View Full Version : Longitudinal dihedral
12-15-2006, 05:29 PM
hi Guys can any of you experts help me here?
I'm new to modeling and i have just finished building my first glider (multiplex DG600 EVO).
in the setup it tell me to set the CG (that i have done) and set the longitudinal dihedral of 1,5.?
i have bought a incidence gauge (multiplex) but i don't know the first thing about setting it up.
can anyone give us a push in the right direction please
i spoke to a guy on the slopes yesterday and he said something the same but the otherway around.
he told me to put the gauge on the wing of the glider and level the glider so the gauge reads 0
then strap the glider down so it doesn't move.
then put the gauge on the tale plane and adjust the elevator until i have got 1.5. but im not sure
12-15-2006, 05:54 PM
Welcome to Wattflyer!
Unfortunately I can not help on the incident meter as I do not have one...yet. :)
12-15-2006, 06:42 PM
"Longitudinal dihedral" ???
If it is the dihedral you can`t do much to it since the wingjoiners are preinstalled I think... or do you have to install them yourself?
If it is the "angle of attack" they could have said so. If so, mount the incidence meter to the wing, adjust the fuselage until you read +1,5`and secure the fuselage. Mount the incidence meter to the stabiliser, then adjust elevator until you read 0`.
1,5 degrees AoA might be necessary for the RG-mod profile...
12-16-2006, 01:37 AM
Hello jd-eye, Welcome to Wattflyer! Longitudinal Dihedral is another term for "Decalage", which is the difference of angles between the main lifting surfaces; The wing and stabilizer.
If, for example, the wing has a flat-bottom airfoil, and you were to draw a line following the airfoil bottom, back to the stabilizer, on most aircraft you would find the stabilizer has a bit of "up", the trailing edge of the stab would be slightly higher than the leading edge. Decalage.
Because of its distance from the wing, the stabilizer exerts a powerful force (leverage or torque) on the wing. The stab is "telling" the wing to fly slightly "up" and the wing will fly at that angle (forgetting stalls, thrust and such, for the moment). This angle that the wing flys at, (presents to the airflow) is called the "angle of attack". Decalage determines Angle of attack, all other things being equal.
Now we look at the airplane from the front; The wings are tilted "up" from level or flat. Dihedral. Another name is "Lateral Dihedral". Make sense?
So you fix the model on a flat surface, with the incidence meter indicating the wing is "flat" in the longitudinal dimension. The wing (if the airfoil is flat-bottomed, again) is level with the surface it's sitting on.
Move the incidence meter to the stabilizer and check the angle; It should read 1-1/2 degrees "up".
These differences in angles, decalage, can be created another way, as jooNorway pointed out. The stabilizer can be fixed and the wing tilted (trailing edge down, it works opposite for the wing) 1-1/2 degrees. This will accomplish the same thing.
I've simplified and left out a lot of other factors but this should get you started! Hope it helps, Good Luck!
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