Trim question

[Gary Dowler]

Was out flying the Ringmaster today. Trying to sort out a few minor issues.

1: wings perfectly level in level flight, but outboard wing dips in both inside and outside turns. I can see what would be the wing surface that looks at the ground in either turn.

2: noticeable difference in turn rate inside to outside, with outside turns being much sharper.   Up elevator has 35 deg, down has 38 deg.  There is a pushrod brace in place, but I can't rule out all flex.

3: loss of line tension on inside turns, but not on outside turns.

I hope I've described things correctly. Any suggestions are appreciated.

Gary

[Howard Rush]

Assuming that the #1 Trimmer of the Western
World has seen this Ringmaster, any advice you will get is from someone who knows less and hasn’t seen it: me, for example.

Did you try to counter a warp with a trim tab?

Do you have a dogleg in the pushrod?  That makes it hard to get enough up.

[Dave Harmon]

Was out flying the Ringmaster today. Trying to sort out a few minor issues.

1: wings perfectly level in level flight, but outboard wing dips in both inside and outside turns. I can see what would be the wing surface that looks at the ground in either turn.

2: noticeable difference in turn rate inside to outside, with outside turns being much sharper.   Up elevator has 35 deg, down has 38 deg.  There is a pushrod brace in place, but I can't rule out all flex.

3: loss of line tension on inside turns, but not on outside turns.

I hope I've described things correctly. Any suggestions are appreciated.

Gary

Hi Gary....
1. too much tip weight....try reducing the weight by half and see what happens.
3. be sure to hold the handle directly in front of you...don't let your arm move to the right (if you are right-handed) when you apply up elevator. Moving your arm to the right will make the plane yaw towards you. (on inside loops)
Be sure the c/g is correct and the center of the lead outs about 3/4" to the rear of the c/g.

[Gary Dowler]

Assuming that the #1 Trimmer of the Western
World has seen this Ringmaster, any advice you will get is from someone who knows less and hasn’t seen it: me, for example.

Did you try to counter a warp with a trim tab?

Do you have a dogleg in the pushrod?  That makes it hard to get enough up.

No warp that I can see, pushrod is straight.

[Ken Culbertson]

Pretty sure you have checked all of this but what your are describing is the way a plane responds if the stab TE is not in alignment with the wing TE with a touch of down thrust in the engine and perhaps too much tip weight.   Unfortunately there is no "trim" you can add to fix the alignment one.  It requires an X-acto and profanity.

Pushrod flex is a real issue with non flapped profiles.  Problem with the guides is that they don't allow the rod to move naturally.  If you can, try slipping a length of small CF tubing over the rod as close to the bellcrank as you can get it without surgery and as close to the elevator horn as is practical.  Hopefully you used a clevis or ball link on the stab so this will be simple.

Ken

[Dave_Trible]

I’d agree- too much tip weight.  You can overcome your other issues with handle adjustments.  The geometry of your handle, how you hold it and the mechanics of your hand and wrist are all factors.  You can do one or both the following:
Pull your down line out a tiny bit-in for up line in regards to handle level adjustment.
You should be using a handle that you can adjust line spacing. Push the up line out a knotch or the down line in a knotch to balance the input you are feeding the airplane.

Dave

[FLOYD CARTER]

Many flyers adjust their handle so it feels "right" and comfortable for neutral, level flight.  This results in a neutral having the handle biased slightly in the "down" position,.  Actually, the human hand tends to give "up" control easier than "down"/  Therefore, a handle biased pointing slightly down in neutral will result in less line movement for down, making you think turns are not equal.

The best plan is to have your handle perfectly "upright" at neutral flight.  Make sure, when elevator is level, that the handle is perfectly upright, with no "down" pointing.

[Tim Wescott]

Pretty sure you have checked all of this but what your are describing is the way a plane responds if the stab TE is not in alignment with the wing TE...

I always check this, and I'm not happy until there is no difference that I can see -- and I can see when the stab is off by 1/16" or so at the tips.

Put the spinner on your toe, and hold the back of the fuselage.  Close one eye.  Look down so that you're sighting exactly down the fuselage (if you're off from side to side you'll throw off what you see).  Now pitch the plane down gently (keeping it aligned side to side) until the stab is even with the top of the wing (you may want to flick the elevator up so it's out of the way).  You want to tilt the plane until you just barely see daylight between the tops of the wings and the bottom of the stab, and you want that sliver of daylight to be dead even.  If it isn't -- adjust something.

