Ice Season!

azure said:
I'm not a specialist either (far from it!) but my understanding was that aerodynamic cooling would be the exact opposite of what you described, due to expansion of air moving in areas of local pressure DEcrease (upper surface of airfoil mostly, I would expect).

Again, I've never heard of anyone actually encountering structural icing due to aerodynamic cooling "in the wild", and I would have thought the effect was insignificant, or at least smaller than calibration errors anyway, and if I saw ice at 2C I would chalk it up to a faulty reading rather than aerodynamic effects. Which is why I asked whether it was more significant than that -- and apparently the answer is no, but that doesn't mean it's a good idea to neglect it entirely. As Matt says, leaving a buffer for whatever reason is a healthy practice.

Thanks for the replies!
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It's true that there is some adiabatic cooling of the air flowing over the top of the wing but the effect is pretty small. If you start with the wing loading of your Cardinal RG (about 16 lb/ft^2) and assume that half the lift is produced by the drop in pressure over the wing (not accurate but close enough for this estimation) you get something like 1/10 inHg of pressure drop. 1 inHg pressure change is equal to about 2°C of temperature change so you'd be looking as a few tenths of a degree Celsius, hardly enough to matter.

In any case, I've seen ice accumulation on wings hundreds of times in conditions ranging from trace to the severe end of moderate and IME it always builds on the leading edges before accumulating anywhere else on the lifting surfaces. On the flip side, TAT (total air temp), which accounts for the adiabatic heating that accompanies the compression at the leading edges (and temperature probes) doesn't represent the surface temperature of the ice collecting surfaces on an aluminum skinned wing because the metal is such a good conductor of heat that there's very little temperature rise on the leading edges.
 
bbchien said:
Well got my first ice last night running up to KJOT to get my younger daughter. Skew T appended; ran down at 2,400 in VMC (Min. Vectoring altitude) and just ran VFR at 2,000 on the way back.

It was MODERATE ice, at the freezing line. LOTS of moisture in the system now moving across the mid country!
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Do you have (or does anyone) have a quick guide to Skew T? I would like to improve my ability to interpret them.
 
gismo said:
It's true that there is some adiabatic cooling of the air flowing over the top of the wing but the effect is pretty small. If you start with the wing loading of your Cardinal RG (about 16 lb/ft^2) and assume that half the lift is produced by the drop in pressure over the wing (not accurate but close enough for this estimation) you get something like 1/10 inHg of pressure drop. 1 inHg pressure change is equal to about 2°C of temperature change so you'd be looking as a few tenths of a degree Celsius, hardly enough to matter.
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That's about what I figured, a few tenths of a degree. But I didn't bother to do even a back-of the envelope calculation on it. I probably should just to satisfy myself that it's negligible. In practice, as I said, I assume a +-2C uncertainty in any OAT gauge indication, so that effect being negligible doesn't mean I would fly along happy as a clam at +1C in IMC.

In any case, I've seen ice accumulation on wings hundreds of times in conditions ranging from trace to the severe end of moderate and IME it always builds on the leading edges before accumulating anywhere else on the lifting surfaces. On the flip side, TAT (total air temp), which accounts for the adiabatic heating that accompanies the compression at the leading edges (and temperature probes) doesn't represent the surface temperature of the ice collecting surfaces on an aluminum skinned wing because the metal is such a good conductor of heat that there's very little temperature rise on the leading edges.
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You say TAT *accounts* for adiabatic heating, meaning what? It sounds as if the gauge would read lower than the sensed temperature to compensate. If it's reading actual temperature at the probe, then it would be reading higher than ambient.
 
spiderweb said:
Do you have (or does anyone) have a quick guide to Skew T? I would like to improve my ability to interpret them.
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Ben, are you a member at Scott D.'s site? He has lots of free tips on the Skew-T but he also has a new (this year) premium workshop on all the gory details. I'm planning on getting it over the break and putting in the time to really learn this. You probably already know as much about the basics as I do, and as far as I know, that's that next step up.

http://www.avwxworkshops.com/
 
azure said:
Ben, are you a member at Scott D.'s site? He has lots of free tips on the Skew-T but he also has a new (this year) premium workshop on all the gory details. I'm planning on getting it over the break and putting in the time to really learn this. You probably already know as much about the basics as I do, and as far as I know, that's that next step up.

http://www.avwxworkshops.com/
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Agree.
 
