G'day to all,

I have a world star 40 which tends to always be climbing at the higher throttle range. Not sure how I should approach rectifying this.[sm=rolleyes.gif]

A. Adjust the Ailerons up the same amount.
B. raise the back of the wing up slightly.

Comments welcomed.

Thanks

Prboz

If you have a computer radio might try making a throttle to elevator mix, so as the throttle increases, the elevator compensates for the lift. Im not sure you will be able to get the plane to stay level at all throttle settings without some kind of mix... for the most part, we trim our planes to be the best at the speed we will most often fly. Add more throttle, or less, and things will change. If you lift up the wing to make up for High throttle, you will likely find that the plane drops at lower throttle settings now.

Tail heavy.

If you have the CG set right, and I mean right... so that at the CG point, the nose sligltly dips, then this is a normal function. Add throttle to gain altitude... requires a bit of down trim for straight and level.

Trim is set for one and only one throttle setting. Once you change the throttle setting, it will either dive (lower throttle) or climb (higher throttle). Set the altitude you want to fly at and then trim the elevator for straight.. hands off.. flight. If you want to climb.. elevator or throttle will do it, but to maintain, you need to adjust something.. throttle or elevator.

CGr

Does this plane have a flat bottom wing? If so, it could be normal. Flat bottom wings tend to want to climb as you go faster. If this is the case, find a throttle setting that you like flying at then use the elevator trim to achieve level flight at that speed. I suspect this is all you are dealing with.

If this turns out not to be a normal characteristic of the plane then look at things like CG, wing incidence, stabilizer incidence, engine thrust, etc. It could also just be out of trim really bad requiring that you adjust the elevator clevis in order to get it right.

Couldn't find "World Star 40" on the Internet but, as Chuck W mentioned, if it is a flat bottomed wing it will tend to rise with added throttle. That's what it's designed to do. You could add down thrust to the engine by adding washers at back mount bolts or shim the rear of the wing up, but you will trade off other flight characteristics.

Raising both ailerons has the effect of lowering the angle of attack and will do it. Try raising both 1/8" at a time.

There is a saying: "Never try to teach a pig to sing. It wastes your time and annoys the pig." If you're looking for speed you need a different airfoil and design than a trainer.

I did eventually find the plane on the World Models site. They say it is semi-symmetrical. Their planes always fly great when built according to the instructions. You may want to double check the CG and the position of the elevator with the trim centered. Moving the CG slightly forward isn't that risky of a thing to do and it may help your problem. It is also possible that you ended up with a plane with an incidence problem. It's not common but it is possible. I had a Sky Raider Mach-2 with a badly twisted wing half. So bad that I couldn't remove the twist by holding it straight and re-shrinking the covering. That plane did roll to the left really good though...

Semi-symmetrical wing, ( just for funnies, there is no such animal as SEMI-symmetrical, however since we know what we mean using the term, let's just do it. OK? )

If you have the wing and stab (assuming a flat or symmetrical stab) at 0° angle of incidence relative each other, then moving ailerons will simply screw up your flight characteristics in different attitudes, maneuvers, and airspeeds. Now when you really learn your machine, depending on the flying job you are performing, some of that may be good.

If you try to adjust with strictly forward CG, (forward of 25% MAC) you just might end up with a model that will be very stable to a point, then fall out from under you as you retard to idle during the final landing maneuver, as the elevator runs out of ability to hold the nose up in a flare with idle engine airflow and especially if the model lands slowly, or if you have to apply a significant amount of up-elevator to hold the nose up, then that can call the stabilizer to stall out on the bottom side. It is using the same airflow-rules that govern the lift of your wing.

The semi symmetrical wing will offer some of the characteristics of a flat bottom wing, but not so much at a given time or place. As others above have said, when the engine is given additional power during stable level flight, the accelerated airflow provides instant lift over the wing increasing some additional lift within its span plus a little. Then the airplane accelerates also in airspeed, thus providing additional lift due to the fact that lift is a function of the square of the airspeed. This creates a climb attitude as long as power available is above power required.

In determining "incidence", downthrust, etc. I suggest you consider the chord-line of the stab to be at 0°. Use that line as the base line. That center line on the plans which was useful in building the fuselage is not understood well by the aerodynamic critters. Stab line is. For example a plan may show 3° positive wing incidence, 1° positive stab. and 3° negative downthrust. Aerodynamically you have 2° positive wing, 0 stab, and 4° downthrust.

Therefore the best solution, used by FFers and hi-wing trainers for many years is the simple downthrust. You can, via experiments, find a downthrust setting that will, when throttle is advanced, tend to pull the nose down to offset the climb from additional lift.
When you get the airplane trimmed at level flight with a good cruise power, when you get the Down Thrust right, it will pull the model down when power is added and stay close to trim, then when you start retarding power for the landing / slow flight, etc. the pulldown goes away and the elevator will very likely be set for a good glide with minor adjustment.

Once you get these basics all squared away, then you just might have fun trying to find out what changes in incidence, CG, and changes in thrust settings can do for you. That is where you learn the most.

Then comes the real downer. In some 60 years of modeling, when I think I have it all figured out, I build something that totally deletes all those HARD FACTS. [:-] So experiment a little at a time and have fun.