The main thing is the angle between the wing and tail. Their relationship to the fuselage reference line only determines how the fuselage lines up with the airflow and that determines how much drag the fuselage produces if it is misaligned by about plus or minus 3 degrees. Because the fuselage alignment is not so critical just set the question aside for a moment and consider the wing to tail alignment. The wing to tail angle is called the horizontal decalage and it is affected by many things. For a given trimmed flight speed it is affected by horizontal tail area, tail moment arm length, center of gravity location, down wash angle of the air flow behind the wing, the aspect ratio of the wing and, the aspect ratio of the horizontal tail. That's why many full scale planes have trim tabs or a means of adjusting the decalage in flight. (The center of gravity location is a function of the stability that you as a pilot find acceptable and varies with pilot skill!) Because the calculation is so complicated, most model designers determine the final decalage by trial and error. That is the main reason that flying stabs are so common! Differences of a fraction of a degree can have dramatic effects on trim and construction accuracy comes into play, providing yet another motivation for adjustable decalage. Cutting to the chase, in your design of the wing and, or tail mounting, make the horizontal decalage easily adjustable so that the setting can be adjusted in increments during the flight trimming process. You need to start somewhere and a horizontal decalage of about 3 degrees is safe. Back to the question of fuselage alignment, the angle of the fuselage to the airflow varies with flight mode. In the launch, the wing is flying at a low angle of attack and the down wash angle is also low. In thermal mode the wing is operating at a high angle of attack and the down wash angle is greater. The difference between these two modes is around 10 degrees. When launching the parasitic drag of the fuselage is at least twice as important as during thermalling so, I would optimise the fuselage alignment for launching by making its axis parallel to the wing chord line but, this is not critical. The question of fuselage alignment can be made even less relevant by making the fuselage as narrow as posssible and of an oval crossection. Regards, Ollie >OK design gurus - > >I am designing a HLG and want to know what you might suggest for wing >incidence and tail incidence. My understanding is that you want a slightly >positive angle of attack for the wing and a slightly negative AOA for the >horiz. stabilizer, relative to a "level" reference line. > >My question is how many degrees of each? > >The wing has a MH32 airfoil, if that helps. > >Thanks in advance, > >Brooks Park >San Diego RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
