Max gross weight

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150man

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150man
How is this figure determined on a typical small airplane?

Is it the max weight an airplane can safely takeoff with? If that is true, then for certain density altitudes, runway lengths, type of runway, (grass or hard surface), and wind conditions, an airplane at gross weight or even under may not be safe.

Does it have to do with how much weight the structure can support? If this is the case then why does the FAA issue permits for ferry pilots to fly hundreds of pounds over GW with extra fuel tanks installed? And why can one buy an STC for a 172N with a powerflow exhaust to increase the weight by 100 lbs.?

Having flown a C150 for ten years, I know what I'm comfortable with as far as weight given the situation I'm faced with, and have flown over weight on many occasions with no problems. In other words, how important is this number for a pilot that knows his plane well and is experienced?
 
Well anytime you're over gross - you're a test pilot, more or less. In general gross weight is often determined by the airplanes ability to go-around in landing configuration in standard conditions. For more info read Part 23.

Obviously one can fly over gross - ferry pilots do it all the time (with FSDO authorization) but it does bring additional risk. At some point there might be structural issues but power is generally the limiting factor for our airplanes.
 
There are many issues which go into determining gross weight. Here are a few:

Structural issues - an airplane is certificated in a certain category, say the utility category, which has a 4.4 (?) positive load factor. That means you won't pull the wings off at 4.4 G's if you observe the published gross. Also, the landing gear has to be able to withstand a drop from a certain height at gross. There are other structural requirements such as seat integrity, etc.

Performance factors - these include a maximum stall speed for certification.

Market requirements - people won't buy an airplane that lacks a certain amount of takeoff and climb performance.
 
If you have access to prior copies of Flying Magazine, Garrison published an excellent and very practical article re. aircraft loading considerations a while back.

For those who are "by-God-bound-and-determined" to fly overweight in spite of published G/W, he concluded that CG exceedences are much more important than weight excursions for most airplanes,
 
wabower said:
If you have access to prior copies of Flying Magazine, Garrison published an excellent and very practical article re. aircraft loading considerations a while back.

For those who are "by-God-bound-and-determined" to fly overweight in spite of published G/W, he concluded that CG exceedences are much more important than weight excursions for most airplanes,
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And he's right, at least until the point you can't climb over the trees at the end of the runway. ;-)

I have an old, old issue of Flying where some guy named Collins was discussing weight/fuel/range isues and wrote that airplanes fly much better over gross than out of fuel.
 
be ready for some funny trim settings...more importantly just remember it will stall allot easier so takeoff/land accordingly.
 
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kyleb said:
I have an old, old issue of Flying where some guy named Collins was discussing weight/fuel/range isues and wrote that airplanes fly much better over gross than out of fuel.
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Perhaps not much better but certainly much farther.
 
Greg Bockelman said:
Anybody have any hard evidence that an insurance company won't pay in such case?
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I've heard "The insurance company won't pay if <fill in the blank>" so many times in aviation, and I don't know how that idea got started. If they wouldn't pay unless you were in full compliance, they would almost never pay - you're violating FAR's by crashing the airplane. ;-)

Insurance companies pre-screen clients to avoid the obvious problems. Once they take you on as a client, you're covered...
 
I would venture to guess that most C150's have been flown over gross on more than one occasion, especially with the typical American of northern European descent pilot/passenger.
 
somorris said:
I would venture to guess that most C150's have been flown over gross on more than one occasion, especially with the typical American of northern European descent pilot/passenger.
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Pretty much anytime there's full fuel and both seats filled.

Unless it's some STC'ed 150 or 152 variant.
 
I've always figured that for the average light single, at least, max gross is simply the weight beyond which the mfr. cannot guarantee any of the other numbers- including G-ratings.
But like any of the "max demonstrated" performance stuff, max gross is exceeded pretty regularly. With mixed results.
 
kyleb said:
I've heard "The insurance company won't pay if <fill in the blank>" so many times in aviation, and I don't know how that idea got started. If they wouldn't pay unless you were in full compliance, they would almost never pay - you're violating FAR's by crashing the airplane. ;-)
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That's generally true. However, deliberate violations of the rules may still void the policy. Read and heed.

Insurance companies pre-screen clients to avoid the obvious problems. Once they take you on as a client, you're covered...
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Again, that's generally true, but if you lied to them on the application, that can void the policy. This is particularly true of things like your claimed experience, accident/violation history, medical status, and flight review status.
 
To answer the original question, it's a combination of performance and structural strength which drive MGW. For all the details, see Part 23 of the FAR's (which isn't in your regular FAR/AIM book), and be prepared for a dizzying array of variable, parameters, restrictions, allowances, and limitations.
 
When I was a newly minted pilot, I was asked to test fly a Cardinal for a friend who was a student pilot and considering buying this particular bird. So we got out there, and the owner said that the four of us (with full fuel) would be fine.

Yeah, sure. At that loading the thing was at maximum nose down trim just to stay level. It's a miracle we survived. Over gross, sure, the plane handled that part just fine. Out of CG was the problem. Learned an important lesson in CG there.

Obviously flying over gross can, in certain cases, be performed safely, as has been proven daily. I don't think that's ever in question. The biggest concern I'd suspect would be an unsafe CG (depending on the plane), followed by structural issues (hard landings), takeoff/climb performance (especially on hot days and short fields), and lastly single engine performance (on a twin).

