Lift-Roll Spreadsheet - Clarify "Twist"  
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Lift-Roll Spreadsheet - Clarify "Twist" - 11/1/2005 7:05:47 PM   
wildblueyawner


 

Posts: 197
Joined: 2/16/2002
From: Covina, CA,
Status: offline 		In Lift-Roll, "twist" (washout) is defined as the "angle of attack relative to the root."

Is this twist with respect to the root of the wing or to the root of each panel?

Consider a 4-panel wing: If twist is with respect to the root of each panel, then twist would be entered as 1 degree for each panel. If twist is with respect to the root of the wing, then twist would be entered as 1, 2, 3, and 4 degrees from root to tip.

Appreciate any clarification.
       Post #: 1

RE: Lift-Roll Spreadsheet - Clarify "Twist" - 11/1/2005 7:24:14 PM   
Dr1Driver



Posts: 3589
Joined: 7/25/2002
From: Spartanburg, SC, USA
Status: offline 		Sure. The "twist" should be constant and smooth along the span from root to tip. Simply turning the tip LE down will not create the desired washout effect. Take a wing you already have. Hold the root and tip and twist the tip LE down about 2 degrees. That is proper washout. Sig, among others, often uses building tabs on the ribs to easily create this "twist".

Dr.1

_____________________________

There's a Hun in the sun!

(in reply to wildblueyawner)
       Post #: 2

RE: Lift-Roll Spreadsheet - Clarify "Twist" - 11/2/2005 12:09:18 AM   
wildblueyawner


 

Posts: 197
Joined: 2/16/2002
From: Covina, CA,
Status: offline
quote:

Sure. The "twist" should be constant and smooth along the span from root to tip. Simply turning the tip LE down will not create the desired washout effect. Take a wing you already have. Hold the root and tip and twist the tip LE down about 2 degrees. That is proper washout.
To the contrary, washout can be along the entire span or any outer portion of the span, and it can vary linearly or non-linearly, the latter we don't see on models due to construction difficulties with built-ups, and the inability to cut spanwise non-linear features in foam cores.

For gliders at least (my situation), aerodynamic efficiency is a high priority, therefore the amount of washout that works for one aircraft can't be applied to another w/o consideration of wing planform and airfoil transitions that can also provide aerodynamic (non-physical) washout...... all of which have a combined effect on tip-stall behavior, the wing's lift distribution, and its tendency for high-speed flutter.

Got the answer to the twist vs root of wing or panel issue. I got careless and simply glossed over it - It says right there on the LiftRoll webpage that "Twist is the change in AOA of a panel from one end to the other"

(in reply to Dr1Driver)
       Post #: 3

RE: Lift-Roll Spreadsheet - Clarify "Twist" - 11/2/2005 11:30:31 AM   
Dr1Driver



Posts: 3589
Joined: 7/25/2002
From: Spartanburg, SC, USA
Status: offline 		Washout on just the outer portion of the wing (how much of the wing is "outer portion"?) wouldn't be as effective as if it's along the whole wing. As for cutting a "twist" into foam cores, it's dead simple. Just block up the TE of the tip template.

It says right there on the LiftRoll webpage that "Twist is the change in AOA of a panel from one end to the other
Ah...I believe that's what I said.

Dr.1

_____________________________

There's a Hun in the sun!

(in reply to wildblueyawner)
       Post #: 4

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