Aircraft design

[billybookcase]

Looking at some of the sexy and less sexy models shown on here, I wondered how new aircraft were designed.

Does someone draw a gorgeous plane and someone else says "cor that's nice, let's build it".

Or does someone say "we need a plane this sort of shape that does this and that", and then wait for designs to come in?

Just wondered like.

BB

[Test Graham]

Neither. Someone says "We need a plane to do this and that" and then the shape is chosen that will deliver.

[Giorgio N]

Graham has already said pretty much how it works.

To add something more, after a specification is received for a plane to do this and that, a number of configurations is proposed and developed to preliminary design level. Sometime these configurations are really very different from each other, although it must be said that the very first thing designers do is to look at all the already existing planes that are designed for a similar purpose and with similar specifications. The second thing they do is to look at whatever design has already been studied in the past in the same compan that can provide useful information for the new plane.

These different configurations are then evaluated against each other and the one that shows better potential is selected and progresses toward detailed design.

The shape of the plane can change quite a lot during this phase, to sort design or manufacturing issues or accomodate modifications of the original specifications. The completed prototype is sometimes quite different from its first design iteration.

The study of all the proposed and intermediate configurations of a plane is a fascinating subject for enthusiasts, and provides a lot of ideas for what-if modellers.

Edited February 4, 2011 by Giorgio N

[pigsty]

Dassault always reckoned that three people were involved: the specifier, the designer, and an artist. And they did produce some very pretty aeroplanes. Even where form follows function ruthlessly, there's space to do something attractive. For instance, Hawker Siddeley didn't have to retain the curves on the leading edge of the Hunter's fin when they designed the Harrier and the Hawk; but they did anyway.

[Giorgio N]

Hawker Siddeley didn't have to retain the curves on the leading edge of the Hunter's fin when they designed the Harrier and the Hawk; but they did anyway.

This is a typical example of the fact that designers often recycle parts used before. And it makes perfect sense ! It allows the use of existing aerodynamic data and most importantly of existing jigs and moulds.

Dassault reused several parts of the mirage III for the mirage F-1 (the windscreen for example), grumman used the same landing gear of the A-6 on the tomcat, and I'm sure there's another load of examples out there.

[Dave Fleming]

This is a typical example of the fact that designers often recycle parts used before. And it makes perfect sense ! It allows the use of existing aerodynamic data and most importantly of existing jigs and moulds.

Dassault reused several parts of the mirage III for the mirage F-1 (the windscreen for example), grumman used the same landing gear of the A-6 on the tomcat, and I'm sure there's another load of examples out there.

Hawker tailfins from the Hawker Hedgehog of 1923 through to the Typhoon (and the evolution can be traced right through to the Hawk) Same thing with De Havilland tails.

IIRC, even the YF-17/F-18 wing planform owes much to the F-5

[Test Graham]

I should add that there are times in history when designers experimented without a requirement, or at least without a specific openly stated requirement. This is rather less common than you might believe from manufacturer-centred histories, but it did occur. For example, it is probably true that Camm began work on a monoplane fighter in advance of any specific requirement, it being quite clear that the biplane fighter had little future. However Service and Ministry (the two being much the same here) elements were continuously involved in the design evolution before a relevant specification (or perhaps more correctly a series of specifications) was actually issued.

The key point, perhaps, is that the companies, the research establishments and the services proceed along intertwining lines, using ideas from all sources. The issue of specifications, or the time a first pencil was applied to a drawing board, are things that arise following meetings, brainstorms and (yes, really) committees. But project drawings and (to a lesser extent) tunnel research is cheap, and disposable. Real work on any aircraft only begins after a requirement has been clarified and expressed. The money, after all, has to come from somewhere, which means a contract, which means an understanding.

[pigsty]

This is a typical example of the fact that designers often recycle parts used before. And it makes perfect sense ! It allows the use of existing aerodynamic data and most importantly of existing jigs and moulds.

Dassault reused several parts of the mirage III for the mirage F-1 (the windscreen for example), grumman used the same landing gear of the A-6 on the tomcat, and I'm sure there's another load of examples out there.

I don't think the Hawker Siddeley tail structures were identical; and I'm fairly sure the F-14's undercarriage is based on the A-6's in general design, rather than being the same bits of metal.

[billybookcase]

Graham has already said pretty much how it works.

To add something more, after a specification is received for a plane to do this and that, a number of configurations is proposed and developed to preliminary design level. Sometime these configurations are really very different from each other, although it must be said that the very first thing designers do is to look at all the already existing planes that are designed for a similar purpose and with similar specifications. The second thing they do is to look at whatever design has already been studied in the past in the same compan that can provide useful information for the new plane.

These different configurations are then evaluated against each other and the one that shows better potential is selected and progresses toward detailed design.

The shape of the plane can change quite a lot during this phase, to sort design or manufacturing issues or accomodate modifications of the original specifications. The completed prototype is sometimes quite different from its first design iteration.

The study of all the proposed and intermediate configurations of a plane is a fascinating subject for enthusiasts, and provides a lot of ideas for what-if modellers.

Thank you Gorgio.

BB

[mrvr6]

Neither. Someone says "We need a plane to do this and that" and then the shape is chosen that will deliver.

thats how it starts then the company get a phone call fom some mod goon saying the plane needs to do A B & C. ok no problem

company then gives prelim designt to mod mod says yep go ahead with it.

80% of the way through development mod rings company to ask how its going. some issues but fine overall is the reply.

mod says good good oh btw the plane needs to do A C X Y Z but B is no longer needed. oh ffs right ok well deal with it.

3 years and several miilion £ later the company is happy with the almost finished plane.

mod says thats great but it now needs to do B C Y & Z oh btw the french have buggered off and your budget has been halved because of the delays

does that sound realistic to you guys in the know??

[Aeronut]

The outer mainplanes and tailfins on the Lancaster and Manchester although different in shape had the same number of identical ribs in their construction.

When they realised they needed a taller fin for the Machester they just spaced the ribs further apart.

When they realised they needed a bigger wingspan for the extra two engines on the Lancaster the same trick was used.

It was my Grandfather who converted the assembly jig drawings - on his kitchen table after his shift had finished!

[The Lazy Builder]

My Dad told me that Blenheim, Beaufort and Beaufighter tailplanes, horizontal and vertical, were all basically the same. There were a number of so-called 'power-eggs' for the Bristol Hercules and, I think, the Merlin that were used on various aircraft during WWII to speed production.

[roys]

Fascinates me that in Britain designers in WW2 were obsessed with inline engines and then the Fw190 came along and was faster!

Hurricane and Spitfire story is a good example of development in a time of need rather than supposition of what could happen.

My father reckons the Spitfire did not need its eliptical wing and was a production nightmare, however one of its edges over the 109 was its tighter turn which I imagine its

more sophisticated wing shape must have helped.

Just read the piece in Empire of the Clouds in which John Farley complains about the lack of wing area to a lot of British designs especially the TSR2 ,which is a most interesting alternative viewpoint, in respect of the mythical status given to it. The Vulcan and Canberras big wing certainly gave them the edge. Also the F-15 which was nicknamed the flying tennis court due to its big wing. Howver big wings give manoeuvrability which was not part of TSR2's brief. What surprises me about the TSR2 was the height of it from the ground which must have been a servicing nightmare. But the brief wanted a rough field take off capability which required a tall undercarriage.

Looks good from a modelling point a view and so does that eliptical Spitfire wing!