Servo for 78" Chipmunk
 

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

RE: Servo for 78" Chipmunk
 

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:D

RE: Servo for 78" Chipmunk
 

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.
http://image.rcuniverse.com/gallery/...s/lg-48842.jpg

Enjoy,

Jim

RE: Servo for 78" Chipmunk
 

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

RE: Servo for 78" Chipmunk
 

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.

RE: Servo for 78" Chipmunk
 

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)

RE: Servo for 78" Chipmunk
 

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.

RE: Servo for 78" Chipmunk
 

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

RE: Servo for 78" Chipmunk
 

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?

RE: Servo for 78" Chipmunk
 

I guess that's why they made throttles:D 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.