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-   -   Rounding Landing Gear Edges, Etc. (http://www.rcuniverse.com/forum/aerodynamics-76/63578-rounding-landing-gear-edges-etc.html)

Jazzy 02-26-2002 07:25 PM

Rounding Landing Gear Edges, Etc.
 
Someone told me that if you round the LE of landing gear the aerodynamic properties will increase. I.E. the plane will fly faster.
I also just heard that rounding the TE on control surfaces that otherwise, according to plans, just need the edge taken off will cause flutter at high speeds. Credence to any of this?

Jeff

Mike James 02-26-2002 07:36 PM

Drag
 
Rounding the leading edges of your landing gear (I assume you mean sheet metal type) will reduce the drag. Whether you can actually see the difference or not is hard to predict.

About the sharp trailing edges. Ollie can probably answer this more definitively then me. I've done both sharp and dull trailing edges, and can't say that I've noticed a difference. I'm sure it has a big effect on certain types of planes, at certain speeds.

Ollie 02-26-2002 09:53 PM

Flutter
 
Every control surface and its associated linkages has a natural frequency of vibration. The stiffer and lighter the system, the higher the frequency. When aerodynamic forces produce deflection that also is periodic, the stage is set for flutter. Blunt trailing edges and rounded trailing edges can produce vortex shedding. The frequency of vortex shedding is a function of airspeed. When the natural frequency of vibration of the mechanical system matches the natural frequency of vortex shedding, flutter results. There are other, more common aeroelastic, causes of flutter too.

Use sharp, gradually tapered trailing edges to minimize vortex shedding and reduce weight. Make the mechanical system as light and stiff as you can. This will generally raise the natural frequency of the mechanical system well above the vortex shedding frequency in models. Mass balancing around the hinge line makes the mechanical system aperiodic. Aerodynamic balance (hinging through the aerodynamic center) minimizes the aerodynamic forces.

Jazzy 02-27-2002 04:51 AM

Rounding Landing Gear Edges, Etc.
 
Shoot!
I knew I should have gone further in my college education, (ASME).
I do understand quite well what you are saying and thank you for your insights.

Jeff


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