While you've got the thing on your foot, look at the wing root and pitch the plane until you can see the same amount of wing above and below the trailing edge.  Now, without moving the plane or your head, move your eye out to the left wingtip, and then the right.  You should see an equal amount of wing above and below the TE at both tips.  If it's different, you have a warp.  You can also see if your TE is straight this way.  If you have the same warp on both wings then you're probably safe to fly, but you should fix it.  If you see a different amount of warp, then you need to fix things.

Pretty sure you have checked all of this but what your are describing is the way a plane responds if the stab TE is not in alignment with the wing TE with a touch of down thrust in the engine and perhaps too much tip weight.   Unfortunately there is no "trim" you can add to fix the alignment one.  It requires an X-acto and profanity.

You can tweak a profile fuselage into alignment with heat, if you're only going a few degrees.  If it's no more than a half an inch up and down on the tips on a 20" stab (so, about 2 1/2 degrees) it should work.  If it's more than that then yes, you need to break out the knives.  (Something that Brett Buck said recently makes me think that this technique will work on full fuselages, too, although probably to a much smaller extent).

I've only done this on rustoleum finishes and a heat gun -- I'd use the same thing on 'coat, only I'd be even more careful about slow heating, and if it was doped I think I'd try the hot towel trick first.  Note that this even works if you've got a glass/epoxy coat on the fuselage -- balsa and just about anything we use for glue or paint will soften at least a bit with heat -- that's all it takes for this technique to work.

Heat the fuselage up behind the wing, slowly and evenly.  I can't tell you how much -- it's always been guestimation for me.  Spend several minutes (it seems like five to me, but is probably less) with the heat gun six to ten inches away so you don't blister the paint (as I write "don't blister the paint" I'm thinking even more about using a hot towel).  Grab the fuselage (not the stab) and twist it so that it's just as badly out of line in the opposite direction.  Then turn off the heat gun and hold it in place for another five minutes to let it cool (putting it in a fixture may be even better -- I haven't done this to untwist a fuselage, but I've done it to take a longitudinal bend out of one).

You may have to give it more, or suck it back the other way.

You will want to check it again the next day or two, and then again before you go flying for several months to make sure it doesn't need more work.  Depending on how deep the heat went, you'll be twisting some opposing stresses into the wood.  As those relax, the thing may or may not develop a twist again -- if it does, just fix it again.  Usually when I do this things settle out after a while, or at least I end up with a plane that will get out of true over the winter and then stay OK for the next flying season.

[Brett Buck]

Was out flying the Ringmaster today. Trying to sort out a few minor issues.

1: wings perfectly level in level flight, but outboard wing dips in both inside and outside turns. I can see what would be the wing surface that looks at the ground in either turn.

2: noticeable difference in turn rate inside to outside, with outside turns being much sharper.   Up elevator has 35 deg, down has 38 deg.  There is a pushrod brace in place, but I can't rule out all flex.

3: loss of line tension on inside turns, but not on outside turns.

  1 suggests too much tip weight, but if you take some out, 3 will get much worse. You must fix the uneven line tension issue before you start taking out tip weight. Generic trimming would suggest that you tweak the wing or trim tab to get the tension the same on inside and outside maneuvers, regardless of how it looks in level flight, but first, verify that the engine is running the same way (speed and "setting") both ways, and that the stabilizer is neither tilted nor skewed with respect to the wing. Even a tiny bit of skew can really screw things up, tilt is a little more tolerable but I am talking about 1/64" in skew, and maybe 3/32 of tilt at the ends of the stab. If either, it needs to be corrected, then retest. If not, then, start tweaking the wing until the line tension is the same both ways, no matter what it looks like.

     I wouldn't do anything about differential turn radius until you resolve the line tension difference, one could easily influence the other. I would also suggest speeding the airplane up to make sure that as you trim, you have enough line tension to cover yourself even at the worst point in the pattern.

    Brett

[Dave_Trible]

Many flyers adjust their handle so it feels "right" and comfortable for neutral, level flight.  This results in a neutral having the handle biased slightly in the "down" position,.  Actually, the human hand tends to give "up" control easier than "down"/  Therefore, a handle biased pointing slightly down in neutral will result in less line movement for down, making you think turns are not equal.

