Beeza

My Feedback: (1)

I'm getting ready to start building a 1/2A Bushwacker, pretty much a
powered sailplane.


The plans scaled down give me 37.5 sq in stab area, I have another similar set of plans
that call for a stab area of 49 sq in-both planes have the same 275 wing area.
So should I increase the size of the smaller stab?

I've settled on 2 channel control, ailerons and elevator. Design question: am I better
off using a long aileron, or short ones out towards the wingtip?

Thanks,
Beeza

DeviousDave

I like 18-23%, 18% is 49sq in. Better too large than too small.

combatpigg

My Feedback: (3)

Just shooting from the hip, I'd say a 12"x 4" total stab area [elevator included] for a wing this size is about right. Difference in weight with a slightly smaller stab isn't much of an issue if built out of sticks.
I think designs that have the stab with a similar planform and aspect ratio with the wing look the best.
It's amazing how quickly one of these will fly out of sight with just a standard reedie.

MJD

My Feedback: (1)

Some folks say 20-25%, DD says 18-23%, and they are all good numbers. Towards 25% is conservative and safe, and I agree 18-23% is a good working range for most of the layouts we deal with. The one factor that is not considered here in any detail is the tail moment, but assuming the aircraft looks somewhat normal and satisfies the TLAR rule, anywhere in that range is going to work very well for you. The stab on your scaled BW is just under 15%, but it has a higher than average aspect ratio wing that is more of a sailplane layout as you already observed - I think it would probably work fine in the smaller scale, but if I was me I'd bring the area up a bit just to be sure. All that happens when you increase the stab size is that you lose a a bit of efficiency by increasing drag - a bit. Unless you are racing or competing in a nation-wide efficiency contest, I wouldn't think twice about increasing the stab to 18-20% area and enjoying the benefits of increased pitch damping and a less-critical CG.


MJD

soarrich

My Feedback: (98)

I would use long ailerons to the tips, hinged on the bottom with 2X the upward movement as downward movement.


I would use long ailerons to the tips

Because Mark Drela said that's the right thing to do and he's a PH D at MIT. He designed the Bubble Dancer and the Supra sailplanes.

hinged on the bottom

The airflow on the top is not attached to the wing that far back on the top it is turbulent after about 30%. The air on the bottom of the airfoil is still attached to the trailing edge. Look at ALL the DLG they are hinged on the bottom.

with 2X the upward movement as downward movement

Without a rudder to to fight adverse yaw the extra movement of the aileron going up will equlize the two wings drag. You can fine tune this later, but on my sailplanes they all have 2x1 aileron differental throws.

combatpigg

My Feedback: (3)

Rich, I've seen a couple of motor gliders that flew so badly it was hard to watch. They most likely could have benefitted from your advice.

MJD

My Feedback: (1)

While he's at it, my son's Nexstar could use some manners. I taught a handful of people to fly on those original Thunder Tiger 40/60 trainers as they were popular and stocked locally for a while, and boxy and generic as they were they flew perfectly smoothly and predictably and were great to learn on. This new fangled magic trainer flies like a garbage scow in comparison, IMHO. Perhaps if I had the patience or cared enough about it to mess with it a bit I could smarten up the flight characteristics to where they are likely supposed to be (maybe not..), but one can imagine the level of interest in that exercise. [sm=redface.gif]

MJD

soarrich

My Feedback: (98)

Nexstar is an odd plane. The wing cuffs make it so if you slow it down the wing stalls but doesn't drop, it feels like you lose your aileron servo, you can actually move the aileron stick lock to lock and get no reaction. When the ailerons go blank you have to switch over to flying with the rudder, sure a student will think of that. The plane is a nose wheel plane, on grass 90% of you problems will be with the nose wheel. The main gear are aircraft specific, though strong. I like the drag flaps they slow everything down for the student. the fuse is hard to repair due to it's shape. The funny wing attachment actually worked well, IE it popped of without damage.

Get a LT-40 Kadet, convert it to a taildragger, and you have the BEST trainer you can buy or make.

planebuilder66

My Feedback: (8)

Glider is the word, with that said, more wing area will = more lift, power is a means to get you aloft, lift of the wing will get the desired flight performance the plane was intended to do, adding too little a wing will hamper the flight performance. Loft time will be squat unless you lower the all up weight to a reasonable 12:1 or better glide ratio.