Is there such a thing as "sweet spot" for CG? [Weight & Balance Question]

AggieMike88

AggieMike88

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The original "I don't know it all" of aviation.
Working on my W&B options for an Angel Flight tomorrow has me wondering if, for my Cessna 182P, there is a sweet spot for the CG that provides a performance edge.....

The numbers I have in FF's W&B are from the POH and create a graphic similar to the attached image. But we have the STC that extends the upper weight limit to 3100 lbs

center_grav.jpg
 
Rear edge. Least need for downforce by the elevator.

Answer would be different for some aircraft.
 
As far back as you can get that sucker.
 
As far back? Is that at Takeoff or Landing loading?
 
Yep James has it. The plane is more stable with a forward CG, but best performance occurs with aft CG.
 
It's an Angel Flight. Load forward. You need smoothness much more than a couple of extra knots.
 
Competition glider pilots have determined 85% aft is the best performing CG for best Ld. Least drag for the elevator position. Too far aft and you are pitch sensitive, too far forward and to much up elevator drag.

Your aircraft may vary.
 
asicer said:
How twitchy is Mike's 182P without the aft loading?
Click to expand...
What does "without the aft loading" mean? The further aft you go, the less stable the pitch is.

And it isn't that much faster.

Besides, without overloading the baggage, it's pretty hard to get anywhere near the aft limit in a 182P.
 
weilke said:
Rear edge. Least need for downforce by the elevator.

Answer would be different for some aircraft.
Click to expand...

Very true, the elevators on my Mooney in cruise actually in the down position (lifting the tail) with just myself, aft loading would make it worst.
OP: Go flying, when in cruise and trimmed correctly, check your elevator position.
 
teejayevans said:
Very true, the elevators on my Mooney in cruise actually in the down position (lifting the tail) with just myself, aft loading would make it worst.
Click to expand...

I believe the same is true for the short body Bonanzas at cruise.
 
If your aircraft has longitudinal stability (returns to level flight on its own after a longitudinal perturbation, i.e. up or down elevator momentarily), then the static and moving components of the horizontal tail are providing a net down force (negative lift). Lift, negative or positive, produces drag and negative lift is a double whammy because the wing has to generate additional positive lift to offset it. That is why max aft CG provides best speed performance (minimum negative lift required from the tail = reduced drag) and minimum stability. Others have already said this in fewer words but statements that some certified aircraft loaded within CG require positive lift from the tail made me feel that more words were needed. I may be wrong but I would be very surprised if inherent longitudinal stability is not a basic certification requirement of aircraft certified in the normal or utility categories. For the standard wing & tail configuration, I believe that down force from the tail in cruise flight is necessary to achieve that. If that isn't so, I'll be happy to learn something.
 
Having recently experimented in the glider with CG relocation, I can attest to aft CG needing less elevator.


It actually flew reasonably well considering.
 
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