Soft outsides, tight insides

[Curare]

Hey guys, I'm just in the process of trimming out my chipmunk, and while I'm getting close on tank height, and the line length is just about spot on, I noticed this morning that my insides are nice and tight, but my outsides open up considerably.

I'm running without the cowl at the moment, so I can make adjustments, so it'll get more nose heavy, but not much, but I don't know if that will make any difference, apart from exacerbate the soft outsides.

I added a little bit of positive incidence on the tail and now I'm thinking I might have overcooked that.

Should I just widen the down line spacing on my handle to get the same feel, or should I crack open the fuselage and add some up elevator to compensate for too much pos on the tail?

Cheers

Greg

[Dave_Trible]

Yes Greg bias your handle or just reset your level adjustment a bit.  I sense differences like that just changing from one airplane to another when I know it was 'spot on' before.  My 'feel ' shifted a little.  If the airplane seems to lay flat upright and inverted then it's about the handle.

Dave

[Derek Barry]

Yes Greg bias your handle or just reset your level adjustment a bit.  I sense differences like that just changing from one airplane to another when I know it was 'spot on' before.  My 'feel ' shifted a little.  If the airplane seems to lay flat upright and inverted then it's about the handle.

Dave

I agree.

Derek

[Brian Massey]

"I noticed this morning that my insides are nice and tight, but my outsides open up considerably."

Where's your CG?  Sounds like it could be a bit tail heavy. Try attaching a temporary bit of weight and make a test flight to see how it responds. I had this issue with an ARF Nobler. I added 1 ounce to the tail and it turns very well both ways now. Still have some handle trimming to do for overall feel.


"Should I just widen the down line spacing on my handle to get the same feel, or should I crack open the fuselage and add some up elevator to compensate for too much pos on the tail?"

If it is tracking correctly in level flight (upright & inverted), I would hesitate to mess with the elevator incidence. If it's tracking great in level flight, that should also indicate your handle is pretty much set up right too.

Brian

[Motorman]

I had the same problem and totally fixed it with a change in engine thrust line.


MM

[Randy Cuberly]

I agree with Derek and Dave.  Work with the handle before you open up the fuselage.  If your elevator was easily adjustable I would probably say do that.  However, take the easy way out first.  If you can't get where you need to be then think about cutting into the fuselage.

Incidentally, this is why most of us silly "experts" use adjustable elevator linkages...makes things much easier.  Tom Morris makes control horns that make this adjustable!

Randy Cuberly

[Steve Helmick]

I'll side with Motorman. Downthrust should improve both the groove and the turn. If it was the other way around, I'd be reluctant to put in upthrust. It's a very powerful adjustment (or misalignment). At very least, you'll learn something, and you can go mess with the handle. Somebody smart once wrote that it was best to fix what was wrong, vs. working around the problem. If the airplane isn't right, fix the airplane if you can.  Steve

[Ted Fancher]

Hey guys, I'm just in the process of trimming out my chipmunk, and while I'm getting close on tank height, and the line length is just about spot on, I noticed this morning that my insides are nice and tight, but my outsides open up considerably.

I'm running without the cowl at the moment, so I can make adjustments, so it'll get more nose heavy, but not much, but I don't know if that will make any difference, apart from exacerbate the soft outsides.

I added a little bit of positive incidence on the tail and now I'm thinking I might have overcooked that.

Should I just widen the down line spacing on my handle to get the same feel, or should I crack open the fuselage and add some up elevator to compensate for too much pos on the tail?

Cheers

Greg

Greg,

You said some things that didn't make sense to me so I'm going to ask a question before I venture any opinion.

When you said you "added some positive incidence to the tail" how, in detail, did you go about doing so?

Ted

[Curare]

Ted, sorry I was probably a little vague, I've added a little bit of positive incidence to the stab, as per RJ Whitley's things that work for stunt article.

It would be less than a 1/2 degree, about 1/32" height difference from the leading edge to the hinge line (3")

I'll futz around with the handle spacing to see what I get get sorted, prior to surgery.

Randy, I did have adjustment in mind, and did acutally build a removable tail cone, but after I found that the mounting pins were fouling the pushrod (I made the fuse too narrow to get it all in, silly me!) I simply glue it on, but it would only take a few slices to get at it if need be.

