Twister Hinging Part II

[Paul Taylor]

Ok guys here is a update:

I had 1/4 oz tip weight. After some input it was determined that I did not have enough.

So I added 3/4 oz’s and flew the plane. When turning it over I was still seeing the OB wing tip. But line tension was much better.
Next flight I added 1/4 oz. Now when turning it over it is showing the bottom of the OB when going inverted and showing the top of the OB when turning over to up right.
I was flying solo today so I could not tell what the wing looked like in level flight. 🥴
So take out 1/8oz? Flap tweak?
I have looked at this wing from every angle and I can see a warp.
Would a video of the wing help?
Thanks

[Ken Culbertson]

Ok guys here is a update:

I had 1/4 oz tip weight. After some input it was determined that I did not have enough.

So I added 3/4 oz’s and flew the plane. When turning it over I was still seeing the OB wing tip. But line tension was much better.
Next flight I added 1/4 oz. Now when turning it over it is showing the bottom of the OB when going inverted and showing the top of the OB when turning over to up right.
I was flying solo today so I could not tell what the wing looked like in level flight. 🥴
So take out 1/8oz? Flap tweak?
I have looked at this wing from every angle and I can see a warp.
Would a video of the wing help?
Thanks

You are describing the classic warp but not necessarily in the wing.  How bad will determine if a tweak or tab will fix it.  You still might be light on tip weight (if you recall mine took 1 1/2 oz which is a bunch for a plane that small) but now that you have enough to keep it in the air get the wings level.  Warps in Twister wings are very common and the bad part is that they just keep doing it.  I had to de-warp mine about once a month in the flying season.  MonoKote made that easy. 

Video always helps!  Try and get side views all the way around and a shot from the top.

Ken

[Brett Buck]

Ok guys here is a update:

I had 1/4 oz tip weight. After some input it was determined that I did not have enough.

So I added 3/4 oz’s and flew the plane. When turning it over I was still seeing the OB wing tip. But line tension was much better.
Next flight I added 1/4 oz. Now when turning it over it is showing the bottom of the OB when going inverted and showing the top of the OB when turning over to up right.
I was flying solo today so I could not tell what the wing looked like in level flight. 🥴
So take out 1/8oz? Flap tweak?
I have looked at this wing from every angle and I can see a warp.
Would a video of the wing help?
Thanks

   So, with positive Gs you roll to the right/positive and with negative G you see left/negative? Sounds like you overshot a bit on the tip weight. For now, since  you are really just getting started, and can't see any small differences in level flight from the center, I would suggest leaving it as is until you work through the rest of the process. This will give you a bit of margin, then, when you are pretty close on everything, start removing it a few grams at a time. At some point as you are removing it, the corners will suddenly feel like non-events, it will just flow through the corner like nothing happened, that is the ideal tip weight.

    If you were down an ounce to begin with, your line tension should be *dramatically improved* , because that is a huge shortfall. Equal-span wings tend to require much more tip weight at a general rule, so that is not entirely surprising.

       Brett

[Paul Taylor]

Thanks guys. I will make a video tonight and if nothing jumps out the will proceed with the trim flow chart.

Stay tuned ….😎

[Ken Culbertson]

Thanks guys. I will make a video tonight and if nothing jumps out the will proceed with the trim flow chart.

Stay tuned ….😎

Brett and I both read your post and see the plane doing the exact opposite.  When the plane is level upright do you see the top of the outboard wing (it is higher than the inboard).  When it is inverted level do you see the bottom of the outboard wing (it is higher).  This is a sign of not enough tip weight.  If it is doing what Brett sees it is too much.  I can truthfully say one of us is right.  Here is something we used to do on a new plane "back in the day".  Set the plane upside down on a flat surface so that the top of the rudder and nose or canopy are all that touches.  Put an old set of lines (on the reel of course) on the inboard tip.  Add tip weight till the outboard wing gently falls and touches.  This will put you in the ballpark and will be sufficient for wings level trimming.

