Bob Urban wrote: > > Hi Ed, > > I have one tenny-weeny little question after reading all the good > stuff. It concerns "don't fly SIGNIGICANTLY over gross...". > > What exact or even approximate numerical point is this? > This is a serious question. > > Regards, > Bob Urban > ////////////////\\\\\\\\\\\\ > > Ed Burkhead wrote: > > > <snipped a bunch of good stuff> > > > Fred Weick, the designer, told me once that he had underestimated the > > importance of good judgement to go with skill and good plane design. > > Don't run into hills, don't continue VFR into IFR conditions, don't fly > > significantly over gross and don't fly VFR at night when there's a > > chance you could get into a cloud and Coupes will do very well for your > > safety.
Well, Bob, here are some thoughts: Point #1: If you fly over certified gross in any airplane, then you are a test pilot flying an untested plane. The Coupe airframe was certified at 1260 lbs, at 1400 lbs, and at 1450 lbs. When they changed from the 415-C to the 415-D there were a few changes that did not relate to flying abilty like the stainless steel sheet over the nose gas tank since it was under the cowl and needed better fire protection and the aerodynamic trim tab that was required to replace the spring trim on older machines. To get the 1400 lbs on the 415-D, they had to do flight testing and, Fred Weick told me, they were unhappy with the full power stall characteristics at 85 hp and 1400 lbs. This is because the slip-stream going over the tail was able to push the tail too far down and allow a bad break and possible full stall leading to a spin. To maintain the spin-proof certification, they decided to change the up-elevator limitation from the normal (for Coupes) 13 degrees to a more limited 9 degrees. This increases the touch down speed as an unwanted side-effect and reduces emergency back-pull when you do something stupid like being too low, slow and nose down on landing. After making about 75 415-D planes, they moved the up-elevator back to 13 degrees, reduced the gross weight back to 1260 lbs and call it the 415-CD. This is why the 415-CD is so easy to convert to be a D. Then the 415-E came out with the superior split elevator. The cut-out in the middle of this elevator allows most of the slip-stream to pass through the split, not affecting the elevator much. To make up for the lessened elevator surface, the split elevator allows 20 degrees of up travel. With the split elevator, all the subsequent models have somewhat the same stall behavior at full power or power off. The 415-D STC and conversion kit you can get from Skyport makes all the important changes that were made to convert a 415-C to be a 415-D with the especially important 9 degress of up travel to avoid the stall problem. Have I ever flown over gross? Ask me privately sometime. Have I ever flown my plane more than 50 lbs over gross? Definitely not. Am I very careful when flying at high gross weights? ** Yes ** Do I remember the grief from when our club president, Jack Harkness, rode to a fly-in with another pilot, they tried to take off in the warm part of the day after the event, couldn't, crashed and burned at the end of the runway, Jack lingering for days before dying of his burns? Because they were over gross for the take-off. Do I keep that in mind? ** Yes! ** Summary: Flying any plane over gross can get you into possible stall/spin trouble or give you take-off problems. The structure didn't change significantly up to 1450 lbs though there were some changes made to allow those higher weights. The issues within this range are mostly aerodynamic.
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