Bird of Time AoA

[Andy J]

Just completing a scratch build of a Bird of Time using a downloaded plan and have now just got to complete the fuselage with its concealed rear stabiliser linkage.

Looking at the plan for the all moving tail plane it strikes me that the angle of attack as drawn is wrong as it looks several degrees larger than that used for the wing. Has anyone else noted this issue?

[Frank Skilbeck]

We built one from the kit, can't remember if the tailplane was at a higher AoA, but we built it per plan and it flies lovely. Remember that because the wing sits on the fuselage then the actual AoA is a few degrees from the fuselage datum.

Also on a thermal soarer you want the plane to be responsive to lift, so the c of g is a bit further back than say a power plane, which means the tailplane will be at a lower AoA than a power plane.

I have the kit plan somewhere so I will see if I can find it and post back.

We built ours as intended, a pure glider , flies great and bungee launches really well.

[will -0]

THis is an all moving tailplane isn't it? In which case the angle of attack is wherever you push the stick to.

[brokenenglish]

Your image doesn't show enough information. The tailplane AoA ("incidence" actually, we're discussing rigging, not airflow) will depend on where the articulation points are located on the tailplane. For example, if the rear articulation is on the lower surface of the t/p, that will obviously change the angle of incidence. You've assumed that both articulation points are on the t/p mean camber line, which may not be the case (I don't know).

[brokenenglish]

Posted by Frank Skilbeck on 28/04/2020 13:41:57:

Also on a thermal soarer you want the plane to be responsive to lift, so the c of g is a bit further back than say a power plane, which means the tailplane will be at a lower AoA than a power plane.

Frank, I think you mean "higher" AoA....

[brokenenglish]

Hi again Andy, I've had a look at the plan and your interpretation appears to be correct. I don't know whether it makes any difference or not, but the tailplane appears to be really tiny in relation to the wing area.

My own "gut feeling" would be that the BoT has a great flying reputation for decades and I would just build to the plan and trust the design.

[Frank Skilbeck]

Posted by brokenenglish on 28/04/2020 18:34:28:

Posted by Frank Skilbeck on 28/04/2020 13:41:57:

Also on a thermal soarer you want the plane to be responsive to lift, so the c of g is a bit further back than say a power plane, which means the tailplane will be at a lower AoA than a power plane.

Frank, I think you mean "higher" AoA....

doh yes