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

[Scott Baker]

Bob,
Based on your description of the delamination areas, I suggest an interim fix until the new canard is built.  Drill two small holes through the outer skin of the affected areas and inject a micro-slurry of Epoxy to re-bond the skin to the foam.  It is my opinion that this will be enough of a fix to 'rest easy' regarding continued flight operations.  Wingco wings do have a propensity to delamination - and I would not be surprised to see additional blisters manifest themselves during high OAT and during flights at higher altitudes.  I frequently have seen blisters appear on canards that a) live in hot temperatures, b) are painted a dark color, and c) operate at flight level altitudes.  Interesting theory regarding gross operating weight.  The canard is designed to flex a great deal during turbulance (tips flexing +/- 6" is not unusual), so tension/compression on the lower/upper skins is considered 'normal' - and I imagine the flex of the canard wing is significantly greater during turbulance than as a result of lifting a heavier weight.  In your case, I believe the contributing factors are high altitude operations and the fact that these are Wingco wings.
Best,
Scott B.
  ----- Original Message ----- 
  From: Bob Jackson 
  To: 'Velocity Aircraft Owners and Builders list' 
  Sent: Tuesday, February 22, 2011 1:47 PM
  Subject: REFLECTOR: Delaminated Canard Top -- Safety of Flight Issues?


  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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