You ask if you know your aircraft is it an issue, and I'd venture probably not, assuming you're staying within that knowledge range. Problem is, you are effectively testing, and eventually could end up outside of safe limits. That can be problematic when that happens if you don't have enough control authority to fix the problem.
 
Ron Levy said:
To answer the original question, it's a combination of performance and structural strength which drive MGW. For all the details, see Part 23 of the FAR's (which isn't in your regular FAR/AIM book), and be prepared for a dizzying array of variable, parameters, restrictions, allowances, and limitations.
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The structural issues exist but I doubt a structural issue often determines mass gross weight on the vast majority of our certified birds. The performance requirements, in particular the go-around in landing configuration, is generally what's going to determine the gross weight. We're always performance limited and generally not structurally limited.

It's pretty common that a STC to a larger powerplant (assuming no additional fuel, and the new engine has similar power/weight as the previous) will provide a higher gross-weight.

Although the 150-150 STC doesn't provide a gross weight increase which makes it fairly unattractive. I suspect they just didn't go through the effort required to get it.
 
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jesse said:
Although the 150-150 STC doesn't provide a gross weight increase which makes it fairly unattractive. I suspect they just didn't go through the effort required to get it.
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I've asked a few people about this who've been through the process. When you go through increasing gross weight, you have to be able to back up the numbers and also prove that the limitation wasn't due to structural requirements.

Looking at the RAM and Colemill conversions, for instance, they have been around for a number of years. I suspect that when they came out, there had been many fewer lawsuits and that the therefore whole process was easier back then. Additionally, I'd guess that Cessna, Piper, and Beechcraft were also probably a bit more open with numbers than they are today.
 
jesse said:
It's pretty common that a STC to a larger powerplant (assuming no additional fuel, and the new engine has similar power/weight as the previous) will provide a higher gross-weight.
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It's also common for those STC's to include a reduction from Utility to Normal category, or other maneuvering restrictions added.
 
Ron Levy said:
To answer the original question, it's a combination of performance and structural strength which drive MGW. For all the details, see Part 23 of the FAR's (which isn't in your regular FAR/AIM book), and be prepared for a dizzying array of variable, parameters, restrictions, allowances, and limitations.
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Part 23 doesn't apply to CAR type certificated airplanes, which is a large majority of the SEL planes out there still flying.
 
jesse said:
It's pretty common that a STC to a larger powerplant (assuming no additional fuel, and the new engine has similar power/weight as the previous) will provide a higher gross-weight.
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fwiw - There are no STCs to increase HP on the cherokee 140
that increase the max gross weight....AFAIK.
 
Bob Noel said:
fwiw - There are no STCs to increase HP on the cherokee 140
that increase the max gross weight....AFAIK.
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Are there any airframe differences between the 140 and 160?
 
Rotor&Wing said:
Part 23 doesn't apply to CAR type certificated airplanes, which is a large majority of the SEL planes out there still flying.
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While that's true, Part 23 is in many ways derivative of CAR 3, and gives a good idea of what the thinking is (and was) about the interplay between performance, strength, and weight.
 
JohnSBA said:
Seems to me that's it for at least some planes, since my POH lists max "ramp weight" as a gallon's worth less than the "takeoff weight."
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I think you meant ramp weight is a gallon more than takeoff weight
 
Rotor&Wing said:
Try to at least read CAR 3 before making such a comparison. :rolleyes2:
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Could you please point out the differences that are so strong you can't gather general details about what goes into airplane certification from Part 23?
 
jesse said:
Could you please point out the differences that are so strong you can't gather general details about what goes into airplane certification from Part 23?
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Writing a synopsis of the differences between the 2 regulations would take more time than I have to devote to that at the moment. In a nutshell 14 CFR Part 23 is more cumbersome/restrictive than the CAR when it comes to aircraft certification. That is why so many manufacturers insisted on keeping the CAR type certificates and amending them even today (50 some odd years later) rather than re-certify under 14 CFR Part 23.

The CAR's are available online if anyone cares to read them, just like 14 CFR Part 23.
 
jesse said:
The structural issues exist but I doubt a structural issue often determines mass gross weight on the vast majority of our certified birds. The performance requirements, in particular the go-around in landing configuration, is generally what's going to determine the gross weight. We're always performance limited and generally not structurally limited.

It's pretty common that a STC to a larger powerplant (assuming no additional fuel, and the new engine has similar power/weight as the previous) will provide a higher gross-weight.

Although the 150-150 STC doesn't provide a gross weight increase which makes it fairly unattractive. I suspect they just didn't go through the effort required to get it.
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If you can take off from a standing or rolling start how would factors change such that you could not go around ?

Kent G
 
Y1GKG said:
If you can take off from a standing or rolling start how would factors change such that you could not go around ?

Kent G
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You don't take off in landing configuration with full flaps.
 
jesse said:
You don't take off in landing configuration with full flaps.
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So if I use approach flaps (20 degree) that would make a significant difference ?

I use 20 for to/lndg normally Be35 J Model


Kent G
 
Y1GKG said:
So if I use approach flaps (20 degree) that would make a significant difference ?

I use 20 for to/lndg normally Be35 J Model


Kent G
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I'm pretty sure every Bo pilot I've flown with has used the "land" setting during the landing.

You would be able to go around easier with approach settings then with landing setting, correct. But you're not going to stop as quick and you aren't taking advantage of all the drag your airplane can produce which will make for safer landings.

The only Bo I've ever flown from takeoff to landing was an A36 (thanks chip) and it handled quite nicely with full flaps.
 
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