Temperatures and Icing

[Magnum]

KSMooniacs post in the OAT thread got me thinking about OAT and icing. He said that he likes to know the exact OAT up to 1dF accuracy.

My IR is only two months old and I have no icing experience at all. I always thought that visible moisture below freezing level is not good. But is it also possible to be just above freezing level (lets say 1-2dC) and still pick up ice? E.g. if the airframe temperature is below freezing (due to a longer flight in colder temperatures)? Or is it negligible as only a little bit of ice will be picked up and acts as a temperature insulation?

How about supercooled rain drops when flying above freezing level? I could imagine that the rain cools the airframe below freezing level and will stick to it.

I was told that the Mooney wing picks up ice better than other wings, so I am very interested in your experiences. 

[calavi]

Personally I have never picked up ice yet but I have been told if that the OAT is 5 Celcius your airframe temperature will be well below freezing. Assuming your in visible moisture ice will accumulate. Keep in mind the mooney wing as a Laminar airfoil. So it doesnt take alot of ice to lose lift, because of the thin layers of air used to produce lift. Especially if your getting clear ice or freezing rain.

[jlunseth]

I picked up a little last summer.  We were in an interesting situation, my IFR course took us right under the edge of a front (we were at 17k and the front was several thou. above us) with severe clear to the north and also below us to the ground, and warm temps nearer to the ground (because it was summer).  So we let it build just a little to see what the effect would be, it was light rime or light mixed and did not build very fast.  Did not take much to drop the airspeed ten knots.  We requested a deviation, altered course a mile or two north, and it sublimated in a matter of minutes.  I would not say the wing picked up ice fast, but then there may not have been alot of ice to pick up in those circumstances.  We have also been in the 20's and flown through clouds not picking up ice, because the clouds were made of ice crystals.  Beautiful to see.  Millions of tiny glistening crystals in the air. I have been in light clouds many times up in the teens and low 20's with no ice because the temps are too low.

There are lots of reasons ice can form at temps above zero.  One reason is that lift is created in part by the air on the upper surface of the wing going faster than that on the bottom, and therefore there is less pressure.  What do the gas laws say about a reduction in pressure?  Temp goes down.  So the air on the wing (if you want to keep moving and generate lift), is going to be cooler than ambient.  Just like the venturi effect.  Also, you could have supercooled droplets falling from a higher altitude that have not warmed above freezing.  The "ice" window starts about 5 degrees above zero C.   

[Parker_Woodruff]

Yup.  I've picked up trace amounts of ice at 35 degrees indicated in the cabin.  I was in the 172 looking up at the under side of the wing.

[Magnum]

Thanks for your info. So the "ice window" starts at approx. 5dC. At what temperature do usually ice cristals form? I heard something around -15 to -20dC.

[GeorgePerry]

5 deg C to -15 deg c OAT is the danger zone. 

Icing of all types can and will occur if the atmospherics are right.  Your best defense against ice is to avoid visible moisture if possible when in this temp zone.  If that isn't practical, keep a close eye on your leading edges.  If you see any accumulation, you must do something to stop the accumulation.  (decend, turn around etc).  continuing on in hopes of "popping out" is where pilots go wrong. 

fly safe...

[Magnum]

As my leading edges are white, does it make sense to put on a stripe of black tape so that traces of ice are easier to see?

[KSMooniac]

You'll very likely be able to see the ice easily enough with white wings, or at least that has been my experience with just a little bit of ice accretion so far.  The stall strips break up the view enough IMO to make it fairly visible.  It also forms on the windscreen, which of course is very visible!  You mentioned supercooled droplets, which are very, very dangerous as it can "run back" and freeze all over the surfaces and add a lot of weight and disrupt the aero performance in a hurry, which is a double-whammy.  All airplanes should steer clear of that at all times!

At night I've put a flashlight against my side window and turned it on to view the leading edges and that works pretty well as a substitute "ice light."  The newest Mooneys with FIKI have a built-in ice light on the fuselage to illuminate the wings.

[Magnum]

Thanks again for all the info. Now I know that icing can happen above freezing levels, all the literature I've read so far said 0dC or below (only AOPA ASF mentioned "around freezing level")

[unicom]

Hi guys,

Just wanted to add my little contribution on that matter (I fly a 1980 mooney M20J)...

I flew 2 days ago from Paris to London. I picked up about 3/4 of an inch of cristal clear ice on the leading edge. Certainly not my intention as it was due to very poor weather forecast.

Conditions: -2°C / 2people on board / half tank/ 3 blades MT prop

What I can tell you is that:

1. accretion goes really fast - it took no more than 2 minutes in this case.

2. The windshied picks ice even faster than the leading edge.

3. When you pop out of the clouds - in blue sky - It will take an anormous amount of time for the ice to melt if you are still in negative temperatures.

4. My wings are snow white and I confirm, no problem to see the ice building up - especially when you see the little triangle (vortex generator) on the leading edge disappearing underneath the ice.

5. When you return in positive temperature, the ice on the windshield melts very fast, it takes a little bit more time for the wings...

Conclusion:

- Don't go in icing conditions as the mooney wing profile as a tendency to pick up ice rapidly but the good news is...don't panic as this good aicraft will still fly !!!

- suprisingly enough I did not notice any weird behaviour of the aircraft  (I didn't try to go below 100kt indicated) ...certainly I lost a few knots but no more...

- I had more ice on the right wing - could that be due to the prop effect ???

- No problem with the prop which is no de-iced.

I hope this return of experience will help...

