Hello all
I’ve been toying with the idea of converting a mono into a bi-plane. What do you guys recommend as far as changes? Do I keep the same wing area, and just divide it between the two wings? Or do I need to divide the chord length as well? Will I need to change the fuse length also? Will I need to make other changes as well? Stabilizer incidence, area? Thanks for any help.
Bob J.

Use wings that result in about 1.3 to 1.5 times the area of the single wing. Doing it that way means that the model will fly about the same for the same weight. The interference between the wings results in some minor losses in overall lifting efficiency. Adding a bit of area compensates for that. Also the closer you can keep the interwing gap to one wing chord or more the better. Again the interference grows the closer the wings are together in terms of chord length.

There's no real hard and fast rules and there's fine examples of oddities but if you stick to these guidlines your chances of an all around better model will be higher.

The simplest way to convert a low-wing monoplane to a bipe is simply to slap on an additional wing of the same dimensions. A friend did this with a Sig Four Star, and the result was a sweet flying, fully aerobatic bipe, powered by a sport .61. It is essential, however, to double the area of the tail feathers. The vertical tail area should be at least doubled, since bipes wings and cabane struts dirty up the air flowing over the tail. I recommend a vertical tail (fin and rudder) with total area of at least 15% of the combined wing area. I don't recommend clipping the wings at all.

Another friend clipped the wings quite a bit of Four Star bipe conversion, and his airplane was not a friendly flyer at all, even with a .91 up front. This was largely due to the effect of mutual wing interference, which lowers the effective aspect ratio. A biplane wing of aspect ratio 5 will have a monoplane equivalent aspect ratio of about 3.5, which means - a whopping increase in induced drag.

Bruce, Rotaryphile
Thank you for the info. I didn’t want to jump into this project completely blind. I want to learn more about model design and aerodynamics, and thought this would be a good first step. (Making a change to an existing design.) Think I’m going to give this a try. Thanks for the help.
Bob J.

I did it with my Hangar 9 Twist. Throughout the previous 10 pages or so, you can find pics of how I did. I've only gotten two flights out of it but so far, it is pretty nice. The wing area is tremendous (1400sq inches and under seven pounds) and although the CG was WAY off, it seemed to fly pretty well. It needs some tweeking, but I think it will fly nice in the end. http://www.rcuniverse.com/forum/m_51...page_65/tm.htm

Sachin

Sachin
Thank you for your reply. This is exactly the type of thing I had in mind. I read through the thread, and picked up a few more tips. Thanks!


BobJ.