Friday, August 10, 2018

Aircraft performance and modern computers

I think most of us are used to thinking about aircraft in terms of aerodynamic and mechanical factors.  What shape, area, etc. are their wings?  How powerful are their engines?  What's the power-to-weight ratio?  How heavily are they loaded?  We usually analyze their performance and capabilities in terms of those factors.

Thus, I was taken aback by this sentence in a report yesterday.

... in 1960, software accounted for 8% of the functionality in the McDonnell Douglas F-4 Phantom, compared with 80% of the functionality in the Lockheed Martin F-22 Raptor in 2010, according to research published in the Air and Space Power Journal.

There's more at the link, which discusses ways to avoid cost overruns on a sixth-generation fighter project.

Intrigued, I looked for the source of that research.  It can be found in the papers presented at the 2018 Professional Development and Training Workshop of the International Cost Estimating and Analysis Association.  That's a heck of a mouthful, but it's apparently a very authoritative body.  The paper in question is this one (link is to an Adobe Acrobat document in .PDF format):

Estimating Future Air Dominance
Methods & Models Track (MM08)
David Stem

Estimating the cost of aircraft programs early in development presents special challenges. The process requires a consideration of the content of the program and various methods to be employed. The Air Force Cost Analysis Agency recently provided cost advice to the Scientific Advisory Board on how aircraft programs are estimated, recent historical experience/lessons learned, and approaches to reduce life cycle costs while the program is in the conceptual design stage.

There's also a set of Powerpoint slides from his presentation (again, in .PDF format).

I'm not going to quote any of that very technical, involved paper here;  but if military and/or aerospace matters are of interest to you, it's worth reading.

I knew that computers were indispensable in modern warfare;  but to think that the USAF's premier fighter is dependent on them for 80% of its functionality and, hence, effectiveness . . . that was an eye-opener.  Effectively, you can now design the most aerodynamically perfect, most mechanically sound aircraft in existence, and still find it worse than useless in combat if you don't have good sensors and computers to guide your weapons.  Alternatively, you may be able to use older airframes and/or designs much longer - even in the face of latest-generation aircraft - by greatly improving their electronics and fitting them with modern weapons.  That's clearly what Boeing and the USAF are considering with the F-15X proposal.  Given the rapid developments in the field of airborne lasers, it may not be inconceivable that something like the F-15 might be flying a century or more after it was first deployed, because its electronics and weapons will make up for its limitations in other areas.

Food for thought.



SiGraybeard said...

A slightly different take: the fighter aircraft is like a handheld gun in the sense that part of the practical limits of what it can do depends on a human. The practical limit for widely used handgun is probably going to stay where it has been for a hundred years: about .45 to .50. A fighter that can maneuver tighter than current planes isn't going to do much good if pilots pass out. Fighter jets have been able to outperform humans for a while now.

So the aircraft that provide standoff superiority - shoot down the enemy before he knows you're there - will depend on sensors and software. Some of it in the weapons.

bruce said...

I remember my dad bad mouthing the latest ship in NOAA'S fleet. His reason, it wasn't designed by people who had been to sea. (It had an enclosed crows nest high up its mast that was later removed because it was insufferable during storms and placed to much weight aloft.) IOWs it rolled excessively during storms or high seas. The earlier ships that weren't state of the art were better platforms to work from.
That despite the older ships not having been designed for specific duty as the newer ones had. So it sounds like a bunch of know it alls had requested feature, components and requirements that the ship couldn't make work.
This was before electronic computers were the rage.

harp1034 said...

They already did that with the B-52.

Aesop said...

This is also why, for the 95% of the planet that will never need to defend against a first-world peer air force, that WWII piston-drive, or let's be serious, even cloth-winged inter-war biplanes are about all the air force they'll ever need for most practical purposes.

Most of the world below would be better served by dirigibles, for that matter, unless and until they decide to start building actual railroads, highways, bridges, and roads in Africa and S. America worthy of the name.

All of the above are sufficiently advanced compared to the local populations' abilities as to appear like magic as it is.

stencil said...

So are science fiction authors' muses moving them to include program analysis along with soliloguy and dialogue as a means of developing plot and character?

Andrew S. Mooney said...

As someone who works in the industry (Well the periphery of it.)

That 80% of the functionality of any aircraft is now electronic is hardly surprising, in that not only are modern aircraft designed to be "dynamically unstable" - They use constant computer adjustment of their wings and aerodynamic surfaces to fly straight or indeed any other flight regimen you ask it to, they also use electronics for situations where in the days of the Phantom, you could perfectly well have used all manner of non electronic devices, and there is no rhyme or reason for such beyond changes in what eventually could be put in the same space in the aircraft.

Cockpit gauges, for example have been replaced with the characteristic bright green "Penitron" screens, air data sensors are now electronic (Try "Flush Air Data Sensor" to see what I mean.) Gyroscopes are electronic ("Ring laser gyroscopes" being the best example.) The throttle is now digitally controlled when before it was literally a cable. The flight surfaces use electricity where in the past you used hydraulics.

Radar is just about the only aircraft system that has been "electronic" from the beginning, and even then it has gone digital because modern arrays can do more by using a computer to process multiple signals.

The rule is basically that since the aircraft's exterior is pretty much fixed, the interior of the aircraft is limited and so space for each component is at a premium. Since electronics are easy to miniaturise, they have wound up dominating the method by which anything gets done on a vehicle from lifting the undercarraige to firing a gun.

Much of it has no purpose whatsoever beyond that.

It's not surprising when thought of that way, and it's also a nice way for the industry to get money out of the customer as these exciting new technologies have the ability to lock you in to the product line, whereas if everything was done the old way, they could go off to your competitors rather than "inexpensively" upgrade whatever they've already bought off you.

Will said...

I think the F-16 was our first dynamically unstable fighter design. (The aircraft can radically exceed pilot blackout limits). Supposedly, there is a non-electronic control interface that lives under the seat, that should enable sufficient control for the pilot to find his way back to base, and maybe even land the thing. It was intended to allow control if the aircraft was too near a nuke detonation, and the resulting EMP fried the on-board electronics. I wonder if they still bother with it, or have they just mothballed the setup by now? I'm thinking they may have figured out how to sufficiently protect the electronics package by now, after all these years.