Just put a solid 1/8" thick tail on a plane I'm scratch building. I left the leading edge of the stabilizer square (not rounded). This is a small 42" span plane. Think it'll do anything weird being square and all?

Being square wont make any difference. depending on the speed of the airplane I may be a bit concerned about it being only 1/8".

There is a good reason why an airplane's leading edges are rounded. If the stab leading edge is square, the drag of the stab is higher and the air flow around that stab will be turbulent. The result is more drag and less elevator(or rudder, if it's the vertical stab) control because of the "dirty air" flowing over the control surface.

You may not notice a big difference in the flight performance of your particular plane, but, in a high-performance aerobatic plane, it can reduce the performance significantly. You should get into the habit of rounding off leading edges.

Also, the trailing edges of the control surfaces(rudder, elevator and ailerons) should never be left square, because the trailing edges have an even greater effect on drag and control, than the leading edges. They should be tapered like an airfoil, not just rounded, for best performance.<br type="_moz" />

The size of the model has some bearing in whether or not the leading and trailing edge shapes matter. Also, there is a worthwhile reason to square off TEs.

First off, the size............ The smaller the model the lower it's Reynolds numbers. The smaller the Rn, the less impact (pun intended) the LE shape has. We all have seen the foamies cut out of sheets of foam. We all have seen how they fly. No real argument about LE shape for small models. Really.

Trailing edges are often left square for a reason. They're much easier to maintain when they aren't so thin they're weak and easy to damage. Their size also matters for much the same reasons the LE sizes matter. Good thing about TE's when they're squared off is they don't add enough drag that anyone notices.

So consider the size of your model when you make decisions about shapes. With smaller models, we really won't notice the differences in performance. In fact, if the models are small enough there aren't any.

What size do the models have to be for the shapes to matter? I think that's never been hypothesized or tested by modelers. Want to provide something useful to the discussion that's about to blow up? Offering observations of models you had would go a long way. Or if you've found something in a text that suggests where the thresholds are.................

I appreciate the responses!

The span is 42". Total weight will be 2-3 pounds probably. Electric powered. Heck, here's the build thread-http://www.rcuniverse.com/forum/m_11490691/tm.htm

Sounds like the square leading edge won't be a problem however if I do have anything funky going on with it's handling I'll look into fixing it.

Thanks

Leading Edges are always rounded, and Trailing Edges are always sharp or square for a reason.

The TE is cut square so the we get separation at both corners, with a stable turbulent wake in between.
The LE is rounded so that the Stagnation point (where the flow splits over/under the aerofoil) can move smoothly around the LE in firmly attached flow, without jumping due to sudden separation.

The result of both of these is that the graph of lift coefficient against angle of attack is straight, or a smooth curve, over the important portion of the graph, the bit that we use, the middle bit. That means that the behaviour of the aircraft is smooth. You might get away with a square cut LE, or a rounded TE.

But if the handling is unexpectedly lumpy, i.e. if moving a control has a small gradual effect then a sudden jump, or if the aircraft tends to waggle around, that's a sign that the TE separation point is waving around, or the LE stagnation point is jumping around, and the prime cause is a rounded TE or sharp points on the LE.

Of course you could get lucky and get away with with it.

Look at some of the current pattern airplane designs. Some have rudders that have a TE that is close to an inch thick. Reasons for this is that the additional drag helps the airplane track, Gives better response around neutral and is more powerful at slow speeds. I once had a 45" Katana electric aerobatic airplane that was very pitch sensitive. I glued on 1/2" strips of depron 3mm thick top and bottom of the stab LE. The pitch sensitivity went away. The tubulence caused by the strips kept the airflow attached to the stab and made the airplane more stable. Carden aircraft designs their airplanes with thick trailing edges because it makes the surface more effective. In full scale it [sharp TEs] will increase efficiency and of course that is important to save fuel costs but us R/C guys don't care about that unless its a pylon racer or sailplane.

In a nut shell, you will gain more stability and surface effectiveness on a small model by leaving them square.
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Do you have a name or two of full scale planes with thick, square TEs on any surface? I've never seen any ever and would really like to see what thickness is being used.

I guess I wasn't too clear. Full symmetrical airfoils with sharp TE is what is used on full scale because of lower drag. On our models, drag on the tail is a good thing.

Yes- the EXtra wings use the thick squared te
the effect (thick low pressure area along the TE)- helps keep the flow on the wing laminar - I have two of the new Splendor patten models and a VisionAire - these all have extremely thick squared TE
Two reasons : one is integrity- the structure is all injected mold modified EPP with internal CF supporting structure

The Splendors are quite fast and track like they are on rails ( the 635 rx must be damped for fast flight or there is a issue with flutter .
having done hundreds of pattern models and IMAC etc., I find these new foamies to be every bit as accurate flyers as any of the wood/ Carbon fiber etc., planes . I was amazed but having three of these things -it is obvious it isn't a imagined thing- they really work.
As others did/do- I also worked for years on nice razor sharp TE for wings stabs and rudder .

No more .

The Gloster Javelin, a British all weather interceptor of the 1950s, had a thick TE on the ailerons, about 15-20 mm thick. This one is at the museum at Elvington, York.

VP1

this is a subject I have really never paid much attention to until I bought a eaglet that had all the tail surfaces square. On three channels the bird was one of the best flying fun birds I ever flew. (been doing this since the 1950's) So, I built three more and carefully rounded the tail surfaces. None Of them could match the flyability of the original.

In short I would leave the surfaces square until it proved detrimental. And yes I have seen larger full stunt birds with square surfaces.

don't make a federal case of it, try it all and have a blast ....That's right I can't explain the why's and weretofors But I am having a lot of fun.

DONNY

I've always built my TE's on Pattern models to 1/8" thickness. Never subscribed to the real fat and even flared TE's that became vogue a couple years ago...don't believe in those.

Squared LE's are non issues for most models too.

However, if one wants the maximum speed for minimum energy input, the better approach is to have rounded LE's, thin surfacesand razor sharp TE's. Don't have to look very far to actually see some of those characteristics in action......pick up any APC prop. In my experience APC props in general are the best in converting available power to thrust..... minimal noise generation also which goes hand in glove with thrust generation

Don't disagree on streamlining -
the thick trailing edges tho are another matter
one application is to "suck" the air on the surfaces more tightly to the surface
another is to just add more centering drag.
Some models have more destabilizing drag-forward- than others and the fuselage just wanders when there is no real difference in pressure-side to side.
The are a bunch of ways to cure this - BUT the thick te is quick n easy.
One method seldom seen -is to change the fuselage planform taper - at the LE of the stab- (the fuselage remains gently tapered, then sharply tapers to the tailpost.
the beauty of this is - you can add vents (exits) in this area and seriously pull air thru the fuselage
Maybe this doesn't look purty - but it sure works-