Where does ice first form on an a/c?

Pi1otguy

Pi1otguy

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I fly mainly 172s and have never been in icing conditions, but I've realized that the upper part of the wing SHOULD be coolest part of the plane due to the low pressure "refrigerating" it. And since many cabin heaters also act as windscreen defroster one would be unable to collect ice on the windows until after the top of the wings have some ice. Therefore is it valid to assume that the pilot of a high wing wouldn't see the ice until the wings are throughly contaminated?

Does air fraction provide any meaning full heating on the leading edges, spars, and front of cockpit? Where have you seen ice first collect/form?
 
Ice is usually formed by impact with precip on the leading edges. I've almost never seen it on the upper surfaces in flight unless it's freezing rain running back across the wing. Most rime and clear ice will form on the leading surfaces first...temperature probes (and wind shield wipers) are a great place to look for first signs...especially if the temp probe is built into the windscreen, cause then it's easy to see the ice from your seat. The other good option is just look out at your leading edges (use a flashlight if needed). If there's significant accretion, you'll see it on the leading edges long before it should be causing any problems. This is, assuming, that your upper surfaces were clean before you take off...that's paramount to avoiding problems with icing without flying through clouds or precip.
 
TMetzinger said:
It usually forms on the sharpest leading edges first.
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'Zactly -- least bow wave, most precip getting through. On planes like a C-172, you usually see it first on on the "turkey baster" OAT probe, followed by the wing struts and horizontal stabs.
 
Ron Levy said:
'Zactly -- least bow wave, most precip getting through. On planes like a C-172, you usually see it first on on the "turkey baster" OAT probe, followed by the wing struts and horizontal stabs.
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On a winter flight last year, we were at 9,000 at night in a C-182T. There was no known icing conditions but I still continued to watch the struts.

I've found the step plates mounted on the struts of a Skyhawk to be a good place to also look at night. The leading edge is a good place to start catching ice pretty early.
 
It doesn't take long to form ice on the windscreen with the crappy Cessna defroster on or off. If you fly into some nasty stuff it'll pretty much all happen at the exact same time. One second nothing, two seconds later, you see it piling on everywhere.

Otherwise if it's slow--Keep an eye on the leading edge, OAT as Ron mentions, etc.
 
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once it starts it doesnt take long to build up everywhere else. I also keep an eye on gear legs, steps, and wheelpants in cessnas, easy to look at.
 
What Matthew and Ron said, but it can change or be where it isn't easily seen. I've had ice form on the windscreen and nowhere else when it's been below freezing and I had the defrost or hot plate on. It melted what otherwise wouldn't have stuck.

What worries me most is what I can't see. The leading edge of the horizontal stab seems to get the most, the quickest once ice begins building. If I look back after cycling the boots, the most pops off back there.

As has been said, the first places I see it are on the OAT probe, leading edges and windscreen, but that doesn't mean it isn't already on the horizontal stab., tail, antennas and other places sticking out that aren't as visible from the cockpit.

Best,

Dave
 
I'll tell you from personal experience today -- wing leading edge.

I flew thru some cloud tops at 9000 today, -4c, expecting some ice in those clouds because I could see a nice rainbow around my a/c shadow while above the clouds. Scott Daennstadt doesn't lie (he has a great WX website, and writes columns for IFR). I determined a plan of action (descend to warmer temps, or climb 0.5k-2k to escape the clouds if ATC wouldn't permit a descent), before encountering any ice. It was a relatively thin (maybe 1.5k thick) layer, so I had lots of options. Still, it doesn't take much moisture in freezing condition to generate ice.

No airmet zulu, but lo, the cloud tops did indeed have some ice. Very light rime, but cost me about 8-9ktas even with a very light buildup. I was watching for buildups the whole time, so I was not caught by surprise. I thought I'd be able to see it on the struts (I have a 182) but it was most obvious on the leading edge of the wing. ATC let me go lower without complaint, so it was a non-event for me. Still, it was my first non-supervised (i.e. without experienced right-seat help) icing event in my 360hrs of flight time. I was aware and prepared, so it was a non-event.
 
