Square 8 Trim Issue

My LA .46 powered Cardinal P has very good line tension everywhere except the top portion of the outside square in the square eight. It seems to get loose and roll in. Poor penetration across the top of the square.

Is this indicating the lines guide is too far forward or too far back?

Or is there some other trimming issue? No rudder offset, very slight degree or two engine offset.

LAST EDITED ON May-15-04 AT 06:53 PM (CDT)
 
Let me start of saying I am far from a expert but this is the plane I fly but with a LA40 and a APC 11x4.I would look at the wings closely in level flight upright and inverted at eye level to make sure it is flying flat (example if you see the top of the wing in upright flight and the bottom in inverted)this would indicated a slight twist in a wing panel.You could also have a tip weight issue,a lack of tip weight.Also flying with the lead outs to far back can cause a lack of tension over head.I have no rudder offset and no engine offset.The only limiting factor with mine now is me.Hope this is of some help.I am not a expert at all but this works for me.

JD:

I'm just finishing trimming on a profile Cardinal myself. K & B .40 power, 10-5 APC prop, 45 oz. our models appear to be set up about the same.

QUESTION: Is the problem ONLY occurring on the outside portion of the Horizontal eight or is it occurring on other similar spots but not to the point of creating trouble ?

I assume that the model is lifting the outboard wing coming over the top during the sharp corner. If that is the ONLY time it occurrs during the entire flight, then it is likely technique, not trim. For some reason you would be running the model out of airspeed and into a stall/stagger situation. Open up the maneuver and keep speed up. Also, you might be pulling up TOO early into the intersection climb, Most of us pull up too late, but it's possible.

More likely the bird does it on all sharp outside turns but you aren't noticing it elsewhere. The model may be "Hinging" or flying a wider turn with the outboard tip than the inboard. This usually is due to too much tip weight or flap problems such as flex or alignment.

The link wire between the flaps on mine was too soft ( my fault, not Brodaks: I picked up the wrong piece of wire from the bench) and as a result the inboard flap moved more then the outboard under load. The result is pulse raising. Check that first. If it's OK with no twist occurring, see that the wings fly level upright and inverted. If the flaps are aligned with each other, rather than a trim tab or bent flap, try tapeing a piece of silicone fuel line about 2" in from the tip and 1" forward of the hinge line on the bottom of the wing which flies low. This acts as a spoiler and makes that small prtion of the wing a lifting rather than a fully symetrical airfoil. It's easy to adjust and experiment.

If this is NOT the case and everthing is flying straight and true, reduce tip weight 1/4 oz at a time until the you get the best combination. Even 1/8 oz makes a difference. Too little weight will reduce tension on the overhead maneuvers. My bird ended up with only 1/4 oz of weight. It squares a bit better with NO tip weight but loses much of the overhead feel. If you followed the plans and left the outboard tip solid, you don't need much lead. My K & B is heavier than your LA so I need a trace less weight than you do.

If your leadouts are at the plan location, they are close to right. Mine ended up with the leadouts 1/8" behind the plan location. REMEMBER, ADJUST ONLY ONE ITEM PER FLIGHT!!!! Keep notes so you don't duplicated.

Mine trimmed out well enough to pull 479 and 480 in Iowa two weeks ago using these techniques on its 13th and 16th flights.

I'll watch for results on the forum or you can E-mail me at [email protected].

Jeff W.

JD: I agree with Max; 1: check to make sure your wing is flying flat, and 2: you may need tip weight. Even a very small amount of tip weight (1/4oz) can make a drastic difference in line tension in overhead and compound maneuvers. At the point in the square 8 you are describing the plane has bled off quite a bit of airspeed, and even small changes in tip weight can have a very noticeable effect.

LAST EDITED ON May-17-04 AT 11:54 AM (CDT)
 
How about a technically correct answer? A perfectly straight airplane in "zero" trim will always have less tension after outside corners and more tension after inside corners due to yaw from gyroscopic precession. Try a lighter prop to reduce the gyroscopic effects. Biasing trim to favor outside tension at the expense of some inside tension is also a possible help. Still, the prop IS A GYROSCOPE. Live with it or try to correct it.