Can someone verify if this is fact or fiction?

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EchoKilo

Pre-takeoff checklist
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EchoKilo
I've always heard from various people over the years that the specs of an airplane as listed in the manual are actually half of what the plane will actually do. So take for example that the Cessna 150 has a useful load of roughly 475 lbs., does that mean 475 is actually half of what it will hold? Just curious. Thanks.
 
Definitely not. The airplane is designed and tested beyond the POH numbers, but not double. Take the G loading for example. The airplane is designed for 1.5x the limit load. If the airplane has a G limit of +4.5 G, it is designed for an ultimate load of +6.75 G. Not every figure is designed with a margin of 1.5. Part 23 has some information on the subject.
 
I'd suggest finding new various people. In terms of performance, typically you'll find that aircraft (especially a well loved 150) will usually under-perform what's in the book. In terms of useful, yes, there are plenty of AK pilots who overload their Supercubs and do just fine but they're still flying outside the certified design limits. Do you like being a test pilot? An illegal one at that? I don't mean to be snarky, but...I don't think I'd like to put 950lbs into the cabin of a C150.
 
EchoKilo said:
I've always heard from various people over the years that the specs of an airplane as listed in the manual are actually half of what the plane will actually do. So take for example that the Cessna 150 has a useful load of roughly 475 lbs., does that mean 475 is actually half of what it will hold? Just curious. Thanks.
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alway heard that to certify they had to pull 3 Gs And the weight that would cause structural failure would be cut to 1/3rd to certify.

anyone know certification rules ?
 
Jesus Christ Tom. How does an experienced A&P think airplanes are designed for 3x limit load? FAR 23.2230 & 23.2235.
 
Only twins will do double what their books say they'll do. ;)

No, no they won't. Disregard. :)
 
Manufacturers test up to theoretical limits and ultimate limits. The POH is written to operational limits set somewhere below design limits. Go beyond the POH and you are then playing test pilot with no engineering support.
A good example is the SF-260. It’s rated +6/-3G’s, but the wing ultimate is somewhere beyond +8.3G’s. The factory ran out of loading capability and deflection range when testing the wing to failure.
 
In engineering the difference between design load or stress and operational load or stress is called safety factor. The safety factor is there to compensate for manufacturing tolerances and material defects. The design load or stress is not available for operational use since any given part may not conform perfectly to its specification.

Illustrating one of the classic arguments between an engineer and a metallurgist: The engineer notes that a material sample passed its 2% elongation test while the metallurgist says that a part manufactured from the material failed under load because of a grain defect identified in a SEM investigation. If the material spec just requires a 2% elongation test then the material was good to go for manufacturing the part. Lawsuits actually do get filed over this stuff and one of them helped pay for my undergraduate degree.
 
EchoKilo said:
I've always heard from various people over the years that the specs of an airplane as listed in the manual are actually half of what the plane will actually do. So take for example that the Cessna 150 has a useful load of roughly 475 lbs., does that mean 475 is actually half of what it will hold? Just curious. Thanks.
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If you load a C-150 double its rated useful load, if you even get off the ground, which I doubt, I guarantee you'll have a looooong scary climbout.

Tom-D said:
alway heard that to certify they had to pull 3 Gs And the weight that would cause structural failure would be cut to 1/3rd to certify.

anyone know certification rules ?
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Absolutely not. Airplanes are designed, as others have said above, with a minimum ultimate 1.5 safety factor over the limit loads. There are additional higher safety factors required in some areas, e.g. fittings, castings, composites. "Ultimate" is where the material breaks. In addition, the material must not "yield" (bend and stay bent) at the limit load, with no safety factor. Most material yield strengths are between 50-75% of the ultimate strength. The aircraft may or may not be static tested to destruction for certification, but it must be flight tested up to the limit loads. The safety factor is, as Clark said, to compensate for uncertainties in design and manufacturing. Load a 3G rated plane to 3G and you can be sure it will survive. Load it to 4.5g and it may or may not break, but it will likely bend and stay bent.

Certification rules are in Part 23.
 
I think some of you are confusing safety factor with performance specs. A safety factor is when you want something to be able to withstand a certain load, you build a margin into the design to assure it will meet the original spec even through variations in manufacture and other concerns. This does not mean it is ok to load the item beyond its original design spec.

An airplane has published performance specs and you can probably exceed most of those specs continually, that is until you can't, then death is a likely outcome. Stick to the limitations, you'll be much healthier for it.
 