Dave Siciliano said:
What worries me most is what I can't see. The leading edge of the horizontal stab seems to get the most, the quickest once ice begins building. If I look back after cycling the boots, the most pops off back there.
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I agree with this. Since ice forms first on objects with sharper edges it will form on the leading edges of the horizontal stab before it forms on the leading edges of the wings. Unfortunately I can't see the horizontal stab on any of the airplanes I fly.

I have seen what an inch or two of ice looks like on the unprotected vertical stab after landing though...
 
I wish I remember who produced it (I think it was either NASA or the FAA) but they showed us a great video in training about icing on tail surfaces and the tail stall that can result. I'll try to figure out what it was or where I can find it...quite an eye opener (pull, don't push if you have a tail stall...but you might need some help).
 
Yeah, I've seen that video too, at skool. I'm sure it must be on the internet somewhere though.
 
BINGO! Awsome...that's even better (more recent) than what they showed us.
 
Ron Levy said:
'Zactly -- least bow wave, most precip getting through. On planes like a C-172, you usually see it first on on the "turkey baster" OAT probe, followed by the wing struts and horizontal stabs.
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While I understand the theory behind the expectation that ice will always form on the sharpest leading edge, IME this isn't always the case. The leading edge of the horizontal stab on my Baron is the sharpest forward facing edge I can easily see and more often than not, ice forms on the more blunt main wing first, especially if it's accumulating very slowly.
 
Dave Siciliano said:
What worries me most is what I can't see. The leading edge of the horizontal stab seems to get the most, the quickest once ice begins building. If I look back after cycling the boots, the most pops off back there.

Best,

Dave
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Dave,

Just make sure you look at BOTH horizontal stabs after cycling the boots...I once got to land a Baron with 2" of ice on the right horizontal stab because I was only checking the left side after cycling the boots :eek:

BTW...the ILS was at 135 kts, clean wing. Buffet in the flare at 120, full stall landing, and was setting the nose down through 100 kts.

Fly safe!

David
 
MauleSkinner said:
Dave,

Just make sure you look at BOTH horizontal stabs after cycling the boots...I once got to land a Baron with 2" of ice on the right horizontal stab because I was only checking the left side after cycling the boots :eek:

BTW...the ILS was at 135 kts, clean wing. Buffet in the flare at 120, full stall landing, and was setting the nose down through 100 kts.

Fly safe!

David
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Thanks David! I try, but can't always look back and see both if I'm really busy. Single pilot and the AP gets turned off once I see meaningful ice accumulate; certainly on the approach. I've begun just cycling the boots frequently on the approach as a matter of course. I hear ya and have seen the icing vids. I keep the speed up and really try to pay attention to anything in the control imputs that feels unusual.

Got to play quite a bit this summer in icing in cloud tops in Mr. P Baron. I could climb or descent to get out, but just stayed there for awhile to see how the systems performed and how the plane felt. Gave me a good 'feel' for things on this plane. The horizontal stab. on my plane has a pretty small radius; so, that's what concerns me the most. The tail stall can occur pretty easily on this plane. I'm not disagreeing with anyone, but by the time I get enough visible ice on the front edge of the wing to feel the need to cycle the boots, I've found there is much more on the horizontal stab. even though it may not look like it until I cycle the boots and see what flies off!! Maybe it's perception, but, it keeps my attention!

Best,

Dave
 
So since the OAT & leading edges (wings & h-stab) seem to be the first to get iced does that explain why some aircraft have rubber on the lead edge of the h-stab? Does the rubber somehow delay icing?
 
Pi1otguy said:
So since the OAT & leading edges (wings & h-stab) seem to be the first to get iced does that explain why some aircraft have rubber on the lead edge of the h-stab? Does the rubber somehow delay icing?
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Does it actually have anything to do with ice? If it's just rubber, and not a boot, it could be to protect the leading edge from FOD kicked up by the tires. Just a hypothesis!
 
