aircraft construction and modification suggestions 1

[Higgler]

I'd like to learn about aircraft construction and modification and would appreciate a reference book suggestion. Modern military aircraft primarily.

I am proposing cutting long thin slots (from 10"x0.01" up to 200"x0.1")in the top of aircraft for adding sensors and need to learn the basic construction techniques. I know, sounds ridiculous with the 200" length.


Probably the best option would be to speak with an aircraft designer or someone who has experience modifying aircraft. Maybe I could pick your brain in a few emails. Knowing me, it'd be about 20 emails over the next 45 days, lots of what if's and how about this's.

Thanks,
kch

 

[Higgler]

Aircraft type will be "various military aircraft, helo's, fighters, bombers, etc". Some of the larger ones maybe can just use the external pods, but the more difficult will be the smaller jets.

40818, I think for now the 200" slot has to be incorporated in a new aircraft design, so we'll stick with a 20" slot for now.

I would certainly think there'd be a method to make a 20" thin slot and inside the aircraft add a 24"x4"x2" thick piece of ?aluminum, steel or titanium with a similar thin slot in the center 20" section, then cover that slot with thick (1") solid non metallic material to create essentially 10x the strength of the original 0.060" thick aluminum skin.

External fairings would gernally have to be very tall for sufficient results, I can't propose them as a general solution.

I could add a part that's say one inch thick externally for most of the aircraft, the part would be constructed of metal and plastic that would be say 24" square and curved to fit the contour of the aircraft. To mount it on the aircraft and make it work, I'd need to cut out a 20" square hole between the fuselage frames and mount the 24" square rigid part to cover the hole, mount it to the frames if that helps. Does that description sound more feasible? The 24" square part would be very rigid.


I'm on travel today, back Friday.
I have a sawsall already, they're a bit rough don't you think?

Thanks all,

kch

 

[rb1957]

kch,

get professional help (though not of the psychoiatric kind !) ... we started with a 200" slot, went to a 20" one (one only, or repeated), started with longitudinal, mentioned circumferential; and now we've added a 20" by 20" hole. it's fine that this is early days in your project, and pretty much we're blue-skying ideas, but (pretty much as you anticipated in your OP) we're all speculating about applications and attendant limitations.

Basically, almost anything you want can be accomplished one way or another. I would suggest that a 2" thick piece of Al probably isn't going to find it's way onto a hi-performance plane (abit too argicultural !)

good luck with your project !

 

[KENAT]

Some more 'cut away' views for you to look at. Like I said before no guarantee of how accurate these are.

http://www.eurofighter-typhoon.co.uk/Eurofighter/structure.html

http://www.eurofighter.com/et_cu.asp

http://www.netmarine.net/aero/aeronefs/rafale/photo08.htm

http://www.electronicaviation.com/aircraft/F-22_Raptor/gallery/257

http://www.publishingsolutions

http://www.com/air_cut.htm

Hopefully gives you some idea that you aren't just looking at skin. There are structures and even systems directly under the skin. If you make major changes to a stucture you've got to look all sorts of things not just the quasi static loads you seem to be considering. What about the effect on fatigue/vibration etc.

Also how are you going to get the access to modify the exisiting airframe, sometimes easier said than done.

KENAT, probably the least qualified checker you'll ever meet...

 

[Higgler]

Kenat,
thanks for the cutaways, scary looking collection of metal.
It seems some aircraft have small spaces on top.

Maybe towed sensors would be easier.

kch

 

[KENAT]

The cutaways don't give all the information. Some of those 'spaces' may be parts of fuel tanks or even if not may have wiring/piping/conduits etc running through them.

Plus they're mostly artists impressions, may not be totally accurate.

I've seen a Eurofighter on the assembly line and several other types in maintenance, there is not a lot of spare room.

Towed sensor may have potential, I assume you mean like a towed decoy. Depending how expensive your device is, people may not be so keen on dangling it out the back. I think towed decoys can probably be jettisoned if need be, is your sensor a bit expensive to be jettisoned?

Also think again about a conformal external fairing or even a pod.

Think about when manufacturers want to increase fuel on F16, F15, Typhoon. They don't rework the internal structure they add on a conformal tank. Minimal structural change at the expense of modifice aerodynamics.

KENAT, probably the least qualified checker you'll ever meet...

