Redux
I agree with (pretty much) everything everyone was kind enough to offer.
Main points: Smooth, coordinated control of the aircraft while turning a CIRCLE around the point by crossing 4 (or more) equidistant points. It is EASIER to use a SMALLER bank. If you don't know what your MAXIMUM bank will be you cannot (in theory) PICK an ENTRY POINT that will be on the RADIUS of the circle.
The SECOND PTS reference that I checked said, "approximately 45 degrees at the steepest point in the turn" as one poster replied here. Another poster reiterated the "45 degree MAXIMUM turn on the private exam' idea, that I had seen.
I get all of the above but if you pick your point based on a 30 degree entry, you cannot turn that one with a 45 and still get a circle.
Herb Martin
Critical Angle of Attack
Problem
Does the critical AOA change when the CG moves forward?
David Moran
Answers
That's an excellent question!
The short answer is that no, it does not. Critical AOA is only a function of the shape of the wing (including things like whether flaps are deployed).
What moving the CG forward does do, however, is increase the *airspeed* at which you stall. As the CG moves forward, the tailplane has to generate more down-force to keep the airplane in balance. This results in the main wing having to produce more lift to keep the aircraft in the air, and thus requires a higher airspeed for a given AOA.
Roy Smith, CFI-ASE-IA
More:
The critical AOA never changes in any given airplane. But you can reach this critical angle through several ways: changing pitch, airspeed, g-load, CG position, whatever. The critical AOA is always at the maximum coefficient of lift, which is given for any aircraft.
So, the AOA at which an aircraft stalls stays the same (otherwise all AOA indicators would be useless), but the speed at which the stall occurs changes with lots of factors.
Patrick
Pitch
Problem
That's only partially true. AOA is the difference between your pitch attitude(*) and your flight path. You really can only perceive your pitch attitude by looking out the window to see where the nose is pointing.
On an ILS, with a -3 degree flight path, your pitch attitude is going to be 3 degrees lower for the same AOA your airspeed would give you in level flight. On a typical VFR descent, you're on about a -6 degree flight path, so your pitch attitude will be even lower for the same AOA. The extreme case would be a spin, where your pitch attitude is nearly vertical, but you are still stalled because the AOA is too high.
Most people are used to stalling by shoving the nose way up in the air while trying to maintain altitude. That's because that's the way the maneuver is taught to meet PTS demonstration requirements. Unfortunately, I think all that teaches people is that you can't stall when you can see the ground out the front window.
But, a more realistic demonstration of an approach-to-landing stall would be to set up constant 6 degree descent at 1.2 VS0 (for most light planes, that's about a 700 FPM descent). If you're lucky, you might find a small airport near you with a 6-degree VASI on a non-instrument runway (check the AFD). If you can intercept the VASI 5-10 miles out and track that during this exercise, that should work fine. Alternatively, try and intercept one of those mythical false ILS glide slopes we're always talking about on r.a.ifr :-)
You're probably looking at something like 1300 RPM and full flaps (like you would be on short final). You will have a distinct nose-down pitch attitude. Now, reduce power to idle and slowly pitch up just enough to bleed off airspeed as you keep the descent rate constant. You should be able to get down close to VS0 like this.
Once you've got that stable, low airspeed, high rate of descent glide set up, pitch up at somewhat faster pitch rate. You should stall, and do so with a significantly lower pitch attitude than you do on a normal PTS-style stall demo. This is what it really looks like when somebody is trying to stretch a glide to make the runway without adding power.
It would be really cool to try this in something like a Mooney with speed brakes deployed! What's the glide ratio with gear down, full flaps, speed brakes, and idle power?
(*) To be more precise, it's the difference between (pitch attitude + angle of incidence of the wing) and your flight path. But, since angle of incidence is constant (on most airplanes!), you can pretty much ignore it
for these purposes.--
Roy Smith, CFI-ASE-IA
You might want to add here that referencing a specific view from the airplane to critical angle of attack isn't the best way to approach this, as you can exceed critical angle of attack and stall the wing in ANY flight attitude; straight up; straight down; or upside down. The view of course will be different in each case. In my opinion at least, referencing AOA with a specific view from the cockpit can be misleading to an overall understanding of how critical AOA and not airspeed should be the reference for stall.--
Dudley Henriques
Altimeter Setting Change
Problem
If a pilot changes the altimeter setting from 30.11 to 29.96, what is the
approximate change in indication?
Altimeter will indicate .15" Hg higher.
Altimeter will indicate 150 feet higher.
Altimeter will indicate 150 feet lower. <- correct answer--
Sorry, but this is really confusing me. If the pressure is 0.15'' less, then surely you have gained 150ft since pressure drops as altitude is gained?
David
Why?
Pressure stayed the same, you just told the altimeter the reference was lower.
Robert Gary
#2
[I may have been redundant below, but saying it two or three ways might give you a method that makes the MOST SENSE to you.]
Ok, the easy part: 1 inch Hg is about 1000 feet. So, 0.15 inches is going to be EITHER 150 up or down, right? You are going to hear "High to Low, Look out below" from others trying to help you -- but this didn't really do it for me although once you understand THIS issue, it WILL help you keep it straight.
Look out below, means that the INDICATED altitude will be lower than the TRUE altitude (people below might be in danger even though you THINK you are high ENOUGH.) So if YOU CHANGE from HIGH setting to LOW setting, you will INDICATE less than before.
This is a HIGH->LOW so it is a DECREASE -- or 150 feet in altitude [indicated --> true]
[Here is another way to UNDERSTAND the issue -- but it is a terrible way to REMEMBER it so you might want to re-read what is above after you either "get this" or "decide it doesn't help": When your altimeter is set to a LOWER VALUE, you are moving the BASE pressure (sea level) UP and this is LESS of a difference between that base and the current altitude setting pressure. So your FEET read lower when your PRESSURE setting is LOWER.]
Another thing to be careful about, SOME of the questions will give you "true altitude read High/Low" while some like this one will be based on "indicated altitude" (as yours above is.) BE CAREFUL that you are reading it correctly.
The PRESSURE you are setting is the BASE, and as you CLIMB the pressure gets lower. The ALTIMETER really reads the DIFFERENCE between these two pressures: Current altitude and the BASE sea level pressures. So a lower base (pressure, not altitude) gives LESS DIFFERENCE as the altitude continues to lower the pressure.
Since ALTITUDE gives a LOWER PRESSURE, reducing the pressure of the BASE gives a SMALLER DIFFERENCE ...a smaller difference between the Sea Level Base pressure and the Current Altitude Pressure.
Herb Martin
If you start over-thinking it you'll get mixed up. It's fine to understand the ins and outs, but in the air just think, "high to low, look out below." Going from "high temp/high pressure". to low means trouble - trouble means you're closer to the ground (AGL) than you think. What makes you think that? Indicated altitude.
So, the IA is higher, but the True altitude is lower. When you take into account the fact that you'll be keeping the plane at the same indicated altitude throughout, you're true altitude is now getting less and less.--
Charles Oppermann,
It's a simple rule: if the numbers in the pressure window get lower, so does the indicated altitude!
Patrick
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