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  #21  
Old 09-28-2022, 11:08 AM
rmarshall234 rmarshall234 is offline
 
Join Date: Jun 2008
Location: San Diego, CA
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I think it is worse. Because as the "manufacturer", you just made the miscalculation for the next owner(s) in line.
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www.robertsairservices.com
RV-3 N333LT - 500hrs PIC
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  #22  
Old 09-28-2022, 12:22 PM
mfleming's Avatar
mfleming mfleming is offline
 
Join Date: Sep 2016
Location: Joseph, Oregon
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Back in my 135 air taxi days in Alaska, we were legally allowed to increase the gross weight of our aircraft.

FAR 91.0323 (b) The maximum certificated weight approved under this section may not exceed - (2) 115 percent of the maximum weight listed in the FAA aircraft specifications.
EDIT: On a 3300lb. Cessna 185, Thats a 495lb. increase

I'm not saying we should do this with our RVs but the FAA doesn't draw a clear line on gross weight for some certified aircraft under some operations. They certainly didn't do an engineering study, as this applied to most air taxi aircraft in use at the time regardless of manufacturer.

My point is, gross weight may not be such a hard and fast number backed by engineering as some seem to indicate.
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Michael Fleming
Joseph, OR
sagriver at icloud dot com

RV-7 Slider #74572
Started 11/2016
Empennage completed 11/2016
Ailerons and flaps completed 3/2017.
Wings completed 12/2017
Started on QB fuselage 01/2018
Sliding canopy mostly completed 10/2020
Wiring and Avionics harness completed 9/2/2021
FWF Completed 11/1/2022
Final assembly Started 11/10/2022
Wings on 11/12/2022

N526RM

Donated for 2022 and so should you

Last edited by mfleming : 09-28-2022 at 12:33 PM. Reason: Add content
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  #23  
Old 09-28-2022, 01:04 PM
plehrke's Avatar
plehrke plehrke is offline
 
Join Date: Sep 2006
Location: Defiance, MO
Posts: 2,021
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Quote:
Originally Posted by terrye View Post
In airplane design, the load factors are specified based on the category of airplane. In the GA certified world, these are normal, utility and aerobatic. Applying these load factors to the weight of the airplane results in the limit load. For example, the positive limit load of an aircraft in the aerobatic category with an aircraft weight of 1600 lbs is (1600lb x 6 g load factor) = 9600 lbs. On top of this limit load, a “safety factor” of usually 1.5 is applied to give the design ultimate load. So, in the example case, (9600 lbs x 1.5) = 14,400 lbs. This is the point at which the structure is about to fail catastrophically.

While normally called a “safety factor”, this is really a catch all for “factors of ignorance”. It includes such things as: defects in the material (aluminum sheet and plate in the case of RVs), defects in manufacture, defects in service, etc. All those things that the designer cannot control.
Terry is correct but one other thing to be aware of is that in aviation at limit load (no safety factor), the structure is allowed to deform permanently, it just cannot fail. Therefore if you exceed limit load (or sometimes called design to load) you should perform an inspection looking for deformed, crumbled, bent, crinkled, wrinkled or maybe even a crack in the structure. That is what is done on commercial and military aircraft. The safety factor, when applied to get to design ultimate load, allows for that gray zone of strength analysis between plastic deformation and when failure occurs. Look at a stress/strain curve and you will see that fracture does not happen at max stress and strain (deformation) is no longer linear with stress. And once you have deformation all bets are off as seen in the stress/strain curve, the structure may no longer be capable of carrying design limit load the next occurrence (ie the structure gets weaker)
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Last edited by plehrke : 09-28-2022 at 01:11 PM.
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  #24  
Old 09-28-2022, 01:06 PM
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airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
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Quote:
Originally Posted by PilotjohnS View Post

So what I hear you all saying is that certifying the plane at a higher gross weight is just as bad as intentionally taking off "over gross"?
Mechanically, there is no difference.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2022 dues paid
N16GN flying 1,200 hrs and counting on 91E10; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
Repeat Offender - 10 empennage in process.
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  #25  
Old 09-28-2022, 02:12 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by mfleming View Post
Back in my 135 air taxi days in Alaska, we were legally allowed to increase the gross weight of our aircraft.

FAR 91.0323 (b) The maximum certificated weight approved under this section may not exceed - (2) 115 percent of the maximum weight listed in the FAA aircraft specifications.
EDIT: On a 3300lb. Cessna 185, Thats a 495lb. increase
Except it is now and never has been legal to do with a Cessna 185 (If I understand FAR 91.323 correctly).