 

[Higgler]

Kenat,
the sensor isn't too expensive in high volume. Less than a typical decoy.

Haven't heard of a conformal tank, makes sense to avoid a large wing pod structure.
What would the typical dimensions range. i.e. 4" thick in center, 36"x48" width and length and triangular shaped?.

Is the tank always on the bottom?

kch

 

[KENAT]

A picture paints a thousand words.

It's the 'odd' shape both sides where wing joins fuselage.

http://www.defense-update.com/products/c/F-16-CFT.htm

It's on the side of the 'intake' under the wing called a FAST pack. If I recal correctly they are permanent on F15E and may have been made structural members but on the F15C they were conformal tanks.

http://www.fas.org/man/dod-101/sys/ac/f-15.htm

Only a wind tunnel model but hopefully pretty obvious where the tanks are.

http://www.eurofighter-typhoon.co.uk/Eurofighter/weapons.html

In addition many older aircraft developed bulged bellys or large spines in later versions to increase fuselage volumes. I don't know if most of these were incorporated in the primary structure though.

KENAT, probably the least qualified checker you'll ever meet...

 

[Higgler]

Thanks Kenat,
I'll probably use a small slot in the skins for one set and for the long slot I'll have to think about it more.

Thanks others for the assistance and the warnings.

kch

 

[KENAT]

No problem, like I said I'm a sucker for this kind of thing.

That said, I just want to amplify some of the warnings one more time and think it would be worth getting someone who really knows what they are doing to take a look before you present to a customer.

Ken

KENAT, probably the least qualified checker you'll ever meet...

 

[Higgler]

Thanks Kenat,
I copied your reference on external pods from the other thread too, in case I need to use one of those companies for sensor placement.

I realize aircraft are touchy area's and finding experts is key. As an Engineer, I've always thought by the end of any job, "why didn't we just talk to him/her in the first place!".

kch

 

[KENAT]

Yeah, those links may help. Actually Adaptive Aerospace might be able to consult or something.

When I interviewed there they'd just done extensive modification to a quasi military 737 to add a big radome dome on the rear end. Ended up looking a bit like the Nimrod AWAC tail.

I'm sure there are other places out there but they're the first to spring to my mind.

KENAT, probably the least qualified checker you'll ever meet...

 

[WKTaylor]

Higgler...

You are playing with fire, attempting make long slits in metallic fuselage skin(s).

Suggest You consider the following...

NOTES:

Assume the sensors are NOT Ribbon-like materials [thin] that could just be bonded to the exterior.

Assume that stealth [low observables] technology is NOT an issue.

Assume that modification-stealth is NOT a factor [IE: OK if obvious to a casual observer].

Brain-storm A. Fasten sensor strips to the crown-skin exterior in airflow direction for minimum drag. "So-what" if they look like scabbed-on strips... as-long-as performance does not suffer significantly.

Brain-storm B. Overlay [sealant-bond] a low-stiffness [composite, rubber, plastic, etc] sensor-skin on the structural skin. This material can contain the sensor-strips.

Brain-storm C. Trim-out the crown-skin, width A/R, and insert a structural composite section with the skin, stiffeners, frame-segments and sensor-strips embedded.

Brain-storm D. Build sensors into external antenna blades distributed all over the acft [fuselage crown, upper wing-skins, H-stab upper skins and/or tips, etc... or into one-big-spiney-back-like antenna, such as on the Australian B737 AWACS.

Regards, Wil Taylor

 

[KENAT]

Picture paints a thousand words.

http://www.fas.org/man/dod-101/sys/ac/e-737.htm

http://www.canit.se/~griffon/aviation/text/100argus.html

http://www.fas.org/man/dod-101/sys/ac/row/saab340.htm

http://www.geocities.com/lucktam/awacs/emb145/Embraer145ASWAEW/

And a story of how not to modify an aircraft which includes bit radomes.

http://www.spyflight.co.uk/Nim aew.htm

KENAT, probably the least qualified checker you'll ever meet...

 

[KENAT]

Someone appears to have thought of this before

http://www.patentstorm.us/patents/5405107-claims.html

This has a little on conformal antenna

http://www.eis.na.baesystems.com/ns/products/ns_antennas.htm

http://www.edocorp.com/AntennaMilAirborne.htm

KENAT, probably the least qualified checker you'll ever meet...