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Date: Thu, 06 Mar 2014 08:06:34 -0500
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From: Charles Brown <browncc1@verizon.net>
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Subject: Re: [LML] Canopy Latch modeling
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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


From: Paul Miller <pjdmiller@gmail.com>
Date: March 4, 2014 6:21:39 AM CST
To: lml@lancaironline.net
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



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<html><head></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =
"><div>a) The canopy is generating lift when closed. &nbsp;More to your =
point, the pressure on the inside of the canopy is higher than the =
pressure on the outside. &nbsp;I'll assert that without citing several =
reasons why it's true. &nbsp; 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. &nbsp;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.</div><div><br></div><div>b) The =
cg moves forward trivially when the canopy opens all the way. &nbsp;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. &nbsp;And the canopy won't open 90 degrees; at small =
openings the cg change is completely =
negligible.</div><div><br></div><div>c) The drag increase will be =
significant. &nbsp;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. &nbsp;Cruise Cd is around .014 so that's a drag increase of =
15% -- at least -- for a 6" opening.</div><div><br></div><div>d) Recent =
posts suggest keeping the angle of attack low. &nbsp;That makes sense to =
me. &nbsp;Adding power makes sense to me; offsets the drag and keeps =
alpha low. &nbsp;Takeoff flap makes sense to me; reduces fuselage alpha =
without adding much =
drag.</div><div><br></div><div>Charley</div><div><br><br><div =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px;"><span style=3D"font-family:'Helvetica'; =
font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>From: =
</b></span><span style=3D"font-family:'Helvetica'; =
font-size:medium;">Paul Miller &lt;<a =
href=3D"mailto:pjdmiller@gmail.com">pjdmiller@gmail.com</a>&gt;<br></span>=
</div><div style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: =
0px; margin-left: 0px;"><span style=3D"font-family:'Helvetica'; =
font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>Date: =
</b></span><span style=3D"font-family:'Helvetica'; =
font-size:medium;">March 4, 2014 6:21:39 AM CST<br></span></div><div =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px;"><span style=3D"font-family:'Helvetica'; =
font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>To: =
</b></span><span style=3D"font-family:'Helvetica'; font-size:medium;"><a =
href=3D"mailto:lml@lancaironline.net">lml@lancaironline.net</a><br></span>=
</div><div style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: =
0px; margin-left: 0px;"><span style=3D"font-family:'Helvetica'; =
font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>Subject: =
</b></span><span style=3D"font-family:'Helvetica'; =
font-size:medium;"><b>Re: [LML] Canopy Latch =
modeling</b><br></span></div><br><br>Let me ask these questions to the =
group, speculation is permitted since we have no data:<br><br>a) is the =
canopy generating lift when closed? If so, does that lift decrease or =
increase when unlatched?<br>b) Does the CG of the aircraft change =
between open and closed canopy in flight?<br>c) Does drag increase =
between open and closed in flight?<br>d) What does a pilot do when all =
that noise and flying paper occurs? &nbsp;Full throttle, decrease =
power?<br><br>Paul<br><br><font class=3D"Apple-style-span" face=3D"arial, =
sans-serif"><span class=3D"Apple-style-span" style=3D"font-size: =
13px;"><br></span></font></div></body></html>=

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