Bob,
I saw no indication that the honeycomb core was replaced with a crush-resistant material (eg hardwood or aircraft ply) in the area of the landing gear mounting bolts. The red-lined photo that Oli posted states that indeed it is done. OK, fair enough.
I have to wonder though since there are so many holes and cutouts in that former (particularly in the lower area around the holes for the gear cylinders) that local reinforcing is more problematic than practical. You can see the honeycomb in the U-shaped cutout for the turbine partially filled with potting compound so any reinforcement would be local which gives rise to the issue of accurately locating the reinforcement pieces during the layup process. The mounting holes are much closer to the cutout in my photo than in the photo Oli posted so perhaps the cutout on the plane I examined was cut oversized. An edge margin (L/D) of at least 3 would be appropriate and that didn't appear to have been achieved.
The wing/stabilizer layups seem structurally questionable as well. I noticed some earlier comments/photos on the FEJ announcement 2011 thread that seem to be particularly appropriate.
ORIGINAL: 757Driver
ORIGINAL: Moerig
I say make a simple vertical spar, one with vertical grain ( or orthogonal ) and one with paper core. Apply force in same plane as wing load, measure and report back. A spar is a double cantilever which has compression and shear forces in the vertical. If open paper core proves better in compression along the ribbon or w length I will eat my hat.
I'll eat my hat too! Honeycomb is only intended to be used as a CORE material in composite sandwich type layups. The wing skins and the like are perfectly acceptable. The stabilator however is a different story. They have the spar tube with what looks like long black screws running through verticle sections of honeycomb. Then what looks like Hysol poured in over the screws. All of this, I believe is not structurally sound. I'm an FAA licensed airframe guy and not just some guy bashing a great looking product. I only wish to see FEJ rethink their use of materials and build a stronger, more reliable, safer airframe.
Apart from the obvious structural design issues, there is also the issue of consistant application of adhesive during the layup process, not to mention the landing gear design. I was also concerned about photos from FEJ stating that they inject foam in spar boxes. Foam isn't noted for it's strength therefore it's applicability in such high stress areas is questionable.
I'm standing by my earlier statement of "I think that the use of honeycomb core technology is an interesting innovation but it needs to be applied correctly and with appropriate design and quality control. There appears to be significant issues with the model's structure which could lead to catastrophic failure."
Regards,
Jim