Trim Question(s)

[Matt Colan]

So I flew my Oriental Plus tonight for the first time in awhile, and there are some major trim issues with it, that are almost hard to describe.

First, I tweaked up the prop to 4.25" pitch from slightly below 4 where it was.  It did immediately feel more positive than it did when I was flying it earlier this year at around the same RPM.  I started flying the pattern and there was a lot i noticed that I didn't like about the plane.

First, it yaws nose out on outside corners, like the outside square, and affects the air speed and line tension of the maneuver.
2nd, outside maneuvers got soft.  This is the easiest thing to fix since we did already figure out the wing was slightly up.
3rd, this one is probably the hardest to describe. On my outside square when I make the turn to go inverted, it feels like I gained about a pound of nose weight and it won't turn.  The next 3 corners are just fine, it's just that turn to go inverted that I didn't like at all.
4th, When I turn from inside to outside on the square 8, it gets soft, but that probably had to do with the fact that the wing was slightly up.

I'm sure the wing not being level would cure half the issues there, but not the yawing, and probably not that turn to inverted on the outside square, or the yawing.

I have 63ft lines from the handle to the center of the plane. I do have rudder offset that I could take out (now that I think about it, taking that rudder offset out, might help the yawing), and the leadouts are about 1 1/2" back from the CG.

What do you guys think that could help cure some of this?

[Doug Moon]

First get the wings level.  It wont trim out properly without that being cured.

Second, move the lead outs forward.  This should help with the yawing. 

Correcting both of these should help some with the nose heavy feel in the corner.  The yaw can make it very sluggish.

If it still there after you have corrected one and two you might want to take out some of the pitch sneak the pipe out a tad.  It could be coming just a tad early and causing that nose heavy feel.

Hope this helps.

[Wynn Robins]

move your leadouts as far forward as possible (as Doug said) then trim from there - my legacy did the same kida thing - moved the leadouts RIGHT to the LE and took out all but 1/4oz tipweight - and is solved it.

[Derek Barry]

It is a balancing act when moving the leadouts forward, as you move them forward you will find that you need to add a little tip weight. Unless you have too much in it right now, then it will just get better as you move them forward. Be careful not to go to far, too much of anything can be bad. I am sure that your new plane turns better than your oriental so you may need to remove nose weight or open up the handle to get the same feel.

Derek

[Matt Colan]

I got two flights on the plane today, and we got the wings level with a trim tab.  The bottom line is, with this plane, is it's underpowered.  I was flying 5.2 lap times and I was having to nurse the plane through the horsepower maneuvers like the square 8 and hourglass.

We were tossing the idea around of putting a PA 51 in it, since it's the same mounts, but it's about 5 ounces heavier and that isn't going to do me any good.  Sometime in the future, I may refinish it, but at this point, I need to start concentrating on flying the Trivial Pursuit for the Team Trials rather than futzing around with a different airplane.

I'll probably just hang this plane up for awhile and get back to it and maaaaybe refinish it, but I'm not sure if it's worth the effort.

[Ted Fancher]

Matt,

1. Is there any rudder offset?
2. Where is the CG located aft of the leading edge halfway out the wing?
3. When you balance the plane at the tips where are the leadouts located with respect to the balance point?
4.  How far apart are the leadouts and is the up line in front or in back?
5. What engine/prop?
 
Also,  Watched your flight video yesterday and will have some comments about it.  (mostly very good but some things you probably need to straighten out if you're gonna whip Ryan) You wanna talk about it here or via email?

Ted

[Matt Colan]

Matt,

1. Is there any rudder offset?
2. Where is the CG located aft of the leading edge halfway out the wing?
3. When you balance the plane at the tips where are the leadouts located with respect to the balance point?
4.  How far apart are the leadouts and is the up line in front or in back?
5. What engine/prop?
 
Also,  Watched your flight video yesterday and will have some comments about it.  (mostly very good but some things you probably need to straighten out if you're gonna whip Ryan) You wanna talk about it here or via email?

Hi Ted,

1) I have rudder offset
2) I'm not sure right off the top of my head, I'd have to figure it out.
3) the leadouts, the center of them are about an inch and a half back from the cg.
4) the upline is in the back and are about a 1/2" apart
5) motor is a PA 40UL swinging an 11.8-3.8 repitched to 4.25. Pipe length is 17 inches and my RPM at launch is 10700.

And you can email me our comments about the pattern

[Howard Rush]

I recommend taking out the warp, rather than trying to compensate with a trim tab.  Trim tabs work fine in the linear range of the wing lift curve, but stunt planes get into the nonlinear part, particularly if warped.  This is a somewhat esoteric phenomenon.  You remember from math or physics that superposition applies for linear systems. There is a tendency for people to assume that it applies for stuff that ain't linear, too.  Such people are characterized by low stunt scores. 

