View Full Version : Why doesn't it rain in clouds?
Help an ignorant father! My six year old son wants to know why aeroplanes don't get wet when they fly through clouds. Can anybody explain?
Captain Stable
25th Jun 2002, 08:48
Aircraft frequently do get wet in clouds! And it does rain inside them.
However, unless it is raining sufficiently hard, the slipstream acts as a cold-air hairdryer and blows it all off.
So next time he's flying in cloud, tell him that, although it may look as if it's not raining, it might well be - so not to step outside lest he gets wet! ;)
It is the vertical movement of water within the cloud that shows up on the flight deck weather radar. Red on the weather radar signifys high speed water movement in the cloud whether it be hail or rain. A steep colour gradient (green, yellow, red) means turbulence and the crew do their best to avoid it.
VFE.
'%MAC'
25th Jun 2002, 18:44
Hey Flaps extended,
You must be talking about a Doppler radar. Airborne radar measures the reflectivity of a target. The strength of a return is generally related to its composition, size, and particularly with atmospheric phenomena, the amount of precipitation. Certainly you can paint red on the radar with no vertical movement. Flying through mountain passes I routinely have the radar on to display areas of granite, with hopefully zero vertical or horizontal movement. Just wanted to clear that up. By the way, I thought vertical movement was magenta to differentiate it from red.
I have never seen a good airborne Doppler radar, they all seem to be lousy after about 20nm. If you fly corporate you may have the latest and greatest, is your experience different?
knobbygb
26th Jun 2002, 10:02
SLF3, the best way to actually view the rain in cloud is at night when the strobes are on. The split second burst of light will freeze the raindrops (not literally) and make them easier to see. Remember though, that even though it's falling vertically, it'll also be moving at perhaps 250+ miles per hour horizontally relative to the aircraft.
Even a six year old (and his dad) understand a hairdryer! Thanks very much.
%MAC,
I believe you're right there but without checking my Radio Nav study notes from the ATPL's I wouldn't know for sure if I got confused with Doppler. Maybe I'll have rootle through my bumf later today.
Must say that what I had to learn to pass the JAR exam and what is actually in practice in aviation these days is probably totally different. JAR have some funny ideas!
VFE.
PS: You are right about vertical movement being Magenta! Surprising how quick one forgets these little things after the exam!
SuperRanger
27th Jun 2002, 11:50
SLF,
once this 'security' thingy is all over (wonder if it ever will), it would be really interesting to show your son how the rain drops looks like in flight (at night with the landing lights on). they comes at you directly (horizontally) rather than our conventional idea of falling rain drops!
SR
So sad, the ripples of September 11th spread so far. The last time we flew as a family was last October: he wanted to ask, but no chance.
And every time we over react something goes out of our lives, and they have won a little bit more. But that is a personal view I'm sure many will not share.