The UIUC group issued a report which covered trips. Indeed, some of the
Eppler sections do benefit from being 'tripped'. However, the dimensions
and placement of the trip can significantly affect the result.
Following the earlier Eppler work, the Illinois group (Mike Selig and
his folks) developed a number of airfoils that didn't need require
trips. In many cases, adding trips didn't accomplish much other than a
modest drag penalty. The recent work by Mark Drela is optimized for low
Re applications beyond what was done at Illinois (hope that's not
stepping on any toes but it shows in the X-Foil and wind tunnel results).
So basically many of the sections used today really don't need trips and
may lose some performance with them. But many earlier sections (a number
of the Eppler airofils as well as the old NACA 4 and 5 digit sections)
had better low Re performance (typically, low speeds) with trips.
The specific UIUC reference is Volume 3 of "Summary of Low-Speed
Airfoil Data", chapter 6, originally published in 1997. The reasons for
tripping the airflow are very nicely discussed in this publication as
well. Airfoils that don't manage the laminar to turbulent transition
well are among the ones that may benefit from a physical trip. The E374
was investigated in the subject report and trips had a significant
response. The SD7037 was also investigated and the trip effect was much
less noticeable.
Subject: Tripping modern airfoils, and why do flaps and spoilers do what they
do?
Bob Dodgson tripped his E214-equipped wings to achieve better
performance. I'm not aware of any other sailplane designers who
recommend this. Does anyone today recommend this as a way to improve
airfoil performance? Was it ever a legitimate idea in the first place?
If it's something that actually works, what kinds of airfoils benefit
most from it?
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