John is also a longtime NAR member. He was the NAR magazine editor from summer '84 when he changed the named from Model Rocketeer to Americsn Spacemodeling until sometime in the early 90s I believe.

I think he also was heavily involved in the restoration work on the Saturn V at Johnson Space Center a handful of years ago. He lives in or around Houston.

Earl

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I had the privilege of seeing John present at NARCON years ago, 2000 or 2001, IIRC, in Dallas. He talked about his sun-seeking Redstone model. It was 5.5" in diameter, IIRC, and had servos that moved the fins, and light sensors in the nosecone that provided inputs to the on-board controller. It was a beautiful piece of engineering.

Listening to him speak, it was abundantly clear the man does not lack for credentials

Doug

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I wonder if he/she is dipping them the way they apply camo to firearms, bow and arrows, hunting gear, and the like.

The decal/skin is disolved in solution and basically floats on the surface, the the item is dip into the solution and comes out cover in the new skin design. pretty cool tech.

That's the ticket,

David

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Involved in both the Houston *and* Huntsville restorations, IIRC.

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I too complimented him on the "skins" of his black and also white Interceptors. Outstanding work!

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He's come out to fly with us a time or two... He and Dave Montgomery partnered to form "Old Rocketeers #724" a couple years ago after Challenger 498 imploded.

He invited a group of us over to his place for a "rocket jam session" so to speak... he's got TONS of great stuff... does some real cutting edge stuff, too... got his own homemade CNC machine... he was making molds for the Apogee Saturn V wraps when we were there... (replacments). I was especially interested in his gimbaled engine guidance system for finless or extremely small fin rockets... very innovative. His current projects are building very large rockets (some upwards of a foot in diameter) that are light enough to fly on model rocket motors (2 G's or less). He showed us some Saturn IB tanks he was making out of heat-set molded depron sheet that were in the about 4 inch diameter range and about 3.5 feet long or so... between that and tubes rolled out of 1/32 birch plywood in the foot or so diameter range, which were EXTREMELY LIGHTWEIGHT, he's doing some REALLY impressive work... That's EXACTLY the sort of thing I get interested in-- not these HPR anti-tank rounds built out of 1/4 inch thick carpet tubes with another couple layers of fiberglass slathered on them...

He was selling some incredibly detailed Mercury capsules... he'd made molds of them and were pulling them-- every screw and shingle on the outside of the Mercury capsule was faithfully reproduced... absolutely amazing detail. He flew one as a Mercury Redstone at NARAM one year, with a horizon sensing guidance system steering the flight via a gimbaled motor mount operated by servos... this was to supplement the scale fins on the Redstone. He's also flown some extremely detailed Saturn V's and a gimbaled engine finless scale model of the Vanguard, which we discussed at length. Unfortunately he hasn't sold the Mercury capsules in a long time...

Later! OL JR

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Your probably thinking of George Gassaway's sun-seeker rocket with steerable fins. John has done a lot of work with gimbaled engines on finless rockets. He uses basically an "off-the-shelf" model airplane anti-crash system with four horizon sensors looking out from a ring up near the nose of the rocket toward the four cardinal points on the compass (in aircraft parlance, two looking out in the pitch axis and two looking out in the yaw axis). These sensors detect the horizon and compare it to the same measurement from the sensor on the opposite side of the rocket, and then if it detects the horizon being "tilted" (meaning the rocket is tilting over from a 'straight up' flight path) it then activates a servo on the gimbaled motor mount to swing the rocket motor in the correct axis to counteract the tilt and steer the rocket back onto the correct flight path. His completely finless Vanguard rocket was the first to use this system, and it worked beautifully by all reports. He also did a Mercury Redstone for NARAM with scale fins using the same system, but I don't recall the fins moving-- just the gimbaled motor mount (he showed us the model, and it was EXTREMELY impressive!)

John also was hired to do some models and stuff for the Saturn V refurbishment at Houston years ago... he had SUCH an extensive library of original materials from scale blueprints and paint patterns, etc. and his models and information was SO impressive that they hired him to work on the restorations themselves... First in Houston and then at Huntsville... John is probably THE most knowledgeable person about scale Saturn V's alive, bar none.

Later! OL JR

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No it was John, no doubt. But George mighta been in attendance. And, you're right, it used RC gear which strived to keep the light balanced.

That said, it mighta had a gimballed motor mount rather than steerable fins. IIRC, John covered the tradeoffs. The gimbal is very effective at low speed, during liftoff, where the fins have little effect. Conversely, the fin steering still works quite well after motor burnout

Anyway, it's been too long to be sure about the rocket - heck, it mighta been 4" instead of 5.5" - but no doubt, that was John Pursley up in the front of the room

...