[Ted Fancher]

Ted, sorry I was probably a little vague, I've added a little bit of positive incidence to the stab, as per RJ Whitley's things that work for stunt article.

It would be less than a 1/2 degree, about 1/32" height difference from the leading edge to the hinge line (3")

I'll futz around with the handle spacing to see what I get get sorted, prior to surgery.

Randy, I did have adjustment in mind, and did acutally build a removable tail cone, but after I found that the mounting pins were fouling the pushrod (I made the fuse too narrow to get it all in, silly me!) I simply glue it on, but it would only take a few slices to get at it if need be.

Greg,  Don't take this the wrong way.  I just need to know precisely how the stab incidence change was accomplished and in what direction.  The reason I ask with such  specificity is that Positive incidence in the stabilizer/elevator is more likely to make the ship turn more briskly on outsides...not insides.  Positive incidence in the stab requires that the "leading edge" be raised in small amounts thus making the "neutral stab/elevator") at a positive angle of attack with respect to the wing (and, if you don't build in downthrust like RJ also--correctly in my opinion--advocates) and the thrustline.

If you've, in fact, built in the positive incidence properly and are experiencing more responsive inside than outside turns something else is haywire  either aerodynamically or with the control system.  I hesitate to raise this once again but...if you fly with the "relaxed/tilted handle" in level flight you might find the best solution is to get your handle more vertical at neutral which will automatically improve outsides vice insides.

Check to make sure your flaps and elevators are neutral at the same time and, if they're not, let me know which way.  If you get more flap relative to elevator in one direction that will make cornering less brisk in the direction that deflects more flap.  If that's the case there is something improper in the internal control setup, allowing unequal deflections inside versus outside.

As others have suggested, unsealed hinge lines can result in more effective flap or elevator in one direction or the other if the gap increases in one direction and closes in the other.  In your case if the elevator hinge line closes with up control and opens with down the tail becomes less effective in outsides and will require more deflection to obtain the same rate of turn.  If the flap hinge line opens up in inside maneuvers and closes in outsides you will have more negative pitching moment in the outsides fighting the ability of the stab/elevator to pitch the airplane in outsides.  the solution is to seal the hinge lines so that there is no change in the gap.

I am not a fan of biasing the handle except in the grossest conditions where the airplane can't be trimmed aerodynamically to fly uniformly inside versus outside.  FWIW, I've never had a stunt ship that, when trimmed, required any significant, measurable difference between up and down line spacing at the handle.

Te

[Curare]

Ted, no offence taken. the positive incidence was acheived by recessing the trailing edge of the stab (not the elevator) but 1/32"  when being fixed to the fuselage. So, as you say, the leading edge is higher than the trailing edge.

I haven't added any downthrust into the aircraft yet, but I do have the provision to do so. Something else to play with at a later date perhaps.

After reading a lot on here and other places about taking pains to get your control geometry right, I did try and spend as much time as I could getting it right. I have around 26° up and down on flap and about 35° for elevator, and the throws appear to be equal or within a degree or so. I had a bit of a fiddle after flying and moving the leadouts a given distance from centre (say half an inch) seems to give me the same up and down throw from centre.

When I had flown it last I hadn't taped the hingelines, as I was curious to see whether I would get any anomalous behaviour (I did), and now they're taped .

Now as an aside, I fly using a Ted handle! I have to admit here, that I religiously read everything that you and Brett Buck type, (Including a lot of your old articles when I can find them), so I fly with a vertical handle, and no differential overhang, and a minimal overhang. (I'm also learning to fly inverted with a vertical handle instead of palm-up but thats a different story).

hopefully the weather will be kind this weekend and I can get out for another round of testing.

Thanks again!

[RknRusty]

A simple solution worked for me when my new plane turned tighter insides and perfect outsides. I simply moved the Up line at the handle 1/4" closer to center. I don't know enough to know if I covered up another problem, but now I can repeatedly fly equal loops in both directions, so well that I thought I should post this reply.
Rusty

[Ted Fancher]

Ted, no offence taken. the positive incidence was acheived by recessing the trailing edge of the stab (not the elevator) but 1/32"  when being fixed to the fuselage. So, as you say, the leading edge is higher than the trailing edge.

I haven't added any downthrust into the aircraft yet, but I do have the provision to do so. Something else to play with at a later date perhaps.

