The Ho II "Habicht" Motorglider
Few additional changes from the Ho I philosophy were planned, except to make it self-launching. We planned a tandem undercarriage with retractable front wheel, and steerable tail wheel.
The Ho II was also built in our home with some help from local glider club members, and a local motorcycle shop. It was ready after nine months, and taken to the Bonn-Hangelar airport in May 1935.
The first flight was made by towing it across the field at low altitude with a winch. We started with the c/g at the forward limit, and gradually moved it aft with trim weights. The aircraft remained docile, and fully controllable.
Although the problems with the "middle-effect" was not solved, the bell shaped lift distribution pattern used on the Ho II, had enabled us to make a large step forward with the stability and controllability of the flying wing.
The landing gear was not entirely successful. The ground roll was unstable with the steerable tail wheel, and there was no shock absorber in the nose strut. The whole undercarriage was modified later. The unfamiliar reclining position, so popular in modern sailplanes, was not a good solution. It was difficult to see out while circling, and during slow flight, the pilots feet would be above the horizon, and higher than his head. Still, we did not make any changes to the cockpit, in order to better study the "middle-effect".
We were able to borrow a 60 HP Hirth engine, and after a three month long modification program, we were able to take off on our own. We had calculated that only 20 HP was needed for takeoff; the excess power of the Hirth engine allowed it to accelerate to 180 km by the time it reached the far end of the runway. The Ho II would climb to 3000 feet in two and a half minute.
The engine was sometimes shut down in flight to explore the aircraft's soaring capability. In such cases, the aircraft was landed without power, since the engine could not be restarted in flight.
The drag rudders were rarely used, since the absence of adverse yaw permitted coordinated turns with the ailerons alone.
Flying the Ho II was easy, and it was much used for practice flights by inexperienced pilots. I used it myself, to obtain my glider rating. Walter lost the propeller at low altitude, during a demonstration before representatives of the Air Ministry, but proceeded to make a routine landing, and roll to a stop before the hangar. A very convincing demonstration, we thought.
Our experiments with the "Habicht" was terminated when the borrowed engine had to be returned. In 1937 we modified the wing tips in an attempt to prove that the induced drag at the wing tip became negative with the bell shaped lift distribution pattern. The wing tips would move fore and aft, pivoting around a 45 offset hinge on the main spar, and serve as elevons. The system was never tried in flight.
For an unbiased report on the handling of a Ho II, here is a summary of Hanna Reitsch's impressions after flying the D-11-187 near Berlin in November 1938:
"This report does not reflect the many improvements on the later Horten models.
The drag rudders are very sensitive, and moves the aircraft around both the roll and yaw axis. The harmony between the controls are poor. Drag rudder had to be used continuously during circling, and correct bank is difficult to establish*.
* Tiny Hanna Reitsch was unable to retract the nose skid and flew with the c/g at the aft limit.