Bubble door flutter

[cjb]

I have a model 7 Super Sport with bubble doors installed per plans. When opening the doors in flight at 80mph everything is fine. Increasing the speed to 100mph everything remained fine for about 20 minutes. Then I noticed the pilot's side door, outer lower corner began to vibrate up and down about 1 inch. It has done this in the past. Slowing the plane made it go away. Today it fluttered that 1 inch that lasted about a minute, then it began to flutter about 3 inches and within another second or so, it was vibrating from 6-8 inches. It looked like the door was going to come off. I immediately dropped power, pulled the nose up, got the airspeed down to below 60mph. At this point it was fluttering still at about 6-8 inches but at a much slower speed. I reached out and pulled the door in. During this time, the passenger door which was also open remained nice and smooth - no action required. It appeared like a little turbulence might have set off the imbalance andIdon't know where it would have stopped had I not taken corrective action. I believe the door might have departed the aircraft.
Has anyone else run into this issue? Does anyone have any ideas? A Kitfox friend who has the same model Kitfox but does not have bubble doors, has not had this flutter issue while flying with his doors open.
Chuck and Bev

[Paul Z]

I've never tried flying with the door open. From what I remember, John McBean said you could fly up to 80 withe the doors open. I'll be trying it next week on my way to Llano, Texas for the STOL flyin.

[Av8r3400]

I'd agree with Paul. Over 80 mph with the door(s) open is asking for trouble. The kind like you had.

Did the fluttering that you experienced loosen up the attachment of the doors to the frames? That much movement, as you described, may have loosened your attachments (rivets?) or wobbled out the drilled holes oversized making the doors loose on the frames.

I hope you didn't do any permanent damage to your doors. :(