Airfoiled Tail Surfaces
 

Why aren't more of the smaller planes designed with airfoiled tail surfaces?

RE: Airfoiled Tail Surfaces
 

They all used to be, but someone decided (long ago) that it would be simpler for kitting if the hardest, heaviest piece of wood available was turned into a slab that would curl up at the hint of covering was used instead.
Evan, WB#12.

RE: Airfoiled Tail Surfaces
 

as long as the surfaces don't twist under load - the shape makes no difference
this idea gets beat around a lot but the real reason for the nice curve is to get strength with least drag.
I just finished a fat wing small electric aerobatic model --and compared to a flat wing -same size -same power - same wing loading same planform - guess which slow flies the best ?
snaps the best etc..

RE: Airfoiled Tail Surfaces
 

Interesting.

I talked to an aerospace engineer about it who is studying here at Miss. State Univ. and he said that the difference on planes under about 65" wingspan or so would not be drastic, but that there is a definite difference. In his mind, it was well worth the little bit of extra effort to airfoil the tail group.

RE: Airfoiled Tail Surfaces
 

For the small planes, airfoiled tails only make sense when there's a measurable parameter involved.. Speed, distance, endurance.
For yanking and banking, it makes no difference.

RE: Airfoiled Tail Surfaces
 

RVM

Like your products!!! Do the job----and are first rate.

I've flown both flat and airfoiled-------many different models-----I agree with Dick.

I also agree with your friend the aero engineer as tests: data from tests; conclusions drawn from that data; and that which truly makes a difference that you can 'feel' without concentrating on the point are, to say the least, elusive.
Even when two similarly qualified people are using the same data, you can and will come up with more than one conclusion.

Leo's Laser 200; all the Pitts I am aware of and many, many other full scale aerobats use flat stabs.
Others like the CAP's (my favorite) use airfoiled.

Personally I prefer the airfoiled stab---------but it is the strength factor without the bloody wires that I'm really after.
I've never seen a difference I could 'find' NACA vs. diamond.

All covered under "likes and dislikes" I am afraid---- (season to taste).
My designs use 0009 root to 0011 at the tip but that is for building ease alone.

Edit addition: at a far earlier point in my life I spent a considerable amount of time with Pattern A/C. Never could see the difference on stab design. There were world beaters with each design.

RE: Airfoiled Tail Surfaces
 

Because it takes less time to make and they don't care that it looks like garbage.

RE: Airfoiled Tail Surfaces
 

Try scaling those small airfoils down---------like doing a hysterectomy on an ant!

RE: Airfoiled Tail Surfaces
 

Lots of great explanations! Thanks!

One thing is for sure - flat stabs do look like crap!

I do like how stiff airfoiled stabs are compared to flat ones...


I was told that the airfoiled stab allows the control surfaces (rudder, elevators) to be more efficient and smoother. Is this applicable to our small models? I do know that the full-size Ultimate uses flat stabs, and it's obviously an amazing aircraft.

RE: Airfoiled Tail Surfaces
 

I've flow both airfoiled and flat and can't say that the difference is enough to feel at all. Mind you I have not flown the same model with the two styles and all else the same.

RE: Airfoiled Tail Surfaces
 

Airfoiled stabilizers and fins tend to soften the feel of the elevator or rudder when they are near neutral. Sort of like building in a bit of exponential. As far as how effective? See above...a myriad of models with one or the other and all fly very nicely, indeed.

RE: Airfoiled Tail Surfaces
 

yeh - the real difference in angle is diminished
therefor : elevator angle change = less EFFECT
now build a shi-t pot ful of em in different thicknesses and prove which is "better"
most airfoil shaping is really a product of getting required strength for the task-
on full scale --this is augmented by the need to reduce non effective drag to minimum--on most of our power models , this factor is very small.
very very small
teensy weensy
tiny

.

RE: Airfoiled Tail Surfaces
 

Quote
I was told that the airfoiled stab allows the control surfaces (rudder, elevators) to be more efficient and smoother. Is this applicable to our small models?
Quote

I've been told the same thing --------(goes back a long way too)--------I have never observed anything approaching it.

We have a flier at our field who goes on and on about it------------------problem is he is a marginal flier on his best day----and that doesn't occur too often;).

I'm certain you have heard similar discussions-------at various experience levels------ as have I.
My example is not intended to belittle your source but rather to point out that "passion" has VDL to do with the facts.

