Jet Rookie Questions: I will be using Spektrum 6020, 6050, and 590 servos in my jet trainer (JetMach 60). My question is are you fellas using metal or plastic servo arms in your jets. If metal, what brand of metal arms are you using? I understand that JR servo arms will fit on Spektrum servos, is that true? My wife purchased the Spektrum servos as a present. She thought she was doing me a great favor so I would be committing social and political suicide if I did not use those servos. She saw where I had made a list of JR and Spektrums and due to her great and well used shopping skills and abilities, she purchased the lesser of the two brands. Got to love her. Any advice would be greatly appreciated. Chic

She sounds like a keeper. ..

Those Servos should work great in that jet. JR metal horns will work fine, I never use plastic horns in a large model mainly because they can twist, that's when they tend to brake.

Swb arems are good as they have a pinch bolt on the servo spline end. Most of the metal horns from hangar 9 and some others you have to almost use a hammer to put them on

Just my 2 cents

Good luck. .

If you are using metal clevis ends on the servo plastic white JR Super servo arms. Nylon super servo arms and spring steel clevis are fine on a 200+mph Flash/UF.
If you are using ball links. Metal JR/Secraft/SWB arms.

Dave

+1

I had JR Heavy Duty White Nylons Arms on my BVM Ultra Bandit per the instruction manual. 200MPH + and a moderately heavy jet, no issues at all. I would not use them with Ball-links due to the torque factor and twisting, but with Sullivan Gold Clevises, they are tough as you need!

Shaz

Hey guys, thanks for the great answers. I'll go with the SWB arms, I like the red color. How about these two questions. What size servo arm should I get (1")? Second, where do I buy the nylon protectors to put over remote receiver antennas to protect and keep them straight? Thanks for the fast and helpful responses. Chic

The heavy duty JR servo arms are part number JRPA215.
They go for $2.50 a pair at your local hobby shop.
They cost about $8.99 a dozen.
The super duty white servo arms are available too...they feature a metal ring around the splines, and are standard with the high voltage servos 8711HV, 8717HV and 9100HVT/S. The set of two arms , cushions and screws sells for $8.99 They are pictured below.


I have found that the major problem with most of the metal servo arms, is that they are drilled and threaded for a ball link. The threaded holes are too large for a Sullivan steel clevis pin.
The JRPA 215 clevis holes are molded to fit a clevis, and are very strong. The weakest part of this servo arm is the splined hole.

4-40 is the appropriate size for model jets.

WOW, I though most of you would be using ball links and not standard clevis'. Boy am I learning a lot. I flew IMAC for a short while and I used ball links exclusively. Harley Condra, will check out the JR HD servo arms. Thank you. Chic

I simply use 4mm clear plastic air line cut to length for the antenna protectors. You can try 3mm but I think it's going to be to small in diameter.

John, you are right. Just found out that Robart 169 Pressure Tubing is the ticket at about 1" long. Thanks for the response. Chic

Chic. Put a small drop, SMALL mind you, on that shoulder before you send that tubing home and it will protect forever. Once they are on, you will never need to remove them anyway. SWB arms are hard to beat but in a pinch the Dubro heavy duties have never failed on any of my jets with the Sullivan golds.

Sorry to keep troubling all of you, but I really need your advice. What size (1", 1.25", etc.) SWB servo arm should I buy for the elevators, ailerons, and flaps. Many thanks. Chic

Go metal if you like the bling factor, but for your plane, all you need is the JR heavy duty plastic arms. Really... Don't waste money

I fly a twin rafale and a F100, and both are plastic all around. The JR Heavy Duty are really really strong arms (and very inexpensive)

As others have said, go metal only if you need ball links (which are usually not needed either)

One thing to remember is the way servo torque is measured. The advertised torque is measured 1.00" from of the center of rotation. The longer the arm, the lower the available torque. Short servo arms produce more torque.
Keep them as short as practical.

