I have been flying a Phoenix extra 330S for some time. A couple of weeks back, the club instructor took it for a test flight and wrung it out. His remark was that the airplane did not recover from a spiral / spin when commanded- it did two complete spins before it flew out after neutraling the sticks. He pointed out that one of the elevator halves had a bit more play and that the deflection on one was more than the other. He was right, since putting a DLE20 on this airplane, I myself have not been too comfortable as the airplane snaps out of line at the top of a loop.

This is a dual aileron dual elevator setup with the pull-pull rudder. I am a novice to transmitter programming and I had someone else set up the airplane for me. When I decided to check out the trim yesterday, first thing I noted was that the two elevator halves neutral was not the same. I corrected the same by opening the clevis and turning them out till I got both the halves fairly neutral. Now, I am using 'mix' rather than 'ailevon' to link the channels. The elevators are linked using mix-2 with elev->flap, 'flap' being chanel 7. Now having neutraled the elevator, I noted that the elevator deflections at low and medium rates were fairly equal- within a mm of each other. However, at 3d rates, one elevator deflects 10mm more than the other. The one that deflects more is the master, so I cant reduce the throw from 'mix'. If I reduce from 'end point', I lose neutral as well as alignment at the other end of the throw and at low and medium throws. If I swap the channels over in the RX, I lose neutral again.

So what (the hell) am I doing wrong? I spent most of the evening trying to figure things out

Ameyam

The first issue and you have been advised about this before is that the airplane is just too heavy. You can't make a Ballerina out of a pig. Second is the elevator issue. If your TX supports dual elevators then why arent you using it? If you are using a JR or Spektrum TX the flap would be for aileron 2 so that tells me you could be using a Y connector on your ailerons which means that is set up poorly too.

speedracerntrixie,

dual elevators = two seperate elevator servos = two seperate channels for elevator = mix required. Thats where I am having the problem. With seperate servos they dont seem to deflect equally

Ameyam

Since you have the elevators on two channels, use the dual elevator function on your radio to control the two channels. The reason for this is that you will want the trim function to work with both sides of the elevator. An ordinary mix will not give you this capablitiy. Then, mechanically set the the elevators so that both line up at neutral. Then use the end point adjustment function in the radio to set the up/down end point on the elebvators to the same amount of deflection.

Bruce

Bruce,

thats exactly what I did on New Year's eve. Before everyone jumps at what I just said, the idea was to fly on Sunday the 1st of Jan.

I started with mechanically adjusting neutral. First I set everything to 100%, then opened the clevises and screwed them all the way in on the rod. Then I unscrewed them counting the turns as I went along. I got 10 turns to neutral on one and 12 turns to neutral on the other. Then I used the subtrim function to make the neutral adjustment. Next, I set 100% deflection on both elevator halves both by sight and by using a scale- after adjusting both the elevator halves to deflect equally by using the endpoint adjustment, I set the neutral again from subtrim (which finally came out to -8 on the one elevator). Having done this iteratively several times, I found that the deflections were fairly close-within a mm or two of each other. Also, the deflections at the lower throws were checked and minor adjustment to the endpoints (about 1 or 2 units) were made to keep the difference between the elevator halves at low, medium and high throws at a minimum. I think I did a fairly good job. Did the same with the ailerons, though it was much faster to do those after I made the mechanical adjustment first.

My TX doesnt have a 'dual servo' setting. I am using a 9CAP and if I am not mistaken, Futaba treats all 'dual servo' setups as mixes. So 'Flaperon' and 'ailvon' are preset mixes. Earlier, I didnt understand why my elevator was linked to flap. Later, after I realised that 'flap' was just a name for channel7, setting up the thing became much easier.

It was 1.30am on the 1st of Jan before I went to sleep and consequently did not fly on Sunday. I will get to test my settings on the coming Saturday

Ameya

http://www.futaba-rc.com/faq/faq-8u-q586.html

http://www.futaba-rc.com/faq/faq-9c-q512.htm

Hope this helps, these are the setups I use, I usually use 7 channel RX in small planes, and I use channel 7 for aux right side aileron, and
channel 6 for right side elevator. I am curious what servos you are using?? once you set neutral mechanically it should stay there indefinitely
unless the servo has slop, or is worn. EPA and high low rates should not change neutral at all. I use a 9C also and have had some problems
with dual elevator servos and ailerons not holding neutral with standard analog servos. I changed them out to digitals and have been fine
ever since. I actually replaced them with new analog servos first and after a bunch of flights the started losing center again so I replaced
with digitals.

I am using 5625MGs. Think the issue is with the geometry. At neutral, pushrods on both sides are not in the same plane

By the way, thats what I did- used mix. The elevators are in 2 & 7 in my case

Ameyam

If both elevator horns and servo horns are at different angles, you will get a differential response on either side, even if you can get them to neutral/zero the same. Similarly, using different holes in the horns will produce different rate response.

Some geometry issues you can't "fix" easily with a radio.

I believe they are in the same hole and the same servo horn angle. They have provided the LHS servo lower and the RHS servo higher so that the arms with opposite orientations lead to both the pushrods being at the same height from the bottom of the fuse. However, I dont know what horn they used for reference because ther rods arent the same height from the fuse bottom in my case. I am using the stock Hitec plastic one side horn. Its in the correct neutral, at 90 deh to the servo centreline. I know because I tried both the neighbouring positions and they arent 90 deg

Ameyam

OK, you said the servo horn is 90 degrees to the servo case. Is the linkage to servo arm at a 90 degree angle also? Servo arms do not have to
be at a 90 degree angle to the case, the 90 degree angle has to be where your elevator linkage meets the servo arm. I believe minnflyer and Ken
have illustrations that can better explain this.