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  #21  
Old 09-23-2014, 05:27 PM
jrs14855 jrs14855 is offline
 
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Default Jan Johanson

Jan Johanson had one time approval from Vans for takeoff at 136% of normal gross weight for the RV4. I believe on later flights this was increased, but can't find anything specific.
10% over gross is standard FAA approval for certified aircraft for long distance ferry flights.
Max Conrad was nearly twice the certified gross weight of the Twin Commanche for the Capetown- St Petersburg flight.
For around the world Hawaii to San Francisco is normally the longest leg. Fuel availability in recent years in the Pacific may have changed that.
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  #22  
Old 09-23-2014, 06:00 PM
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Quote:
Originally Posted by N941WR View Post
To be clear, RV's and other homebuilts are "Certified" airplanes. They are certified in the "Experimental - Amateur Built" category.
Actually, they are certificated, not certified. They have been given a special airworthiness certificate. They are not certified to meet any standard.
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  #23  
Old 09-23-2014, 06:22 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Jesse View Post
Actually, they are certificated, not certified. They have been given a special airworthiness certificate. They are not certified to meet any standard.
A "Type Certificate" is what they are missing.
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  #24  
Old 09-24-2014, 07:37 AM
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Alan Carroll Alan Carroll is offline
 
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Quote:
Originally Posted by RVMike View Post
As I will likely be making my first venture into the Experimental world after 40> years of flying with an RV-4 purchase, I am as usual a bit confused. So, does the definition of gross weight and it's legal implications change since the aircraft is certified in the Experimental category? Some are 'certified' with 1500 gross, others with 1600 lbs. I am aware of the fact that aircraft can be safely operated above published gross weight (Alaska FAA regs allow a 10% increase in some situations..) and that yes, once must be careful as always. Results may vary, this is not advice from me, and this remains between you, me, and the NSA. I also know ramp checks can be very rare but one must always be prepared, and that was not the reason for my question. I am just continuing on the path of knowledge to some day reach the lofty goal of being an RV-4 aviator. Thank you very much.
Its worth reflecting on the fact that increasing GW beyond the designer's recommendation makes your aircraft even more "experimental" than it would otherwise be. To believe that adding an extra 100 pounds will have no impact performance or safety is purely wishful thinking. How risk-averse are you? How well informed is your passenger?
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  #25  
Old 09-24-2014, 09:49 AM
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Mark Albery Mark Albery is offline
 
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In the UK amateur built aircraft go through a type approval process that has been delegated to the Light Aircraft Association. They have a Type Approval Data Sheet similar to the TCDS for certificated aircraft. In most cases they accept Van's recommended limitations but will deviate if they have sufficient evidence to either raise or lower it.

For the RV-4 they have approved 1550 lb MTOW and all UK RV-4s will have that limitation. I'm not aware of where the 50lb concession came from, but such concessions are usually hard to gain and need some kind of engineering justification.

RV-4 TADS is here
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  #26  
Old 09-24-2014, 11:21 AM
nauga nauga is offline
 
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Quote:
Originally Posted by Alan Carroll View Post
To believe that adding an extra 100 pounds will have no impact performance or safety is purely wishful thinking.
To believe that all who chose to cert to a higher gross weight did so without assessing the performance or 'safety' impact is equally misguided.
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  #27  
Old 09-24-2014, 11:43 AM
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pierre smith pierre smith is offline
 
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Default Consider

Keep in mind that an RV-4 at 1500 lbs, pulling 6 G's, which it is rated for, loads the wings to 9,000lbs. If the same airplane weighed 36% more, or 2,040 lbs, it would take almost 4.5 G's to load the wing to 9,000 lbs, well above the Utility category and as long as no aerobatics were performed, where's the problem, as long as the CG is within limits?

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  #28  
Old 09-24-2014, 11:56 AM
nauga nauga is offline
 
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Quote:
Originally Posted by pierre smith View Post
Keep in mind that an RV-4 at 1500 lbs, pulling 6 G's, which it is rated for...
It's only rated to 6 at or below aerobatic weight (1375? off the top of my head), 4.4g above.

Quote:
Originally Posted by pierre smith View Post
Utility category and as long as no aerobatics were performed, where's the problem, as long as the CG is within limits?
Presumably you're going to take off and land at some point in your flight so understanding the loads under those conditions at increased weight is equally important
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  #29  
Old 09-24-2014, 12:04 PM
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rbibb rbibb is offline
 
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Quote:
Originally Posted by pierre smith View Post
Keep in mind that an RV-4 at 1500 lbs, pulling 6 G's, which it is rated for, loads the wings to 9,000lbs. If the same airplane weighed 36% more, or 2,040 lbs, it would take almost 4.5 G's to load the wing to 9,000 lbs, well above the Utility category and as long as no aerobatics were performed, where's the problem, as long as the CG is within limits?
A valid point but only one consideration. The location of the additional weight adds structural and dynamic response considerations as well. Perhaps the are most 'unknown' as to the effect of additional weight is the changes to dynamic response of the aircraft. Obviously this this impacts control response (roll rate, etc) but also the aero-elasticty of the air frame and things like spin characteristics.

While you might not exceed the 'G' limits of the wing spar will you have enough control authority to recover from a spin or prevent entering one? The math is hard to impossible to completely model this in any simplified way therefore extensive testing is used to validate designs. Spin chute anyone?, etc.

Hence increasing gross weight is simply putting more experimental in the experimental. Not that it can't or shouldn't be done but careful testing should validate before blasting off thinking that because the wings didn't fall off that is the end of it.
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  #30  
Old 09-24-2014, 03:18 PM
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Alan Carroll Alan Carroll is offline
 
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Quote:
Originally Posted by nauga View Post
To believe that all who chose to cert to a higher gross weight did so without assessing the performance or 'safety' impact is equally misguided.
I think you're absolutely correct. I'm not implying that these aircraft haven't been tested thoroughly in their heavier configurations; presumably they have. However, the laws of physics dictate that the performance and safety margins will be reduced, and no amount of testing can change that. The question is how far can you acceptably go. The designer has "weighed in" with his opinion, which I certainly do not feel qualified to disagree with.
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