Blizzard Flying

[vontresc]

While shoveling my car out of the snow today I heard a couple of jets take off from the Madison airport. This got me to thinking. How much is the take off performance affected when taking off in a snow storm? Does the snow you are sucking into the engines, and all that bleed air for the anti ice affect performance?

Just curious.

 

[Everskyward]

While shoveling my car out of the snow today I heard a couple of jets take off from the Madison airport. This got me to thinking. How much is the take off performance affected when taking off in a snow storm? Does the snow you are sucking into the engines, and all that bleed air for the anti ice affect performance?

Having the engine anti-ice and the wing and stab anti-ice on affects performance since it robs bleed air from the engine, so that factor decreases performance and increases the runway length required. It also decreases the climb performance which could be limiting. Runway length required also increases a lot if there is snow on the runway (whether it is currently snowing or not) because of the increased stopping distance in the event of an aborted takeoff.

 

[Ted]

From a practical perspective, how much power does having the engine/wing/stab anti-ice on rob? Like what sort of changes in runway required and climb rate would you have? I guess I always think of jets as having so much power it'd be imperceptible, but I'm not a jet pilot, and I have no idea how much air/power those systems rob.

 

[EvilEagle]

I would imagine that it depends on the the jet. When we turn it on in the Eagle, you don't even notice. Still climbs at ~6k'/min.

 

[nddons]

While shoveling my car out of the snow today I heard a couple of jets take off from the Madison airport. This got me to thinking. How much is the take off performance affected when taking off in a snow storm? Does the snow you are sucking into the engines, and all that bleed air for the anti ice affect performance?

Just curious.

Were those jets as in business/commercial, or as in WI ANG F-16 jets? Just curious as well.

I hope you were able to dig it out - I heard Madison got 18" of snow! We only got about 10" in western Waukesha county.

While spending 4 quality hours with my snowblower this morning, I heard two formations of geese flying IFR. Pretty impressive, and something to think about when flying IFR myself, not that there's much I could do about it.

 

[wpierce]

Not really an answer to your question but an interesting aside...

I was in the jump seat of one of our company Dassault Falcon jets coming in to land and we were going to enter some clouds so they put the de-icers on. It felt like someone had stepped on a brake pedal.

 

[Everskyward]

From a practical perspective, how much power does having the engine/wing/stab anti-ice on rob? Like what sort of changes in runway required and climb rate would you have? I guess I always think of jets as having so much power it'd be imperceptible, but I'm not a jet pilot, and I have no idea how much air/power those systems rob.

I would imagine that it depends on the the jet.

Definitely! But I will give a "for instance" example for the "Twin Cessna" 680 since that is what I fly now. Someone else might be able to give another example.

I'll start out with my home field, KAPA which is 5885 MSL. We'll say the altimeter is standard and the temperature is -10C with no wind. I'll use the maximum takeoff weight which is 30,300 lbs. With the runway dry and anti-ice off the takeoff field length required is 4584 feet with a second segment climb of 6.4%. If you turn the engine/wing/stab anti-ice on the takeoff field length increases to 4596 (not much difference) but the second segment climb decreases to 5.3%. That is actually pretty good compared to other airplanes of this class.

If you have compact snow on the runway the takeoff field length required increases to 5950 feet, .2" of slush or wet snow increases it to 7050 feet and wet ice increases it to 10450. This is mostly due to the increased stopping distance rather than much increase in takeoff distance although slush or wet snow will also slow the acceleration.

I know someone is going to ask about second segment climb so I am being proactive and providing this link.

http://books.google.com/books?id=m5...resnum=9&ved=0CD0Q6AEwCA#v=onepage&q=&f=false

 

[Ted]

I know someone is going to ask about second segment climb so I am being proactive and providing this link.

You know me so well, seeing as I was going to ask about that.

Thanks for the info, Mari, that puts some numbers to it. Very interesting!

 

[wabower]

A 5 to 6% climb gradient might sound pretty good until you do the math and realize it means 300' to 360' climb per nautical mile (6,000'). As anybody who's done it (in the sim or in the airplane) will testify, it doesn't feel like you're gaining much when you're skipping off across the prairie, or across the bay after departing KSFO with the Golden Gate bridge coming up as the lowest point on the horizon.

 

[Skip Miller]

I knew a pilot of a Fokker F-100 commercial airliner (aka the Barbie Dream Jet) who called the anti-ice system the "anti-climb device".

-Skip

 

[Everskyward]

As anybody who's done it (in the sim or in the airplane) will testify, it doesn't feel like you're gaining much when you're skipping off across the prairie, or across the bay after departing KSFO with the Golden Gate bridge coming up as the lowest point on the horizon.

You could always just fly under it.

 

[Let'sgoflying!]

ref: CE 525, Williams FJ44 high bypass turbofan engines:

-Snow into the engine, affecting its power - none listed in manual. I can't imagine any effect. Very heavy rain, perhaps. I don't think snow has the mass.
-Bleed air affecting power and both TO/Climb performance
With anti-ice on, our BFL goes up by about 50%. We only have to reduce power by about 5% N1 fan speed in the climb ie from 95% to 90%, so climb is not obviously different. However, most of our performance charts are based upon SE ops. Our second segment climb drops from 6.2 to 5.7%, the first with no bleed air, the second with full anti-ice.

-bleed air as an air brake: We do not notice any change in noise or feel or pitch etc when the full anti-ice/deice is going. However, in order to keep these things running we require >70% N2 (turbine speed). So we find that descending into icing conditions, sometimes we have to ADD power to penetrate the cloud deck - and to make it down with power on, we might have to throw out the boards (speedbrakes)- there is your feel of "stepping on the brake pedal" when anti ice is used, in this airplane anyway.

-contaminated runway really affects BFL.. The chart says a bfl of 2200' for dry pavement goes to 4250' with compacted snow, to 6300' with 1/8" water (things are better with more water,surprisingly) and zooms 15000' with wet ice!

(I am really tired so hope I read the charts correctly!)

 

[wabower]

If you're willing to bet the work crews don't have the cables hanging down.

Everskyward;527519]You could always just fly under it. [/quote]