After reading a lot on here and other places about taking pains to get your control geometry right, I did try and spend as much time as I could getting it right. I have around 26° up and down on flap and about 35° for elevator, and the throws appear to be equal or within a degree or so. I had a bit of a fiddle after flying and moving the leadouts a given distance from centre (say half an inch) seems to give me the same up and down throw from centre.

When I had flown it last I hadn't taped the hingelines, as I was curious to see whether I would get any anomalous behaviour (I did), and now they're taped .

Now as an aside, I fly using a Ted handle! I have to admit here, that I religiously read everything that you and Brett Buck type, (Including a lot of your old articles when I can find them), so I fly with a vertical handle, and no differential overhang, and a minimal overhang. (I'm also learning to fly inverted with a vertical handle instead of palm-up but thats a different story).

hopefully the weather will be kind this weekend and I can get out for another round of testing.

Thanks again!

Greg,

Gotta admit, you appear to have done all the measurable things right so I've pretty much shot my wad on off the cuff suggestions.  Couple of additional thoughts about the airborne performance.

Is there a significant difference in line tension during insides and outsides?  Are the wings level upright and inverted? Do the wheels line up so you can see just the inboard or no more than about one third of the outboard wheel AFT of the inboard (this must be, of course, a calm wind observation).  Does the fuselage look to be parallel to the ground in level flight upright and inverted and, if not,  does it appear to "drag" the tail when in upright or inverted flight?

Just throwing darts here. 

If you get frustrated you can always do what others are suggesting and bias the line spacing at the handle to improve your ability to fly equal appearing maneuvers...doing so, however, is always a compromise as something aerodynamic is causing the problem and a mechanical adjustment can mask it but not cure it.

Good luck and keep us informed.

Ted

[Ted Fancher]

p.s. 

This is an IC powered ship with conventional prop rotation, right?

Ted

[Dave_Trible]

A simple solution worked for me when my new plane turned tighter insides and perfect outsides. I simply moved the Up line at the handle 1/4" closer to center. I don't know enough to know if I covered up another problem, but now I can repeatedly fly equal loops in both directions, so well that I thought I should post this reply.
Rusty

. Rusty what you got was something a little closer to an equal feel both ways.  When you hold your handle and look at it from the palm side including your wrist (the pivot point or 'bellcrank bolt') you'll notice for most of us the wrist is not on center with the handle and line attachments at all.  It's usually lower and thereby creating a natural bias towards the up line.  We learn to fly this way and adapt to the bias.  The down is naturally slower.  Your adjustment actually reduced the bias.

Dave

[Steve Helmick]

Hey guys, I'm just in the process of trimming out my chipmunk, and while I'm getting close on tank height, and the line length is just about spot on, I noticed this morning that my insides are nice and tight, but my outsides open up considerably.

I'm running without the cowl at the moment, so I can make adjustments, so it'll get more nose heavy, but not much, but I don't know if that will make any difference, apart from exacerbate the soft outsides.

My recollection is that the plastic Super Chip cowl is about 3 oz. That's pretty heavy IMO! Most either make a balsa cowl or use the kit part to make a plaster mold for a cowl of  FG/CF/epoxy...and then pitch out the kit part.

I added a little bit of positive incidence on the tail and now I'm thinking I might have overcooked that.

If you'd "overcooked", it would turn tighter outsides than insides, so stop worrying about that!

Should I just widen the down line spacing on my handle to get the same feel, or should I crack open the fuselage and add some up elevator to compensate for too much pos on the tail?

Actually, with soft outsides, you'd want to add down elevator. Also helps the groove, sometimes, but not always. Can make the fuselage not appear to fly level, either upright or inverted.

Cheers

Greg

How did you align the engine/wing/stabilizer? Incidence meters or eyeball or something between? Using the kit wing cutout, edge of the fuselage and the notch for the stabilizer for alignment most likely isn't good enough, no matter who makes the kit. I put my comments in Italics and Navy Blue to help pick them out. Also made a few of your statements bold for others to notice and re-read.  OBTW, you are following the plane with your arm on outsides, right? Some have trouble learning outsides because they don't, so I thought I'd mention it. I'm still voting to put some downthrust in that puppy for a flight, before messing with the handle. Steve

[Curare]

Ted, thanks for all the help. I really do appreciate it.

