RC_MAN

My Feedback: (11)

For the life of me I don't understand why most manufacturers spend time to get pannel lines, cockpits etc right and then slap on a basic exposed servo & pushrod. I would gladly spend the extra few dollars to have a scale plane that does not loo like a toy.

Any ideas besides possible flutter prevention?

Thanks

Peter D.

rhklenke

My Feedback: (24)

You've got the main reason right there. Developing a hidden linkage that could take the power of a JR 8711 and apply it effectively (i.e., strong enough and slop-free) to a surface like an aileron is not a trivial, or inexpensive, task. Using a servo arm and horn is a proven, robust, inexpensive, and light way to transfer the torque from servo to surface...

Bob

Guillermo Ibanez

My Feedback: (1)

For some jets like the F-16 that has only ailerons, I think that a torque rod can be used. A rod embeded into the aileron with two or three arms inside the aileron and with the conecting arm to the servo, hidden inside the fuse (just like elevators mechanics is designed). I think that for rudder can be done the same. Just my opinion

BRG

DelGatoGrande

My Feedback: (23)

because this way we increase the distance from the hinge so the torque

find more about torque nature here:

http://en.wikipedia.org/wiki/Torque

my 2c

olnico

Well I am a big supporter of half hidden linkages.



Most companies don't offer them because they don't know how to compute them and it is then too risky for their business.

I've made a series of threads on how to design proper control surfaces for jets. I clearly recommend half hidden linkages there for scale and geometry reasons.
If the design is done correctly ( power requirements ) there is no risk of flutter with these linkages and the mechanical advantage is maximized.
Have a look here:
http://www.rcuniverse.com/forum/m_92...tm.htm#9266994

and here:
http://www.rcuniverse.com/forum/m_92...tm.htm#9272010

olnico

Note that we cannot talk about hidden linkages on jet models ( when the servos are in the flying surfaces ) because the speed and power requirements involved dictate for long control horn.
A typical value on a 1/6 th scale plane is a 1,5 cm/0,6 inch control arm.
So the control side of the linkage has to stick outside on non torque rod actuated surfaces.
Once again, please refer to the links above to see how to compute such requirements...

rhklenke

My Feedback: (24)

Possibly. You do have to realize though that for elevator surfaces, typically a large diameter troque rod - that is necessary to resist twisting - can be used. For ailerons, which are usually much thinner, the torque rod has to be smaller in diameter, and thus is more succeptable to slop due to the twisting in the torque rod itself.

The main reason, as Oliver reiterated, is that you need the lever arm to handle the torque from the servo to the surface...

Bob

Boomerang1

Nice job Oli, that's how I like to do them if possible.

What's the point of spending 200 bucks on a servo if you can't show it off to anyone. How can anyone say wow, you are the man, got the new brushless, digital, hi torque, high voltage, unobtainium gear, 9 ball bearing super servo if it's neatly hidden away?

That's why the inside of most jets look like a display stand from Festo, it's 99% about the show.

Mine, on the other hand, look like a garage sale! - John.

as722

My Feedback: (1)

They are toys.

drdoom

My Feedback: (9)

You said it your self flutter. 10 to 30 grand no flutter,good.
10 to 30 grand flutter, Bad...real bad.

Ron Stahl

My Feedback: (12)

One of the local guys here built a F-16 a years ago and inststed it have all internal linkages. which I warned him against. Every time we flew it it had rudder and or aileron flutter at high speed until we moved the linkage to a std R/C style exposed setup. He didn't belive me when I calculated the required torque at over 300 in/oz to move the rudder 10 degrees and hold it there at 180mph which was easliy posible with the engine he had. installed. Rudder is the easiest surface to get flutter on since it has no aero load if the plane is straight. BV had an addendum to the Bandits years ago where you put a 90degree strip from plastruct at the trailing edge of the rudder to aero load the rudder to one side and it stoped the buzzing. Bottom line is what Bob said "a servo arm and horn is a proven, robust, inexpensive, and light way to transfer the torque from servo to surface... "

AVIOJET

The BVM F-16 had all linkages hidden and no issues with flutter.

Happy New Year from Spain

Jesus

furloughed ual

My Feedback: (31)

I'm building a big SM F-86 right now for a customer. I did the ailerons using an internal linkage with all the proper geometry (short servo arm and the internal horn as far from the hingeline as possible, keeping all the linkages 90* to the servo arm, etc, etc) and used metal servo arms and a 340 oz servo. I powered it up ans tested it for slop. It was pretty good....I was 90% sure it would be ok.....but for the price of the plane, that 10% of uncertainty made me do a half exposed link similar to Oliver above....now it is absolutely positive and solid with no play.....there wont be that 10% of doubt when it's flown hard. Not scale, butseeing $15K make a smokin crater because it looked great just prior to impact isn't worh it for me. There is a compromise between absolute scale and functionality.

