Designing an aircraft - where do you start?

[Golf Echo 30]

When an aircraft manufacturer decides it wants to design and build an aircraft to suit a particular market, what would be the starting point for the engineering/design team? For the sake of example, the proposed aircraft would have to carry 300 passengers for 5000 miles.

Is it a question of designing the fuselage size to accommodate 300 passengers and then adding wings/engines or would the entire engineering team sit down and try and hammer out the outline design on day 1? If the latter, is there are particular area that is key?

Apologies for what is an incredibly simplistic question on a very complicated subject.

Many thanks

GE30

[grounded27]

I am sure there are a tonne of ideas out there.

There is no question that the MFR is going after a market. Engine efficiency makes all profitable, aerodynamic efficiency usually pays off better on larger aircraft designed for longer flights. "simplistic" yes there are many ideas, "complicated" the regulating CAA's make any new endeavor difficult. I am interested to see how safe and reliable the 787 will be?

[gonzobluefuzz]

First step : design a component that fails somewhat regularly(every few years or so is enough).
Second step: build an aircraft around step 1, with little regard to access, common sense or guidance (IE AMM ref "obtain access to....")

tongue is in my cheek

please disregard this comment

g

[piggybank]

gonzobluefuzz your remark has the utmost truth in it. Despite looking sexy at times aircraft and helicopters must be the most poorly thought out of machines for maintenance. My first pointer for whats needed is force the designers to work on the tools for a year, out in the cold or a wet jungle night time and at the end of a torch and then after that one year let them loose on the designing.

[Genghis the Engineer]

Various ways to look at this.

When I used to teach aircraft design, I taught that you start from four pillars of design...


(1) What is the best available technology solving similar problems?
(2) What regulations do you have to meet?
(3) What is the operating environment?
(4) What are the role requirements for the aeroplane?

Once you got a good understanding of that (which is, actually, a LOT of work), you would then identify what - if any - new R&D was needed.

From there, the design process is reasonably inevitable and good engineers will get to the right design solution with nothing more than hard work and enough man-years.

G

[Avionker]

And don't forget the Access Panel Rule.

1) Calculate the required size and optimal location of the panel to allow unhindered access to components.

2) Reduce the panel in size by 20% and move it 8 inches forward or aft, and 5 inches above or below optimal position.

3) Sit back and laugh at the thought of maintenance engineers losing skin, blood and fingernails, and possibly dislocating various joints, whilst attempting to carry out so called routine maintenance tasks.

[TZ350]

gonzobluefuzz [Quote

First step : design a component that fails somewhat regularly(every few years or so is enough).
Second step: build an aircraft around step 1, with little regard to access, common sense or guidance (IE AMM ref "obtain access to....")

tongue is in my cheek

please disregard this comment

g [Quote]

Substitute "automobile " for " aircraft ", delete " every few years ", and you have what was the primary " qualification " for a design engineer at British Leyland and Jaguar.............

[matkat]

I was part of the maintainability team for the A400 I can tell you that we did use a DMU to see if items could be accessed by a average sized mechanic we even did this to get behind a PCU for the cargo door there was a fair bit of success but invariably some failures but we tried

[NutLoose]

And don't forget the Access Panel Rule.

1) Calculate the required size and optimal location of the panel to allow unhindered access to components.

2) Reduce the panel in size by 20% and move it 8 inches forward or aft, and 5 inches above or below optimal position.

3) Sit back and laugh at the thought of maintenance engineers losing skin, blood and fingernails, and possibly dislocating various joints, whilst attempting to carry out so called routine maintenance tasks.

I always looked on aircraft engineering as being a bit like a Gynecology, except the hole tends to be smaller, further away and on the whole tends to smell better too.......



Wasn't the short sterling bomber designed so the wings would fit in a standard RAF hangar? and also that BEA specified a weird seating capacity for the Viscount ? and when asked after it was built, it turned out they specified it to the seating capacity of their passenger buses in use, makes sense really......

[Genghis the Engineer]

Originally Posted by NutLoose

I always looked on aircraft engineering as being a bit like a Gynecology, except the hole tends to be smaller, further away and on the whole tends to smell better too.......



Wasn't the short sterling bomber designed so the wings would fit in a standard RAF hangar? and also that BEA specified a weird seating capacity for the Viscount ? and when asked after it was built, it turned out they specified it to the seating capacity of their passenger buses in use, makes sense really......

Frivolously put perhaps, but you make the very important point that maintainability is only one of a massive list of things that need to be got right (and will all get compromised against each other) in designing an aeroplane.

Use of standard components, manufacturing cost, performance, fitting in a particular hangar/hold/deck, capacity, evacuation, fire, crashworthiness, flying qualities, payload, maintainability, structural strength, fatigue lift....

... all has to be adequate. So, maintainability (and many other things other than primary safety) get compromised.

Hard to remember when you exist in an world where one consideration (e.g. maintainability) is important. Pilots are the same - hard to get many pilots to think far beyond what's in the cockpit.

G

[old,not bold]

In the late 70's, me 'n my team went to collect a new Skyvan from Belfast. The aircraft was, as usual, not ready as promised, so we stayed at Shorts' expense for a week. One evening the Head of Design (or whatever the title was) got the job of entertaining us.

We asked how and why the Skyvan was designed, a fair question if you look at a Skyvan.

"Well," he said, "it was like this. The military wanted to carry a Landrover into short strips, so we thought we'd need a box for it." He drew a box on a tissue, with a Landrover inside.

"Then we put a wing on top, to keep it out of the way, and so that the middle bit could carry the fuel." He drew a wing cross section.

"Then we thought about a pilot," he drew a chair with a pilot on it, on a development drawing below, "and to keep him warm we put a sort of nose around the front." He drew a shape to enclose the pilot.

"Then we thought that it would take a bit of keeping straight, so we put two bloody great fins and rudders well back from the main bit," he drew a fin/rudder on another development drawing, "and then we sort of connected them to the main body". He drew the connecting structure.

"And finally we gave it a couple of engines and a fixed undercarriage with huge wheels to make it an ATV, and Bob's your uncle." He finished the design in the 4th drawing.

Now that, my children, is how a real aircraft is designed. And it worked*, with a better STOL take-off performance than a Twin Otter with a lower payload.

I've managed to preserve his drawings ever since. Here, exposed for the first time, is the very sheet of paper. You must appreciate that the drinks were flowing freely while this was going on, so the drawing accuracy began to reduce.



* Once it got a decent engine, the TPE 331, although even that had a habit of exploding unexpectedly.