Cowl Flaps, and other General Piston engine questions

[anthony_d 32]

Afternoon,

 

I just downloaded the Carenado Seneca 2. A fine bird with some fantastic sounds. It's got me following their engine start up procedures, and I'm ending up asking myself "what happens if I do x & y". So first off:

 

Cowl Flaps:

I'm guessing these are ventilation dampers that open up to let more air circulate around the engine for cooling purposes. Does anyone know if their function is simulated by x-plane or Carenado? I'm guessing it's operation will have an effect on the oil temperature. And if oil temp gets too high, does that lead to an engine fire I wonder?

 

So I tried it, one engine with cowl flaps closed and one with cowl flaps open. Throttle on full & parking brake on. Cylinder head temp for closed cowl flaps got to 400 degC faster (though not much faster). Alas there was no engine fire (or other appropriate malfunction) after 10 mins of red lining. When throttle was retarded, oil/cylinder head temp decreased more slowly with closed cowl flaps.

 

Alternate Air:

No idea if any effect can be observed with alternate air on or off. I'm guessing it's used if the carburettor is choked with ice? That said, there's no button for carburettor heat, so maybe it's a fuel injected engine.

 

Magnetos:

Turn one off and the engine RPM drops by about 100 rpm. Looks good

 

Alternators:

I'd expect having these on or off would have an effect on the engine performance, but there's no discernable difference in RPM, manifold pressure or fuel flow, just the alternator amps. Switching on your electrical consumers (lights etc...) however does increase the alternator load :-)

 

Fuel Pumps:

Obviously these do increase fuel flow, but what else do they do? There's no change in engine rpm or manifold pressure.

 

General Engine Behaviour:

Occasionally these engines will cut out on the ground when idling. As per the manual, it tends to happen after turning some corners while taxiing. Sometimes I can't get the engines to start at all if they're cold without first applying some throttle. It all strikes me as being rather, well, from a time when machines needed some love and attention to keep them going. I like it! I want my planes to be fussy beasts.

[wb5okj 26]

Cowl Flaps: Keep them open on the ground. I usually keep them open most of the time as long as the temp stays in the low green and not below, at high altitude you may have to close them,only if the temps get below the green.

 

Alternate Air: Used in emergencies

 

Magnetos: Turning them off is part of the check at run up before takeoff. Each on should drop about 100 rpm. Should not be more than 75 rps difference between the two.

 

Fuel Pumps: On when starting the plane, I keep them on until after takeoff and established climb. Turn them back on when landing. I turn them on for upwind leg of the landing.

 

Alternators: These should be left on. If turned off you are using batteries only, and sooner or later the batteries will go dead, You shouldn't notice much change with them off or on, untill your batteries go dead.

[alfletcher 5]

Hi Antony

 

I’m not familiar with the Seneca but I know for sure the Alternate Air as an effect in case of blockage of the Static port, which drive 3 instruments (Altimeter, Variometer and Tach). If a blockage occurred all three instruments will freeze. Activating the Alternate Air lever allow the air inside the cabin into the static system resuscitating those instruments. As you can see, it has nothing to do with the carburetor.

 

The Magneto behaviour seems fine. Look for a Seneca P.O.H. to find the maximum allowable drop value. For the C172 it’s 125 RPM.

 

The Alternator has no impact on the engine performance since it only supply energy (voltage) to the battery and the electrical bus. Turning off the Alt Switch simply put all electrical need on the battery so it’s a very dangerous thing to do because it will drain fast.

 

Maybe someone else could elaborate on other aspect.

Happy flying

 

Alan