Edit addition: If memory serves me correctly the F-4 Phantom has a "flat" stab ---anhedral but flat. More than a 'fair' performing A/C too. As I remember it, it is so thin they put guards on the leading edges when hangared. That info though is hearsay as I never saw it first hand------.

RE: Airfoiled Tail Surfaces
 

Nah, my source isn't a nazi about airfoiled stabs. He's an aerospace engineering student, and is more than aware he still lacks knowledge and experience. His rationale behind it is simple, and agrees with mine: it looks better, is a bit more aerodynamically efficient (though in our models, the difference is probably not even measurable in anything but the fastest of the fast) and is stronger, so why not do it?

Thanks for the excellent information. I'm glad I asked, as I've learned a fair bit from this discussion. :)

RE: Airfoiled Tail Surfaces
 

If it feels good do it - just don't go blind--

RE: Airfoiled Tail Surfaces
 

The next time you talk with him ask him If Dr. (Gus ) Raspet's ghost still haunts the hallowed halls of the aero engineering area.

RE: Airfoiled Tail Surfaces
 

All that effort to make a airfoil shaped stab and you still have that airflow discontinuity at the elevator hinge line due to the bevel that has to be there in order to have movement clearance. And let's not forget that the elevator control horn and pushrod and maybe even the servo control horn is out there in the airstream. Sometimes it's easy to get obsessive about one little design feature while "swallowing a camel" with the rest of the plane.

RE: Airfoiled Tail Surfaces
 

To me it's a lot about what looks right as well as flies right and a slab stab and elevator doesn't look right. I probably wouldn't be able to tell the difference in performance but my eyes still work pretty well. When I see a slab on the back of the plane it tells me the builder was trying to cut corners (or not depending on your perspective). If it wasn't like that on the full scale it sure doesn't belong on the 1/? scale.

RE: Airfoiled Tail Surfaces
 

The horizontal on the F-4 is an inverted cusped airfoil.
True flat airfoiled horizontals disappear on full-scales much above the size of an Aeronca or a Pitts.

RE: Airfoiled Tail Surfaces
 

Hah! I have heard bits and pieces of that story several times. Apparently, he still wanders the halls. If not, then the myth is alive and well.

Did you attend MSU?

RE: Airfoiled Tail Surfaces
 

Ah but see there are solutions for that as well. Have you ever seen a "shrouded" hinge line? The sheeting on the stab extends past the trailing edge a bit. Then the leading edge of the elevator(s) are rounded to allow them to move inside the shrouds. The result is less disruption of airflow. Also, the control horn can sometimes be mounted inside the fuselage on the elevator joiner thus keeping the horn and pushrod inside the fuselage. My current scale project is being constructed in exactly this fashion.

RE: Airfoiled Tail Surfaces
 

Shrouded hinges? Yes, I think I see those every time I look out the window of a commercial transport plane. Probably well worth doing once you have gotten the cylinder head properly baffled and shrouded for effective cooling with minimun cooling drag, once you have the muffler inside the fusilage instead of having it hang off the side of the plane, after you have installed a retract system that has flaps that close and seal the holes that the gear retract into. I think you get my point. Before straining at gnats, first make sure you're not swallowing a camel.
Then on the other hand, drag is not nessesarily a bad thing for aerobatic airplanes. It helps braking on the downlines.

RE: Airfoiled Tail Surfaces
 

Some argue that one thing that can make a plane better is not worth doing if everything else that can be done to make it better is not done.

I disagree.

Every little thing helps. Just because you you have an exposed hingeline does not mean that airfoiling the surfaces will not be beneficial. It just won't be quite as beneficial as it otherwise may have been.

Ideally, if I had the knowledge, tools, resources and time, my models would take advantage of every possible improvement that I could implement.

RE: Airfoiled Tail Surfaces
 

Ok. Who says a flat stab isn't airfoiled shaped, wrong, it is a symetrical airfoil. does it not have a rounded leading edge and most of the time a tapered trailing edge.


Keep The Faith: Johnny

RE: Airfoiled Tail Surfaces
 

I am scratch building a plane at the moment that has a foiled horizontal stab. The foil is added on to the top and bottom surfaces of the built up stab like ribs. They increase the overall thickness of the stab from 1/4" to about 1/2", but the spars are still only 1/4" thick, so the foil does nothing to add strength. And it's hardly a speed demon either - it's a Tyro Major, a 3 channel trainer from the 70's.