I have to say I'm a little confused about what is being said here. However I think Don and Mike are essentially agreeing.

For symmetric non-tapering airfoils (i.e., constant thickness) blocking a wing up at the tips results in positive dihedral and a non-flat wing top. Joining the wing with no blocks so that it's flat on the table (either inverted or upright - makes no difference) results in a zero dihedral wing with both the LE and TE being level. These are the scenarios with older constant chord, constant thickness wings such as the Super Pacer, New Era and Warlock (70's designs).

For symmetric thickness tapering airfoils (i.e., thickness thins toward the tip) blocking up a wing can result in one of three outcomes: 1) a top-bottom symmetric wing with zero dihedral and level LE and TE; 2) a top-bottom assymetric wing with taper positive dihedral, a flat top and non-level LE and TE and; 3) a top-bottom asymmetric wing with positive dihedral, an angled top and non-level LE and TE.

Many classics with symmetric thickness tapering airfoils (such as the P8 I believe) were often designed to have wings with flat tops when joined. That would correspond to scenario 2 above. The wing tip is blocked up to make up for the percentage difference in the airfoil thickness between the root and tip. An alternative way of joining the wing without blocks which results in the same dihedral is to join the panels inverted on the flat table keeping the wing chord also level with the table. This typically requires blocking up the tips at the TE to hold the airfoil parallel to the table.

With such wings a line running from root to tip joining the chord centerlines also represents the LE centerline. If the panels are joined inverted flat on the table, then this line ends up being angled with respect to the table surface. That angle represents the dihedral angle and is not zero (as Mike points out) despite the wing having a flat top. Don, the 6' straight edge should touch the wing top along the span when positioned at the max thickness of the wing but the LE and TE should not be straight. The degree to which the LE is not straight corresponds to the percentage taper of the airfoil thickness toward the tip.

As a last thought regarding classics designed in the 80's, models which had top-bottom symmetric stabs (i.e., no anhedral) often had flat top wings so also had dihedral (case 2 above). Models which had top-bottom asymmetric stabs (i.e., anhedral stabs) typically had over positive dihedral to prevent adverse roll coupling (case 3 above). The former sounds like the case of the P8 and many others (e.g., Deception) while the latter is the quintessential case of designs such as the Curare and Tiporare. Modelers who have built these last classics with flat top wings and anhedral stabs have discovered the undesirable flight characteristics of the plane - the over positive dihedral is important. I'm just using the term "over positive" to differentiate it from a flat top wing with positive dihedral.

This is how I understand it. If this is wrong please enlighten me. Wouldn't want to build any further wonky classic wings!

David

P.S. Glad Dean Pappas is reading this thread. Perhaps he and Mike can help to clarify.