Since you guys are the experts using this engine I thought yall might have the most insite into the problem. I just purchased a TOC Chipmunk & I am going to put a Ryobi 31cc on it. I have several new Hitec HS425BB servos but I'm not sure if they are up to the task. The wing also has flaps so there will be 4 servos on the wing, the elevator is dual servo, & the rudder is pull-pull. I will only be flying this for sport flying so I was thinking I would be fine with a sport servo. If I need hi torque servos, what about the JR-Sport ST125MG servo. My radio is a JR 6102. Another possible servo would be the Hitec HS-475HB. I like the Hitec prices. Let me know what you think. $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$[:@]

Plane Stats.

Wingspan: 78"
Length: 66"
Flying Weight: 10.5lbs
Wing Area: 1054sq in
Engine Size: 1.20

The rule of thumb is "1 oz of torque per sq inch of area" of moving surface that means elevators, ailerons, rudder or flaps; so you'll need to do some calculations

My plane (Bridie Stick) with a Homelight 30 has two 422's on the elevator and one on the rudder.

The rest of the servos are Futaba 3004's

I'm just a sport flyer. Plane seems to do just fine.


Enjoy,

Jim

Do you have a larger picture of your Bridie Stick?
I'd like to see it.

I also have a Robinhood 80 with all standard servos with just one on the elevator. But it has a OS 91 Surpass glow engine.

The Chipmunk is supposed to be delivered Monday. With four servos for the wing, two for the elevator, & pull-pull on the rudder, I'm not sure what to do. Since I started this post I've done some more research & the HS-475 looks pretty good also. I have four 425's already so regardless I have to buy 4 more servos. Decisions, decisions, Decisions.

HS-425-SPECS:
SPECS: Length: 41mm (1.6") Weight: 45.5grams (1.60 oz)
Width: 20mm (0.8") Transit Time: 0.20sec
Height: 36.5mm (1.4") Torque: 43.4 oz-in





HS-475-SPECS: Speed: 0.23 sec/60 degrees at 4.8V
Torque: 4.4 kg-cm (61 oz-in) at 4.8V
Length: 38.8mm (1.52")
Width: 19.8mm (0.77")
Height: 36.0mm (1.41")
Weight: 40g (1.41oz)

I have a SR. Kadet 76" wing span and 16.5" chord on Floats.

Would you think it would be big enough for gas conversion?

It came with futaba 3003 servos.

That plane is designed for a .40 2 stroke glow engine. There is not a gas engine out there for a 40 size plane.
KADET SENIOR
Wingspan: 78 in (1981 mm)
Wing Area: 1150 in² (74.2 dm²)
Weight: 6 lbs (2720 g)
Length: 62 in (1575 mm)
Radio Required: 3 Channels, 3 Servos
Engine Required:
.29-.40 in³ (4.8 - 6.5 cm³) 2-Stroke Glow
.35-.45 in³ (5.7 - 7.4 cm³) 4-Stroke Glow

Everyone is talking about +1000 sq.in. for a small gasser.

This is a slow flyer, over 1000sq. in. wing.
Push the nose back a bit to help balance it, reinforce the firewall and fly it scale.
A Toro weighs about 2 pounds ready to go.

It should lift the plane off the water pretty easily.

Why not?

I guess that's why they made throttles Make sure you have enough prop clearance. You'll be going up about 6" on diam.(From around a 10x6 to at least a 16" prop.