I just started flying a plane I haven't flown in 2 years. It pulls to the gear during left rudder KE and to the canopy in right rudder KE. It otherwise is a fantastic flying airplane - it's a 1.20 size Yak54 that flies better than my Wind 110.

How common of a coupling is this, or does it sound like a crooked fuse or something? What would be a typical cause?

What you are describing can happen even with a perfectly straight airplane, in which cas the culprit is spiral airflow.

The expensive fix is counter rotating props.

The less expensive fix is to decrease the incidence (drop LE; raise TE) in the right stab and increase the incidence of the left stab an equal amount. The AOA of the right stab dominates pitch behavior with left rudder KE, and vice versa. If the stabs are not adjustable, you can still make this "tweak" if the elevators use separate servos or a "Y" pushrod.

Moving the CG forward will tend to reduce the amount of differential behavior in the left and right KE.

Regards,

Per Dave's explanation....Let me add that for a nonadjustable stab, the right elevator will require up trim and the left an equal amount of down trim. It shouldn't take much more than 1-1 1/2 turns at the clevis. There have been some other but less effective measures discussed over the years also, such as raising both ailerons slightly. Also larger stabs tend to be more prone to this flight behavior than smaller stabs.....

Think of what's happening with top left rudder; the right stab half is hanging below in relative cleaner air which makes this half's trim more effective or more dominant.

This type of flight behavior can often occur when a model is nearing very good trim.

I think you have your trim issue stated backwards,,
Probably , it pulls to the canopy on right knife, and to the belly on left knife.

Unlessyour elevator halfs are already out of wack! (right elevator up left elevator down )in the rest position.
If this is the case you will have left rudder trim and left aileron trim as well , also it will be yawing to the right on pulls to up lines and pull louts as well

There is no way the airplane is doing what you discribed unless ,the c/g is at 20% MAC, unlikely, or the elevator halfs are uneven to start.
Never! ,, trim elevator halfs different to trim knife edge issues.If you think you need to the airplane is not set up correctly.
your g/g is too far back for the wing Inc your flying.

The "spiral prop wash" has no effect on knife edge. its just BS pit talk ,your airplane is just not set up correctly
Reverse pulls on knife are 99% of the time due to c/g and inc. settings unless something is crooked or not adjusted properly.
Everything else is fall out from that!
Bryan

Brian,

Joe stated his condition here. It isn't backwards. Top left, push to belly, top right pull to canopy.

You are wrong is stating the elevators have no effect. You are also wrong in stating spiral airflow has no effect on knife flight.

It is possible that Joe's wing incidences, right and left may be off and he should make sure that it they are set correctly before doing anything else.

Hi Matt,
Opps I`m wrong, not trying to step on your toes. I read it wrong But I`m right on the fix and the cause
I read it backwards on the outcome,and just remembered it wrong (what knife edge is doing what).I deal with this all the time.
If the wing inc. was off he would be carrying aileron trim.

If you adjust the elevator half opposing each other the center elevator trim effeciency is cut in half. you loose your down line trim power and need more down elevator mix for down lines . So now then you ,move the c/g back to compensate for that so you can trim a little down elevtor in ,causing the knive edge problem to get worse. not even to mention the ailerons needs trim or left rudder trim.

If the Spiral slip stream was our problem,
Why wouldn`t we have aileron trim mixed for level flight for power off ,power on or, opposing elevator trim mixed for landing after the power has been removed? It just sounds good and official to blame in on the Aero Jargon LOL
,Either the stab halves are off already ,elevator halves are off, c/g s to far back or, he has too much down thrust. nothing else can cause this problem. Not even the Spiral slip stream!

Guys,
Why would we build perfectly true airframes and then adjust them crooked ,that Jut don`t make sense.
we go through extreme efforts to build perfect airplanes and settle for crooked settings?
If we have spiral slip stream why dont we adjust the wings crooked ,or adjust the fuse length to make the rudder hit the left side of the spiral?
Or, find the problem on anything but knife edge? no where else , and it is dependent on how much rudder is used. Don`t you think if there were any spiral that the wing, gear , stabs would not straigten it out?

Matt,
I didn`t say adjusting elevators would not correct "THAT" Problem it`s just a bandaid for" That" problem a short cut, that will bite you elsewere.
anytime you adjust the elevator halves to correct that problem you cause 4 other trim compromises.
I can prove spiral slipstream is not the cause of the adverse knife issues do it all the time,it`s just a excuse we have used to stop trimming our airplanes. Mixing radios also made us lazy

I`ll say it again , Down thrust and rear CG is the Scourge of trimming pattern airplanes.
and the start of ALL compromises.

