Overweight or out of CG

skidoo

skidoo

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skidoo
Here is a hypothetical. I see that my CG limit charge shows a constant limit of 46" aft regardless of weight. But, the forward limit is reduced aft as weight increases. If one draws a line for the slope as weight increases, the forward limit will meet the aft limit at about 400 lbs over gross. So, here is the question.

Suppose that a situation arose where your life depended on getting from point A to B (sea level) and it had to be done regardless of regulation or limit. There are only two choices allowed. You have a choice of either being at gross weight but 2" forward of the CG limit or you can be 200 lbs over gross, but in the center of the CG range as interpolated above.

From an entirely technical standpoint, which would entail the least risk of crashing and why.
 
how long are the runways, what are the weather conditions, what climb performance is required for the flight? what does the W&B envelope look like?
 
How much is the gross weight of the aircraft? 200lbs over gross for a J-3
could be a lot different than 200 lbs over gross for a Matrix.

But to answer your question, if the temp was cool or cold, I'd be happier
200 lbs over gross in my 140 than 2" forward CG. My 140 will run out of
stabilator at a forward CG even if I'm below gross. Plus, I have the 160hp
engine, so the aircraft is more like the 160 than the 140.
 
Having tried with less than satisfying results to land a 58 Baron that was loaded (by the owner) a couple inches forward, I'll take the extra weight in the envelope every time. Garrison wrote an interesting article in Flying Magazine a while back if you're interested in the details.

FYI, the forward CG slope line doesn't necessarily remain consistent until it intersects the aft line. The military publishes a heavy ops chart for the King Air 200 that most civilian pilots never see. Military MGTOW is 14k vs 12.5 for us. The forward line (that is consistent with the one you describe for your plane, just different numbers) slopes consistently to 13.5k, then again becomes a parallel line to the aft line up to 14.k

skidoo said:
Here is a hypothetical. I see that my CG limit charge shows a constant limit of 46" aft regardless of weight. But, the forward limit is reduced aft as weight increases. If one draws a line for the slope as weight increases, the forward limit will meet the aft limit at about 400 lbs over gross. So, here is the question.

Suppose that a situation arose where your life depended on getting from point A to B (sea level) and it had to be done regardless of regulation or limit. There are only two choices allowed. You have a choice of either being at gross weight but 2" forward of the CG limit or you can be 200 lbs over gross, but in the center of the CG range as interpolated above.

From an entirely technical standpoint, which would entail the least risk of crashing and why.
Click to expand...
 
tonycondon said:
how long are the runways, what are the weather conditions, what climb performance is required for the flight? what does the W&B envelope look like?
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OK, say on a 182, 3100lb gross, 10000 ft runway, clear, calm, dry.
 
The short answer is that I'd rather be overgross than out of CG, but of course, this raises the obvious question of "if I'm overgross, how do I know that I'm in CG?"
-harry
 
mantakos said:
The short answer is that I'd rather be overgross than out of CG, but of course, this raises the obvious question of "if I'm overgross, how do I know that I'm in CG?"
-harry
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Ditto. If you can get airborne and avoid obstacles the primary issue with excess weight is a lack of climb performance. If you remain below the published max GW Va you can't overstress the wings (above Va you might be able to overstress the wings if while staying within the published max g limits). If you are loaded ahead of the forward CG limit you might not be able to flare the airplane for landing and you can experience a tail stall under certain circumstances that wouldn't stall the tail if the CG was within limits.
 
Overweight isn't really a huge concern for me provided I can depart the runway and climb. With enough length you can easily determine if a departure is possible.

Out of CG, is something, I have little interest in messing with.
 
jesse said:
Overweight isn't really a huge concern for me provided I can depart the runway and climb. With enough length you can easily determine if a departure is possible.

Out of CG, is something, I have little interest in messing with.
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One has to consider gross weight in figuring load factor, too, however... which affects V-speeds and, sometimes, the ability for the wings to remain on the plane. :D
 
I'm not willing to try the experiment in real life...but how much of the overweight is in fuel...and how much will burn off during flight? The plan may be able to take off and fly nose-heavy...landing will be tricky unless landed hot to give enough lift to the elevators so you don't land on the nose.
 
I'd rather go over gross. Remember, a 60 degree bank doubles the g-forces on your plane, effectively doubling your weight. The plane can still fly.

