No Chill Perception in Freefall

[chrismgtis 0]

I have heard instructors say they got that initial shock of the temperature difference after an exit, but that they don't notice it very much after a few seconds. I personally don't think I've ever noticed how cold it was in the 7 jumps I've done.

Under canopy I did notice the cold, but in freefall I never noticed it even as I was standing at the door. The adrenaline starts pumping when that door opens though.

Rodriguez Brother #1614, Muff Brother #4033
Jumped: Twin Otter, Cessna 182, CASA, Helicopter, Caravan

[pilatus_p 0]

EDITIED TO AVOID OFFENCE: This post not aimed AT you kallend, i just hit reply to your post as was nearest to my mouse ...

nerd mode

Little internet snippet on re-entry burn up: http://www.newton.dep.anl.gov/askasci/eng99/eng99459.htm

As far as I'm aware, aerothermodynamic heating happens when you are going over supersonic speeds, and the temp rise occurs across the shock wave due to some complex flow relations. I remember doing a little calc on the temp rise of concorde's wing leading edges due to shock (about 120 deg C I think)

Newtonian rate of cooling, that is cooling due to wind, is proportional to the airspeed and the temp diff between the air and the object. If the object (eg you) is the same temp as the air already, it wont get any colder because the process is driven by temp difference, unless as noted above the object is wet (dont pee yourself in the plane). Still, I guess there must be some heat rise due to the friction - though I'm more inclined to think it would be the air that gets warmer ....

My brain hurts

Ross

http://www.teamtechnology.co.uk/troll.htm

[Lastchance 0]

Here's a question, If it's ten degrees at altitude, what is the windchill temp with a freefall speed of 120 mph?

I may be getting old but I got to see all the cool bands.

[pilatus_p 0]

Ey up, better ask a weather girl.

Remember, wind chill is a perception that we have due to the fact that we sweat. Its the same reason a fan cools you down - it isnt making the air colder, its just speeding up the evaporation of sweat at the same time as causing cooling (newtonian cooling as referred to above).

An inanimate dry object will cool to the temp of the air (10C in your example) and no further. But you have your own muscles, nerve endings, internal squelchy processes going on, generating body heat and regulating how much you sweat. The very surface of your skin theoretically could be 10C or lower (due to forced evaporation of sweat) but underneath the skin you will have a temperature gradient, due to the things I just mentioned and this keeps you warmer.

Each persons percpetion will vary, though you can put a rough figure on it like weathergirls do.

If I remember rightly its called psychrometry, so actually you need an air conditioning engineer.

No, not psychometry. Thats about job interviews.

Ross

http://www.teamtechnology.co.uk/troll.htm

[yamtx73 0]

Approximately -25.75 degrees F

The only naturals in this sport shit thru feathers...

[Lastchance 0]

Thats not to bad actually, considering that here in Montana we can hi 50 below without windchill.

I may be getting old but I got to see all the cool bands.

[nathaniel 0]

Sounds like numbness to me. The nerves on the surface of your skin lose effectiveness and basically shut down for a while. Also your body reduces circulation to the skin and thus slows down the rate of heat transfer away from your body. After the initial shock of changing environment I bet these two factors are enough to eliminate cold as a distraction until your muscles, bones, and body core start dropping in temperature, causing stiffness, pain, and shivering respectively.

For most people / most skydives it probably doesn't progress to serious hypothermia under ordinary skydiving conditions because the skydive is over before the effects can build and because healthy bodies are pretty good at reacting automagically.

My advice is to do what your parents did; get a job, sir. The bums will always lose. Do you hear me, Lebowski?

[CrazyRick 0]

Could be that your having so much fun that you just don't care about the cold.

[MarkM 0]

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this gets me thinking though, at 120+ mph is there any chance of air-resistance/friction warming you up a bit? my whole body gets the chills when the door opens but once out it only tends to be my face that feels so cold

When i skydive from the space station it burns, and the goggles do nothing!

[champu 1]

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Approximately -25.75 degrees F

Be careful using wind chill calculators (or any calculator/formula for non-linear phenomena) with extreme parameters like 120mph. You can't always be sure the numerical approximations the author made are well-behaved that far out.

[SansSuit 1]

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I'm assuming it's adrenaline keeping you warm ...

I believe that adrenaline does have alot to do with things. Last winter I made 2 jumps on the same day under nearly identical conditions and altitudes. The only difference was I was nekkid on one and had my usual winter jumping gear on the other.

