Balanced turning questions

[Matt Brown]

I posted on facebook about my maiden flights on my new Pathfinder LE from RSM. While going through the early flights getting a feel for it, I felt like it turned much better inside than outside. Several guys on facebook suggested shortening the elevator pushrod. This makes some sense to me and is on my list of things to consider. I wanted to analyze things further before cutting into my plane. I didn’t have room for a hatch back at the elevator so I just covered the area with a silkspan patch. I don’t want to cut it out until I’m sure that’s what it needs as I have to go through the refinishing process afterwards.
I set my controls up best I could during the build. I locked the bellcrank to neutral and played with pushrod lengths to get throws as equal as possible. After the maiden, I went back and took some basic measurements again. When I pull the up line, I get 1-5/8” up elevator travel and 1” of down flap. Conversely pulling the down line such that I get the same 1-5/8” down elevator travel I also get 1” of flap up travel.  The 1-5/8” of up travel is max up throw. However I do get a bit more down elevator throw at the mechanical limit. I get 1-7/8” of down with about 1-1/4” of up flap. To me, this seems like it should turn outside better but it definitely doesn’t feel like it to me. It feels like it’s mushing through outside sharp corners whereas it really pops through insides.
Can someone help me understand what may be happening?

Pathfinder LE
Ro-Jett .67 on header muffler
13-1/8 x 4.5 3 blade carbon prop turning 8600
63.5 oz
64’ Spectra lines
5.6-5.7 lap times right after takeoff
No wrist bias in the handle
I did try to adjust throw bias in the handle but plane still felt mushy in outsides

Thanks, Matt

[Paul Wescott]

I think you’re going to have to cut into the tail and move the horizontal stabilizer down so it’s directly in line with the wing.  Otherwise turbulence from the flaps will affect the stab/elevator differently during up/down control input or inside/outside maneuvers.  Or so I’ve heard.

[Ken Culbertson]

I think you have done the "due diligence" on the controls.  I seriously doubt you are reaching the stops on the controls so the extra on one side is not that important.  I have only flown one Pathfnder and it was well balanced by the owner so that is no help.  Before changing the pushrod, which you may need to do anyway as a final trim (I can't think of a plane I have not had to do it on) check the thrust line.  Do you have any down thrust?  It is not uncommon to need a little.  I know this sounds silly but can you quantify "better".  Do you mean tighter, faster or tracking?  My planes all fly equally inside and outside on the first two once trimmed but for some reason I get better tracking outside.  I think that is due to what Paul Described.   My next one is an inline twin so that may change!

Ken

[Dan McEntee]

  Make sure there is nothing flexing in the controls. No pushrod flex and no slop in the pushrod connections to the horns. Borrow some Robart incidence meters and put one on the wing, power plant and stabilizer. The wing should be set at zero, and then see what the other two read. I follow the Bob Whitely set up as listed in "Things That Always Work" that was in an article he wrote for Stunt News years ago. Basically it's wing set at 0 with flaps neutral, power plant has at least one degree down and one degree right thrust, and stabilizer had 1 to 2 degrees positive incidence.. I have been setting up my models this way ever since I saw the article when it came out and have never had issues with hunting and models always groove well. I can usually do the pattern on the first flight if I have a known good engine/tank combination installed. Any differences in inside and outside turns were simple line spacing adjustments. Also, do you seal the hinge lines on wing flaps and elevators?  If not, seal those with tape. Numerous threads on that on the forum. Make any changes one at a time and fly several flights to evaluate them. If you are doing the pattern you should not need much. Your lap times might need to be picked up a bit. If 5.6 and 5.7 are accurate, it may just be too slow for that airplane. Shoot for 5.4 to 5.5 and see how it feels. A few tenths can make a big difference. Line sweep also could be looked at.
  Type at you later,
  Dan McEntee

[Matt Brown]

As best I can measure, everything is 0-0-0. My Robart incidence meters both want to stick a bit on that last half degree or so. Usually lightly tapping the meter will settle it halfway close. The plane flies very well though both inside and outside loops, tracking very good. It’s the square corners and sharp exits of maneuvers that really stand out. Insides really turn very tight and crisp. Outsides just kind of mush through. Second corner of the hourglass seems fine but the outside exit of the first half of the wingover on the very first flight just mushed as did subsequent wingovers. The next corner of the wingover(from inverted to vertical) didn’t seem too bad though.
I may try some down thrust next time out. May also go ahead and cut into it and adjust the pushrod. Weather doesn’t look promising anytime soon though.
There is also the possibility that it is purely a perspective issue on my part. I’ve had several SV11 ARFs, both electric and glow. They all seem to turn better insides than outsides.

