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 |
#11
|
|||
|
|||
"Robert Moore" wrote in message
. 6... (Malcolm Teas) wrote Think about density altitude. At -20 C and sea level, the density alt is just under -10000 feet according to the my trust E6B. At -40 C and 9000 feet pressure alt, the density alt is -10000 feet. Better get a new E6B. :-) He got the wrong numbers, but it IS true that the density altitude winds up about the same for both calculations (around -5000'). So maybe the answer IS something that has to do with density altitude. I think it's more likely a limitation on the engine (to keep MP within limits), rather than some altimeter thing. But it seems logical that density altitude is the problem, in this particular example (that may or may not apply to other aircraft, of course). Pete |
#13
|
|||
|
|||
"Peter Duniho" wrote in message ...
"Robert Moore" wrote in message . 6... (Malcolm Teas) wrote Think about density altitude. At -20 C and sea level, the density alt is just under -10000 feet according to the my trust E6B. At -40 C and 9000 feet pressure alt, the density alt is -10000 feet. Better get a new E6B. :-) He got the wrong numbers, but it IS true that the density altitude winds up about the same for both calculations (around -5000'). So maybe the answer IS something that has to do with density altitude. I think it's more likely a limitation on the engine (to keep MP within limits), rather than some altimeter thing. But it seems logical that density altitude is the problem, in this particular example (that may or may not apply to other aircraft, of course). Pete I suspect it is related to the maximum power output from the engine (not MP, because that is not related to density altitude). Engine power increases roughly 2% per 1000' decrease in density altitude. At -5000' you will be developing 110% of the rated horsepower. That is a nice round number, and could very well be the reason for the limitation. |
#14
|
|||
|
|||
"Peter Duniho" wrote in message ...
"Robert Moore" wrote in message . 6... (Malcolm Teas) wrote Think about density altitude. At -20 C and sea level, the density alt is just under -10000 feet according to the my trust E6B. At -40 C and 9000 feet pressure alt, the density alt is -10000 feet. Better get a new E6B. :-) Or, perhaps, remember how to do density alt. calculations. Yep, I messed up there. He got the wrong numbers, but it IS true that the density altitude winds up about the same for both calculations (around -5000'). So maybe the answer IS something that has to do with density altitude. Well I get a density alt of about -5000 for sea level and -20 C, and 5000 for 9000 foot press. alt and -40 C. This is with my revised E6B. grin So, 4000 to 5000 less than the pressure altitude at least. -Malcolm Teas |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
FA: WEATHER FLYING: A PRACTICAL BOOK ON FLYING | The Ink Company | Aviation Marketplace | 0 | November 5th 03 12:07 AM |
Cold Weather Flying | Jose Vivanco | Owning | 27 | October 16th 03 11:27 AM |
Eurofighter - useless in cold weather and fog? | Peter Kemp | Military Aviation | 9 | September 13th 03 04:37 AM |
XMRadio Satellite Weather Has Arrived | Richard Kaplan | Piloting | 37 | September 2nd 03 02:51 PM |
And they say the automated Weather Station problems "ASOS" are insignificant because only light aircraft need Weather Observations and forecasts... | Roy | Piloting | 4 | July 12th 03 04:03 PM |