There's a film floating around of someone doing a Bob Hoover-esque routine in a Partenavia. Sure you can try to keep the loading down within the allowable range, but screw up and you'll find the "ultimate" limits. The film shows the wings folding up on the plane while his wife watches just off camera.
 
The VAST majority of certification rules of general aviation airplanes are not in Part 23. Even the King Air 90 is still a CAR3 airplane, for the most part.
 
If your going to load a 150 at twice the allowable load,be sure to take ,and post pictures of the takeoff.
 
When you are on an airliner and can view the wing tip, preferably from an over-wing seat, and NOT next to the window, sit up straight and note the location of the wing tip relative to the window while at the gate. Next, during flight, note the location again. I was on a transatlantic flight on some plane I don’t remember, but estimated a 5-6 ft upward defection.
 
I was employed at Boeing* when they did static testing of the C-17 wing spar. I remember it failed at 128% of a 150% design limit. Quite a boo boo. The fix was to add stainless steel straps to reinforce the area subject to early failure. When tested after the mods it failed at 149% and was deemed acceptable by the Air Force. Even big, multi-billion dollar companies screw up and that's why structural testing is performed.

*The C-17 was actually a McDonnell Douglas design.
 
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172andyou said:
Lighten up Francis.
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636258002123728460-AFP-AFP-MV9RR.jpg
 
455 Bravo Uniform said:
When you are on an airliner and can view the wing tip, preferably from an over-wing seat, and NOT next to the window, sit up straight and note the location of the wing tip relative to the window while at the gate. Next, during flight, note the location again. I was on a transatlantic flight on some plane I don’t remember, but estimated a 5-6 ft upward defection.
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I really hate it when a wingtip defects.
 
EchoKilo said:
does that mean 475 is actually half of what it will hold?
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It is not that linear: 475 x 2. The limitations you see in your POH/AFM are the results of numerous dynamic tests (flight) and static tests (ground) to determine the “load limits” and “ultimate limits” during certification.

A theoretical example: the 150 wing structure might be able to handle 9x the load (475 x 9) but the floor structure can only handle 3x the load (475 x 3). So when they determine the certification limit and ultimate loads they calculate an empty weight at X and a maximum weight at Y. From which you calculate a useful load of 475 lbs.

Another angle on limit/ultimate loads. To keep with your useful load example, since I don’t know any specifics for a Cessna 150, I’ll use a AS350B3 helicopter which has two certified maximum gross weights—one internal and one external. Sitting on the ground it has a useful load of “475 lbs.” But after pulling it into a hover the useful load increases by 950 lbs to 1425 total. The reason is the landing gear limit load will be exceeded with max gross weights over 5200 lbs but the rotor limit loads can handle 6150 lbs max gross weight.

The actual process is much deeper than this and way beyond my social position/pay grade.
 
EchoKilo said:
I've always heard from various people over the years that the specs of an airplane as listed in the manual are actually half of what the plane will actually do. So take for example that the Cessna 150 has a useful load of roughly 475 lbs., does that mean 475 is actually half of what it will hold? Just curious. Thanks.
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I am going to go with fiction and stick with the POH... But hey... that's me... :D
 
FlySince9 said:
not for nothing, but JC doesn't care so please refrain...
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I believe that as a solid copilot JC does, indeed, care about aviation. He’s flown as a required crew member on more flights than you can shake an overweight stick at.
 
Dana said:
If you load a C-150 double its rated useful load, if you even get off the ground, which I doubt, I guarantee you'll have a looooong scary climbout.
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Up here you’ll just have a fast ride through the airport fence. You can even do it without overloading it in the summertime if you don’t have a few hundred more pounds of stuff handy. :)
 
Craig said:
Manufacturers test up to theoretical limits and ultimate limits. The POH is written to operational limits set somewhere below design limits. Go beyond the POH and you are then playing test pilot with no engineering support.
A good example is the SF-260. It’s rated +6/-3G’s, but the wing ultimate is somewhere beyond +8.3G’s. The factory ran out of loading capability and deflection range when testing the wing to failure.
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God I love that airplane. . .c'mon lottery. . .
 
flyingron said:
There's a film floating around of someone doing a Bob Hoover-esque routine in a Partenavia. Sure you can try to keep the loading down within the allowable range, but screw up and you'll find the "ultimate" limits. The film shows the wings folding up on the plane while his wife watches just off camera.
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