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Jeff,
If you would please bear with me for a little story, which I will follow with the answer to your question.
These two guys went moose hunting in Alaska. They chartered a single engine airplane that dropped them off in a remote area. They arranged to meet the pilot at the same location a week later.
A week later, when the pilot lands he finds the hunters with a huge moose that they want to bring back with them. The pilot is very concerned that the airplane may not be able to carry that much weight. The hunters are very insistent; last year they came to same spot in the same make make and model airplane, hunted an even bigger moose and the pilot did not have any problems loading it in the airplane for the flight back.
With this existence proof, the pilot decided to load the moose and take off. But the plane was just too weighed down and despite his best efforts it was unable to clear the surrounding mountains and crash landed about 50 feel short of the peak. Due to the pilot's great skill, the the plane came to a rest with no injuries. The two hunters exited the airplane, surveyed the area and then one said to the other: "Isn't that where we crashed last year? Looks like we made it about 200 feet higher up the mountain this year"
The moral of the story is that just because someone has managed to convince a DAR to sign off on a higher gross weight, it does not mean it is a safe thing to do or a good idea. Do you know if the fuselage, the wings and the landing gear can take that much extra weight? What is the safe operating CG range at this increased weight? What are the stall characteristics at the increased weight? What is the takeoff performance? What are the flutter margins at this increased loading? What are the various V speeds at this increased weight? Do you have engineering data to answer these questions?
Your DAR is doing the right thing in questioning how you came up with the weight and the CG range you came up with. If you go with the factory weight, you can look to them to provide you the engineering data to justify the numbers they have published. If you go with something higher, you really need to justify why those numbers are safe -- N-numbers are no substitute for engineering data. If you can get engineering data from the people with higher gross weight, you should be able to use that and will not have to develop your own. But if they can not provide you with engineering data because their DAR did not ask for it, then all you are saying to your DAR: There are these other DARs that did not ask for data, so you should not either. Maybe you should be asking the people with higher gross weights the name of their DARs, not the N-numbers of their airplanes.
Fly safe.
Hamid
Jeffrey Liegner, MD wrote:
Please everyone post their approved weights for their IVPs. My DAR may bulk at anything over factory 3550 lbs unless I can show N numbers with higher weights. I'm looking for 3800 lbs, but believe some have 4000 lbs approved.
Jeff L
99% done. DAR on 1/22/05
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