Matt

[Dave_Trible]

Something you might look at is whether the airplane is yawing badly in corners.  If the rear lead out is the down line it might be.  Just for a starting reference hang the airplane from both lead out on ONE hook.  Then set your incidence meter-with bar removed-on the side of the fuse near the balance point.  Adjust the lead outs until you have about 1 1/2 to 2 degrees nose down.  This should be close enough to begin and will tell you if this is the root of the problem.  Another thing is to have someone on the outside tell you if the wings are really level.  If not you may get different line tension one way than the other which will affect how much control pressure is being applied.  Lastly if everything else checks out I will revert to handle adjustments.  Sometimes just resetting in tiny amounts your level adjustment will correct what you are feeling and seeing.  If you think about it while flying do you sense needing to hold a bit of 'up' or 'down' pressure to keep the plane level either upright or inverted?

Dave

[Jim Svitko]

I have had planes that turned better (tighter) in one direction than the other.  I could have sworn that I had everything 0-0-0 but somewhere along the way, something got out of whack.  I remember an Oriental that drove me nuts.  I can't remember if it turned tighter inside or outside, but I ended up cutting into it, changing the stab incidence, and getting everything back together.  I had to do some guesswork here regarding the amount of incidence change to make but I guessed right.  It is turning the same in each direction now.

Although you say you have everything 0-0-0, that might not be the case.  As far as those Robart incidence meters go, I never use that "needle" indicator.  I use the bubble level.  I never trusted that needle indicator.  And, when you use that meter to check wing incidence, where are you mounting that device?  Those plastic angles that hold onto the leading and trailing edge might not be seated very well.  I can also see where you could get different readings if mounted in different places.

Another problem I have seen is incorrect flap to elevator setting.  I will notice this on my planes when I go inverted.  If I have to tilt the handle one way or the other to maintain level flight while inverted, I will adjust the elevator pushrod clevis to lengthen or shorten the pushrod as necessary.  Every plane I build now has a hatch on each side so that I can have access to that clevis.  And, just because the flaps are at zero (neutral), it does not automatically mean the elevators have to be at zero.  I have had to trim a few planes by setting the elevators a bit up or down with respect to flap zero.  Making this adjustment also minimized the problem of the plane turning tighter one way than the other.

[Dan McEntee]

I posted on facebook about my maiden flights on my new Pathfinder LE from RSM. While going through the early flights getting a feel for it, I felt like it turned much better inside than outside. Several guys on facebook suggested shortening the elevator pushrod. This makes some sense to me and is on my list of things to consider. I wanted to analyze things further before cutting into my plane. I didn’t have room for a hatch back at the elevator so I just covered the area with a silkspan patch. I don’t want to cut it out until I’m sure that’s what it needs as I have to go through the refinishing process afterwards.
I set my controls up best I could during the build. I locked the bellcrank to neutral and played with pushrod lengths to get throws as equal as possible. After the maiden, I went back and took some basic measurements again. When I pull the up line, I get 1-5/8” up elevator travel and 1” of down flap. Conversely pulling the down line such that I get the same 1-5/8” down elevator travel I also get 1” of flap up travel.  The 1-5/8” of up travel is max up throw. However I do get a bit more down elevator throw at the mechanical limit. I get 1-7/8” of down with about 1-1/4” of up flap. To me, this seems like it should turn outside better but it definitely doesn’t feel like it to me. It feels like it’s mushing through outside sharp corners whereas it really pops through insides.
Can someone help me understand what may be happening?

Pathfinder LE
Ro-Jett .67 on header muffler
13-1/8 x 4.5 3 blade carbon prop turning 8600
63.5 oz
64’ Spectra lines
5.6-5.7 lap times right after takeoff
No wrist bias in the handle
I did try to adjust throw bias in the handle but plane still felt mushy in outsides

