REFLECTOR: Delaminated Canard Top -- Safety of Flight Issues?

[Bob Jackson]

After 350+ hours of flying, yesterday while cruising at 18,000' with perfect
light from a setting sun, we noticed some 'bubbling' along the top surface
of the canard.  Once back on the deck, a little coin tapping confirmed that
the top canard skin had delaminated in several places.  The worst bubble is
right under the fifth set of VGs counting from the canard tip inward, and
was about 6" long (fore-and-aft) and 2 to 3" wide (side-to-side).  This
bubble looked like it was raised almost 1/4" in flight at altitude!  On this
flight the gross aircraft weight was about 3400 pounds.

 

In addition while in the air, another area of delamination that extended
nearly to the canard tip, along the top of the spar and several inches
fore-and-aft (but only separated about 1/8" above the canard foam) was
visible.  On a subsequent flight just up to 5000 ft (and about a 3100 #
aircraft gross weight), only the slightest amount of delamination bubbling
could be seen, and only under the 5th set of VGs.  

 

I believe our plane is more susceptible to canard delamination because of
our very high max gross weights (3600 pounds), and high altitude operation
(up to 25 Kft) where the sea level pressure air trapped inside the canard on
take-off will be pushing outward on the canard skin when we're cruising at
altitude before the pressures can equalize.

 

Our canard was made by Alan at Wingco close to 15 years ago, and apparently
he was using a two step vacuum bagging technique at the time that Dwayne
Swing says was generally more prone to delamination than the standard canard
construction process outlined in the manual.  We still need to 'coin tap'
test the bottom of the canard to make sure we don't have any delamination on
the bottom.

 

Eventually, we plan to build another canard that is a foot or two longer to
better carry our higher aircraft weights and canard loadings -- so it
doesn't bend up as much in flight, which will also create delaminating
stresses.

 

The questions for the group are:

1.	How much of a safety of flight issue do you think it is to continue
flying with this degree of canard delamination until we can repair it or
build a new canard?
2.	Who else has experienced canard delamination, and did you have
similar 'extenuating circumstances' to ours (like high gross weight or high
altitude operations) that might help to explain it.  Also, was it with a
Wingco 'Fastbuild' canard?

 

Thanks,

Bob Jackson

N2XF

 

 

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