BTW, John's wasn't the only truly impressive presentation I saw at the two NARCON's DARS hosted in 00 and 01. Ted Mahler, who posts here sometimes, had a wonderful presentation on R&D. To this day, I rank it as one of the best presentations I've ever attended, and I've been to lots of high-tech conferences!

...

BTW2, I found these picture albums from the two events:

http://www.angelfire.com/scifi2/rocketport/narcon2000/
http://www.angelfire.com/scifi2/rocketport/narcon2001/

And looky here (2001):



Speaking of Ted, here he is with yours truly (2001):


Doug

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Oh, I don't doubt you saw John speaking... he's excellent at explaining his ideas and is a great presenter... I think you just have some facts about the projects confused-- This is sorta been a pet project of mine for a good while, not that I have the technical abilities to pull it off myself...

The "sensors" on John's rocket didn't actually make use of the light-- as he explained it to me, they "see" the horizon by sensing the carbon dioxide in the atmosphere, which appears "black" to the sensor. Therefore the "sky" visible to the sensor appears "black", while the horizon and all the "land" below it appears "white" to the sensor, because it's only looking out through a much less distance through the atmosphere to the horizon (which is usually only a couple miles away or so on flatlands, versus looking straight up through about 20 miles of atmosphere, and maybe a hundred or more miles of atmosphere looking out into the sky above the horizon, which is MUCH more distant at altitude than the actual horizon is (someone posted something recently about watching jet contrails that was fascinating-- most are anywhere from 20-60 miles away or more unless they're directly overhead (or nearly so).

Anyway, the sensor compared how much "black" it saw on one side with how much "white" it saw on the other side, and vice versa... so long as both sensors were seeing equal amounts of black and white, say roughly half, the rocket "knew" it was going straight up. If one side was showing say 75% black and the other side saw say 75% white, the "box" the sensors were plugged into interpreted that electronically to mean the rocket was tipped over and was leaning toward the "white" side. Then it would send a proportional signal to the correct servo guided by those sensors and swing it appropriately to steer the rocket back toward the "black" side and thus even them back out to both be at ~ 50/50... Of course the sensors 90 degrees out did the same thing for yaw sensing that the other pair did in pitch, and had another servo clocked 90 degrees to the first to gimbal the motor in yaw.

I asked about the finless aspect of it, since he did a finless Vanguard rocket and I wondered how the guidance system worked once the motor burned out. He basically told me that the rocket pretty much kept flying straight, though there was a little more "drift" from the flight path over time, especially as the rocket decelerated near apogee... Rocket motors generate virtually zero thrust during the coast phase, but it's not COMPLETELY zero-- the motor is still burning a delay grain (slowly) and releasing smoky gas out the nozzle of the motor, so there is a SLIGHT amount of corrective impulse, but the motor has to gimbal MUCH farther and the effect is very small, meaning it takes a long time to act. Basically he told me that if everything is working right, the rocket SHOULD burn out going virtually straight up, with "zero rates", meaning it's not swinging off-course or anything, and so Newton's Third Law kind of applies-- an object in motion tends to stay in motion unless acted upon by an outside force. So basically if the rates are nulled at burnout, the rocket shouldn't be rotating around any axis (pitch or yaw-- John's system completely ignored the roll axis) and should continue going straight until acted upon by outside forces (which tend to be cumulative over time).

