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We picked up rime ice.

pierre smith

pierre smith

Well Known Member
IFR in IMC to Beaufort, S.C. yesterday, we picked up rime ice in the clouds, transitioning from 4,000' to 7,000'. It was 22 deg OAT, so I figured that any moisture would be frozen.....not so, it froze on the windshield and leading edges. We kept an eye on it and stayed above the clouds, noting the loss of 12 MPH..probably the landing gear and tailfeathers were also iced up.

Do super-cooled droplets stay liquid that cold? Apparently so.

Best,
 
Pierre, once on top and no longer adding to the problem, did the ice sublimate or did it stay for most of the flight?
 
pierre smith said:
IFR in IMC to Beaufort, S.C. yesterday, we picked up rime ice in the clouds, transitioning from 4,000' to 7,000'. It was 22 deg OAT, so I figured that any moisture would be frozen.....not so,..
Click to expand...

I guess that must be a 22 F. Prime icing temperature there and it can occur down below 0 F.
 
Yeah Pierre,
The weather north of you in NC yesterday was just good enough that I could go VFR and stay out of the clouds for just the reason you state. It was snowing at surface but I still didn't trust the clouds.
 
I picked up some ice last week in the bonanza on a trip to HSV. It was 26 deg F in a layer from 4-7000, I got on top in the clear and the ice did sublimate. I was surprised that the moisture was not frozen. Being from the southeast, I am afraid of ice and try my best to avoid it. Therefore, I have little experience in dealing with it.
 
Nope

humptybump said:
Pierre, once on top and no longer adding to the problem, did the ice sublimate or did it stay for most of the flight?
Click to expand...
No, it stayed on, about 3/8" thick and about covered the leading edge for a couple of inches. We descended quickly, to avoid picking up more ice and it came off kinda quickly once the temps got around 36 F.

Best,
 
I've picked up ice I a very wide range of temps at lower altitudes. Most all aircraft I have flown have the limitation of anytime TAT is 10c or below anti-ice systems must be selected on.

Just the other day at +13 I didn't select anti-ice and experienced what you did Pierre, ICE! And guess what happens next? The temp went up 1 degree and the airplane started yelling at me because it was to hot for anti-ice :mad:

The one aircraft I remember was a Challenger where they indicated in the AFM at altitudes above FL210(i think that was the altitude...give or take a thousand ft) anti ice was not needed due to the ice being crystals. While other aircraft don't state that and therefore must be used.

I know I am not talking RV's, but your experience is a great one to pass along to all of us while flying without anti-ice systems.

Flying in icing, departing in areas of frost...these are great topics to review and respect! Great Post!
 
pierre smith said:
Do super-cooled droplets stay liquid that cold? Apparently so.

Best,
Click to expand...

22F is not supercooled, and the way I understand it, if you saw it on the leading edge of these airfoils, your tail most likely had a pretty decent layer growing, search around and there is an inflight portrait of someone with quite a bit of ice on his tail
 
This comes from AC 00-6A, Aviation Weather

SUPERCOOLED WATER
Water droplets colder than 0 C are
supercooled. When they strike an exposed object,
the impact induces freezing. Impact freezing of
supercooled water can result in aircraft icing.
Supercooled water drops very often are in abundance
in clouds at temperatures between 0 C and
-15 C with decreasing amounts at colder temperatures.
Usually, at temperatures colder than
-15 C, sublimation is prevalent; and clouds and
fog may be mostly ice crystals with a lesser amount
of supercooled water. However, strong vertical
currents may carry supercooled water to great
heights where temperatures are much colder than
-15 C. Supercooled water has been observed at
temperatures colder than -40 C.
 
bruceg said:
This comes from AC 00-6A, Aviation Weather

SUPERCOOLED WATER
Water droplets colder than 0 C are
supercooled. When they strike an exposed object,
the impact induces freezing. Impact freezing of
supercooled water can result in aircraft icing.
Supercooled water drops very often are in abundance
in clouds at temperatures between 0 C and
-15 C with decreasing amounts at colder temperatures.
Usually, at temperatures colder than
-15 C, sublimation is prevalent; and clouds and
fog may be mostly ice crystals with a lesser amount
of supercooled water. However, strong vertical
currents may carry supercooled water to great
heights where temperatures are much colder than
-15 C. Supercooled water has been observed at
temperatures colder than -40 C.
Click to expand...

interesting, i was thinking supercooled was defined as extremely negative temperatures, never thought about the technical definition, learn something everyday!
 
