SOP of bail out once they get into spin. And they didn't even have TFTA FCS which would stop pilots from getting into spin. Spin to me is more probable than battle damage over the entire life of the aircraft.

Singha · Post by **Singha** » 06 Mar 2017 13:44

i read somewhere while older metal ac skin could be riveted up with patches to cover holes, any composite panel that sustains damage needs to be replaced in totality. which should be simple if manufacturing is upto the mark and std tolerances are followed to stock up all such body parts in BRDs and some parts in bases. but I recall reading the F22 fell short on that and hence each F22 has its own parts pipeline (!?)
for Tejas we need to make sure that no such unique poor tolerance parts go out.

JayS · Post by **JayS** » 06 Mar 2017 14:12

Singha wrote:i read somewhere while older metal ac skin could be riveted up with patches to cover holes, any composite panel that sustains damage needs to be replaced in totality. which should be simple if manufacturing is upto the mark and std tolerances are followed to stock up all such body parts in BRDs and some parts in bases. but I recall reading the F22 fell short on that and hence each F22 has its own parts pipeline (!?)
for Tejas we need to make sure that no such unique poor tolerance parts go out.

Would really depend on which location and part it is. You wouldn't be doing it on a structural parts or skins on key locations at least. If its some non-critical location and matter of some holes, why it wouldn't work to rivet same piece of metal on the composite panel..? Also one need not replace entire panels for composites as well (Else imagine some small damage on fuselage of B787 and they would have to replace entire fuselage section which is single piece). But one key issue with Composites is detection of damage. It might look like its all good from the surface and in next flight, you loose entire tail..!!

But since War is a special scenario, it could be handled with ample parts stacked up and making sure that you can replace them quickly on the airfields by the maintenance crew. Also they could come up with filed-friendly repair procedures for some common type of damages. Incorporate some features in design to handle some of the issues, and handle some others externally. I guess Tejas has evolved in this respect with those 50-odd changes to ease maintenance as one example. And it will keep improving in time. With MK1A operational, we would have more user friendly MK2 and even better AMCA in future. Key is not to drop the ball just because its imperfect. And we are rather good as it sadly.

Karan M · Post by **Karan M** » 06 Mar 2017 15:03

shiv wrote:
ramana wrote:Shiv, Look at pics of A10 which was designed with combat damage survival in mind.
ramana that is what I said in my post.

In fact after diligently following aircraft specs and descriptions for decades in the (now defunct) Observers books series (I have a collection of about 20-25 of them) the only aircraft ever that had a claim from design stage to be resistant to battle damage was the A-10. No other aircraft among at least 100 different designs carried such a claim.

Su-25, Shivji.

IMHO Dileep is asking for unobtainium by asking for combat proof avionics. Only way to achieve that is redundancy + extra shielding. Both will result in incredible weight penalty.

At best designers can uparmor certain areas and avionic bays, but the performance shortfall is there. We are in a state wherein even Su-30 MKI (12.5T thrust per engine) has restricted flight envelope with 2 jammers.

Now lets think about replicating within the aircraft 2 sets of critical wiring etc.

tsarkar · Post by **tsarkar** » 06 Mar 2017 15:57

shiv wrote:
Dileep wrote:Shiv, a shrapnel may just puncture the skin, or it may sever a cable, or damage an LRU. Problem No 1 is, will it fly back? Problem No 2 is can it get back into the fight? Currently, I don't think option 2 is there.
.
This is equally true for 3rd gen metal skinned aircraft with rods and cables. Holes without internal damage can simply be patched up. Stories about such events are numerous. If it flies back it is capable of flight and what repair is possible depends on the damage.

In terms of damage to Tejas or any other aircraft of its generation,

Problem No 1 is taken care of by designers. Getting home is much better because of multiple redundancies

Problem 2 has gotten worse - for all aircraft

Some parts in problem 2 are easy

Damaged LRU's of flight control system and avionics can be easily swapped

Damaged Cabling, whether fly by wire or fly by light, can be easily repaired by swapping the entire cable harness.

