On Thursday, March 31, 2016 at 10:20:59 AM UTC-7, BobW wrote:
Major snip...

My apologies: I thought you were actually interested in discussion the
technical details of the design. I guess by your non-response my
calculations are correct...


They may be or they may not be, and if you're designing such a craft as Dale
Kramer is attempting, I've no doubt you can find qualified people to look over
your shoulder. This is America, have at it!

Given the original topic of this thread (which I took as a "Hey guys! Lookit
this...and oh by the way, here's how you can kick in some money if you're
sufficiently interested in funding further experimentation." sort of post),
"your calculations" seem to have become something of a
terribly-important-to-you sub-focus...probably more important to you than to
many/most of the original intended audience.

I offer this opinion as a degreed aerospace engineer having little
personal/user interest in hybrid VTOL flight, "hybrid" in this context meaning
capable of (some) verticality but of primarily "fixed-wings-based" horizontal
capability. Given today's materials, I simply don't see "serious practicality"
on any near horizon for it...similar in that sense to (say) man-powered
flight. Nevertheless, both are technically interesting (to many, including
me); both have been successfully performed; both will (probably) continue to
be investigated and perhaps even advanced (maybe even in my lifetime). And if
you somehow or other engage my interest sufficiently, I might even be
motivated into "calculation checking" beyond merely noting something I've
missed seeing anyone else note, i.e. that the "main prop atop" configuration
is arguably inherently stable in descending, vertically-oriented, flight
simply by the expedient of momentarily lessening "lower down" thrust. That's
not to suggest the physics of such flight are simple, but to rather suggest
the "balancing a pencil upon one's fingertip" analogy previously noted herein
is more appropriate for a rear-exhaust rocket than a "top-biased descender."

Respectfully,
Bob W.

I never viewed stability in hover as an issue. After all, there are 6 thrusters at a decent distance from the CG that can be used to balance the a/c (quad copters do it routinely). The susceptibility of the a/c to toppling in ground winds is a different issue (imagine a 30 kt gust just as the a/c was touching down). Another issue is the pilot/seat pan will become a huge airbrake as the a/c is transitioning from horizontal to vertical flight. This will produce a pitching down moment while the a/c is trying to pitch up. The seat pan, be automatically driven, could be part of an unintentional positive feedback loop (the a/c pitches down due to drag, followed by pitch up when the seat pan retracts, then repeat the last two actions).

The power calculation is very simple and can be found in numerous references. Here is one very good one (pg. 9-5):
http://web.aeromech.usyd.edu.au/AERO...ents/p-401.pdf

I have already explained my motivation: providing a fact-based critic for potential investors. I have had CEOs flat-out lie to me about their company's situation (Country Wide Financial, Massey Energy); if someone had exposed those lies to me it could have saved me thousands of dollars (this is not to say Dale is lying about anything!).

Thanks for the thoughtful response!

Tom