Would anybody have the time to be able to explain to me the pros and cons of trailing edge thicknesses, have seen some top models (2metre) with thick trailing edges and some with very thin, which is considered better, and why?


Thank You

A trailing edge of about 1/8" thickness tracks better. If it's thin and sharp, the plane can skate a little. And if it's too thick, then you get some pronounced turbulence issues. But 1/8" seems to be about right for my taste. Your results may vary.

-Mike

I have seen pics of Christophes Oxalys and the trailing edges are massive, so it must go a little deeper than that explanation Mike

It doesn't, not much deeper at all. Don't make the mistake of thinking these guys are aerodynamic gurus, they're mostly trial and error.

-Mike

Trial and error or not their results are just as valid....thick TE's work, I would consider 1/8" the minimum and 3/16" a better choice for ailerons and elevator. Rudder I have gone as high as 3/8" with good results, I find 1/8" on the rudder too thin and the plane is less stable in yaw (especially on uplines).

A good pilot can start a whole thick trailing fad for this season. I agree with Mhester, its just trial and error. Nothing more nothing less. I bet if one of the top pilots won with a .60 sized bird you would all have new Dirty Birdie's for next season. LOL

Baaahhhh...Baaahhhhhh....

I'm no expert, but I did stay at a H.I.E. last night..........I would think there is definately some aerodynamic advantage to having some thickness at the TE. IMO it gives a more definate zone where air over the top and bottom of the wing can merge with a turbulent zone bound between them. With a sharp TE, it would seem like the the turbulent zone where the two flows mix would vary in location relative to the TE, somtimes above, and sometimes below varying the drag axis and thus affecting tracking. As with any other design factor, I'm sure there is a tradeoff or at least a point of diminishing returns on this....Richard

Its a fad if one guy does it for one season and doesnt do it the next, its something completely different if many people try it (for a number of years now) discover the same results and go in that direction....

I have done thin and thick TE, on the same model......there is validity in it.

Thick TE started to show up back 5-6 years ago and are still around today, I dont think its a fad anymore.

Trial and error although slow and painful (and usually costly) is a very effective way of getting good information....you can crunch numbers all day but real world testing is tough to beat.

If you dont mind me asking,which plane did you try both thick and thin trailing edges on and what advantage did thick show in real life?

Thanks

Lets all run out and buy new wing kits for our favorite models. LOL

Remembering back on my aerodynamics classes- there is a burble of turbulent air behind the trailing edges. I'm not so sure how much some slight variations in balsa would effect anything measurable when you think of different airflows at any given time across the span. Aoa, yaws, and wing shapes would be major factors causing relative chaos past the trailing edge. All end up becoming vortices.

The Cessna 150 is thick with those dimples, or whatever you call them in the ailerons. The F-104 TE is sharp enough to slice skin.

I think my thinnest TE is about 1/8. That is thin enough for me due to hangar rash!

I tend to disagree with it being trial and error if designed and tested properly. Some people may approach the design that way, but there would be properties involved for the aerodynamist.

Where is George Hicks when we need him???

I have done it on both a ZN Line Evolis XXL, and ZN Enigma... same results both times. Plane had a much better feel around neutral, basically felt more locked in than with the thinner TE's.

Yeah but 3/8" on a rudder? Man, that's THICK for a 2 meter.

Oh and because of this thread I just went and measured the TE's on my new plane....3/16" all the way around LOL And yes it does feel very locked around center, but the design is very clean also.

Let me try and explain this: Model aerodynamics is part science and part voodoo. Sometimes what looks great on paper is dog poo in application, there are simply too many variables. Hence why trial and error becomes so important. If it works, you stick with it. If it doesn't, you change it....and the "features" bleed off onto other designs, and so on and so on. And speed plays a factor here as well.

And this is why so many current designs look so much alike.....form follows function to a great degree. The longer the patterns and rules stay somewhat stable, the more the planes will be similar in the end...until we change the rules or patterns to an extent where something new is now advantageous, and the cycle repeats.

Blech....if it works, use it. If it doesn't, trash it. Thicker TEs work on the current designs.

-Mike

Yep 3/8" on the rudder, I did a lot of experimenting last year with this....uplines have never been the same, super straight.

Just a side note, as I do not have anywhere near enough experience to comment on this issue.

CPLR uses brown paper/foam wings, so the thick trailing edge may not be for aerodynamic reasons, but structural?
Just a thought.

Cameron McDonald

CPLR's finish is indeed brown paper - but over a conventional balsa veneered foam wing.

The theory is (and it is a valid one) is that the dimples it produces induces a turbulent boundary layer over the skin of the wing, rather than a smooth laminar flow layer. This prevents the boundary layer from breaking away from the wing until higher angles of attack - thus the wing will stall at a higher angle of attack. It is the same reason that a golf ball has dimples - it stops the air flowing over it from separating too early and reduces drag and hence increases range.

How much you would notice the difference on these models is debatable, but if anyone can he can!

