"More or less make bottom wing at 0 degrees and top wing just a hair negative" - from Dan's post above
I have read this also, but don't know where. Is this primarily for full scale planes and RC models where upright flight handling, stalling, and landing manners are most important? Would this apply or be relevant to a CL airplane?
Does the hair negative incidence for the top wing translate to just don't have it positive?
I am building a 38Spl and have the wings done and the fuse almost done. I have been planning on aligning everything at zero - zero. Now I am wondering...
The negative incidence concept has been mentioned in earlier posts in this thread above.
Hal deBolt wrote about it in his article on the deBolt Bipe in the July 83 issue of Model Builder. The airplane dates back to the 40's with flat bottom airfoil. Remember, this article discusses his thinking in the design evolution of that airplane over 40 years prior to his MB article. In his article, he wrote:
"The proper use of decalage can enhance longitudinal stability. The law ways that if you fly the forward wing at a higher angle of attack than the aft wing, then the forward wing will stall first, thus the forward wing will lose lift while the aft wing maintains it. In that case the center of lift automatically moves rearward tending to pivot the nose downward at approximately the center of gravity, or control pivot in this case once the nose comes down, the forward wing gets it lift back and you are flying safely once more. ... The Bipe uses two degrees of negative incidence in the rear wing for this purpose."
Now, fast forward to the Dutchess/Dancing Girl/Tiger Rag/Cavalier series of biplanes by Peter Miller. (Dutchess - Aeromodeller, Aug 74; Dancing Girl - Model Airplane News, Feb, 75; Tiger Rag - Model Aviation, Mar 82; Cavalier - Flying Models, Nov, 99) These four designs represent a even longer series of airplanes by Miller. In his two part 1974 article on the Dutchess, Miller does not mention any wing decalage. Then, with his 1975 article on the Dancing Girl, Miller mentions stability problems with all of his previous biplane attempts. He then references the old deBolt Bipe article with "1
o negative incidence on the top wing, so I tried it and the stability problem vanished..." In this article, Miller then explains the evolution from 10% to 18% airfoils with the Cavalier and "Instant success, Cavalier flew the full schedule." In his 1982 article on the Tiger Rag, Miller writes "The layout... seems to be the optimum for this type of model: thick wing section, equal area for both wings (with the thrust line passing just above the center line of the gap between the wings), large stabilizer and elevator with big control deflections -- and no flaps. Light weight is also a critical factor. ... Care must be taken with the lower wing seat to ensure that it sits a 0 degrees incidence." The plans for his Tiger Rag show the top wing to be mounted with "-1
o incidence". Then, in his 1999 Flying Models article on the Cavalier, he summarizes the series by saying his Cavalier proved he had hit the right formula with the 18% section and 1
o negative incidence on the top wing. His article mentions the "vital 1
o negative incidence" in the top wing.
TROSTLE NOTES:
1. I am not sure of the accuracy of the information deBolt provided in his 1983 Model Builder article regarding the negative incidence on the bottom wing. Somehow, deBolt's findings from the 40's was later translated by Miller and others that it is the top wing that is to have negative incidence. (These later developments were prior to the Model Builder deBolt article.) I would certainly go on the series of articles and plans by Miller and use the 1
o negative incidence on the TOP wing.
2. There are several "successful" biplane designs that have been mentioned in this thread, like the Hutchinson Stearman (based on the J.C. Yates design which is very close to scale), Sheeks' Staggerwing (semi-scale), Jim Hunt's TravelAir (scale), Hinton's "59er", Claus Maikis' Duetto, Don Yearout's Biceps, the several Italian and Japanese designs (if plans are available) and on and on. I would recommend as a starting point to use the Miller Cavalier. It is the result of a long evolution of CL biplane stunters. If not just build to his plans, then at least use his layout for proportions, airfoil, and the negative incidence on the top wing. You will also need lightness and power.
Keith
Topic: Precision Aerobatic capable biplane. (Read 19784 times)