Walkera 4#6 Bell Head Upgrade - HM-4#6-Z-40 Bell Head Upgrade features a 45 degree Stabilizer Bar which gives the 4#6 a totally new flying experience. Factory installed weight blocks (instead of paddles at the end of the stabilizer bar), significantly increases the stability of a traditional rotor head design, but as a trade off, it flies a bit slower. If you like your 4#6, but find it too much of a challange, this might be the perfect solution!