PROPELLER SELECTION GUIDE
ARTICLES
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This isn't meant to be an authoritative set of rules.  It's just a helpful guide to get you started in the right direction.  These sizes are for glow engines. 

Just remember these simple rules. 

FAST PLANE: Higher pitch, smaller diameter.

SLOW PLANE: Lower pitch, larger diameter.

A large, draggy plane such as an old-timer biplane can't be made faster by choosing a prop for greater speed because of the excessive parasite drag of the plane, so choose the appropriate propeller to let these beauties fly slowly the way they are supposed to.

TWO STROKE PROPELLER GUIDE (original source unknown)
ENGINE SIZE
STARTING PROP
ALTERNATE PROPS
.049
6x3
5.25x4, 5.5x4, 6x3.5, 6x4, 7x3
.10
7x4
7x3, 7x4.5, 7x5
.15
8x4
8x5, 8x6, 9x4
.19 - .25
9x4
8x5, 8x6, 9x5, 10x4
.20 - .30
9x6
9x7, 9.5x6, 10x5,
.35
10x6
9x7, 10x5, 11x4
.40
10x6
9x8, 11x5
.45
10x7
10x6, 11x5, 11x6, 12x4
.50
11x6
10x8, 11x7, 12x4, 12x5
.60
11x7
11x7.5, 11x8, 12x6
.70
12x6
11x8, 12x8, 13x6, 14x4
.78 - .80
13x6
12x8, 14x4, 14x5
.90
14x6
13x8, 15x6, 16x5
1.08
16x6
15x8, 18x5
1.20
16x8
16x10, 18x5, 18x6
1.50
18x6
18x8, 20x6
1.80
18x8
18x10, 20x6, 20x8, 22x6
2.0
20x8
18x10, 20x6, 20x10, 22x6


FOUR STROKE PROPELLER GUIDE (original source unknown)
ENGINE SIZE STARTING PROP ALTERNATE PROPS
.20 - .26
9x6
9x5, 10x4, 10x5
.40
11x6
10x6, 10x7, 11x4, 11x5, 11x7, 12x4, 12x5
.45 - .52
11x7
10x7, 10x8, 11x8, 12x4, 12x5, 12x6
.60 - .70
12x6
11x7, 11x8, 12x8, 13x5, 13x6, 14x5, 14x6
.80
13x6
12x8, 13x8, 14x4, 14x6
.90
14x6
13x6, 14x8, 15x6, 16x6
1.20
16x6
14x8, 15x6, 15x8, 16x8, 17x6, 18x5, 18x6
1.50
18x6
15x6, 15x8, 16x8, 18x6, 18x8, 20x6