A Design That’s Still Evolving
There are very few aspects of the design that have remained unchanged from the first iteration. Even the fuselage was stretched from it’s initial shape in order to accommodate the longer PT6 turboprop engine before it was apparent that folks did not want to pay the fuel bill and we switched to the diesel engine.
The last couple of days brought yet another improvement to the design. This time it was from the results of the work Mark is doing on the FEA of the canard. He discovered that the internal hinge arms that I had designed for the elevator were going to flex too much when under load. I really like the idea of having the hinges internal as it’s just another place where we can reduce drag.
As you can see below this is the canard and elevator with the top skins removed already showing the new hinge design:
Looking more closely you can see there is now a vertically oriented arm that will be made out of flat 1/4 inch aluminum stock. In this orientation it has very little movement when under load. There are two channels that each have two rollers that allow movement without jamming. The rollers are slightly smaller diameter than the slot so one only contacts the top of the slot and the other only the bottom. This way they can rotate in the correct direction while not permitting any jiggling movement of the elevator. We want the elevator to not have any movement other than that created by the movement of the side stick.
Next we can see the elevator in the max 15 degree upward deflection which is the direction that will force the nose of the Raptor sharply downward in flight. Here the sets of rollers are all the way forward in the slots.
Lastly the elevator in the full 38 degree downward deflection which is for maximum lift. The rollers are all the way aft. Given that we are going to experiment with flaps on the main wing there will be a stopper on the elevator that only allows max deflection when the flaps are deployed. In normal flight without the flaps the max deflection will likely be around 30 degrees. The coefficient of lift of the canard and elevator with 38 degrees of deflection is over 3 which is excellent for what we need to get the nose up with flaps deployed.
From below you can see how clean the canard and elevator are. Nothing hanging down causing unwanted turbulence.
So, we still get the benefit of reduced drag and once again Mark has made another contribution to improving the Raptor design all while showing me that I still have a lot to learn about engineering. This is definitely why I like having guys in my corner that are smarter than me.
It won’t be that long now until we are actually making these parts. How exciting is that.
