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Here's a good one that actually Lou Fields was fond of.

If you are flying out of an airport that is at high altitude, how will this affect your sight picture on climb out?

not affected, assuming you IAS is the same.

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Fly safe,

David

To maintain the same IAS, you would have to pitch down. Higher altitude, less air moving through the pitot static system. More importantly, your engine has less power=less thrust, and there is less air moving over your wings.

He liked to ask this question because it showed "correlation" in understanding a concept, rather than to ask what happens to performance with higher altitude flying. How does this affect you while you are in control of the airplane? Pitching to a normal sight picture during departure - shortfield with an obstacle - at a high density altitude, could put you in a precarious position. Rather, be aware that airplane performance will be less, and pitch appropriately.

Interesting, I'll have to give this some more thought/research...
As my first thoughts were this...
Think of the lift formula
L = CL 1/2p V2 S
We've agreed IAS is the same, therefore the
[1/2p V2] (thinner air "p" but a faster TAS "V2") part of the lift formula (IAS) would be the same, so the CL (AoA) must now be consistent with a given AoA for a given IAS which would give the same sight picture, yes? In straight and level...

I acknowledge that there are differences in a climb to S&L.
L < W in a climb, but made up in the vertical component of thrust.

TAS would be faster, but how could there be less air over the wings or thru the pitot/static system if IAS [1/2p V2] is the same?

Thrust. Agreed, is less at altitude and for this reason I could now see that as there is less thrust (less excess thrust), less propwash over the inner wings, and less vertical component of lift from thrust may give us a lower nose attitude for the same IAS...

Power. There of course would also be less excess power resulting in less rate of climb, but if the IAS is the same, wouldnt the AoA also be the same?, resulting in the same sight picture.

The thrust (vertical component of) is the part I need to nut out. Less thrust. I reckon in there's the answer. All the rest I think I can make sense of (I think:)

You've got me thinking

Hmmm, good question
Please keep em coming!

cheers,

_________________
Fly safe,

David

the V in the dynamic pressure (1/2pV2) equation is not indicated airspeed, it is true airspeed. for a given indicated airspeed, your true airspeed will increase with altitude, so that is where the pitch down comes from.

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Everyone must believe in something, I believe that I will go flying.

Here's something else to think about. In the performance charts, the IAS for best rate decreases. Why?

OK, good question...
Climb performance is based on excess power.
The Vy is at a given TAS based on max excess power.
As height increases, if we maintain a constant TAS to maintain Vy, our IAS must be less than our TAS.

_________________
Fly safe,

David

Interesting Q/A's... I can't add to that part of the discussion, but let me add something immediately practical. My website now calculates density altitude for all airports, based on reported altimeter, temperature and dew point. Interesting to see d/a compared with station elevation.

To view, you mouse over METARs (circular icons).

http://maps.avnwx.com

Enjoy
-Peter

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-Peter Buckner
maps.AvnWx.com

Nice site Peter. I'm posting the link on the Cirrus owner's website, if that's OK.

Dan

because I dont know the lift formula does that mean im never gonna be a pro-pilot?

theres always something that john and martha king leave out

You'll be a pro-pilot when you instinctively look outside the plane and see you're not getting the climb performance you expected and intuitively know to lower the nose without having to ponder an equation. The lift equation has two primary purposes:

1. To get commercial and CFI candidates thinking about factors that effect lift

and

2. To outdo one another in an online forum with minute details.

The lift equation is a party favor for nerds. Sean Tucker and Mike Goulian are NOT pondering the lift equation as they pull through a reverse Immelman in front of 50,000 airshow spectators.

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Inst: "So how far out so we make our initial call-up?"
Student: "10 miles"
Inst: "OK, let's make that call"
Student: "Airport Traffic, Cessna 172, 3 miles east..."

"You'll be a pro-pilot when you instinctively look outside the plane and see you're not getting the climb performance you expected"


sweet been a pro-pilot since day 2.