HPA

Just making sure I am giving accurate info.  Fellow was building a Guillow Lancer with a flat elevator.  The plans call for an airfoil elevator.  I believe that adds live to the rear of the plane and changes how you balance the plane.  With a flat elevator he is much more likely to need nose weight?  The Arrow I built has the balance point way to the rear of the wing (see pic) and it seems to fly nice and stable. Is what I was telling him correct?

Hi pedwards, I think I see what you mean. There are just so many variables at play. Just one example - the airfoil section hz tail would presumably be slightly heavier - more wood - so require noseweight to balance . . .

Stephen.

I'm a bit late with this query, but anyway here are some further points.

Without going into too much detail, air foiled tails are most beneficial when highly cambered airfoils are used on the wing as used in competition FF models.
Airfoiled - that is cambered tails, will develop lift over a wider range of angle of attack, allowing the wing to fly at a much higher angle as well - developing more lift, and thus producing a slower glide.

However the position of the CG is more dependent on the stability required and to a lesser extent on fine trimming the glide angle of attack.
I would expect to be able to trim the airfoiled stab Lancer to a slightly slower speed with the CG slightly further aft.

As Stephen mentions - the flat stab may be heavier for the same stiffness as an airfoiled stab , and require extra nose weight for the same CG position.

Hope it flies well.

John

What you are saying makes sense. I can only compare with the Arrow where they moved the balance point way aft on the wing.  I still suspect with a flat elevator it will need more nose weight and a different balance point. I know when they convert the Lancer to RC they usually go with a flat elevator but you do have a lot of motor weight to help balance.

There is one other point re CG and trimming - especially with duration and sport models, and that is not to overuse CG movements to achieve trim.

As the main function of the CG is to provide sufficient stability - trimming the model should be done with changes in the wing and tail incidence settings.

Thus use the recommended CG to start and balance the glide with say changes to the tail incidence. I usually start without the prop installed(this shows small changes in the glide more clearly), with a false nose plug and balanced to the design CG.

Them a quick check with the prop installed and balanced to the design CG - no power, will usually retain the good glide but steeper with the extra drag of the prop.

Then power flying alterations should be done with thrust line alterations.

Finally very small movements of the CG can be used to slow the glide or reduce stalling.

I hope I'm not being over the top here - it's just I feel that moving the CG too much for trimming can lead to going around in circles, especially with non scale models where there is more leeway with moving the tail and wing.

John