Now that you say it, I believe that there are several (military) aircraft projects that have huge delays exactly due to changing specifications. The people maki

Now that you say it, I believe that there are several (military) aircraft projects that have huge delays exactly due to changing specifications. The people making the contracts did not have a clear vision about what they actually want and there are several parties involved who want different things crammed into one vehicle. As the process moves on, the requirements get adjusted to meet the new political power balance. The commerical planes, I believe, were designed with a clear goal and are in many ways an incremental improvement on the previous (proven to work well) models. So in essence you need: A clear vision of something that is acutally achievable. Plus you need to communicate that vision.