construction methods · 2016. 10. 30. · construction methods (metode konstruksi) beberapa metode...

CONSTRUCTION

METHODS

1. STRESSED-SKIN ATTACHMENT.

2. BONDED STRUCTURE

3. MACHINED SKIN / INTEGRAL STRUCTURE

4. Chemical Etching

5. Honeycomb construction

6. Doubler Plates

7. Flanged Lightening Holes

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Construction Methods (Metode Konstruksi)

Beberapa metode (cara) me-manufaktur struktur pesawat – akan dibahas disini secara singkat.

• Skin (kulit) dari struktur pesawat udara – mungkin terbuat dari metal (logam) atau bahan komposit.

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Untuk pesawat terbang metal –

Skin biasanya :

– Dibentuk terlebih dulu (pre-formed) menjadi kurva/lengkungan yang diperlukan, sebelum digabungkan ke frames, stringers, dsb.

– Dibuat dari Al alloys (paduan Aluminum) dan kedua sisinya dilapisi dengan Aluminium (Alclad).

– Pada sebagian pesawat terbang, mungkin dilapisi dengan paduan Magnesium (Mg-alloy).

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• Beberapa bagian dari struktur –mungkin dibuat dari Ti (titanium) atau Baja tahan karat (stainless steel).

• Logam-logam (metals) ini lebih berat, akan tetapi menahan panas lebih baik, sehingga dapat dipasang dekat jet engine exhaust (knalpot mesin jet).

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STRESSED-SKIN ATTACHMENT : • Pada pesawat udara metal (metal aircraft) – SKIN

dilekatkan ke frames, stringers, dsb. dengan cara:

1) Riveted : Menggunakan rivets, y.i. Biasanya countersunks atau dimpled – rata (flush) dengan skin di- bagian luar pesawat untuk mengurangi hambatan aerodinamis (aerdynamic drag).

2) Bonded : Bonding - adalah suatu proses pelekatan (adhesive) memakai synthetic resin adhesive dan sering disebut dengan nama dagang-nya “Redux Bonding”. Perlekatan (bonding) memerlukan bonding agent (perekat/lem), heat (panas), dan pressures ( tekanan).

Construction Methods – Stressed Skin Attachment

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Stressed-skin Attachment – (samb) :

• Pada Sebagian parts (bagian-bagian) dari struktur rangka (airframe) kemungkinan juga di lekatkan dengan menggunakan bonding.

Untuk pesawat terbang komposit – Perlekatan (attachment) dengan menggunakan :

– Special fasteners,

– Bonding; atau

– Frame-nya dibangun integral (menyatu) dengan skin.

Construction Methods (Metode Konstruksi)- STRESSED-SKIN ATTACHMENT

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Construction Methods (Metode Konstruksi)- STRESSED-SKIN ATTACHMENT

Me-rivet skin ke rib

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Construction Methods (Metode Konstruksi) : di -Rivet dan di- Bonding

Bonded stringers Riveted stringers

BONDED STRUCTURE : • Adhesive Bonding is a Method of Joining :

– Metal to Metal. – Metal to Wood. – Metal to themo-setting Plastic.

• A bonded metal to metal joint – is normally stronger than a riveted joint because : – The whole of the faying surfaces are joined. – There are no holes drilled to weaken the metal. – There are no stress concentration areas. The

stresses are evenly spaced-out across the joint.


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BONDED STRUCTURE :

• The process does not cause corrosion and is not attacked by fungi or other organisms, nor it is affected by water, gasoline, oil, or other common solvents.

• Where the process is used on the outside panels of aircraft : – It provides protection against leaks (rain water

and floats/hulls on those aircraft that land on water).

• On pressurized aircraft : - it provides for a pressure tight joint. It also produces a smoother aeodynamic finish.

Construction Methods (Metode Konstruksi) - BONDED STRUCTURE :

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Bonding is also used in the construction of :

–Metal stiffeners to wooden floor panels.

–Brake linings to break shoes.

–Honeycomb structures.

–Parts of cars and many other non aircraft uses.