Pi1otguy said:
So since the OAT & leading edges (wings & h-stab) seem to be the first to get iced does that explain why some aircraft have rubber on the lead edge of the h-stab? Does the rubber somehow delay icing?
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I think what you're seeing is the deicing boot. We spent all day today using our's...I'll try to get some pictures/videos of it in use tomorrow. Basically, all it is is a flexible rubber diaphram with a half dozen or so channels running through it. When you "pop the boots" or "cycle the boots" it shoves high pressure air through the channels thus expanding them about an inch or so; the hope is that any ice that has formed on the boots will get cracked and come off in the air stream. It's a pretty neat system. It's not 100%, but it's a lot better than nothing if you need to be able to get through (or get out of) the ice. Thought it is possible that it's just FOD protection, if the a/c has black rubber on most of its leading surfaces, it's probably deicing boots.
 
Just don't leave the boots on, or the ice will build up over them and render them useless.
 
Bridging. I don't know how other systems work, but ours cycle automatically for that exact reason.
 
For a second I thought I've missed a piece of life saving equipment on the 172's. FOD protection i guess I learn something new each day.
 
I've got the rubber strip on my h-stab. Kept from getting chipped by gravel when the plane used to live in Alaska.
 
We have the rubber "boots" on the H stab on our birds. It's strictly to protect the leading edge from FOD.

On the S-3A, we used a heavy clear tape on the leading edge of the wings as well as the horizontal and vertical stabilizers. It started out clear but ended up more yellow over time. It may have helped drop any ice as well. All those edges used bleed air for deicing.
 
smigaldi said:
Really? I always saw it first on that little step on the wing strut.
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Yeah, I thought that's where I'd see it too. I kept checking, figuring that's where the ice would be visible first, but I never saw any there. It was obvious on the leading edge though.

I'd like to get some of the black anti-chip tape for the struts -- the TR182 I flew out west had it and ice really showed up on it.
 
Collection efficiency is inversely proportional to the radius of the collecting surface, so things with a small radius collect ice first...things like wire antennas, OAT gauges, struts, etc. The leading edge of the horizontal stabilizer will collect ice about three times as fast as the leading edge of the wing, so if you can see ice on the wing you can be sure that the horizontal stab has a head start. Believe me, you don't want the horizontal stab to stop developing lift.

On most airplanes there is a small radius around the edges of the windshield, where the metal piece that hold the "glass" in place meets its surface...that means that ice will begin at the lower edge of the windscreen and creep up. If you fly a low wing, and the gas caps protrude above the wing surface, you will see ice form on their leading edges. And don't forget the prop...it has a very small radius leading edge and just loves ice.

Bob Gardner
 
I thought bridging was an OWT, and that NASA had debunked it?

Cheers,

-Andrew
 
astanley said:
I thought bridging was an OWT, and that NASA had debunked it?

Cheers,

-Andrew
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Andrew, there was a reasonably detailed article on Aviation Online International a few months ago pretty much dispelling the bridging issue on modern booted aircraft. Still, there are times it can occur. The old advise about not cycling boots until there is an inch of ice has pretty much been debunked. Still, I don;t constantly cycle boots. I have a manual system, so, they don't cycle automatically as on some planes. I do cycle the boots as require in cruise and wait until there is about 1/2 inch, but pay attention to other things like handling, airspeed decay and other indicators there may be ice where I can't see. As part of my approach routine; at least look during the approach and after the FAF cycle any time I see any significant accumulation. As has been said, I can't really look back at the horizontal stab. during a single pilot approach when hand flying and that's a big concern; so, almost anything visible on the leading edge and I cycle the boots. Try to cycle them on short final if possible. Keep my speed up if carrying any ice to prevent a tail stall. Didn't think about one side working and not the other; so, I'll start worrying about that now :yes:

Best,

Dave
 
astanley said:
I thought bridging was an OWT, and that NASA had debunked it?

