bcfhigdon

My Feedback: (5)

Just started on my Phoenix 8. Nowhere on the plans does it show what the dihedral is for the wing. Can anyone help me with this? Thanks for the help, Clint

R_G

My Feedback: (1)

Maybe this will help.

RG

bcfhigdon

My Feedback: (5)

Answers my question. Thanks for the instructions this will help. Clint

crankpin

My Feedback: (15)

Phoenix' - Usually 1" under each tip when joining.

Crank

frequent flyer

My Feedback: (6)

Clint

I had sent you an email days ago. Did you not get it? As I said in the email, it is zero. If you were to put 1" blocks under each wing tip it makes it zero. It is to say the Leading and Trailing edges are straight. I used a six foot straight edge on the table , drew center lines on the trailing edge and line everything up when joining the the wing halves.

Don

Please note I made your fuselage with West Systems Epoxy Resin and Polyester Resin is not recommended for anything being attached to it. Use epoxy on epoxy only for best results. If you need any other help feel free to ask.

MMcConville

My Feedback: (4)

Just a comment. I dont remember the proper dihedral in the P8, but I do know it is NOT zero (straight on the CL). It required some dohedral. Zero will result in adverse roll coupling.

Taurus Flyer

Mike,
Wouldn't be the vertical position of the CG interesting to write about! Above, on or below CL?
Cees

frequent flyer

My Feedback: (6)

Mike

Well maybe saying Zero is misleading. As I said and did above 1" block under each wing tip when gluing the halves together makes the proper dihedral. At least that is always what I have been told. I know on my KAOS plan it says 3/4" blocks under each tip. It is really the dihedral created by the airfoil becoming smaller and smaller as it goes out to the tip. When I had a straight edge on the center line of the trailing edge it was straight.

Don

MMcConville

My Feedback: (4)

The amount you prop up the tip is completely dependent on the airfoil thickness root and tip. It will be different for every airplane. Regardless of how its done, if the TE is straight when viewed from the rear (also meand LE straight when viewed from the front then there is zero dihedral.

My point is that this isnt ideal for the P8. It needs some dihedral to eliminate roll couple.

frequent flyer

My Feedback: (6)

The Plans I have show nothing and the Instructions I have are the same as the ones posted above. Do you have any others possibly? I checked my wing again with a 6 foot straight edge and it appears to be straight. Although when built I put 1 inch blocks under each wing tip. Now that the wing is complete and the wing pan is installed it is difficult to check exactly.

I set my wing on the table level and used my laser level and there seems to be about 1/4" away from straight flat on the trailing edge. The top is flat.

frequent flyer

My Feedback: (6)

After talking with a few of the other guys that have done the P8 and flown them they all said that they built them straight. A couple of guys also said that the P8 wasn't designed to have any dihedral. For what it's worth.

dhal22

Don, I will check the vintage competition P-8 that I have. The original owner was a serious competitior, didn't he sell 25-30 pattern planes from this era?

crankpin

My Feedback: (15)

I'll go with Mike, 1" under each tip.

Frequent Flyer, thanks for all the kits you are providing to everyone that wants to build a vintage pattern plane. You are doing us all a great service.
Tom Scott's P-5 in flight attached.

Attached, two more picture's, one of Wagner's electric P-8 build thread, looking straight on, and another of a P-8, you can see the diehedral in the wing. Whatever the outcome here, it is all in good conversation about the old birds.

Vince

doxilia

My Feedback: (3)

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.

bcfhigdon

My Feedback: (5)

Got his info from a guy who has an original Aero Composites P8. Says the dihedral is cut in the core.

doxilia

My Feedback: (3)

If that's the case, then that would be scenario 3 of the attempted dihedral description above for airfoil tapered symmetrical wings. The fact that the Phoenix series (most of them have swept wings I believe) seems to require additional dihedral from a flat top wing, makes me wonder whether this is due to the fact that the wings are swept back. A wing with a 1" gap under the center over a ~63" span is not a great deal but it still ends up being an anhedral wing when the model is flying inverted. I wonder how the P8 fares inverted in this respect.

Since there are few flying or soon to be flying P8's around and about, perhaps each builder could describe their wing and how the planes behave in flight. We've seen Kevin's P8 flying in videos and it looks like an excellent flyer!

David.