How do you determine what a "safe" overweight condition is?

PPC1052 said:
Saying that failure is not probable without some consideration of actual conditions is like trying to determine the probability of rolling a 1 on a die without knowing how many different sides the die has.
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Yes, but that probability is always no more than 0.5. :)

Never seen a 1-sided die.
 
jimhorner said:
Great, mission accomplished. More sky for me! :D :D

One aspect of flying and of being a good pilot, to me, is about proper risk management. Why needlessly contribute to the risk of failure by exceeding the limits? When I do aerobatics, I'm pretty sure I know how to do a loop, a roll, and spins, but I still wear a parachute in case the previous guy pulled 7G on the 6G rated airframe one too many times.
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That's one of my problems with exceeding the specified limits. You may get away with it once or twice or twenty times, but at some point, it can bite you badly. And if you are renting, you don't have any idea how many times that limit has been exceeded in the past.
 
JOhnH said:
That's one of my problems with exceeding the specified limits. You may get away with it once or twice or twenty times, but at some point, it can bite you badly. And if you are renting, you don't have any idea how many times that limit has been exceeded in the past.
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Exactly. One of the benefits of owning vs renting is that no one else is mistreating the plane. One still doesn't have full certainty of what happened to the plane in the past, but it's better than the rental situation... When I put my pride and joy away in the locked hangar after each flight, I KNOW that it'll be in substantially the same condition as it was when I locked the hangar doors.
 
Bottom line is that an aircraft is certified to its published limits. You can go to the POH and understand exactly how it should perform under a given set of parameters within those limits. Exceed the limits and your results WILL vary in ways that may not be predictable. Exceed them by just a little and you probably won't notice much difference. Exceed them by a lot and you WILL notice a difference. But if you are looking for a magic number or percentage representing some sort of actual-with-a-wink-limit, then you will not find it. That is because 1) there are many more variables to consider other than just weight; and 2) the attorneys said so.
 
Alexb2000 said:
Gross weight brings out a lot of absolutism, while something like exceeding the published service ceiling is cool.
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Service ceiling is the max altitude where a single engined plane can climb 100 fpm at gross weight at forward CG limit on a standard day.

Hence, it's performance related.

It is NOT a Limitation.

So your analogy is flawed.
 
FastEddieB said:
Service ceiling is the max altitude where a single engined plane can climb 100 fpm at gross weight at forward CG limit on a standard day.

Hence, it's performance related.

It is NOT a Limitation.

So your analogy is flawed.
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There are circumstances where exceeding (or getting close to) the service ceiling is a really bad idea.

But if you're flying at 15000 (with oxygen) in a 172 at 10000 AGL, the consequence of exceeding the service ceiling is that you'll sink unless rising air holds you up. BFD. If, on the other hand, you're doing that because you're overflying the summit of Mt. Whitney (14500), that's a bit of a problem.
 
MAKG1 said:
There are circumstances where exceeding (or getting close to) the service ceiling is a really bad idea.

But if you're flying at 15000 (with oxygen) in a 172 at 10000 AGL, the consequence of exceeding the service ceiling is that you'll sink unless rising air holds you up. BFD. If, on the other hand, you're doing that because you're overflying the summit of Mt. Whitney (14500), that's a bit of a problem.
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Service ceiling means climb is down to 100fpm with perfect speed and technique. So yeah, if the down draft exceeds 100fpm you start descending. But thats true with any airplane. If the downdraft exceeds the ability of the aircraft to maintain speed and climb, then it must by necessity trade energy for altitude . . . until you reach the critical angle of attack and then weeeeeeeeeeee
 
Hocky said:
So as I said I know nothing about aviation but there are some of the same elements there I assume, so looking from the outside in I strongly suspect that I can safely do things with my certified plane beyond the official spec.
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Define "safe". Among other things, MGW is determined by a minimum specified climb rate under standard conditions. If you go over MGW, there is NO WAY to coax more climb rate out of the physics of power and excess lift. Its not an engineering issue, it's a physics issue. So is 400 fpm safe? Is 300 fpm safe? Is 100 fpm safe? What happens to your climb rate if the temp is above standard, or the mid-time cams are slightly worn, or pilot technique is not perfect? Operational margins ate set to account for the vast majority of variable op conditions that will be encountered without compromising safety.

