ORIGINAL: partisan
Ok... My quickie 500 weighs 3.9 pounds and has a o.s. .46ax. That is a power loading of about 136. I think I can build the smaller one right at 2 pounds. Using a .15 or similar will net around the same power loading.
My plan is to build the frame, making it wide enough for the battery which seems to be the biggest item. After I know how much the frame weighs I can adjust the mAh of the battery to get to 2 pounds.
My next question is if I just scale down the plans, can I skip half the wing ribs to save weight. I can't see needing something like 22 ribs in a 35 inch wing.
Also should I have the plans printed at 70% original so I can copy the stab/rudder design or could I do some math and get it close.
I think a rib every 3 inches gets the job done OK with this size plane. A 70% size copy of your plans ought to give you what you want. If you want speed then figure you don't want the wing any fatter than 3/4 inch, so this makes building the wing more challenging as you go for "thin-ness" Assuming a 7 inch chord, if you really want some speed a 5/8" thick airfoil is more like it.
I've built a P-51 like this with a flat bottom airfoil, full depth hard balsa spar that was built directly over a 1/16" balsa bottom sheet. The wing's leading and trailing edges were slivers of hardwood and the "riblets" were fairly thick balsa scrap. The whole works gets sanded with a "long board" before it gets the 1/16" top sheeting. The idea is to shape / sand what looks like a nice, smooth airfoil that doesn't have any dips or flat spots. The high point of the airfoil [where you place your spar] should be about 2.5 inches from the leading edge.
1/16" balsa is capable of slight compound curvage, but I sheeted the top with 2 seperate pieces. Your Q350 wing will be constant chord, so 1 sheet for the top will work...but it's more hectic to make all those little glue joints in one fell swoop. It's easier I think to sheet the top in 2 seperate operations.
I've found that 350 mah NIMH packs and HS81 servos work well with ".15 size" planes. A 3 oz Hayes tank is a nice size that allows a fairly slim fuselage with some extra space for padding.
Otherwise, a 2 oz Hayes tank will allow you to stuff the battery way up front if you end up with a design that has a short nose. This is a slight "pitfall" with scaling down some designs because the engines get disproportionally lighter as you drop down in size. The tendency is for tail heaviness to creep in.