Icing

[dramsey]

I did a search on icing and came back with a few comments related to carb icing but nothing on airframe icing. My curiosity lies in how those fuel cap vents do in inadvertent icing. I am planning on an IFR legal bird. . Im religious about staying out of known ice but have encountered unforecast ice several times in my flying life. I dont really have a concern about the airframe because I act NOW to get out, its just losing my entire fuel supply due to all the fuel caps vents freezing over. If I were that unfortunate, I would be all over the rudder to try to force fuel out the vent and clear the plug. But I may overthinking something thats never happened. Anybody out there willing to share icing experience in a Bearhawk?

My worst personal story was on a training flight for my instrument rating in my old Mooney. The instructor had me file in the clouds. There was no forecast or known icing. We picked up ice at our filed altitude and I requested minimum vectoring altitude to try to get out of the clouds. It did not get us out of the clouds, but I did succeed in slowing/stopping the rather rapid build up ice. I had lost 30 knots in airspeed. I shot the approach into the airport and we got out of the plane. We had 1/2 inch on the leading edge of the wings and 5/8 on the tail. Since that time decades ago I have never picked up more than a trace of ice. Another Mooney pilot years later tested the limits of the airframe picking up 2” on the leading edge all while listening to the stall warning and figuring he was going to die. He snapped photos showing the incredible build up only after he saw it starting to melt off. Okay thats my icing “ice breaker”. Anybody care to share Bearhawk experiences?

[Bcone1381]

A few decades ago gathered 9 winter seasons in turbo prop and piston twins in the Great Lakes area. It's not a Bearhawk. But it's experience, and I believe the ice will indeed plug the fuel cap vent holes. Rime, Mixed or Clear. It will seal it up.

[kestrel]

Generally, any forward facing surface that doesn't have something close in front of it will collect ice. Cessna puts its fuel vents behind the wing strut up near where it attaches to the wing. it gets less dynamic/pitot pressure there, but at least it is less likely to ice up.

[Rollie]

I iced up my Patrol pretty good a few years ago. Once I realized that the droplets on the windshield weren't running off but were frozen, I turned to exit the area and by the time I was in the clear I couldn't see through the windshield. The wing and lift strut leading edges had a little over 1/8" of rime. I don't recall even thinking of the possibility of the fuel vents freezing up, but maybe I did. I flew about 10 minutes to get back to an airport with no issues. On a positive note I learned that my heat system, which diverts some hot air to the windshield, would clear ice off the windshield in just a few minutes- something I never intended to test. Also, since I have no idea just how much the airfoil is impacted by ice, I kept my approach and landing speed higher than usual.

The vents will probably clog with ice given a bit more time, but at least in my case it wasn't immediate.

[rodsmith]

I wonder if drilling some small holes on the horizontal portion of fuel tank vent would prolong the time before you lost fuel flow. With enough icing would probably close up, but you are going to have a lot of other problems as well. Picture of the vents I used with an opening on the under side as well as the front. The front opening has a fine mesh screen which would probably freeze over immediately, the other opening isn't very far back so might not stay open long. My takeaway, immediately exit icing conditions. My only icing experience was on my long instrument training flight between Anchorage and Kodiak in my Maule. No forecast for icing, we started picking up ice at 6000' just south of Homer, initially my instructor wasn't too concerned but shortly decided we needed to get out of it, canceled IFR and descended to 1500' over the ocean. Still below freezing but out of the clouds, did a high speed approach and landing at Kodiak, still had about a half inch of ice on the leading edges.

DSCF2238.jpg

[kestrel]

rodsmith, the picture is a bit fuzzy and quality data would require testing, but in general the non-forward facing ports or portions of ports will reduce the desired pitot pressure.

A streamlined post in front of a forward facing vent will act as an inertial separator. The air will flow around the post and impact/enter the forward facing vent. The water/ice will be forced to the side but won't follow the airstream back behind the post as well as the air does. It isn't perfect and may require testing to get the best advantage but would help. ....as evidenced by Cessna using the strategy.