Philippe

 

[fantom]

6. If you have the factory optional windshield blower, don't count on it doing any good with ice. It won't.

[eldeano]

Just another kind of unrelated side note:  This mooney is my first real low wing experience, and I was surprised by how much ice I picked up on the wings by taxing through puddles in cold temps. I to have white wings, but it is not hard to see the ice.  I actually had to turn back and have my wings deiced in Elmira NY after I failed to avoid puddles when taxing, and build up enough ice to be concerned.  Temps were above freezing, but my airframe was not.

[FullyArticulate]

A cross country back in January between Billings and Spokane was -20' C. I was between layers, but occasionally would go through a cloud for a few seconds. By the time I landed, I had 1/2" on the leading edge of rime. It came off in long strips that were fun to play with on the ground.

I was taught -20 was too low for icing, but I definitely collected it. If I weren't in between layers, there's no way I could have completed that flight (or gone for more than 15 miles or so).

 

[BorealOne]

I've picked up ice at temps in -35C OAT climbing through stratus layers near the Great Lakes and Hudson Bay. If the atmospheric conditions are right, icing is a possibility. Temperature + cloud type is likely to be a better indicator of icing risk than temperature alone. 

[jetdriven]

if its +10c  TAT to -40C  SAT and visible moisture, it is considered icing conditions. I have seen ice from +5 all the way down to -40 in turboprops and jets.  It doenst  take much ice to bring down a Mooney, and just a little more to bring down a known ice piston twin.  Me?  My Mooney stays on the ground if I cant avoid these conditions.

[jlunseth]

The +10, is that for jets?  I could see that happening if there is some kind of venturi effect at play, such as air moving over the wings at such speed that the pressure on top of the wing drops signficantly.  Sort of like carb ice, which can happen at very warm temps.  Doesn't make sense to me though that ice would form at +10 C unless there is something else going on, like a cold airframe or a pressure drop, that's pretty warm.

[donshapansky]

I recently flew back from UT to TX at 17,500' and started to pick-up rime at very low rate, I immediately decended to 15,500 and stayed in the clear. The accumulation stayed on until 8 C and 9000', that's the second time I have seen ice stay on at well above freezing temps. I think the airfoil and forward speed has something to do with it. 

[bnicolette]

A good review for those of us in the cold country.  Probably most have seen this but it's always good to see it again.  A bit corny (reminds me of the King School tapes), but tolerable.

[jetdriven]

The aerodynamic cooling effect comes into play but how accurate is your thermometer?

[jlunseth]

I have picked up a small amount of ice twice now.  Both times were benign, there was an easy escape.  I have noticed a few things.  First, the speed loss is significant, 10-15 knots with only a slight rime build-up on the wing leading edge.  I don't think I would want to build up much.

Second, ice is where you find it.  We did one long trip with a fuel stop this summer, so two climb outs, both through a thick layer of stratus-type rain clods.  In both cases we had water streaming over the wings in temps a few degrees below freezing.  There was an inversion, and the temps went up 6-9 dC when we broke through the layer.  Maybe that prevented freezing in the clouds, don't know, but we got no ice.

I have not seen ice in temps below -20 C but I am sure it can happen.  The trick is to look at the clouds, if they have sharp edges (even if irregular) they are wet and may have ice.  If the edges are fuzzy and blown out, that is ice crystals.  Even in crystals it is possible to get induction icing in any engine.  The crystals plug the air filter, and switching to the alt. air may be necessary.  Have seen that happen once in the flight levels.

[donshapansky]

I have dual temp units, the Mooney original and the EDM 930, which is more accurate by quite a bit!

[aerobat95]

Quote: jlunseth

Even in crystals it is possible to get induction icing in any engine.  The crystals plug the air filter, and switching to the alt. air may be necessary.  Have seen that happen once in the flight levels.

[Ron McBride]

Sorry dumb question, in a Mooney is the ram air the alternate air?

In my 69F, the alternate air is a spring loaded door located in the lower cowl, inside. It only opens when the vacuum is to great, hopefully only when the airfilter is clogged with ice. It pulls warmer air from inside the cowling. Do not open your ram air in ice, it can damage the fuel servo, and may restrict the air flow into the engine.

I do not Know about J's etc.  An E is probably the same.   C's and G's should have carburator heat.

Ron

[jetdriven]

I have read somewhere that when tthe ram air is open in icing conditions, ice blocks the impact tubes in the throttle body, which shuts off the fuel. It can happen sunddenly and the only cure is descending into warmer air (ram air on at that time) to melt the ice. 

[unicom]

As winter is slowly settling down, I had the very unpleasant experience to pick up about 1" of ice during a flight from Paris to Geneva 2 weeks ago. That already happened to me 18 months ago (see post above) but I can hardly get used to it... 15 kts speed loss and high ground ask for some sort of rapid solution !

I had the pleasure to meet Margrit Waltz 2 years ago in Greenland as I was returning from Kerrville. She is a very famous ferry pilot with a world record of +700 transatlantic crossing, a vast majority of them on Mooneys as she has been ferry pilot for the company for many years.

As I was wondering how she managed to cope with icing conditions during all these years, I started to search the web hoping to get some kind of advice from her huge experience. I found this article that I wanted to share with you to get some feedback:

http://www.mooneyevents.com/waltz.html

'When asked about a Mooney’s performance in the icing conditions common to the North Atlantic from September to May, Waltz said that there is a speed drop when the first inch of ice goes on the wing -- but that the Mooney speeds up again as the ice progresses further on the aircraft profile. She presumes that it is because the laminar airflow is restored on the Mooney and noted that the speed resumption does not occur on thicker wings like the Baron or Bonanza.'

As anybody ever experienced that ?

Cheers,

Philippe