Ever wonder why your airplane bounced around in the wind? If you have any surface trimmed less than perfect the change in wind speed or direction will make you pay for compromises. Down thrust is the worsed offender second,, you guessed it C/G

Bryan

I figured out "tweaking" the stabs in 1989 while trimming a Tipo.....it pulled to the canopy in KE with right rudder, but was dead straight in KE with left rudder. Much of the prevailing wisdom at the time was to shift the CG aft slightly to have a plane that pulled less to the canopy in KE with right rudder, and pitched an equal amount to the belly in KE with left rudder. I found by slightly reducing the incidence of the left stab and increasing the incidence of the right stab an equal amount, I was able to have the airplane pitch an equal amount to the canopy in either KE. I then moved the CG back slightly (resulting in a slight bit of down elevator trim) and the plane had zero pitch coupling in KE. I cut the wing in half 4 times, adjusting the dihedral each time until there was zero roll coupling in KE. Electronic mixing is always the last resort

Every plane I have owned since that time has had some amount of twist in the stabs (or elevators if the stab is fixed) to balance the right/left KE behavior. I've never had to change rudder trim or aileron trim because of twisting the stab, and I've never seen loop tracking suffer from the twist in the stabs.

June 2011, I had 2 Bravos within 1 oz flying weight of each other (#1 being 1 oz heavier than #2), and to the best of my ability to accurately measure incidence, control throw, CG, etc, they planes were identical. Both had the same amount of twist in the stab, and both had the same behavior in KE. I replaced the single prop Neu setup on the #2 plane with a Contra unit, and moved the lipos slightly aft to maintain the CG. The #2 plane now weighed 1 oz more than #1 and in right rudder KE it pitched to the belly, and in left rudder KE it pitched an equal amount to the canopy. I removed the twist from the stabs, and the plane had zero pitch coupling on either side.

My conclusion -
Spiral airflow is real, and twisting the stabs is an effective way to reduce or completely mitigate some of the undesireable effects, and I've found zero down sides to twisting the stabs. I don't advocate twisting the stabs until all other parameters are addressed - proper geometric alignment of all surfaces, all surfaces warp free, etc.

I've flown a number of Hebert designs over the years (including some of his personal planes) and all have flown well.....so I would never suggest that Brians trim methods are BS.....but as with many things, there is more than one way to skin a cat.

Joe - try the stab / elevator tweak, and let us know how it works.

Regards,

Just questioning your deduction in the results of your test Dave...

Was is the spiral airflow that was changed or was it the reduction in torque being cancelled.

Just curious how to we would decide which is causing the need for stab adjustment, torque or spiral flow?

Respectfully curious...

Chuck

Having just had a quick peek in Scott Stoops' book, I will take a stab at this. KE is a side slip manuver, therefore adverse yaw comes into play. Level flight (and coordinated turns) are not side slip manuvers subject to the effects of adverse yaw. Years ago I remember reading in aviation texts about the spiral slipstream. There were line drawings depicting the airflow around the fuselage, having main effect on the rudder (or the stab acting as rudder in KE).; it is not so much an aerodynamic effect on the wings as I recall so no real need to trim ailerons for effects of spiral slipstream, or elevators for normal, coordinated flight regimes such as landing. The aero jargon is not so much to blame as the engineers who wrote the aerodynamics I guess, LOL. Happy to stand corrected if I misunderstood these texts or the question at hand. Cheers! Dana
<br type="_moz" />

Both torque and airflow are being changed.

So far as what is causing the trim change in pitch....it is the spiral airflow. Torque is oriented on the roll axis, not the pitch axis.

Regards,

Lots of good reading here.

Unfortunately, the stab is a 2-piece design connected by an epoxied carbon tube and controlled by one servo. Not much to adjust there.

I was going to say that now the plane is electric, it has a 2" larger diameter prop. However it had this tendency 2 years ago with 2-stroke and 4-stroke motors, so that shouldn't be the only culprit.

The CG is the farthest AFT I've ever had in an airplane. I moved it up slightly, but have to work through that flight by flight. Unfortunately it was very windy on Saturday, so trim flights were pointless.

Other than knife-edge coupling, this plane flies better than I could have imagined. It was windy, I was out of practice, and I only have 2 flights on this plane in 2 years, and experimenting with electric setups:
I was blown away by straight the plane flew. My spotter even noticed that for the first time I actually made a correction during a slow roll. Usually I'm just holding on hoping for a straight line. During 1/2 reverse cubans, I usually need some major correction after the roll. With this plane? NOTHING!