I have no idea, nor do I wish to learn, what a 60 degree bank will do if the plane is out of CG.
 
Cap'n Jack said:
I'm not willing to try the experiment in real life...but how much of the overweight is in fuel...and how much will burn off during flight? The plan may be able to take off and fly nose-heavy...landing will be tricky unless landed hot to give enough lift to the elevators so you don't land on the nose.
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one thing worth noting is that if the extra weight is in the wings that actually reduces the bending moment on the wings vs. having the extra weight in the fuselage.
 
tonycondon said:
one thing worth noting is that if the extra weight is in the wings that actually reduces the bending moment on the wings vs. having the extra weight in the fuselage.
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That's the reason for some a/c having a maximum zero fuel weight, correct?


Trapper John
 
Steve Foley said:
I'd rather go over gross. Remember, a 60 degree bank doubles the g-forces on your plane, effectively doubling your weight. The plane can still fly.

I have no idea, nor do I wish to learn, what a 60 degree bank will do if the plane is out of CG.
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Bank angle has nothing to do with G-forces. You can be at 1 G at any angle of bank. You can be at 2 G at any angle of bank. etc.

Pulling on the yoke/stick (increasing on the angle of attack) increases the G forces. Turning the yoke/stick (increasing bank) does not.
 
Timely article about some people local to me that died in a crash last year.

A small, private plane was overloaded and improperly balanced when it crashed and killed all six aboard in West Virginia a year ago, the National Transportation Safety Board said.....


The NTSB said the plane weighed about 4,902 pounds at takeoff, which was about 332 pounds over the manufacturer's limit of 4,570 pounds.
Click to expand...
http://www.chicagobreakingnews.com/...d:+ChicagoBreakingNews+(Chicago+Breaking+News)
 
skidoo said:
Suppose that a situation arose where your life depended on getting from point A to B (sea level) and it had to be done regardless of regulation or limit. There are only two choices allowed. You have a choice of either being at gross weight but 2" forward of the CG limit or you can be 200 lbs over gross, but in the center of the CG range as interpolated above.

From an entirely technical standpoint, which would entail the least risk of crashing and why.
Click to expand...
Can't say from the information given. Here's why...

You have no idea until you try it whether you can rotate for takeoff with the cg 2 inches forward of the limit. You could go zinging down the runway and off the end with the yoke full aft -- or maybe not, but you won't know until you try it. OTOH, you can make some good guesses on the aircraft's performance at 200 lb over gross if you interpolate the curves for takeoff/climb performance. If those curves says you won't make it over the trees, you can be pretty sure that taking off 200 lb over gross won't work, and your only chance of escaping the Hovitos Indians is to offload the extra 200 lb and hope the plane rotates on command. OTOH, if the curves say you can make it 200 lb over gross, you're probably better off keeping the cg inside the envelope and not pulling any excessive g-forces during the flight. So...

How hot? How long a runway? Elevation? How high the obstacles? Any wind? With that information, you can make a good guess on your ability to get out 200 lb over gross, and then you can choose between taking off heavy or out of cg. And if you guess wrong, dying in the crash will probably hurt less that what the Hovitos Indians will do to you, anyway.
 
Capt. Geoffrey Thorpe said:
Bank angle has nothing to do with G-forces. You can be at 1 G at any angle of bank. You can be at 2 G at any angle of bank. etc.

Pulling on the yoke/stick (increasing on the angle of attack) increases the G forces. Turning the yoke/stick (increasing bank) does not.
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My guess is that most readers understood what I meant. Sorry you didn't.
 
Steve Foley said:
My guess is that most readers understood what I meant. Sorry you didn't.
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Perhaps most. But based on things I hear and read, not all.

Sorry, but this is one of my pet peeves. 'We" say that banking increases stall speed so often that at least some pilots start to believe it. And that is at best just plain wrong. At worst it results in dead pilots.

Consider the ever popular stall / spin on the base to final turn. What is the "explanation" given for this? The pilot was TRYING TO AVOID TOO MUCH BANK and was skidding around with the rudder while pulling on the yoke. Why was the pilot trying to avoid BANKING and not trying to avoid PULLING? Because he/she has been taught over and over and over that stall speed goes up with bank - the pull is assumed to be understood. Bad assumption.
 
rottydaddy said:
One has to consider gross weight in figuring load factor, too, however... which affects V-speeds and, sometimes, the ability for the wings to remain on the plane. :D
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With most certified airplanes, you are going to be able to take on a considerable amount of weight over gross without the wings falling off. Lots of ferrying is done with them way over-weight, etc. No, you cannot count on book performance or Part-23 behavior if you're overweight. But matters are much worse when you're out of CG.

