[AR] Re: Dempster Turb-O-Prop
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Thu, 11 Feb 2021 19:24:41 -0500 (EST)
On Thu, 11 Feb 2021, Norman Yarvin wrote:
How much do you want to bet? :-) Google 'rocket on rotor' for (among
other things) videos of helicopter rotors powered by tip rockets.
Speaking of which, it's been kind of a mystery (to me, at least) what
went wrong with Roton. The company started out with just such a
scheme (tip rotors with the rotor acting as a pump), switched to a
slightly more conventional arrangement (still with the engine rotating
and that doing the pumping but no rotors pushing air), then ran out of
money, whereupon the people doing the engine development formed Xcor
and went to a completely conventional arrangement...
As I understand it, the original tip-rocket scheme didn't have anything
much wrong with it, except that there were limits to how far you could
scale it up without pioneering major new rotor technology, and the
near-term payloads kept growing. Hence the switch to the rotary engine.
That in turn succumbed to some combination of money shortage and technical
issues. It wasn't simple to do, and if I've got this straight, the best
prospects for further investment seemed to want a more conservative engine
approach. At that point, the engine team got let go. Didn't help enough,
so a bit later, Rotary Rocket essentially folded. Meanwhile, some of the
engine team formed XCOR.
...Having the rotor acting as a pump seemed like an easy alternative to
turbopumps...
Well, it's an *alternative* to turbopumps, but the "easy" part is more
doubtful. :-) Trouble is, it means that your engines spend their working
lives at very high G, and this tends to make hot metal sag... and making
it thicker *doesn't help* because that adds mass too! Jeff Greason said
(some years later) that in such a system "you have to clever your way out"
of every stress problem, and that it really made him lose enthusiasm for
rotating machinery. Hence the change of approach.
Henry
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