I am building in fiberglass, and my control surfaces have hotwired foam cores and vacuum bagged fiberglass skins, then hinges in each are imbedded with flox in high density foam blocks. After much careful fixturing and checking, I have built two ailerons and one flap with the three hinge bearings as perfect as I can tell. But one flap, well less good. The center hinge is about 1/16" (1.5mm) aft of the line from the end bearings... Bearings are sphericals press fit in the control surface hinge pieces.
I immediately thought about removing the hinge, making a new one, and installing it. Then I told myself not to go off half cocked... There is risk in doing this, of damaging the skin and cores and fairing already completed. There is always some level of error in parts - we can not build "perfect", even if we try to be perfect. So, anybody have a tolerance for allowable misalignment between hinge pieces? How about a basis for coming up with a tolerance? And no, I will not accept the idea that everything must be as perfect as I can make it... that might be nice, but no airplane would ever fly if that were really applied...
Now, besides the desire to make the parts perfect, we have flight loads due to aerodynamics, and I have a pretty good estimate of the maximum of these loads. I fully recognize that the aero loads will create a simple curve in the wing with g's and the flaps will sag upwards from its hinges under these same lifting forces - I sized the flap skins and gaps to prevent this deflection from making the flaps press on the lip of the upper skins. I am planning to seal the flaps with a foam rubber seal at the nose of each flap, so the actual gap can be a little big without big leakage and drag.
Just to let you know I am trying to be realistic, I have gone back to my calcs and am working out how much load I would get in the bearings if I build the fixed hinge halves to fit with zero inherent load at zero flaps, and then deflect the flaps to max. I will share that when I am sure of my numbers. Checking tomorrow morning and comparing to the loads from all other sources too.
So, does anyone have a set of tolerances for position errors in controls surface hinges? Any basis for the tolerances? We know that there has to be some level of tolerance, right?
Billski
I immediately thought about removing the hinge, making a new one, and installing it. Then I told myself not to go off half cocked... There is risk in doing this, of damaging the skin and cores and fairing already completed. There is always some level of error in parts - we can not build "perfect", even if we try to be perfect. So, anybody have a tolerance for allowable misalignment between hinge pieces? How about a basis for coming up with a tolerance? And no, I will not accept the idea that everything must be as perfect as I can make it... that might be nice, but no airplane would ever fly if that were really applied...
Now, besides the desire to make the parts perfect, we have flight loads due to aerodynamics, and I have a pretty good estimate of the maximum of these loads. I fully recognize that the aero loads will create a simple curve in the wing with g's and the flaps will sag upwards from its hinges under these same lifting forces - I sized the flap skins and gaps to prevent this deflection from making the flaps press on the lip of the upper skins. I am planning to seal the flaps with a foam rubber seal at the nose of each flap, so the actual gap can be a little big without big leakage and drag.
Just to let you know I am trying to be realistic, I have gone back to my calcs and am working out how much load I would get in the bearings if I build the fixed hinge halves to fit with zero inherent load at zero flaps, and then deflect the flaps to max. I will share that when I am sure of my numbers. Checking tomorrow morning and comparing to the loads from all other sources too.
So, does anyone have a set of tolerances for position errors in controls surface hinges? Any basis for the tolerances? We know that there has to be some level of tolerance, right?
Billski
