Go Back  PPRuNe Forums > Non-Airline Forums > Private Flying
Reload this Page >

Flying & Light Frost

Private Flying LAA/BMAA/BGA/BPA The sheer pleasure of flight.

Flying & Light Frost

Old 25th Feb 2016, 16:04
  #21 (permalink)  
 
Join Date: Aug 2002
Location: United Kingdom
Posts: 2,510
Likes: 0
Received 0 Likes on 0 Posts
Some misunderstanding/confusion here between frost and ice. Frost is formed when air is cooled below its dewpoint and that dewpoint is below 0C. If conditions are right, a cold-soaked airframe (well below 0C) descending into a relatively warmer/moister environment will cool the air in contact with it, perhaps sufficiently to form a layer of frost - the presence of supercooled water droplets/visible moisture is not required. The effect is more common in aircraft descending rapidly from high altitude (e.g. military/commercial jets) but is not unknown in light aircraft.
BillieBob is offline  
Old 25th Feb 2016, 16:56
  #22 (permalink)  
 
Join Date: May 2005
Location: France
Age: 68
Posts: 1,109
Likes: 0
Received 2 Likes on 1 Post
Yes, frost and ice (when discussing flight) are two different things, even if they both comprise frozen water.

Pre-flight:
Frost may form on any exposed surface if the conditions are right. Think of it as 'frozen dew'.
Ice may also form if conditions are right, e.g. freezing fog with a light breeze. The windward edges of the airframe can build up rime ice due to the super-cooled water drops being blown onto the impinging surface. I have even experienced rime ice on my motorbike's mirrors and my gloves while riding in such conditions.

Both frost and ice (and snow) must be removed before flight (Exceptionally, a few allowable areas may have light frost remaining, as described in #13).

In-flight:
Frost may form on super-cooled surfaces if a flight in sub-zero temperatures is followed by flight through humid air as described by BillieBob. Normally, the actual airframe warms up quite quickly but the fuel will stay at a sub-zero temperature for quite a while and the skin in contact with the fuel may get some frost, normally on the underside of the wing, unless the tanks are really full. I have not seen frost developing on any other part of the airframe, e.g. on the fuselage as described by the OP.
Ice can form in many ways; the most common being rime ice. As previously described, super-cooled water droplets impact the leading edges and a small proportion freezes immediately with the remainder flowing back a distance until it too freezes. The proportion that freezes instantly is greater, the colder the water droplet. This implies that temperatures just below freezing can result in more 'flow-back' before total freezing occurs, which is bad news as the area covered will be greater. Nevertheless, the formation of rime ice tends to restrict itself to 'leading edges' only.

As frost will (generally) only form in the vicinity of the fuel tanks, there is not much that can be done to remove it until after landing. If you are concerned about a build-up of frost (and you can see it), then consider a handling check and an increased approach speed, as described in previous posts.
Ice however is much more serious and therefore should be avoided or removed, if you have the equipment fitted to do so.

Post-flight:
Frost may form anew in the same way as it did pre-flight, i.e. as 'frozen dew' on a cold surface. This is what I believe happened to the OP as he taxied in.
The pre-existing frost in the vicinity of the fuel tanks may persist and even grow, depending on the air temperature and humidity. It may require removal prior to further flight
New Ice could form if you were taxying in freezing fog, but then the preceding landing would have been quite 'interesting' as well!
eckhard is offline  
Old 25th Feb 2016, 19:46
  #23 (permalink)  
Thread Starter
 
Join Date: Sep 2015
Location: London
Posts: 442
Likes: 0
Received 0 Likes on 0 Posts
Thank you Eckhard for such a detailed response. Much appreciated. I think this sheds a little light on the subject!

Thank you for everyone else for commenting! Much appreciated, especially the course of action that everyone would take. Surprising how many would consider doing control checks - I remember reading about an A380 captain for Qantas doing just that after one of the engines exploded in flight.

Hope someone other than me learnt something as a result on this!

Best Wishes,
alex
alex90 is offline  
Old 26th Feb 2016, 00:29
  #24 (permalink)  
 
Join Date: Jan 2008
Location: Canada
Posts: 628
Likes: 0
Received 0 Likes on 0 Posts
I do not agree that frost can form on an aircraft in flight. The many references I can find to the formation of frost refer to calm, still, or static air being necessary for formation. My experience over four decades of Canadian winter flying has never shown "frost" forming on a moving plane - only on a motionless one, in calm air.