The best plan is to have your handle perfectly "upright" at neutral flight.  Make sure, when elevator is level, that the handle is perfectly upright, with no "down" pointing.

Hi Floyd.  I’m afraid my comments were misunderstood. In the case of level adjustments I’m talking moving the attachment or cable in or out maybe 1/16”.  You’d not see any difference looking at the handle without a bubble level- but the feel and inputs will be quite different.  This this why I still prefer a cable handle.

Dave

[Peter in Fairfax, VA]

I'm curious as to why a cable handle would be superior to a hard point type.  Please explain the thinking.

The reason I ask is that a hard point sounds better, in several respects.  First, most do offer the same capability to make one line longer or shorter relative to the other, the same capability that most cable handles offer.  But the hard point handles often have a further capability to adjust line spacing, something that many cables handles lack.  Also, hard point handles are thought by some to offer a more solid attachment, acting less like a spring. 

Again, though I use them, I am wondering what is so great about cables handles. 

thanks,

Peter

[Dave_Trible]

I’m a little short on time at the moment but a lot of it I’m sure is just what you get used to.  I make my own so I have near total adjustment in all directions including line spacing in 3/32” increments.  In my mind “hard point” occurs wherever a ridgid attachment goes to a connector or cable exit.  That can occur at your knuckles with a cable handle or 1-2” out on a hardpoint.  Extending out simply deadens the response, like adding nose weight or narrowing line spacing.  I like having the feel and feedback from having the ‘hardpoints’ Just ahead of my knuckles.

Dave

[Howard Rush]

Also, hard point handles are thought by some to offer a more solid attachment, acting less like a spring. 

That's the main advantage of hard-point handles, I think.  I've been making my own.  Line length adjustment is by different length clips.  That wouldn't be practical for combat, but it's OK for stunt.

[Gary Dowler]

Thank you so much!  A lot to read and understand.
Closer exam on a clean plane shows there is a little warp in each wing. But it's about the same each side. A slight rise in the TE about mid point on outboard wing, and similar but closer to the fuse on inboard wing.  But a bigger issue is the H stab. Tim's suggestion of how to examine it in comparison to the wing showed that the H stab is tiled about 2 deg, perhaps 3, with it lower on the outboard side.  Going to try the heat trick to correct it, though this one is covered in monocoat and I'm not sure how it will respond to a heatgun. So I'll try a hot towel on it first.

Engine thrust was brought up. Thrust angle on both axis appears to have zero offset.

 because I do want it to fly correctly, I will be replacing the music wire pushrod with a CF one, and adjustable clevise connections. I'm at least the 3rd owner of it, so I am finding and correcting things as I go.
Tomorrow I'm back to work, but I'll get a new flight in as soon as I can to see what changes.

Thanks to everyone! 

Gary

[Ted Fancher]

Hi Gary,

A little late getting here but see some interesting suggestions.  Not surprisingly, I've got a couple that haven't shown up yet.

The first of two things that caught my attention was your statement that the wings are "level" in level flight both upright and inverted  (which is better than average evidence that whatever warp "twists" are in the 2 wings appear to balance themselves out in steady state flight).

The second thing was your comment that the outboard wing dropped Earthward significantly in both inside and outside maneuvers...which is, in general, inconsistent with the wings being level both ways in steady state flight.  This anomaly encourages finding a reason why it is happening.

Another possibility worth investigating is the relationship between where the CG is located at the wingtips and how far aft of that location the leadouts exit the wingtip.  If the leadouts exit the wingtip too far aft of the CG the airplane in level flight may well fly wings level but may be yawed "away from" the pilot and the inboard wing, therefore ahead of the outboard.  You can check this by comparing how much of the outboard wheel can be seen aft of the inboard wheel in level flight (It's important to check they are equal distance forward of the leading edge at rest first) or by suspending the ship by the leadouts and observing how far off vertical the straight leading edge is due to the aftward of the leadouts.  Also of interest to know how far apart the leadouts are at the wingtip exit.