Yes, what we've been taught generally about the freezing point of water is not too accurate. Zero C or 32 F is the freezing point of water that contains imperfections, such as dust or smaller particles, such as smoke or minerals. Without a nucleation (freezing initiation point) site, it doesn't freeze until much colder. It is also more difficult to get droplets to condense in the air without these nucleation sites. At least this is what I understand...
 
Live and learn. I mentioned the standard adiabatic lapse rate to my wife and said that I hope we don't accumulate ice but that we may. It was 46 deg F on the ground, so 7,000' would yield around 22 deg or so and it was spot on.

I figured that any moisture would be ice crystals but not so. Quite a few guys on here have posted that super-cooled water droplets can be much colder and when they impact a wing below freezing temperatures, they freeze instantly. I read all that during primary training but seeing it firsthand is a valuable lesson.

We didn't carry a big load of ice but did lose 12 MPH TAS...so the rest of the plane probably iced as well. After we landed, water was dripping off the wheelpants and gear fairings, so they had to have been iced as well.

The control response remained the same and, as usual, the -10 was quite impressive. During the trip home today, I told the wife that we're not going into those clouds again:) and stayed at 3,500', below them. We were showing 32 deg. F at that altitude.

Ice doesn't necessarily need to ground you but you have to be sure of a way out. I'm speaking to the IFR crowd here because it could have been nasty.

A concern was losing airspeed indications because I don't have a heated pitot. GPS can suffice but rest assured, the next annual will include installing one.

After the trip home fron Key West, in green and yellow bands of rain, my confidence level in the Trutrak system and the -10 has grown proportionately and marvel at this airplane's capabilities and utility, but nevertheless, realize my limits and comfort zone which I'm expanding at a calculated rate.

I'd suggest to you guys without an instrument rating, to put it on your bucket list. Your RV can be so much more useful and do trips when other guys are staring at the clouds and a little precip....and it could save your life!

Best,
 
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As I recall, anti-ice was required between 0 and -20?C when I did this for a living. That would be from 32 down to -4F, Pierre.

It appears you were in a prime icing temperature range.
 
Heated pitot not required in the US.
Alex is correct about needing nucleation sites. This is the operating principle for many older sub atomic particle detectors (cloud chambers, bubble chambers).

As I recall the AirFrance airbus that crashed in the south Atlantic encountered icing at very cold temperatures (-30C? -40C? I need to look it up) although this may have been ice crystals clogging the tube, as opposed to liquid water freezing (?).

Pierre, do I recall that you use a Dynon efis system? If so it is important that you have it connected to your GPS and have updated your software in the past year or two. Without that newer software and a gps ground speed, it is my understanding that the Dynon can lose its attitude reference solution in the event of pitot icing.
 
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Yesterday (3/2/13) I made a short flight below a 2100 AGL cloud deck 30 miles North of Detroit. Visibility was >30 I could see downtown DET easily. I was testing a new prop. When I landed, the wings had a spattering of rime ice crystals on the LE. OAT was 20F. Apparently the air wasn't as clear as it appeared :eek: There were snow showers in the area, but none where I was flying. Supercooled water droplets are pretty clear!
 
Thanks..

BobTurner said:
.....
Pierre, do I recall that you use a Dynon efis system? If so it is important that you have it connected to your GPS and have updated your software in the past year or two. Without that newer software and a gps ground speed, it is my understanding that the Dynon can lose its attitude reference solution in the event of pitot icing.
Click to expand...

Yes, I have a D-100/D120 and they do "talk" to my 430W. I also have an ADI 2 as attitude backup.

There's quite a bit of winter left yet guys, so be very careful. Amazingly, it's 26 deg F here in central Georgia this morning and we have wheat to fertilize with granules, so we'll be getting frost off as well.

Best,
 
pierre smith said:
There's quite a bit of winter left yet guys, so be very careful.
Click to expand...

Pierre,

I'm surprised, if you had ice in various spots on the airframe, that your fuel vents didn't ice up too. Can you speculate as to why you didn't have problems with the vents icing up? Do you have larger 3/8" vent lines, NACA vents, fairings over the vents, or what?
 
Nope

Mike, the vents are the standard Van's vents with no fairings and they may well have had some ice on them....another reason to avoid ice!

