Replies to This Discussion

Permalink Reply by Paul Bonasera on September 6, 2014 at 2:00pm

You as the builder can set any gross wt. that you want. If the plane won't get off the ground or breaks in the air then you went too far!!!   I would not go any higher then what the engineer that designed the plane set as the limit. If you look at the CH 750 it was 1320 and then with mod's went to 1440. personally I am building mine as per the planes for 1440 but setting the gross at 1320 to stay in the limits of light sport and I don't mind the added security that the airframe is stronger that I need.

Just my way of thinking,    Paul

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Permalink Reply by Lawrence Van Egmond on September 6, 2014 at 10:10pm

My wings were done when the 1440 mod came out but I have all the revision 3 mods on the rest of the plane. I went the other way and set my gross at 1200 pounds so my plane can be flown on an ultralight license here in Canada. It is very little paper work to increase the gross weight if I upgrade my license.

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Permalink Reply by Paul Bonasera on September 9, 2014 at 6:30pm

If I recall the 701 was made for the power of the Rotax 582, and there have been much larger, heaver, more powerful engines installed ( Rotax 100 HP, O-200, Corvair 120 hp, even a turbine).  All this goes to show how well designed and or over built Chris Heinz made the 701 in the first place.  

I just hope the same over building went into the 750 for my peace of mind.

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Permalink Reply by Bob Pustell on September 7, 2014 at 9:44pm

How much expertise do you have? (Or, how much can you draw on from friends with Aeronautical Engineering degrees or whatever.........). A skilled engineer designed our planes (thank you, Chris Heinz!) and set the max gross, G limits, Weight and Balance limits, etc. He had some extra margin in his design to allow for imperfectly built planes. How close to perfectly in line with the design is your particular plane? If yours is perfect and if you can calculate how much extra strength Chris put into the airframe as margin for poor builds, you could "borrow" that margin and certify your machine for a higher weight. I do not have that expertise so I will stick with Chris's numbers.

One builder in this group, a Doctorate Aeronautical Engineer, certified his 601XLB for about 1450 pounds as I recall. He knows his airframe like nobody else does and he has the knowlege to figure the margins and such. I do not.

I know of another builder who flew his 601XLB at 1600 pounds (or in that general area, been a while since I was told of it, number is close, for sure) during the flight test phase just to see if it would even climb. It did, just barely. It was on a calm day, he did no violent maneuvers and he worked up to that weight gradually, using increasing amounts of ballast. He does NOT plan to use those weights in normal operations, but he did test it. Only God knows how much margin that plane had left for turbulence, G forces, etc at that weight, but it flew. I will take his word for it and not test my bird up that high when it is finally flying. I am too big a coward.

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Permalink Reply by Russell Shimunek on September 8, 2014 at 5:55am

I have no previous building experience, but the guys at the factory said it could be done. With my extensive flying experience, I don't enjoy pushing the envelopes all that much anymore. If the 650 had a better useful load, it would have made my decision a LOT easier.

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Permalink Reply by David Josephson on September 9, 2014 at 5:09pm

You have a lot of options for increasing the useful load, mostly with engine choice and with build philosophy. For your basic, phase 1 build and flights, you should be worried about every ounce (Bill Lear is quoted as saying that if you do that for ounces, the pounds will take care of themselves.) Then if you want to add something, you can decide whether that 3 pound widget is worth a half hour of reserves. For engine choice, see http://www.zenith.aero/group/stolch750/forum/topics/750-engine-weig... for some real info. There are also options if you want to work out a different loading assumption than the +6/-3 G ultimate rating (+4, -2 limit) Zenith uses, but then you are designing a different airplane and need to review all the other assumptions that are being made too.

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Permalink Reply by Walt Snyder on September 9, 2014 at 7:33pm

On that note, on another bush pilot forum one of the pilots announced he had increased useful load by 150 pounds. He got divorced.

Walt Snyder

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