I support this with the knowledge that to prevent formation of frost on valuable crops, helicopters are flown over low, or fans used to disturb the air. It must work, it's been done for years. I can also assert that an aircraft flown with frost in non critical areas at takeoff, will land back with that frost gone due to sublimation in flight - moving air.

I have seen frost form on the fuel tank skins of a "wet wing", but not otherwise.
9 lives is offline  
Old 26th Feb 2016, 08:35
  #25 (permalink)  
 
Join Date: May 2005
Location: France
Age: 68
Posts: 1,109
Likes: 0
Received 2 Likes on 1 Post
Thanks Step Turn,
Your observations tally with mine. I guess the frost I have seen on the fuel tanks has formed after landing and not in flight.

So, we can deduce that the frost that the OP saw on his Cessna formed during the taxi-in and not in flight.
eckhard is offline  
Old 26th Feb 2016, 19:39
  #26 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes on 0 Posts
Ice can distort the flow of air over the wing, diminish- ing the wing's maximum lift, reducing the angle of attack for maximum lift, adversely affecting airplane handling qualities, and significantly increasing drag. Wind tunnel and flight tests have shown that frost, snow, and ice accumulations (on the leading edge or upper surface of the wing) no thicker or rougher than
a piece of coarse sandpaper can reduce lift by 30 percent and increase drag up to 40 percent. Larger accretions can reduce lift even more and can increase drag by 80 percent or more. Even aircraft equipped for flight into icing conditions are signifi- cantly affected by ice accumulation on the unpro- tected areas. A NASA study (NASA TM83564) showed that close to 30 percent of the total drag associated with an ice encounter remained after all the protected surfaces were cleared. Nonprotected surfaces may include antennas, flap hinges, control horns, fuselage frontal area, windshield wipers, wing struts, fixed landing gear, etc.
Some unwary pilots have, unfortunately, been caught by surprise with a heavy coating of ice and no plan
So there you go Frost no thicker or coarser than a piece of course Sandpaper can reduce lift by 30% and drag by 40% so don't risk it

Full article worth reading linked below

http://flighttraining.aopa.org/pdfs/..._Icing.pdfPace

Pace
Pace is offline  
Old 26th Feb 2016, 20:36
  #27 (permalink)  
 
Join Date: Jan 2000
Location: U.K.
Posts: 267
Likes: 0
Received 0 Likes on 0 Posts
So,when you put"frost"in your spellchecker, it comes out "ice" ?
dash6 is offline  
Old 28th Feb 2016, 19:59
  #28 (permalink)  
 
Join Date: Feb 2009
Location: England
Posts: 858
Likes: 0
Received 0 Likes on 0 Posts
Some poor understanding of icing, ice and frost in the some of the above posts.

Car deicier is not an approved fluid for use on an aircraft, it is also not an anti ice, nor do you know what its holdover time is. It may well get rid of the ice but you are introducing a water based fluid onto the wing and you have no idea what will happen to that fluid in sub zero temperatures apart from at some stage it will refreeze.

I do not agree that frost can form on an aircraft in flight. The many references I can find to the formation of frost refer to calm, still, or static air being necessary for formation. My experience over four decades of Canadian winter flying has never shown "frost" forming on a moving plane - only on a motionless one, in calm air.
Frost can form on and around cold soaked fuel tanks underneath the wings after high altitude flight . Certainly very common on all the jet types I have flown especially after a rapid descent and it does form in the air not just magically after touchdown!

On two types I flew you had to do an overwing tactile test before flight in temps below 6 degs. Note -overwing only.

Attempting to take of with hoar frost on the wings makes you a test pilot or just an idiot-good luck.

https://assets.digital.cabinet-offic...2004_N90AG.pdf

So my question is: would this accumulation of very light frost be of any consequence? We're not talking about heavy ice forming, just very very thin, light frost. (perhaps even lighter than what can be seen on your car in the morning after a frosty night)
One of the problems with hoar frost, not understood by many pilots, is that if the same amount of top surface frost could (and it cant) form in the cruise the aircraft may well be perfectly flyable due to the ample margin above the stall speed. However during the low speed transition from lift off to climb speed, with a much lower margin above the stall speed caused by the ice, the pilot may experience a stall and loss of control, the other danger is that the stall characteristics in such a stall may be unconventional or more marked that a normal stall.

