Fwd: Re: Vanes, box shealding & landing frame

>At 10:45 AM 5/25/2004 -0600, you wrote:
>>John Carmack,
>>
>>I was wandering if you folks had any concerns about the deep
>>enclosure around the jet vanes?  It seems to me it may cause
>>some problems with the gas dynamics for controlling the thrust
>>vectoring.  It seems that as the vanes deflect a significant amount
>>the gases are going to impinge on the side of the box and basically
>>have the steering effects basically canceled out.  Also it would
>>seem that at extreme vane deflection the back pressure behind and
>>to the side of the vane and the box could be the cause of the
>>stress failures of the shaft and vane that might not of other wise
>>have happened in such a constricted volume.
>
>The vanes should only tip +/- 15 degrees or so, and we aren't fully 
>expanded in the nozzle, so the jet isn't as wide as it looks.
>
>
>>Have you considered instead of the shielding box, instead covering
>>the bearing and servo motor with a low profile as possible high
>>temperature flexible thermal insulation blanket, perhaps made of
>>fiberglass or  nominex?  Also perhaps the servos could be moved
>>further up and away from the exhaust backwash by coupling them
>>the the vane shaft by a universal joint and thus moving the servos
>>up and way, say up to 60 degrees.
>
>Blankets would tend to get soaked in propellant during the warmup, and any 
>edges that can start flapping near a supersonic exhaust will fray 
>rapidly.  We like having solid metal surfaces down there.
>
>We want to avoid adding linkages if possible.
>
>
>>I know that the system is now an experimental steeping stone to
>>your next vehicle, and thus your trying to keep it as simple as
>>possible.  The landing gear looks to have a very narrow foot print
>>and only a modest amount of sideways motion on touchdown
>>would result in the vehicle toppling over.  Have you considered for
>>at least the first free flights putting 'training' struts out on the
>>landing structure?
>
>We have the GPS position hold working now, so we expect to set down with 
>almost no sideways velocity.  Also, the CG is quite low, so it isn't as 
>tippy as it looks.
>
>A wider stance would be nice, but I am not going to do any kind of 
>deployable landing gear if I can at all avoid it.  We could spread the 
>base by about a foot each way before we ran into problems with 
>transportation, but then we would lose the option of just fairing the 
>entire base in for better aerodynamics.
>
>
>>I know its probably going to be a while but when you plan on having
>>the vehicle going to higher speeds and altitude, have you
>>considered putting a angled down facing camera with a RF link?
>>The idea is that if the vehicle encounters control problems or
>>unexpected drift and possibly has to land out of direct view of the
>>ground control station, such as having to land it on the other side of
>>a hill or tree.  This would make possible last minute adjustment to
>>avoid undesirable landing locations that the auto land code would
>>have no way of knowing about.  Also along those lines any
>>thoughts about some sort of close range terrain sensors such as a
>>IR or ultra sonic ranger.  I know you have a GPS system but it
>>can't take into account the odd little topography issues if you have
>>to land further away from your takeoff point.
>
>Actually, we may be doing higher and faster flights next weekend.  As soon 
>as we prove out the basic jet vane control, everything is set for boosted 
>hops.  We can't go very high with a 15 second burn time limit, but it will 
>still do some accelerating and deceleration.
>
>If the vehicle is landing out of sight, we have had a failure of a nature 
>that likely means it isn't going to "land" at all.
>
>Ultrasonic rangefinders don't work at all next to a rocket engine.  We 
>tried that very early on in our development process.  We used a laser 
>rangefinder on our manned lander, which worked ok, but I have concerns 
>about kicked up dust confusing it.  There is a decent little radar 
>rangefinder from Roke that I have been considering buying as a backup for 
>the GPS, but I haven't bit the bullet on it yet.  It is only 10hz update, 
>so you can't get a decent velocity signal from it, but it should be able 
>to coast with the inertial system.
>
>John Carmack