Add cockpit shaking when carb icing affects aircraft performance

[wlbragg]

Currently there is little evidence that there is carb icing taking place. It's been stated that the aircraft runs "rough" when this condition causes ice to build up and restrict fuel flow. This fix will add a shaking effect that is meant to simulate "running rough".

See https://forum.flightgear.org/viewtopic.php?f=25&t=42734&start=15#p426780

This is a very simple addition to Nasal/engine.nas

if ( carb_ice > 0.149 ) shake_view();

....
      # since the carb_icing_rate gives an arbitrary final value, the rate is then scaled down by 0.00001 to ensure ice
       # accumulates as slowly as expected
       #carb_ice = carb_ice + carb_icing_rate * 0.00001;
       carb_ice = carb_ice + carb_icing_rate * 0.00001 * carb_rate_mult;
       carb_ice = std.max(0.0, std.min(carb_ice, 1.0));
       if ( carb_ice > 0.149 ) shake_view();
...

[hbeni]

Cool!
However, I interpreted "running rough" not as shaking, but as the RPM and power not stable.
What exactly is a rough engine?

What I think to remember from my years old memory of running a carbureted car:
when I had icing, the power would drop significantly, like letting go of the gas pedal (despite pressing it). Pressing the pedal made things worse. I don't recall shaking or such, but rises and drops in power, like when i shortly press and let go of the pedal.

I feel we need some footage from reality here?
Probably David Megginson can tell us something.

[wlbragg]

I agree, the main purpose is to get an indicator that we can notice in the sim. Falling out of the sky is a rather rude indicator that something is wrong. :) I don't think vibration is out of the question, but a real shake like when starting the engine may be too much.