What Airfoil Should I Use?

[telnar1236]

I saw this post and I was going to recommend Drela's AG35 and AG37 airfoils, but it looks like someone beat me to it. At the Reynolds numbers an rc plane flies, it's hard to beat them for L/D ratio.

 

[Matthewdupreez]

I'm probably not thinking of all the ideas here, but if you are working on adjusting the CG location, here's what comes to mind:

Because the tail extends out further than the nose (usually) small weight changes at the tail require larger weight changes at the nose -- so it's a critical area to pay attention to.

Like you say: making the tail lighter could be a good idea, but you have to work with materials available and you also need to maintain enough structure. Sometimes lightening holes are used, but then you need to cover the structure with some sort of film or tape. In some cases it might help to pay attention to smaller details like how much glue you use.

I couldn't tell if this was an RC airplane or free flight? But if you have RC gear, then of course you could move your tail servos forward and use longer pushrods. You could push your battery as far forward as possible since that is usually the heaviest bit of avionics.

If you are rebuilding the fuselage along with the tail, then another thing people often do is design a longer nose, or push the wing mounting point aft so the airframe comes out closer to the desired balance point on it's own.

Sometimes it's fun to notice WW-II fighters or racers with giant engines and where the pilot is seated. Look at any 2-seater tandem open-cockpit airplane and usually the pilot flies in the back seat and an optional passenger is in the front seat close to the CG. The noses on WW-I fighters were often *very* short because the engines at the time were heavier. I find it interesting to look at how modern gliders are designed and where they put the pilot. I have an xuav talon with a pusher prop, and in this case the fuselage forward of the wing is very long to help offset the weight of the motor in the rear.

So all of this is fun. Figuring out how to balance a large network of design tradeoffs, come up with something that flies nice (performs well, handles well), and looks cool all at the same time.

thanks man.... i rebuilt the nose heavier... doubled up the foam so it is useful heaviness... then i also reduced the weight of the tail from 50grams to 15grams.... i also shortened the boom... now it weights all up weight with wing 156grams and a wing area of 4567 of so square centimeters....
and it now does not want to land... yay...

 

[Matthewdupreez]

30 meter/90 ft glide with no control