If, in fact the airplane flies yawed out as a result of the above it means the inboard wing is "leading" the outboard wing and, as lift is increased during maneuvering, the right/outboard wing may well be generating less lift than the left/inboard.  (DEFINITION FOR WHAT FOLLOWS: Optimally, air should flow over a wing more or less in a straight line from the leading edge to the trailing edge.  To the extent that the flow of air is "diverted" from this path and flows toward the wingtips the lift produced by the affected area will be reduced) This differential would occur due to two factors.  First, the degree of spanwise flow of air over the left/inboard wing will be significantly reduced due to the natural barrier to spanwise flow provided by the fuselage. The loss of lift will therefore be negligible.  The right/outboard wing, however, will suffer both the full effects of the spanwise flow of air toward the wingtip as well as suffering at the wing fuselage juncture where the excessive leadout rake makes the fuse a barrier to appropriate airflow over the innermost part of that wing.

The net result of maneuvering under such conditions is that the inboard wing will generate more lift during maneuvering than will the outboard wing, thus,  potentially being a contributor to the "outboard wing toward the ground" conundrum  during maneuvers both inside and outside.

I bring up the CG location because the Classic Ringmaster was designed for and most often powered by the little 6.5 oz Fox .35 with no muffler and took off with maybe 3.5 oz of fuel.  If your ship is powered by something heavier than that sporting a muffler and burning more fuel the odds are pretty high your CG might be well ahead of ideal and the more nose heavy it is the greater will be the effects of all of the above yammering!

Anyhow, give us some more data about your ship: the CG location aft of the leading edge; leadout location and distance of both aft of the CG and distance between the up and down leadouts; which leadout is in front and which aft; What engine and muffler (if any) are in use; how much of the outboard wheel can you see behind the inboard in level flight (and, if you're comfortable checking during maneuvers, does more of the outboard wheel become visible while doing loops); what is the line spacing of your handle and what size bellcrank does it drive.

Ted Fancher

P.S. The misaligned stab/elevator is well worth correcting.  Let us know the results of your correction.

[Gary Dowler]

Ted,
Power on this is a older Fox 25, with muffler, but a smaller tank and only 2oz fuel. It will still fly 5 min on 2oz.  Prop, if anyone is interested, is a TopFlite 9-6 wood number. Switched to a 9-5 on second flight because of a cracked prop on landing. This seemed to change nothing of consequence.

I cut into the wing today. 3" nylon bellcrank is in there. Discovered that the bolt holding it in had backed out to where it was stopped by the top sheeting.
Here is what greeted me


Note that the spar was nearly severed by the builder. The pushrod was held on by a washer that had been glued on with a glob of sigment or ambroid.

Gary

[Howard Rush]

The plywood floor may serve to retain the pushrod, so Ambroid may suffice to hold on the washer. 

Assuming this is the classic Ringmaster wing, the spar mod is OK.  The spar is structurally useless.  We used to install the spar without glue, so when we crashed and the wings pivoted forward at the LE joint, the spar wouldn't pull the ribs apart.  Put a doubler on the hole in the sheeting, though.  You might also tighten the bellcrank bolt.

[Gary Dowler]

Repairs underway. After rereading many posts here I really started to look critically at things. The more I looked, the more I found that needed attention.
As mentioned above, the stab was tilted outward between 2-3 deg. Then I made solid pints on each wing to measure off of and realized it was also crooked. Side to side difference (fore & aft at the stab TE ends) was  3/8".  Didn't think heat was going to fix this. Cut the stab off, as well as the old offset rudder.  Made a new straight rudder, then reset the H stab square with the wing from all directions.  Glue is drying now.
Also replacing the 1/8" wire pushrod with CF and an adjustable connection at the horn. The pushrod brace was indeed causing some interference with up elevator. It's gone.

Also, I removed and weighed the tip weight. It has a weight box built in. Only .34 oz

Gary

[Ken Culbertson]

Repairs underway. After rereading many posts here I really started to look critically at things. The more I looked, the more I found that needed attention.
As mentioned above, the stab was tilted outward between 2-3 deg. Then I made solid pints on each wing to measure off of and realized it was also crooked. Side to side difference (fore & aft at the stab TE ends) was  3/8".  Didn't think heat was going to fix this. Cut the stab off, as well as the old offset rudder.  Made a new straight rudder, then reset the H stab square with the wing from all directions.  Glue is drying now.
Also replacing the 1/8" wire pushrod with CF and an adjustable connection at the horn. The pushrod brace was indeed causing some interference with up elevator. It's gone.

Also, I removed and weighed the tip weight. It has a weight box built in. Only .34 oz

Gary

I had a rather lengthly post disappear but I can sum it up with what you just did and look at that spar opening.  It looks like it will still bind at full deflection of the aft line.  Also, being a ringmaster you might want to use the 2nd or even the 1st hole on the bell crank unless you have a super long flap horn.  Ringmasters don't take or even like a whole lot of control, especially fast moving ones.