All planes are different, even ones from the same plans so my Twister is going to be different from yours BUT I never had much sucess with it till I added tip weight then trimmed the inboard flap chord 1/8" and added a small "Wart" to the outboard flap.  In other words, a tradeoff.  It needed the tip weight for normal flight and it needed the other changes to compensate for having too much tip weight for corners.

I am still betting that you have a small warp! 

Ken

[Howard Rush]

Brett and I both read your post and see the plane doing the exact opposite. 

That's because of an ambiguity of the description of the maneuver used to flip the airplane over.  Some facts (which you probably won't believe, because nicer people have told you different):

Bank angle in level flight won't tell you much about tip weight.   The effect of tip weight is greatly amplified in maneuvers.  If you see the top of the wing in outside loops and the bottom of the wing in inside loops, you have too much tip weight.  If the airplane gets light on the lines in both inside and outside loops, you have too little.  You may be overdoing the tip weight changes: two grams is a significant change. 

The line reel thing comes from long-ago stunt lore and has no physical basis. You might as well use your hat or a Tom Waits cassette tape. 

If your wing has a warp (you said it does, but we assume you meant that it doesn't), a tab will balance the warp for some loop radii, but not all.  This is because the wing section lift curve is nonlinear.  Somebody here has probably drawn pictures explaining it. 

Fiddling with flap area asymmetry has a very subtle effect and not worth the bother for an established design--not until you get tip weight within a gram, anyhow. 

There is no physical basis for equal flap area. 

[MikeyPratt]

Hi Paul,
I agree with all the post but it sounds like you getting there, Good Job.  To remove small amounts of tip weight, just clip off the corners of the weight.  If you have too much, trim off a little more, piece of cake!

Later,
Mikey

[Brett Buck]

Brett and I both read your post and see the plane doing the exact opposite.

   Which is why I was asking for confirmation of my interpretation. In any case, he is up an entire *1 ounce* in tip weight from before, that's such a huge leap that he is starting over - which is OK because he wasn't too far down the road anyway. I sure wouldn't take any out until it was closer in other ways, then, very slowly start removing it.

    Brett

[Paul Taylor]

Yes it is doing the opposite. Before I was seeing the OB top as just as it turned over and rolled into the circle going in to free flight. Now it’s not turning in and no more free flights.
I did shoot a video last night but I had someone PM me to check the distance between hinge lines.
Well I’m am not sure how this happened cause I was checking and rechecking as I glued the stab in. But it’s off by a 3/16 between hinge lines and 1/4 from tip to tip.

[Brett Buck]

Yes it is doing the opposite. Before I was seeing the OB top as just as it turned over and rolled into the circle going in to free flight. Now it’s not turning in and no more free flights.
I did shoot a video last night but I had someone PM me to check the distance between hinge lines.
Well I’m am not sure how this happened cause I was checking and rechecking as I glued the stab in. But it’s off by a 3/16 between hinge lines and 1/4 from tip to tip.

  That's bad, but fortunately. relatively easy to fix.

    But,. just so we are perfectly clear about the current situation - when you turn inside/positive G, which direction does it roll (i.e. do you see the top of the wing, or the bottom)?  When you turn negative G, which way does it roll (do you see the top or bottom).

   Too much tip weight = see the bottom of the wing in positive G/inside turns, see the top of the wing in negative G/outside turns
   something crooked = see the same side of the wing in both positive and negative G maneuvers, or see nothing one way and a lot the other.

    Brett

[Ken Culbertson]

Just to be clear, the green line is the one you are going by.  I am sure there are lots of tricks but when I do the stab I cut two 1/4" sq balsa strips to the exact length I want and put vertical tabs on them to but up against the wing and stab.  I tack them in place with some CA or pin them so that the stab cannot move out of alignment with the wing.  Only then do I glue in the stab.  I leave the sticks on till the glue is firmly set.  Don't forget to make sure it stays level with the wing. 

Now get it straight - Ken

[Howard Rush]

...I had someone PM me to check the distance between hinge lines.
Well I’m am not sure how this happened cause I was checking and rechecking as I glued the stab in. But it’s off by a 3/16 between hinge lines and 1/4 from tip to tip.

