Do airplanes tend to float when landing in cold weather?

[jliltd]

Scott Black gets an A+. That is one of the most beneficial aspects of our airspeed indicators showing indicated speed. If we always use the same speed on the airspeed indicator no matter the environment, our approach will be equivalently safe. Granted our ground speed will vary. This can be a real gotcha when a pilot used to flying at sea level flies into a high-elevation airport. The pilot's instincts will tell him he is coming in too fast to land even though the airspeed indicator is at the same value. There have been many stall spin accidents in the patterns at mountain airports when a flatlander pilot tries to slow to a speed he is used to sensing rather than nailing the same indicated approach speed used back home. Trust the airspeed indicator despite the trees passing by much faster (or slower) than you are used to. Same exact thing applies to hotter or colder ambient temps. Trust the instrument.

Jim

[snopercod]

I think we all understand the theory: A pitot tube in free air will compensate for the changes in air density and give us a (supposedly) accurate indication of the lift of the wing under all conditions. But what about when the Pitot tube is 24" off the runway? I just don't know how ground effect affects IAS, if at all. I have read that the induced drag goes down by almost 50% within 1/10 of wing span over the ground. That would be the same as adding power. So maybe the float I experienced was due to that, not some characteristic of the cold air. I'm still learning...

Anyway, here's a short video clip showing the difference in ground speeds during a landing at BJC (8,000' density altitude) and LQK (800' DA). Indicated airspeed was 75 Kts during the flare on both landings. At Denver, the centerline stripes were just a blur.

https://www.dropbox.com/s/2um5zel7g3...nding.mp4?dl=0

[lr172]

Originally Posted by jliltd

Scott Black gets an A+. That is one of the most beneficial aspects of our airspeed indicators showing indicated speed. If we always use the same speed on the airspeed indicator no matter the environment, our approach will be equivalently safe. Granted our ground speed will vary. This can be a real gotcha when a pilot used to flying at sea level flies into a high-elevation airport. The pilot's instincts will tell him he is coming in too fast to land even though the airspeed indicator is at the same value. There have been many stall spin accidents in the patterns at mountain airports when a flatlander pilot tries to slow to a speed he is used to sensing rather than nailing the same indicated approach speed used back home. Trust the airspeed indicator despite the trees passing by much faster (or slower) than you are used to. Same exact thing applies to hotter or colder ambient temps. Trust the instrument.

Jim

This makes more sense to me. I was always under the impression that cold, dense air produced more lift. You're saying the ASI compensates and provides a constant speed for all conditions. It is my understanding that the colder air is providing more lift and accounts for slower landing GS when cold, low, etc. and higher GS when hot, high, etc., as explained by Jim above. It's just that we don't have to compensate for it when using the ASI to set landing speeds.

Larry

[Canadian_JOY]

Do airplanes tend to float when landing in cold weather?

Depends on how cold, and for how long it has been cold. If it's been cold for quite a while the water will be frozen and you'll find your airplane will float quite nicely atop a layer of that stuff called "ice"! :-)

(Sorry, I just couldn't resist!)

[Vlad]

Originally Posted by Canadian_JOY

Do airplanes tend to float when landing in cold weather?

Depends on how cold, and for how long it has been cold. If it's been cold for quite a while the water will be frozen and you'll find your airplane will float quite nicely atop a layer of that stuff called "ice"! :-)

(Sorry, I just couldn't resist!)

Nothing wrong with floating when cold. Go Float! No wake!

[snopercod]

Originally Posted by Vlad

Go Float!

So Vlad, how was your braking action on that lake? LOL! ...and what about directional control? Did you ever have to step out of the aircraft and push the tail around to aim the plane where you wanted to go?

[Ed_Wischmeyer]

Calculate the difference in density altitudes and see what you find...

[Scott Hersha]

If your AOA system is reliable, in a position where you can see it, and you've become comfortable flying AOA, then that is your most reliable reference on any approach. The wing stalls at the same AOA in a particular configuration (like full flaps) regardless of air temperature.

[snopercod]

Originally Posted by Scott Hersha

If your AOA system is reliable, in a position where you can see it, and you've become comfortable flying AOA, then that is your most reliable reference on any approach.

Thanks, Scott. I have an AFS Sport system and, so far, it's never let me down. On my plane, three amber LEDs seems to work well on final approach. On my bouncy cold weather landing, I was only seeing 1 amber LED. This landing wasn't so bad - I only floated a little bit. It's the same landing I posted earlier, but from the cockpit cam:

https://www.dropbox.com/s/c8dhrcv61g...ckpit.mp4?dl=0

[Vlad]

Originally Posted by snopercod

So Vlad, how was your braking action on that lake? LOL! ...and what about directional control? Did you ever have to step out of the aircraft and push the tail around to aim the plane where you wanted to go?

Braking action zero directional control minimum minimorum. I did push the aircraft to aim in right direction.