Ho IV b With Laminar Wings

After the initial flight, the aircraft was brought to Hornberg for further tests. It soon became evident that the Reynolds number was too small for a laminar airfoil on the outer section of the wing, as flow separation problems degraded performance. The most important feature of this aircraft however, was not the laminar airfoil, but the radically new construction method.

The external dimensions were the same as the Ho IVa, but the new airfoil made the wing a lot thinner, and new materials were required. It was therefore decided to use the composite materials first tried with the Ho V a, but with molded, instead of built up parts. The main spar was laminated with duraluminum to obtain the required strength. The D-tube was molded in 6 ft. long sections, and cemented to the main spar with only a few nose ribs. The panels consisted of two thin layers of plywood, with a core of resin-impregnated corrugated cardboard sandwiched in between. These were formed and cured between male and female molds. The center section structure, and the wing tips were made of metal as before.

We continued to use the prone pilot position, since it had worked out well with the "a" model. We did make some improvements: Arm and elbow room, oxygen installation, the parachute under the pilot as protection etc. The control pushrods had temperature compensating features for high altitude flying. The drag rudders doubled as auxiliary spoilers, to supplement the air brakes, which were installed behind the false spar.

There were also improvements to the landing gear. In consisted of two spring-suspended skids, the forward retractable. A retractable wheel was attached to the forward skid, giving the aircraft a desirable nose up attitude for takeoff. In this attitude, a second wheel in the rear skid would touch the ground, greatly improving ground handling. When the forward skid was retracted, the wheel was pulled into the skid, and remained there during landing, so that the aircraft stopped on its two skids only.

Assembly was easy with built-in quick disconnects. A "Kranich" trailer was used for ground transport.

Scheidhauer made two test flights in Gottingen before the aircraft was shipped to Hornberg. The tricky behavior of the craft was immediately evident. Most prominent was the aircraft's tendency to suddenly drop a wing and wanting to spin, quite contrary to what had been experienced with the Ho III and IV a! Loss of control would occur at speeds as high as 48 MPH, and recovery made at very high speed, further complicated by severe wing flutter at speeds above 65 MPH!

On January 18, 1945, Hermann Strebel was soaring the aircraft near Gottingen, when he suddenly entered a spin. Witnesses on the ground said the aircraft recovered from the spin, then the wings started to beat up and down like a big bird, until one wing broke off. Strebel jumped clear, but fell to his death when his parachute failed.

The flutter problem had been evident on the IV a as well, but only at speeds in excess of 80 MPH, and it could be dampened by application of both drag rudders.

Wing flutter on a swept wing glider is difficult to avoid, since any flexing of the wing, from whatever the cause, has the effect of an elevator movement. In Argentina, we were able to bring the flutter under control by appropriate mass balancing of the elevons.

10 Ho IV b's under construction near Rottweil in 1945, were not completed.