Flying with aft(er) CG

SixPapaCharlie

SixPapaCharlie

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Generally I have 2 adults up front and backseats empty or kids back there.
Recently when doing the young eagles deal I flew with a largish adult + 1 largish kid in back and a small kid up front

I have always heard the plane will fly differently as the CG moves but it was way more work too.

We were well within range but it didn't take moving much weight at all to change how it flies and the difference was hard to describe but it felt like a lot more work.

It felt as though I wasn't climbing as well and more of a mushing forward feeling and lots more corrections to maintain my climb etc. Airspeed was fine but everything just felt off.

This is not something we really did much in my training and it hasn't come up much as most of my flights are solo, or me and an adult or fully loaded but 2 little kids in back. That was a little different but not AS noticeable as the aft C.G.

Maybe it is something you just have to do a lot but it was a lot less fun feeling like I am fighting the plane the whole time.

As a student CG was brought up regarding its impact on stall recovery but not much was discussed about general flying characteristics, climbing, descending, landing, etc with CG changes. Certainly something to consider practicing during your training.
 
SixPapaCharlie said:
Generally I have 2 adults up front and backseats empty or kids back there.
Recently when doing the young eagles deal I flew with a largish adult + 1 largish kid in back and a small kid up front

I have always heard the plane will fly differently as the CG moves but it was way more work too.

We were well within range but it didn't take moving much weight at all to change how it flies and the difference was hard to describe but it felt like a lot more work.

It felt as though I wasn't climbing as well and more of a mushing forward feeling and lots more corrections to maintain my climb etc. Airspeed was fine but everything just felt off.

This is not something we really did much in my training and it hasn't come up much as most of my flights are solo, or me and an adult or fully loaded but 2 little kids in back. That was a little different but not AS noticeable as the aft C.G.

Maybe it is something you just have to do a lot but it was a lot less fun feeling like I am fighting the plane the whole time.

As a student CG was brought up regarding its impact on stall recovery but not much was discussed about general flying characteristics, climbing, descending, landing, etc with CG changes. Certainly something to consider practicing during your training.
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A good idea in any airplane you fly is to systematically fly the airplane at weights and CG's inching ever closer to the limits. Add 50 pounds and move the CG 0.25" (or whatever) at a time until you hit the aft limit at full gross. Do the same for the forward limit if hitting it is a possibility with the aircraft.

If you're not comfortable doing that, get an instructor to fly with you. And it isn't fair to use people as self loading ballast while you're testing your limits in the airplane - best to do that with inert baggage.
 
I've learned with 2 adults in the front, I need ballast in the baggage area (cherokee 180). I have 2 water tanks (those blue things), one 4 gal (26-30#) and the other 8 gal (56# - yes, I know water weighs 8# but I never fill to the top). Depending on what's in the backseat determines which tank I use. In the summer, even if it's just me, I have one of the tanks with me, just in case I land someplace unexpected.

There have been times I've had 4 adults - it was very cool (Feb) and absolutely legal both in W&B and CG. Will never do that again. Had another pilot with me (short 20 min trip for lunch) and we kept looking at each other in amazement. I was prepared at all times to turn around and go back. Climb wasn't the greatest but we got to 4000 AGL slower than normal but we got there.

When I fly YE, I never take 2 adults in the back on the first flight of the day. During the summer, I never take 2 adults period. Too hot.

This afternoon, runway altitude 5800, DA 9700. Welcome to Colorado. Arizona's worse for heat, but we start higher. I spent the day in my office in the basement.
 
SixPapaCharlie said:
Generally I have 2 adults up front and backseats empty or kids back there.
Recently when doing the young eagles deal I flew with a largish adult + 1 largish kid in back and a small kid up front

I have always heard the plane will fly differently as the CG moves but it was way more work too.

We were well within range but it didn't take moving much weight at all to change how it flies and the difference was hard to describe but it felt like a lot more work.

It felt as though I wasn't climbing as well and more of a mushing forward feeling and lots more corrections to maintain my climb etc. Airspeed was fine but everything just felt off.

This is not something we really did much in my training and it hasn't come up much as most of my flights are solo, or me and an adult or fully loaded but 2 little kids in back. That was a little different but not AS noticeable as the aft C.G.

