Plane's performance degrades over the course of flight

[mike2060]

I am having a major problem. The 172's airspeed slowly goes down over the course of a flight. Twice in the last week I have been stalling at 60 IAS at 6000 feet. Today I started at about 110 KIAS and now am down to 60 KIAS. The tachometer goes down as well. It was at 2300 and now is down to 2000 and I can not maintain 6000 feet. I have pitot heat on fwiw. I am using FSGRW.

[FlipS]

Did you go to the hangar with your airplane?

[Erlk0enig]

I also discovered this once. First I went crazy about my engine wear, but then it turned out that the up-and downdrafts injected by Active Sky Evolution were a bit too much for the cessna's engine performance to keep the plane levelled. So, just a thought to check your weather settings...

[Hook]

I am having a major problem. The 172's airspeed slowly goes down over the course of a flight. Twice in the last week I have been stalling at 60 IAS at 6000 feet. Today I started at about 110 KIAS and now am down to 60 KIAS. The tachometer goes down as well. It was at 2300 and now is down to 2000 and I can not maintain 6000 feet. I have pitot heat on fwiw. I am using FSGRW.

If pitot heat was required, then it's likely that your airplane was accumulating ice. Many people have said that icing is not modelled in FSX... you may have found otherwise.

My best guess is that icing is modeled by adding weight to the aircraft. While this is not how it works in real life, the effect is similar enough in the sim. Prop icing is also modeled (which will slow your RPM).

Hook

[mike2060]

I am having a major problem. The 172's airspeed slowly goes down over the course of a flight. Twice in the last week I have been stalling at 60 IAS at 6000 feet. Today I started at about 110 KIAS and now am down to 60 KIAS. The tachometer goes down as well. It was at 2300 and now is down to 2000 and I can not maintain 6000 feet. I have pitot heat on fwiw. I am using FSGRW.

If pitot heat was required, then it's likely that your airplane was accumulating ice. Many people have said that icing is not modelled in FSX... you may have found otherwise.

My best guess is that icing is modeled by adding weight to the aircraft. While this is not how it works in real life, the effect is similar enough in the sim. Prop icing is also modeled (which will slow your RPM).

Hook

I leave on pitot heat all the time. Pitot heat only affects the pitot tube and shouldn't affect the planes performance. I only mentioned that I had it on so no one would ask me if I had it on.

Maybe it is prop ice? But it was -15/-16 out. Not sure how likely prop ice is at that temp.

[mike2060]

Did you go to the hangar with your airplane?

Yes the first time it happened I overhauled the plane while in the air to no avail.

[Hook]

I am having a major problem. The 172's airspeed slowly goes down over the course of a flight. Twice in the last week I have been stalling at 60 IAS at 6000 feet. Today I started at about 110 KIAS and now am down to 60 KIAS. The tachometer goes down as well. It was at 2300 and now is down to 2000 and I can not maintain 6000 feet. I have pitot heat on fwiw. I am using FSGRW.

If pitot heat was required, then it's likely that your airplane was accumulating ice. Many people have said that icing is not modelled in FSX... you may have found otherwise.

My best guess is that icing is modeled by adding weight to the aircraft. While this is not how it works in real life, the effect is similar enough in the sim. Prop icing is also modeled (which will slow your RPM).

Hook

I leave on pitot heat all the time. Pitot heat only affects the pitot tube and shouldn't affect the planes performance. I only mentioned that I had it on so no one would ask me if I had it on.

Maybe it is prop ice? But it was -15/-16 out. Not sure how likely prop ice is at that temp.

Ok... what's the first indication that you have that you're in icing conditions? In FSX the pitot tube freezes up. I fly without pitot heat just so I can monitor icing conditions. The pitot heat doesn't affect aircraft performance, but icing sure does.

I mentioned that I believe the icing is modeled by increasing the aircraft weight. This is typical smoke-and-mirrors used in computer simulation: it's not the correct effect, but mimics it close enough. What happens if you're flying along and your aircraft weight increases by a few pounds per second? Well, you'll notice that your angle of attack will slowly increase. This causes drag to increase. This slows you down. This was the effect you described. Add to that the RPM dropping, which happens when the prop ices, and it's reasonable to assume that you were in icing conditions.

I found out about icing the hard way once. I was flying the default Goose into known icing conditions. By the time I knew I had a problem, it was almost too late to find an emergency landing field. This was with Active Sky weather and no other add-ons that affect ice.

Hook

[Great Ozzie]

I mentioned that I believe the icing is modeled by increasing the aircraft weight. This is typical smoke-and-mirrors used in computer simulation: it's not the correct effect, but mimics it close enough. What happens if you're flying along and your aircraft weight increases by a few pounds per second? Well, you'll notice that your angle of attack will slowly increase. This causes drag to increase. This slows you down. This was the effect you described. Add to that the RPM dropping, which happens when the prop ices, and it's reasonable to assume that you were in icing conditions.

I found out about icing the hard way once. I was flying the default Goose into known icing conditions. By the time I knew I had a problem, it was almost too late to find an emergency landing field. This was with Active Sky weather and no other add-ons that affect ice.

I think it is too Hook (fwiw ).

Similar experience but with the FS9 de Havilland Comet (using it in FSX).

Going to see if I can find some icing conditions now w/ the 172.

[mike2060]

The reason I didn't think it was icing was because I know you can press "m" and it removes it (didn't work for me this time). FSX has a bug where it will give carburetor icing to planes that don't even have one, so if one presses "m" it turns on "carb heat" and it goes away. But I did forget about prop icing. So I guess it must be icing then. Next time it happens I will descend to a lower altitude to see if that helps.

Thanks guys.

[Oracle427]

Did you change the default key mapping for carb heat? I thought that the default key is H.

[Great Ozzie]

The reason I didn't think it was icing was because I know you can press "m" and it removes it (didn't work for me this time).

Hey Mike,

It is "H" that is for Carb Heat / Engine anti-ice.

"M" is for the Magnetos.

"C" is for Cookie ("that's good enough for me").

http://www.youtube.com/watch?v=Ye8mB6VsUHw

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Yes, right Oracle, those are the defaults.

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Going to see if I can find some icing conditions now w/ the 172.

I did a little KDCA - KBWI - KGAI (D.C. to Baltimore to Gaithersburg) yesterday afternoon and hunted around from 3000MSL to 9000MSL but could not find a thing (except a frozen pitot). There were Pireps of light to moderate icing but I didn't find "it".

I think maybe a better time would be a case of freezing rain (like a warm front overrunning cold air) looking for moderate to severe reports.

[mike2060]

Lol thanks. I have used H before, don't know why I thought it was M now

[GrahamP]

I almost feel I should apologise for asking this but are you leaning the mixture as you climb above 3,000 feet?

[Great Ozzie]

I almost feel I should apologise for asking this but are you leaning the mixture as you climb above 3,000 feet?

I actually have done this on multiplayer, as I routinely use automixture (not in the A2A 172 tho -- just keepin' it real)... and the server was set to use manual mixture.

[mike2060]

I almost feel I should apologise for asking this but are you leaning the mixture as you climb above 3,000 feet?

Yes I did. I am thinking it is icing that was the problem.