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We picked up rime ice.

Data

Due to privacy concerns this post is presented as to protect the pilots identity.

Just as a data point.

I know of a pilot who has had some ice build up on a -4, -7a, and 2 different -10 airplanes.

All of the fuel tanks did not collapse and were vented per van design.

The -4 had ice up to 1/4in on it and had no pitot heat. Pitot never froze.

The -7 had ice up to 1/4in on it and had no pitot heat. Pitot froze over and airspeed indcator dropped to -0-. After 5-10min in thawing conditions the airspeed started working.

One of the -10's did not have heated pitot and airspeed never froze over but only had trace ice on that one.

The other -10 had a Dynon heated pitot and has had 1/4in of ice on it. Airspeed has never failed on it.
 
FWIW, I have picked up ice twice on my 7A, once it was for a short duration but the rate was quicker than I had ever expected it. I quickly climbed higher where I would be out of the cloud. The second time, I was in the soup for a long duration as I had not much choice in scaping it but it was not much build up 1/8 or so. My pitot started freezing which my dynon pitot heat took care of it right away but no effect on the air vent to the tank.
 
Thanks for the responses. I guess 1/4" line is far more capable than I thought. Perhaps the ID is small enough to keep bugs out too.
 
Weasel said:
Pitot froze over and airspeed indcator dropped to -0-.
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I just read about how this can happen if the pitot freezes over slowly.

When your pitot gets completely frozen over quickly, it actually traps the pressure inside the tip of the pitot tube. Your airspeed starts to read erroneously, but not zero. As you climb with a frozen pitot, your indicated airspeed will increase. The opposite happens as you descend. You can go on quite a ways and not realize you even have a frozen over pitot tube if you are in straight and level flight.

And when you finally realize what is going on and turn on the pitot heat, the ASI will do things that make your eyes get as big as saucers.
 
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Mile High Relic said:
I just read about how this can happen if the pitot freezes over slowly.

When your pitot gets completely frozen over quickly, it actually traps the pressure inside the tip of the pitot tube. Your airspeed starts to read erroneously, but not zero. As you climb with a frozen pitot, your indicated airspeed will increase. The opposite happens as you descend. You can go on quite a ways and not realize you even have a frozen over pitot tube if you are in straight and level flight.

And when you finally realize what is going on and turn on the pitot heat, the ASI will do things that make your eyes get as big as saucers.
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Correct. and I will add. If it does drop slowly to -0- it probably indicates you have a leak in the pitot tube somewhere
 
Ice at really low temps

In a former life as a CFII I too used to believe that once you got below a certain temp, you were not susceptible to icing... I even explained that to the examiner giving me my CFII rating to which he replied "You seem like a smart, experienced aviator!"

Fast forward a few years, I was holding above Jackson Hole at 15000' for 30-40 minutes in IMC with a temp around -35C (In a twin turboprop equipped with all the icing bells and whistles)- no worries, too cold for ice, right? I noticed my airspeed beginning to drop off and some light rime on the wing- Both my airspeed indicators slowed to 90 knots or so (slightly above stall in this airplane) but the GS was still showing 180.

I diverted to Idaho Falls and shot the ILS down to mins with no airspeed indications (not bragging, but it made for a great job interview story!)- turns out the aircraft had an ingenious design where the heated pitot tube lines route through the unheated forward baggage compartment, which is where the crystals refroze and created the blockage.

1st moral of this story: Even approved, somewhat sophisticated aircraft can get into trouble in any icing

2nd moral of this story: ALWAYS assume that you WILL get ice in visible moisture with temps near the freezing point and below!
 
Dave Bernard said:
...........1st moral of this story: Even approved, somewhat sophisticated aircraft can get into trouble in any icing

2nd moral of this story: ALWAYS assume that you WILL get ice in visible moisture with temps near the freezing point and below!
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Great advice...and thanks. That's why I stayed out of the clouds on the way home.

One other thought...this post has generated quite a bit of participation and confessions of some of you guys on here:)

I, for one, have learned quite a bit and will implement the fuel check valve system and a heated pitot. Aaaah, confession is good for the soul:)

Best,
 
+1 Pierre

This kind of stuff also helps new builds. I will also be utilizing a check valve setup for alternate vent air. I don't plan on flying into icing conditions, but then again, I've never met a pilot who did...
 
Why planes?

Can someone explain why we almost never ice up our vehicles although we drive in visible moisture around and below freezing all the time? (at least up north we do)

The one time I picked up some ice on my -10 it accumulated about 1/8" on the leading edges and a short distance back on every surface facing relative wind, including leg fairings, wheel pants, HS, wings, air inlets. The windshield got a little rime ice but I could see forward OK, no ice on any other windows. Also the first 10-15" out from the spinner on the prop iced up, leading edges only. I could see through the moisture/virga (it was around 31 F) to the airport and had clear air behind so I was confident that I would be OK. I was through it in 5-10 minutes and landed immediately, never noticed any speed or control system changes. Some of the ice stayed on in my unheated hangar for several days.

Just wondering if the science of ice accumulation has to do with pressure drop, pressure increases, or something around those curved surfaces facing into the wind. And/or, does it increase with RV speeds?
 
Icing has little to do with pressure drops. The inertia of the droplets is high enough that it doesn't follow the airflow around the wing, it just goes straight and hits the leading edge.
Icing in cumulus clouds is mostly due to liquid drops at lower, above freezing temperatures, being carried up by updrafts to below freezing temperatures. Clearly that cannot happen on the ground. Also, we live in a dirty world, and most of that dirt is down low. Recall the discussion of nucleation sites? I'd guess that the exhaust from the last car put out enough particulates to prevent super cooled drops from forming.
The truth is that while the 'visible moisture, below freezing' conditions can frequently exist, actual icing is often not there. Which is exactly why there is so much discussion about risk vs benefit.
BTW, While I personally am okay with trace or light icing - if I have a solid gold escape route, and am doing something about it - if I encounter freezing rain I do a 180. The potential rate of accumulation is well beyond my comfort level.
 
PS I have had icing on a car. Years ago (young and stupid) I had a VW with no defroster. I began to get ice on the windshield. My brother cranked open the sunroof (boy was it cold!) and reached out with a long handled ice scraper and de-iced us as went went! Too bad it's not that easy in an airplane.
 
Well, well!

At our EAA meeting today, I was asked about my fuel vents and ice. We looked at the vents and whaddya know....they're slanted backwards!

In other words, the 45 deg taper is on the reverse side, not facing forward to pressurize the tanks...probably had ice on the front side but the rears remained open and allowed venting.

I didn't build this airplane but have never had a fuel delivery issue, so they're staying that way...keeps impacted insects out too.

Best,
 
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