If you get a chance to go to a NASA Social, I recommend taking it. They’re wonderful! Last week I was lucky enough to attend my fifth. For this event we saw demonstrations of the LEAPTech project at the NASA Armstrong Flight Research Center. Friday I showed what LEAPTech is (“Leading Edge Asynchronous Propeller Technology”), Saturday I tried to take you along on our trip out onto the Rogers Dry Lake to watch a LEAPTech data run using HEIST, and yesterday our visit to the F-15 hangar was covered.
The next stop was a wonderful place I first saw last November on my first NASA Social. Robert “Red” Jensen invited us into the Subscale Flight Research Lab (SFRL), where he’s been building remotely piloted, scale model aircraft for many years. If a mission or experiment is too dangerous, too untried, or too expensive to try with a full-sized, piloted aircraft, Red and his crew will build and fly a model to test the concept until it matures enough to step up to the full-sized, piloted stage.
In doing this, there are constantly needs for unique parts. Whether it is a structural part for a plane or just a case to hold some equipment in the plane, the SFRL is using 3D printing to quickly and cheaply build and test parts. Even if a part will eventually need to be machined, building it first with 3D printing lets you make sure that it’s correct, and make changes if necessary.
Behind Red in this picture you can see their 3D printer. It’s a big one, with a 10 x 10 x 10 inch printing cavity, and a manufacturing resolution of 1/10,000 inch. Not something that the average hobbyist will have, but it lets them do in hours or days what would take weeks or months if they had to do everything in steel or aluminum.
Shelved for the moment in the SFRL are “Droid 1” and “Droid 2,” used in numerous previous experiments. There’s an excellent NASA video here that shows how “Droid 2” was used in development of AutoGCAS. (That’s “Automatic Ground Collision Avoidance System” to you and me.)
I went into the AutoGCAS system at some length in my previous article, but the short version is that software has been developed to work with a plane’s autopilot and keep track of where the plane is compared to a 3D map. When a ground collision is imminent, AutoGCAS takes over from the pilot and flies the plane to safety (usually in a matter of seconds) before returning control to the pilot.
When the system was developed using “Droid 2” (see that video) the software and 3D map of the entire planet were put on a cellphone, which was used to control “Droid 2.” Yeah, a cellphone. One. No mainframes, no PCs, no huge, fancy computer systems. A cell phone.
This software is currently flying in many US military jets. Red told us that it has been credited with at least two “saves” in the past few months in aircraft involved in the Middle East, and there may be more that they don’t know about. In addition, a version is being worked on that will be available to private pilots (like myself) and while it won’t interface with the autopilot to take control, it will run on a tablet or smartphone to warn the pilot of imminent danger and to tell them which way to go to escape.
Behind Red in this picture you can see his current big project, a newer, larger model to test the Prandtl wing design. (We’ll talk more about that below.) Student interns have opportunities to work in the SFRL (under staff supervision) to build models such as this. The Prandtl design is an interesting one and I’m looking forward to seeing where this next series of tests goes.
In the foreground you can see a octagonal (eight rotors) drone which is being assembled to monitor test flights from a new perspective. For example, the F-15’s we saw yesterday, flying at 600 mph, aren’t very good at chasing a scale model flying at 60 mph. But a drone like this could do it quite nicely.
Here’s the camera rig on the bottom of the octagonal drone. These guys get to do the coolest things with the neatest toys! How do I get a job here?
Following the SFRL tour, we were taken to get a close look at the Lunar Landing Research Vehicle (LLRV). Again, this is something that I had seen in November, but then it was mostly hidden back behind the original M2-F1 lifting body. That pioneer aircraft is now at the Museum of the Air Force in Dayton, so we got to get a much clearer view of the LLRV.
In that previous article I have links to a couple of videos about the history of this vehicle as well as other details. In brief, five of these aircraft were used during the Apollo program to train the astronauts to land on the moon. Neil Armstrong almost died when one went out of control (he ejected out, his parachute opened when he was just feet above the ground, he went back to his office and finished the afternoon as if nothing had happened) and all of the astronauts who landed on the moon trained in this vehicle or one of the others in Houston. In total, three of the five were destroyed in crashes, but they got the job done. Flying the LLRV turned out to be an excellent simulation for landing on the moon.
The LLRV was powered by this General Electric CF-700-2V turbofan engine. It was mounted to point downward on a gimbal so that it could be pivoted and aimed through a wide range. There were also some very clever hardware-based simulation modes, which would automatically compensate for factors such as wind gusts, which of course would not be found on the lunar descent.
