Elevators with 2 Servos

[Stephen Grigg]

Ive been flying my Harmon Rocket all year with a Y lead joining both servos to the eithr side of the elevator,so any adjustment has been made on the push rods to have both sides equal an no problems.i took my Cap 232 to the field for a test flight with a bigger heavier engine.My expert refused to test fly it because I didnt have the 2 halves of the elevators set up on seperate channels.Now he is a real fuddy duddy whose opinions change like the weather.I only wanted a test flight to ensure it flies fine and the C of g is correct with the heavier engine,so to set my tranny up on 2 channels would be a one off and I havent yet firgured out how you do it.What is the opinion of you experts,Im happy with the set up on my Rocket and have found no problems

[Biggles' Elder Brother - Moderator]

On elevators with two servos I always use a Y-lead - I find it more convienent and easier to set up. On ailerons I prefer separate channels because of the flexibility it gives on set up.

 

Another, less significant, factor is; while you can fly a plane on one aileron (not well maybe but you can do it) - you can't fly it on half an elevator (well I couldn't!). So while there is a marginal benefit in having some redundancy in the aileron system (two servos into two channels via two independent sets of wires) - there is no such advantage in the case of elevators.

 

BEB

Edited By Biggles' Elder Brother - Moderator on 08/12/2010 23:51:59

[Ross Clarkson]

Stephen,

 

I have pm'd you.

With help from Timbo, i have set my Yak up with 2 servos and i must say, it seems to be a really good way.

That and the fact that it is meant to have 2 servos and has the fuselage cut for 2!

Is the Cap 232 meant to have 2 servo's for the elevators?

[Stephen Grigg]

Yes ross the Cap and Harmon Rocket both have 2 elevator servos.I wondered the advantage to this as opposed to one.Some of my models have one servo and 2 pushrods connected theat was on my Extra 300.Why is it difficult to control a model with only half the elevator working.I saw on collegue lose half his models elevator and it was fine.I suppose it depends what the not working half is up to

[Ross Clarkson]

Well i suppose BEB answered the advantages of 2 servos.

I'm not really sure of the answer of why it is hard to fly with only one elevator, but i should imagine it would be something to do with the way it would react!

If only one elevator half moved, i would think it would then act more like an aileron movement and produce roll rather then pitch, or both at the same time!!

If i am wrong, i am sure someone will correct me!!

[kiwi g]

for what its worth. I use a smart-fly servo equalizer when using two elevator servos.

My reasons are , unlike a y lead the smart-fly allows for one lead to be used on two servos and these two servos can be adjusted just like on a radio channel.

Its great when problems occure with uneven movements of surfaces.

Check them out . google     smart-fly.com

[Danny Fenton]

I have been criticized for only using one elevator servo on some of my models, but I have never had a problem (reaches for the nearest bit of wood to touch!) The problem with two servos as BEB says is that depending on the position of the failed servo output when it fails you may not be able to control the model.  And also as Ross says depending on the model only moving half the elevator will introduce some roll.

A far better way is to use two servos via an arm connected ACROSS the outputs disc, the pushrod is connected at the mid point of the arm, that way if a servo fails you will still have half the throw available on both surfaces. Duncan Hutson shows this in one of his books.

 

I once built a .20 ic pylon racer, and in my wisdom only fitted one strip aileron to reduce drag. I only just got that down in one piece. When I turned left it shot up, and when I turned right it nose dived, impossible to handle

 

Cheers

Danny

[Ultymate]

I like twin servos on elevators, with a good trannie you can have tailevators set up so the two elevator halves can act as ailerons as well, this is great for control in torque rolls ie prop hanging. The two elevators are right in the prop wash  and give excellent roll control whist prop hanging 

[Vecchio Austriaco]

The Y cable is simple and as long as your servos are really equal and the geometry is the same on both sides it works perfect.

And with my flying style the tailevators are not necessary.

[Former Member]

[This posting has been removed]

[Engine Doctor]

 I have to agree with Eric Bray on this one . A "Y" lead works well as long as the servos dont bounce . ( some servos bounce and have difficulty centering when fitted to a Y lead)  The kiss principle always worked  for me. Only add on's I'd recommend is possibly a servo reverser y lead so as to get a symetrical set up with identical movement on both halves of elevator and Plug locks or tied plugs so there is no pssibility of the lead coming unplugged . Was your test pilot afraid to test fly it and used this as an excuse ?

[Wolfie]

Posted by Danny Fenton on 09/12/2010 10:10:43:

A far better way is to use two servos via an arm connected ACROSS the outputs disc, the pushrod is connected at the mid point of the arm, that way if a servo fails you will still have half the throw available on both surfaces.

 

Cheers

Danny

 I'm with this approach. It sounds like the only one where a failure would be 'graceful' and not assymetric.

[Stephen Grigg]

No ED he is a drama queen and loves to make a fuss,its a low self esteem ego thing

[Simon Chaddock]

Wow!

An "expert" who refuses to fly a plane because the elevator halves are not on separate channels.

 

I would suggest that the risk of a loss of control when flying an RC plane are ((in descending order):

The pilot

The radio link

Control linkage failure

Servo failure

Electronic failure

 

I know which one worries me!

 

[Myron Beaumont]

Surely, if you have a servo to suit  the purpose /application ,why use two ? Having said that,I do have two standard servos on my Extra 300s' .60 elevator halves (Seagull). It came as an ARTF (the only one I have by the way) & it works fine .Maybe there is more stress than we realise on elevators ?

[Former Member]

[This posting has been removed]

[Stephen Grigg]

As I only want to fly this model to ensure it flies OK to sell it,Im inclined to set it up on a Y lead and get Ross Clarkson to test it for me

[Malcolm Fisher]

As for flying with only "half" an elevator, the Sonata E electric glider some years ago had exactly that set up. Admittedly an electric glider is a different kettle of fish from a CAP232.

 

Malcolm

Edited By Malcolm Fisher on 10/12/2010 20:59:24

[Ross Clarkson]

Posted by Stephen Grigg on 10/12/2010 19:55:28:

As I only want to fly this model to ensure it flies OK to sell it,Im inclined to set it up on a Y lead and get Ross Clarkson to test it for me

 

Ha Ha, fine Stephen, just let me know when!!!!

I take it you don't value the model!!!! lol

[Stephen Grigg]

Youll need the practise for the Yak,and before you do it Ill sign the disclaimer.Ive already watched a club mate crash one of my most treasured models so Ill soon get used to it.

[Ross Clarkson]

Ha Ha, deal Stephen.

[Garry Pollard]

Bring it up to my site Stephen, We fly any old rubbish here, and provide bin bag LOL

Garry

[Stephen Grigg]

I have my own bin bags Gary I had a goodly period of everthing going well then a spate of calamities starting with a mate,but nearly all were repaired.

[Mowerman]

One of our club members has a large Yak with a dual Rx setup (Rx1 = throttle, left aileron, left elevator. Rx2 = rudder,right aileron,right elevator)

On a recent flight He found the throttle control not working so had to fly round in circles with the engine on part throttle untill the fuel ran out. The model was still controllable, if a bit sluggish, and when the fuel finally ran out was able to land without dammage.

On checking the model He found that the battery lead to Rx1 had become disconected leaving only Rx2 in control.

From the above it can be seeen that Half an elevator still allows control and will not act as an aileron.

Obviously this applies mainly to models with dual Rx.

However some models use two servos on elevator due to the elevators being separate and not easy to link to a single servo (does that make sense?)

Edited By Mowerman on 11/12/2010 13:14:30

[Ross Clarkson]

Top stuff Mowerman, thanks.