Discussion - engine and fuel system controls
I have no particular reason for raising this subject, it's just one which annoys me from time to time.
Once upon a time I was briefly allowed to earn my living in the back of a fast jet. Taking a typical aircraft, the Hawk, one had
- A throttle
- A start button
- A fuel cut-off
And basically that was it.
Now at the other end of the scale I spent today tinkering with my Raven-X, which is a Rotax 2-stroke engined flexwing. This has:-
- A throttle
- A choke, for starting
- A fuel cut-off / tank selection lever
- An ignition switch
- An electric carb-heat switch
A similar but more modern aircraft, say a Quantum 15-912 would have
- A throttle
- A choke, for starting
- A fuel cut-off lever (only one tank)
- Two ignition switches
- A starter button
Now on the other hand, if the local runway emerges from the floods, I also get occasionally to fly my 1/17th of a PA28, this has:-
- A throttle
- A primer
- A mixture lever
- A throttle friction lever
- A carb heat control
- A combined ignition / starter switch
- A fuel tank select / cut-off device.
If it had a VP prop, add in an RPM governer control. That is 8 separate controls, compared to 5 on a modern microlight, and two (throttle and ignition) on a modern car. So what could reasonably be automated:-
- Carb heat does not need to be as used on the standard Lycontinental installation. On various microlight installations I've seen coolant based carb body heating, coolant based air intake heating, electrical carb body heating - all of which can be left permanently on without any significant power loss and only the electrical system needing any kind of function indicator - the others will work so long as you have coolant.
- Choke / prime. This has been automated on cars for 20 years, why are we still mucking about with them on aeroplanes, and flooding our engines when we get them wrong.
- Fuel tank selection / cut-off. Anybody flown a 4-tank Piper - it's an ergonomic nightmare and totally unecessary. If one must have a multi-tank system the technology to automate balancing and use has been with us for 40+ years and is totally reliable - in most cases it only consists of large bore hose and some baffles.
- Fuel cut-off. Why? Cars simply have a cut-off solenoid connected to the ignition switch. If one wants to make sure there is no fuel in the lines at shut-off (so as to isolate an engine fire for example) a simple timing device would suffice to solve this.
- Throttle friction. Really. Is it really beyond a modern design engineer to make a lever that stays where it's put in a vibrating environment without the forces being excessive? For that matter, was it beyond them 30 years ago?
- Mixture. Cars manage without, using very simple and inexpensive computers programmed to give optimal running based upon measured density altitude and EGT to ensure that isn't exceeded. Link this to the throttle so that if more than 75% power is selected it defaults to fully rich and we've automatically got rid of another control in the cockpit to muck about with. Ensure a failure mode of fully rich (plus a failure indicator light) and the 10^5 reliability issues can be swept away.
- RPM control - same applies surely. Fine is only needed above 75% power, the rest of the time the system should be defaulting to best-for-cruise for a given power and density altitude, so lets combine this with the mixture control in a simple ECU that defaults to fully fine in the event of a failure.
- Mag switches, this is an area I'm slightly unsure, but... The ignition circuit is only functioning for a fraction of each cycle, during running it should be possible to continually test them for system capacitance which should fall within specific values. One circuit out of limits, an automatic warning light. But I may be wrong about this.
So I present you with Genghis' 21st century engine and fuel system controls:-
- A throttle
- A run / stop control.
- And if absolutely necessary, a 1-2-both mag circuit switch for checks.
Eliminating 4-6 cockpit controls that clutter the place up, can be wrongly operated and distract pilots from the serious business of enjoying the view.
Or am I missing something?
G