Turbulate or D box?

[sleepy gomez]

As my mind wanders about thoughts on FF power: Do the turbulator spars often found on these planes offer more efficiency than a D box with smooth LE ? In other words, do the turbulator spars do little more than keep the airfoil shape so the covering does not sag between ribs. Your thoughts would be appreciated. SLEEPY

[danberry]

The D-Box is for torsional rigidity.

[sleepy gomez]

I understand the D box is for  rigidity. My Question is in regards to the smooth LE surface of a D box TYPE of surface versas the multi "turbulator" spar type LE . If you had a D box wing would you add turbulator "threads" to it.

[Tmat]

It depends on the airfoil used and the size/weight on the model (Reynolds number). Some airfoils would benefit from turbulators, and some might not need any.

Tmat

[danberry]

I understand the D box is for  rigidity. My Question is in regards to the smooth LE surface of a D box TYPE of surface versas the multi "turbulator" spar type LE . If you had a D box wing would you add turbulator "threads" to it.

I don't.
I have done it but I don't notice a benefit.

[Yak 52]

It also depends where you want the benefit within the flight envelope. A smooth sheeted d-box and an accurate airfoil will probably improve high speed (ie penetrating or fast launch) but turbulating stringers may improve sink rate in the glide. This is definitely a noticeable effect on handlaunch gliders when I've added a strip turbulator.

Are we assuming equal weight for each? Obviously the lighter construction would have a better sink rate too.