CFII oral exam guide questions?

Michael wrote:
Then you really didn't understand the physics of how a pitot tube
works.

Think of a pitot tube as an energy conversion device. There is energy
in moving air. There is energy in pressurized air. A pitot tube is a
device for converting the former into the latter. An ASI is actually a
pressure gauge (usually a brass bellows that drives the needle) that
measures the difference between the ram pressure and the static
pressure. The ram pressure is always going to be higher, because the
speed of the airplane is forcing air in, and pressurizing it.

I understood that. I just way over estimated how much air went through
the pitot tube. Any tube that has a hole in the front and a smaller
hole in the back would do the job. The net pressure to the A/S
indicator would be less but that's just a calibration issue. So I
understood the concept but over estimated the flow.

-Robert

Michael wrote:
I always thought it was worthwhile to show an instrument student a
disassembled compass. Once he sees how the counterweight works to
compensate for the vertical component of the magnetic field, turning
errors are obvious

Seeing stuff opened up is always useful. My FBO has a sectioned
carburator sitting around in one of the classrooms; I take every
opportunity to show people how it works inside. Some of them actually
pay attention :-)

I also like to pull the cowling off planes and show students what's
underneath. Many have never seen anything more than can be seen from
the oil filler door. It's very instructive when you see things like
the alternate air control opening up a little door on the air filter
housing, or tracing out the wires from the plugs to the magnetos.

Well, it can be done - but WHY? There is some value in knowing that
the radio determines whether to use the VOR or LOC circuitry based on
the frequency selected. There is much value to understanding the
difference, especially as it applies to the validity of a VOR check for
LOC/ILS ops. Memorizing what the actual frequencies are seems rather
pointless.

I agree that knowing which are VOR and which are LOC is not terribly
practical for most pilots, but knowing which are NAV and which are COM
is. I've seen more than one pilot keep spinning the knobs on the COM
radio trying to to figure out why they can't find 116.6 to get the
ATIS.

Well, Jim, it almost COULD work that way, but it doesn't. :-[
VOR azimuth angle is measured by a phase comparison
between two sinusoidal signals, not a time-delay measurement.
The VOR reference signal is frequency modulated on a subcarrier,
while the azimuth signal is from amplitude modulation on the
radio-frequency carrier, caused by the VOR's rotating cardioid beam.

Separately, DME distance is measured radar-like, by the time it takes
for the ground transponder to *reply* with a delayed pulse-pair
to an interrogation transmitted from the aircraft.

"Jim Macklin" wrote in message news:vhDjg.137276$k%3.119945@dukeread12...
You can explain how a VOR/DME works with a simple visual
model.

There is a large lake with an island in the middle. There
is a lighthouse with a rotating beacon that makes one
revolution a minute. It has a white beacon and a green
beacon, when the white beacon is passing North, a big strobe
light on top flashes and a very loud horn sounds.

You see the strobe light flash and 6 seconds later see the
green beacon sweep by. Where are you? 216 degrees from the
beacon. Ten seconds after the strobe, you hear the horn,
how far away? 2 miles.

VOR is the same, just faster.

--
James H. Macklin
ATP,CFI,A&P

1) He showed me disassembled instruments when describing how each works
(how well can most of us explain how an altimeter really works inside,
I thought a mag compass was ball shaped )


I always thought it was worthwhile to show an instrument student a
disassembled compass. Once he sees how the counterweight works to
compensate for the vertical component of the magnetic field, turning
errors are obvious - as well as why there are no turning errors while
taxiing. Accelerationa and deceleration errors are equally obvious.

Calling Jay, calling Jay. Disassembled instruments would be way cool in
your aviation themed motel.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

Well, Jim, it almost COULD work that way, but it doesn't. :-[
VOR azimuth angle is measured by a phase comparison
between two sinusoidal signals, not a time-delay measurement.
The VOR reference signal is frequency modulated on a subcarrier,
while the azimuth signal is from amplitude modulation on the
radio-frequency carrier, caused by the VOR's rotating cardioid beam.

It's indirect, but isn't a measurement of phase difference of two
different waves the same as the measurement of the time difference
between crests (once you take into account the frequency and the speed
of light)? It's like saying the alimiter measures altitude. It's not
technically correct (and yes, the difference is meaningful under some
circumstances) but gets the job done.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

"Jose" wrote in message . com...
Well, Jim, it almost COULD work that way, but it doesn't. :-[
VOR azimuth angle is measured by a phase comparison
between two sinusoidal signals, not a time-delay measurement.
The VOR reference signal is frequency modulated on a subcarrier,
while the azimuth signal is from amplitude modulation on the
radio-frequency carrier, caused by the VOR's rotating cardioid beam.

It's indirect, but isn't a measurement of phase difference of two
different waves the same as the measurement of the time difference
between crests (once you take into account the frequency and the speed
of light)? It's like saying the alimiter measures altitude. It's not
technically correct (and yes, the difference is meaningful under some
circumstances) but gets the job done.

Jose
--


The time domain and the frequency domain are related conventionally
through a mathematical manipulation called the Fourier Transform.
However, the measurement methods used in the two domains
are considerably different.
The VOR system was designed for measurements in phase space.
DME, of course, was designed for the time domain.

Who cares how it works ?

R u going to build one or fix one ?

