posted 01-26- 01:06 PM               

Ok, go here: http://www.monmouth.com/~jsd/how/htm/title.html#mytoc

This is a great site! Here are some relevant comments from the site. I was 1/2 correct about adverse yaw - some adverse yaw does come from extra drag on the lifting wing in a turn - unless there is aileron differential. The other 1/2 has to do with the fact the the aileron movement forces a new AOA on the wing - the outer wing gets more AOA causing the lift vector to tip back - contributing to advers yaw as well. The lower wings reduced AOA pushes the lift vector forward furthermore contributing to adverse yaw.

Quotes:

...As you can see in the figure, the force vector for the downgoing wing is twisted forward, while the force vector for the upgoing wing is twisted rearward. This pair of fore-and-aft force components creates a torque around the yaw axis. You need to deflect the rudder to compensate.

Some people try to argue that these force-components should be called "drag" forces since they are directed fore and aft, in the same direction as the overall relative wind. However, it is much better to think of them as components of the local lift, since the twisted lift remains perpendicular to the local relative wind. The strongest argument is this: a drag force should dissipate energy in proportion to force times airspeed, but it is clear that the twisted lift forces do not dissipate energy. 10

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Here's another trick, which you may have noticed on many airplanes: when one aileron goes down a little, the other one goes up a lot. (This is called differential aileron deflection .) The designers were trying to arrange for the upward-deflected aileron to generate a lot of parasite drag. If they do it just right, the drag force is just enough to provide the needed yaw-axis acceleration during a steady roll. The so-called Frise aileron is similar, but it has lip that sticks down into the airstream when the main part of the aileron is deflected up. Again, the purpose of the lip is to generate drag on the wing with the upward-deflected aileron.

I would guess that adverse yaw is too detailed to be modeled in SDOE. The lift vector would need to be based on a virtual wing angle that conciders induced AOA due to aileron deflection into account - so the lift force would not always be perpindicular to the physical wing. As suggested above, the wing with downward aileron (the upward moving wing in the roll) would have the lift vector tilting backward - causing a yaw tourque in an opposite direction of the turn.

My RC gliders all use the "differential aileron deflection" trick. I always thought this was to maximize roll rate with the least drag (roll rate to drag ratio? heheh)

Whew...

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-Sv =FC=

WWI in SDOE!

posted 01-26- 01:12 PM               

Quote:

My friend Larry has a sailboat. It doesn't have ailerons. You steer it with the rudder. 15 This changes the direction the boat is pointing. As shown in figure 8.11, this causes the water to flow crosswise past the hull, creating a sideways force that eventually changes the direction the boat is going.

All the same words. can be applied to an airplane. Keeping the wings level, you press the right rudder pedal. This causes the airplane to yaw to starboard. As shown in figure 8.12, air will then hit the fuselage on the port side, creating a sideways force 16 that will gradually shove the airplane around in a right-hand turn. (There will also be a lot of drag, but that is not our concern at the moment.) The force of the wind on the rudder (needed to yaw the plane) is smaller than, and in the opposite direction to, the resulting force of the wind on the fuselage.

In powered flight, the horizontal component of thrust will make an additional contribution to the boat turn.

To reiterate: the airplane will turn to the right if you hold the right rudder pedal down — even if the wings are not banked. Of course, turning the airplane properly (using the wings) is ten times more effective and more efficient than a boat turn.

So all we need is an airfoil for the fuse! Will this work? Let's try it!!! I am thinking we need a semetric airfiol - I bet the fin or hor. stab airfoils are symetrical. Then we just need to set the airpoint correctly. This will be interesting...

posted 01-26- 01:34 PM               

Man it is so sad that you are talking to yourself here.. (not a joke but really where is everyone else)

Anyway thats sounding pretty damn interesting. We need this even not for proper rudder but just cause every damn part of the airplane creats drag and life in real life and so it should in the game.

posted 01-26- 01:36 PM               

Oh yeah keep up the good work man you are doing some great stuff and always breaking some new ground.

posted 01-26- 01:43 PM               

Hey SV it seems you know a lot about airfoils and FM programming - maybe you could put you knowledge in a fine doc (or exists it already?)

posted 01-26- 02:05 PM               

I hope someone is documenting all this great stuff we are getting to add to the ops documents.

posted 01-26- 02:25 PM               

I think the trick will be positioning the new airfoil near the CG - that way it will not affect the yaw like the fin does. Also it would be nice to really boost the drag coef for this airfoil, as stated above - this fuselege drag should be high. This new airfoil should also allow for a real skidding decsent - what is called when you do that? When you give full rudder and opposite aileron to bleed alt fast on landing without increasing airspeed... When you fly in the biplane at Rhinebeck he really pushes the plane over - it feels like 45 degrees LOL - my favorite part of the flight - almsost brushes the trees on the way down to the narrow field - like a field goal!

I need to find my old de-bug version of SDOE - the one that shows you the force vectors. Is this in the currect SDOE beta? It should be

posted 01-26- 02:45 PM               

I would leave the cylinder there for basic frontal drag - and add a fin at CG that would have a real symetrical airfoil that would generate a lift force at sideways AOAs. With 0 AOA there would be no lift and no drag. At lease this is the theory

-Sv

posted 01-26- 08:48 PM               

The new airfoil I added represents the sides of the fuse - especialy the broad flat sides that WWI planes tend to have.

I still need to experiment with surface area, and exact airpoint location. Right now it is at the CG giving it the most dramatic turn rate - I suppose it should be back somewhat at the theoretical center of lift for the fuse. More experimenting to come, but right now I am too excited!