
Oct 03, 2006, 03:30 PM  

Looking at your photos, you might need to reconsider the size of the model if you intend on having 250 Sq. In. of wing area. It would appear that the root chord of the wing appears to be about 50% of the fuselage length and the tip chord looks to be about 30% of the fuselage length.
In the top view, the wingspan looks to be just a little over 50% of the length. Here is a site I found from Wikipedia that has info on the Viper craft. Viper info on Wikipedia They have info on 2 models, the Mark II and the Mark VII. The one you have pictured in your post is the original Mark II. According to the specs provided, the Mark II has an overall length of 8.4 meters (27.6 feet) and a wingspan of 4.7 meters (15.4 feet) with a height of 2.7 meters (8.9 feet). So using these numbers, I get a wingspan of 56% of the fuselage length. I measured a side view photo of the Mark II if I got a 50% fuse length root chord and 30% tip chord. With these numbers, I can calculate the Wing area to fuselage length ratio, and solve the equations for fuselage length given a 250 Sq. In. wing area. Without boring you with the math, if you keep the same proportions as the original, the wing area (in Sq. In.) is equal to the fuselage length squared (In inches) divided by 4.545. Conversely, if you know the wing area, and want to find the fuselage length then the length is equal to the square root of the length x 4.545 Fo example, a Viper 10" long would have a wing area equal to (10x10)/4.545 or 22 square inches. One that is 29" long (your proposed size) would have a wing area equal to (29x29)/4.545 or 185 square inches. Using the other formula, to solve for fuselage length based on a known wing area, the fuselage length would be equal to the square root of (250 x 4.545) or the SqRt of 1136.25 which is 33.7 inches long. If you plan on cheating the scale outlines a little bit, and increase the wingspan slightly, you could acheive your desired 250 Sq. In. of wing area with a 29" long fuselage. At true scale, a Viper with a 29" fuselage would have a wingspan of 16.24", a root chord of 14.5" and a tip chord of 8.7 inches. If you stretched the wingspan to 21.5", and left the root and tip chords the same, then the wing would have 249.4 square inches of wing area. How does that sound to you? Lucien 
Nov 15, 2006, 11:18 PM  

Great
That's just great, I want to build one of those Vipers when I get a chance if you decide to post the plans, maybe if you lose some anhedral and get the right CG it will fly fine.
I too did something based on the Viper, it's a mix between the Viper and a conventional jet, the result is this: http://www.rcgroups.com/forums/showthread.php?t=582634 She flies great and it's very stable. regards! JR 
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