CG Swept wings with curved tips

[Turbolax]

I've just completed a MiG-17 with a larger-than-scale wing. The usual C of G calculation diagrams don't seem to explain the importance of the curved tip. Does this have any bearing on the calculation? I tried using the conventional MAC diagram but ended up with splintered balsa and 3 months of repair. Also, does the trailing edge root extension on the MiG also alter the position of MAC? Should i just calculate 25% of the wing area back from the nose and set the C of G as that? Does anyone know where on a MiG-17 the actual balance point was?

[BMatthews]

Did you match the larger than scale wing with a larger than scale horizontal stabilizer?

The wingtips shown in this drawing below would not cause any significant problem. However the stabilizer is small by model standards even with a scale wing. Making yours larger is probably much more to blame than anything else.

http://www.fas.org/nuke/guide/russia/airdef/mig-17-line.gif

In this case I think you can ignore the little root extensions. Do your MAC for the basic contant chord wing and select a suitable CG from that. Any area in the root extensions will make your CG even that little bit more conservative anyway.

The other determining aspect of CG location is the Tail Volume Coefficient. You may want to do a search on that and run the numbers on your planform. It may tell you that even a normally conservative 25% isn't good enough for this small stab'ed layout.

[vintage1]

I would make up a balsa chuck glider and test fly it on something like this.

It will probably get you as close as anything else, and is more fun...

[Ollie]

Another possible contributor to the crash is tip stall. Swept back wings are notoriously suceptable to tip stall and one as swept back as the MIG might need as much as 10 to 15 degrees of wash out to tame it.

[Sparky Paul]

I get this for a 25% c.g. on the MiG-17 with Jean-Claude's computator..
And I'll go with Ollie's assessment of needing more (or some) washout.
I spent YEARS trying to get my PSS F9F-6 Cougar to fly above eye-level on the slope, in any strength wind. C.g.s went aft, went forward.. It was one of the best-repaired planes I had.. Couldn't do anything with washout though.
It's now landfill, although in good condition.. sob! :(