page_title: Horten Ho 229
section_title: Radar absorbent material (RAM)
hierarchical_section_title: Horten Ho 229 / Claimed stealth technology / Radar absorbent material (RAM)
caption_attribution_description: English: This is the composite/laminate cross-section, of the layers of wood, unified with a glue containing a mixture of sawdust and charcoal. The sawdust was used to add fibers and strength to the glue, given it's increased thickness required to the contain charcoal dust.
context_page_description: The Horten H.IX, RLM designation Ho 229 was a German prototype fighter/bomber initially designed by Reimar and Walter Horten to be built by Gothaer Waggonfabrik late in World War II. It was the first flying wing to be powered by jet engines.
  The design was a response to Hermann Göring's call for light bomber designs capable of meeting the "3×1000" requirement; namely to carry 1,000 kilograms of bombs a distance of 1,000 kilometres with a speed of 1,000 kilometres per hour. Only jets could provide the speed, but these were extremely fuel-hungry, so considerable effort had to be made to meet the range requirement. Based on a flying wing, the Ho 229 lacked all extraneous control surfaces to lower drag. It was the only design to come even close to the requirements, and received Göring's approval. Its ceiling was 15,000 metres.
context_section_description: After the war, Reimar Horten said he intended to mix charcoal dust in with the wood glue to absorb electromagnetic waves (radar), which he believed could shield the aircraft from detection by British early-warning ground-based radar that operated at 20 to 30 MHz, with a wavelength of 10 to 15m (top end of the HF band), known as Chain Home. This charcoal glue treatment was planned for the never-made production model, however it remained unclear if the V3 prototype had benefited from a preliminary iteration of this technology. 
  In 2008, a team of engineers from Northrop Grumman undertook electromagnetic tests on the V3's multilayer wooden centre-section nose cones. They tested over a frequency range of 12 to 117 THz, with wavelengths of the order of 10 microns. The cones are 19 mm (0.75 in) thick and made from thin sheets of veneer. The team observed that the "Ho 229 leading edge has the same characteristics as the plywood [of the control sample] except that the frequency [do not exactly match] and have a shorter bandwidth." The team who had assumed the presence of carbon black from visual inspection went on to conclude that the "similarity of the two tests indicates that the design using the carbon black type material produced a poor absorber."" The Smithsonian Institution has since performed a technical study of the materials used on the prototype and determined that there is "no evidence of carbon black or charcoal" thus invalidating the proposed presence of carbon black to explain the slightly different absorbent property of the prototype wood compared to the control sample of plywood used in the Northrop Grumman testing.
caption: Cross-section of the Horten H.O.229 composite wood laminate
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