9
$\begingroup$

I'm a student pilot and here at my school we have the older gen DA40s which have individual lever for mixture, pitch and power.

I was looking at this video of the DA40 NG, and got quite curious as to how everything from prop to mixture is automatically controlled, and on top of that you don't need to do any run up checks!

Tried using google but nothing really came, so I thought this would be the right platform to ask and satisfy my curiosity.

Improve this question
$\endgroup$
1
  • 2
    $\begingroup$ Don't worry for Google. Soon, the first result you'll get will be this question. $\endgroup$ – Manu H Feb 6 '20 at 9:43
8
$\begingroup$

According to Diamonds website the NG engine is a:

Austro Engine AE 300 turbocharged common-rail injected 2.0 liter diesel engine with 168 hp and EECU single lever control system

The prop is a:

3 blade MT hydraulic constant speed propeller features advanced blade geometry for efficient performance, low vibration and noise. It is automatically controlled by the engine’s digital engine control through a conventional hydraulic governor.

From the sounds of it, it is as close to a full FADEC (Full Authority Digital Engine Control) unit as you can get

It is controlled by a computer module just like your modern fuel injected car.

Improve this answer
$\endgroup$
9
  • 1
    $\begingroup$ The question isn't how does it work, it's more why it isn't on all airplanes. It's really the same engine technology that has been in widespread use in cars for 40 years. $\endgroup$ – GdD Feb 6 '20 at 9:06
  • $\begingroup$ @GdD when an "engine controller" goes on a car one is basicly helpless. The aviation version is redundant, but there are still risks of this happening in mid-air. Engine controllers (and turbos) have done wonders for engine performance and reduction of emissions, and adding in prop pitch control with fuel/air control just makes it better. $\endgroup$ – Robert DiGiovanni Feb 6 '20 at 9:56
  • 2
    $\begingroup$ @MSalters If an aero engine ran at the same power levels as your Focus (for limp-home mode) the pilot would be likely to have a very bad day. $\endgroup$ – Mike Brockington Feb 6 '20 at 12:19
  • 1
    $\begingroup$ @MikeBrockington: It lost ~50% of its power. I think larger two-engined planes should even be able to continue a take-off when that happens? But in general it gives you far more flexibility in selecting a landing site. The idea is to turn a very bad day into a rather annoying day. $\endgroup$ – MSalters Feb 6 '20 at 15:48
  • 2
    $\begingroup$ @MikeBrockington It'd be like losing an engine on a twin, except without the asymmetrical thrust problems. Anyway you can have computer control without computer total control; for the first 10 year of computers all they did was fine-tune; they did PWM to a mix-control solenoid on the carb, which tweaked the mix to keep the mix stochiometric based on what the O2 sensor was saying; but its limits of travel were sane driveable values. You could remove the computer and drive almost normally, maybe get 1 MPG worse (so 6 MPG instead of 7 lol). $\endgroup$ – Harper - Reinstate Monica Feb 6 '20 at 19:30
2
$\begingroup$

As stated above in the last answer, it’s turbodiesel powered. Like the DA-42 and DA-62, the engine is basically power by wire, using a primary and secondary Engine Control Unit (ECU) computers, each with a dedicated battery backup, both for engine control and control over the constant speed propeller.

Improve this answer
$\endgroup$
2
$\begingroup$

Aside from the fact that the engine is computer controlled...

the reason you don't have mixture control is Diesels don't use that.

Gas engines need to breathe a stochiometric mix of air and fuel, i.e. proportioned correctly so there's just enough fuel for the oxygen admitted. Too fuel-lean and it won't burn. Power is controlled by partially blocking the air intake with throttle plates (hence, vacuum). Getting the mix stochiometric under all conditions is a hard job, and that's what the carburetor does. The mixture control helps you fine tune what the carb cannot.

In a diesel, you gulp in a full shot of air (throttle plates: Gone), and compress to a high compression ratio and high heat. This means when fuel is injected, combustion is both certain and spontaneous. So they don't need spark plugs, and can happily run lean (mixture control: Gone). Spontaneous means the engine intake drawing in a fuel-air mixture is out of the question; it would ignite too soon. The engines are direct injection.

Diesel power is controlled solely by how much fuel is injected per cylinder. That is done at the fuel injection pumps. One pump per cylinder that pumps at the appropriate time in the stroke, driven by a cam. Each pump has an adjustment that decides how much fuel is injected. And this is controlled by a "fuel rack" which sets all pumps the same, and the fuel rack is the "throttle".

I always thought diesel's simplicity would make it ideal for aircraft, but the high compression ratio requires stronger cylinders and makes diesel engines heavier, and that's an issue.

Of course nowadays, in their mad pursuit for EPA Tier 4 emissions, they use computers. One common trick is to eliminate the mechanical cam and rack with sensors and EFI to inject at the right time. But they don't have to do that. It's a reliability vs emissions numbers call.

Improve this answer
$\endgroup$
1
$\begingroup$

Other answers concentrated more on the 'mixture' and FADEC side of things. I'll show what it does with the prop speed. This is actually simpler and is explained right in the flight manual (p. 7-25).

The prop speed is pre-programmed to follow the engine lever:

DA-40 Prop setpoint curve

So, it only uses highest RPM at takeoff power, and then reduces it at cruise settings. At very low settings it 'unloads' the prop by commanding higher RPM (which it may not reach). This may increase windmilling drag though, and this is a common complaint about automaitc prop control.

It is not necessary to have FADEC for such programming. Cirrus aircraft use mechanical linkages to achive a similar control.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.