Of course there are a couple caveats to the system, especially as they pertain to finless rockets using engine gimbaled guidance... first, it works better if the rocket has SOME fins, even if they are extremely undersized, like a Saturn V with scale fins, or a Redstone-- it works with finless rockets, but the dispersions to the trajectory after burnout start adding up fairly quickly and the rocket may be going sideways around ejection time... Second, if the rocket IS finless, it needs to have a certain "in-built stability" to the design to keep it stable after the engine burns out when corrective forces from gimballing fall to near zero. IOW, the CG/CP relationship is STILL important-- engine gimballing will not make a completely unstable design fly stably-- perhaps during powered flight, but as soon as the motor burned out, it's going to flip ends in mid-air... For instance, the Vanguard was an excellent rocket to fly finless-- the upper stage and lower stage were both about 50% of the rocket's length, putting the transition near the middle of the rocket. The first stage was larger diameter than the upper stage, which meant that the CP was shifted rearward (sort of like 'cone stability'). This helped the CG/CP relationship. The additional weight of the sensor ring and "black box" that controlled the system was placed near the nose of the rocket, along with the battery, and only servo wires and small servos were placed at the back to swivel the engine, and the gimballing motor mount was kept as light as possible to keep the CG as far forward as possible to improve the CG/CP relationship. Basically he said he'd tested the design on a subscale "demonstrator" before he ever added the gimbal equipment, and could make a Vanguard fly stably without fins using noseweight alone. So we got to talking about "hammerhead" designs like say, Ares I, which has a larger upper stage and a smaller diameter lower stage, with a reversed transition to taper down between the two-- basically this kind of rocket is the wrong shape to fly as a gimbal-controlled model rocket-- it's natural stability due to the inverted transition and larger upper stage diameter shifts the CP very far forward, requiring a LOT of noseweight to move the CG far enough forward to make the rocket stable... and of course the motor mount, gimbal, and servo weight all works against that, and it's not particularly practical to move that stuff forward... Basically as soon as the motor burned out, an Ares I design would want to "flip" and fly tail-first as soon as the gimballing thrust could no longer overcome the aerodynamic forces... unless one used a prohibitive amount of noseweight.

More to come... OL JR

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Continued...

Now, I read about George's sun-seeking rocket with great interest-- sort of the same idea, but using a "shaft of sunlight" streaming in from the tip of the nosecone down onto an array of photosensors on a plate at the back of the nosecone/payload section, which sensed changes in the flight path by the voltage generated by the sunlight falling on the sensors... this information was fed into circuits that then steered fins via servos proportionally until the sunlight was basically falling 'straight down' inside the rocket to the center of the sensor disk. Again, pitch and yaw were controlled, but roll was not. An interesting system to be sure, but of course unless the sun was directly at zenith, the rocket would 'lean over towards it' as soon as it left the launch rod, and continue flying directly toward the sun as long as the fins could generate sufficient aerodynamic force to keep it flying on that path (near apogee the thing slows down enough that basically it "flops over" because the fins will crank "hard over" and can't keep it going straight... sort of the same thing with a gimbaled engine mount during coast phase with little/no thrust... it goes 'hard over' but the corrective forces are virtually nil).

Now I've also read about an interesting system that was designed and described on the Brittain Fraley website-- he basically did the same sort of thing George did, but instead of a flat plate array of sensors working like the cardinal points of the compass to keep the sunlight falling "straight down" onto the sensor plate, his were arranged as a sensor cylinder, and wired so that the "center sensor" was to have the highest voltage reading, meaning the sun should be falling directly on it. The sensors on either side of this central sensor should have lower voltage readings, since they were pointing off-angle to the sun, say 45 degrees on either side of the "central sensor" and another pair flanking them 90 degrees from the central sensor (IIRC). These sensors would "compare voltages" and if either of the flanking sensor had higher voltage than the 'center sensor', it was obvious that sunlight was falling more directly onto that sensor than the center sensor, and so it would proportionally activate a servo to turn the fins in opposite directions to rotate the rocket about its thrust axis until the center sensor had the highest voltage reading, meaning it was pointed directly at the sun. If the sensor on the other side of center read higher, it would steer the opposite direction, thus keeping the center sensor pointed directly at the sun compared to the other sensors. This system did NOT control the rocket in pitch or yaw, ONLY IN THE ROLL AXIS. He built this system to make his rocket a stable camera platform for aerial photography, without the sickening spin-induced twirl caused by rockets with slightly misaligned fins or fins with imperfect airfoils and such. He had video of the system on a camera rocket, one video with the system on, and one with it off-- the one with it off started spinning almost as soon as it left the launch rod (though not bad-- maybe 3-4 revolutions through the whole flight, but enough to be distracting and make the video less useful for seeing things on the ground). The video with the system on was rock-solid from liftoff until apogee-- there wasn't over maybe 10 degrees of turn to either side of "centered" once it lifted off (there was a slight turn at liftoff as the rocket cleared the rod and "locked onto" the sun and kept it centered on the center sensor, but after that, the roll was virtually nil). Of course as the rocket neared apogee and the airspeed dropped to the point the fins were no longer effective at generating correctional forces, the fins could be seen to eventually go "hard over" as the rocket "flopped over" at apogee just before ejection. Of course the fins were basically "flailing around' during descent under the parachute, since they couldn't generate sufficient corrective force due to the low velocity under parachute, though the sensors were still trying to lock onto the sun...

Anyway, it's all really fascinating... John's probably forgotten more about rocketry than I'll ever know... LOL

Later! OL JR

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