1: Upgrade prop shaft ratchet and reinstall.
While we knew we could make do on the Ivanpah trip without this device, there are several good reasons to have it installed:
It allows the propeller to be easily spun separate from the transmission drive. This is handy when we're working on the prop hub or want to align the prop with the tower to tie it up when not in use.
It allows the pilot to grab a big handful of brake without overloading the drive (one of the reasons it was there from the start)
It will be needed to allow us to keep the inertia of the propeller from feeding slack line to the spool drive system which we still may use for the official NALSA record runs.
2: Upgrade the drive axle shaft ratchets.
It appears so far that the drive axle ratchets are stout enough for the job at hand (as long as I remember to engage both of them), however we have been surprised at the speeds we have reached and simply aren't sure how much faster we will go. With increased speed comes increased HP demands -- we're likely going to have steel hubs made and use bigger ratchets just to be sure.
3: Install the rest of the pilot adjustable variable pitch system.
As you saw from the video, the drive up to wind speed is excruciatingly slow. This is because currently our pitch must be set for the entire run before the start and so obviously we use a setting optimized for the higher end. It's like starting your car in a very high gear -- not the best way to get off the line. Again from the videos one can tell that once the vehicle gets past wind speed, the prop hooks up and the acceleration becomes comparatively brisk.
NALSA rules will not allow us to have a variable ratio transmission -- with such it is possible to turn the propellers rotational momentum into short burst of speed, thus it is not allowed. However, when the prop shaft and drive axle shaft are connected through fixed gearing, there is no way to use a variable pitch prop in a way that allows acceleration through energy recovery so variable pitch will be allowed.
As noted previously in the blog, we made the prop hub variable pitch capable -- there were two reasons we didn't finish the process and finalize the linkage:
I was intent on demonstrating that not only could a vehicle be built that could go DDWFTTW, but I was also intent on demonstrating the simplest version of one that would self-start and go from a standstill to well above wind speed. In Ivanpah we were able to do this easily. Looking forward, if we want to do it again we can simply unhook the VP system.
Accepting the invitation from NALSA to attend the Ivanpah event put a crunch on our construction schedule. By the time we knew about that event through the invitation, what was going to be a three month build had to be finished in just two months. We had to make some time tradeoffs and one of the items that we could afford to temporarily axe was the VP system.
4: Aerodynamic improvements.
The higher speeds we have achieved have quadrupled the aerodynamic drag as compared to the project goals. To maximize our record speed, we need to make fairings for various components. These should include:
- Deck over and under between the main frame rails. This will make the front fuselage essentially a hollow box. Currently air can spill in and around this area increasing our effective frontal area. We only want to have to split the air once.
- Install some aero improvement around the pilot. This might be a recumbent bike fairing or some sort of stretchy 'body wrap' that goes over the pilot and velcros down to the sides.
- Change the pilot seating configuration slightly to get the pilot less in the airflow.
- Fair the pylon uprights -- a rather straightforward task with several ways to go. Flexible mylar sheet over ribs or just one layer of glass over wire-cut foam.
- Treat the rear axle assembly frame and rear of vehicle -- again, rather straightforward tapering down to nothing.
- Wheel spoke covers. We'll have to custom make these to match our wheels -- perhaps mylar again cut to roll into a cone or again maybe fiberglass over a foam cone and solvent away the mold.
- Prop spinner and perhaps even an aero treatment behind the prop thrust box.
5: Paint and logos
- We'll be hitting the whole thing with a coat of paint to take the edge off the ugly. Perhaps the BUFC (big ugly cart) will simply become the BFC.
- We'll be having several Joby Energy and Google logos printed to be displayed proudly and conspicuously on the cart.
We'll get to it over the next few week and keep everyone up to date on the progress