Impacts fly funny if the hinge lines are not parallel, but is that true of all stunt planes?  I can't think of a reason why they should be parallel.  Perhaps Brett would explain.

[Paul Taylor]

  That's bad, but fortunately. relatively easy to fix.

    But,. just so we are perfectly clear about the current situation - when you turn inside/positive G, which direction does it roll (i.e. do you see the top of the wing, or the bottom)?  When you turn negative G, which way does it roll (do you see the top or bottom).

   Too much tip weight = see the bottom of the wing in positive G/inside turns, see the top of the wing in negative G/outside turns
   something crooked = see the same side of the wing in both positive and negative G maneuvers, or see nothing one way and a lot the other.

    Brett

I see the bottom when turning over to inverted and top turning back.
I took out 1/8 oz and will try again. Also will align the hinge lines.

[Paul Taylor]

Just to be clear, the green line is the one you are going by.  I am sure there are lots of tricks but when I do the stab I cut two 1/4" sq balsa strips to the exact length I want and put vertical tabs on them to but up against the wing and stab.  I tack them in place with some CA or pin them so that the stab cannot move out of alignment with the wing.  Only then do I glue in the stab.  I leave the sticks on till the glue is firmly set.  Don't forget to make sure it stays level with the wing. 

Now get it straight - Ken

The green line is off and I measured between the tips also. Both are off.
I will use the stick method. Sounds good. Thanks

[Ken Culbertson]

Impacts fly funny if the hinge lines are not parallel, but is that true of all stunt planes?  I can't think of a reason why they should be parallel.  Perhaps Brett would explain.

I am going out on a limb and partially agreeing with you, especially on a profile.  CF will throw the tail out on a profile.  It may be just a tad, or it might be a quarter inch or more.  Surely some engineer has come up with a do-dad to measure it.  As soon as it flexes (twist?) your nice parallel hinge lines are gone and you have an alignment that is producing outward yaw or roll or both.  Thigs that make you go Hummm....

Ken

[Brett Buck]

Impacts fly funny if the hinge lines are not parallel, but is that true of all stunt planes?  I can't think of a reason why they should be parallel.  Perhaps Brett would explain.

    There was a school of thought for a while about that - that you could either tilt or skew the stab in order to implement a Rabe Rudder effect. I tried the tilt, it was way too sensitive, and was thinking about skew. Then I talked to Paul Walker about it, and found that his airplane became unhinged (heh) with 1/64" of skew. Subsequent investigation found a bunch of airplanes where the skew moved around in various conditions - most notably Ted's "Pond Scum" Trivial Pursuit - would work great in some conditions and terrible in others. We even tracked it to the sun position, and the "bad" days were with the sun on the side of the fuse sitting in the pits, and the "good" days had the pits so the fuselage lined up with the sun.

    For trigonometry fans 1/64" represent 0.03 degrees of misalignment. Building a balsa-wood airplane to tolerances of 16/1000ths of an inch is beyond almost all of us, keeping it that way is out of the question.

     To the point on the Impact, one of the aspects of the design that scared be off was stuff like this - it has stellar performance when it's right, but the difference between just right and noticeably off is extremely fine and takes extensive effort and many many flights to keep it that way. My airplane is intentionally designed to be extremely stable in all the alignments and less sensitive to trim adjustments because I know for certain I am not going to be able to do enough flights to continually adjust things in increments of a few grams or a few thousandths. Even if it costs me a fair bit of weight trying to stiffen or stabilize the alignment, and some aerodynamic performance in making it insensitive (in particular, relatively low aspect ratio and more-or-less square tips.

    There are some downsides to that approach, but it's what *I* think I need to have a hope of being competitive.

     Brett

[Brent Williams]

Comment removed to keep the thread focused on diagnoses and tuning.

[Ken Culbertson]

    There was a school of thought for a while about that - that you could either tilt or skew the stab in order to implement a Rabe Rudder effect. I tried the tilt, it was way too sensitive, and was thinking about skew.

