The craziness continues!
My continuing flirtation with Aviation:
I've purchased a 90% complete Mitchell U-2 Flying Wing!
(Which in Aviation math usually means, 90% is left to be done.)
Show Stopping Discoveries!
One very cold day recently, I went out to the field to make the final measurements for the new seat mount. Much to my horror I found some structural cracks - they are "Show Stoppers"! All along we have been aware that there are several places where the builder departed from strict adherence to the drawings. Now I know I may have to completely dismantle the aircraft for inspection and I've decided to rebuild the aircraft to the original specifications as much as possible. So I can't see meeting my original goal of having the craft in the air within a year from the date of purchase.
With the seat removed and in conjunction
with the effects of the cold temperatures I finally saw some major structural
damage. See the cracks in both of the bottom wooden structures (the
designer calls them "skids" - he started his career as a
sailplane designer in the '30s when they actually used skids).
Since the builder's seat sat directly on the skids I believe they were probably cracked when the big guy got bounced around during his accident with the runway light. At this point it appears that in cold weather the metal framework enlarges the splits by moving part of the split skid with it. But with the seat in place, or in warm weather, the damage to the skids were not easily noticeable.
We'll never know what caused the splits nor will we ever understand for sure why they weren't discovered sooner. Needless to say I'm bummed to find that I may have to totally dismantle the airplane, not only to fix the skids but to also look for additional hidden damage. There is a particular concern about the area where the main gear mounts to the spar because that area is known to be a failure point from hard landings, etc.
|The view of the right skid
- the split is noticeable at the end of the skid but it is harder to see
as it stretches all
the way forward toward the left edge of the picture frame.
According to the plans, there are supposed to be .040 metal doublers bonded to each side of the skids at each attachment point where bolts penetrated the skids. And the connecting bolt should be centered in the depth of the skid. I had missed the builder's omission of the doublers until after I found the cracks.
|The view of the left skid - this skid suffered the most damage as the split clearly continues forward out of the frame. The plans call for a laminated skid but these appear to be cut from the wrong species of wood and are not to the correct shape either. We will have to re-manufacture the skids in laminated wood or perhaps carbon fiber.|
|We had been aware of several other modifications the builder made to the plane which are not reflected on the drawings. Here the skids are longer and continue further into the rear of the plane than indicated on the drawings. The tail support is not as per the plans - I suspect these tubes might be an attempt to stabilize the builder's version of a tail support and castering wheel.|
The main spar
caps contain curved, laminated sections just outboard of the
main gear. The various sections of the spar caps are joined
together by bonded scarf joints. If the laminated skids above represent the builder's
ability to follow the drawings and his general workmanship, can the spar caps be trusted? Structural
epoxy is slightly flexible and is not effected by freezing, however there
are woodworking bonding agents out there which are effected by
freezing. We didn't find the separated laminations until after
several days of hard freezes which may simply indicate that he didn't use
the correct bonding agent for the skids (no sign of epoxy) but he may have
used the right stuff on the spar. So we have a mystery to solve - to
determine for sure that he used a structural epoxy on the spar.
This project is stopped until we have a chance to do an inspection and possibly a teardown of all the critical areas, and assemblies etc. I'm concerned at this point the project may not be salvagable!