Will you fall out of the sky if you are 50 lb over gross and within CG? Likely not. But your safety margin will be significantly compromised. If there is an incident, the FAA and any litigants will (rightly) not be amused.
 
FastEddieB said:
Service ceiling is the max altitude where a single engined plane can climb 100 fpm at gross weight at forward CG limit on a standard day.

Hence, it's performance related.

It is NOT a Limitation.

So your analogy is flawed.
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Page 2-6 under limitations Piper Turbo Arrow

http://pbremer.home.xs4all.nl/POH-PIM/Turbo Arrow IV.pdf

Page 2-14 under limitations Cessna T182T

http://dpwiese.mit.edu/POH/C182T_IM_2004_navIII.pdf

I don't feel like finding any more but they're out there.
 
I can't open those on my phone right now but yes, sometimes altitudes are a limitation. I know that is the case in the Cirrus where it's given as a maximum authorized altitude under Limitations. But that's not a service ceiling.

I'll check out those two links when I'm home and back on Wi-Fi.
 
Alexb2000 said:
Page 2-6 under limitations Piper Turbo Arrow

http://pbremer.home.xs4all.nl/POH-PIM/Turbo Arrow IV.pdf

Page 2-14 under limitations Cessna T182T

http://dpwiese.mit.edu/POH/C182T_IM_2004_navIII.pdf

I don't feel like finding any more but they're out there.
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There appear to be some real limitations related to turbochargers. I suspect the fully closed waste gate above the limit may result in undesigned operation.

A naturally aspirated 182 does not have this limitation. The service ceiling is performance related.

The bottom line is, read your POH.
 
FastEddieB said:
I can't open those on my phone right now but yes, sometimes altitudes are a limitation. I know that is the case in the Cirrus where it's given as a maximum authorized altitude under Limitations. But that's not a service ceiling.

I'll check out those two links when I'm home and back on Wi-Fi.
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Just to speed this part of the conversation along. I will absolutely climb as high as is required for the safety of the flight regardless of service ceiling limitations. I have owned one of the referenced aircraft and I have climbed above 20K when I felt it was the safest option and I would again if facing the same scenario. That's why I am reluctant to throw stones on threads like this because each situation is different. If I were flying in remote Canada or Alaska and could choose to fly over weight or leave some fuel behind and take my chances, I'll take door two. Those that proudly proclaim they've never violated anything ever and there is never a reason to, have probably spent most of their time in the pattern.

We should emphasize good judgement vs. strict adherence to rules.
 
I think mags need to be pressurized to work reliably above a certain altitude.

A NA Cirrus SR22 is still climbing well at 17.5k, but was not certified to fly above that.
 
warthog1984 said:
In structural design, there are serviceability limits (you haven't damaged the plane) and design or ultimate limits (the plane's bent/broken, but survives long enough to get the people on the ground).

There may very well be a 50% margin above legal limits before you rip the wings off the plane in-flight, but you're most likely going to start causing permanent damage at 5-10% above the POH limits- in a new plane. In an older plane that has seen heavy flying time, pushing the legal limits may be ill-advised.
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This post is where I think this thread takes a wrong turn.

Earlier I stated that my POH design load limit is 150% published. Later someone provided the definition of design limit.

Did ya'll forget they are also CERTIFIED for flight operations in the utility category, which means it can spend its life at 4.4G which is wAAAy more than. 150%.

Did I miss something?
 
Jaybird180 said:
This post is where I think this thread takes a wrong turn.

Did ya'll forget they are also CERTIFIED for flight operations in the utility category, which means it can spend its life at 4.4G which is wAAAy more than. 150%.

Did I miss something?
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Yes, you forgot something. Normal operations is defined as the certified flight envelope- in this case +4.4g. A Design strength 150% of the required would than be: 1.5*4.4g = +6.6g design strength. Unless you fly with the flaps down, in which case 1.5 * 3.0g = 4.5g design strength.

