If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Why does a prop ice up so apparently readily?
On Mon, 07 Nov 2005 22:56:42 +0000, Peter
wrote: The other day I was talking to a commercial pilot of a big twin passenger turboprop. He has been iced up a few times and recently was down to 200fpm climbing flat out through FL150; looking out of the window he saw a bit of ice on the wings but enough on the prop for it to be visible while the prop was rotating. /// At 200kt IAS at FL150 his airframe temperature should be SAT+9C. At 300kt TAS the TAT should be SAT+12C which nearly puts him out of the stratiform cloud icing range of 0C to -15C or so. /// What puzzles me is the prop. Assuming a SOP of max revs if icing is likely, much of the prop is going at between mach 0.5 and mach 0.8, with a temp rise of 15C to 30C, so even on a slow piston aircraft only the innermost part should ever ice up. Is this true? // Peter. Let's run a sanity check. Lapse rate 2 degC/1000ft (can be less) Airframe Cold day = 5 degC MSL at FL150 = 15 X 2 = 30 degC drop from 5 deg = -25 degC SAT + 9 to SAT + 12 = -16 degC to -13 degC Std day = 15 degC MSL at FL 150 = -6degC to -3 degC Prop Cold day -25degC + 15 to 30 degC = -10degC to +5 degC Std Day -15degC + 15 to 30 degC = 0 to 15 degC One is warned that glaze can accrete very, very fast. I oversimplified with the lapse rate, but I conclude that it's easy to be in an accretion phase at FL150. Did I miss something? Brian Whatcott Altus OK |
#2
|
|||
|
|||
Why does a prop ice up so apparently readily?
On Tue, 08 Nov 2005 08:46:43 +0000, Peter
wrote: Brian Whatcott wrote: Did I miss something? Yes, I was talking about *aerodynamic heating* of the prop and suggesting that - over most of its length - it ought to be sufficient to prevent icing. ....and did I not account for aero heating, using the figures given by you? Brian Whatcott Altus OK |
#3
|
|||
|
|||
Why does a prop ice up so apparently readily?
You are assuming that you are getting your calculated aero heating even
though the air is full of supercooled water. Mike MU-2 "Peter" wrote in message ... Brian Whatcott wrote ...and did I not account for aero heating, using the figures given by you? Yes, but I don't think icing works that way. The reason is that supercooled water won't (generally) exist below about -15C to start with, so if the aerodynamic heating increment exceeds 15C one doesn't get ice. So, if e.g. the SAT is -25C and the aero heating is 20C, the airframe part will be at -5C but it won't ice up because there wasn't liquid water in the -25C air to start with. Any water would have been in solid (frozen) form, as in e.g. cirrus clouds, but a -5C airframe flying through that won't accumulate ice because the crystals don't have time to melt and convert themselves into drops of liquid which could stick. That's my understanding, anyway. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Why does a prop ice up so apparently readily? | Brian Whatcott | General Aviation | 2 | November 9th 05 12:02 AM |
Why does a prop ice up so apparently readily? | Mike Rapoport | General Aviation | 3 | November 8th 05 02:52 PM |
Why does a prop ice up so apparently readily? | Mike Rapoport | Piloting | 2 | November 8th 05 02:52 PM |
Ivo Prop on O-320 | Dave S | Home Built | 14 | October 15th 04 03:04 AM |
IVO props... comments.. | Dave S | Home Built | 16 | December 6th 03 11:43 PM |