Servo torque question II
 

A couple of days ago I asked a question on the flap servo for my Byron AT6. My linkage binding problem was solved through excellent suggestions by forum members. However, one member questioned whether I had sufficient torque for the size of flaps. Checking the instructions, Byron doesn't specify a particular size of flap servo, other than to suggest a heavy duty servo. Other control surface servos are suggested to be a minimum of 48 oz/in. All of mine are the Futaba 89 oz/in size.
The AT6 has a three section flap driven by one center mounted servo, which is a Futaba analog @ 89 oz/in size. The total flap size is 60" in width by 3". Any thoughts on what torque rating I should be looking at. I have yet to fly this plane, so I don't have any flap operational experience.

RE: Servo torque question II
 

That would be me..................:)

First question, is this the giant scale Byron AT-6 with the 101 inch wingspan? If so I find it hard to believe that "other control surfaces" only have a minimum of 48 oz/in. As a large model aircraft inspector that sets off many alarms under my cap.

One of the go to formulas in the AMA 520-a booklet for the LMA program is.............

The minimum torque requirement formula a conventional control surface is calculated as follows.

Minimum torque = A *Chord *Span * Chord/3 * Servo Arm/Control Arm

A = Airspeed factor (see Table 1)
Chord = average control surface chord (root chord + tip chord) / 2
Span = control surface span
Servo Arm: the distance from the center of the servo arm to the control linkage attachment.
Control Arm: the distance from the hinge line to the control linkage attachment

Table 1 states that a Propeller aircraft whose flight regime includes modest aerobatics, including loops, rolls, inverted flight and spins has an airspeed factor of 1.5.

Plugging in all of your information, if you use a 1 inch servo control arm and the control horn is 1.5 inches into the flap, would be (1.5 * 3 * 60 * 1 * (1/1.5) = 180 oz/in) .................. just a slight bit more than the 89 oz/in Futaba servo you currently have.

If it were me I would double check the surfaces in conjunction with the LMA formula and install servos accordingly. My KMP AT-6 recommends a minimum of 100 oz/in servos on the control surfaces .......... and it's wingspan is only 87".

I realize that the Byron At-6 is not over 55 pounds so servos of slightly less torque could be used. But with the availability of high torque servos being what it is these days (and not breaking the bank) why take the chance?

Cheers

RE: Servo torque question II
 

The size of the flap servo.....ok look at it this way....if the servo you have is too weak then you won't be able to either put the flaps down or keep them down.....so put a load on the flaps with your finger once they're down and see if you can push them back up...
When it comes to servos always buy a bigger servo....My standard servo any more is a HiTech 5645.....Why...because you rarely go down in aircraft size....if you do then you have a servo that will work....ok if you go bigger then you probably have a servo that will work unless you're into giant scale.....
Did you plan on using a 6V battery?

RE: Servo torque question II
 

One thing to remember, is that most of the Byron planes were designed in a time when none of todays high torqure servos were around. About the strongest at the time was a Kraft servo, which Byron used in most of their planes, and it wqas only 45-48 oz-in in torque. This was the servo they recommended. I had at least 6-7 Byron planes, all using Kraft 45 oz-in servos, and never had any issues with not enough servo torque. BTW, these servos were plastic geared, and we ususally only used 1 on each function. I guess we just didn't know as much then as we do now.

RE: Servo torque question II
 

On-line servo torque calculator:

http://www.mnbigbirds.com/Servo%20To...0Caculator.htm

According to that calculator, that servo will allow a max deflection of 45 degrees at landing speeds.

Some good reading about the use of flaps:

http://www.modelairplanenews.com/Med...ager/flaps.pdf

RE: Servo torque question II
 

I like that on line servo calculator ............... enough to bookmark the site ...........:)

Good article on flaps as well....

There are also many other tools available. A search for Excel spreadsheets will give some interesting information for those that are really into the deep equations of this subject.

RE: Servo torque question II
 

Thanks to all for their input.

RE: Servo torque question II
 

Those Byron planes were way way ahead of their time. It amazes me how many are still flying. Bob