Horten Ho III

The pilot stretched flat on his stomach, bent slightly at the waist and knees, feet resting on rudder pedals hinged above his heels. A padded chin rest supported his head which projected into the leading edge of the wing. Clear plastic panels formed the leading edge for several feet above, below, and to either side of the pilot. Visibility was good and drag greatly reduced. However, neither view nor pilot comfort in the H IIIf approached the outstanding qualities of the semi-prone layout Reimar Horten developed for the Ho IV and Ho VI sailplanes.

One pilot was killed and another wounded when several Ho III and other gliders in a competition on August 6, 1938 were swallowed in a thunderstorm. Four Horten Ho 3 appeared at the Wasserkuppe in 1939, where Scheidhauer made Gold-C distance, by flying over 200 miles.

The Ho III 1938 Rhön Contest Challenger

The third Ho III was finished, and the second Ho V well underway as the time to build an aircraft suitable for the 1938 National contest came. We wanted to continue our research, but at the same time keep the risks of new experiments to a minimum, and still come up with an improved sailplane.

We had planned an enlarged version of the Ho II with 20 meter span for some time, but feared that the "middle-effect" would cancel out other aerodynamic advantages. The parabola shaped center section was considered and rejected, due to our limited knowledge of possible side effects. We finally settled for the slightly enlarged Ho II.

The root chord was reduced, giving the wing slightly less taper, and also increasing the aspect ratio.

Two aircraft were laid out; the first with ear-shaped additions to the elevons to reduce adverse yaw in a rear c/g configuration, the other with a "fore-wing" mounted above the nose in a further attempt to combat the "middle-effect".

To minimize the washout step created by the up elevons during slow flight, two sets of elevons were used; the inboard set with less up and more down movement. All control rods were equipped with ball bearings to avoid the friction problems of the H II.

The selection and training of the contest pilots began four months before the contest. Three Ho II's were used by four candidates. After four weeks, the first Ho III was added, giving each pilot his own aircraft. They practiced cross country and instrument flying, and knew that if their instruments failed while in the clouds, they could simply pull the stick all the way back to remain below red line speed without any danger of spinning.

Following a cross country flight task into the wind from Bonn to Cologne, two of the pilots declared the task impossible, while the other two, Werner Blech and Heinz Scheidhauer, landed in the Cologne area; Scheidhauer after a nine hour flight. Our pilot selection was thus determined.

The second Ho III was finished just before the contest. D-12-348 was to be flown by Blech, while Scheidhauer would fly the older D-12-347. Another Air Force Unit entered the Ho II D-11-187 piloted by Kurt Hieckmann.

The two Ho III's established themselves somewhere in the middle of the standings during the contest. Blech had some noticeable altitude flights on instruments, while Scheidhauer's efforts were directed towards cross country flights. The Ho III would outperform the conventional sailplanes in thermals, due to its ability to make tight coordinated turns. The Ho II also did quite well, despite its inexperienced pilot.

The contest did not end without tragedy:

On August 6th, a large cumulus cloud was building over the Wasserkuppe, attracting several gliders, including both the Ho IIIs. While they were inside, the cloud quickly developed into a massive thunderstorm, unexpected and not in the weather forecast.

After about one hour, an Ho III became visible, obviously out of control, and hit the ground near Poppenhausen. It was Blech's machine, empty, the canopy and parachute was missing, - apparently a normal bail out. The aircraft was full of holes from hail, otherwise still in flyable condition. A spectator saw Blech's parachute descending with the pilot motionless in the harness. His neck was broken from undetermined reasons. His death might have been caused by hypoxia, since his barograph was found to have gone off its scale at its 25000 ft. limit.!

Heinz Scheidhauer's aircraft and parachute came down near Wustensachsen. He had bailed out after hailstones splintered his Plexiglas enclosure as well as the plywood covering, and was found unconscious, hanging in a tree. His barograph also showed an altitude in excess of 25000 feet, a height thought to be unreachable by sailplanes. Scheidhauer eventually recovered in a hospital, where he was treated for severe frost damage.

The Ho II with Hieckmann left the same cloud at 15000 feet, and landed safely 80 miles away. On the following day, he demonstrated the capabilities of his aircraft, both in ridge soaring and aerobatics before the public.

The Ho III, with its light wing loading and small turn radius, was well suited for both ridge and thermal soaring, and its stability and gentle behavior made it ideal for instrument flying. Still, the middle-effect problems continued to trouble us.

With the blessing of our Air Ministry, ten H III b's were started. Four of these appeared at the Wasserkuppe in 1939, where Scheidhauer made Gold-C distance, by flying over 200 miles.

Unfortunately, very little progress was made otherwise that year.

With the blessing of the Air Ministry, ten Ho 3b were constructed in Bonn, some would be converted to a "d" model, with the installation of a Walter Micron engine and conventional pilot position. Lastly a Horten IIIf and a possibly two seater IIIg were built in 1944 at Goettingen.

The Ho III b - The Ho III Work Continues

Sailplanes from the entire country were brought together at the glider school in Braunschweig. Among these were two Ho II's and five Ho III b's. I suggested that the two Ho II's be replaced by two Ho III b's in storage at Wurzburg-Kitzingen, in order to standardize the fleet. The two aircraft were then shipped to Peschke for overhaul by rail. They arrived with their wings cut in half, in order to fit them in the railroad car! Both aircraft had to be totally rebuilt.

For the planned invasion of England, the Ho III b's were to be modified to carry ammunition. A 400-lb capacity pallet was fitted into the center section, and four 50-lb compartments were built into the wings, with access from above. With a full load of 800 lb. plus pilot, the Ho III flew even better than before, and was able to soar, despite a 250% increase in wing loading!