Construction Methods (Metode Konstruksi) - BONDED STRUCTURE:

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MACHINED SKIN / INTEGRAL STRUCTURE :

• Metal aircraft is made up of several parts riveted / bonded together.

• For Large aircraft – the separate parts run into their thousands with rivets running into their tens of thousands.

Q : Each joint is a potential corrosion hazard. Why ?


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ANSWER: Each joint is a potential corrosion hazard, BECAUSE :

Galvanic corrosion – when two metals are joined together there is a possibility of galvanic corrosion, particularly when the metals are different or have had different heat treatments. Another hazard is crevice corrosion.

If the whole of the aircraft skin, . . .

Construction Methods (Metode Konstruksi) - MACHINED SKIN / INTEGRAL STRUCTURE:

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If the whole of the aircraft skin, including the stringers, frames, longerons, brackets, window cut-outs, etc., were manufactured from one piece of metal, then this would eliminate these two corrosion problems.

This type of construction kown as MACHINED

SKIN OR INTEGRAL CONSTRUCTION -

Construction Methods (Metode Konstruksi) - MACHINED SKIN / INTEGRAL STRUCTURE :

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MACHINED SKIN OR INTEGRAL CONSTRUCTION – also eliminates many of the problems associated with riveting – i.e. Weakening the structure by drilling and producing stress concentration areas.

• Integral construction is expensive. Example: Large slab (1,5m x 0,3m x20m) of Alum. Alloy – are milled

into shape by a computer controlled milling head, - working in a similar way to a sculpture. Milling most of the metal away to produce skin, say no more than 4 or 6 mm thick with all the “attachments” part of the skin.

• This milling is carried out on a milling bed 40 or 50m long using a moving gantry up to 5m high.


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First wing skin machining of the Bombardier Global 7000 / Global 8000

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• The process – gives a structure with a higher strength /weight ratio than before - with all the advantageous relating to corrosion, stress concentration, ...etc. That had been discussed already.

• It also produces a “perfect “ external aerodynamic skin.

• It is expensive, using large milling beds with computer controlled milling heads and with 90 % of the original metal being milled away.

[ At a large manufacturer this “ Alum. waste” is returned to the supplier for recycling or returning back to the melting plant].


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Milled Wing Skins – give : Maximum Strength and Rigidity with Minimum

Weight.

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Figure 1-35. The skin is an integral load carrying part of a stressed skin design.

Chemical Etching : • The “machining” may be done by chemical

etching. • For small amounts of metal removal the metal

may be removed by chemicals. • The parts that do not require metal removal - are

protected by an applied protective process and the complete part is then dipped into a bath of acid solution.

• The solution will “eat away” at the metal it can get at, leaving the protected metal area untouched.


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Chemical Etching –(cont’d):

• At the appropriate time, the metal is removed, the etched areas neutralized, the protection on the protected areas removed, and the metal is ready for its anti-corrosive treatments.

• By repeating the process several times with different areas treated with the protective coating, complex shapes can be produced.


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Honeycomb construction : • This type of construction may be used in the

manufacture of aircraft structures including flooring and flying control surfaces.

• When a panel bends the high stresses are felt on the outside surfaces, with little or none felt in the middle – the same as in beam bending theory – so why not have all the metal on the outside where it matters.

• Having a skin made up of several layers is called Sancwich Construction and like most things it is not new.


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Honeycomb construction – (cont’d):

• It was used in the construction of wooden aircraft.

• The Mosquito (2nd World War fighter bomber) had a fuselage skin made up of plywood – balsa wood – plywood, all glued together with wood glue.

Construction Methods (Metode Konstruksi) - Honeycomb construction

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*) Plywood facings with balsa wood core.

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DeHavilland Mosquito (2nd World War fighter bomber)


• Modern sandwich construction methods usually have:

– The outside skins of Al alloy or carbon fiber with

– The “filling” of Aluminium or composite honeycomb.

• These are all bonded together using the Redux or other bonding process.


- Honeycomb Construction:

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Figure 7-17. Honeycomb sandwich construction.

Construction Methods (Metode Konstruksi) - Honeycomb Construction:

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Figure 1-37. The honeycomb panel is a staple in aircraft construction. Cores can be either constant thickness (A) or tapered (B). Tapered core honeycomb panels are frequently used as flight control surfaces and wing trailing edges.

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Construction Mehods (Metode Konstruksi) - Honeycomb Construction:

Honeycomb Structure – Wing Leading Edge

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Honeycomb Structure – Wing Leading Edge

Doubler Plates : • A Doubler Plate may be used in the aircraft

structure where there are extra stresses to be allowed for.

• They may, of course, be milled into the structure but they may also be riveted or bolted into position.

• They may also be used as extra strengthening around lightening holes in place of flanging.

• A fitted doubler plate will also provide a fail safe type of construction.


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Construction Methods (Metode Konstruksi) - Doubler Plates

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doubler

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Doubler is used as extra strengthening around holes / openings (e.g. lightening holes in place of flanging).

Fail-safe Spar Construction

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Failsafe Spar: should one member of a complex structure fail, some other member would assume the load of the failed member. 13/10/2016

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Lightening Holes : • Are Holes cut in Rib sections, Fuselage Frames,

and other Structural Parts inside the aircraft, by the manufacturer, to decrease weight.

• To keep from weakening the member by removal of the material, flanges are often pressed around the holes to strengthen the area from which the material was removed.

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Flanged Lightening Holes :

• A flange (a small lip) – formed around the edge of the hole, so that the whole structure is stronger and more rigid.

Flanged Lightening Holes :

– Reduce the weight of the structure.

– Increase the strength and rigidity.

– Allow for inspection access.

– Allow for the routing of pipelines, cables, etc.


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• Lightening Holes - should never be cut in any structural part unless authorized.

• The Size of the Lightening Hole and the Width of the Flange formed around the hole – are determined by Design Specifications.

• M.S. (margins of safety) – are considered in the specs so that the weight of the part can be decreased and still retain the necessary strength.

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Construction Methods (Metode Konstruksi) - Flanged Lightening Holes

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Construction Methods (Tetode Konstruksi) - Flanged Lightening Holes

Lightening Holes – may be cut by one of the following Methods:

(1) Punching out, if the correct size punch die* is available. (2) Cutting out with a fly cutter mounted on a drill. (3) Scribbling the circumference of a hole with dividers,

and drilling around the entire circumference with a small drill, allowing enough clearance to file smooth.

(4) Scribbling the circumference of the hole with dividers, drilling the hole inside the circumference large enough to insert aviation snips, cutting out excess metal, and filing smooth.

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*die: a machine tool for stamping

Flanging Lightening Holes :

a. Form the flange by using a flanging die, or hard wood or metal form blocks.

b. Flanging die consists of two matching parts, a female and a male die.

c. For flanging soft metal, dies can be of hardwood, such as maple.

d. For hard metal or for more permanent use, they should be made of steel.

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e. The pilot guide should be the same size as the hole to be flanged, and

f. the shoulder should be the same width and angles as the desired flange.

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• When flanging lightening holes,

–place the material between the mating parts of the die and

– form it by hammering or squeezing the parts together in a vise or in an arbor press.

• The dies will work more smoothly if they are coated with light machine oil. [Figure 4-166]

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• When flanging lightening holes,

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Figure 4-166. Lightening hole die set.

Miscellaneous Infos

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Dehavilland Mosquito

• The famous British Mosquito--known to many as "Mossie"--was a versatile aircraft used extensively during World War II.

• Constructed primarily of plywood with a balsa wood core, it had excellent speed, altitude and range.

• First flown on November 25, 1940, the Mosquito entered production in Mid-1941 and was produced until well after the end of the war.

• Almost 8,000 Mossies were built in Great Britain, Canada and Australia. Although best known for their service with the Royal Air Force, Mosquitos were also used by several U.S. Army Air Forces units for photo and weather reconnaissance, and as night fighters.

• It served in Europe, the Middle and Far east and on the Russian front. In fact the Mosquito reigned supreme among General Purpose types; and of the grand total of 7,781 Mosquitos built, 6,710 were delivered during the war years.

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construction methods · 2016. 10. 30. · construction methods (metode konstruksi) beberapa metode...

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