Last edited by Pull what; 28th Feb 2016 at 20:36.
Pull what is offline  
Old 29th Feb 2016, 01:41
  #29 (permalink)  
 
Join Date: Jan 2008
Location: Canada
Posts: 628
Likes: 0
Received 0 Likes on 0 Posts
Frost can form on and around cold soaked fuel tanks underneath the wings after high altitude flight . Certainly very common on all the jet types I have flown especially after a rapid descent and it does form in the air not just magically after touchdown!
Should we expect the formation of "frost" on a jet wing, descending from high altitude, to be representative of typical GA flight scenario? I have never flown a jet, and perhaps these conditions can exist in that environment, but I have yet to see "frost" in four decades of flying all kinds of propeller aircraft during Canadian winters.... (I sure have seen ice though ).

I agree that we should not be test pilots with varied or worse prohibited configurations of an aircraft. However, being surprised by a stall shortly after liftoff in a light GA aircraft has me thinking that the pilot was along for the ride, rather than flying the aircraft. If you unstick an aircraft, and it flies to your liking, it should fly better as you allow it to accelerate during the climb away. If, on the other hand, you get it airborne, and then slow it down and stall, you weren't doing it right! If you try to unstick it at the appropriate speed, and it resists your effort, you might consider aborting the takeoff!
9 lives is offline  
Old 29th Feb 2016, 07:37
  #30 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes on 0 Posts
White frost is a solid deposition of ice which forms directly from water vapour contained in air.

White frost forms when there is a relative humidity above 90% and a temperature below −8 C (18 F) and it grows against the wind direction, since air arriving from windward has a higher humidity than leeward air, but the wind must not be strong or it damages the delicate icy structures as they begin to form. White frost resembles a heavy coating of hoar frost with big, interlocking crystals, usually needle-shaped.
You are both right as white frost cannot form in strong wind conditions and what forms on a wing with high speed air flowing over it is more likely to be hoar frost which technically is not frost

Pace
Pace is offline  
Old 3rd Mar 2016, 21:27
  #31 (permalink)  
 
Join Date: Sep 2001
Location: Toronto
Posts: 2,471
Received 10 Likes on 4 Posts
Car deicier is not an approved fluid for use on an aircraft, it is also not an anti ice, nor do you know what its holdover time is. It may well get rid of the ice but you are introducing a water based fluid onto the wing and you have no idea what will happen to that fluid in sub zero temperatures apart from at some stage it will refreeze.
Perfectly correct, but on a practical basis will do a proper job of dissolving the frost. Remember that after application the stuff has to evaporate, aided perhaps with the spongy side of your windshield squeegee.

Once the wing is clean and dry with no ice in nooks and crannies, who cares how it got that way.

On a nice morning after a frosty night, this approach can get you an properly clean wing, but if there's freezing precip, I'd be turning around before I got to the airport.

Mechanical scraping between the rivet lines got me an interesting low level excursion over the ravine at the end of the runway until I had another 15 kts or so. After that I took to carrying windshield washer fluid.
RatherBeFlying is offline  
Old 5th Mar 2016, 09:49
  #32 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes on 0 Posts
Rather Be Flying

We are not talking about deicing larger aircraft where a proper deicing rig is used with the correct fluid but cleaning a wing on a small aircraft

Its not ideal but car stuff will cleanly remove it. Its up to you to dry the clean wing off before flight

Pace
Pace is offline  
Old 5th Mar 2016, 10:06
  #33 (permalink)  
 
Join Date: Nov 2000
Location: Cambridge, England, EU
Posts: 3,443
Likes: 0
Received 0 Likes on 0 Posts
OK folks, you're not gonna like this story ...


Once Upon A Time some decades ago:


Me (having inspected aircraft before lesson): There's some frost on the wings
Instructor: Well spotted ... now let's go flying.


So the instructor was a test pilot, not an airline wannabee hours builder, but all the same don't try this at home kids.
Gertrude the Wombat is offline  
Old 5th Mar 2016, 11:10
  #34 (permalink)  
 
Join Date: Jan 2008
Location: Canada
Posts: 628
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Pace View Post

Its not ideal but car stuff will cleanly remove it. Its up to you to dry the clean wing off before flight

Pace
I agree that "car stuff" is not ideal. It may contain methyl hydrate, which can have corrosive affects on aluminum. Drying the wing off afterward will not prevent corrosion risk if the methyl hydrate has seeped between lapped skins or into the structure. For aircraft in my care, the only liquid I would apply would be those approved for that purpose - on aircraft.

Me (having inspected aircraft before lesson): There's some frost on the wings
Instructor: Well spotted ... now let's go flying.
The regulations (Canadian, anyway) do not state that aircraft will not fly with contaminated wings, they state that a pilot is not permitted to attempt the flight. Some aspects of flying require good preplanning, frost prevention is certainly one of them.
9 lives is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell or Share My Personal Information

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.