The Ho III d Motorglider

A Ho IIIb was converted to the "d" model in Bonn during the 1941/42 winter, by the installation of a small Walter "Mikron" engine with a two-bladed propeller at the trailing edge of the center section, provided the necessary thrust. The Mikron engine was a substitute for a Zundapp engine, that was not available.

Troubles plagued the project in the beginning, and it was October before the first powered flight was made. Constant engine problems kept the machine on the ground most of the time, and not until a larger engine with 50% more power was installed, did our troubles subside.

From then on, the licensed workmen in the plant were encouraged to fly it, and considerable flying time was accumulated.

In February 1943, I had the opportunity to demonstrate the Ho III before Professor Prandtl. While I explained my bell shaped lift distribution theory, Scheidhauer made a very convincing flight demonstration of its forgiving slow flight behavior, by doing whip stalls at hangar roof level. This resulted in a for us very favorable report from the professor to the Air Ministry.

The Ho III e Motorglider

The initial problems with the Mikron engine led us to try a somewhat less powerful "Volkswagen" engine, as this reputable power plant had the added advantage of being air cooled. We also planned to use an automatic folding propeller. The overhead propeller shaft would be driven by five V-belts.

The power plant was built into an all new center section, while surplus H III b wings were used.

Heinz Scheidhauer made the first flight in January 1944. Here is his account of a subsequent flight:

"It is February 22nd, 1944, on a beautiful clear winter morning. It is quite cold; the sun is just rising in the Southeast. In the lee side of the hangar , I can feel the air warming around 10 AM, and soon cumulus clouds are forming over a nearby stone quarry. I observed the clouds for a while with my stop watch, to see how long they remained over the quarry in the stiff NE breeze. It appears that one could soar over there, and soon the Ho III with VW engine and folding propeller is brought to the starting line. At 10:48 I take off. I notice that the cumulus clouds have disappeared, I might just get there when the thermal cycle starts again. I shut down the engine, and glide silently toward the quarry cliff, which I reach at 50 meters above the edge. Here I find a weak windblown thermal, and struggle back up while the strong wind carries me away."

"Gliding back to the cliff, I find myself below the edge, and begin to circle again. The low altitude does not worry me; I can fly out of the quarry and down the valley at any time, and restart the engine. But now I feel another thermal! I circle tightly at 60 km/in, struggling upward inch by inch. I extract the maximum performance from the Horten, and manage to rise above the cliff again. I am close enough to recognize the faces of the quarry workers, who seem to enjoy watching me. Despite the tight turns at almost ground level, I feel safe in the Horten, knowing that it will not spin under any circumstances. After seemingly endless circling, I catch a stronger thermal, and climb quickly. I wipe my face; that was hard work!

As the thermals weaken, I again head for the quarry, and arrive at 50 meters again. Another struggle to 250 meters and a glide back. This time I arrive with 100 meters to spare. It is getting better! The next thermal takes me right up to the base of the now beautifully developed cumulus cloud. I turn on the electric Turn and Bank instrument, and continue another 400 meters into the cloud. Here the lift dissipates into just choppy air, and I start the engine and continue climbing. I break out on top at 1400 meters. Now I notice that the engine is running rough, with a strong vibration. I shut it down, thinking that the folding propeller might have failed, and glide back to the airport. The flight lasted over an hour, and after landing, I inspect the propeller. The leading edge of the folded blades are coated with a thick layer of ice! Some has broken off, causing the unbalance."

The Ho III f Prone Position Glider

Three Ho III b's were modified in 1943 to familiarize pilots with the prone position used in the Ho IV and planned for our supersonic aircraft.

This position had several advantages: it was less tiring on long flights, one could endure higher g-loads, the visibility to the front and down was unsurpassed, and a smaller cockpit cross section could be used. Crash survival was also found to be very good.

Ho III F, LA-AF, accumulated 100 flying hours in less than a year at the Klippeneck airfield. It was the first flying wing to be tested with a c/g launch hook.

The Two Place Ho III g

2 two-seaters were completed in Gottingen in 1944. Both used Ho III b wings and a radically modified center section. The pilots sat upright in tandem; a full set of controls were installed in both cockpits. The purpose of the aircraft was simply to provide a trainer for flying wing pilots.

Flight training with the two "g" models were conducted at the glider schools at Klippeneck and Hornberg between July 1944 and the end of March 1945.

Pilot Josef Eggert flew the Ho IIIg twenty times during September 1944, amassing 14 hours and 17 minutes of total flight time. Eggert reported excellent handling qualities but he apparently preferred not to grapple with adverse yaw. Horten test pilot, Heinz Schiedhauer, and another experienced glider pilot, Hermann Strebel, conducted test flights of models equipped with various additional test equipment.

Specifications - Ho IIIa and c

Usage	Performance sailplane
Fuselage Construction	Steel tube
Wing Construction	Wood
Capacity	One person
Span	20.4 m
Sweep Angle	24.3 degrees
Taper Ratio	10
Wing Root Thickness	20% chord
Wing Root Depth	3.25 m
Rib Spacing	0.4 m
Wing Area	36.0 m2
Aspect Ratio	11.6
Pilot position	Seated
Mid-section width	2.4 m
Cockpit width	0.80 m
Cockpit height (from seat)	0.95 m
Empty weight	220 kg
Ballast	water
Additional payload	80 kg
Maximum weight	300 kg
Wing loading	8.3 kg/m2
Stall speed	37 km/h
Landing speed	37 km/h
Minimum Sink	0.48 m/s at 45 km/h and 8.3 kg/m2 loading
Best Glide Ratio	28:1 at 60 km/h and 8.3 kg/m2 loading

 

The fuselage and other parts of a Ho 3 are visible at the Simthsonian Institute in the US.