


There are a ton of scratch build plans available online. You should be able to find some links by searching these forums.
Have you built from schematics/CAD drawings before? I was interested (and still am) in doing a scratch build, but was highly encouraged to build a kit first. Kits come with everything precut, usually by laser, so it's pretty precise. I'm going to do a kit first, then think about a scratch build. 





Quote:
Pick a basic design. For a basic parkflyer, follow these "rules": Distance between motor and leading edge of wing: .75 mean chord length. For example, if your wing is 6" wide, the wing would sit back ~4.5" Wing aspect ratio of ~4:1 to 5:1. Ailerons ~15% of wing area. Stabilizer ~20% of wing area. Elelvator ~35% of Stabilizer. Fuselage length from trailing edge of wing ~1.5 to 2 times chord to middle of elevator. Factor in construction type, weight, wing loading, etc. Start by trying to build from scratch a proven design  say a SS, but with a builtup wing. Then move up the food chain. 






hi,
scroll down on the rcgroups home page! https://www.rcgroups.com/forums/forumdisplay.php?f=136 there's the aircraft modeling science forum. 





Tony, If you can find a copy through one of the S/H bookstores buy a copy of Gordon Whitehead's "Scale Aircraft  Models for everyday flying". Though you are asking about trainers this book covers everything including basic design, airfoils, CG location and construction techniques. Thing to bear in mind is that it was written 26 years ago and for IC power. Nevetheless, it is a first rate overall guide and I still refer to my copy even though I've been building for 50+ years. Good Luck






Another book is "Aircraft Workshop: Learn to Make Models that Fly", by Kelvin Shacklock. There are plans for a good highwing trainer and gives you a list of the materials you will need. He takes you stepbystep through building the plane. This book does goes through some of the basics of model design (not real indepth), but gets you building plans from scratch.






Design Guidelines for Electric Powered Model Aircraft (from Maxcim.com)
Select model and scale (or size). Determine wing area in square feet (span in inches x avg. chord in inches / 144). Work out total weight for desired wing loading: For typical 05 to 40 sized models: Less than 15 oz/sq.ft for a floater 1520 oz/sq.ft for a cabin sport model/trainer 2028 oz/sq.ft for a sport low wing, 30's, warbird, etc. Over 30 oz/sq.ft  You're on your own! Determine power input required: Level Flight: 25 to 30 Watts per pound. ROG off smooth surfaces, reasonable climb: 40 to 50 Watts per pound. (ROG = Rise Off Ground) ROG off grass, Sport Aerobatics: 50 to 60 Watts per pound. Pattern: 70 to 100 Watts per pound. (Note that the actual calculation of these values depend upon the lift and drag coefficients, and so the higher values should be used for draggy airframes.) For a typical current of 25 Amps and a cell voltage of 1 volt per cell, determine the number of cells required (Total Watts divided by 25). Select the MaxNEO motor for the power and number of cells defined. Geared motors will generally give better performance for all but racing applications by allowing the use of a larger diameter, higher pitch, more efficient prop. The maximum airframe weight (including the radio and servos) will be the total weight less the motor/battery/controller (the "motor power system") combined weight. Can you build it that light and still achieve the required strength? Generally, the "motor power system" weight should represent about onehalf of the total flight weight. Determine the approximate stall speed: Stall speed (mph) = 3.7 x sq. root of wing loading (oz/sq.ft) The propeller pitch should give a theoretical "propeller speed" of at least twice the stall speed, and preferably 3 to 4 times the stall speed. The propeller diameter should then be chosen to give the required current draw of about 25 Amps. (The diameter should always exceed the pitch). As a final check, when it is all put together, the measured static thrust should be at least one third of the total model weight. Note that static thrust measurements are only meaningful if the propeller diameter is at least 150% of the pitch (e.g. 12x8). Using the 1700 mAh cells will give a full power duration of around 4 minutes at 25 Amps (1.7 x 60/25). Going back to the power loading required for level flight (section 4 above) then allows estimation of the maximum "cruising" time. Actual flight time will of course be less than this due to the full power used at takeoff. Finally, always use thick multistrand wire (no less than 14 gauge or 2.5 sq. mm), good connectors (e.g. Sermos or Powerpoles) and a high efficiency, high rate speed controller that can handle the required number of cells and current. If you find that you cannot satisfy all of the above rules with some particular model, BEWARE! That first flight could be quite interesting. http://www.charlesriverrc.org/articles_modeldesign.htm 


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