The engine had 4,200 pounds of thrust, but the LLRV with a pilot and fuel weighed almost 4,000 pounds, so the LLRV could barely get off the ground more than 500 feet, hover, maneuver, and land. The total time of a flight was usually only five to seven minutes, with a total flight endurance capacity of just ten minutes. After using all of the engine’s thrust to take off and climb to several hundred feet, the engine was throttled back to hover and simulate a descent to the lunar surface.
The pilot’s compartment on the LLRV was sparse and designed to simulate the Apollo Lunar Module as much as possible. The controls were as close to the LM’s as possible. You can see how visibility in the pilot’s compartment was deliberately restricted, to closely match what the pilot would see on descent to the moon. Pitch, roll, and yaw were controlled by sixteen small hydrogen peroxide thrusters, mounted in pairs.
Large yellow and black striped handle connected to the ejection seat. In an emergency (three of the five vehicles had them and used the ejection seat) it would take the pilot out at 14 Gs to about 250. The seats developed for the LLRV were the first “zero-zero” ejection seats, meaning that they were designed to work on a vehicle with zero altitude and zero airspeed. Up until that time, ejection seats in military fighters primarily used small rockets or spring systems to simply get the pilot clear of the aircraft, assuming that once separated from the plane the plane would get out of the pilot’s way and there would be significant altitude for parachute deployment. A zero-zero seat on the other hand uses a much larger rocket and drives the pilot up and away from the aircraft, immediately and rapidly deploying the parachute, allowing it to be used even from a resting position.
Above I talked about the new, larger Prandtl wing being built by Red Jensen in the SFRL. Here’s the smaller one, which was built by students in the SFRL in 2013 and recently finished its test program. This one is being boxed up to be sent to the Smithsonian Air & Space Museum in Washington, DC.
The Prandtl wing attempts to correct a basic flaw in every wing built, from the Wright Brothers onward. There’s a phenomenon known as “adverse yaw” which will swing the nose of the aircraft in the direction opposite of the direction of turn when the aircraft banks. In other words, if you turn left, the nose will try to swing right, and vice versa. In a conventional airplane, this is countered by use of the rudder or very fancy computer controls. (Think of the B-2 bombers for the latter.) If this isn’t done correctly, you get an “uncoordinated” turn, which can make your passengers queasy or be quite dangerous a low speeds. (Why am I hearing my flight instructor repeating “Step on the ball!!” over and over?)
On the other hand, as we were asked, have you ever seen a bird with a vertical stabilizer or rudder? Obviously not – so how do they do it? The answer might have been found by Ludwig Prandtl in the 1920s. Prandtl was a pioneering engineer and mathematician who developed many of the key concepts we use today in aerodynamics. His theoretical wing controls adverse yaw by using wingtip controls instead of a rudder. (Birds do it by using their muscles and feathers to warp and change the shape of the wing, creating a similar effect.)
NASA Armstrong will be testing their larger model in the upcoming months. Depending on how it goes, in thirty years your commercial airliner from LA to Dallas might be shaped more like an oversized B-2 flying wing instead of the standard “tube & wings” design. (Gee, wouldn’t it be more efficient in that design to use a LEAPTech design to power it? Hmmm… I’m seeing some synergies here.)
This scale model of an F-15 fighter (1/4 scale?) was built and flown remotely to test multiple advanced systems that are now in everyday use on the aircraft still in service.
The final thing in this hangar is that large wall mural you can see over on the far side behind the other NASA Social attendees in our group (and Kevin Rohrer leaning on the LLRV telling us about it). I wish that I had gotten a better picture of it, but the story we heard about it was just fascinating to me.
The mural was put together (it’s a composite photo) and from the start of the Shuttle program at Edwards it gathered mission patches and crew signatures. Beginning with the earliest “free flight” drop tests of Enterprise, all the way through the final Shuttle landing at Edwards with Discovery finishing the STS-128 mission in September 2009, crews and support staff would celebrate a successful mission by applying mission logos along the top and finding a place to sign.
To a geeky space cadet like myself, this makes the mural invaluable. To everyone at NASA Armstrong (then named NASA Dryden) it was something that was sort of in the way when they were remodeling. They of course didn’t just trash it, but it got cut out of the wall and stored here until they can figure out where to put it. It might go to another museum, such as the Museum of the Air Force, or to some other NASA facility. For now, it’s just gathering dust here with the LLRV.
(If they end up not being able to figure out what to do with it, they have my number. I’m thinking it would look FANTASTIC in my house somewhere. Just sayin’.)
(And no, I’m not sure that The Long-Suffering Wife would agree with that decorating choice, but she loves me and I’m sure we could figure it out. Right, dear?)
Tomorrow, I’ll finish up with two more stops on our tour of the Center and some final comments.