Thanks, Matt

       I rereading your original post, you have more "down" controls than you do "up controls.  Something isn't right with control horns. The square turn outside as you describe it sounds like classic stall from too fast and/or too much control input. With significantly more throws in the "down" mode, they are going farther faster that the "up" inputs. If you are comfortable with level flight both upright and inverted, a way to test it is to move your down line closer to the center of your handle about 1/8" at a time, reset neutral,  and carefully test fly again and see how it turns outsides then. It's hard to say what's wrong in the controls. if the bell crank is sitting square and even, then your flaps should be also. If you adjusted the controls to get what you have and there is something off at the bell crank and flap horn, that will affect the elevator also. The bell crank throws should be even  lock to lock. You may never need that much control, but it should be even. The flap horn could be out of square or the elevator could be also. I'm going to take a wild guess that your controls are biased to the up side, and that is what gives you the extra throw to the down side. When you move the control from level, the down input will be faster. You don't mention what your line spacing is, but that may be helpful to know. I think a few test flights with the down line moved closer to center, then reset neutral and test fly will tell you something. I would do that before adjusting the down thrust.. Unfortunately, the only way to know what the controls are doing would be to cut some access hatches  in the fuselage. You can see the horns that way, but trying to see the bell crank will be tricky.
  Type at you later,
   Dan McEntee

[Rick Campbell]

Read "Balancing for Pitch on CL Stunt Ships" by Chris Lella published in the July 1976 Model Aviation magazine. You can access it through the AMA digital archives. It really helps to better understand this situation.

[Steve Helmick]

If it's easy, try a little downthrust. If that doesn't get it done, adjust the elevator pushrod shorter.

Many years ago, a club member built a really nice Brodak Profile Cardinal. It didn't fly all that well, and I got pressured into flying it, which I didn't really want to do. But I did, and I think a few insides and outsides made me not want to fly any more tricks. Upon landing, I suggested 1/2 turn on the elevator pushrod (to give a wee bit of down relative to flaps). One more flight and it flew so much different, I was impressed and did some triangles. At that time, I still wasn't doing the full pattern. What I learned is that it doesn't take a big adjustment to make a huge difference. I'd cut that silkspan hatch out, adjust it and cover the hole with the piece of silkspan and clear packaging tape.  Steve

[John Miller]

As best I can measure, everything is 0-0-0. My Robart incidence meters both want to stick a bit on that last half degree or so. Usually lightly tapping the meter will settle it halfway close. The plane flies very well though both inside and outside loops, tracking very good. It’s the square corners and sharp exits of maneuvers that really stand out. Insides really turn very tight and crisp. Outsides just kind of mush through. Second corner of the hourglass seems fine but the outside exit of the first half of the wingover on the very first flight just mushed as did subsequent wingovers. The next corner of the wingover(from inverted to vertical) didn’t seem too bad though.
I may try some down thrust next time out. May also go ahead and cut into it and adjust the pushrod. Weather doesn’t look promising anytime soon though.
There is also the possibility that it is purely a perspective issue on my part. I’ve had several SV11 ARFs, both electric and glow. They all seem to turn better insides than outsides.

Matt

Greetings Matt. It troubles me to hear that you have, as close as you can measure, 0-0-0 incidence. I just checked the original CAD files that were supplied to RSM for the kit. You should be getting 1 to 2 degrees of downthrust as that is what the plane was designed with. Did you use the parts, (formers) supplied with the kit. The thrust line is established with the engine crutch being built as designed. The side view of the nose shows the downthrust but doesn't call it out. It is clear though that the mounting beams are angled down slightly.

Now, that may not be the reason you are experience the turning differences you site.

I think we all, or at least I can say I, try to build my planes to tolerances that are almost impossible to reach given the methods and materials we use. It's a good goal to build and align our model as accurate as possible. I've caught myself trying to maintain + or - .005 tolerances. Even when built using really good jigs, with the way our wood swells and twists throughout its service life, that kind of precision, that tight of a tolerance, is always a moving target.

This truth came to me in a head slap moment when I saw Trians beautiful "Revolutions", molded carbon fiber precision-built model, fly essentially still in trim, after having a new nose and wing replaced after a mishap.
The above information is not given to discourage anyone from building as accurately as they can.
It's also one of the answers why most airplanes built as close to identical to a previous one, usually winds up with different trim solutions. Good pilots have told me that identical designs just aren't identical in real life. I think it's our material and building methods.

All that was to get my feelings for the "Why for" and possibly a good solution, for your problem, unequal turns.

In my opinion, you need to make the elevator pushrod shorter. How much? Well, until the turns are equal. I don't believe the engine thrust line is the dominate force causing the problem. The downthrust is called for in the design, but many model planes have been successfully trimmed for competitions with 0-0-0 incidence. You can give Gordan Delaney, the designer a call. He will likely give you much the same, but possibly better help than I've tried to give you.

I really hope you get it trimmed out. I can only speak to the one I have. It's a sweetheart.