It is only allowed on specific older aircraft that were originally certificated under the Department of Commerce, and later the CAA, and even then it is under very specific requirements that are not relevant for privately operated aircraft.

In my opinion not at all relevant to modern aircraft, RV's included.

If interested, people should do a bit of research on the origins of why this was allowed. My take is that it was a willingness to trade some levels of safety in order to increase others.
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Opinions, information, and comments, are my own unless stated otherwise.
You are personally responsible for determining the suitability of any tips,
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Scott McDaniels
Hubbard, Oregon
Formerly of Van's Aircraft Engineering Prototype Shop
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #26  
Old 09-28-2022, 04:33 PM
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mfleming mfleming is offline
 
Join Date: Sep 2016
Location: Joseph, Oregon
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Quote:
Originally Posted by rvbuilder2002 View Post
Except it is now and never has been legal to do with a Cessna 185 (If I understand FAR 91.323 correctly).

It is only allowed on specific older aircraft that were originally certificated under the Department of Commerce, and later the CAA, and even then it is under very specific requirements that are not relevant for privately operated aircraft.

In my opinion not at all relevant to modern aircraft, RV's included.

If interested, people should do a bit of research on the origins of why this was allowed. My take is that it was a willingness to trade some levels of safety in order to increase others.
Without going into the intricacies of the FAR...when doing the oral on a 135 check ride and asked to do a weight and balance, the 115% rule indeed was allowed for C-185s, C-206s, Cub's and whenever else we flew. At least in the '90s, this rule was applied across all bush planes regardless of the vintage.

That being said...As I indicated in my original post, I'm not advocating this for our RVs and I am personally adhering to the Van's published gross weight for my build...

This example was illustrated to show that the gross weight was not a hard line in the eyes of the FAA.
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Michael Fleming
Joseph, OR
sagriver at icloud dot com

RV-7 Slider #74572
Started 11/2016
Empennage completed 11/2016
Ailerons and flaps completed 3/2017.
Wings completed 12/2017
Started on QB fuselage 01/2018
Sliding canopy mostly completed 10/2020
Wiring and Avionics harness completed 9/2/2021
FWF Completed 11/1/2022
Final assembly Started 11/10/2022
Wings on 11/12/2022

N526RM

Donated for 2022 and so should you
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  #27  
Old 09-28-2022, 05:15 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
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Default Record Breakers

For most of my life I have been fascinated by long distance flights in small airplanes, starting with Max Conrad in the early 60s. Currently Bill Harrelson's record breaking flights have been of interest. Guam to Jacksonville FL, 7038nm nonstop, a new world record.
I think all those airplanes may have been a bit over gross. Maybe two times the normal gross.
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  #28  
Old 09-28-2022, 05:30 PM
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airguy airguy is offline
 
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Location: Garden City, Tx
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Quote:
Originally Posted by jrs14855 View Post
For most of my life I have been fascinated by long distance flights in small airplanes, starting with Max Conrad in the early 60s. Currently Bill Harrelson's record breaking flights have been of interest. Guam to Jacksonville FL, 7038nm nonstop, a new world record.
I think all those airplanes may have been a bit over gross. Maybe two times the normal gross.
Different animal there - those are being done under ferry permits - a specific one-time-only exemption for some particular reason.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2022 dues paid
N16GN flying 1,200 hrs and counting on 91E10; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
Repeat Offender - 10 empennage in process.
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  #29  
Old 09-28-2022, 06:13 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,978
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Quote:
Originally Posted by mfleming View Post
Without going into the intricacies of the FAR...when doing the oral on a 135 check ride and asked to do a weight and balance, the 115% rule indeed was allowed for C-185s, C-206s, Cub's and whenever else we flew. At least in the '90s, this rule was applied across all bush planes regardless of the vintage.
All I know is the first paragraph implies it is aircraft vintage specific.
Just because it is “what was done” doesn’t mean it was correct.
__________________
Opinions, information, and comments, are my own unless stated otherwise.
You are personally responsible for determining the suitability of any tips,
ideas, etc. obtained from any post I have made in this forum.


Scott McDaniels
Hubbard, Oregon
Formerly of Van's Aircraft Engineering Prototype Shop
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #30  
Old 09-28-2022, 06:38 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,900
Default Certification

I think the Conrad Comanche's were probably Experimental research and development.
The Lancair may have only required testing for the proposed gross weight.
Harrelson beat a solo around the world record held by Conrad for decades.
The Conrad single Commanche is in the museum in Liberal KS, with all the tanks. I got to sit in The Conrad Twin Commanche with all the tanks installed.
The right seat was a tank with a thin piece of foam. No visibility to the left. I can't comprehend sitting in that airplane for close to 60 hours.
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