After sitting in the seat it was determined that our setup was not as comfortable as it could have been. The seat back was too upright and some modifications had to be made to decrease the incline. We lowered the seat back cross member which meant that the upright tubes had to be shortened. After removing some rivets we cut the tube, redrilled some holes, and refitted the tube fittings and seat belt straps.
Our first post of the new school year has the team installing the wing jury struts. The jury strut assembly is comprised of 4 sections of streamline aluminum extrusions that provide support between the main wing struts and the wing at the inboard compression strut. The assembly is riveted together via strut connectors and attached to the wing and main struts via eye bolts. The many pictures below document the process.
We ended the 2019 school year by fabricating and installing the wings. The tubes for the jury strut assembly still need to be cut and installed as do the wing tips. Then it’s on to bending the wing ribs. Once that takes place we will cover the wings with Dacron sailcloth. The many pictures that follow illustrate the wing build process.
We took some liberties and strayed from the original seat design and proceeded with our own original design. The many pictures that follow outline our design and fabrication process for the E-Hawk seat plates and cushions.
We decided to implement the steerable tail wheel on our E-Hawk. There are options for a fixed tail wheel and also a tail skid. Our design deviates somewhat from the original design. The original design relies on a couple of complex aluminum machined parts. Instead we decided to go with 4130 steel plate and tubing that would be welded.
Now that the landing gear and brakes have been installed, it only made sense to initiate a taxi test. Since the plane will not fit out of the building in its current state, we had to complete the mission indoors. It goes without saying that this was the first taxi test ever within the Sullivan Center’s 3rd floor project space. Who knows, this could even be the first ever indoor taxi test of an electric aircraft, by a high school student.
We completed our first motor run-up with the prop installed. With our small 24S, 6.6Ah test pack we were able to peak at about 7kW before our 60A circuit breaker cut-out. The graph below depicts data that was logged on the motor controller for a run not shown in the video. The max power attained in the video footage tops out at about 4kW. We are not sure why the data captured for current (and power) is so noisy. We will have to investigate.
The propeller is in! We have decided on a NG-D 3-blade pusher, ground adjustable pitch propeller from E-Props. The blades are full carbon as is the hub. The diameter is 125 cm. It’s rated for a max rotational speed of 3200 RPM when driven by electric motors. In this blog we describe the process of making an adapter plate and installing the prop.
Time to get the brakes functioning. The rotors and calipers were installed a couple of weeks ago when we attached the landing gear. We are using hydraulic brakes actuated simultaneously from a single lever on the control stick. So for now no differential steering. In the future we might come up with some clever way to regulate pressure individually to each caliper for differential steering if necessary.
The motor and controller for the E-Hawk have arrived. We decided on the Rotex Electric REX30 Motor and the HBC series controller from MGM Compro. The plan is to run the motor at either 86V (24s) or 100V (28s) depending on the battery we end up with. The motor is rated at 20kW max, and 8kW continuous. The motor is a 4-turn wind which yields a kV of 40 rpm/V. The controller is designed to work up to 120V and 280A continuous. The weight of motor and controller are 5.2 kg and 1.5 kg respectively.
In this installment of the blog we also design and build a minimal electrical system consisting of a small battery pack, circuit breaker, some enable switches, and a potentiometer. This allows us to power-up the system, learn how to configure the controller, and perform some preliminary tests.