[Matt Colan]

I recommend taking out the warp, rather than trying to compensate with a trim tab.  Trim tabs work fine in the linear range of the wing lift curve, but stunt planes get into the nonlinear part, particularly if warped.  This is a somewhat esoteric phenomenon.  You remember from math or physics that superposition applies for linear systems. There is a tendency for people to assume that it applies for stuff that ain't linear, too.  Such people are characterized by low stunt scores. 

Hi Howard,

The wing is a foam wing so if there was a warp, it would be pretty hard (I would imagine) to take out a warp in a foam wing. Ill check to see if there are any warps in that wing

[RC Storick]

Hi Howard,

The wing is a foam wing so if there was a warp, it would be pretty hard (I would imagine) to take out a warp in a foam wing. Ill check to see if there are any warps in that wing

I bet if you were here we could get it out. Its hard to do on a foamie but if you get it hot (super heated steam) you can bend a 2x 4

[Ted Fancher]

I bet if you were here we could get it out. Its hard to do on a foamie but if you get it hot (super heated steam) you can bend a 2x 4

Is one of the wing tips on crooked...acting like a tab?

[Tim Wescott]

You remember from math or physics that superposition applies for linear systems.

Howard, he's in high school.  The don't introduce linearity and superposition and that stuff until calculus at least, if not differential equations (well, and in physics and engineering classes).  In my case they either didn't introduce it emphatically enough or I was too dim to get it the first time around -- I remember taking quite a while to grasp the concept, and not realizing until well after differential equations classes that instead of an arm-long recipe of properties I could just subject a differential equation to the superposition test to know if it was linear.  (Once I got it into my head that a system is linear if and only if superposition applies, however, life became easy).

I would expect that less than 10% of the folks on this forum know what a linear system is, and remember that superposition is the defining characteristic of same.  I'd be mildly surprised if the number is over 1%, except that there seem to be a lot of engineering types flying CLPA.  Heck, among the circuit designers that I work with I think it's around 20%, unless they're forcefully reminded.

There is a tendency for people to assume that it applies for stuff that ain't linear, too.  Such people are characterized by low stunt scores. 

We're going to have to poll the top 10 at the Nats to see if you really need to know what a linear system is to fly stunt.  I think not, although if you have the rest of what you need, being enough of an engineer to know probably helps.

[Brett Buck]

Howard, he's in high school.  The don't introduce linearity and superposition and that stuff until calculus at least, if not differential equations (well, and in physics and engineering classes).

      I don't know what you are talking about. Both topics were introduced in high school even in 1978 in central Kentucky, and while I didn't grasp the full implications at the time, it was certainly notionally clear enough. And in any case, both Howard and I have talked to Matt and I certainly don't expect that this would be beyond his capabilities to understand, or to figure it out if he didn't.

    Brett

[Tim Wescott]

I know Matt's a smart cookie, and if you say he can understand, I'll believe it.

I still hold to the rest of my statement -- when I start babbling about linear systems to fellow engineers who aren't working daily with closed-loop control systems I often get crossed eyes in response; I wouldn't expect that knowing (or even understanding) the concept is necessary to being able even to understand that adding trim tabs to control warps just introduces additional weirdness, nor would I expect that its understanding is necessary to flying well.

[Matt Colan]

Is one of the wing tips on crooked...acting like a tab?

Possibly, I'm not really sure, I'll have to look at it closely.

I flew two patterns with it today, and I'm going to shorten the lines a foot and see what that does.

The way this plane flies, I think it resembles the olden days where power was limited and you really had to work to get it through a pattern.  This plane floated through the square 8, vertical 8, hourglass, overhead 8 and the 2nd half of the 4 leaf.

[Steve Fitton]

Just out of curiousity Matt, what are the laptimes at the beginning/middle/end of the flight?

[Matt Colan]

Just out of curiousity Matt, what are the laptimes at the beginning/middle/end of the flight?

Good question.  My answer is I don't know.  At the beginning of the flight, I'm somewhere around 5.2.  It feels like about the same speed by the end of the flight, and probably goes to 5.1.

[Derek Barry]

Possibly, I'm not really sure, I'll have to look at it closely.

I flew two patterns with it today, and I'm going to shorten the lines a foot and see what that does.

The way this plane flies, I think it resembles the olden days where power was limited and you really had to work to get it through a pattern.  This plane floated through the square 8, vertical 8, hourglass, overhead 8 and the 2nd half of the 4 leaf.

Matt, there is plenty of power in a PA 40. I used one for years in a similar sized plane that was not very light. That plane put me in the top 5 for the first time. I know that you don't have the extra room to bring it to the team trials, but if you did, we would get it fixed. What nitro are you running?

[Matt Colan]

10%. we can't use any more nitro because when I sent the motor to Randy to have it rebuilt after the crash, he opened up the venturi for me and I'm getting the perfect run time on 6 ounces of fuel. It quits around 10-14 laps after the clover. I have a gallon if 15% and I could try it but I'm not sure how much gas mileage I'm going to lose.

