preparing for commercial oral and practical

Mortimer Schnerd, RN wrote:
Mark T. Dame wrote:
The intricacy's of weight and balance similar to the knowledge test
questions. Load, fly, unload, fly, refuel, load, fly unload, refuel....
what's your weight, where's your CG, what about if you have to hold, when
will you reach bingo fuel and where will your CG be then? Talk to a Bonanza
owner about CG changes with fuel burn.
Additionally, your CG probably changes when you retract your gear.
That's one of my commercial DE's pet points.


While being technically correct (if he says so), what difference does it make?
Are you going to fly with the gear down to keep the CG in the same place that
you used to figure your W&B?

Cocktail party facts....

Not at all. We're talking about a commercial pilot checkride. As such,
you need to know more than for a private certificate. The point of the
exercise is to show the examiner that you understand these concepts and
actually do it.

Additionally, you do have the gear in both positions in flight. You
have it down at take off. You need to make sure that putting it up
isn't going to put your CG outside of the envelope right after take off
when you are still low, slow, and nose high. This could lead to a
departure stall. When you are landing, you put your gear down well
before you touch down, and you will be low and slow on final. The
difference between gear up and down may be a factor.

Now, as Jose pointed out, on the Arrow it's not very significant, but
that doesn't mean that it's that way for all planes.

Finally, as I said, we're talking about a checkride. Checkrides often
have you do things that you may not do in your day to day flying, but
you need to know and understand in case you need it. In any case, I'm
just giving advice on what to expect on the checkride.


-m
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Now, as Jose pointed out, on the Arrow it's not very significant

Actually I wasn't implying (half an inch) that it wasn't very
significant - when the CG range is only a handful of inches, it's
significant. And certainly when you're near the edge it bears watching.

Jose
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Jose wrote:
Now, as Jose pointed out, on the Arrow it's not very significant

Actually I wasn't implying (half an inch) that it wasn't very
significant - when the CG range is only a handful of inches, it's
significant. And certainly when you're near the edge it bears watching.

At the risk of arguing semantics, I wasn't saying "insignificant" only
"not very significant". I don't have my Arrow book here, but I believe
the CG range is around 10 to 12 inches. If you load well within the
envelope, the half inch is not going to have an appreciable affect on
aircraft performance.

But I'm getting off topic: what should someone expect on their
commercial checkride.

Make sure to do a W&B for gear up and gear down with takeoff fuel and
landing fuel. If the examiner doesn't care, then no big deal, but if
the examiner wants to see it and you didn't do it, then you have a
strike against you. On checkrides, you'll get plenty of strikes without
creating ones that could be easily avoided by a little bit of prep work.

Even if the examiner doesn't want or expect it, it can't hurt to have it
(unless you do it wrong).


-m
--
## Mark T. Dame
## CP-ASEL, AGI
## insert tail number here
## KHAO, KISZ
"The way to make a small fortune in the commodities market is to
start with a large fortune."
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Mark T. Dame wrote:
Jose wrote:
Now, as Jose pointed out, on the Arrow it's not very significant

Actually I wasn't implying (half an inch) that it wasn't very
significant - when the CG range is only a handful of inches, it's
significant. And certainly when you're near the edge it bears watching.

At the risk of arguing semantics, I wasn't saying "insignificant" only
"not very significant". I don't have my Arrow book here, but I believe
the CG range is around 10 to 12 inches. If you load well within the
envelope, the half inch is not going to have an appreciable affect on
aircraft performance.

But I'm getting off topic: what should someone expect on their
commercial checkride.

Make sure to do a W&B for gear up and gear down with takeoff fuel and
landing fuel. If the examiner doesn't care, then no big deal, but if
the examiner wants to see it and you didn't do it, then you have a
strike against you. On checkrides, you'll get plenty of strikes without
creating ones that could be easily avoided by a little bit of prep work.

Even if the examiner doesn't want or expect it, it can't hurt to have it
(unless you do it wrong).

Yes, and it is also just good operating practice, check ride or no. I
have it in my spreadsheet so that it calculates both CG locations and
all I have to do is enter the fuel expected at takeoff and at landing.

