340cudaman

I have the E-Flite 68" DHC2 Beaver and want to use a 3 Bladed Prop. The 1 in the photo is a 10-6, the blades are 2 3/4" past the cowling.
What is the rule of thumb for prop size. I haven't built this type of aircraft before with so much frontal area. Would the 11-6 be the right size?

Thank you in advance.

skylark-flier

First, let me say I know little or nothing about ELECTRIC powering of planes. However, with 50+ years experience with glow engines - the rule of thumb there is to subtract 1" if going from 2-blade to 3-blade, add an inch if going the other way.

On all my planes, control-line, radio, whichever, if I'm running a .45 engine (depending on just which one) I might use a 11" 2-blade prop but to go to 3-blade I'd have to use a 10" prop.

Your DHC2's original specs are:

[TABLE="width: 99%"]
[TR]
[TD]Wingspan:
[/TD]
[TD]68 in (1735mm)
[/TD]
[/TR]
[TR]
[TD]Overall Length:
[/TD]
[TD]43 in (1090mm)
[/TD]
[/TR]
[TR]
[TD]Wing Area:
[/TD]
[TD]565 sq in (36.4 sq dm)
[/TD]
[/TR]
[TR]
[TD]Flying Weight:
[/TD]
[TD]4.9–6.2 lb (2.2–2.8 kg)
[/TD]
[/TR]
[TR]
[TD]Motor Size:
[/TD]
[TD]Power 25 or Power 32
[/TD]
[/TR]
[TR]
[TD]Radio:
[/TD]
[TD]6+ channels with 6 mini servos
[/TD]
[/TR]
[TR]
[TD]Servos:
[/TD]
[TD](6) JR SPORT™ MN-48
[/TD]
[/TR]
[TR]
[TD]Trim Scheme Colors:
[/TD]
[TD]UltraCote® White (HANU870); Dark Red (HANU871); Gold (HANU879)
[/TD]
[/TR]
[TR]
[TD]Prop Size:
[/TD]
[TD]APC 12x8E
[/TD]
[/TR]
[TR]
[TD]Hardware Included:
[/TD]
[TD]Yes
[/TD]
[/TR]
[TR]
[TD]Speed Control :
[/TD]
[TD]60 amps
[/TD]
[/TR]
[TR]
[TD]Recommended Battery:
[/TD]
[TD]3S 11.1V 3200mAh Li-Po
[/TD]
[/TR]
[TR]
[TD]Flaps:
[/TD]
[TD]Yes, prehinged
[/TD]
[/TR]
[TR]
[TD]Approx. Flying Duration:
[/TD]
[TD]10 minutes
[/TD]
[/TR]
[/TABLE]

Seeing the original 12x8 prop, if you can find an ELECTRIC 3-blade prop that's 11x7 or 11x8 you should be just fine, at least as far as the motor is concerned. Whether there's enough hanging out beyond the cowl is another matter entirely. A case in point, when I powered my Great Lakes biplane I had to go from a .45 engine to a .60 in order to turn a prop that was long enough to get past all the front end. You might consider staying with that 12", maybe going to a 3-blade at 12" and getting a larger motor to turn it.

Just a thought.

Charlie P.

Drop down 1" in dia. from the two-blade reconnemded prop.