Fortunately, we only stayed up at 7,000' for 20 minutes or so and let down into warmer air. Might never know just how much of a bullet we dodged:eek:

Best,
 
BobTurner said:
Hi Dave,
I'll bet you can't quote an FAR that says this.
Bob
Click to expand...
14CFR 91.9(a)
14CFR 91.13(a)
14CFR 91.103

Prohibited may be a bit strong. Can't directly for Part 91 operations ... but here is how it works...
The aircraft would have to be demonstrated to meet these requirements:
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2023.1419-2D/$FILE/AC23-1419-2D.pdf
and be properly identified in the POH.

Otherwise you'd have to beat case law like Administrator v. Curtis. Not likely.
Others have been there ...

"The discretion afforded to and, indeed, demanded of a pilot operating under Part 91 has limits.

When operating under Part 91, you cannot exercise that discretion carelessly or recklessly, lest you violate FAR 91.13. If you exercise poor judgment and fly into icing conditions which you knew or should have known about based upon all of the information available to you, you are likely to be sanctioned if discovered."

http://www.aerolegalservices.com/Articles/Known Icing Conditions.shtml

http://www.aerolegalservices.com/Articles/Known Icing Conditions 2009-02-25.shtml

http://download.aopa.org/epilot/2009/090126icing.pdf

http://www.faa.gov/regulations_poli....cfm/go/document.information/documentID/74471

http://www.faa.gov/other_visit/avia...afety/safo/all_safos/media/2008/SAFO08006.pdf

http://www.ehfc.net/KnownIcingConditions.pdf

http://lists.kjsl.com/pipermail/beech-owners/2007-April/028341.html
 
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pierre smith said:
Mike, the vents are the standard Van's vents with no fairings and they may well have had some ice on them....another reason to avoid ice!
Click to expand...
Now that could be REALLY bad :eek:
In RvAiator there is a photo of an RV that had a plugged fuel vent ... tank destroyed.

One would hope that there is enough heat from the cowl to keep it warm enough. Maybe a hole in front of the vents is in order...
 
Dave,
You answered correctly but as you noted the word icing isn't mentioned by name. 91.103 doesn't mention it. Most enforcement actions cite 91.9 since normally certified aircraft since the early 1970's have a POH that says "flight in icing prohibited". But my operating limitations contain no such statement. That leaves 91.13, the 'careless and reckless' clause that the FAA falls back on when they are unhappy. In a flight like this, where light icing was encountered but the flight was safely completed in an uneventful manner, it would be a stretch to call it careless or reckless.

So as far as I can determine flight in known icing is not prohibited for E-AB aircraft, as long as it does not get to a careless and reckless condition.

Bob
 
MauiLvrs said:
Would have to be on both to keep from collapsing the tank ... No?
Cabin heat alone may not be enough...
Click to expand...

How do you collapse an aluminum tank?
What am I missing here? :confused:

The weather has really been screwy here in the south this winter. Snow one day and then 65 degrees two days later.
 
Really?

BobTurner said:
So as far as I can determine flight in known icing is not prohibited for E-AB aircraft, as long as it does not get to a careless and reckless condition.

Bob
Click to expand...

Right, flying your RV into known icing is neither careless, nor reckless?
 
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I meant to use common sense. The FAA itself defines "trace icing" as not being hazardous to unprotected aircraft, if exposed less than an hour. So yes, if I had a recent pirep of trace icing in a layer I was going to climb thru, I would not consider it reckless to proceed. I have great respect for ice, and have cancelled flights because I saw no safe retreat should ice be encountered. But with proper cautions I don't think you need to cancel each and every flight where a chance of icing is forecast.
 
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JDanno said:
How do you collapse an aluminum tank?
What am I missing here?
Click to expand...

If I stood on one foot between my fuel tank ribs, I am pretty sure 225 lbs would cave .032". Our mechanical fuel pumps are capable of pulling our tanks in with this much force over the area between the ribs if the vent gets clogged with ice or mud daubers nest.
 
Good Airfoil!

Well, it was not on the list of design requirements, but I am comforted and pleased to hear that the RV-10 airfoil works ok with ice on it. I did design it to achieve a modest amount of laminar flow at cruise condition with the flap at -3, and I'm sure part of your 12kt loss is from loss of laminar flow on the wing.

I suspect that fuel vents are warmed enough by the exhaust flow to prevent icing, but I don't really know that for sure.
 
BobTurner said:
So as far as I can determine flight in known icing is not prohibited for E-AB aircraft, as long as it does not get to a careless and reckless condition.Bob
Click to expand...
Bob,
While I agree with this ... after one reads a dozen or two


Wayne Gillispie said:
Our mechanical fuel pumps are capable of pulling our tanks in with this much force over the area between the ribs if the vent gets clogged with ... mud daubers nest.
Click to expand...
That's what collapsed the RV8 tank.
 
