Effects of CG on cruise speed

Hello All,
Does anyone know if the location of the CG effects the cruise speed in
something like a Skyhawk of Skylane? In other words, given the same
weight, will the cruise speed at 75% power be higher or lower if the CG
is moved from near its forward limit towards its aft limit.

I think the aft CG will result in a higher cruise speed because the arm
between the center of lift and CG will be reduced (assuming CL is
behind the CG) and the tail will have to do less work.

Any ideas?

Higher. Moving weight aft means that the download on the horizontal
stabilizer is reduced.. Less elevator deflection means less drag.

Bob Gardner

"gman" wrote in message
oups.com...
Hello All,
Does anyone know if the location of the CG effects the cruise speed in
something like a Skyhawk of Skylane? In other words, given the same
weight, will the cruise speed at 75% power be higher or lower if the CG
is moved from near its forward limit towards its aft limit.

I think the aft CG will result in a higher cruise speed because the arm
between the center of lift and CG will be reduced (assuming CL is
behind the CG) and the tail will have to do less work.

Any ideas?

gman wrote
I think the aft CG will result in a higher cruise speed

That's the way we did it in the airline business.

Bob Moore
PanAm (retired)

Yep. And you'll know you went too far back when 1) you've exceeded the
CG range in the POH and 2) when the a/c gets uncomfortably squirrly in
all axis or axii or whatever.

....seeking the middle of the range keeps things comfortable and allows
for some shifting, weighing errors, and such.

Bob Gardner wrote:
Higher. Moving weight aft means that the download on the horizontal
stabilizer is reduced.. Less elevator deflection means less drag.

Bob Gardner

"gman" wrote in message
oups.com...

Hello All,
Does anyone know if the location of the CG effects the cruise speed in
something like a Skyhawk of Skylane? In other words, given the same
weight, will the cruise speed at 75% power be higher or lower if the CG
is moved from near its forward limit towards its aft limit.

I think the aft CG will result in a higher cruise speed because the arm
between the center of lift and CG will be reduced (assuming CL is
behind the CG) and the tail will have to do less work.

Any ideas?

Bob Moore wrote:

I think the aft CG will result in a higher cruise speed

That's the way we did it in the airline business.

Bob Moore
PanAm (retired)

Heh. "This is the captain speaking - would all fat *******s please take
up the empty seats in the back of the plane, please...Your cooperation
is greatly appreciated"

gman wrote:

I think the aft CG will result in a higher cruise speed because the arm
between the center of lift and CG will be reduced (assuming CL is
behind the CG) and the tail will have to do less work.

I would think the CG that requires the least amount of trim would be the
most efficient. If that is in fact true, the most efficient CG would
vary for different aircraft.

Maule Driver wrote:

...seeking the middle of the range keeps things comfortable and allows
for some shifting, weighing errors, and such.


Don't forget fuel burn. But does anybody know how much faster if you do
load it farther aft?

Was it really necessary for me to say that the CG should be kept within the
operating envelope? Are newgroupies so anal that everything must be spelled
out? The manufacturer provides loading information so that pilots can choose
where they want the CG to be depending on their needs...the OP is obviously
opting for speed, and loading to the aft edge of the envelope is just as
valid as a more central loading.

Bob Gardner

"Maule Driver" wrote in message
m...
Yep. And you'll know you went too far back when 1) you've exceeded the CG
range in the POH and 2) when the a/c gets uncomfortably squirrly in all
axis or axii or whatever.

...seeking the middle of the range keeps things comfortable and allows for
some shifting, weighing errors, and such.

Bob Gardner wrote:
Higher. Moving weight aft means that the download on the horizontal
stabilizer is reduced.. Less elevator deflection means less drag.

Bob Gardner

"gman" wrote in message
oups.com...

Hello All,
Does anyone know if the location of the CG effects the cruise speed in
something like a Skyhawk of Skylane? In other words, given the same
weight, will the cruise speed at 75% power be higher or lower if the CG
is moved from near its forward limit towards its aft limit.

I think the aft CG will result in a higher cruise speed because the arm
between the center of lift and CG will be reduced (assuming CL is
behind the CG) and the tail will have to do less work.

Any ideas?

Com'on Bob, Chill.

I almost wrote something like "I just wanted to add my 2 cents to the
ol' sage's answer"

I was just rambling with my thoughts on rearward CGs. Your answer was
accurate and complete as always. Heck, you wrote the book.

Bob Gardner wrote:
Was it really necessary for me to say that the CG should be kept within the
operating envelope? Are newgroupies so anal that everything must be spelled
out? The manufacturer provides loading information so that pilots can choose
where they want the CG to be depending on their needs...the OP is obviously
opting for speed, and loading to the aft edge of the envelope is just as
valid as a more central loading.

Bob Gardner

"Maule Driver" wrote in message
m...

Yep. And you'll know you went too far back when 1) you've exceeded the CG
range in the POH and 2) when the a/c gets uncomfortably squirrly in all
axis or axii or whatever.

...seeking the middle of the range keeps things comfortable and allows for
some shifting, weighing errors, and such.

Bob Gardner wrote:

Higher. Moving weight aft means that the download on the horizontal
stabilizer is reduced.. Less elevator deflection means less drag.

Bob Gardner

"gman" wrote in message
egroups.com...


Hello All,
Does anyone know if the location of the CG effects the cruise speed in
something like a Skyhawk of Skylane? In other words, given the same
weight, will the cruise speed at 75% power be higher or lower if the CG
is moved from near its forward limit towards its aft limit.

I think the aft CG will result in a higher cruise speed because the arm
between the center of lift and CG will be reduced (assuming CL is
behind the CG) and the tail will have to do less work.

Any ideas?

Heh. "This is the captain speaking - would all fat *******s please take
up the empty seats in the back of the plane, please...Your cooperation
is greatly appreciated"

Fat ******* #1: I'll do it for $300. How much is fuel per gallon?

Jose
--
The monkey turns the crank and thinks he's making the music.
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