When my dad cropdusted, there was a spot on the runway they would mark. If they couldn't take to the air by that spot they were too heavy to fly. They always loaded to where they had a ceiling under 1000 AGL. If the engine had ever quit they would have been dead. Never had the ability to dump the load in either Stearman.
 
smigaldi said:
Timely article about some people local to me that died in a crash last year.

http://www.chicagobreakingnews.com/...d:+ChicagoBreakingNews+(Chicago+Breaking+News)
Click to expand...

After a quick peak at this it leads to a few questions.

Appears he loaded at or near MAX GW then added fuel. Over at take off by about 56 gallons. Then that he ran short before he anticipated and was landing tail heavy.

Doesn't lugging the excess weight around take more energy / fuel to lift and to keep it in the air. Thus the increased fuel burn over the same plane lightly loaded.

Looking at the 172RG POH CG has the major effect on stall speed and weight on take off distance. Aftet that they are no longer listed as factors for RATE OF CLIMB, TIME FUEL AND DISTANCE TO CLIMB, CRUISE PERFORMANCE, RANGE, ENDURANCE or LANDING DISTANCE.

Since I can fly solo at starting at about 1,850 lbs with a little fuel and MAX GW is 2,650. Doesn't the extra 800 LBS effect performance in all of those categories?
 
Great responses. Sounds like a consensus that being within CG is most critical. So, I would like to expand the question to this:

Are you comfortable if the CG is within the envelope, but near the forward CG limit, or would you re-adjust distribution or add ballast to bring the CG closer to the center?

I am thinking that it may be best (and provide consistent flying characteristics) if I always aim for being at least 2" from either limit on this AC. It has a range of 33" to 46" empty to between 41" and 46". Or perhaps even closer to center between 38" and 42" at the low end to 43 to 44" at gross.

I guess what I am wondering is if the best compromise is in the center. Or if the envelope is biased on one end for safety. Are there margins with the envelope limits. I am not comfortable being loaded right near a limit and not having additional margins for safety.
 
As long as I'm within CG, I'm not inclined to spend a lot of time trying to "optimize" it. I generally place stuff within the cabin based on need, the stuff I might need to access during flight goes in the back seat, the stuff I don't goes in the baggage compartment. I'll make compromises if I have to, to meet CG, but I'm not going to put something in the baggage compartment that I think I might want access to during the flight, or move a front-seat passenger to the back, just to be closer to "optimal" CG.

Really, there are enough things to worry about for a long cross-country flight, and it takes me long enough as it is to get in the air, I'm just not looking for more things to "perfect", the impact just isn't all that significant.

Besides, on any given flight, the CG is going to shift throughout the flight as you burn fuel.
-harry
 
I usually put any unneeded stuff as far aft as possible. aft CG (within limits) gives a slightly better cruise speed. like harry says in some airplanes you have to pay attention to the CG shift as fuel is burned although in most airplanes i've flown the shift is either negligible or forward. I think the 421 shifted slightly aft as fuel burned
 
skidoo said:
I am not comfortable being loaded right near a limit and not having additional margins for safety.
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That's fine if that's what you want to do, but you give up some utility in the process.

It's not that hard to look at the W&B chart and load up to see how things are near the edges of the envelope. You might find that it's just not that big a deal.


Trapper John
 
skidoo said:
Great responses. Sounds like a consensus that being within CG is most critical. So, I would like to expand the question to this:

Are you comfortable if the CG is within the envelope, but near the forward CG limit, or would you re-adjust distribution or add ballast to bring the CG closer to the center?

I am thinking that it may be best (and provide consistent flying characteristics) if I always aim for being at least 2" from either limit on this AC. It has a range of 33" to 46" empty to between 41" and 46". Or perhaps even closer to center between 38" and 42" at the low end to 43 to 44" at gross.

