Sportflier

I've recently finished a Balsa USA 1/4 scale Cub, 28 cc Ryobi conversion, 17 pounds. This is the first model I've built anywhere near this large. I've test flown it with the standard Futaba S3004 servos (44 in.oz.) but I realize this is not the way to go. What size servos would be more appropriate? How many in.oz.'s if I have one servo for each aileron, one for each half of the elevator, and one for the rudder.
Thanks for any help.

Allan

BJH424

My Feedback: (10)

Allan: I few my 1/4 scale cub for years using Futaba S148's using only one for the elevator. You should be fine!
Brian H.

Wayne22

My Feedback: (2)

I have HS700 series quarter scale servos all round...now, they have the smaller, lighter, and more powerful digital servos out (I probably could have saved a pound or two in wieght!!)

My recommendation is to get the best servos you can afford....you will never be sorry having too much servo, but you will with too little! Keep in mind that Ryobi vibrates quite a bit, and your servos have to live and function in that environment.......

Highflight

My Feedback: (4)

Whip momentum of a control surface can cause considerably higher loads than the control surface experiences in normal flight and can destroy a standard servo with no warning.
For example, if you let the tail drop hard to the ground on landing, the size and weight of the elevator can strip the standard servo gears from whip momentum. I've even seen aileron servos strip out (1/3 scale Cub) when those huge barn door ailerons slammed down on a less than gentle landing.

I always figure that "giant scale rules apply" when installing servos into an aircraft with more than 80" wingspan. It's about that point where control surfaces start getting larger, and it's also at that point where an extra pound of servos doesn't make any appreciable difference to the aircraft because larger airplanes can handle extra weight easily due to their larger flying surfaces.

Besides, there are lots of 80oz+ size servos made that are now available in "standard" size servo cases and weights. There is no excuse at all to NOT use stronger servos in the larger aircraft. I personally consider 80oz. a minimum for any giant control surface, with an 80oz+ on EACH aileron, 80oz + on EACH elevator half, and 120oz+ on the rudder by itself.


Highflight

airbatic

Allan

I too fly my 1/4 Cub with S148 servos. One in each aileron, one for rudder, one for elevator, and one for throttle. I concur with Brian H. You're fine.

Kraus

CK1

My Feedback: (60)

If you can afford it... go with at least 60 in./oz servos , if you cant afford it ...Dont fly a giant scale airplane...

Safety is the issue, would you feel comfortable knowing that a giant scale plane flying over your head has s148 servos in it?
This may work for a few very gentle flyers but the majority of us push our equiptment pretty hard.
Use the best you can afford ,Please!!!!!!

cublover

My Feedback: (47)

ck1,,hehehehehe...good one...sport flyer....you never said if you were going to fly it scale or do 3d with it....LOL...I've been use'n airtronics standard servos for years with no problems...not one wreck with them failing...so for you info...I'm use'n standard

JuniorPilot

i'm going to be using 3004's all round or hitec equivelent

BillPTC

This is an accident waiting to happen. If you have an accident in this modern world of sue happy people you will lose.
As a bear minimum have at least 80oz servos. As inexpensive as they are now a days go for it. Peace of mind is sure nice when you have hundreds of dollars invested and 14 lbs overhead.
Bill

airbatic

BillPTC,

Don't be such a worry wart. These are just wooden models.

Kraus

LuvBipes

My Feedback: (4)

My Sig 1/4 scale Clipped Wing Cub (Saito 150 around 15lbs) has about 100 flights on it over 3 years with ballbearing topped s148 servos on everything except rudder (2 aileron and 2 elevator servos). On rudder I'm using a Hitec 65 oz servo. I fly this thing quite aggressively and have had zero problems up to now. FWIW, a 40 oz servo will produce the same usefull force on a control surface if the control rod is attached to the servo arm 1/2" from center, as a 80 oz servo using a 1" servo arm. If your linkages are solid and control throws moderate (no 3D), than standard servos will work just fine on a big Cub.

Of course, if you can afford stronger, more expensive servos, do it. There is down side other than the $$$ cost. By the way, Futaba is now offering a cheap (around 25 bucks) high torque servo called the 3010.