Someone said something about this being related to a plane very close to trimmed - maybe that's really the case? Hard to believe since it was my 3rd plane and I didn't really try that hard, but maybe

Hopefully I can get this thing dialed in soon and start winning some contests.

This model appears to have pretty straight airflow.

Was very interested by the discussion, Bryan and Dave. (Two people I hjave a lot of respect for) And I, being a tech type, immediately searched the internet for spiral slipstream references. Saw a good video with smoke.

http://www.youtube.com/watch?v=H8nKz...eature=related

This shows the smoke in flight, I don't see the spiral. Full scale pilots reported many times the oil and soot patterns on the fuse, indicating spiral, but it occurs equally and in the same direction for multi-engine planes with props counter rotating. Also interestingly, there is a shortage of actual data. Meaning, none. There was ONE report "Stick and Rudder" which simply made the assumption, without quantifying or proving the effect of spiral slip stream. Saw plenty of props in water, didn't seem relevant to me since there was no wing between the prop and spiral. Nor does slip stream theory hold up since similar effects are seen on pusher prop applications.

"P" effect, however is greatly quantified. I don't know, me. Would like to see some actual data. Seems interesting, would justify the large expense for contra setups if proven. If not, then it's either "P" effect, wing tip deflection or just a fad. It would be nice to know for sure.....

Brian Clemmons

When I first read this thread I was hoping Bryan H would chime in. I knew what his answer would be, but better coming from him than me. I've been flying Bryan's designs exclusively for about 4 years, and I've never once seen any of them require anything other than changes to CG and wing incidence to correct a pull or push on knife-edge (or up and downlines for that matter). In fact, I've seen elevator halves so minutely off yet cause non-stop trouble when pulling an upline. "Twisting" the stab is not the answer.

Going beyond what Hebert addressed, here's a little theoretical stuff on P Factor: P Factor is a potential for issues only when at a very high angle of attack. Even then, the spiral slipstream is irrelevant during knife-edge because even if it is there, the tail is probably below it due to the high angle of attack. The only part of P Factor that could come into play is the uneven lift (thrust) generated by the prop because the downward side is producing more thrust than the upward side. When this happens you will see the airplane pull towards you when flying right to left, and pull away when flying left to right, the direction of rudder used for the knife-edge would be irrelevant to this cause. For the most part, though, we don't fly a high-alpha knife-edge in pattern.

I knew you'd pick up on that; better clarification....If elevators didn't do anything in knife edge flight, then mixing would be totally ineffective

As far as CG and downthrust, definitely agree. Bryan, your arrow explanation makes this simple to visualize

Many people who are experts fail to understand how massive air is

My old coach Harry Roe had a great name for most of this type of discussion. He'd call it "aerodramatics". It's simply amazing how often someone who says, "This is an absolute truth in trimming" is so often incorrect. Now I'm seeing that downthrust is a terrible evil. I sure am glad for these forums, because I didn't know that for the 37 years I've been trimming pattern models.

There are so many trim issues caused by the use of a single propeller that until you experience a model without all those issues you really don't know what you're talking about. I sure wish Harry was still around to see what he pushed me to try back in 1982. I didn't have the engineering skills to make the Contra unit I built back then work well enough. But at least I can experience it now.

first... do an upline with power and bang the rudder.... see if it does what you describe.... (Do seperate upline verticals testing left rudder and then right rudder)

then....
try doing a downline at idle power and see if the phenomonon still exists...

if it does this on an upline with power, but not on a downline without power.. prolly it is a prop/P-Factor dealy-bob.. otherwise something else going on....

Unless your airplane requires zero mix you can`t understand the perfection of flight on a pattern model.
Tony,I dare say your running mix now, and a strake to Boot! is the Contra destabilizing your airplane ,,How could that make it better?
and where is the improvement! you really baggered me at the Nats for running one on the Valiant and laughed when I told you the reason for it.



I hope the Contra is an improvement, I`m making a large investment in the Idea by designing and importing an airplane around it.
I`m all about advancing the great Ideas in this Hobby and Brenner has a Beautiful unit, I admire it weekly.

I`m still very invested in the glow airplanes and what they deliver, they can be made to fly better than Electric with more flexibility in speed for conditions and breaking for flow control, with 2 times the flying time per flight. The new 1.75 is a beast of a motor and the easiest YS to run in years. we are running the same diameter prop as electric with better braking force, off throttle ,cruse and idle.

