The AV-4: why it's a bad idea

Roger Burton West
13 October 2003

R. Talsorian Games' Cyberpunk RPG introduced the concept of the AV-4 to the gaming public. In its original incarnation, this vehicle was the engine from a Harrier VTOL attack aircraft, coupled with a new (unstreamlined) superstructure and control system; it was about half the weight of the original Harrier, achieved mainly by removing control and lift surfaces, and would carry several people or a significant cargo payload. (Later versions were deemed to be custom-built rather than using surplused engines, but the principles are the same.)

This is an attractive idea. The problem, for a game nominally consistent with reality, is that it doesn't work. This article attempts to explain some of the reasons why.

Later books introduced other "AV" style vehicles, i.e. depending on one or more vectored-thrust jet engines to sustain lift; these arguments apply to them as well.

What are the AVs good for? We're told they're used by police and corporate troops for urban assaults, by some emergency medical services, and as corporate transports. However, none of these is a role which cannot be fulfilled by a conventional helicopter or tilt-rotor aircraft, at rather less cost (especially since fuel is said to be scarce). The only advantage which an AV might have over one of these vehicles is the ability to operate in confined spaces; however, any space confined enough to prevent helicopter operations is (a) likely to be very demanding of the pilot of the rather less manoeuvreable, if smaller, AV; (b) likely to have poor air circulation, leading to exhaust gas reingestion and engine failure - particularly since, at least in the AV-4, the engine air intake is low on the front of the vehicle.

The AV's only real advantage over the helicopters and tilt-rotors is in speed, and a tilt-jet aircraft (such as we're told exist in the Cyberpunk world) could easily outperform it here.

The jet exhaust from the rear nozzles of a Pegasus jet engine is at approximately 700 degrees Celsius. Unlike the exhaust of tilt-rotors and helicopters, this makes significant demands on the operating environment; even a simple landing and take-off will do significant damage to most surfaces. (This is, however, consistent with the general uncaring attitude of most of those rich enough to operate such vehicles.) More significant is foreign object ingestion, a problem when operating the real-world Harrier from rough strips: the jet exhaust blasts loose small objects, which are then ingested into the air intakes, causing first-stage turbine blade fractures and other major damage. This seems to restrict the AV (and other tiltjets) from operating in many of the urban environments for which it is in theory designed.

The AVs rely for lift on the continuous operation of their engines at high output. This inevitably produces a large column of superheated air, perfect for tracking with an infra-red missile. It's not likely to be possible to baffle this exhaust: too much efficiency is lost. Many people in the Cyberpunk world have access to infra-red missiles... this rather seems to rule out any role with significant opposition (including corporate transport, and in some places even medical/police; certainly the "tank-busting" AVs given in later books are very vulnerable to this sort of attack).

I think the AV can reasonably be considered demolished. So what does make sense? Consider the historical lesson: a vehicle designed to do many things does none of them well. Most urban operations will continue to be conducted with helicopters; where more space is available, and higher speeds are wanted, tilt-rotors and tilt-jets become useful. But the concept of a lifting wing, whether fixed or rotating, seems likely to beat out a pure vectored thrust solution for some time to come.