However, damaged skin and structural parts is beyond squadron engineering capabilities. For that matter, even beyond BRD capabilities.

For metal aircraft, damage like the ones shown here can be repaired by aircraft fitters. The structural & surface damage can be respectively welded / fitted.

http://www.bharat-rakshak.com/IAF/histo ... adron.html

For composite aircraft, whether F-22 or Tejas or Rafale, there will be need for factory shipped parts, until that point of time 20 years from today when BRDs and Squadron Engineering gets autoclaves for CFC curing or - even better - 3-D printing.

Its impossible to keep stocks of structural parts of entire aircraft. Most likely some aircraft will be cannibalized for spares until HAL ships parts.

Dileep is right, the aircraft wont be able to get back into the fight as of today. 20 years from now, I speculate structural parts being 3-D printed.

The last time this type of technology shift happened was in early WW 2 when aircraft production moved from wood to metal.

Even the famous Hurricane and Mosquito were built of wood. The Hurricane even used fabric on wings.

tsarkar · Post by **tsarkar** » 06 Mar 2017 17:13

Some updates on my earlier post.

Composite manufacturing of parts has started at IAF 11 BRD since 1997

http://www.bharat-rakshak.com/IAF/Today ... 11BRD.html

Page 191 onwards of the following book has extensive details of structural repair of composite parts of MiG-29 at IAF 11 BRD with NAL assistance.

https://books.google.co.in/books?id=Uth ... te&f=false

shiv · Post by **shiv** » 06 Mar 2017 17:31

Karan M wrote:
Su-25, Shivji.

My original post mentions both A-10 and Su 25. The Su-25 was IMO a "me too" effort by the USSR

JayS · Post by **JayS** » 06 Mar 2017 18:30

Singha wrote:i read somewhere while older metal ac skin could be riveted up with patches to cover holes, any composite panel that sustains damage needs to be replaced in totality. which should be simple if manufacturing is upto the mark and std tolerances are followed to stock up all such body parts in BRDs and some parts in bases. but I recall reading the F22 fell short on that and hence each F22 has its own parts pipeline (!?)
for Tejas we need to make sure that no such unique poor tolerance parts go out.

tsarkar wrote:
Page 191 onwards of the following book has extensive details of structural repair of composite parts of MiG-29 at IAF 11 BRD with NAL assistance.

https://books.google.co.in/books?id=Uth ... te&f=false

Singha saar, there you go. A nice SDRE method for repairing damaged composite part, without having to change entire panel.

Singha · Post by **Singha** » 06 Mar 2017 19:25

looks like on the harrier, one has to remove the entire wing and its wing box and then replace the engine with a crane!

https://upload.wikimedia.org/wikipedia/ ... 150058.jpg

http://i.imgur.com/TGJDnVt.jpg

shiv · Post by **shiv** » 06 Mar 2017 19:43

I am not sure how far I can take the car analogy but way back even in the 1980s it was easy to buy fiberglass with resin off the shelf and simply patch up dents and corrosion holes in the body of a car - something that came in very useful when I bought my first Datsun rustbucket in 1984. Simple bullet/shrapnel holes in the skin with no structural implications should be "patchable" easily.

Keeping surfaces "stealthy" in aircraft is a different issue, but in cars stealth is augmented by preventing a potential buyer from seeing rusty corroded parts.

Zynda · Post by **Zynda** » 06 Mar 2017 19:55

^^Car analogy applies to a certain extent. Only in aerospace structures repair, the repairs are classified based on skill & equipment available i.e. the technicians training & equipment out in the field will be minimal when compared to base depot repair stations. Commercial OEMs (& I am sure MIL OEMs too) have to publish documents which list out approved detailed repair procedures for various types of damages. Also quality check & control procedures are more rigorous in aerospace applications.

More than stealth, many a times for skin external repairs, maintaining aerodynamic smoothness becomes the primary criteria (and hence stealth as well). Anyways , there are well established repair procedures for both metallic & composite structures. The literature posted by tsarkar for MiG-29 vertical tail root joint article is a good example of SDRE repair document