Q-talk 122 - Mar/Apr 2007 - index
- Category: Q-Talk Index
- Published: Wednesday, 23 December 2009 16:24
- Written by Doug Humble
- Hits: 2627
Quickie Builders Association
Together we build better planes!
Issue Number 122
Repair of Broken Canard
Submitted by Charles Kuhlman and Harold Dirks Marshalltown, Iowa Q2 N32DK
In August a few years ago our Q2 suffered a landing incident that left it with a broken canard on the left-side. The break occurred about one-third span away from the wheel pant, as shown in figure 1. It was a fairly-clean, chord-wise break that snapped off the canard and the elevator, as shown in figures 2 and 3.
We were faced with a decision, do we repair the canard or do we start over and build a new one? We considered the advantages of going with the LS-1 canard, and we talked with several people about the repair, including Scott Swing, who cautioned us to scarf well the old glass around any repaired areas and to put about one extra layer more than the original layers of glass over the repair, to keep the repaired canard from becoming too stiff.
Since the canard and elevator were the only damaged parts on the plane, and we had sufficient leftover materials from our original build of the plane, we decided do the repair. This article is a short description of the steps and methods we used to accomplish the repair.
The repair began small with fixing the elevator. First, the broken glass and foam were removed around the break in the aluminum tube and a new piece of smaller diameter tube was nested inside the old tube and riveted in.
Figure 4 shows the elevator with foam removed and tube repaired.
The next step was epoxying a couple of layers of bid and uni cloth onto the sanded glass inside of the elevator, followed by carefully fitting several pieces of foam into the open area of the repair and microing them in.
Figure 5 shows the elevator with foam replaced and ready for final micro fill and sanding.
Next came sanding and shaping the foam and micro, and scarfing the glass edges around the repair on both the top and bottom of the elevator. Then a few layers of bid and uni cloth were added to the outside bottom and top as shown in Figure 6. This completed the repair of the elevator, except for filling, sanding and painting.
We next turned our attention to the canard and fitted the broken parts together at the top of the canard. See Figure 7. Using long straight edges we perfectly aligned the two sections of the canard back into its original shape. We then bondoed several straight 2 X 2 boards on top of the canard in a spanwise direction to act as a splint and hold the canard rigid. You can see two of these boards in place at the leading and trailing edges of the canard in Figures 8 and 9 (the boards remained in place throughout most of the canard repair work, except for the final glassing on top.)
At this point the plane was turned upside-down to continue the repair. The repair began with removing all of the damaged glass and foam. Next the missing parts of the canard top glass were filled with bondo and sanded along with the inside top glass to form a substrate for epoxying some layers of bid and uni glass to the inside of the canard. The last layer of this glass was peel-plied so it would bond with the micro-slurry used to glue in new foam pieces in the same way as was done for the elevator.
After the new foam was in place and micro-filled and sanded, and the edges of the original glass were appropriately scarfed, the canard bottom layers of new bid and uni glass were epoxied in place and peel plied. See Figure 10. The bottom glass in back was epoxied to the original spar cap of the canard and peel-plied.
The next job was filling and sanding most of the new bottom glass to the original contour. The front edges of the bottom glass were peel-plied to provide a surface for bonding with the top glass of the canard.
We next turned the plane right-side up and went to work on the top of the canard. This work consisted of removing the 2 X 2 boards and Dremeling out the bondo we had put in to take the place of the missing top glass. Next came the sanding and scarfing of the old top glass down to the new glass on the inside of the canard. After that came the new bid and uni cloth for the canard top, followed by epoxying in a newly-made section of slot core.
The last task was to micro, sand, and paint the canard, both top and bottom, and replace the vortex generators. See photo below for the final result.
The plane was turned over at least 4 times during the repair with the aid of several friends and members of the local EAA Chapter 675. The last time it was upside down, we performed a wheel alignment (ala David Gall's alignment procedure). Also, during the repair time we took time to do a valve job on the engine and change the brakes from single-lever, single-master-cylinder operation to dual-lever, dual-master-cylinder operation.
The dual brake levers are on the left side of the cockpit and are hand (finger) operated. We have found this setup to be quick to learn and after a bit of taxi practice, it seems to feel natural. We are happy with the wheel alignment and the dual brakes
The plane has flown several hours now and will be on full flying status again once the snow, ice, and cold weather have left Iowa. From the way the plane now handles and from a few bounces on landing, it feels just like it used to. We think the repair was a complete success and it put the canard back to its original strength and flexibility.
More photos on this canard repair can be found in the Members Only area of the QBA web site.
Articles from this issue:
Where was Sam hiding? - by Doug Humble
Q2 & Dragonfly Compared - by Doug Humble
Another Note From North Of the Border - by Louis Baltus
Runway 27 L - Dave Richardson - by Susie Richardson
Runway 27L - Robert Justin - by Doug Humble
QBA on the Grow - by Doug Humble
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