I am thinking of blowing up the Dolphin for the LA 46 ... from 510 sqs and 49" ws by say 15% and that would make the wing area about 586 with a ws of about 56" ... what happens with this plane as you go up in percentage is the wing length starts to not match the area.. @ 18% the area becomes about 600sq and the ws is about 58" IMO the wing area should be in the 640 to 680 range... also 3 " flaps become 3.5"... everything becomes relative.
You have made some good points. However, the above is incorrect. While it is true that increasing the 49" span by 15% will make it about 56", the area will increase from 510 sq in to 674 1/2 sq in, rather than 586. Area increases as the square of the dimension. So your new area is 1.15 x 1.15 x 510 sq in = 1.3225 x 510 sq in = 674.475 sq in. Likewise, increasing the plan size by 18% will give you 39% more area, or about 710 sq in. These are pretty big planes for an LA .46.
You're right about scaling large amounts though. If you don't scale the circle, speeds, and turn radii to match, things aren't as likely to work the same. Scaling weights and power" (in the real sense) are not the same (e.g. material thicknesses that don't scale, and scale weights give different wing loadings, etc.) and cannot generally be scaled to match scaling of other effects and dimensions => compromise. The "best" proportions for a a .15-powered stunter are not likely to be the very "best" for a .60-powered one. If a large change in size is for the fun of flying a given design at a new size, I'd probably look at successful stunters of the new (Edit: engine) size and scale to create equal wing areas, as long as both are flapped or both are flapless. That means that your scale factor will be the square root of the ratio of the new area to the old area.
For instance, for the example above, if you have chosen to increase the area from 510 sq in to 586 sq in, then the scale factor will be the square root of (586/510) = square root of 1.149 = 1.072. Tell the copier to make a 107.2% copy or an incrase of 7.2% in linear size.
Note that if your copier cannot go to the tenth of a percent, you're stuck with 584 (with 1.07 scale factor) or 595 sq in (1.08 scale factor), plus or minus their own error. I've had people who could adjust their sizes by the 0.1 % incriments and correct to my pocket-calculator suggestions as well as those whose equipment couldn't do that, or as Keith mentioned, couldn't adjust lenght and height to match. Some really aren't competent either. So, results vary.
I don't know whether much has been said previously here on this topic, but a SSW Forum search will probably find many threads of interest. Searches in both places might prove useful.
SK
Topic: Expanding plans (Read 6777 times)