Q-talk 89 - Patillo Armadillo Spar Fix
- Details
- Category: Q-Talk Articles
- Published: Wednesday, 23 December 2009 16:24
- Written by Jim Patillo - San Francisco CA
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Thanks to all of you who have offered interest, advice and help in the repair of my airplane. You know who you are! The spar and wing has been repaired and I will be painting within the next two weeks. Then it's back to the Big Blue Yonder!
I believe there were several positive lessons that surfaced from this exercise. First, the understanding of what caused any failure is essential in making an adequate repair, as John Ten have points out.
Second, you should inspect Q200 spars on a regular basis and be on the look out for any marks, however insignificant, before and after installation. I believe this failure occurred at the factory as the result of a poor load testing procedure. The problem could arise again if you are unfortunate enough to get a weakened spar and place the stress point on the top of the wing like I did.
Third, we learned a good deal about the carbon spar that will be helpful for others in the future.
Fourth, a repair for that area has now been put in place and will be severely tested before recommending it.
Finally, many of us believe I could have flown the plane for quite a while without noticing any degradation. Then one day the wing would have failed on a hard landing, or worse yet, in the air just takeoff and we would have never known the real reason for the failure.
Now, the history of the problem. Upon doing my yearly inspection, I found what appeared to be a very slight scratch/mark in the passenger side spar area (BL 11.5) of my Q200. It was almost too small to detect. Sanding away the charcoal Zolitone revealed a crack in the top of my spar about .040 wide, 3.5" long, running up over the top from about 340 degrees to about 30 degrees. Initially I thought the crack was all the way through the spar, but later discovered that the crack was about .030 deep. (The spar in that area should be about .075 thick). I also discovered that there was foam inside my spar @ BL11.5.
The decision was made to treat the crack as a complete failure, i.e., repair it in the same way as the two spar halves were originally put together. Fortunately, there was enough room (about 8" left / 6" right) on either side of the crack to make the repair. The foam core was cut out in front of the spar about 4" and behind the spar about 3" and 14"W to allow a 360 degree view to completely inspect the damaged area and then make the repair.
The repair was straight forward. The spar was sanded just until I saw carbon the full 12" width . I tapered the existing top and bottom spar caps. I installed (3) 12" wide full wrap bids on 45 degree with offset overlaps. Then I installed (30) x 5"W x 10.5" offset uni plys on top and 25 offset uni plys on bottom of spar.
Note: Because I had to cut the top of the wing skin all the way to the fuselage side to access the spar, it presented a problem, i.e., no way to tie back into the uni on the top of the wing at the fuselage side wall for about 4". To fix this, I cut out a 6" square of foam from the underneath side of the top wing skin (past the fuselage) and did a reverse lay-up (same schedule as top of wing) under the top skin from bottom side. This allowed for a new skin to be placed under the original top skin with a 2.5" lip inboard from the fuselage side. Confused yet? Tied back into the existing fiberglass wing stringer (between foam cores at about BL14) with 3 bid 45 degree to the spar. Glassed 3 bid 45 degree back onto inside of elevator bracket. Filled in the foam cutouts with blue small cell foam. Glassed the top and bottom of the wing and spar with 45 degree uni per original plans. Repair was a piece of cake at about 40 hours of work. The worry and torment before starting took several hundred hours!
The repair turned out extremely well with little to no visible change in appearance when complete. Another plus was that I was able to open up the low-pressure area on the belly like Bob Malechek's Q200.. This along with my oil cooler should keep the oil temps in the 190-200 degree range on really hot days, fully loaded.
Today I flew for about 45 minutes and the plane performed flawlessly. Take off weight was 1,080 lbs. and landing weight was about 1,056 lbs. I made two landings and checked the spar and surrounding areas which came out clean as a whistle.
In the end, Bob Farnam and I agreed, the greatest point load the plane will see is on the ground and the best thing to do was fly the airplane. We concurred that unless a static load test was done accurately and with the utmost care, the potential for damage was significant. We have never been able to pull more than 3 G's in any scenario in the air. Gust and wind shear loading may increase this number, I am just not sure but have not seen it in 110 hours. During the flight I saw no more than 1G on the meter. The plan is to fly a few more sorties with this weight, then gradually increase loads before Saturday to 1,300 lbs. After the fly-in, I will go to 8,000 - 10,000 ft. with chute and increase loads to max.
The repair took about 150 man hours of labor and quite frankly, was not all that hard, just labor intensive. This endeavor proved that a repair this severe is still doable with some thought and planning. Since this is the first repair of its kind that I know of, I will call it the Patillo Armadillo. If, God forbid, anyone ever needs to duplicate it, I will be available for commentary! It is good to be in the air again.
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