a) The canopy is generating lift when closed. More to your point, the pressure on the inside of the canopy is higher than the pressure on the outside. I'll assert that without citing several reasons why it's true. Next, the canopy lift will decrease when it's unlatched; the canopy will rise until the sum of the moments around its fwd hinge point are equal. That is, it will rise until the delta P from bottom to top decreases to *just enough* to offset its weight minus the gas strut contribution.
b) The cg moves forward trivially when the canopy opens all the way. If the canopy weighs 50 lb, and it opens 90 degrees, a rough hack indicates that the cg would move forward about 0.6 inches, or 7% of the total allowable cg range. And the canopy won't open 90 degrees; at small openings the cg change is completely negligible.
c) The drag increase will be significant. If the canopy opens six inches, then using a typical Cp for an aft-facing step of -0.1 and assuming no change to the pressure on the upper surface (that means I'll calculate a minimum value for the drag; the real drag will be greater), you'll introduce a delta Cd of about .002. Cruise Cd is around .014 so that's a drag increase of 15% -- at least -- for a 6" opening.
d) Recent posts suggest keeping the angle of attack low. That makes sense to me. Adding power makes sense to me; offsets the drag and keeps alpha low. Takeoff flap makes sense to me; reduces fuselage alpha without adding much drag.
Charley
Date: March 4, 2014 6:21:39 AM CST
Subject: Re: [LML] Canopy Latch modeling
Let me ask these questions to the group, speculation is permitted since we have no data:
a) is the canopy generating lift when closed? If so, does that lift decrease or increase when unlatched?
b) Does the CG of the aircraft change between open and closed canopy in flight?
c) Does drag increase between open and closed in flight?
d) What does a pilot do when all that noise and flying paper occurs? Full throttle, decrease power?
Paul