I guess what I am wondering is if the best compromise is in the center. Or if the envelope is biased on one end for safety. Are there margins with the envelope limits. I am not comfortable being loaded right near a limit and not having additional margins for safety.
Click to expand...
Certain airplanes like being closer to the middle than others...they just "fly better" in mid-range CG's. But if I'm in, I'm in, and I'll go fly. Unless you have some hard data for an airplane that says it's safer farther from the limits, I'd say that would be a fairly arbitrary attempt at increasing safety.

Never flown an airplane out of aft CG, but I've flown a couple out forward (unlike Wayne's experience, it wasn't a 'loading' problem so much as a problem with a mechanic calculating a new weight and balance for an equipment change when he wasn't nearly as smart as a fifth-grader.) Let's just say it's "definitely noticeable", and I have no desire to do it again.

Fly safe!

David
 
skidoo said:
OK, say on a 182, 3100lb gross, 10000 ft runway, clear, calm, dry.
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Well, you just made the answer pretty easy. This is straight out of the C182 TCDS:

Special Ferry Flight Authorization. Flight Standards District Offices are authorized to issue Special overweight ferry flight authorizations. This airplane is structurally satisfactory for ferry flight if maintained within the following limits: (1) Takeoff weight must not exceed 130% of the maximum weight for Normal Category; and (2) The Never Exceed Airspeed (VNE) and Maximum Structural Cruising Speed (VC) must be reduced by 30%; and (3) Forward and aft center of gravity limits may not be exceeded; and (4) Structural load factors of +2.5 g. to -1.0 g. may not be exceeded. Requirements for any additional engine oil should be established in accordance with Advisory Circular AC23.1011-1. Increased stall speeds and reduced climb performance should be expected for the increased weights. Flight characteristics and performance at the increased weights have not been evaluated.
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There's your answer.
 
You made this a theoretical question, but it was practical for me on a recent phase check for my student solo privileges. Between the CFI and me in a Skyhawk we were 550 pounds in the front seat. I calculated the W&B like seven times and even only fueled to the tabs, we were forward CG. I had a 20lb bag of kitty litter with me ready to ride in the tail to balance us out. At full fuel there's really no way to make it work: you're either forward CG or overweight.

So here's my question. Page 6-9 of the POH says the moment arm for the front seat is 37. But it's actually 34-46, for the seat adjustment. I'm tall, so I ride pretty far back. Just how far back? I guess I should measure.
 
NelsonMinar said:
You made this a theoretical question, but it was practical for me on a recent phase check for my student solo privileges. Between the CFI and me in a Skyhawk we were 550 pounds in the front seat. I calculated the W&B like seven times and even only fueled to the tabs, we were forward CG. I had a 20lb bag of kitty litter with me ready to ride in the tail to balance us out. At full fuel there's really no way to make it work: you're either forward CG or overweight.
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Time to buy a 182.
 
I was told some years back that the plane in the movie "Flight of the Phoenix" (I forget if it was the original or remake) crashed after going over the hill in the last scene because of forward CG and the pilot died.
 
Capt. Geoffrey Thorpe said:
Perhaps most. But based on things I hear and read, not all.

Sorry, but this is one of my pet peeves. 'We" say that banking increases stall speed so often that at least some pilots start to believe it. And that is at best just plain wrong. At worst it results in dead pilots.
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Every chart I've seen on FAA tests and training publications indicates that load factor and stall speed increase with bank angle.

Per the graph below, a 60-degree bank introduces a load factor of 2 and an increase in stall speed of 40% over that experienced in level flight. How am I misinterpreting this?

attachment.php


And, on topic, I'd pick to depart over gross before out of CG, if as you say "my life depended on it."
 

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TangoWhiskey said:
Every chart I've seen on FAA tests and training publications indicates that load factor and stall speed increase with bank angle.

Per the graph below, a 60-degree bank introduces a load factor of 2 and an increase in stall speed of 40% over that experienced in level flight. How am I misinterpreting this?
Click to expand...

The stall speed rises by the square root of the load factor. A 60-degree level banked turn produces 2G loading, the square root of which is 1.41, or 41% over the 1-G stall speed. At four G, the stall speed would double.

Dan
 
TangoWhiskey said:
Every chart I've seen on FAA tests and training publications indicates that load factor and stall speed increase with bank angle.
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I would tend to agree with Capt Thorpe's pet peeve...oversimplification is far too common and has the potential to be far too deadly.

Load factor and stall speed increase with bank angle in coordinated, "level" turns. That last part is often implied or assumed, but not always stated, unfortunately, and doesn't even address airspeed as a relative constant in place of altitude.

