2 QRC questions

kidicarus5897 · 02-28-2008, 01:37 AM

So I ran out of my company approved reading material on a 3+ hr flight today, and the QRC was sitting there all lonely, so I read the end; Doors and Misc, and I have two questions about some of the stuff in there. First, on p.2-244, they talk about "a constant 1 'g' level turn" when discussing vertigo. Now, I am no physics wiz, but it would seem to me that in turning level flight, the g force will always be a value greater than 1 due to constant acceleration in the turn. Maybe they meant constant g turn.....
Second, in regards to mach tuck, p.2-235 says something like "the center of pressure on TOP of the wing moves aft, causing a pitching moment downward." I have always thought of the center of pressure as acting through the bottom of an airfoil. Maybe they are talking about the shock wave on top of the wing moving aft. But the center of pressure below the wing moves aft, furthur from the center of lift and causes the the aircraft to pitch down. Discuss, oh wise pipe
Yariv? Vortex? anyone?

Upay · 02-28-2008, 01:54 AM

If you aren't holding your altitude you can keep 1g in a turn (i.e. descending).

randomguy · 02-28-2008, 08:15 AM

Doesn't matter if you think of center of pressure as acting from underneath or suspending from above. If that imaginary point moves rearward, away from the center of gravity, the plane will pitch down.

kidicarus5897 · 02-28-2008, 02:50 PM

Quote:

Originally Posted by Upay

If you aren't holding your altitude you can keep 1g in a turn (i.e. descending).

the QRC says 'level' turn. no decent

kidicarus5897 · 02-28-2008, 02:52 PM

Quote:

Originally Posted by randomguy

Doesn't matter if you think of center of pressure as acting from underneath or suspending from above. If that imaginary point moves rearward, away from the center of gravity, the plane will pitch down.

but think about what causes the airfoil to pitch down. A force behind the CG moving more aft. At least the literature I have real else where refers to the ceter of pressure below the wing. You are right though, the result is the same

randomguy · 02-28-2008, 04:41 PM

Quote:

Originally Posted by kidicarus5897

but think about what causes the airfoil to pitch down. A force behind the CG moving more aft. At least the literature I have real else where refers to the ceter of pressure below the wing. You are right though, the result is the same

Right. It's only semantics- whether you think of the high pressure below the wing pushing up or the low pressure above pulling. Same spot, same result.

Yariv · 02-28-2008, 07:10 PM

the defintion of center of pressure is the location of the average of all pressure on the airfoil. which suggests that it's near the bottom of the airfoil, since pressure is lower at the top when lift is produced. I can't find any mention of the vertical location of cp nor any use for knowing if it's on top or bottom...

as for the G in the turn, the whole idea is useless since we don't have a G meter. I'm sure they meant constant G turn, and we agree it's more than 1 G in a level turn.

in both cases the QRC is simply using too many words. that's what you get for reading it. when you're done you know less than before you started!

kidicarus5897 · 02-28-2008, 11:23 PM

I've got another one for you. What the hell is a "direct view window?" and how do we remove it? p. 2-187 in the QRC. I would assume it is the front windscreen, but I doubt there is a qrc procedure to remove it............

And do we really have 2 different EGPWS escape guidance maneuvers? One for mountainous terrain and one for non-mountainous terrain? The former says to pitch to 25-35 degrees initially, the latter says 10 degrees initially, then 25-35 if ground contact seems iminent. In a PC, do I ask if I am currently over mountainous terrain??

All this new stuff I am learning........

Yariv · 03-01-2008, 03:16 PM

Quote:

Originally Posted by kidicarus5897

I've got another one for you. What the hell is a "direct view window?" and how do we remove it? p. 2-187 in the QRC. I would assume it is the front windscreen, but I doubt there is a qrc procedure to remove it............

And do we really have 2 different EGPWS escape guidance maneuvers? One for mountainous terrain and one for non-mountainous terrain? The former says to pitch to 25-35 degrees initially, the latter says 10 degrees initially, then 25-35 if ground contact seems iminent. In a PC, do I ask if I am currently over mountainous terrain??

All this new stuff I am learning........

I don't speak portugese but apparently a direct view window is the window where you can directly view your 9 and 3 o'clock. and yes we have two different procedures, and yes you're reading too much! the whole idea of cfit is that you may not be where you think you are (i.e. american 757 in cali) so if in doubt go to 25*. but if in IAH for example (no mountains for hundreds of miles) 10* would do. luckily the book does clarify that in mountainous terrain "with or without radar control" go to 25*, so at least you dont' have to ask the sim instructor if you're in radar control...

another example of the book having too many words.

kidicarus5897 · 03-01-2008, 03:32 PM

Quote:

Originally Posted by Yariv

I don't speak portugese but apparently a direct view window is the window where you can directly view your 9 and 3 o'clock. and yes we have two different procedures, and yes you're reading too much! the whole idea of cfit is that you may not be where you think you are (i.e. american 757 in cali) so if in doubt go to 25*. but if in IAH for example (no mountains for hundreds of miles) 10* would do. luckily the book does clarify that in mountainous terrain "with or without radar control" go to 25*, so at least you dont' have to ask the sim instructor if you're in radar control...

another example of the book having too many words.

Well, I don't speek portugese either, and I am not really sure what that has to do with a direct view window. So the direct view window is so you can directly view your 3 and 9 o'clock, That's pretty inutitive........ let me guess, that's out of Vol 2