Leadout Rake / Yaw

[Brent Williams]

Looking at this picture of Igor Burger's plane from the 2022 FAI Championship, I can't help but notice the amount of yaw.  I know Igor has his preferences for trim and employs a Rabe Rudder.  It works pretty effectively for Igor, obviously.  However, is this amount of yaw and/or leadout rake anything like what Paul Walker, Chris Cox, Howard Rush, ect are dialing in on their electric ships?

*picture edited to enhance lines*

[Trostle]

Looking at this picture of Igor Burger's plane from the 2022 FAI Championship, I can't help but notice the amount of yaw.  I know Igor has his preferences for trim and employs a Rabe Rudder.  It works pretty effectively for Igor, obviously.  However, is this amount of yaw and/or leadout rake anything like what Paul Walker, Chris Cox, Howard Rush, ect are dialing in on thier electric ships?

How do you determine yaw from that picture?

Keith

[Brent Williams]

It's very faint.  I'll try to enhance the picture.

[Ken Culbertson]

It's very faint.  I'll try to enhance the picture.

If you are referring to the leadout angle, it doesn't tell you anything about yaw taken without the full context as to the camera angle and the position of the flier.  It could just as easily be yawed in as out.  His rudder shape makes it difficult to see if the Rabe is extended or not and the washout in the picture makes it hard to see if he is turning.

Ken

[John Park]

If you are referring to the leadout angle, it doesn't tell you anything about yaw taken without the full context as to the camera angle and the position of the flier.  It could just as easily be yawed in as out.  His rudder shape makes it difficult to see if the Rabe is extended or not and the washout in the picture makes it hard to see if he is turning.

Ken

And, of course, you can't see how much bow there is in the lines.

[Dave_Trible]

Could be quite a bit of bow in the lines while the airplane is in near-knife edge.  Not much pulling line tension at this point.  With lead out positions a little further back it might also affect the appearance of what is happening.

Dave

[Jim Hoffman]

I evaluate yaw magnitude in level flight by looking at the stagger of the landing gear as seen  from the handle.  Leadout sweep strongly influences yaw.  Most competitive electric stunters, in my experience, fly with noticeable yaw as seen by the pilot.

[Dennis Adamisin]

I thought I could measure yaw angles on the picture, but when I measured a 7 degree apparent angle between the CL of the fuse and the flap hinge line, realized any other angular measurements were also moot.  Thus started looking at the elements that would affect the yaw.

* Leadout position APPEARS to be farther aft than would expected, however without knowing CG position this too means nothing.  I know I have had NO JOY with aft lead-out position, but others have succeeded with it.

* What can be seen are a pretty healthy amount of rudder offset (affecting static yaw), and a large tab on outboard flap, affecting yaw & roll in maneuvers.  Just this summer I learned a new appreciation for even small amounts of rudder offset, while the flap tab remains on the logical "things to try" list...

* Most importantly, it does not come down to just one thing.  Leadout offset, rudder offset, engine offset, tip weight, distribution of side area, tabs on the flap, etc. ALL contribute to the total trimmed package.  Adjustable features are a good thing, but be prepared to have to adjust EVERYTHING, likely in multiple combinations!


BTW, given Igor's past & present success, it looks like his adjustments work pretty darned good!

[L0U CRANE]

Notice the small black mark?.. line?.. on the inboard tip? It is halfway between the leadouts.

Just as an ideal measure, consider the model as ONLY the CG spanwise, lengthwise, and from top to bottom. For ibest 'streamlined' flow, the fuselage should fly with the fuse centerline tangent to the flight path at the CG, no? That centerline meets the air at differing angles ahead of and aft of the CG. (The flip side of the flight path curve at the distances from the tangent point.) These angles are quite small, even when checked at the prop and at, e.g., the elevator hingeline...

Lines have drag - they make what Pete Soule' called an accelerated catenary - greater where the speed though the air is greater. (A caternary is the natural sag curve of a uniform load, on a uniform  cable supported at its ends. Line drag is not uniform: it is affected by airspeed. Once lines go inside the structure, air drag no longer acts on that part. Well, duh...

The 'LINE...' programs allow (allowed?) estimating the curve AT the leadout guides. That angle, extended to the CG, creates no torque couple trying to rotate the fuse in yaw. If the extended angle points ahead of the CG, it tends to cause nose-in yaw, and vice versa. When control inputs are made, 'pull' is no  longer equal on both lines, the yaw tendency appears, accordingly. But with close-set leadouts, the shift is (generally) slight. Other things correct, or counter, the tendency.

The lines should not bend due to the leadout placement, at neutral. The bellcrank pivot placement is irrelevant, but the 'aim' of the 'pull force' through the guides should  go to the CG to reduce rubbing and bending.

The 'aim' might be adffected by relatively large changes of CG when flight trimming.  Moving the guides to suit the CG can reduce or solve this.

So. without knowing more about the model's 'form' and conditions in that picture, we can't make any practical guesses or claims.

IMHO..

[Igor Burger]

Looks like sooner or later I must write another article, this time about fuselage and yaw trimming  it comes again and again

But no time and too little language ability ... not to mention necessary pictures (but here I have idea about someone  I hope she is not reading  )

[Steve Helmick]

I like to setup the LG so that the outboard wheel is 2" ahead of the inboard wheel when bench trimming, just as a conversation starter.  

Seriously, I doubt that many models have the wheels located exactly spot on, relative to the CG or whatever reference we wish to use. Most especially with wing mounted LG. I sure wouldn't use the wheels or LG struts as a reference. It would make sense to have a contrasting mark on the inboard wingtip corresponding to a similar mark on the side of the fuselage...at least while in trimming stages. Steve

[Steve Helmick]

Yup. With appearance points (or "peerince oinks" as our Ozzie correspondent would write) not many AMA guys would leave the marks on the wing tip and fuselage (aka "fugalug" for Matt) for contests.    Steve

[Craig Beswick]

Yup. With appearance points (or "peerince oinks" as our Ozzie correspondent would write) not many AMA guys would leave the marks on the wing tip and fuselage (aka "fugalug" for Matt) for contests.    Steve

Ahhh just to clarify Steve.
He is a Kiwi hiding out, ah sorry, living in Australia.

[Steve Helmick]

Ahhh just to clarify Steve.
He is a Kiwi hiding out, ah sorry, living in Australia.

My apologies! It must be stressful...  Steve

[Igor Burger]

Robby got it, model has markers from masking tape easy to remove or relocate and yes it is still in trimming phase, as my model is right now 4 weeks old 

however that picture shows previouse model from last year