Split Elevator Trimming
 

I am trying to figure out a trimming problem that may relate to split elevators ie each side on a different channel. In doing loops or half cuban 8's or sharks teeth type maneuvers, when the plane comes over the top it tends to fall off to the left as it goes inverted. I am trying to figure out if there is a small difference in the elevator sides such that when I give it up to come up into a loop or over into inverted, it goes to the left. I hope I am being clear enough. How do I tell which elevator half my be pulling up more than the other and causing the plane to deviate off course ?? I cannot see a noticeable difference in the two elevator sides but the plane definitely goes over to the left as I pull through the top of a loop. Any suggestions

Bill

RE: Split Elevator Trimming
 

Bill,

As weird as this is going to sound it works well. I'm sure someone else will have other ideas.

Take 2 pieces of nice straight balsa sticks and tape them to the top of each elevator so that they meet right behind the rudder. Now move the sticks on the transmitter and you will see if they are moving equally and at the same time

I suggested this over in the Wildhare forum and the guy went so far as to use spring type clothes pins and glued the sticks to them. Easy to do and will definitely show the problem. I have also since done the same thing (spring type clothes pins) and it really does work well.

EDITED for really bad wording on my part YUK [:'(]

RE: Split Elevator Trimming
 

Bubbagates has the answer. That is the only way to see what is actually happening. I tape toothpicks on the ends of the balsa sticks to really fine tune their deflection.

Be sure your mechanical set-ups are identical on each half.

Ryan

RE: Split Elevator Trimming
 

Never thought of the toothpicks, cool idea. [sm=thumbup.gif]

RE: Split Elevator Trimming
 

After you're done making sure the elevator halves are exactly the same run Peter Goldsmith's trimming sequence from the Model Aviation Feb and Apr issues in the Scale Aerobatics section. It is also posted here on RCU in a condensed version...just do a search for "Peter Goldsmith".

Basically you could also have a dynamic balancing issue (wingtip weight) even if your wings weigh the same, if the weight it distributed differently in each wing then under a load (pulling G's) your plane will pull to one side...or wingrock in a harrier/elevator.

Do the trimming, in order, you'll be happy you did!!! :D:D:D

RE: Split Elevator Trimming
 

Flyintiger is right. I had a wingtip weight issue also. I had to add 1.5 oz to one of my wingtips because evertime I pulled a vetical upline the plane wanted to go left while in the radius to the upline (needing weight on the right wingtip). I added the weight and if flies great.

Ryan

RE: Split Elevator Trimming
 

The problem I face is that no matter what you do, you always need to use sub-trim on the servos. It's recommended to keep the subtrims as low as possible but sometimes it's not avoidable at all.

So, when you say mechanical set-up, I assume that you are talking about the control rod lengths.

RE: Split Elevator Trimming
 

Anyone found that trimming schedule by Peter Goldsmith? Can you post the link if you have?

Thanks

RE: Split Elevator Trimming
 

When you guys need to find something on RCU, just type what you're looking for in the search box on the upper left, by the "Tower: Search tool.

I just typed in "Peter Goldsmith" and it was a few articles down...

http://www.rcuniverse.com/forum/m_28...tm.htm#2819925

Have fun and good luck trimming! ;)

RE: Split Elevator Trimming
 

Take a look at my elevator setup article ([link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=486]HERE[/link]). I specifically show Hitec, but it works with all servos. The absolute key is getting the mechanicals perfect... do this and you will NEVER have elevator half problems again....

I have never used sub trims even once on elevators, even on my JR8611 equipped planes. Touch sub trim and you blow your symmetry
DP

RE: Split Elevator Trimming
 

DP,
I have read and reread your article several times.

However you are using the programmer to bring the subtrims to zero. In other words you are programming the neutral point.

You cannot get an absolute 90 deg. servo arm to servo if you don't use subtrim.

Maybe I am missing something.

RE: Split Elevator Trimming
 

If you use a single wire run to a Smart-Fly equalizer, then connect the servos to the equalizer, you will have the ability to reverse one servo, and set end points / centers of each servo independently. The equalizer is a good cheap solution (a lot less $$ than a Matchox). Unfortunately, if you are using two channels to the elevator servos you will never be able to get an accurate EPA with the radio because once you mix the channels, the ATV settings (and therefore end points) are not equal between channels.