However I wan`t to work with the contra system.I won`t be relying on it to improve the flying, or trimming, Just to improve the flexibility of power/brake setup.thats a tough Challenge over what I`m now using.
If you know me I will admit when I`m Wrong But till now, the things the Contra is supposed to fix because of "spiral Slip stream" I have already fixed with perfect trimming on a single prop glow setup.
If the contra is better you Know I will be the first to switch and admit I was wrong
I`m already trimming with no mix so it can only get better right
If trimming a airplane for no mix was not important, why would anyone invest 2-3000.00 bucks for a contra setup to improve the mix like the claimes I hear here?

I already have designs that use no right thrust and no down thrust, the Shinden being one of them, it`s Glow so that rules that argument out.
it also has no need for reversed trimmed elevator halves to fly both knifes and has no roll out .pitch out on knife edge loops, no mix on any intergrated rolling of any kind, every input is pure with no need to guess a counter hold on other control surfaces. Until you fly an airplane this pure you can`t quantify it.

I hear thing beat around like (if we make the nose skinny the airplane will fly more pure with the Contra units to help with yaw ) or reflexing the TE of the surfaces will make it better and less sensitive around neutral. or I have a draggy fuse it`s better for speed control. These things are not boats. Yes reflex on the surfaces do work But it`s another bandaid.
The airplane flies on the Wings, and this is where 60% of the drag is the other 40 is in the prop and gear the wing is where 100% of the flying is, This is where we need to do all the adjustments and modifications. Eveywhere else on the model except the Engine/Prop is a waste in effort to improve the flying compaired to what is gained on the wings.

I know what causes reverse knife issues I fix them over the Net every week ,the guys flyng sportsman do it through e-mail.
I know what causes the Need for down thrust ,and the effects or affects of using it has to trimming and what it degrades in setup.
I know what causes the need for right thrust and why we use it I know the design flaws that require it, its not yaw,"P" effect, or spiral slip stream
I know what causes the need for left rudder to thottle mix.
I know what causes pull in the up lines.


Do you think I would be this bold in public if I could be proven wrong
has any one ever told me I was full of SH^*(well don`t go by that)
I challenge anybody to meet with me with their airplane, using any system I`l prove it!, be prepaired to re-learn your habits of flying around that stuff.

BY the way no body Asked me to prove I know "spiral slip stream " does not cause a knife edge tuck to the belly on left rudder and pull to the canopy on right rudder.

I have learned over the years that Great fliers make poor trimmers and they just don`t understand what the fuss is all about.
Trust me I work with great flyers, they would rather mix it out than be bothered into knowing the reasons why it needs to be fixed.

I wish I could write and Nice and Elegant as Dave But these are my ramblings, the information here is no joke, provable and not meant to step on toes or sound high and mighty. I just get tired of old bad information rehashed to a new generation of trimmers.

Dean Pappas put the fire under me 25 years ago with the desire to search for perfection. I hope I can pass this along to a new generation.
I promised My self I would avoid RCU on this topic and address it on my website ,,But I couldn`t help it
Holdng the truth and not sharing was killing me LOL

Bryan

There are certainly several ways to skin a cat and in the past I spent countless hours mixing out trim problems. I was mix mad.
Then I listened to Byrans methods and removed the mixes, moved the CG considerably further forward, increased the incidence to compensate and it was a revolution IMO. Sure there was some small issues that could have been tweeked further (I just added some slight mixes back in, well I was an addict) but the aircraft and it's performace where just simply, transformed.
How much time was lost chasing a model simple because the CG was to aft beggers belief!

+1 Bryan!!

Bryan, you're really like a Cajun version of me. You really get fired up when someone disagrees with you! Your description of our very short conversation at the 2010 Nats is a perfect example. If you remember, you at one point before that said that if you needed to add any kind of fins or strakes that those were just band-aids to improper model design. So when I saw all the stuff you tacked on to the Valiant, I asked you about it. You of course had an answer. I don't remember laughing at anything you said but I'm sure that is what you think happened. I know I certainly found your change in position to be amusing, so maybe I did. If you found that offensive, I apologize.

I have been an advocate of forward CG for years. I never bought in to the aft CG theories, but frankly it does work for some fliers. It just never worked for me. But every now and then I got my butt kicked by someone doing just that.

I have never found the need to have a model with zero mixes. I won the 1989 Team Trials with a model that had so many mixes it would scare you if you saw it. Do I think it's a nice goal to reach? Sure, but my goal competing in pattern contests is to win them. If this "Don Quixote" pursuit of the perfect model takes away from your actual performance at a contest because you were too busy trimming a model to get the 3% mix down to zero instead of learning how to do that rolling loop, then it is a negative.

The simple fact is that there are, as DaveL pointed out, a lot of solutions to the same problem. I'm glad you feel that you have all the answers and that you are the only owner of the truth. It's good to be sure of yourself.

