Horten Ho II

Also built in their home, the Horten brother's second design Ho 2l was ready after nine months. Three "l" subtypes were then constructed at Lippstadt, Germany, in 1937, and taken to the Bonn-Hangelar airport in May 1935. The pilot was in a reclining position, transparent panels were supposed to ensure visibility but they did poorly. Stability was much better than with Ho 1, although not all problems were solved.

To keep the frontal dimension to a minimum, we decided to put the pilot in a reclining position in our next project, so that he would remain within the wing contour. Transparent panels would be installed around the leading edge to provide visibility. The elevator system would be redesigned to avoid the reversal problems of the Ho I.

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.

The world famous German test pilot Hanna Reitsch flew it near Berlin in November 1938, and wrote a quite negative report:

Comfort:	Mediocre.
Visibility:	Poor.
Entry/exit:	Athletes only.
Instrument panel:	Fair.
Gear operation:	Only possible for long armed pilot's.
Steering friction:	Unacceptable.
Takeoff:	Stick all the way back to break ground.
Landing:	Simple, with good glide path control.
Stability:	Difficult to assess, since the stick remains where it is put due to friction.
Pitch response:	Normal.
Roll control:	Unfriendly, some flutter in turbulence. 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.
Sideslip:	Imposible.
stall/spin:	No combination of control inputs could make a wing drop, with the stick all the way back, the speed stabilizes at 55 MPH or less in a gentle mush.

 

Specifications

Usage	Experimental
Fuselage Construction	Steel Tube
Wing Construction	Wood
Capacity	Pilot
Span	16.5 m
Sweep Angle	29.5 degrees
Taper Ratio	8.4
Wing Root Thickness	20% chord
Wing Root Depth	3.5 m
Rib Spacing	0.4 m (0.2 at the wing leading edge)v
Wing Area	32.0 m2
Aspect Ratio	8.5
Pilot position	Seated
Mid-section width	2.4 m
Cockpit width	0.8 m
Cockpit height (from seat)	0.70 m (plus cockpit bubble of 0.3 m)
Empty weight	250 kg
Ballast	water
Additional payload	80 kg
Maximum weight	330 kg
Wing loading	10.3 kg/m2
Stall speed	42 km/h
Landing speed	42 km/h
Minimum Sink	0.7 m/s at 60 km/h and 10.3 kg/m2 loading
Best Glide Ratio	24:1 at 72 km/h and 10.3 kg/m2 loading
Maximum Speed (horizontal)	230 km/h
Maximum Speed	230 km/h