[AR] Re: Spartan: Hovering hybrid
- From: Ben Brockert <wikkit@xxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Fri, 17 Oct 2014 22:02:28 -0500
Pixel, Texel, and Morpheus all hovered with a gimbaled engine just a few
inches from the CG. It worked. The bigger issue for squat vehicles is with
propellant distribution rather than control authority.
On Friday, October 17, 2014, David Hein <davehein@xxxxxxxxxx> wrote:
> Multiple engines make sense if the lander has a short and wide profile.
> The center of mass is very close to the engine, and a single gimballed
> engine would not have much of a moment arm to work with. Gimballed mounts
> work better when the rocket is long and narrow, and the center of mass is
> located at a larger distance from the engine.
>
> I would think that a 5-engine configuration would work better, where the
> center engine provides most of the thrust, and the 4 outer engines are
> smaller and mostly used for attitude control. With the 5-engine approach,
> variances in the thrust of the 4 outer engines would have a smaller effect
> on stability than with the 4-engine approach.
>
> Using a large central engine would require maintaining the center of mass
> over the main engine. On the other hand, the 4-engine configuration would
> allow for the center of mass to be off-center, and move as the burn
> proceeds, so it does have that advantage over using 5 engines.
>
>
> On Friday, October 17, 2014 9:17 AM, Jonathan Goff <jongoff@xxxxxxxxx
> <javascript:_e(%7B%7D,'cvml','jongoff@xxxxxxxxx');>> wrote:
>
>
> Korey,
>
> The four engine design was abandoned because the engines were crap and
> highly inconsistent from engine to engine. I can say that because they were
> my design and I was soooo glad when we finally killed those and went to the
> new engine design. We tried to move too fast from single engine sort of
> working on the test stand in a fixed configuration to four flight engines.
> We were also outsourcing our GN&C at the time, and there were issues with
> how that was handled. By the time I left in 2010, I think we had the GN&C
> and engines to a point where we could've done a 4 engine vehicle had we
> wanted to... we were just still at a point where a single engine vehicle
> was a lot easier to work with.
>
> Multi-engine liquid VTOLs probably only start making sense when:
> 1- Your engines have enough development on them that they are reliable and
> consistent from vehicle to vehicle
> 2- You are getting near a "step function" in the engine size versus
> development cost curve, where doing multiple copies of a smaller engine
> would be a lot cheaper than developing a big new engine.
> 3- You're getting the rest of your vehicle to flight reliability levels
> where engine-out actually makes a difference reliability-wise.
>
> Masten will get there if it keeps plugging along. And it could go there
> today, it just doesn't make sense for them at the moment. It probably makes
> sense at XS-1 scale though.
>
> Anyhow, all that is conjecture since I left there over four years ago. If
> they let Dave Masten respond, I'd love to see how his thinking compares to
> mine.
>
> ~Jon
>
> On Fri, Oct 17, 2014 at 8:07 AM, Korey Kline <k2@xxxxxxxxxxx
> <javascript:_e(%7B%7D,'cvml','k2@xxxxxxxxxxx');>> wrote:
>
> Did Masten ever get the four engine version to hover? Has anybody?
>
> On Fri, Oct 17, 2014 at 9:50 AM, <joesmith@xxxxxxxxx
> <javascript:_e(%7B%7D,'cvml','joesmith@xxxxxxxxx');>> wrote:
>
> Even Armadillo was able to hover. Masten as well.
>
> On Fri, 17 Oct 2014 00:38:03 -0700, George Herbert <
> george.herbert@xxxxxxxxx
> <javascript:_e(%7B%7D,'cvml','george.herbert@xxxxxxxxx');>> wrote:
>
> For some reason I jump straight to a single centerline hybrid with cold
> nitrous gas attitude control, but each to their own...
>
> George William Herbert
> Sent from my iPhone
>
> On Oct 16, 2014, at 2:44 PM, "Troy Prideaux" <GEORDI@xxxxxxxxxxxxxxxx
> <javascript:_e(%7B%7D,'cvml','GEORDI@xxxxxxxxxxxxxxxx');>> wrote:
>
>
> Jon,
>
> You’re thinking in liquid mode ie. LOX. You need to think monoprop
> oxidizers eg. Nitrous or Peroxide. If you look at Nitrous:PE for example,
> the performance for O:F ratios between 5:1 to 10:1 is pretty much the same.
> The internal bond energy of the oxidizer provides a significant portion of
> the propulsion energy.
>
> Saying that, I generally agree that typical hybrids aren’t suited for
> this application although if your expertise is in hybrids and you’re really
> comfortable with them…
>
>
> Troy
>
>
> ...Because once you've done all the work to figure out how to do fire
> and throttle valves, building another set with slightly different
> characteristics is just too hard. Much easier to deal with a chamber that
> changes geometry throughout the burn, and where you have no real control
> over mixing efficiency.
>
> I mean, cool if they can pull it off, but I've got to scratch my head on
> why they'd do it that way. There *are* places where hybrids might make
> sense, but I have a hard time believing a hovering vehicle is one of them.
> Unless bobbing around like crazy in a semi-controlled fashion is good
> enough.
>
> Sorry if that came off overly negative, I just wonder about people's
> design choices sometimes.
>
>
> ~Jon
>
>
> On Thu, Oct 16, 2014 at 8:12 AM, Mark C Spiegl <mark.spiegl@xxxxxxxxx
> <javascript:_e(%7B%7D,'cvml','mark.spiegl@xxxxxxxxx');>> wrote:
>
> I have no connection with these guys.
>
> They're building an LLC type vehicle using hybrid rocket motors instead of
> biprop.
>
> http://www.spartanproject.eu
>
> --MCS
>
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