Note1: design strength is not a no-damage strength; it is the ultimate strength at which the aircraft (or some part of it) will completely fail. The damage threshold (yielding) is more likely along the lines of 1.05 * 4.4g = 4.6g.

Note2: load is not a strict function of g limits- there's a reasons maneuvering speeds exist.
 
He also missed that utility category has a much lower max gross weight than normal catrgory for the same airplane.

Yield forces are not accelerations.
 
warthog1984 said:
Yes, you forgot something. Normal operations is defined as the certified flight envelope- in this case +4.4g. A Design strength 150% of the required would than be: 1.5*4.4g = +6.6g design strength. Unless you fly with the flaps down, in which case 1.5 * 3.0g = 4.5g design strength.

Note1: design strength is not a no-damage strength; it is the ultimate strength at which the aircraft (or some part of it) will completely fail. The damage threshold (yielding) is more likely along the lines of 1.05 * 4.4g = 4.6g.

Note2: load is not a strict function of g limits- there's a reasons maneuvering speeds exist.
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Thank you for clarity. So what you're saying is that: my wings won't fall off and neither will the OPs provided there are no abrupt control deflections??? Is that about right?
 
MAKG1 said:
There appear to be some real limitations related to turbochargers. I suspect the fully closed waste gate above the limit may result in undesigned operation.
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The Arrow has a fixed wastegate to start with.

With a variable wastegate, operating above the altitude where it is closed doesn't do anything bad. All that happens is that manifold pressure starts to drop along with increasing altitude. For some reason, some turbo installations act a bit squirrely right after you reach critical altitude but they dont blow up or anything.
 
Worth pondering what effect over gross would have on an aircraft's flight envelope:

figure3.gif
 
FastEddieB said:
No.

The right gust at the wrong time can do it as well.
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Not if the aircraft is flown well below maneuvering speed.

Aircraft dont fall from the sky or fold up their wings because they are flown 10% over gross. There is no published CG envelope and the aircraft will stall at a higher speed than one is used to and in something weak like a 172 you may not have enough power for a go-around with flaps.
 
Jaybird180 said:
Thank you for clarity. So what you're saying is that: my wings won't fall off and neither will the OPs provided there are no abrupt control deflections??? Is that about right?
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I'd suggest that neither you nor the OP truly understands the discussion or the issues being brought up.

Further, if you overload an aircraft and exceed the structural limits of that particular aircraft; even if you do not reach catastrophic failure there will be more than enough physical evidence for the FAA and NTSB to determine what you did and yank your pilot certificate.
 
If you do not have "Aerodynamics For Naval Aviators" in your library, download it now - easy to Google and free as a pdf.

Then turn to page 345 and begin reading the last paragraph where it says, "the operation of any aircraft..."

That's a summary. Sprinkled throughout the text are various descriptions of the effect of weight on various aspects of aircraft performance.

Enjoy!
 
PPC1052 said:
I would not agree with this statement. If you grossly exceed the limits, you are not likely to come out fine. Whether catastrophic failure occurs is not just some random roll of the die, with the probability of failure > 0.5. The probability is dependent upon how much you exceed the limits by, and how many factors combine against you. You simply cannot state with any certainty what the probability of catastrophic failure is without a comparison of the actual flight conditions to the actual limits. In other words, you cannot state whether the chance of failure is 0.0001 or 1.0 without knowing what the actual loads/flight conditions are compared to the actual limits.

Saying that failure is not probable without some consideration of actual conditions is like trying to determine the probability of rolling a 1 on a die without knowing how many different sides the die has.
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What part of my post do you not agree with? You only quoted a very small part which was opposite the theme of my post. That said, you seem to be suggesting that there's a reasonable probability that a single transgression is going to be catastrophic. While that's certainly possible, since just as I don't know the flight conditions you don't either, neither of us is in a position to identify how likely that is. My point however is that even when it works out well for that flight (as it will in a majority of cases, where majority means you're only slightly beyond tolerances... grossly out of tolerance is when failure probability is closer to 1.0), it doesn't work out in the long run for a few different reasons.
 
warthog1984 said:
I'd suggest that neither you nor the OP truly understands the discussion or the issues being brought up.

