Aristo-cat C.G. question

[coosbaylumber]

Aristo-cat C.G. question


I have the original article from Model Airplane News circa 1964 and copy of original plan and talked to the original draftsman for the plan.



Problem?

There is no center of gravity shown nor mentioned anyplace.



I understand that Midwest also kitted the airplane, but was a C.G. shown on their plan?

This is an early day aerobatic A/C and the modern calculations do not fit considering that this A/C now weighs even less then thirty years ago. It flies sort of screwey right now. Jumps here and there. "Think" about going there, and you have arrived. The tail skeg is just full of scratches. It acts like the fourth main wheel right now as it touches down so often. The whole A/C is at a bit above five lbs. whereas the original was closer to seven.

The old formulae works out that such that I need even less down pressure, and less weight on rear wheels. The original designer (now dead) made up yet another A/C two years later of similar size and power. 'cept he moved the wing forward a good two inches. This latter one flies normal.

Can I correct the jumping around via a changed incidence?
Do I need to add ballast to bring it back to original weight again?



Wm.

[JetPlaneFlyer]

Calculate the correct CG here: http://adamone.rchomepage.com/cg_calc.htm.. A 10% static Margin should be safe.

Twitchy control response usually indicates too rearward a CG but this would be made worse by moving the wing forward, not better. Maybe you just have too much control movement?.. It's hard to say without a lot more details of the model.

I'd certainly not change the incidence. Any changes needed to incidence will be obvious once you get the CG right. I'd also not even think about adding ballast to make the model heavier... lighter = better ;)
Steve

[Texas Buzzard]

As JPF said, the CG sounds like it's too far to aft.

Does it seem to "HUNT"? As in just thinking about elevator input makes it climb or dive?

If that is the case then leave everything else as is AND JUST ADD SOME WEIGHT UP FRONT.

Years ago I had a new Biplane that was so eratic in pitch that I was lucky to get back on the ground in one piece. I added lead twice to tame it. If the CG is too far forward the plane should safer to fly. Also try to cut down on the elevator throw a bit. :)

[coosbaylumber]

Tex.....

I can easily get the A/C to fly straight and level. But (I think) a gust at altitude will send it off in some direction at about the time I intended to make a course change. The control surfaces move about 1/4 to each way right now. Not excesive I would think.


Some folks say to add weight more to rear, then would never need a nose wheel. For it would never touch the asphalt. The motor, radio gear, and most everything now is much lighter than originally was. Had been considering adding weight until original flying weight was arrived at. Then go from there.

Wm.