The best solution is to remove the 2-channel mixing and go with the equalizer on a singel channel (ELEV), then adjust EPA and center on each servo independently using the method in my article. Once you have this done, when you move the sub trim, both surfaces will move the same amount and you will not lose symmetry.


There are of course, other ways to do it, but for me this way works the best. I have always been able to get excellent results using this method and if done right, it works on the first try. Before doing this I used the two-channel method and I always was fighting the sticks correcting trims or had planes that would snap out of high rate maneuvers.

It is amazing how a small differential in the surface movement or center / end point alignment can throw off the entire trim.

DP

RE: Split Elevator Trimming
 

Thanks to all of you for excellent suggestions. I am going to take the advice and really focus on making sure the elevator halves are really in synch and moving the same degree of deflection. I will use the balsa sticks / toothpicks to really try and fine tune the two halves. I am also interested in the comment in the one article about not using 2 channels and mixing but using a Y connector etc. I had a close look at how the elevator halves are moving and I think there is a discernable difference in speed of deflection between the two sides. To my eyes I think there is a delay or one side is moving slightly slower than the other. This must have something to do with the 2 channel mixing and master / slave functions. Should be a fun weekend working through all of this. Thanks again, I really appreciate your thoughtful responses. True test of this will be back in the air !!

Bill

RE: Split Elevator Trimming
 

What is the best way to adjust the two halves using separate channels if not using progammable servos?

RE: Split Elevator Trimming
 

I have a 9C radio, when using mix to multiple surfaces on a channel whether elevator or aileron, there is a delay to the mixed surface. You will see this with the pointers described above, the mixed servo will look a little sluggish compared to the main channel. A matchbox/equalizer makes it go away.

RE: Split Elevator Trimming
 

Thats what im using now..9C..Im just skeptical about adding another possible point of failure between the servos and the RX

RE: Split Elevator Trimming
 

Brian - that's exactly what I am seeing - I also have a 9C (and really like it). The mixed channel is definitely delayed in movement compared with the master channel. I am thinking I am going to have to go to a Y connector and one reversed servo to straighten this out.

Bill

RE: Split Elevator Trimming
 

Instead of the Ailevator mix, I use a p-mix with channels 2 & 5 for elevators. The Futaba website has a FAQ that explaines how to do this. No lag between the servo halves and the deflection and speed are identical. If using 2 & 8 the lag will be more noticable. I don't think the speed of the servo is reduced, its just that the lag makes it appear slower.

Ryan

RE: Split Elevator Trimming
 

Ill have to try the pmix..thanks

RE: Split Elevator Trimming
 

I cant get it to work with channel 5..according to the Futaba Faq you need to use channel 7..How did you do it with channel 5?

RE: Split Elevator Trimming
 

No matter which way you mix it w/ the 9C there is a servo lag. It really makes a difference in the pulls. The only workaround that got them at the same speed was to use a Pmix for each elevator half (the Ch2 slot on the receiver is then empty), then they were both sluggish.

Im using pretty fast servos (3421sa) and if the servo speed isnt as fast as the lag you may not noticed any problem.

RE: Split Elevator Trimming
 

Do it like the Futaba site says, just use 5 in stead of 7. Just make sure you go back the the auxillary page a set ch5 to null.

Ryan

RE: Split Elevator Trimming
 

It looks like the radio manufacturers have a real problem here...there should be no lag in a master and slave channel...this needs to be fixed. Much complexity and annoying extra programming or parts are required for what should be a simple program. FRUSTRATING! [:'(]

RE: Split Elevator Trimming
 

That might have been me...
Here are the ones I made

RE: Split Elevator Trimming
 

Heres the FAQ about the lag and minimising the effect:

http://www.futaba-rc.com/faq/faq-8u-q594.html

Other FAQs including the dual elevator setups:

http://www.futaba-rc.com/faq/faq-9c.html

Seems like they would come up with a better work around for this than buy a more expensive radio. This was the second time I had applied dual elevator servos but this was on a competition plane so It was bugging me what was wrong. Took me some time to figure it out since the endpoints were right. I also made sure servo arms and linkage were the same length etc...

Anyway, a new radio is in the budget but the equalizer or matchbox will do for now.