@ John: Thank you again for your hint regarding US Army flight testing. Unfortunately, I didn't find an appropriate photograph in their reports in the web. Therefore, I wrote an e-mail to Fort Rucker, asking for some pictures and permission to use them.
@ scy: Thank you very much for your detailed description of the conditions and procedure during testing. I've noticed that AAEE Boscombe down doesn't exist anymore. However, I'm not sure about the rights to use their images. Thus, I've contacted the British Ministery of Defence hoping they may provide information about the rights-holder of the photographs.
Anyways, thanks again to both of you for your help.
Finally, I've got a rather simple question: Are you still in business or already retired?
Kind regards,
MarSch