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Vintage and old timer models Discuss nostalgic vintage aircraft

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Old 05-04-2015, 11:36 PM   #1
abborgogna
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Default Calculate the CG on Old Time plane

Anybody know how to calculate the CG on a under cambered wing with a lifting horizontal stabilizer? I am in dire need of some help.
Andy
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Old 05-05-2015, 12:09 AM   #2
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Gets very complicated SOMETIMES.

True lifting stab you can push the CG back well past 60% MAC. Before even attempting that we need photos of the aircraft.

Its far more common for a plane, such as the current Telemaster series, to have a lifting airfoil at the tail but to have significant "decalage" forcing the tail plane to actually be pushing down rather than lifting. Then you'd go back to the standard of appx 25% to 33% MAC of the main wing.
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Old 05-05-2015, 12:54 AM   #3
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Here is a picture. The plane is Sal Taibi's power house with a 36" wing from Bob Holdman. Bob and his helper both suggested a 50% CG starting point and yes the horizontal stab does lift. They also suggested a 1.5-2 degree incidence between the stab and the wing. It is currently built into the design go give the wing a 1.5 degree positive incident relative to the stab. This maybe backwards of what I really want. Yet that is how the plans produced the fuselage sides. Maybe I am reading the incidence meter incorrectly, it is a digital incidence meter and maybe it is really negative incidence from wing to stab.

As you can see I am confused and could use any help you provide. If you need to see a side view of the wing rib, or a close up of the horizontal stab let me know and I will post a picture in this thread.
Andy


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Old 05-05-2015, 01:27 AM   #4
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Go with the recommended CG.

I've pushed CG back to 40% on a plane with a flat plate tail plane. 50% is not extreme for a lifting tail. I've seen CG at 80% of main wing before for a FF model.

Expect the elevator to be sensitive compared to what you would expect with a more forward CG and stall recovery might be difficult so avoid stalls.
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