- Oct 18, 2003
- Saline Michigan
We really should not go telling a new batch of folks Hollman's stuff was good guidance on anything.Martin Hollmann wrote some books that are very good at explaining how to design composite aircraft structures, listing material properties, how to perform structural and FEA on them, and even aerodynamic flutter analysis. His widow is still selling them through his AircraftDesigns.com website. There are other good books out there on this subject, too, so other than illiteracy, there is no good excuse for not crunching the numbers and verifying the design is sound before ordering materials. If you’re building a tube & fabric airplane with <100hp, then go ahead and draw those chalk lines on the hangar floor, but for a high performance aircraft, to eschew the now ubiquitous design resources is negligent at best, stupid at worst...so why would someone want to help fund this?
Hollmann's approximations on composites are unreliable for design and downright scary to this engineer. His shortcuts have resulted in major misses on composite structural designs when tested. Lancair two seaters built to his designs proved much weaker than he anticipated, requiring iterations of test and beefup because he did not understand structures and materials. He never even acknowledged that he screwed the pooch, and I believe it was a case of he had no idea what he did not know.
In his FEA work, the codes he demonstrated do not handle directional materials/composites well, so the methods are then unreliable for composites. All of his modeling was based upon his erroneous approximations of lamina load/strain relationships - very much GIGO.
Then the entire topic of FEA is one that requires both significant training and experience before reliable results can be expected. GIGO applies again, and I am reluctant recommend it to folks. The first step is to do the more conventional closed form calcs and much of what we do in airplanes can indeed analyzed and designs settled with those calcs - no FEA needed for much of it.