Q; for any perf engineers out there

[buzid]

Is the 'ideal' runway horizontal profile shaped like an ever so slight convex dish, concave dish or just plain flat? If not flat, why not?

Thanks.

[Genghis the Engineer]

An interesting question. You could play around with the basic field length equations and try and find out. I'm not sure if anybody's tried.

But, I'd say the ideal runway has a moderate upslope and higher friction surface on the last quarter, and is level for the first three-quarters.

G

[john_tullamarine]

Not a question to attack in a simplistic way.

Depends on things like ...

(a) the aircraft AFM data,
(b) how you want to handle the first segment gradient and distance,
(c) which case is limiting at a given Hp and OAT,
(d) what the obstruction profile is like for the particular runway,
(e) the extent to which the AFM permits unbalancing


.. and, at the end of the day, the sums just give us an idea of what the aircraft might do in a repeatable world - which doesn't always have a great deal to do with the real one in which we do battle ... not the least of which is represented by roller coaster runways.

ICAO does have a recommendation to weight the varying slopes somewhat but, at the end of the day, there still remains a bit of art in the science, especially if an operator wants to factor in some corporate risk assessment rather than just screwing the AFM sums for the maximum weight without any consideration for real world conditions ...

However .. it is good fun to play with ..

[buzid]

Thanks for the responses.
I guess I should have termed the question: If you were going to build the ideal runway from scratch for a general multitude of applications, would it be ......etc.

I seem to recall the American military were doing some pioneering work like this on some Pacific Island runways? Could be x wired...

Thanks, Buzid

[john_tullamarine]

Even then the question's solution is complex, running to considerations of

(a) the (very) high capital cost of developing runways suitable for the larger civil transports - tactical strips for aircraft such as the C130 etc might suit however

(b) (a) leads to questions of return on capital, however that may be addressed

(c) to optimise the solution for one Type under a small range of boundary conditions might not be optimal for another

etc ..

[moggie]

I suspect that slopes are like strong head/tail winds - the advantage you gain one way is not as great as the disadvantage the other. I refer to head winds slowing you down so much that turning round and using the tailwind does not recover all that disadvantage.

A bowl shaped runway - does the upslope on the second half have a greater negative effect than the gain in the first half? If there is more down than up, how bad is that for landing (bearing in mind that weight for weight you need more runway to land than take-off).

A crest shaped runway will give a nice boost later but will have hit you hard initially.

Building runways that are good in one direction means that they will be bad in the other.

As I say - I don't know the answers, these are just speculative thoughts.