I applaud all those guys out there that are designing models and eventually making them available to us mere mortals. Just in case you hadn't noticed Bryan, I didn't design the Onas I've been flying for a while. And I didn't design the Nuance I'm flying now. I don't have the drive to put out that level of effort anymore. But I have designed Team Trials and Nats F3A winning models in the past. If I ever decide I need to design another pattern model, it might look different then either one of those models. But if it ended up needing some mix here and there, I would hardly consider it a failure. And if I had to add a fin or a strake to it, it would still not be a failure.

Pattern is about seeking perfection in flying the maneuvers. Everybody has their way of trying to achieve that perfection. I have seen great fliers that could fly the box the model came in better then most. And I have seen great designers that have moved forward the evolution of the models we fly, but have never achieved high placings at the major meets. The guys that have been consistently top placers at the big contests are usually some combination in between these two positions. Proving again that some form of compromise is usually the best path.

Yes me too. I've had Arrows that required something similar. Indeed we are not talking 1/2 degree or more on tha stabs; more like a tenth give or take. The one thing that got a bit lost in all of this diatribe from more experienced folks is the fact that Joe, the original poster of the question has an ARFie he's trying to fix. ARFies are very seldom built as accurately as we want in Pattern.....

Also a clarification on the downthrust....I typically will set-up my planes with zero downthrust. However, it isn't unusual for zero DT to require slight adjustment to fly a better envelope. I'm not talking a degree or more...more like a tenth or two, half at most.

BTW- I absolutely loved the contra Bravo. It has terrific manners with all of those extended surfaces, and in quite a heavy crosswind to boot. The 3 rolls opposite in Masters required practically no rudder...it was cheating at its finest (LOL). Guess I'm gonna investigate this route on my Delta

Here's a question. What reference line are you using to set zero downthrust? Is it a line drawn on the fuse? Is it compared to the wing incidence? Or the stab incidence?

The Contra does make those opposite rolls very easy. The symmetry of the model is so much better with it. No difference in right or left rolls or snaps. Stall turns are the same. It's just a significant improvement.

Matt, I understand fully what Joes issue are on a arf, It can still be fixed correctly. What has happened to guys like you and I ,where are the Modelers at any more Gees!
I`m not saying Dave`s fix will not do the job it will.
But what happens when he moves up to advanced and has to fake a snap or spin entry because his airplane is tail heavy?
another switch or mix,
Dave is very Talented and a well practiced pilot and has learned to fly around the issues he has trimmed for. Joe stands a better chance now to learn correctly and his skills will give him a advantage in the end.

You call it a Diatribe I call it usable Info LOL it`s only unusable if it`s wrong.

Perfection is perfection ,setting it up imperfect to make the airplane fly near perfect is retarded.
Yes ,you can do it ,but it`s just like learning scales in Music. There is a reason why the teacher demands you learn a particular way
because she knows when you go from "Twinkle Twinkle Little Star" to playing real music, Fundamental foundation is what gets you there.
No different than building a fuse. get a crooked front ,end with a crooked tail.


Tony, I bet you could not fly that same airplane in today`s pattern, demands have changed.10 fold.
Also , may be laugh was a stretch ,it was more of a grin and chuckle I do like that we can talk and keep cool. I take nothing personal because I know I`m right I proved it over and over again,and I`m passionate because ,I fell into the same trap of fixing things when I first started designing airplanes ( that same statement about elevator halves, down thrust, lowering a stab for pitch ECT.ECT.) they only half worked (just like playing a blues scale to church music), and I have proved them to be incorrect.
But guess what,I stand by the Statment anything glued or bolted on a airplane to fix a" mix "is a Band Aid and will cause other mixes.usually three other mixes because there are three axis to trim.

I was not using the strake for Mix Fixing, but for something else. and I have since learned a set up that does not require it any longer.and learned ,why I needed it in the first place.

I know what a top flier can do with a poor set up I marvel at their abilities. I work with one of the Best and have worked with The best in the business. But ,you will never hear their trim set up ,they don`t have one, they just out fly the design no matter what it is.
Yes, they are skilled at the right part of the sport, Practice.

Tony I know you and I agree on lots of trimming ,forward cg, ect I`m trying to advance the learning here, if I were wrong I could be tripped up, but you tell me the mix ,I tell you the fix simple as that.
A mix is a indication of the airplane fighting the force arrangment under demands greater than Neutral trim. nothing more.

Any one want to prove the spiral airflow theory wrong?

I know Dick is reading maybe he is tired of my spelling by now
May be he can prove it wrong with a foamy.

Bryan