Horten Ho I

Reimar was still in school and Walter in the military; all the construction and testing was done on their spare time and own funding. The tests of the Ho I started in July 1933 at the Bonn-Hangelar airport. It glided from altitudes of 150 to 300 feet. The maximal gliding speed was estimated 228 km/h, and 170 km/h were actually reached. The glider had many stability problems; which the Horten brother tried to fix in-between tests.

Studies of the stability and controllability of flying wings would continue with our first sailplane. We were hoping to establish the center of lift on each wing half, and also to see if it was possible to steer the aircraft with wing tip drag rudders, instead of the traditional vertical fin-rudder arrangement.

My brother and I was also hoping to improve our own piloting skills on the H I, as our total flying experience amounted to less than one hour in a primary glider.

We planned a mean chord of at least one half meter, and a root chord large enough to accommodate the pilot This meant a wing with steep taper. A keel structure contained the seat, 10 cm below the bottom wing surface, and the canopy protruded 30 cm above. The root thickness was 60 cm, which, with a 20 % airfoil thickness resulted in a root chord of three meters.

The resulting triangular wing had an almost straight trailing edge, with two elevators in the center, flanked by two ailerons. The washout was 7 degrees, with most of the twist outside Y= 0.75 (the last quarter of the half span).

The elevators were moved by pushrods, the ailerons by cables, all attached to a conventional stick. The rudder pedals were linked to drag rudders near the wing tips. They could be operated separately for directional control, or together as spoilers something that had not yet been introduced on other sailplanes. With no workshop available, and no financial support, it was necessary to build the aircraft in our home with personal funds.

[Flight Tests] started in July 1933 at the Bonn-Hangelar airport. Like our models before, the glider was launched with a bungee cord, resulting in glides of 150 to 300 feet at altitudes of six feet or less.

During these tests it was established that the central elevator location was quite unsatisfactory, as it would change the airfoil and washout with each movement, sometimes with surprising results. The Haps-effect of a down elevator caused us to remove forward trim weights, which almost doubled the gliding distance. But it also set the stage for dangerous reversal of elevator response.

The tests continued with car tows to 100 feet altitude, and straight glides. Now we discovered that application of aileron caused a strange level skid, instead of the desired bank!

The drag rudders also responded differently than conventional rudders. The latter causes the aircraft to move a certain amount in response to the input, then stop. In contrast, our flying wing kept turning until a short application of opposite rudder was given. We ended up turning the aircraft by the drag rudders alone, and found that the resulting skid produced the necessary bank. This discovery led us to try a 1000 It winch launch, and fly back to the starting point.

The aileron problem was finally solved by enlarging them, and increase their up travel to the point that the airflow under the up aileron separated, and created the necessary compensating drag.

We were now ready for the first aerotow. Walter towed to 3500 feet, and after releasing from the Me 23, glided down with gentle turns. During the landing, the elevator reversal became evident again, and the aircraft suddenly nosed into the ground during flare-out. Fortunately, it was only slightly damaged.

The elevator reversal/ problem was eventually solved by moving the c/g forward again, so that less down elevator was needed, and the flaps effect avoided.

The following summer I was approached by the District Chief of our National Aero Club. He wanted me to demonstrate the glider at the upcoming air show at the Bonn-Hangelar airport in June. My test program had progressed very slowly, since I was still in school, and had limited funds to pay for tows. I agreed after obtaining a promise of free aerotows to complete my tests, and an airworthiness permit to compete in the Rhone contest the following month.

I was unable to get out of school during the first week of the contest, but the second Sunday found me all set for the aerotow over to the Wasserkuppe contest site. My brother Walter was on his last day of military leave. He had managed to borrow a Klemm 25 towplane, and was taxiing out to the runway when the Airport Police informed us that our takeoff clearance was denied. The reason was that a squall line was approaching from the west. The fact that we were heading east failed to impress the authorities, and the aircraft were returned to the hangar.

At 2 PM, after the front had passed, came the permission to depart. Soon our two machines, connected by a 300 ft. steel cable, had overtaken the squall line. We Hew low in the valleys to keep out of the clouds and avoid lightning strikes. The turbulence was terrifying, and at times I was unable to see the Klemm! We finally broke out over Vogelsberg and could see the Wasserkuppe ahead. I released and headed for the west ridge while Walter reversed course and disappeared, to catch the night train back to his base. I spotted a Grunau Baby at about 600 feet and headed for it. I was anxious to test the performance of my glider against this new design, but severe fatigue from the turbulent flight soon overcame me, and I turned towards the landing area. As I turned final over the Worstensachsen road, I saw to my dismay that I would be landing short! The skid hit an invisible rock, and splintered with a sickening crunch!

So, there I was on the "Kruppe", with a damaged glider and no crew . . .

It was Wednesday before the glider was repaired and a new permit issued. The contest ended on Friday, so with little chance of accomplishing anything, I called up DFS in Darmstadt and talked to Alexander Lippisch. I told him what had happened, and offered him the glider for free, if he would send a towplane to tow it to Darmstadt. Lippisch said that was not possible.

With no chance of a place in the competition, I got a launch on the west ridge, and struggled over the unfamiliar terrain until I had sufficient altitude to fly over to the other side, where I landed near the south ridge.

The H I earned us a "Construction Price" of DM 600, but no financial support was promised for our next project.

A week later the glider school Director ordered me to remove myself and the glider from the Wasserkuppe. I made one last "farewell" flight in the H 1, then I dismantled it, and burned it the following day.

Specifications

Usage	Experimental
Fuselage Construction	Wood
Wing Construction	Wood
Capacity	One person
Span	12.4 m
Sweep Angle	23 degrees
Taper Ratio	6:1
Wing Root Thickness	20% chord
Wing Root Depth	3.00 m
Rib Spacing	0.30 m
Aspect Ratio	7.3
Pilot position	Seated
Mid-section width	4.20 m
Cockpit width	0.60 m
Cockpit height (from seat)	0.90 m (0.60m wing thickness, 0.30 m cockpit bubble)
Empty weight	120 kg
Ballast	water
Additional payload	90 kg
Maximum weight	210 kg
Wing loading	10.00 kg/m2
Stall speed	45 km/h
Landing speed	60 km/h
Minimum Sink	0.80 m/s at 60 km/h 10 kg/m2 loading
Best Glide Ratio	21:1 at 72 km/h 210 kg/m2 loading
Maximum Speed	228 km/h (170 km/h actually flown)