Line tension appears to be consistent throughout, and I can't see the outboard wheel pant for the inboard one so I figure I'm tracking ok. wings appear to be level, but I haven't had anyone eagle eyed enough to tell me for sure. It's carrying a bit more tip weight that it needs right now, as it tends to hinge a bit.  AS for whether it's dragging it's tail, that I can't tell you, I'll have to watch for that.

Steve, you bring up some good points, let me go through them peice by peice.

Firstly, this isn't your average kit chippy. It's carrying more area, and no assymetry (and a foam core wing with a fat LE) tail moment arm has been extended by 3" and the nose moment reduced by 1" the the tail has been built up rather than using the planks of mahogany in the kit, and the cowling is a carbon fibre one weighing less than an ounce. In fact, the only parts of the plane than came out of the box are the wheel pants, engine rails and canopy!

point 1.My recollection is that the plastic Super Chip cowl is about 3 oz. That's pretty heavy IMO! Most either make a balsa cowl or use the kit part to make a plaster mold for a cowl of  FG/CF/epoxy...and then pitch out the kit part.

True, that's why I pitched it as soon as I'd taken a carbon copy of it.

point 2.If you'd "overcooked", it would turn tighter outsides than insides, so stop worrying about that!

Cool, I'll breathe a sigh of relief!

point 3. Actually, with soft outsides, you'd want to add down elevator. Also helps the groove, sometimes, but not always. Can make the fuselage not appear to fly level, either upright or inverted.

Yeah, as I was saying I haven't checked it, but I can say that if it was, it wasn't enough to draw my eye to it dragging it's backside around.

point 4. How did you align the engine/wing/stabilizer? Incidence meters or eyeball or something between? Using the kit wing cutout, edge of the fuselage and the notch for the stabilizer for alignment most likely isn't good enough, no matter who makes the kit. I put my comments in Italics and Navy Blue to help pick them out. Also made a few of your statements bold for others to notice and re-read.  OBTW, you are following the plane with your arm on outsides, right? Some have trouble learning outsides because they don't, so I thought I'd mention it. I'm still voting to put some downthrust in that puppy for a flight, before messing with the handle. Hoff Steve

Wing and stab decalage is checked using my workbench (a large flat sheet of glass), by measuring from the table top up to the LE & TE. Wing is set at 0° as stated before the stab is running 1/32" positive at the LE. Motor mounts are set at 0°. Wing alignment in relation to the fuse is reasonably easy with a straight TE, and foam shucks, and the stab is set with it's hinge line directly parallel to the wing hinge line, and stab tilt is zero. (I tend to build alignment jigs rather than use my mk1 eyeball).

As for flying, yeah, I follow the plane all the time. I learned that the hard way!

I've still got some more trimming to do, and now that I've sealed the hinge lines, I'll try again, see if that fixes it, then move on to downthrust, then handle spacing.

Thanks guys!

[Ted Fancher]

Greg,

This may sound funny because I'm sure you didn't do it, but...

When you glued the stab in with positive incidence you didn't then set the controls with the elevators up a bit to get them zero zero with the wing did you?

If so the classic solution is to drop the elevator down a bit at a time to get the turn rates the same...with the Fitz fix (+ incidence) it generally isn't necessary but I build all mine stuff zero zero (except for down thrust) and anticipate having to drop the elevator a bit because outsides are a little soft.  Most do require some but I'm reluctant to assume it will be necessary, ergo, don't follow David's very successful for him choice to build it in.

Checking the fuse in level flight upright and inverted is often a good tattle tale of what's happening.  If the tail is dragging low one way and high the other adjust the elevator in small steps in the direction you'd give control to level it out.

Ted

[Steve Helmick]

A glass benchtop is great, if the bench under it is flat, or if you shim under the glass to make it flat. Not saying yours isn't, but glass isn't magically flat, either.  Glass does conform to whatever is supporting it, although I'm not convinced that everybody realizes it. Many say their benchtop is glass, but never say that it's flat, or how they got it that way.  Steve

[Curare]

Steve, having seen glass deflect like saran wrap in my time, I know full well that it's flexible.

My bench originally was a pool table slate, which had been levelled and shimmed for flatness when I moved house not that long ago.

Since then I stole a large piece of TSG from a glass works (from a bus) and shimmed it with sheets of paper, so I feel I can hang my hat on it for being within a thou or two over the 4'x3' sheet.