Thanks!

I’ve always greatly appreciated this forum.

- Thread starter kudo
- Start date

Thanks!

I’ve always greatly appreciated this forum.

It is easy to read and contains all basics you need to start the design of a general aviation aircraft.

Despite that, are you interested in how to design the "form" of the fuselage, or the "strength"?

As for structural strength, you either need FE analysis or knowledge. For our plane, the fuselage is built from carbon and honeycomb, so the minimum thickness required for touching it without creating a hole is already stronger than what you expect from load in heavy turbulences . Still we perform a lot of FE to be sure.

kudo, Think of a fuselage as a 3 dimensional truss. the loads

Thanks!

I’ve always greatly appreciated this forum.

pass thru the hard points of engine, wing, tail surfaces, and

on some designs the undercarriage. These loads are calculated

by solving moments into three axis forces. There are several

flight conditions to look at and for each the G forces such as

3.8 for general aviation, +10,-8 for aerobatic or 2.2 for

jet transports. The loads are reacted by the shortest load paths

practical for strength and weight savings. Tensile strength is one starting point to calculate the cross sectional area of a load

path but often buckling of a section determines the cross

sectional areas. Then you choose a type of structure such as

tube and fabric, or aluminum sheet metal 6061 or 6063, or

the wood with many gussets approach. I do S2 glass and epoxy

primairly for the ease of making compound curves and flat bulkheads as bracing. With composites the thickness of the layup more

often than not is determined by withstanding handling

damage of ramp rats or the general public at airshows who

have a hard time with not touching. The chrome moly tubing

can develop numerous faults due to rust, overloading, less

than optimal landings and still not kill you if you inspect a

few things before flight. Lest I forget, the moldless composite

often called Rutan moldless like a Varieze,or Cozy also

sometimes referred to a surfboard construction is an option

of stressed skin with a little monoque flavor thrown in the mix.

I would suggest you first do a design study of a tubular

engine mount to get a feeling for the triangulation and cross

sectional areas required. It uses the same boring moment

equation as calculating a highway bridge. Then start attaching members for wing hardpoints, cabin loads, fuel loads, tail

surfaces. From there it is a short jump to wooden structure

and a little more for sheet metal. Composites add in the use

of core between 2 layups of glass with solid chunks of layup

or phenolic plastic at the hardpoints. In any event calculating

and reacting load forces is common to all constructions and

that in my view is clearest when designing tube structures.

I have a bookshelf full of textbooks which seem more

directed to expressing everything in calculus notation. Very

little practical use formulas are presented and the examples

are a struggle if only calculus is used. I took all the higher

forms of math in engineering school and decided it gave

good insight into how things are related and where and how

formulas are created. However you can either bone up on

infintessimly small elements, things taken to infinity, and

integral this or differential that or.... you can design the

structure. Remember the Spitfire, P51, B29, SR71, ME109

Spruce goose and the list goes on were all done before the

Univac computer in 1955 and CAD system I use today. I did

finite element analysis on my corrugated spar wing done

entirely with S2 glass and it showed 40G load capability. The

loads were from a wing analysis software which plots forces

for the entire wing surfaces rather than assume every load

is at 1/4 of the chord and they get transferred there

by some magic. Also loading gets reduced approaching the

wing tips.

wizzardworks

There is a LOT of good info crammed in Wizzardworks' post.kudo, Think of a fuselage as a 3 dimensional truss. the loads

pass thru the hard points of engine, wing, tail surfaces, and ... wizzardworks

Hey Wizzardworks, could we convince you to let the line wrap function work and then use paragraph breaks?

Home building an airplane is already a massive thing. As a mechanical engineer with a structures and analysis background, I can tell you that designing your own is insane. I should have bought plans for a Cozy MkiV and built it. I am far from done with my design and the Cozy would have already toured the country a few times... If you are looking to build, select a design and build that airplane to the plans. You will have a far higher likelihood of flying it that way.

Next, do you have background in any particular material sets? How about any serious likes or dislikes in material sets you have worked in. I know that I would never complete a sheet metal airplane. Pick your material set based on what you like working in. If you have no experience, I would recommend visiting the shops of builders in your local EAA chapter and doing the workshops on wood and fabric and welding and fiberglass at Oshkosh. If you find you do not like building wooden ribs, a wood wing ship will never be finished...

Then you can go about build choices. If you still want to design your own ship, have at it. It is keeping my brain engaged in retirement. Most of the skin of composite and even aluminum skinned airplanes is set not by strength or stiffness, but mostly by being thick enough to survive construction and the real world, and spacing of ribs, bulkheads, and longerons to allow panels to stand the airloads on them.

Welcome to the Monkey House...

Billski

Once you know the cockpit external dimensions and mission, you can start sizing the wings, engine, tail, etc. Raymer’s small book is great for initial sizing.

Then do the first weight and balance study to determine length of aft fuselage, etc.

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