Control Linkage Question - 1/4 Scale Dynaflite Decathlon
In need of advice.
I am attempting to move up to larger scale planes (30 cc - Gas) after many years of flying smaller nitro planes. So gas powered is new to me as well as the needs of larger scale planes.
I recently purchased a 30 cc Dynaflite Decathlon that had the bottom of the fuse pretty well ripped up,and the landing gear was torn out. After I bought it I also noticed a wrinkling on the one side of the stab when I flexed it. I was surprised to see this because I tested the stab at the gentleman's house. I don't believe he knew about the stab break either. I'll have to strip the covering and find out what broke and redo the tail wires.(not a problem) The repair is going very well.
To the Question:
I decided that I should go over the plane with a fine tooth comb, so to speak. I want to set everything up as correct as possible. Each elevator servo is connected to the elevators by a solid rod from running from the servo to the control surface. The rudder is set up as a pull-pull system with flexible cable to the control horn. I have noticed that the cable gets really sloppy on the side opposite of the pull when the rudder is deflected, is this due to the location of the control horns?(more detail below)
Being that I am used to seeing smaller planes, I am used to also seeing the control horn connection point directly above the hinge line. I have included two pictures below (click to enlarge) that show the pin point connecting on the control horns of both the rudder and the elevator being not in line with the hinges. My question is (to someone who is used to doing large scale planes): From looking at the pictures, is this setup wrong? (the location of the elevator and rudder control horns)? and what problems would this setup create?
I was also wondering if someone could identify the control horns that were used on this model (are they dubro?) or do you think they came with the kit?
Thanks in Advance for the responses,
Congratulations on your jump to larger models.
From what I can see, your concerns are valid.
I don't use that style control horn, but I would think that they would need to be located near the hinge line.
I wouldn't use the "easy connector" on the elevator servo arms, either. They, in my opinion, are suitable only on park flyers.
The slop in the pull/pull system comes from improper spacing on the servo and rudder connections. They need to be equal distances.
From what I see, I would look at everything on this model. It looks, to me at least, that it was assembled by someone with limited experience.
I suggest that the fuselage (tail section included) be completely stripped of covering, and thoroughly inspected. Check all the glue joints. Make sure that you fix the stab.
Good luck with your jump to larger models. I find them to be quite enjoyable.
Get rid of the EZ-connectors! 4-40 solder clevises using silver solder. Other than that, it looks okay.
The geometry of a 'closed loop' control system requires that the control horn holes and the hinge pin are in alignment.A second demand is that the width of the connection holes be the same distance at the servo as the flight surface, and equally spaced from the center.
Ditto, plus look for information on pull pull set ups on this and other r/c sites. Cross over, parallel cables, tension of the wires, off set arms etc. will be good for you to know so you can dial in yours without slop on one side. It can be frustrating but nice when you get it working right. Good luck.:)
I just started using pull-pull on 2 planes -- 69" Yak and 58" Pitts. Getting used to what hardware is out there and how to install it is a bit confusing.
I don't think that there is any need to get the wires tight. But the wires do seem to straighten out a bit after they are installed, so think about how to adjust them after a few weeks (connectors that can be screwed in or out to adjust length).
Although this is probably heresy, I'm not all that concerned with getting the control surface connection exactly at the hinge line, or getting the wire separation distance exactly the same at the control surface and the servo. I think that close will do on both counts. (It was hard for me to get 2 servos side by side in the fuselage, for pull-pull on both the elevator and rudder. I had to reduce the length of the servo arms to fit 2 servos in.) You could probably even put a bit of differential in by making the length from the control surface a bit different on the pair of connecting wires.
But pay attention to the physical movement. There must be enough control surface movement, and it needs to be crisp enough to avoid flutter. Good luck.
as noted earlier, replace the EZ-connectors!
on the pull pull set-up, that is why cables are used, so that oversized servo arms can be used!
it allows the servo to get more deflection! and relies on wind to keep tension on one cable till it equalizes!
it's a good set-up, most modern 3D ships use it!
as long as you can reattach the elevator control rods, without getting binding with the rudder arms, you should be good to go!
In close quarters room can be gained by raising one servo higher, by 1/4", allowing room for the cables...Reversing one front to rear will give room for the longer arms if necessary.
Exactness isn't mandatory, just suggested...The result of inaccuracy is tight cables at neutral,one going loose on deflection, and binding on different set-ups.
We can only tell you how to do it correctly....you use as much of it as you want.
BIGGER is BETTER !
I did my first pull pull on the Cap in my Avatar. I stated a long discussion in one of the popular forums about the whole process. I'll search to see if an can fine it and will edit this post is I do. The short scoop is to make sure the point where the cables hook up is directly over the hinge line on the control surface. Then the cable attach point on the servo needs to be directly in line with the output shaft on the servo. That has been documented in an earlier post. My cables go slightly slack when the rudder is deflected and I have never had any flutter.
After you do the first one it is old hat the second time around.
Ken-I read that thread, and some of the stuff they discuss is pure science fiction..
My theory on things is-"Simplicate, and add lightness".
I said early on -equal lengths on horns and arms, lines through the hinge pin.There is no way to do it simpler. The tirade over there made my brain tired...and you know what they ended up with ? you guessed it.
"What happens in a tailslide?"....the airplane goes backwards, and the tight cable pulls the control surface.
Maybe it's just me...........
Wow, a timely thread for me too. I am just now completing the assembly of a 28% Fly Baby and it calls for a rudder pull-pull. I never realized how critical all the measurements and hinge lines etc would need to be.
Already I realize I need to drill new holes in my rudder links!
Hope you don't mind, more questions to follow.
Many Thanks again,
I was looking at my CAP last night. The cables had loosened a bit. I had about 3/8 movement at the end of the rudder. I had no issues with flutter and the plane flew fine. IMO, there is just no reason or worry to make everything "perfect". Yes work to get it as close as possible, but don't fret if it's not perfect.
Decathlon repair update.
(click on images to enlarge)
All damaged wood cut away.
Wood replaced on fuse side and landing gear base.
Bottom formers designed and enlarged from small instruction manual (formers not shown on true plans) 3M77 used lightly to attach paper template to ply. Part cutout out on delta scroll saw and paper templates peeled off after sanding.
Start of covering with balsa.
Balsa covering finished.
Landing gear installed.
Sanding finished, start of re-covering.
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