And we all know what happens when you ASSUME....











SOMEBODY ends up lookin' like a friggin' idiot!:D
 
skidoo said:
Are you comfortable if the CG is within the envelope, but near the forward CG limit, or would you re-adjust distribution or add ballast to bring the CG closer to the center?
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If it's easy, I'll move load aft -- saves gas. And that's the only reason I'd move load within the legal cg.
 
TangoWhiskey said:
Every chart I've seen on FAA tests and training publications indicates that load factor and stall speed increase with bank angle.
Click to expand...

And misinformation, repeated often enough, apparently becomes accepted as fact.

Per the graph below, a 60-degree bank introduces a load factor of 2 and an increase in stall speed of 40% over that experienced in level flight. How am I misinterpreting this?

attachment.php
Click to expand...
It's not the bank, it's the pulling on the stick to make the turn level that makes the load factor go up. All of these charts have a sometimes stated, but sadly often only implied "while maintaining constant altitude" attached to them. The chart wrongly attributes the effect (loading) to bank angle and not the increase in angle of attack necessary to maintain altitude at that bank angle. (Strictly speaking, the condition isn't constant altitude, it's no vertical acceleration)

Label the graph "load factor and stall speed increase as a result of maintaining altitude during a turn" and it would be correct.

Label the graph "load factor and stall speed increase as a result of BANK" and it is just plain wrong. And like I said before, it's misinformation like this that leads to dead pilots.
Lets take an example:

According to the chart, what is the load factor at 90 degrees of bank? Somewhere around infinity. Way more than any airplane could withstand. So, by that chart (if indeed it was "bank" that caused the increase) it would be IMPOSSIBLE to bank 90 degrees, right? I hope you realize that is just plain nonsense. Find an acro capable airplane and do some wingovers where you reach 90 degrees of bank, near zero air speed, near zero G, ball in the center coordinated at the top. BTDT. And I ain't never pulled no wings off at 90 degrees bank.

And, on topic, I'd pick to depart over gross before out of CG, if as you say "my life depended on it."
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On that, point I will agree wholeheartedly.
 
Jeanie said:
I was told some years back that the plane in the movie "Flight of the Phoenix" (I forget if it was the original or remake) crashed after going over the hill in the last scene because of forward CG and the pilot died.
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It was the original. The story I saw was that it was not very stable (and forward cg would make that better, not worse), but the director wanted one more shot despite Paul Mantz's concern about thermal turbulence and recommendation to wait for the next day. Mantz relented, and died for his decision. And that's why you never see Jimmy Stewart (well, Paul Mantz, really) land the Phoenix -- just take off.
 
jesse said:
Time to buy a 182.
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It seems the 182 has a similar issue. In my calculations with Pilot/Passenger (350 lbs), full fuel, rear seats empty, and no baggage, the CG is 1/2" forward of the limit. I have been told that the 182's, especially the newer models, tend to be nose heavy. I asked the pilot who ferried mine about this and he said that just be prepared for the nose to drop significantly when power is cut. So, I am thinking that perhaps this common expectation is because with two persons in front only, the CG is so far forward. So, if with two persons, I always added 80 lbs (max limit) to the most rearward area, this would shift the CG 2" rearward and bring it within the envelope.

Perhaps this would make the nose heavyness less so. I have yet to fly the airplane and want to reduce my risk of nose damage...
 
There's no need to add ballast to get 2 inches aft of the fwd cg limit in a 182. If you load a 182 within the book limits, and trim it properly in flight, you won't have these problems, even with two in the front and no ballast but your nav bags on the back seat. When I see folks having trouble holding a 182's nose up on landing, it's usually because they didn't trim for proper speed on final.
 
Capt. Geoffrey Thorpe said:
And misinformation, repeated often enough, apparently becomes accepted as fact.


It's not the bank, it's the pulling on the stick to make the turn level that makes the load factor go up. All of these charts have a sometimes stated, but sadly often only implied "while maintaining constant altitude" attached to them. The chart wrongly attributes the effect (loading) to bank angle and not the increase in angle of attack necessary to maintain altitude at that bank angle.
Click to expand...


Gotcha! And on that point, I agree with you wholeheartedly as well. The "level turn" was assumed; doesn't apply the same way to a coordinated descending turn from base to final.
 
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