Know how to operate the equipment and not how the equipment operater -

M.


"Robert M. Gary" wrote in message
oups.com...

Mitty wrote:
You might look at:

http://www.dauntless-soft.com/PRODUC...?DMODE=FAATEST

I have used their software for written tests and found it to be very
good. I tried the "RideReady" Commercial oral package when it was
very new, a couple of years ago and at that time I thought it was kind
of weak.

They don't appear to have anything for the CFII . As it turn out, my
instructor knows an enourmous amount of stuff and I'm spending late
nights learning stuff I never thought I'd know.
1) He showed me disassembled instruments when describing how each works
(how well can most of us explain how an altimeter really works inside,
I thought a mag compass was ball shaped )
2) He also explained how VORs really work (I thought they broadcast
actual radials but they actually time the difference between a
reference signal and a rotating sweeping signal).
3) He expects me to memorize the freq of markers and be able to
distinguish a loc freq from vor freq by looking at the freq number.
4) Even the stuff I thought I knew was wrong. I thought lots of air was
always running through the pitot tube and out the drain hole.
Apparently only a very, very small amount of air comes out the back of
the drain hole and the actual volume of air running through the pitot
is very small. Looking at all the books, I got the impression air was
just rushing through.

-Robert

Robert M. Gary wrote:
I understood that. I just way over estimated how much air went through
the pitot tube. Any tube that has a hole in the front and a smaller
hole in the back would do the job. The net pressure to the A/S
indicator would be less but that's just a calibration issue. So I
understood the concept but over estimated the flow.

Mea culpa. There was actually something you didn't know (or didn't
consider) but it was so obvious to me that I never even thought about
it. And really it's much less obvious than the physics - unless you
happen to routinely build and design stuff. I say this by way of
explanation and apology.

You're right - you could in theory have any tube with a bigger hole at
the front and a smaller one at the back, and the indication would be
less but could be calibrated out. There's a reason it's not done that
way, and it has nothing to do with the physics and everything to do
with manufacturing practices and standards.

ASI's are interchangeable, and it would be a maintenance nightmare not
to have them interchangeable. Imagine that every pitot tube had to
have its own matching (calibrated) ASI. Often the pitot tube is made
by the manufacturer. Fortunately they rarely fail, because
replacements are sometimes very expensive or even impossible to find.
Piper made its own pitot tubes for a long time. Go try to find one for
a short winger.

ASI's will all fail eventually. They're made with brass bellows that
are soldered together. The solder joints move and hold (just a little)
pressure. Eventually they are guaranteed to leak. The leak will show
up as a too-low airspeed indication.

So for practical purposes, you really need a pitot tube that supplies
approximately the right ram pressure.

Michael

Mark Hansen wrote:
I thought this allowed rain water to drain as well. Otherwise, couldn't
the water build up and eventually get into the pressure line to the
ASI?

If there is a hole, then yes, it will drain water as well, because
there is flow into the tube. But without a drain hole, there is no air
flow into the pitot tube at all - so how will the rain drops get in? I
suppose if you flew through a heavy enough rain it could happen - but
that implies flying the plane IFR, and it's pretty rare for a plane to
be IFR capable and have no pitot heat. Rare, but not unknown.

Michael

I've used this analogy many times to explain VOR operation to students.. but
using one rotating beacon and the flash.. I like the idea of adding the horn
for the distance.

BT

"Mark Hansen" wrote in message
...
On 06/13/06 12:08, Jim Macklin wrote:
Just like the rotating beacon at the airport, the two lights are 180
apart and rotate on the common shaft.

Yes, you could have just one light rotating, but two identifiable beacons
makes the system more useable and faster.

English lesson... "white beacon passing North...green beacon sweeps by"
Seems that both are moving.

Thanks, but I don't really need the English lesson.
Your description made it sound like there were two rotating
beacons, and I couldn't see why that was necessary to make
the point. I asked the question so you could clarify.

Having one rotating beacon seems to illustrate the functionality.
If the point is to make the system easy for a student pilot to
understand, why not keep it simple?

The "useable[sic] and faster" issue isn't really necessary for
the student to understand how the system works, IMHO :-)

I do like the analogy, though.

Thanks,





"Mark Hansen" wrote in message
...
| On 06/13/06 11:15, Jim Macklin wrote:
| You can explain how a VOR/DME works with a simple visual
| model.
|
| There is a large lake with an island in the middle. There
| is a lighthouse with a rotating beacon that makes one
| revolution a minute. It has a white beacon and a green
| beacon, when the white beacon is passing North, a big strobe
| light on top flashes and a very loud horn sounds.
|
| You see the strobe light flash and 6 seconds later see the
| green beacon sweep by. Where are you? 216 degrees from the
| beacon. Ten seconds after the strobe, you hear the horn,
| how far away? 2 miles.
|
| So are both the white and green beacons rotating?
|
| Don't you just need an omnidirectional strobe (with horn for
| distance measurements) and a single rotating beacon?
|
|
| VOR is the same, just faster.
|
|
| Steer your boat so the bow always points to the light and
| you've got an ADF homer.
|
|
|
|
|
|
| --
| Mark Hansen, PP-ASEL, Instrument Airplane
| Cal Aggie Flying Farmers
| Sacramento, CA



--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA