Difference between rain ice and rime ice
 

I thought the answer to the below could be a) or b). Can anyone explain the difference between rime ice and rain ice please?

Upon landing after a flight through light rain above the freezing level, you discover some ice on the surfaces of your aircraft. The ice is cloudy and brittle. Which form of ice is this?
a) Rime ice
b) Rain ice
c) Hoar frost
d) Clear ice

I see that in the last couple of weeks you have posted twelve questions here all related to weather. This isn't learning. I suggest you sit down and discuss the questions with your instructor so you'll understand the answers rather than just asking others to give you those answers.

Better still, go and start learning your way through the textbooks!

G

Fujii, I'm surprised and disappointed by your reply. I have read the Meteorology text book. I've passed the last 9 meteorology tests I've taken on PPLcruiser (see attached). I could probably take the exam now and pass, but I want to understand the answers, which is what most of my threads on here have aimed to do. I disagree that posting questions on here is not learning. I've learnt loads from the replies on here, and they have helped me to understand the answers. I thought that was what this forum was about to be honest.

I love my flight school but unfortunately each time I have gone there with a list of questions, they have been too busy to answer them all. And in some cases, they've said they'll have to take it away and get back to me.

The combination of reading the books, taking PPL Cruiser tests, reading online, and asking on here has been excellent for me. I'm very grateful for the help I've had on here.

Go on ! What's the right answer? Someone tell me

I think that's a really unfair assessment of his questions. He's clearly shown in each post that he's tried to understand why any answers he's come across are incorrect and has clearly come here looking for explanation from the 'experts'. I empathise massively from doing my training when seemingly similar topics would contradict each other (e.g. it took me ages to understand how a high pressure system with descending air could allow high temperatures which ought to create lifting air).

I'm rather with Fuji here.

Trying to understand the topic would involve talking about forms of icing and his understanding of them. Trying to simply pass the test involves posting the questions and asking what the right answer is.

G

Gerard, it looks like you are just trying to do what a lot of people do with multi guess questions. Find the answer and select it without understanding the subject.

In your ice query, the answer is in the question, read it. There two types of airframe icing, rime and clear. As the ice described is cloudy and brittle, it isn't clear. Answers b and c are red herrings.

Mixed ice is sometimes mentioned but that is just what is sounds like, a bit of each.

Maybe you dont get rain ice in Aus but it certainly exists and can be the most severe icing you will get, normally rain ice will be not far below freezing so will be a form of clear ice. Hoar frost is also a real form of airframe icing but is formed by sublimation. For the OP, the colder the moisture the more freezes on impact which forms ice with lots of air in it and is cloudy and brittle and breaks off easily, this is Rime ice and will be from small water droplets as larger ones will not normally stay liquid at colder temperatures. If it is not so cold then only a little freezes on impact, the rest then runs back freezing as it goes and forming a clear solid layer of ice that is hard to remove, this is clear ice.

Foxmouth, from what you have described, rain ice is just another name for clear ice. I haven't come across the term in any met course I have done nor a quick internet search. There are references to freezing rain which forms clear ice on contact with an airframe. Is it a distinct phenomenon or just a description of one way clear ice can form?

Well nobody as yet has told the OP the answer, most likely because they all don't know !


So let's stick my neck out and say it's... A
.

scifi, I reckon I covered it in #8 whilst prompting the OP to read the question which follows most multi guess questions. One correct, one maybe and a couple and a couple to confuse. Had the OP known the definition of rime ice, "cloudy and brittle," it was there in the question.

Scifi, if he cant work that out from the info I gave then he does not deserve to pass!
Fuji, rain ice is a form of clear ice but not the only form of clear ice which can also form from suspended water drops as well as rain. The other thing with rain ice is that you can get it when flying in air that is above zero in the warm sector when flying below a cold front overhang, the rain comes out of the air in the cold sector above you below freezing temp and hits the aircraft that is flying in air that is maybe 1 or 2 degrees above freezing, if you have just descended into the warm sector from above the freezing level the airframe will still be below zero and you can have a real problem! There are some great images of rain ice on Google, most of these are on the ground where the aircraft (and any other structure) is sitting below zero and the surface is below freezing.

foxmouth is correct.

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As for those grumbling about gerard's questions I couldn't agree less with you. Not once has he merely asked for the 'staff answer' - which he invariably knows already. His questions are always about understanding the theory.

I'd echo Oggers there. Sometimes something explained in a different way can make something click if the textbooks aren't working. I enjoy reading these threads too it tests my own understanding at the same time.

From what I recall with icing the size of the droplets is the main difference, small water droplets freeze instantly on impact with the leading edge forming rime ice, whereas larger droplets impact then run back over the wing surface before freezing there as clear ice.

I must admit I could never get my head around 'supercooled water droplets', which do not freeze until contacted by a foreign body.


I can only think it is the same principle as the 'Condensation Nuclii' found in Champagne and fizzy drinks.

scifi, now you've done it, supercooled droplets and condensation nuclei. Just when I was starting to understand chemtrails.

Condensation nuclei in fizzy drinks???? I know how they work in clouds, but not Champagne.


SciFi - ice isn't just very cold water, it's gone through a physical change from a liquid, to a solid with a crystaline structure. Making that change requires energy, and something to kick off the change. So, if you put no loads whatsoever on a drop of water, and keep cooling it, it hasn't had the initiation to create the use of energy and change form. Give it something to latch onto - like a bit of wing it just hit, and that initiates the state change into crystaline solid, which then transmits itself very quickly through the liquid until it's all changed.

You can demonstrate this at home - have a look at this short video...

https://www.youtube.com/watch?v=kEHdyiBMgAg

G

As I have understood it rime ice and clear ice can form in flight. Clear is more dangerous because it can build up very quickly and comes from supercooled water droplets which can be like rain or just suspended.

Rime is often found in cold clouds typically stratus in winter but sometimes cumulus.

Hoar frost is only collected on the ground through sublimation.

Any body want to correct me?

Thanks for the explanations all! :)

fujii, you've learnt something about 'rain ice' from the experience of another pilot on here, as have I. That's one of the benefits I like to get from these threads and I'm glad to see you have too! :)

Thanks for those who agree with me that I am actually trying to further my understanding. Oggers, the irony of the claim that I'm just trying to learn the answer is that if I've pasted a) b) c) d) then PPL Cruiser has already told me 'the answer'. But I want to understand more. I had struggled to find much on rain ice, as fujii has since, and so I came here to ask for explanations and experience. I got both and am grateful!

engineno9, I'm glad the threads provide some benefit to you. I had considered just not posting my questions here any more! You're right that something explained a different way can make something click and pprune has really helped for that.