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BabtridgeMcJoystick

OK what did I do wrong :)

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Hi there

 

I am learning to fly, and am loving the experiences so far. There's been a lot of tweaking, reinstalling, buying addons etc, but thats all part of the fun isn't  ^_^  :unsure: Every time I do something wrong, especially something catastrophic, I like to learn from it! So this one seemed pretty useful...

 

I was just trying P3D out to make sure it was stable on my machine before adding in ORBX and co, and I took the Mooney Acclaim out for a spin. So far I have been focusing on Cessnas only, so I don't have a clue about this aircraft. I had never had the weather set to wintry conditions, so I gave myself some driving snow. Nice effect, but I thought "maybe I can get above the weather" and put it into a climb.

 

I am still learning about prop and mixture levers and when to use them, but I was a bit surprised that neither of them seemed to make a difference when I started losing power. The fuel flow gauge said nearly zero, so I flipped on the fuel pumps (note this was an air start so I assume everything needed for normal flight was running?). No change, starting to bleed off speed and altitude.

 

I looked at the indicated airspeed and it was stuck on zero, so I assumed it had iced. I found the pitot heat switch. Just as I flicked it on, the engines roared into life, beeping started and I overstressed the airframe, I guess from the combination of slight dive and added engine power?

 

So, what happened? Can you ice up fuel lines, and my turning on the pumps broke through it somehow? Or does the Mooney just not like climbing in the cold? I noticed you cannot select "both" fuel tanks in the Mooney, only one or the other.

 

Nice looking plane though, for default :D

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First, your carburetor iced up.  That is what air comes into the engine through.  When the air comes through it adds fuel into the air.  

 

When flying in icing conditions you have to turn on carburetor heat.  This routes incoming air around the exhaust (around, not through) to heat the air and prevent it from icing up the carburetor and preventing air from coming into the engine.

 

We don't always fly with carburetor heat on if it's not needed, because hotter air reduces engine performance.

 

carburetor-icing.gif

 

Carb Icing Potential: http://www.boldmethod.com/images/pages/learn-to-fly/systems/carb-ice/carb-ice-potential-chart.jpg

 

Note on the carb icing potential chart that it's possible to have carb icing up to 90-100 degree temperatures!  How can this be?

See the "Venturi" in the carburetor above?  Since it gets narrower there it's called a Venturi after the Venturi effect.  The air naturally speeds up to get through the narrow Venturi.  When the air speeds up the pressure drops--natural phenomenon-The Venturi Effect.  Since the pressure drops the temperature also drops.

 

Note that this principle is the same way most wings work.  I say most, because Symmetrical airfoils are a bit different.

You'll also note on the chart that Dew Point is a huge factor in icing.  Dew point is the amount of moisture in the air.

 

If the temperature is 70 degrees F, and the Dew Point is 60 degrees F, then there is 90% humidity.

You see, the closer the dew point is to the temperature, the more likely you are to encounter icing.

 

 

Why the engine came to life when you turned on Pitot heat is a good question.  Typically Pitot heat only heats up the Pitot tube that is used to measure airspeed.

 

Faa_pitot_static_system.JPG

 

 

Perhaps you descended out of icing conditions long enough for the ice to melt and hit the pitot heat at the same time?  A coincidence?

 

Maybe the aircraft was coded like that?  Or something else fishy going on?

 

Overstressing the aircraft:

 

Since you didn't have any engine power you likely pointed the nose down to keep from stalling and started gaining a lot of speed.  You may have been already over the aircraft's Vne, Never Exceed speed, when the engine came to life, and you pulled on the stick a bit too much.

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Hi there

 

Thank you so much for a superbly detailed reply, I really appreciate it. It all makes perfect sense, especially the part about the venturi effect. I will definitely be studying the chart you provided, that's a cool (no pun intended) bit of info.

 

Just before I put pitot heat on, I flipped on the fuel pumps, I don't know if that could have had an effect? But I think you may be right with saying that I just came out of icing conditions - the nose had been dropping for a while.

 

Anyway its a great way to learn, making mistakes like that in a sim is probably the only way to make mistakes like that!

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