I think the trap that gets set is that the canopy can sit down in its closed position without being latched. The friction of the canopy against the
canopy seal keeps the canopy closed while rolling down the runway at low AOA. Then once the airplane is rotated for liftoff and the flow field changes with the higher AOA, the canopy is pulled open. So setting up high speed taxi tests that would include
rotating for takeoff would be risky.
I expect when the canopy opens that it changes the horizontal stabilizer’s AOA in proportion to how much it is open. I think higher airplane AOAs and
higher beta/side slip angles increase how far the canopy opens. In the Geraldton, Australia accident, witnesses report the canopy being open as much as 30 degrees while the plane was turning at low speed – probably from high AOA and the side slip – ball wasn’t
in the middle. So the dynamics of the canopy changing how far it is open as the AOA and beta change and thus changing the air flow over the tail effects the airplane’s pitch attitude, can create an ever changing stability and control challenge for any pilot.
That’s what was reported by the surviving Longmont, Colorado pilot’s open canopy crash landing.
I expect the temptation of a pilot reacting to the canopy being open in flight is to slow down thinking that it might allow them to get the canopy down
and latched. The slower speed, though, just means a higher AOA and a wider open canopy with more pitch instability. I suspect that flying faster might improve the pitch instability.
From these bits of evidence and conjecture, I think anyone finding themselves in an open canopy situation should fly straight ahead and climb to several
thousand feet above the ground before experimenting with turns and configuration changes and figuring out what is most stable. Once a stable landing configuration for flaps, airspeed, and power setting is determined, the airplane approach and landing should
be flown with minimal changes to that configuration, small bank angle turns, minimum power changes, etc.
Yes, I wouldn’t recommend anyone deliberately flight test this. But, if someone finds themselves in this situation, if they can get to altitude and
figure out how best to configure for best stability on approach and landing with the canopy open, that would be very helpful…
Valin
From: Lancair Mailing List [mailto:lml@lancaironline.net]
On Behalf Of Dennis Johnson
Sent: Tuesday, February 25, 2014 9:36 AM
To: lml@lancaironline.net
Subject: [LML] Legacy Accident History Update
Regarding concerns about taking off with an open canopy in the Legacy, Mark Summers, a new Legacy pilot, has asked me to post a message here advising that there is a discussion about open canopy problems in the Vans RV-12 at this link:
Personally, I remain a little skeptical about this perceived problem. On one hand, I can't imagine aerodynamic forces that would cause the canopy to open more than a few inches and have second hand knowledge of a Legacy open canopy on
takeoff that exhibited no problems. On the other hand, there have been fatal accidents following an open canopy on takeoff, which cannot be ignored.
It would be nice if someone could offer a plausible explanation of forces that could open a Legacy canopy more than a few inches. Even better if someone did high speed taxi tests with the canopy unlatched, with a video camera on a chase
car recording the results. But I'm not volunteering!