[Motorman]

If you have 1-5/8 up and down with 1" flaps both ways that means you did a good job on the controls. The fact it travels more down at full lock doesn't mean anything. It would turn better on the outsides if it did but you're not going full lock either way.

If you shorten the push rod it will give you more lift for the insides wich would seem to the opposite of what you need but, I think most planes are set up to have level elevator with the flaps hanging slightly down. It helps you groove in level flight is my understanding and all my planes are set up that way.

Most planes have  a tiny bit of positive incidence in the stab because the opposite would cause allot of problems. If you tried to get it to zero you may infact have up elevator built in. Hope not.

I have fixed several planes that had uneven turning problems by adjusting the thrust line. Make some thin brass shim stock washers to put under the engine bearers. Pretty much an instant fix.

I don't use line offset to adjust my handle but I do have a way to set neutral that works for me. Before take off hold the handle where neutral feels natural to you and hold it there as the plane takes off. If it hugs the ground shorten the up line, if it jumps up too quick shorten the down line.

Good luck, hope you don't have to cut into it.

MM

[Steve Helmick]

Unlike John, I've found thrustline mistakes are highly effective and not good. MM made several comments that I agree with 100%; both thrustline changes and neutral adjustment at the handle. None of this stuff is easy, but it is educational and therefore good for you.  Steve

[Air Ministry .]

" As best I can measure, everything is 0-0-0. "



Its not unusuall to run Plus. Stab. incidence .
Jose talks of 3/16 Down Elevator needed on all Pattern Master .60's . Reading this , cunning , or is that forethought , has us trying + inc. I think it was 3/ 32 across the whole kaboodle .
As In , Elevator carefully aligned with stab. The center of the L . E. is 3 / 32 above the T. E. center .My dunger flys good , equal each way .But you wanna be 6 ft. 20 stone , and fit ,
to wrestle with a pattern Master .60 .

Fred Flinstone alignment .

Masking Tape say 3/16 Sq. ( with inner edge chamferd to 20 or 30 degrees )  or double sided tape . or cheap superglue ( thatll flick off clean ) balsa to the upper & lowwer L.E. at the front .
Holding a thing vertical with them butted even against it ensures exactness . side to side. Parrallel to L E . A inch or two long . If the Stabs FLAT your in way easier .

Its the long trick . a Metre or more and increments are easier discerned  . ( A steel straight edge 3 ft. across the prop driver - and a large square - if thrust lines the issue , a little downthusts usually o.k. . NOT up .)

THAT should get the L E as deep as the center . ( the objective )  SO A STICK Over & Below - run parrallel . Same Gap all along . 1/2 Sq building supplies straight stuff . or inch by quater . or balsa sheet .

IF they tilt down Fwd. your doomed . Neg. Incidance . If theyre up say a quater , round the wing , it'd be fine . Drawing a degree angle 7 measuring at distance explains that .

BUT INITIALLY , try a Big Jim ( amopugst others ) and dial in say 3/16 down elevator at neutral flap ( you can wind some out later ) and see iif it evens the feel and suchlike .

[Air Ministry .]

In the days of fabric covered controls . say 1/2 inch ROPE was doped at the T E , six or 8 inches , fabric over . as a TRIM for neutral ailerons . ( and elevator / rudder load / bias ). Top or Bottom .

So a quick dodge if the pushrods non adjustable , would be a few inches of 1/8 Sq. stuck on top ? ? of the elevator trailing edge , as a TEST . or is it the other side . mighta been cald CORD .

[Brett Buck]

I posted on facebook about my maiden flights on my new Pathfinder LE from RSM. While going through the early flights getting a feel for it, I felt like it turned much better inside than outside. Several guys on facebook suggested shortening the elevator pushrod. This makes some sense to me and is on my list of things to consider. I wanted to analyze things further before cutting into my plane. I didn’t have room for a hatch back at the elevator so I just covered the area with a silkspan patch. I don’t want to cut it out until I’m sure that’s what it needs as I have to go through the refinishing process afterwards.
I set my controls up best I could during the build. I locked the bellcrank to neutral and played with pushrod lengths to get throws as equal as possible. After the maiden, I went back and took some basic measurements again. When I pull the up line, I get 1-5/8” up elevator travel and 1” of down flap. Conversely pulling the down line such that I get the same 1-5/8” down elevator travel I also get 1” of flap up travel.  The 1-5/8” of up travel is max up throw. However I do get a bit more down elevator throw at the mechanical limit. I get 1-7/8” of down with about 1-1/4” of up flap. To me, this seems like it should turn outside better but it definitely doesn’t feel like it to me. It feels like it’s mushing through outside sharp corners whereas it really pops through insides.
Can someone help me understand what may be happening?

