This week I attended my fifth NASA Social. At the NASA Armstrong Flight Research Center the main focus was the LEAPTech project. Yesterday I wrote about what LEAPTech (“Leading Edge Asynchronous Propeller Technology”) is and what it has the potential to mean in the not-so-distant future. Once we had seen presentations from several of the project scientists and engineers, we headed out onto Rogers Dry Lake to see a test run of the initial LEAPTech test rig.
Due to the nature of the work being done there by the Air Force and NASA Armstrong, one does not normally get access to the lake bed at Edwards Air Force Base unless one works there, has a security clearance, and has a reason to be out there. As has happened at every NASA Social I’ve attended, this was a point where the “geeky, über-cool” factor ratcheted up a couple of notches.
Once out on the lake bed runway, we got our first opportunity to see the test rig up close and personal. As you can see, it’s a basic, heavy-duty truck rig that’s been modified quite a bit. The two primary modifications in the HEIST (“Hybrid-Electric Integrated System Testbed”) serve to lift the wing up out of “ground effect” and into “clean air”, and to dampen out almost all of the vibrations and bumps coming from the rolling truck body.
From the front you can see that this test setup has eighteen props. It’s quite a departure from the normal one or two big engines on today’s propeller-driven airplanes. It’s hoped that the difference will allow a 500% increase in power efficiency, a huge increase in low-speed maneuverability and stability, and a drastic reduction in the noise created by the propellers.
This is what a couple dozen NASA Social members look like taking pictures, taking selfies, tweeting, Instagramming, FaceBooking, and so on.
We were fortunate that it was only about 75°F out there, although the wind was a real pain. As with any desert locale, in the winter it can be brutally cold out here, and in the summer it can be way, way over 100°F.
Here you can see the propellers on one side of the test wing. Notice that the propellers on alternating blades are counter-rotating. Also notice the video camera rig on the top and all of the data cables coming down the support framework.
If this wing seems small, note that one of the aspects of LEAPTech is that the added efficiency of the design in generating lift will hopefully allow a significant reduction in the size of the wing. The wing, propellers, and test rig here are smaller than they would be on a two- or four-person aircraft, but not by much.
As mentioned yesterday, in designing their tests to be carried out this way in the real world, the LEAPTech team is able to quickly test a whole range of variables quickly and much more cheaply than they could using a wind tunnel.
For example, in testing for noise reductions or power output, does it matter if the blades counter-rotate? Does it matter if every other one counter-rotates or is there another pattern that gives better performance? Is it better to have all the props the same size, or should they be larger on the inside, or on the outside? How does changing the arrangement and size of the propellers affect the loading on the wing and the amount of lift generated?
These are all questions that can be put into mathematical models, but models all have assumptions and approximations built in them. By comparing the models’ predictions against the real world data, the models can be refined and improved. The models in turn can then be counted on to give more reliable predictions. This feedback between the two systems is a powerful way to make significant progress quickly.
Once we’re all done taking pictures, it’s time to back off a few hundred meters for safety reasons. Safety is a key component of everything they do at NASA Armstrong and Edwards Air Force Base. We saw this all the time during our stay – FOD removal & control, safety briefings, insistence that we all slather ourselves in sunblock before going out onto the lake bed, and other precautions were constantly in place to make sure everything went smoothly and safely.
It obviously paid off. We didn’t have a single casualty among the NASA Social attendees!
The HEIST rig trundled off a mile or more down the runway, soon visible only the the tiny cloud of dust that it was kicking up. It was soon lost in the mirage on the lake bed surface. After we all got our camera gear ready, we got the heads-up from one of the test engineers that the run had started. Again we could see that tiny plume of dust, but now it was coming toward us.
There was a wicked wind coming from the north (our right) and on this run the HEIST was running almost directly into the wind. This was a relatively low speed test as measured by the rig’s ground speed, 40 mph. By going directly into the 27 mph wind, the effective speed of the air over the wing was 67 mph.
After disappearing into the distance to the north, after a minute or so we got the word that the HEIST was coming back. This time with the wind at their back, they were driving along at 65 mph, but with the 27 mph wind at their back, their effective speed of air over the wing was only 38 mph. That gives them a nice range of data sets. From our vantage point standing still near the runway, we saw only the difference between the 40 mph first run and the 65 mph second.
After the runs were over we got one more chance to take pictures and ask questions out on the lake bed. Then it was back on the bus (in a non-sunburned conditioned we hoped, after putting on all of that sunblock goop and, as one person put it, “smelling like the crowd at Santa Monica beach”) and back to the conference center for lunch and more Q&A with the project engineers and scientists.
Tomorrow, a couple more notes on the lake bed, then we’re off to see some of the other aircraft and projects being run by NASA Armstrong.