Cheers,

-Andrew
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There is A LOT of argument going on over this, around here too. Personally, I still believe in it. We have auto-cycling boots, but I've see them get cycled, blow ice off, cycle again 5 minutes later with another 1/2 inch + on the wing and nothing. Wait another minute...nothing. We went a half hour the other day, cycling the boots ever 5 minutes, and not blowing anything off. The only difference between the leg in which that happened and the previous leg (when the boots worked as advertised) was that we were in clear ice/freezing rain instead of rime to mixed icing. Best we could tell, the ice had gotten blow off the boot, but was still holding on and accreting aft of the ice protection. As it started to collect new ice, it wasn't forming directly on the boots, so they were, basically useless. We finally got lower and were speed restricted in the decent and the combination of warmer air and change of airflow over the leading edge was enough to peel off a good bit of the ice. I know it's not the textbook definition of bridging, but it's pretty close, and if it can do that, I don't see why bridging is impossible.
 
Teller1900 said:
There is A LOT of argument going on over this, around here too. Personally, I still believe in it. We have auto-cycling boots, but I've see them get cycled, blow ice off, cycle again 5 minutes later with another 1/2 inch + on the wing and nothing. Wait another minute...nothing. We went a half hour the other day, cycling the boots ever 5 minutes, and not blowing anything off. The only difference between the leg in which that happened and the previous leg (when the boots worked as advertised) was that we were in clear ice/freezing rain instead of rime to mixed icing. Best we could tell, the ice had gotten blow off the boot, but was still holding on and accreting aft of the ice protection. As it started to collect new ice, it wasn't forming directly on the boots, so they were, basically useless. We finally got lower and were speed restricted in the decent and the combination of warmer air and change of airflow over the leading edge was enough to peel off a good bit of the ice. I know it's not the textbook definition of bridging, but it's pretty close, and if it can do that, I don't see why bridging is impossible.
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Would you believe David Sweet, from BF Goodrich Aerospace? At an FAA International Conference on Aircraft Inflight Icing that I attended in 1996, he said that their research using modern boots showed that there is no such thing as ice bridging. He explained that back in the 1930's the inflation tubes were much larger in diameter and the inflation pressures were low compared to today's systems, and that those two factors meant it took longer for the tubes to inflate/deflate. No comparison with the small diameter, high inflation pressure systems today. And his company makes the boots.

Full disclosure: He did say that ideally, ice loosened by the inflation cycle will blow off entirely...but in the real world there will be flecks of ice left adhering to the boot between cycles. He did not consider this to be a problem.

Bob Gardner
 
I don't know, I've seen a lot more than "flecks" left on the boots after blowing them (anywhere from a few bits to a few feet to almost the entire boot left covered). I'm not saying he's wrong and it happens or that he's absolutely right and it doesn't, but from my experience, boots are far from perfect and there's definitely something getting left, even if it's not "bridging" by definition.
 
I've seen a lot more than "flecks" left on boots too, although I don't think I've ever seen ice bridging. There are things you can treat the boots with, like ICEX that makes them slick so that ice breaks off cleaner and is less likely to adhere to them when the boots are cycled.

I like bleed air much better. TKS not so much so.
 
Everskyward said:
I like bleed air much better. TKS not so much so.
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Why? I'm just curious what the relative advantages and disadvantages are. It seems TKS would have the advantage of the fluid running back and helping to clear "non-protected" surfaces, but the major disadvantage of having to refill the fluid and the potential for running out of fluid. :hairraise:

I don't know much of anything about bleed air. :no:
 
from what ive heard, TKS is fairly innefective unless it is started before the icing encounter begins. this obviously would cause an issue in an inadvertant icing encounter. only what ive heard though, i have no firsthand knowledge with TKS
 
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