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Plain vs. split flaps

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addaon

Well-Known Member
Supporting Member
Joined
Feb 24, 2008
Messages
3,976
Location
Kanab, UT
I've been thinking about split flaps vs. plain flaps for my flying wing design. I haven't been able to get enough information about split flaps to make a sane decision. Thoughts?

Pro-plain flaps:
• Well-understood
• Moment easiest to estimate (for pitch-neutral flap application)
•*Quite effective
• Low drag at moderate deflections, so usable for takeoff (reducing ground angle)
•*Max lift at sane (45° or so) deflections

Anti-plain flaps:
• Another complete airfoil to build

Pro-split flaps:
•*Lower moment, allowing slightly bigger flaps (but estimates are hard to come by)
•*Higher max lift for landing
•*Lower moment (according to Raymer; can this be confirmed?)
•*Lower drag for a given lift (I find this really hard to believe... confirmation?)
•*Potentially easier to construct (pre-made sandwich surface?)
•*Volume above split flap is small but useful (fuel lines from tanks to engine without going through fuselage, etc)
• Gain effectiveness with thicker airfoils, like the ones being used

Anti-split flaps:
• Max lift at insane (60° or so) deflections
•*Higher drag? Maybe? Maybe not?
• No way to balance surface... ridiculous actuators needed? Flutter concerns?
• I'd imagine much dirtier air behind them than plain flaps... pusher prop efficiency? Prop fatigue?
 
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