Dave,
Yes, I'm sorry I brought it up. Too many misinterpretations. I just wanted to point out that the FARs do not explicitly prohibit it, just as the FARs don't say not to fly in thunderstorms. Just use some common sense. I think the key is to have a plan, and do something, even if that's a 180, if you encounter ice. Most of the pilots who get into icing trouble are those who just continued on, doing nothing.
Bob
 
BobTurner said:
So as far as I can determine flight in known icing is not prohibited for E-AB aircraft, as long as it does not get to a careless and reckless condition.Bob
Click to expand...
Bob,
I wrote our POH the same way. While I agree with what you say ... after one reads a dozen or two FAA cases, I probably wouldn't expect them to see it that way should there be an incident. They may likely decide that as permitted isn't specified then it's prohibited.

In any case, it is nice to have some performance data points.

Wayne Gillispie said:
Our mechanical fuel pumps are capable of pulling our tanks in with this much force over the area between the ribs if the vent gets clogged with ... mud daubers nest.
Click to expand...
That's what collapsed the RV8 tank.
 
scsmith said:
Well, it was not on the list of design requirements, but I am comforted and pleased to hear that the RV-10 airfoil works ok with ice on it. I did design it to achieve a modest amount of laminar flow at cruise condition with the flap at -3, and I'm sure part of your 12kt loss is from loss of laminar flow on the wing.

I suspect that fuel vents are warmed enough by the exhaust flow to prevent icing, but I don't really know that for sure.
Click to expand...

Steve,

The fuel vents on the 10 aren't on the belly, like other RV models. The plans call for them to be coming out the wing root fairings, but several people have re-routed them to prevent fume build-up. I'm thinking a NACA vent could help prevent problems from ice, but might promote problems with critters. Has anyone gone with 3/8" vents instead of 1/4" on the RV10 to add safety margin. FWIW, I like the idea of the inline check valve, but wonder how well you can control the pressure differential that opens or closes it. Wayne or anybody, can you give me the type of check valve you used (i.e. part # * Pictures)? Thanks.

Mike
 
I did slip a short piece of 3/8" alum tube over the 1/4" vent tube and prosealed in place. I installed an oval piece of screen over fwd facing slant cut to prevent mud dauber nesting.

Here was my choice for check valve...

http://www.mcmaster.com/#7775K51

Or for high dollar swing check valve like our Airflow boost pumps have in them...

http://www.parker.com/portal/site/P...00+SERIES+SWING+CHECK+VALVE+FOR+LIQUID+OR+GAS

and tee fitting...

http://www.aircraftspruce.com/catalog/hapages/an825.php

or...

http://www.aircraftspruce.com/catalog/hapages/an826.php
 
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Alternate vent

Wayne, if I understand this correctly you are providing an "Alternate Vent" which will open via the check valve if the primary vent gets plugged. Where do you route the alternate vent to prevent it from icing? Do you leave it in the wing root?
 
Wayne,

Thanks for the good info and links to the parts. I'm assuming then, that the check valve wouldn't work below 10 deg F, but your assumption is that below 10 degrees (in the wing root), there likely won't be icing outside because it's too cold (i.e. water's already frozen in the air)?
 
I believe the 10 F limit is on the O ring seal. So on cold days it will still open, but might not seal as well as it should when closed. e.g., if you refuel on a cold day and overfill the tank, some of the excess may drip into the wing root area instead of out the external vent. And this can be avoided or minimized by orienting the line to the check valve upwards, as shown in the reference above.
 
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3/8" lines??

I've been wondering why Vans calls for 1/4" vent lines when the fuel system pumps fuel away in 3/8" lines, which seemingly would impart a negatvie pressure on the tank, even if the vents aren't clogged. Any thoughts from you engineers? Dan, you listening?:)
 
I am not an engineer but wish I was. Too old(42)to go back to school now.

There are 7.48 gallons in 1 cu ft of gasoline. We remove 25.5 gph(our RV-10 FF at takeoff), which is 0.425 gpm or 3.4 cfh or 0.06 cfm. We breath approx .21 cfm. Take a 1/4" tube that is 1' long and see how you can breath through it. Our fuel tank vent only requires 1/3 as much air during takeoff.

I think it has to do with the viscosity of the fluid, but will let someone else explain that.
 
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