Raising hinges

[Frank S]

Let me see if I am able to make an explanation understood. it has been a long time since I had to make a gate go up hill when opened and I may make things more confusing than they need be. .
Start with looking straight down from the top of the hinged and opposite posts draw a line from the center of 1 post to the other. Assume this to be the centerline of the thickness of the gate. in its closed position. now draw a line from the center point of the hinged post perpendicular to the closed gate center line. These will be our beginning reference points next make a circle centered on the top of the hinged post a couple inches larger than the diameter of the post it makes no difference if the post is round or square at this point but a square post would have an inscribed diameter or a circumscribed diameter inscribed would be the radius from the center to the center of one of the flat sides as a circumscribed diameter would be the radius from the center to one of the corners. just to explain where we stand.
Once you have determined the diameter of your circle this will be the reference for the distance to the center of axis for the top hinge later we will make our debarkation point of the axis for the top hinge lower down on the post positioned as high or a low as you want to have the top of your hinge located down from the top of the gate.
Now the fun part comes. I would normally design my hinges for a gate such as this to be behind the post by locating the centers at a 45°ange between the open and closed position. so we will try this method for now you can alter it to suit your desires. So what we are going to do is make an imaginary point on the circle we had drawn around the top of the post. and draw a line from the center of the posts through that point allowing it to extend outwards a few inches.
We are done with the top view for now we will name this our top plane, but will return later. Now draw a vertical line extending down from the center axis of the top plane to where the bottom plane will be to represent the height of the post we are going to create a view of the opened gate I am going to name this the right plane is could just as well be the left plane depending on whether you are opening the gate away from you hinged on the right or the left. Now that we have established the planes exitance. we want to draw an imaginary line from the circumference of the top circle down to the bottom as well remember this is the axis point of the distance the top of the top hinge will be placed form the post. Next draw a line the distance from the base of the posts to where you want the top of the top hinge to be located .Next start as the base of the post and draw a line to the left at the suspected angle of the inclination for simplicity we are going to use your stated 8° for anyone else needing to make a similar gate their angles may be different. Now that we have established the base line of the slope up from the post with the gate in the opened position we need to draw a line down from the hinge axis top to the inclined line this line must be perpendicular to the line that is drawn at 8° Next we will need to draw the hinge axis line down from the top hinge axis point to the base at 4° from the post this line should be equidistant between the centerline of the post and the previous line, Next we are going to draw a line at the height of the bottom of the lowest gate hinge from the center of the post horizontally to the line that is drawn at 4° and make note of the length this will be the radius from the center of the post to the center axis of the bottom hinge. We are now almost done about all we have to do at this point is if you are planning on using the common gate strap hinges all you have to do is screw them in at the heights you want them at 4° angle from the post at halfway between full open and full closed the centers of their axis matching the 4°line On the gate when it is closed the strap hinges will need to be bent the top one will be short and the bottom one a little longer, When the gate opens it will not remain straight up vertical but will lean some the reason for placing the hinges in the positions I have laid out is to compensate for the angle of the incline in the open position while allowing the gat to be straight up and look like a normal gate.
since the hinges are not mounted at 90° to the closed position but at about halfway between you may find some adjustment to the length of the bottom one stickinig out from the gate and the post may be necessary to achieve the result you need for instance you may have to set the center of axis of the hinges at 5°instead of 4 or if you place them further around to the back of the post you may be able to go slightly less with the angle but much longer on the lengths that the center axis of the hinges are from the gate.
I hope this helps and if not too confusing will steer you towards making your gate function as required.