Nurflugelphobia

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Aerowerx

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Fixxed area contributes to stability but movable area does not. Bird's tails are not rigid so can not have a very big affect on stability even when spread open.
I wondered when you would jump in here, Norm.

Good point about moveable tail. Didn't think of that viewpoint, which reinforces the concept of it being a control surface!
 

Aerowerx

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But it has very little sweep...so it might be better than swept pure nurflugel:
Like most things, "it depends". This is not a fair comparison anyway. A transport aircraft needs a fuselage to carry things, and pretty much needs a tail.

And a certain amount of sweep actually helps on a flying wing, but you can also have too much sweep. The optimum seems to be somewhere around 20-30 degrees.

Also, keep in mind that a decent flying wing will have a higher static margin than seen in typical tailled aircraft. As much as 20% in some cases. That is where many people get in trouble. They try moving the CG back to get that "magical" 8-10%, then wonder why they end up looking at the grass from underneath. A high static margin on a flying wing will virtually eliminate the stall-spin, or flip-backwards-then-tumble, problem (not my idea---it is in Nickel's book).
 

henryk

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Like most things, "it depends". This is not a fair comparison anyway. A transport aircraft needs a fuselage to carry things, and pretty much needs a tail.

And a certain amount of sweep actually helps on a flying wing, but you can also have too much sweep. The optimum seems to be somewhere around 20-30 degrees.

Also, keep in mind that a decent flying wing will have a higher static margin than seen in typical tailled aircraft. As much as 20% in some cases. That is where many people get in trouble. They try moving the CG back to get that "magical" 8-10%, then wonder why they end up looking at the grass from underneath. A high static margin on a flying wing will virtually eliminate the stall-spin, or flip-backwards-then-tumble, problem (not my idea---it is in Nickel's book).
"it is in Nickel's book"=

=the only BKB1-A is tumbleresist ! (pp. circa 200...)
 

mcrae0104

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Fixxed area contributes to stability but movable area does not. Bird's tails are not rigid so can not have a very big affect on stability even when spread open.
Thanks for pointing me straight, Norman. (I wouldn't want to be accused of being a bell-shaped denier.)
 

mcrae0104

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All-flying control surfaces or otherwise, presumably this would account for the difference between "stick fixed" and "stick free" NPs.
 

Aerowerx

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How is that applied to an all-flying vertical surface or to stabilators?


BJC
The area still remains fixed in your examples, even if the surface is moving.

Actually, a confusion in terminology I think. What Norm meant by "fixed" is a constant area, not "unmovable". A bird's tail does not have a constant area, but changes with flight mode.

Norm, please correct me if that is not what you meant.
 

Norman

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The area still remains fixed in your examples, even if the surface is moving.

Actually, a confusion in terminology I think. What Norm meant by "fixed" is a constant area, not "unmovable". A bird's tail does not have a constant area, but changes with flight mode.

Norm, please correct me if that is not what you meant.
Actually I did mean "fixed" in the sense of a fixed fin although said fin can be adjustable (such as with a jack screw) as long as it's not free to flop around in the airstream. A stabilator must be aerodynamically balanced on an axis such that a pitch excursion will produce a normal force without much moment around that axis. Theoretically, if balanced properly, a stabilator will not flop around freely in the airstream so it can provide both stability and control.
 
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Norman

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The two terms for stability are Longitudinal and Lateral.


And directional stability.

The vertical fin of a conventional airplane produces a skid/yaw moment ie plane skids left=tail swings the nose left. Swept wings also produce a skid/yaw moment due to the differential drag of the unequally swept wings when the plane is in a skid or crosswind. The nonlinear twist described in Al Bowers' paper enhances the skid/yaw moment due to sweep by tilting the lift vector near the tips forward.
 
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Aerowerx

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...Theoretically, if balanced properly, a staliator will not flop around freely in the airstream so it can provide both stability and control.
Don't they also need an antiservo tab, or the pilots will find it rather disconcerting?
 

pictsidhe

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I wasn't considering the conceptual lifting body designs, which are not yet viable.

Am I forgiven, or do I have to walk on my knees to Reimar Horten's grave?:)
Not yet viable? Stop digging that grave hole! I think not yet extant is more accurate. Wasn't there a funky faceted thing buzzing around some years back? It looked pretty roomy to me.
I 'fess up to my own design dabbling being predicted to fly too much like a turkey for my liking, that doesn't mean that they all will! I know that there are smarter people than me out there working on this.
 

Speedboat100

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Like most things, "it depends". This is not a fair comparison anyway. A transport aircraft needs a fuselage to carry things, and pretty much needs a tail.

And a certain amount of sweep actually helps on a flying wing, but you can also have too much sweep. The optimum seems to be somewhere around 20-30 degrees.

Also, keep in mind that a decent flying wing will have a higher static margin than seen in typical tailled aircraft. As much as 20% in some cases. That is where many people get in trouble. They try moving the CG back to get that "magical" 8-10%, then wonder why they end up looking at the grass from underneath. A high static margin on a flying wing will virtually eliminate the stall-spin, or flip-backwards-then-tumble, problem (not my idea---it is in Nickel's book).
30 deg sweep increases the drag by 20%. Funny that Al says rudder causes 20% drag increase on his videos.
 

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