Latest Model Aviation, page 40, Feb. 2017

[Steve Helmick]

This issue came today, and has some stuff on having thicker control surfaces than wing/stab TE's, control surface LE's and other aero stuff, like vortex generators. Anybody heard about any of that stuff? Well, I thought I'd just axe y'all. Seems like it's supposed to be a big deal; maybe The Next Big Deal. Steve 

PS: I'm hoping that Howard can scope it out and give the article his thumbs up or thumbs down before we waste our time.

[Steve Helmick]

Howard? Anybody? I'm not recycling this issue until I get some Aeronautical guidance on these burning issues. Has anybody actually read it?  Steve

[Gerald Arana]

I haven't seen it yet. Years ago (as I recall) there were airplanes with thicker control surfaces than the fixed surface. I don't recall how that worked out but apparently it wasn't to popular.
Personally, I prefer a thick TE, ie. about 1/8" and square.

In my old glider flying days, (racing) a razor sharp TE had the least amount of drag, squared off was next and a rounded TE was the most draggy. Of course in CL that is probably preferred....

I would imagine that a thicker control surface with a squared off TE would perform well, although I haven't ried it ..........yet.

Jerry

[tom brightbill]

Saw it, read it. I was amazed that it was even published (prior to Howard's review, I assume). But how does it apply to drones? Come on Howard!

[Chris McMillin]

I was caught red handed leaning my forearm on Dave's vg's when launching last week, Brett's retort was it probably wouldn't fly any differently if one or more was removed, even still I adjusted my posture and was approved as Thundergazer launcher.
Seems there is some debate about if they work, but Whitely's says they dId make a difference on his latest Derringer.
Chris...

[Chris McMillin]

There were several full sized acro ships with ailerons thicker than the wing trailing edge popular in the 90/2000s, Extra,Sukoi, Yak, Giles, Zivko, etc... the theory being the surface would have boundary layer "hang on" longer in extreme aoa, blah, blah. I've flown several and they have very high roll rates that hang on, alright. Or was I?
Several aileron retrofit kits were produced for Pitts wings to take advantage of the same theory. My buddy bought a kit lately that has none of that, but has more area and stiff construction with cf leading edge sheeting a third flying wire and wood wing leading edges. Evidently torsional stiffness is more important than fat surfaces.
Most homebuilts have flat trailing edges, even little ones. Science has made it easier to build in this case? When I was into air racing crewing on Unlimiteds you would see stock pointy, stock blunt, and every mod imaginable in between. In this case the most powerful engine that ran the whole race was the winner!
Chris...

[Steve Helmick]

Jerry, as stated, the subject issue of Model Aviation came to my mailbox on January 26, 2017. This leads me to suspect that you didn't notice the article and already round filed the issue. I almost did that, myself. Hence, my making the original post, and bringing it up again. I want to know if any of this stuff would apply to CL Stunt. We already know that VG's cause a significant reduction in Appearance Points.  Steve 

[Brett Buck]

     There was an earlier thread on this, I think, but the concept (getting better feel around neutral and/or getting better response around neutral) is, to me, a far better goal than trying to soften it up around neutral. You really need to have positive response around neutral to be able to get maneuvers started and stopped neatly. The Igor logarithmic flap connection has a similar effect, lots of elevator response around neutral and not as much flap.

    Just my opinion, but all these exponential controls, "elevator thinner than flap", various other things intended to soften up the response around neutral is a big mistake. We have spent the last 20 years trying to trim them to do just the opposite.

     Brett

[Paul Walker]

The Igor logarithmic flap connection has a similar effect, lots of elevator response around neutral and not as much flap.

     Brett
[/quote]

I think you have this backwards. Around neutral the flap moves more than the elevator. As the elevator deflection increases, the flap slows down. More flap in rounds, less in hard corners.


BTW, my 1992 WC plane had thicker flaps than wing TE thickness. Flew great!

Don't know why I stopped doing that.

[Matt Neumann]

Since we are on the subject, I am finishing up (finally!) an A-26K plastic model.   On the right side of he rudder there are vortex generators.  None of the left side.  Anyone know why?  This is a twin so I am curious as to why one side and not the other.

[proparc]

Howard? Anybody? I'm not recycling this issue until I get some Aeronautical guidance on these burning issues. Has anybody actually read it?  Steve

 

[Chuck_Smith]

I read it. I would rate it as informed but not factual. There were two glaring issues the that lead me to think the author isn't a SME for incompressible flow.

First - while the author made a passing reference to sealing the hinge gap, not doing so will have a major impact on the flow pattern and he didn't incorporate it in his flow visualizations. And I'll give him some leeway as a visualization tool, but the boundary layer thickness he implies by the pictures is way out of proportion.

Second - and this is the big one - the author's pictures are textbook examples of flow visualization for full-sized aircraft. Boundary layer phenomena are affected by the Reynolds number. To imply that an R/C airplane wing with say, a 12 in. chord going 60 mph is dynamically similar to a full-scale going 100 mph is just not true.

I've used zigzag tape on full-sized airplanes. It really had very little effect, if any. Adding (or repairing) gap seals was much more effective and had the added benefit of reducing the control forces.

Using vortex tape on my full-sized HP-10 sailplane was inconclusive. I kinda maybe think it might have had slightly better aileron response at altitudes over 12K feet, but down below cloud base it just collected bugs and added drag. I suspect there wasn't enough chord out there for the Reynolds number to get high enough to worry about separation. All I can say for sure is after I removed it it was a lot easier to clean the wings.

[Chuck_Smith]

BTW, If you want turbulator tape try www.wingsandwheels.com.

Search for "turbulator tape" and you an get different zigzags or dimple tape.

[Joe Bowman]

Since we are on the subject, I am finishing up (finally!) an A-26K plastic model.   On the right side of he rudder there are vortex generators.  None of the left side.  Anyone know why?  This is a twin so I am curious as to why one side and not the other.

Matt,  This is just an assumption on my part.   The vortex generators were only on the right side due to the time period (mid 1950's to early 1960's) not as much was known about them but they demonstrated that it helped increase performance in certain cases.  The K model had higher horse power engines than the B & C models they were modified from and would have required more Ruder authority, VMC demonstrations would have noted the increase in airspeed at which VMC would have occurred.  In this airplane the left engine being the critical engine therefore more right rudder authority was needed.  Left rudder authority was likely ok.  this would have been the cheapest and quickest fix.  apparently problem solved and did not bother to put them on the left side. 
   Having said all of this.  All of the the twin engine aircraft I have flown that have VG'S installed, have them on both sides of the rudder.I am probably going to get a lot of grief over this post but since no one answered your question I thought I would try.