Unique Alternator Control

[dpansier]

I recently spent time going thru some patents regarding the control of alternators in fuel efficient vehicles.

I found the designers have come up with some very novel alternator control devices that save significant amounts of fuel. In addition to measuring battery voltage some of the alternator control devices have the ability to monitor the engine load, road speed, electrical load demand, engine and ambient temperature. By carefully monitoring these parameters, the alternator output is controlled to meet the electrical demands using the least amount of engine horsepower and improving the fuel consumption numbers of the vehicle.
For example, the battery was not charged when going up a hill and heavily charged on the way down.

Thinking through this exercise on how this information could be used to improve the efficiency of our sport planes I realized many of the gains would not apply to our aircraft needs as the engine loading parameters are quite different.

One thing apparent was the power requirements of the alternator, a fully loaded 60 amp alternator can demand 5 or more horsepower.

A simple method to recover this lost power on takeoff would be to install a switch in the alternator field control wire, the switch would open when the throttle was firewalled and closed when slightly pulled back allowing the alternator to provide normal output. The throttle method could be used with fixed pitch props and the high RPM prop control could be used with constant speed props.

Not sure if I can feel 2.5% improvement in the seat of the pants with 200HP total but with a fixed pitch installation the % would be greater.

These thoughts are worth what you paid for them.

[glenn654]

D.,

I think you are on to something worthwhile, aviation gains are small but add up.

Think about all the work done to get a 2.5% improvement in prop efficiency, if you have the knowhow to pursue this idea I think it is worth it.

I believe the improvement in fuel efficiency would be well worth it at $6.00+ per gallon of Avgas.

Glenn Wilkinson

[BobTurner]

A lot (most?) aircraft have a pullable CB on the field circuit. East to pull to do a test. But...
Alternators are pretty efficient, and 60 amps at 12 volts is almost exactly 1HP. And unless you've got landing lights and pitot heat on, you may only be pulling half that. So it's about the same as turning rpm down from 2600 to 2590.

[Jordan1976]

Airplanes are even more different.

Not generating power in a car climbing a hill makes sense because there is a very good chance that within a short period of time, you will be going back down a hill, and the driver will be requesting braking. You might as well put the energy in the battery instead of heat in the brakes. But in general, GA airplanes don't have brakes in flight.

If you don't run the alternator at take off, but then click it on 1,000' off the ground, you are still climbing, and there's no good data you'll be using the engine to slow down the plane anytime soon. So why does it matter if I run it at takeoff or 2 minutes later? I still need the same number of watts, and I can't grab those watts from somewhere they would have been wasted, so there's no fuel savings. You just get slightly better climb performance and then slightly slower cruise (or higher fuel flow in cruise).

In order to save fuel with an alternator in a plane, you need data that you are about to start a descent where the pilot actually wants *braking* out of the engine, and to shut off the alternator for a time before that event so you can then power the alternator in the descent. But this only works if the descent is a full zero power descent, not just a 40% power descent. In a car when you are on the brakes you are always at zero engine power. In a plane, much of our slowing down is just less engine power, not none.

The only other way I can think of to save power is to not run the alternator when the engine is ROP. If you have a power management technique that quickly gets you from takeoff to LOP ops, you might be able to do this. This would then mean you only steal energy from the engine at times that it is running most efficient. Given that most aircraft batteries only have 20-30 minutes of capacity to run much of a load, and you don't want to be discharging your battery deeply, you need to get from takeoff to LOP within a few minutes for this to be very functional.