P51p

Hey Guys,
I have a Katana with a 40cc engine and the plane always deflects to the right everytime I do a loop. I have a servo on each side of the elevator and a servo reverser on the second servo, I have checked the elevator to make sure they deflect at the same rate and angle. All seems good.
Could the engine thrust angle have anything to do with the plane going to the right in a loop?


Thanks
Graham

planebuilder66

My Feedback: (8)

laterally ballance the plane, hold the spinner and the tip of the tail, make sure it doesn't favor one side all the time. If that's good, check to see if the elevator and wing are square to eachother and the rudder isn't crooked. You should really try to trim the plane out in the air and land to check to see if one surface is low or if the rudder is fighting the alerions. Engine thrust would be apparent all the time, as you throttle up it will pull and when you let off it will glide straight, same goes for down thrust, too much it will drag it downward, not enough it will climb like crazy, being a symetrical wing, it shouldn't produce any lift.

fadi

plus one for lateral misbalance  you have a heavy right wing I assume...

bubbagates

My Feedback: (32)

My question would be is deflecting meaning that the nose is going that way or is the right wing dropping or both?

Also, where in the loop is this happening?

P51p

I will double check the balance laterally but, the plane flies fine laterally, almost no trim needed on the alerions.

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P51p

bubbagates:

The nose &amp; right wing tend to point and drop to the right. This happens at about 1/4 way into the loop. I am starting to wonder if I have a weak servo on theleft elevator that maycause the plane to pitch right when Igive it full up on the elevator? Thisweak servo may only be apparentwhen under heavy load, because during normal flight it works fine. Not sure? Would a servo reverser used on the elevatorcause this problem?


Graham

bubbagates

My Feedback: (32)

Graham,

It could be a weak servo or I'm thinking more along the lines the right servo is moving a bit faster than the left one which or they are not set exactly equal all the way through the complete movement. Most people will only check neutral, full throw up and down, but never bother to check everywhere in between.

It's really easy to check

Get two spring type clothes pins and glue some very straight balsa sticks the them, about 18 inches long should do it for each one. Clip each one to each elevator half at the exact same point and turn everything on. Now line the sticks up so they meet behind the rudder and slowly move the elevators. The sticks will show you if the right is moving faster or more than the left.

I have seen servo reversers cause this issue as well where the one with the reverser on it is actually slower. If slower is the case, some radios allow you to slow down a given servo

Depending on your radio, you may be able to mix two elevator servos together on two different channels and remove the reverser if that appears to be the problem

If this was happening at the very top of the loop I would agree with a lateral balance issue

You could verify this to a point by simply doing a very small pull for the loop, basically a nice big gentle loop, and see if it goes away or is less. If it goes away or is less than it's certainly an elevator issue. The stick method is by far the best way<br type="_moz" />

P51p

bubbagates:

Thanks for the info. I will try the sticks tonight on the elevators.

P51p

bubbagates:

I tried the sticks last night and it seems that the elevators deflect at the same rate for about 70% of the range of travel. I only use about 40% of the travel to do a loop, so Idon't think this is the problem. Not sure what else to try?


Graham

bubbagates

My Feedback: (32)

Lateral balance but that normally shows at the top of the loop. Just because you have only a tiny bit of aileron trim does not mean one wing is heavier that the other or some other factor is not at work.

Also, I would take someone elses advice and verify the vertical stab is truley vertical and straight.

planebuilder66

My Feedback: (8)

Even the littlest slop in a elevator or alerion linkage will give problems, a weak servo or one that has a dead spot in it can show it's ugly face sometimes. What happens in an outside loop? same thing? Check engine thrust, as airspeed slows down, rudder becomes less effective, engine thrust will take over and show it has too much or too little thrust.

P51p

Engine thrust angle is 2 degrees right. May be I'll reduced it the 1.5 degrees right, see if thatfixes the pitching. Also, I did not mention that when I fly inverted it flies great, so I think if Ihad a lateral balance problem it would show up in inverted flight. So this leaves me with two possibilities (1) weak servo or (2)thrust angle. Any thoughts?


Graham