    I am not sure, but try a different test - presumably, the leadouts are even when the elevator is neutral. Measure the deflection when you move the leadouts 1" in either direction. You want it to be the same.

   I would note that the "max" movement probably doesn't mean anything, you will not be able to get anywhere near the maximum movement.

   You also don't mention whether or not you have sealed the hinge lines. If not, seal the hinge lines and start over.

     Brett

p.s. Also, I am not sure about the wing area on this airplane, but 1.625:1 elevator/flap ratio is A LOT of difference. For that to be right,  it would need to extremely low wing loading. Too heavy with that ratio and it will for sure "mush" or stall with too much deflection.  That means even a slight asymmetry in the wing LE shape miught cause it to stall differently inside and out, leading to your apparent turn difference.

    I am not familiar with the airplane at all, but I would suggest starting with 1:1, lacking any other information.   As mentioned above, I think you really need to make easy adjustments possible, if it means cutting something or building fairings to gain clearance, I think you need to do that.

[Matt Brown]

    I am not sure, but try a different test - presumably, the leadouts are even when the elevator is neutral. Measure the deflection when you move the leadouts 1" in either direction. You want it to be the same.

   I would note that the "max" movement probably doesn't mean anything, you will not be able to get anywhere near the maximum movement.

   You also don't mention whether or not you have sealed the hinge lines. If not, seal the hinge lines and start over.

     Brett

p.s. Also, I am not sure about the wing area on this airplane, but 1.625:1 elevator/flap ratio is A LOT of difference. For that to be right,  it would need to extremely low wing loading. Too heavy with that ratio and it will for sure "mush" or stall with too much deflection.  That means even a slight asymmetry in the wing LE shape miught cause it to stall differently inside and out, leading to your apparent turn difference.

    I am not familiar with the airplane at all, but I would suggest starting with 1:1, lacking any other information.   As mentioned above, I think you really need to make easy adjustments possible, if it means cutting something or building fairings to gain clearance, I think you need to do that.

Sealing the hinge line is on today’s list of things to do to the plane.
Can’t really compare/calculate the travel ratio flap to elevator by the measurements I gave as the width of the elevator and flap vary the travel the quickie way I measured it. Had I measured with a degree’d throw gauge then that would work out. The horns and pushrod was setup for 1:1 travel initially during the build.

[Air Ministry .]

A soft pencil , like a HB ( not to sharp ) or is it 2H , or a felt marker - should wash off . later . maybe ! .

So getting a dead aft ' neutral / center line , line / mark - 1/4 or so long REFERANCE . then hang from a leadout . CAREFULLY . they hurt your foot if you play Tarzan & the nail pulls out . ( oops ) Just as well the foot was under it .

SOME , just hanging , the FLAP ( & elevator ) is just ' so far ' . a bit of weight on it to get FULL DISPLACEMENT of control surface . What with paint , newness , angles & oiling hinge pins // etc .

a dot at the flap T.e. , in line withit . A offcut of 1/16 six in long , to bridge a gap , if needed . So its ALIGNED EXACTLY . the dot . AND the other one . THEN ' are the Two Dots equispaced from your  megaacurate C/L line .

Some of mine want the flaps & elevators grasping , after storage , and leaning onem Full deflection ( or more ) to FREE OFF for full movement . THEN carefull glareng at surfaces to see theyre exactly alinged side to side .


The TEST is to see IF it sits at Equal Deflection , with just ts own weight . Dosnt hurt to glare at fuse to see if its just outside level , too . However , whacking / leaning onit , SHOULD get exactly equal deflection .
Till you decide otherwise . as in if it NEEDS ' pre set ' to equal the turns . Just to try'n de muddify the waters . On that .  Pretty Basic first principle set up .

But Neg Stabs useless . A iota + usually benificial , with the stab. up from the wing centerline . Im starting to think unequal all hights , gets a ' pre load ' that steadies & halts ' hop ' / bounce , as in it ' locks ' outa squares etc better , not so easilly deflected either . but traks as youd want it . Hopefully . We shall see . Engine & wing centerlines , anyhow . So it follows aft too . But I dont usually have 25 % tailplanes .
so almost irrelevant waffle . Or regurgetation .