### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### blane.c

##### Well-Known Member
Model.

If you figure MAC for the normal bi-plane and both wings the same size and CL 25% of MAC, it is 75% of MAC of the forward wing. But considering that the total of both wings has 15% more lift than normal monoplane wing of same area then forward wing has 30% more lift than the rear wing if both are the same size? So adjusting the CL to compensate for the difference in lift must be quite an interesting equation?

And angle of incidence, that is just a big question mark.

#### Magisterol

##### Well-Known Member

View attachment 119961
Looking at the article, not a single formula. Just theory. In the end it is trial and error. Don’t expect performance from trial and error designs. You can make them work, but for less performance than a proven design. I am assuming this is the reasons 99% of the airplanes are monoplane, tail in the rear designs.

#### AeroER

##### Well-Known Member
I am still looking for the original Nenadović thesis from his graduate work in France the 1930s. The contemporary reporting about it in France at that time suggested that the right combination of slotted wing was actually *more efficient than the equivalent monoplane* (presumably equivalent in overall span and area). If anyone has access to online technical research tools and can pull up a PDF of the original, I’d be very grateful.

“Recherches sur les cellules biplanes rigides d'envergure infinie”
Author: Miroslav Nenadović; Université de Paris
Publisher: Paris, E. Blondel la Rougery, 1936
Dissertation: doctoral Université de Paris 1936
For similar work, hunt down papers authored or coauthored by Bruce Selberg at the University of Missouri-Rolla in the 70's and 80's.

His grad students did a pile of work on the topic. I recall that Selberg patented a biplane rotor for helicopters. I wrote a vortex lattice program in 82-83 to analyze multiple wings in essentially any stack or stagger as a independent study. I probably still have a copy of the paper, but it would need to be rewritten before I would show off the work.

#### blane.c

##### Well-Known Member

View attachment 119961
Yes I have seen and read this information before, and now again. It is important to note additional information contributed by cluttenfred who began this thread and other contributions. One parameter to meet is the trailing wing is one span behind the first "or" at least for me more clearly the leading edge of the trailing wing is in vertical plane with the trailing edge of the leading wing, in the pictures this seems to be the case of the airplane. Another parameter is that the gap should be 1/3 the span ... this is not clearly the case in the pictures, the gap appears to be greater than 1/3? So one would expect inferior results from the pictured aircraft based on the premise that the gap is greater than 1/3 the span. In the drawing aircraft we can see that the gap is 1/3 the span and that because of wing taper the wings have dihedral in order to maintain that gap, also the upper/higher wing has less dihedral than the bottom/lower wing so as that the average dihedral is "normal". Clearly this idea has been well thought out if you pay attention to detail. The Starck aircraft seem to follow these guidelines/rules and seem to perform admirably considering the power supplied.

It seems to me that some good work has gone into this Nenadovic' wing since before I was born and bringing it to light nearly 100 years since it's inception could be enlightening. Many could benefit.

#### blane.c

##### Well-Known Member
For similar work, hunt down papers authored or coauthored by Bruce Selberg at the University of Missouri-Rolla in the 70's and 80's.

His grad students did a pile of work on the topic. I recall that Selberg patented a biplane rotor for helicopters. I wrote a vortex lattice program in 82-83 to analyze multiple wings in essentially any stack or stagger as a independent study. I probably still have a copy of the paper, but it would need to be rewritten before I would show off the work.
I would find that interesting.

Starck 20