Shaun Evans

Hi,

It can easily be done with a little planning and a conducive airframe. I don't see any reason why jet tail surfaces would have exposed linkages. If you MUST have them on the wings, you can hide them with a little craftiness or a pylon...

mick15

Here is my contribution to concealed linkage.

m

MNModels

Hi,

I have build and flown the SM 1/5 f86. Al went well until high speed pass - flutter. I changed the aileron linkages to outside with no problem what so ever.

Be warned. I think when you have a nice large trailing edge to work with it is possible to hide the linkages. At the mean time i use the pylon of drop tank to hide the linkages of aileon.


Regards

Morne

Ali

My Feedback: (5)

Give me an exposed linkage any-day. After all they are only toys and I would prefer a working toy over a broken one that looked great all the way up till the point it fluttered. ( As I found out on my first Airworld Cougar )
Not only that on many of the internal linkage set ups I have seen they have had to drop the ATV on the servo so much that the resolution was lost.
Sure if its a huge plane where you can get the horn far enough away from the hinge point to get a good mechanical advantage then great. Otherwise I will happily live with an exposed linkage.
Regards Al

rolsen12

In one word. K.I.S.S Keep It Simple STUPID......

Jetpilot24

My Feedback: (21)

There used to be a company that made hidden torque rods. They conected directly to the servo output shaft. they had 2 set screws to hold the torque rod to the output shaft cap. You had to put a flat spot on the torque shaft. The other end of the torque shaft was bent at about a 45 degree angle. The bent end would fit into a ply box that would go into a pocket in the control surface. I used them on a JHH F-100 and they didi not have any slop in them but for the life of me I can not remember what they were called or who made them.
Maybe someone here has used them in the past and can remember.

Joe L.

ColinW

Do you mean these http://www.irfmachineworks.com/rds/ ? It is some time since I contacted them but they still have a web site.

Shaun Evans

Hi,

I'm not advocating using them at all costs or when it's mechanically impractical, I just think that sometimes, broadbrushed 'rules' drive some companies to do things certain ways even when it doesn't make things any safer. For example, the ailerons on our F-16 have an internal torque rod. One of my customers ended up cutting a hole in the wing and installing his servo there because, as he reported to me, some friends of his at his club urged him to for safety's sake. In the end, the size of the lever arm on his external linkage (the control horn) was half the size of the stock one which cut his mechanical advantage (for slop and torque) in half. Additionally, he cut through the carbon cloth layer, rendering that extra strength in the wing itself meaningless. Moral: Just because it's external doesn't mean it's stronger or safer. It depends on the design.

SCALECRAFT

My Feedback: (13)

It was done before all the out of the box, ready to bolt together arfs were available.

Maybe its because not many know how to or want to take the time.

Steve

Robrow

To answer the original question we don't need any calculations......the main reason we have exposed linkages is because our servos have a rotary output which in most cases has to be converted to linear movement. The full size control surfaces we are talking about are moved using hydarulic actuators which have linear movement already.

Incidentally even using linear hydraulic acuators a lot of full size aircraft still have part of some linkages external but use fairings/covers to protect/streamline.

Whatever happned to the linear servo?

Rob.

bambam102

http://www.firgelli.com/

olnico

All the electrical linear servos I know are using electrical motor. They transform the rotary motion of the motor into translating motion through a screw jack system.
With this type of technology you have to choose between power or speed ( ie depends on the screw pitch ).

For example, the Firgelli PQ12f is a high force linear servo that has a speed of 7mm/s.

Lets compare it to the Jr3421 which weight and size are comparable ( 25 grs vs 19 grs and 33,02 mm x 14 mm x 25 mm vs 36,5 mm x 15mm x 22mm )

The PQ12f will output 15N at 20 mm or 30N.cm
The JR 3421 will output 65oz/in or 45N.cm in the same conditions.

The PQ12f has a linear speed of 7mm/s
The JR 3421 has a linear speed at 1 cm of 10 mm in 0,18 s ( two 30 degrees segments in 0,18 s ) or 33 mm/s.

So for comparable torques ( although the JR servo is 50% torquier ) the rotary servo is 5 times faster than the linear one.
This type of linear servo would be simply useless in a jet aircraft ( too slow or too weak ).

Airbus has been striving for a long time to fit electrical linear servos in their aircraft. The technology has not yet been able to offer acceptable solutions for fast applications.
Hydraulic screw jacks are used for stabilizer trim purposes at the present time.