The instruction manual or plans of a well engineered model will call out the servo type, the arm length the surface deflection on all control surfaces. Also, the neutral position of the servo arms will be shown, in order to establish the proper aileron differential.

Actually, torque is independent of the distance from the centre. Force is what varies. Torque is measured in force/distance. So, the longer the distance, the lower the force and viceversa
So, if a manufacturer advertises 300 oz/in, it means that at 1.00 from the center, the force is 300 oz. At 2" it will be 150 oz of force, and at .5" it will be 600 Oz of force. But the torque is the same at every distance

That's what I said. Measured at 1.00 from the center of rotation.....

My belief, is that, since we can't insure these jets, my insurance is that I use the best available for the jet. IF you are using metal geared servos ( I didn't look up the numbers), why use plastic servo arms? I also use all ball-link on my main flight controls and flaps. The plastic servo arm becomes your weakest point on the rigging system. I have had plastic servo arm splines strip and fail. So, for the extra $100 worth of metal servo arms, verse loosing a couple thousand dollar jet and engine, was it worth it to go cheap? So, for peace of mind on my jets, I know that I did everything possible to elimiate an issue for failure. I love SWB arms with the double locking bolts. Again, this is just my humble opinion and from my experience of flying jets and large scale planes. Dan

Hello Dan, like all the other responses, I appreciate yours. I wanted to believe that ball links would be the way to go, but I saw many jets (2013 FIF Event) that used straight clevis' so I did not know which way to go. The Spektrum servos listed, that I will be using, are all metal gear thanks to my wife. Luv ya darling. Smile. I guess I feel more comfortable using ball links even though most guys may think using ball links would be overkill as well as using the metal gear servos. I reviewed the manual for the Jetmach 60 and no recommendations for servo arms was given only that standard servos should be used. So I guess I will order 1" SWB servo arms for 6 servos, a double servo arm for the rudder, and ball links for the arms and the control surfaces. Any further comments would be greatly appreciated. As a teacher, I know one method of learning is by listening to others who are more knowledgeable and I certainly do not want to learn by making toooooo many mistakes on my own. Thanks guys. Chic

Glad to share. Just remember, that if the one inch is too long, I have cut the metal ones down with a Dremel and tapped them again.

Dan, just visited the SWB website. Looks like I will go with aluminum servo arms for clevis' on the servo side and ball links on the control surface side. Does that sound reasonable? Chic

I haven't looked lately, but usually, the SWB arms are already tapped for 4-40, which means that a clevis pin will be too small for the tapped hole of the arm? Thus a flutter issue. Or, did they come out with some new ones that I don't know about? Of course, you can always drill a new pin hole.

Force, not torque... torque is constant

Some years ago, we flew Rookies and other jets with JR and Futaba servos not as good as the current Spektrum, Savox, etc... and also used the Du-Bro heavy duty plastic servo arms, and Sullivan metal links.. (wich are still my favorites) . Correct geometry applied with good quality hardware is far more important that the "bling" factor, IMO.

Metal arms are great for 3D gassers who need long and rigid servo arms for gigantic surface movements. Use one of this long ones on jets and soon you will realize that is not a good idea. And even if you think about using a short metal servo arm , remember that the servo case is made of plastic, and the servo mount in the wing and fuse is not attached in anything "metal rigid" either..

By the way, congrats to your wife .. she is wise!

Thick plywood and fiberglass behave like jelly at speed.. The amount of force caused by dynamic pressure (and if you are unlucky enough aeroelastic forces) can be extremely high at the servo mounts and structure, pulverizing everything as fast as a blink of a eye.. (but leaving the metal servo arm intact, LOL)

But anyway, this is just my humble opinion, I am not a space engineer..

It isn't as much as the metal servo arm, as it is the metal servo arm's female spline to the male's servo metal spline. Just one more prevention failure point; prior to the all failure point that you describe. Besides, he has placed his order now!