Maybe it is something you just have to do a lot but it was a lot less fun feeling like I am fighting the plane the whole time.

As a student CG was brought up regarding its impact on stall recovery but not much was discussed about general flying characteristics, climbing, descending, landing, etc with CG changes. Certainly something to consider practicing during your training.
Click to expand...

An aft CG by itself won't affect climb rates or cause "mushing" at normal flying speeds. The most noticeable effects of an aft CG are the reduction in pitch stability and the decrease in "stick force per g". Put the two together and it's easy to over-rotate on takeoff, harder to maintain a constant climb rate, and chances are you'll balloon in the flare if you don't anticipate the change in control feedback.
 
SixPapaCharlie said:
It felt as though I wasn't climbing as well and more of a mushing forward feeling and lots more corrections to maintain my climb etc. Airspeed was fine but everything just felt off.
Click to expand...
That should be expected for the combination of extra weight and cg near the aft limit.

This is not something we really did much in my training and it hasn't come up much as most of my flights are solo, or me and an adult or fully loaded but 2 little kids in back. That was a little different but not AS noticeable as the aft C.G.
Click to expand...
When I train someone with no prior experience in planes of more than 2 seats, I try to get them at least one flight loaded to near max gross and near max aft cg so they can experience that for the first time with an instructor in the right seat.

Maybe it is something you just have to do a lot but it was a lot less fun feeling like I am fighting the plane the whole time.
Click to expand...
You didn't say whether you actually ran a W&B, but if you were "fighting the plane the whole time", I have to wonder whether "a largish adult + 1 largish kid in back and a small kid up front" might have put you a bit aft of the legal aft limit.
 
I'm going to exercise my "right to get smarter" here for a moment.

The way I learned it, CG limits impact as follows:

If you have a CG too far forward, your elevator may lack the authority to pull the nose up, particularly at low speed (think landing flare).

If you have a CG too far aft, you may not be able to push the nose forward if you get into a stall.

Is that basically correct (again, I always reserve the right to get smarter, and am seriously asking for experts to correct me if wrong)?
 
I have an ipad for Foreflight. That is the only apple product that I have allowed to persist in my household ;)

What is the app called?
 
Jesse (board moderator and world's best pilot) built one for iPad/iPhone called WnBPro. It allows you to enter all the data to build one for your specific airplane as well as having a library to draw from. Nice app. I've got it with the WnB built for both C-172's I routinely fly.

John
 
JeffDG said:
The way I learned it, CG limits impact as follows:

If you have a CG too far forward, your elevator may lack the authority to pull the nose up, particularly at low speed (think landing flare).
Click to expand...
Correct. And to a certain extent, this is self-correcting, because if you get it far enough out of forward limits, you won't be able to rotate for takeoff. You'll also see some performance losses due to the extra induced drag of both the extra tail downforce required to hold the nose up plus the extra wing lift required to match the extra tail downforce..

If you have a CG too far aft, you may not be able to push the nose forward if you get into a stall.
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Not so much -- you'd have to be incredibly far aft to have insufficient elevator power to push the nose down, and you would have long ago passed the point where instability had already killed you. See Dr. John Decker's discussion on this here on his "See How It Flies" web site. What kills you with excessive aft cg is your inability to control the plane in pitch -- control forces get so light, and the pitch response becomes undamped to the point you'd be overcontrolling and chasing pitch until the airplane went out of control. For a classic example of that happening to a Piper PA31T with fatal results, see NTSB AAR 78-1.
 
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The plane will however fly most efficiently with the CG at the aft limit, as there is the least amount of aerodynamic drag present. (Strictly speaking, it would fly most efficiently if the CG was coincident with the center of lift barring the effects of pitch control instability, but obviously you wouldn't want to fly that way.)
 
Bottom line is: Put the heavy people close to the CG, whether they like it or not.

Bob Gardner
 
Sac Arrow said:
The plane will however fly most efficiently with the CG at the aft limit, as there is the least amount of aerodynamic drag present. (Strictly speaking, it would fly most efficiently if the CG was coincident with the center of lift barring the effects of pitch control instability, but obviously you wouldn't want to fly that way.)
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Some Bonanzas generate a small amount of positive lift at the tail when the CG is at the aft limit. A bobweight on the elevator cable provides the FAA required stick force per g.
 
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