Balance isn't something to be taken lightly. Being 200 lbs over gross
typically isn't a big deal (I'm NOT recommending it), but being an inch
aft of the CG limit can be fatal.


Matt

Mark T. Dame wrote:


Additionally, you do have the gear in both positions in flight. You
have it down at take off. You need to make sure that putting it up
isn't going to put your CG outside of the envelope right after take off
when you are still low, slow, and nose high. This could lead to a
departure stall. When you are landing, you put your gear down well
before you touch down, and you will be low and slow on final. The
difference between gear up and down may be a factor.

Bull****. Somebody mentioned that the gear will make a 1/2" difference
in CG. I personally don't believe that, it's way too much. But
assuming it's true no airplane falls out of the sky by going from the CG
on the aft limit to 1/2" past the aft limit.

Newps wrote:


Bull****. Somebody mentioned that the gear will make a 1/2" difference
in CG. I personally don't believe that, it's way too much.

You don't have to believe it. If it's in the book, that's what you use.
It's not a matter of opinion. It is what it is.


But
assuming it's true no airplane falls out of the sky by going from the CG
on the aft limit to 1/2" past the aft limit.

No it doesn't. It affects the stability, the stall speed, and the
ability to recover from a stall. In an Arrow, I don't think it will
matter a hill of beans, but in a Cutlass, it might.

But the point of the conversation is preparing for the commercial
checkride, not whether or not raising the gear on a specific model of
airplane will move the CG too far aft for safe operation.


-m
--
## Mark T. Dame
## CP-ASEL, AGI
## insert tail number here
## KHAO, KISZ
"Help stamp out and abolish redundancy!"

"Mark T. Dame" wrote in message
...
Newps wrote:


Bull****. Somebody mentioned that the gear will make a 1/2" difference
in CG. I personally don't believe that, it's way too much.

You don't have to believe it. If it's in the book, that's what you use.
It's not a matter of opinion. It is what it is.

The POH for this PA-28R has "Moment due to retracting landing gear = +819
in-lbs" beneath the CG Range and Weight Chart, so I'm going to plan
accordingly for the exam. Thanks for the heads up!

-c

Somebody mentioned that the gear will make a 1/2" difference in CG. I personally don't believe that, it's way too much.

I showed the calculation. It's in the Arrow book.

But assuming it's true no airplane falls out of the sky by going from the CG on the aft limit to 1/2" past the aft limit.

No, but with thinking like that, if you decided to fly an inch out of CG
and ended up an inch and a half...

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
for Email, make the obvious change in the address.

Jose wrote:
Somebody mentioned that the gear will make a 1/2" difference in CG. I
personally don't believe that, it's way too much.

I showed the calculation. It's in the Arrow book.

But assuming it's true no airplane falls out of the sky by going from
the CG on the aft limit to 1/2" past the aft limit.

No, but with thinking like that, if you decided to fly an inch out of CG
and ended up an inch and a half...

I don't see a half inch of change, but it is still a fair amount
(0.34"). Here is my spreadsheet calculation from my last flight.
Unfortunately, the formating from Excel gets hosed pretty badly.

The point is that nobody knows for sure how far past the aft limit is
too far for any given flight condition and operating past the aft limit
at all is just dumb. The only thing dumber is not even knowing that you
are aft of the limit.

Matt

Piper Arrow PA28R-3009 N3705T

Quantity Weight Arm Moment
Airplane empty 1552.65 84.53 131253.15
Oil 15.00 29.50 442.50
Fuel 50 300.00 95.00 28500.00
Pilot and front seat passenger 385.00 85.50 32917.50
Rear passengers 125.00 118.10 14762.50
Baggage 30.00 142.80 4284.00
Gear retraction 819
2407.65 88.11897493 212159.65 Gear down
88.45914066 212978.65 Gear up
Gross Weight (2500 max) Center of Gravity Total Moment

I don't see a half inch of change

Depends on your gross weight. The lighter you are, the more change
you'll see. I used 2000 lbs, and rounded up a bit.

Jose
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