mixing build methods.

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gunners

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So looking at my planed build, I was pondering ways to keep it under 12500 lbs. (The flying winnebago sea plane.) I was curious if it was considered bad practice to build a fuselage out of aluminum then for the wings build a aluminum frame then cover with fabric. If that is justfine how feed fabric effect the strength of the wing when compared to aluminum skin? Also are there any good books on this?
 

BJC

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BJC
 

gtae07

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Mixing build methods is not unusual—I believe the Sportsman has a composite fuselage and metal wing; the Bearhawk has rag-and-tube fuselage and metal wing, I think the Tailwind has rag-and-tube fuselage with a wooden wing. I could swear there’s one out there with a metal fuselage and composite wing but I can’t remember for sure. And many WWII-era aircraft used fabric-covered control surfaces.

Anyway, point is, it can and has been done. Whether you do it or not, and which methods you mix, is a trade study like anything else in aircraft design. Unfortunately, there are no simple rules-of-thumb for converting build methods; you basically have to do a fresh design in each material and compare the results.
 

BJC

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The Edge 540, lots of Extras, and a few others use composite wings with tube and fabric fuselages.


BJC
 

Aesquire

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SeaRey uses aluminum "ultralight ladder frame" fabric covered wings and tail surfaces, with a Composite hull with an aluminum frame to support seats, engine and wings.

an aluminum sheet metal covered wing uses a different design than a fabric covered wing, because fabric isn't strong in the same way.
 

Dana

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Many airplanes of the 1940s used aluminum fuselages combined with fabric covered wings. In many cases later models replaced the fabric with aluminum. Welded steel tube fuselages combined with wood or aluminum wings are also very common.

A fully aluminum skinned wing will resist torsion, while a fabric covered wing will not, unless it has a closed aluminum D-tube leading edge.
 

wsimpso1

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Wings, tailplanes, and fuselages are usually separate structures. Different structures are fine.

Each type of wing has its own requirements. If the skin is anything but fabric (or a polymer film), the skin contributes structurally which can allow lighter spars and either cantilever wings or single struts. Decide to go fabric covered, and it usually needs two struts per side and a sturdier spars.

Whatever, have fun, do the structures right per the books.

Billski
 
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Riggerrob

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Sure!
You can combine different construction methods within the same airplane. The key is matching the best material, with the best manufacturing method with the best structural usage in different parts of the airplane.
For example, the Sportsman STOL uses a steel tube cage around the cockpit, a composite fuselage skin with sheet aluminum flying surfaces. Steel tubing works well around the cockpit because of all the holes needed for doors, windows, etc. plus the need for strong-points to bolt on wings, landing gear and the engine. Curved, streamlined panels on the rear fuselage are easiest to build with composites (fiberglass). Finally, the single curvatures of flying surfaces are quickest to build with sheet aluminum.
No single construction method is better, it is just better for different components.

Airspeeds also determine construction materials. During World War 1 it was rare to see airplanes dive at 200 mph. so they were mostly fabric covered. Since few of their engines exceeded 200 hp. light weight was also important. Fabric cover may be light-weight, but it does not carry any structural loads, so internal structure (wood or tubing) has to be braced left, right and center with wires or diagonal solid members. deHavilland made a radical contribution when they glued flat sheets of plywood around the cockpit. Laid on the bias, plywood replaced all the diagonal bracing, while vastly reducing parts-count (Pietenpol was one of the first homebuilts to copy DH's method.

When they wanted to cruise at more than 200 mph. they needed to reduce the number of struts and wires hanging outside. Tony Fokker started by building box spars completely enclosed in wings. Fokker still needed curved wooden ribs to complete the wing shape. A few years later, manufacturers started building D-spars where the curved leading edge carried torsional loads with the spar web still carrying bending loads. By using the (plywood) leading edge skin to serve two purposes (aerodynamic and torsional), they were able to reduce parts count and simplify construction. The aft 2/3 of the wing was still a mixture of spars, ribs and fabric cover (e.g. early versions of Hurricane and Spitfire) but as speeds increased, they eventually completely skinned wings with aluminum to stiffen them. All aluminum skins can also be built to the tighter tolerances needed for flight faster than 300 mph.
During World War 2, most control surfaces were still fabric covered because this helped balance and reduced the risk of flutter. By mounting the aileron spar and D-tube forward of the aerodynamic balance point, ailerons were already heavily weighted at the front and they only needed smaller balance (anti-flutter) weights.
Compound curves have always been difficult to from in sheet metal - without expensive production presses - so as soon as fiberglass became available during the 1950s, Piper, Bede and many homebuilders started building curved, non-structural parts (wing tips, engine cowlings, etc.) out of molded fiberglass. Female molds are labour-intensive to build, so that limited homebuilders. These days, many fiberglass/composite structural airframe parts are pre-molded at a factory then shipped out to kit-builders who glue them together at home. Kit-suppliers can justify the cost of precise female molds because they can pull hundreds of parts from a single mold and once molded, minimal hand-finishing is required before painting.
 

gunners

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Sure!
You can combine different construction methods within the same airplane. The key is matching the best material, with the best manufacturing method with the best structural usage in different parts of the airplane.
For example, the Sportsman STOL uses a steel tube cage around the cockpit, a composite fuselage skin with sheet aluminum flying surfaces. Steel tubing works well around the cockpit because of all the holes needed for doors, windows, etc. plus the need for strong-points to bolt on wings, landing gear and the engine. Curved, streamlined panels on the rear fuselage are easiest to build with composites (fiberglass). Finally, the single curvatures of flying surfaces are quickest to build with sheet aluminum.
No single construction method is better, it is just better for different components.

Airspeeds also determine construction materials. During World War 1 it was rare to see airplanes dive at 200 mph. so they were mostly fabric covered. Since few of their engines exceeded 200 hp. light weight was also important. Fabric cover may be light-weight, but it does not carry any structural loads, so internal structure (wood or tubing) has to be braced left, right and center with wires or diagonal solid members. deHavilland made a radical contribution when they glued flat sheets of plywood around the cockpit. Laid on the bias, plywood replaced all the diagonal bracing, while vastly reducing parts-count (Pietenpol was one of the first homebuilts to copy DH's method.

When they wanted to cruise at more than 200 mph. they needed to reduce the number of struts and wires hanging outside. Tony Fokker started by building box spars completely enclosed in wings. Fokker still needed curved wooden ribs to complete the wing shape. A few years later, manufacturers started building D-spars where the curved leading edge carried torsional loads with the spar web still carrying bending loads. By using the (plywood) leading edge skin to serve two purposes (aerodynamic and torsional), they were able to reduce parts count and simplify construction. The aft 2/3 of the wing was still a mixture of spars, ribs and fabric cover (e.g. early versions of Hurricane and Spitfire) but as speeds increased, they eventually completely skinned wings with aluminum to stiffen them. All aluminum skins can also be built to the tighter tolerances needed for flight faster than 300 mph.
During World War 2, most control surfaces were still fabric covered because this helped balance and reduced the risk of flutter. By mounting the aileron spar and D-tube forward of the aerodynamic balance point, ailerons were already heavily weighted at the front and they only needed smaller balance (anti-flutter) weights.
Compound curves have always been difficult to from in sheet metal - without expensive production presses - so as soon as fiberglass became available during the 1950s, Piper, Bede and many homebuilders started building curved, non-structural parts (wing tips, engine cowlings, etc.) out of molded fiberglass. Female molds are labour-intensive to build, so that limited homebuilders. These days, many fiberglass/composite structural airframe parts are pre-molded at a factory then shipped out to kit-builders who glue them together at home. Kit-suppliers can justify the cost of precise female molds because they can pull hundreds of parts from a single mold and once molded, minimal hand-finishing is required before painting.
Very good in depth explanation thank you for sharing.
 

PTAirco

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I've always had an irrational dislike for mixing materials and methods in an aircraft design. For one thing, you'll need different tools and different skills and maybe even different workshop conditions. Just complicates matters, during construction and later during maintenance. I get that sometimes one method or material has certain advantages in one area, but it still bothers me to see all this different kind of stuff in one structure. The CFM Shadow was one such design, Cockpit made from prefabbed honeycomb panels, spars of wood and glass, aluminium tailboom , fiberglass landing gear legs, foam wing ribs; the only thing missing was carbon because back then it wasn't really available. Even the wing root shear pins were made of steel epoxied into aluminium tubes.

Like I said, it may be an irrational dislike and I guess my tube an fabric biplane combines a few different methods and materials, but I draw the line somewhere.
 

wsimpso1

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PT,

Even the traditional rag and tube biplane is mixed construction. The fuselage is usually welded thinwall steel tube, the wing is usually bonded wooden structure or sometimes a multitude of aluminum pieces, the tailplanes are wood or stee tube, the visible covering is mostly fabric, but wheelpants and cowling and other fairings are any of aluminum or composites or plywood. If that combination is not "mixed", I don't know what is.

The designers used materials and processes that made sense even in the "golden age".

Billski
 

gunners

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I've always had an irrational dislike for mixing materials and methods in an aircraft design. For one thing, you'll need different tools and different skills and maybe even different workshop conditions. Just complicates matters, during construction and later during maintenance. I get that sometimes one method or material has certain advantages in one area, but it still bothers me to see all this different kind of stuff in one structure. The CFM Shadow was one such design, Cockpit made from prefabbed honeycomb panels, spars of wood and glass, aluminium tailboom , fiberglass landing gear legs, foam wing ribs; the only thing missing was carbon because back then it wasn't really available. Even the wing root shear pins were made of steel epoxied into aluminium tubes.

Like I said, it may be an irrational dislike and I guess my tube an fabric biplane combines a few different methods and materials, but I draw the line somewhere.
Yeah I am questioning if this will make any sense once it all said and done. I have kicked around an aluminum hull for landing on water the the rest of the aircraft would be aluminium and fabric construction. If I go that route I will have to give up speed.
 

wsimpso1

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I don't know about that. Through WWII, almost everything had some fabric covering. Wittman Tailwind is a fast airplane with fabric covered tailplanes and control surfaces and fuselage.
 
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