rikhye

Well I can handle a flat bottom aerofoil... but what should i expect in a symetrical aerofoil.

Should the angle of incidence be zero in that ?

Fourthwind

My Feedback: (22)

It should be what ever the manufacture recomends. it can differ from plane to plane. If you have mastered your trainer, you will enjoy the maneuverablity of the symetrical airfoil wing.


FW

Crash Master

Keep in mind that with a symetrical airfoil you may lose some if not most of the "float" characteristic of the flat-bottom. Also with symetrical you need to be prepared to "fly" the plane - in that where you point it is where it will go until you change the direction thru transmitter input(s).

If you aren't 100% sure you are ready for full symetrical, try one of the semi-semetrical airfoils. Still keep a lot of the "float" but flies much better inverted and for learning basic aerobatics.

Just my .02 worth,

HarryC

My Feedback: (1)

The stability is not governed by the wing section. Pitch stability is controlled by the static margin which is a function of distance from the Neutral Point and the Neutral Point equations have no parameter for section. Lateral stability depends upon factors like dihedral, sweep, CG's vertical displacement relative to the wing etc.

We mostly encounter flat bottomed wings on trainers and things like Piper Cubs, which have also been designed by the other factors to be stable, thus leading some people to think that it is the flat bottomed wing which leads to the stability. But you could replace the flat bottomed wing on your trainer with a like for like symmetrical wing, and you will have the same stability.

Harry

crosswind

For what it's worth, I think you'll enjoy the fully symmetrical wing after flying your trainer. Like Crashmaster said, it'll go where you point it if it's properly built and trimmed without changing pitch so much with different throttle settings. I personally found my first symmetical wing plane as easy to fly as my Johnny Casburn trainer (that shows how long it's been!), which I still have. It's certainly nothing to be afraid of in my opinion. It just won't have any self correcting tendency. By the way, most if not all of the trainers I've seen certainly don't have enough self correction to prevent a crash when you let go of the sticks! And thanks Harry, for that aerodynamic explanation. But could you explain why most trainers have a flat, or nearly so, bottom wing? I would think a more symmetrical wing would be better. Slower flight?

HarryC

My Feedback: (1)

Exactly so. The cambered wing has a higher lift co-efficient than an uncambered wing, so at the same speed and angle of attack it develops more lift. Since we need only the same lift from either wing, the cambered wing can be flown at a lower angle of attack for the same speed. Then at some slow speed when the uncambered wing has reached its stall angle, the cambered wing still has some angle in hand and can be flown down to a lower speed before its stall angle is reached.

Model fliers have quite a few myths, based apparently reasonably on what they see. Like the idea that stability comes from having a flat bottomed wing, or that inverted flight is easier with a symmetrical wing. Neither is true, what we see is stable trainers which often, though not always, have flat bottomed wings for quite different reasons than stability, but we tend to equate the flat bottomed wing with the stability because you can't obviously see the static margin and don't know of its existence. A pupil of mine has a Precedent Hi-boy trainer. It has a symmetrical section and is a pig for pulling its nose up the moment you touch the throttle open, or stick the nose down and it instantly pulls back up level. Yet the club's Thunder Tiger Trainer which has a flat bottomed wing is much more neutral in pitch stability.

In full size I have recently been flying a Robin 2160 with symmetrical section, and a Yak 52 with a classic flat bottomed section. Both are highly aerobatic. The Robin is much more pitch stable than the Yak, and as a consequence it drops the nose hugely when inverted whereas the Yak barely does so. The Yak is much the easier to fly inverted and stays in a dive much longer than the Robin which pulls out quickly, yet the Robin has the symmetrical section!

Wing section is not the determining factor in stability. It is just that we tend to be using flat bottomed wings to give slow flight on the same planes that we have designed to be stable.

Harry