Good Luck - Ken

[Gary Dowler]

Ken,

Your post was one of the ones I read in depth.  Don't know yet about any new pushrod clearences, don't have it assembled yet. But I will, very soon.
Mine is not a "fast" Ringmaster.  Runs very close to 5-5.2 sec laps on 64' lines. Guess that's a little fast, but it flies good. I'm not doing anything to change the rather modest appearance of it, just improving its function.

Gary

[Brett Buck]

As mentioned above, the stab was tilted outward between 2-3 deg. Then I made solid pints on each wing to measure off of and realized it was also crooked. Side to side difference (fore & aft at the stab TE ends) was  3/8".

     Given that we have very good evidence that even 1/64" of skew can cause all sort of havoc in some conditions, 3/8 seems a bit much! Cutting it off and straightening it up is the only solution.

      Brett

[Ken Culbertson]

I concur that the rear spar is useless in a Ringmaster so don't worry much about getting rid of anything that even comes close to the pushrod.  I think it was meant to be a jig and they just left it in.

Make sure to reinforce the area you cut out to access the bellcrank.  I use a couple of 1/2" strips of 1/64 plywood or 1/32 bass with the grain span wise epoxied under the cutout and clamped till they set.  Gives you a way to put the piece back without losing strength but it is not that big a deal on a Ringmaster with that log of an LE if you want to skip it.

I wish you luck, nothing brings back memories more than a well trimmed ringmaster whizzing through a pattern it was never intended to fly - but it does!

Ken

[Ken Culbertson]

I always check this, and I'm not happy until there is no difference that I can see -- and I can see when the stab is off by 1/16" or so at the tips.

Tim - I have used your method for years but recently I have found another trick that may help.  The Cell Phone.  I put mine in a table vice so that it is at least 4' above the ground and stand back a couple of feet, close the eye and do what you do until one day when I was taking some pictures of my front scoop to evaluate where to put stuff I noticed that I also had also had a picture of my stab/wing/rudder(s) alignment.  I think you are being generous with the 1/16".  I will bet you can detect 1/64" especially if you do it in a dark room with some back lighting.

Ken

[Tim Wescott]

     Given that we have very good evidence that even 1/64" of skew can cause all sort of havoc in some conditions, 3/8 seems a bit much! Cutting it off and straightening it up is the only solution.

      Brett

Yes!  And I'm sorry I didn't mention it myself!

Gary, while you're at it, check that the wing is square to the fuselage the same way you checked the stab.  If it's not on the money -- what Brett said about cutting and resetting.  You'll want to make sure you're measuring to an equal-span point.  I'd measure out from the fuselage to the wingtips.  I think that the Ringmaster, as designed, has equal span wings, but you don't know how it was built.

[Brett Buck]

Gary, while you're at it, check that the wing is square to the fuselage the same way you checked the stab.  If it's not on the money -- what Brett said about cutting and resetting.  You'll want to make sure you're measuring to an equal-span point.  I'd measure out from the fuselage to the wingtips.  I think that the Ringmaster, as designed, has equal span wings, but you don't know how it was built.

    I would measure from the LE of the wing, since it's (nominally) straight.  I would carefully check everything about the airplane, but if the wing is also built with some sort of shape defect (like, "parallelogrammed", or with the LE joint not straight), the entire thing becomes a rebuild, or just living with some of the problems, since it's not practical to fix it compared to building a completely new airplane - which, given it's a ringmaster, is a week of evenings at most.

       Brett

[Ken Culbertson]

   ....or just living with some of the problems, since it's not practical to fix it compared to building a completely new airplane - which, given it's a ringmaster, is a week of evenings at most.
       Brett

My vote goes with the living with it senerio.  Of all the allignments that can be off and the plane still fly well the wing to fuselage is IMHO the least important on a fun fly plane. (Not so on a PA where visible yaw is going to coat you points).  If you get the stab and rudder square with the wing and the thrust line is right, an out of line fuselage is just going to look funny but it will fly right.

If however there is no attachment to the plane and it is going to be a real pain to fix, Brett is right.  With CA it's 1 day to build, 1 day to redo the things you messed up and 1 day to monokote.  Not sure whet he does with the other 4 evenings