[Derek Barry]

10%. we can't use any more nitro because when I sent the motor to Randy to have it rebuilt after the crash, he opened up the venturi for me and I'm getting the perfect run time on 6 ounces of fuel. It quits around 10-14 laps after the clover. I have a gallon if 15% and I could try it but I'm not sure how much gas mileage I'm going to lose.

It should not affect your run time too much. If you are not getting the power you use too and nothing else has changed, 99% of the time it is a lack of nitro. Another trick you can try is to put solid lines on your plane. I have
had planes that didn't fly very well, I put solids on to reduce the drag and there was a great improvement in performance. There is nothing wrong with adding some pitch to the prob either, If you do not have enough power or
speed all of the trim problems will be multiplied. Matt, always start with the simple stuff first! Playing with props and nitro is a good place to start.

Another question; are the hinge lines sealed?

[Derek Barry]

What brand fuel are you using? All I use is SIG Champion! I have found that Sig seems to give the most bang for the buck when it comes to nitro levels. Thats just me though.

[Steve Fitton]

When you get a chance Matt try getting accurate times from all aspects of the flight.  I know on my Dreadnought it turned out that it was losing 3 or 4 tenths of speed from beginning of the flight till the end.  For some reason I couldn't really detect or feel it except as expressed as poor overhead and vertical maneuver performance.  When I got to Muncie Eric V and Bill Rich instantly noticed the problem when they timed the flight and a simple pipe adjustment fixed the problem.  Its worth checking for this, because a simple adjustment on the motor side can sometimes fix all those trim "issues".

[Matt Colan]

It should not affect your run time too much. If you are not getting the power you use too and nothing else has changed, 99% of the time it is a lack of nitro. Another trick you can try is to put solid lines on your plane. I have
had planes that didn't fly very well, I put solids on to reduce the drag and there was a great improvement in performance. There is nothing wrong with adding some pitch to the prob either, If you do not have enough power or
speed all of the trim problems will be multiplied. Matt, always start with the simple stuff first! Playing with props and nitro is a good place to start.

Another question; are the hinge lines sealed?

We don't use solids because we're on grass, and they're not the easiest to take care of (as it seems to me).  My current pitch is 4.25 and it made a noticeable difference from where it was (slightly less than 4).  I'll give the 15% a try.

Yes the hinge lines are sealed.

What brand fuel are you using? All I use is SIG Champion! I have found that Sig seems to give the most bang for the buck when it comes to nitro levels. Thats just me though.

Yep, I'm using SIG Champion for the PA.

[Doug Moon]

I have flown one of these planes and I noticed right away it doesnt have the tail power of your more modern stunter.  I think you would be going backward with a larger heavier motor. 

I also agree with DB that the 40UL should whip it around no problem.  Once you have the level and the LOs in the right position along with the correct TW curing, or at least close. 

The rest will be cured with the correct prop choice.  This will also reveal the power in the motor more clearly.

A smaller diameter can relieve that sluggish turn you talked about.  And you can still get plenty of pull with less diameter.

What are the length of the lines? Eye to eye. 

But for the most part I think you will spend along time chasing the performance of your TP.  BUT in the long run this will be a great learning exercise.  Trying to get this plane to do what the other did while you build out a new stunter for next year.  Be sure to note it all down as you go.  Also learning to fly good patterns with less that ideal setups can really sharpen your skills and once you pick up the well trimmed rig it will be like power steering. 

[Matt Colan]

I have flown one of these planes and I noticed right away it doesnt have the tail power of your more modern stunter.  I think you would be going backward with a larger heavier motor. 

I also agree with DB that the 40UL should whip it around no problem.  Once you have the level and the LOs in the right position along with the correct TW curing, or at least close. 

The rest will be cured with the correct prop choice.  This will also reveal the power in the motor more clearly.

A smaller diameter can relieve that sluggish turn you talked about.  And you can still get plenty of pull with less diameter.

What are the length of the lines? Eye to eye. 

But for the most part I think you will spend along time chasing the performance of your TP.  BUT in the long run this will be a great learning exercise.  Trying to get this plane to do what the other did while you build out a new stunter for next year.  Be sure to note it all down as you go.  Also learning to fly good patterns with less that ideal setups can really sharpen your skills and once you pick up the well trimmed rig it will be like power steering. 

The length of the lines eye to eye are probably 61ft.  I measured them yesterday, and center to center, the length of the lines are 63 feet, 5 inches.  i'm going to shorten it a foot because it's really falling out of the sky in the power maneuvers, and the pipe is trying to keep the airspeed going (keep in mind this is also in stunt heaven conditions).

I didn't think of the diameter, that could give some better performance.  Also I did notice that handle is off to what I was flying, I need to move the down line one notch down, which also may be a factor in the sluggish outside.

[Doug Moon]

Yes take off some length.  You might even end up at 59'.  That seems like a magical number for some reason on planes that size.