I have tried skew.  1/16" at the tip of the stab.  Didn't do much.  Maybe it was not enough.  As long as you are going to fly a profile, I guess you just build the fuselage as stiff as you can then live with it.

ken

[Paul Taylor]

So I need to move the stab 1/16th of a inch to get it lined up hinge line to hinge line.

So after reading above that may not really be Necessary. Maybe fly it with the 1/8th oz removed from the tip and see if that make an improvement?

Thought?

[Brett Buck]

So I need to move the stab 1/16th of a inch to get it lined up hinge line to hinge line.

So after reading above that may not really be Necessary. Maybe fly it with the 1/8th oz removed from the tip and see if that make an improvement?

Thought?

     Maybe you don't need any more assistance, but, you have never clearly verified the symptoms as requested above.

     But, yes, I would straighten out the tail skew (although I bet it moves around far more than that in different conditions), then, proceed down through the process. The next step would be getting the rudder and leadouts adjusted for minimum yaw transient, then, go back to correct the tip weight, then on down through the procedure.

  Note that this process doesn't have an end - it goes on until you wipe out or retire the airplane. I evaluate trim on every single flight, even competition flights, and make changes as necessary.

     Brett

         

[Ken Culbertson]

So I need to move the stab 1/16th of a inch to get it lined up hinge line to hinge line.

So after reading above that may not really be Necessary. Maybe fly it with the 1/8th oz removed from the tip and see if that make an improvement?

Thought?

I didn't mean to mislead you into thinking that it did not need to be fixed, it does. Which stab tip is closer to the wing, the inboard or the outboard.  The skew I was referring to has the inboard stab tip a bit closer to the flap hinge line.  The theory was (I don't know of anybody doing this today) that the twist of the fuselage in flight would make them line up parallel.  Great theory but who knows how much they really flex?  Judging from how many times I have to iron down wrinkles on the fuselages of my profiles, it is a lot.  One day I might just strap a camera on mine and find out.

Ken

[Paul Taylor]

Sorry Brett I thought I answered the question.

Yes it is now doing the opposite as it were it was in my first thread. Now that I added more tape wait I am seeing the bottom of the outboard wing on the plane turns over two converted and when I roll it back to upright I’m seeing the top of the outboard wing. I now have line tension and I’m not having flyways like I did earlier. So I think this confirms that a quarter ounce of tip weight was not enough. I have since removed 1/8 of an ounce of tip weight. I don’t see any warps in the wing and so I think my next task is to fly the plane again to see if the tips are still dropping. I hope to have another set of eyes watching the next flight and I’ll report back - let me know if this doesn’t answer your questions. thanks again.

[Paul Taylor]

I didn't mean to mislead you into thinking that it did not need to be fixed, it does. Which stab tip is closer to the wing, the inboard or the outboard.  The skew I was referring to has the inboard stab tip a bit closer to the flap hinge line.  The theory was (I don't know of anybody doing this today) that the twist of the fuselage in flight would make them line up parallel.  Great theory but who knows how much they really flex?  Judging from how many times I have to iron down wrinkles on the fuselages of my profiles, it is a lot.  One day I might just strap a camera on mine and find out.

Ken

Gotcha - The difference is 1/8 in with the OB being closer. So splitting the difference I would have to move the OB hinge line 1/16th closer.

[Ken Culbertson]

Gotcha - The difference is 1/8 in with the OB being closer. So splitting the difference I would have to move the OB hinge line 1/16th closer.

Any outboard skew needs to be fixed.  It gets worse in the air not better like inboard skew.

Ken

[Motorman]

I wouldn't measure from tip to tip. That method can have allot of pitfalls. You have to be sure the wing span (and tail span) are exactly the same on both sides and your wing is perfectly square with the fuselage to say the least.

Just hook your tape measure into the flap leading edge, make sure the tape is square with the hinge line and judge from there. This is a direct measurement that doesn't depend on other dimensions.

Motorman