I felt the cold infinitely more on the jump with a jumpsuit than the one without. I attribute that to the adrenaline that flows on a nekkid jump.

I have fingers that have been frost bitten in the past. They caused me more pain on the clothed jump even though I wore gloves on both jumps.

Peace,
-Dawson.
http://www.SansSuit.com
The Society for the Advancement of Naked Skydiving

[kallend 1,623]

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i really think it is not as cold in freefall , as it is with the door open in the plane. i usually tell my students that there is no wind chill factor in freefall, and that i dont know why, or if it is even true, but it certainly seems to be the case.
are there any physicists out there,who can comment on that.?

There is a definite "cold spot" in an Otter with the door closed, at the extreme rear starboard side of the cabin, due to a blast of wind coming over the top of the door. As a frequent rear float, I often get to sit there and can get quite chilled on the climb to altitude. I notice that it is always slightly warmer when the door is opened due to the reduction in the blast.

...

The only sure way to survive a canopy collision is not to have one.

[JohnMitchell 14]

I only notice the cold when it hurts. Other than that, it's easy to ignore.

Pretty amazing, though, to be in a 100 mph wind at 0 degrees, wearing only a jumpsuit and sweatshirt, and not really being bothered by it.

• Quote

[superhina 0]

Freefall or under canopy is not problem for me.
Packing the shute in cold hangar is f...... freeze to me.

[Froggy 0]

I always jump an open face helmet, thin baseball gloves, and most of the times have just a t-shirt under my jumpsuit. I don't feel cold in freefall, unless it's really cold by my standards (like -20 Celsius or below). However, I can definitely feel my hands freezing under canopy when it's cold, probably because of limited circulation when you have your arms raised for toggles...

--------------
We were not born to fly. And all we can do is to try not to fall...

[phoenixlpr 0]

I think the main factor is time. If you dressed on some level it takes some time to chill out. We are jumping out from a warm aircraft. You might spend 10-20 seconds with climbing out and max 60-70 seconds with freefall. So we can be exposed to high speed winds for 90 seconds only.

I use 2 pairs of gloves in the winter. I don't feel cold in freefall, but I feel cold after I have landed specially from my fingers.

[jakee 1,254]

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I don't feel cold in freefall, but I feel cold after I have landed specially from my fingers.

Yep. While its never bothered me in freefall, I have been known to cry like a girl when my fingers are thawing out after the canopy ride in winter

Do you want to have an ideagasm?

[Travman 6]

I know when I started out, I would not notice the cold on 4-way, but I would on solo. Not sure about these days since I haven't done a solo in a very long time.

[Broke 0]

perhaps it is a combination of things, because I sure did feel the cold untill I was under canopy.

I ordered myself a set of silk long johns. It is a tight weave, so it keeps the wind down. Better than Underarmor and cheaper too.

There is something interesting about seeing snow come into the plane when you open the door.

Divot your source for all things Hillbilly.
Anvil Brother 84
SCR 14192

[Orange1 0]

In my logbook, around jump 25, is written "noticed how cold it was in freefall" - i.e. the first time! I tend to still notice it if I do solos & it's really cold, but not in RW where I am still far too busy concentrating on levels and slots .

Skydiving: wasting fossil fuels just for fun.

[chigbee 0]

I would say that it is a combination of adrenaline and an elevated heart rate. When I am skiing in extreme cold I freeze on the ride up and for the first 30 seconds or so of the run. After that I am always comfortable no matter what the temp is.

[Liemberg 0]

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My brain hurts

To make matters even worse:

On your way down, the temperature of the air around you will typically rise 0,6 C per 100 meter
Our brain anticipates that while our asses freeze by the door in slow climbing aircrafts.

Psychology and physics - the most powerful combination on the planet!

"Whoever in discussion adduces authority uses not intellect but memory." - Leonardo da Vinci
A thousand words...

[pilatus_p 0]

I think I like EVERYTHING about this post.

Especially the tagline!

Ross

http://www.teamtechnology.co.uk/troll.htm

[llkenziell 0]

All I know is that is freezing when the door opens, then I can't feel the cold until under canopy =P

"Living like fallen angels who lost their halos" - Unknown Prophets

-Love Life-

[flyangel2 2]

I've always felt the cold. The lower my jump numbers the less I minded the cold. The higher the jump numbers have gotten, the less I jump when it's cold. Hence the reason I just do tunnel time during the winter. Unless I travel some place warm.

May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view. May your mountains rise into and above the clouds. - Edward Abbey