Further, if you overload an aircraft and exceed the structural limits of that particular aircraft; even if you do not reach catastrophic failure there will be more than enough physical evidence for the FAA and NTSB to determine what you did and yank your pilot certificate.
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I understand, but I want you to get off your high horse and see the flaw in your absolutism explanation.
 
Jaybird180 said:
Thank you for clarity. So what you're saying is that: my wings won't fall off and neither will the OPs provided there are no abrupt control deflections??? Is that about right?
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I wouldn't say that. Who knows how many times that bird has been abused in the past and that last weak link finally decides to give way.
 
Can anyone point me to an NTSB report of any 172 folding up in flight short of going into a large thunderstorm? There are many out there that have over 10K hours, been beat mercilessly their whole lives by students, been flown overweight, etc. There are many here operating 50 year old aircraft of all types that have been through who knows what and we don't have them folding up in flight.

There are many more important things to worry about.
 
JOhnH said:
I wouldn't say that. Who knows how many times that bird has been abused in the past and that last weak link finally decides to give way.
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I don't get this argument. If there has been abuse then who says you can even fly safely within spec? And what about annual inspections? Aren't those supposed to pick up any issues like cracks or other signs that something serious is happening?

If there is some structural weakness in the plane because it was abused, I don't want to fly it at 50% gross. So you're saying it is okay to fly it at max gross with a "weak link"?
 
Hocky said:
I don't get this argument. If there has been abuse then who says you can even fly safely within spec? And what about annual inspections? Aren't those supposed to pick up any issues like cracks or other signs that something serious is happening?

If there is some structural weakness in the plane because it was abused, I don't want to fly it at 50% gross. So you're saying it is okay to fly it at max gross with a "weak link"?
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:mad2:
 
Alexb2000 said:
Can anyone point me to an NTSB report of any 172 folding up in flight short of going into a large thunderstorm? There are many out there that have over 10K hours, been beat mercilessly their whole lives by students, been flown overweight, etc. There are many here operating 50 year old aircraft of all types that have been through who knows what and we don't have them folding up in flight.

There are many more important things to worry about.
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Yeah. Like how the insurance company refuses to cover you after you damage/wreck/injure/kill with an overloaded airplane, even if the overload had nothing to do with the accident. Seems to me you risk your current net worth and most of what you'll ever earn just by wilfully violating the law.

Dan
 
You need two airplanes to find the max safe weight. Take plane one and start loading it up. After each successful take off add more weight until finally you wind up in the weeds off the end of the runway. Remove this wreckage and remove the last object that caused you to crash. This then will tell you the max safe weight your plane can carry.:rofl:
 
Hocky said:
So is that a "yes" or a "no"?
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I try not to fly my own airplane at max gross so I am certainly not going to tell you it is ok to fly at max with a compromised component.
 
Hocky said:
So is that a "yes" or a "no"?
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The fact that you are pushing boundaries when you are still a complete novice is making people think that you are a statistic waiting to happen.

The design engineers, not operators, own any margins above published limitations. Debating it is pointless and hurts your credibility.

At this point in your career, accept it as gospel and move on. There is much to learn and, if you want to ever be considered an aviator, that learning never stops.
 
C182P said:
That said, you seem to be suggesting that there's a reasonable probability that a single transgression is going to be catastrophic.
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Not really. What I am saying is you cannot know what the probabilities are without knowing how much you have exceeded the limits by, as well as having a full understanding of the implications of how much you have exceeded the limits by. In some cases, exceeding the limits has a minimal chance of failure. In others, you have certainty of failure. Unless you know where you are in the spectrum, you cannot assume you will probably be okay, or that you will probably crash and die.
 
paflyer said:
The fact that you are pushing boundaries when you are still a complete novice is making people think that you are a statistic waiting to happen.

The design engineers, not operators, own any margins above published limitations. Debating it is pointless and hurts your credibility.

At this point in your career, accept it as gospel and move on. There is much to learn and, if you want to ever be considered an aviator, that learning never stops.
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No wonder N00bs cant learn; its authoritarianism like this that prevents it. I am sure Cap'n Ron will be along to tell you about that one too.
 
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