Geico266 said:
Snow by itself doesn't seem to cause problems for me, unless the show is mixed with rain. Just plain snow doesn't stick because it is frozen. I've flown in snow for hours. You can see it when the strobes flash.
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The neatest thing is flying in snow in an airplane with landing lights in the leading edges of the wings - You can actually see the boundary layer!
 
Remember looking back on how you used to fly VFR before you did your instrument training, and thought, how did I ever survive without what I know now? After watching Scott's SkewTlogP workshop I had another one of those how did I survive thought moments, this time about flying in IMC without the information conveyed in this workshop. Worth every penny.
 
The first place I always noticed it was on the outdoor temp thermometer. NASA is right though the worst ice ica has always been on the leading edge of the stabilator. If I have it n approach it is a faster landing with no flaps.
 
flyingcheesehead said:
The neatest thing is flying in snow in an airplane with landing lights in the leading edges of the wings - You can actually see the boundary layer!
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One night in the 310 coming into Williamsport I got that effect. Looked like something out of a Star Wars movie!

It was also a bit disorienting, because it gave you a weird sensation of speed.
 
scottd said:
Read this e-Tip that I sent to my members that discusses SLD.
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Thanks Scott. I'm sure I read that tip a while ago, and was probably half-remembering it as I wrote that. ;)

So, just for clarity then, ALL SLD is considering to be freezing rain or freezing drizzle? I thought anything under 100 microns or so would be too small to be perceived as drizzle, more like a fine mist. Also, what about the kind of conditions that are called freezing fog, when based at the surface?
The problem is that most outside air temperature gauges are the immersion type. There's actually more literature/studies that discuss errors with this type of equipment than there are studies about airframe ice. Once such a sensor gets wet or collects ice, you'll find that the temperature you get may be far from the truth.
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I'm embarrassed to say that the only OAT sensor I know about on my plane is the one connected to the analog gauge over my head, which I rarely glance at because it's hard for my ancient eyes to read. I'm pretty sure my JPI's OAT readout is fed by a different sensor and I don't know where that one is mounted.
 
Henning said:
Especially when you have no equipment.:hairraise:
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Yeah. I've gotten SLD a few times in the Aztec. Not fun. That said, between the boots and the fact that the Aztec handles ice better than any other plane I've flown, so it wasn't a particularly big deal in it.

The 310 does substantially worse in ice. What it has going for it is a lot more power, speed, and better climb rate, so you can get out of icing faster.
 
Ted DuPuis said:
One night in the 310 coming into Williamsport I got that effect. Looked like something out of a Star Wars movie!

It was also a bit disorienting, because it gave you a weird sensation of speed.
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Yeah. Precip can give some interesting sensations. Another weird one that you reminded me of is the only time I've experienced acrophobia in an airplane. I was flying through rain in the 182 at night, and I had the lights on so I could tell when I was IMC or not. The landing lights on the 182 are in the left wing and not only have the main beam forward and downward, but a "leakage" beam about 80 degrees up and down from straight ahead. The downward-leaking beam was reflecting off the raindrops falling below and gave me the most vivid visualization of altitude I've ever had. The raindrops looked like they were falling into a gigantic hole below me in the darkness, and with the raindrops the "hole" looked nearly endlessly deep, like you'd see in movies or something. Crazy!
 
Ted DuPuis said:
Yeah. I've gotten SLD a few times in the Aztec. Not fun. That said, between the boots and the fact that the Aztec handles ice better than any other plane I've flown, so it wasn't a particularly big deal in it.

The 310 does substantially worse in ice. What it has going for it is a lot more power, speed, and better climb rate, so you can get out of icing faster.
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I got it in the Travelair one February night on a No Gyro approach; only time I had resigned to dying.
 
Henning said:
I got it in the Travelair one February night on a No Gyro approach; only time I had resigned to dying.
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I hope to never have one of those moments, but the keyword is hope. It can happen to me -- hopefully I'll be able to post about it one day instead of someone else posting about it for me posthumously.
 
Apache123 said:
I hope to never have one of those moments, but the keyword is hope. It can happen to me -- hopefully I'll be able to post about it one day instead of someone else posting about it for me posthumously.
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You just keep trying and see if you can pull it out your ass.
 
As I mentioned a few days ago - last week I was flying through clouds where outside was +2 and inside was -2 and sometimes 0 and I was picking up rain, then some rime, then rain which melted the rime, then that misty kind of drizzle then it was frozen, then it melted -

Finally got the descent to 4000 and out of 4700 it was all just water. . .
 
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