James

It's all science. It does seem like voodoo to some people. I disagree that there are too many variables. For pattern, there is a finite set to deal with as in real planes. If the designers of real planes had that attitude, we would still be losing test pilots every day! Of course speed plays a factor. It's a plane. This isn't a big mystery and it certainly is easier than rotary wing aerodynamics.

The aerodynamic design for pattern is already changing. People just aren't noticing it yet. There are a few things I could do with my Widebody that would definately be different, but I'm just not inclined to mess around with it right now. Other people are. There is plenty of room to improve on the pattern that we fly right now.

The only reason "Theory" exists, is so that engineers can stand around scratching their heads mumbling "theoretically that shouldn't have happened"LOL. In life more often than not theory and practice are 2 different things.LOL


If the theory's worked we would have had the perfect pattern plane designed 30 years ago. Wait they did it was the Dirty Birdi. LOLOLOLOLOL

Christophe doesn't use brown paper anymore, he uses Oracover (I think) yet has retained his thick trailing edges.

I spoke to Quique about it and he said it feels softer around neutral and you get a touch more drag for downline braking.

Angus

Aerodynamist friend once explained that in full scale sometimes thick trailing edges are used to get more effect out of control surface without increasing control force as much. Aerodynamically control surface area seems almost as large as it would if it continues to sharp point. And the effect is stronger in slower speed where more control is usually needed like landing and T/O.

If you need more rudder and your model is already 2M you can install triangle spar to the trailing edge. I once had as wide as 12mm almost 1/2 inch and didnt notice anything bad behavior. Yrt knive edge and stall turns got better.

Structure stiffness versus weight is better when thickness ingreases.

Then design a pattern plane and get back to me. Been there, done that, quite a few times.

We don't have wind tunnels. We don't have million dollar budgets and teams working day in and day out figuring out the intricacies. It's usually just a few guys coming up with a solid idea, building it, flying it, and saying "yep" or "nope". Aerodynamic design is very specific to a particular airframe and what you intend to do with it. We aren't Boeing. And to keep things in a constant state of flux, we keep changing the "what we intend to do with it" part. So many of the constants...aren't.

I think we may be discussing different levels of design. us pattern guys are chasing absolute perfection, and it doesn't exist. Some things just work better than others. I could design a flying box that would fly great, but it's not what I'm looking for. Same with the rest of the designers.

"voodoo" is just an expression many of us use...it refers to the unknowns that seem to either bless you or bite you in the arse, no matter what the math said. It's real. I think my test pilots would be fine with my attitude, I haven't lost one yet [8D]

Now I have to load up and get to Andersonville for a contest.
-Mike

Lot of different points of view from mostly modellers , would really like to hear from the specialists ( if there is such a thing!!), George Hicks's point of view would be very interesting, personally I think this should not be one of those "VOODOO" things, cannot believe this should be a grey area with all the aerodynamic knowledge out there

papadontscreech- I agree. You are right when wondering what G. Hicks would have to say.

Mhester- how do you know that I haven't designed a plane or two? Sheesh. Take a few deep breaths and chill out. I fly pattern too, so you aren't alone.

If you read what I wrote, you may see that I was talking about people with degrees in this field, or long careers like Claude McCullough. And, you don't normally buy a freaking wind tunnel. You try and get some donated time, or you rent a few hours. I still disagree with your vision of aerodynamics being too many variables to understand. Also, I think you are wrong about aerodynamics relating only to specific airframes. It sounds like you don't want to learn.

I'll be in Andersonville on Monday.

Given sufficient time and funds you could design an F3A model and know precisely how it would fly before you even cut your first piece of balsa. This is how modern airliners are built. However this cost millions of $$ to do which is why it is effectively restricted to the design of airliners and military aircraft.

We are involved in the design of aircraft costs at most a few thousand $$. This might seem like a lot - it is for most individuals, but compared to the budgets for designing a new fighter jet for instance it is peanuts. Therefore it is generally not worth going through the expensive process of computer simulation of new model aircraft.

The next step down from computer simulation is of course the testing of models in wind tunnels. Whilst cheaper than full simulations it is still quite expensive to do any meaningful tests (a half hour borrowed in a wind tunnel just would not be worth the effort). And as you would need to build one if not several models to go in the wind tunnel, why not just build a real model and try flying it and see what happens?

Now this does not mean that aerodynamic theory does not have any place in the design of F3a models. It's just perhaps not as rigorously or as obviously applied during the design stage. You might not even know you are using it, but every time you make a change that makes an improvement you are effectively doing by trial and error, or educated guess, or intuition, what you could equally have tried and tested on a computer or in a wind tunnel. It just would not have been cost effective or practical for models costing such a relatively small amount of money.

There are of course overlying aerodynamic principals governing how all pattern models fly - that is why most of them look so similar now. These govern things like the required layout and relative areas of the wing and tail etc. The model specific differences come in at a secondary level, and a thick trailing edge will be this kind of secondary effect that will be effective on some models, less so on others. Ultimately if it works ok on one model then use it on that model. It might be worth trying on a different model but don't necessarily expect it to have the same level of effect. The reasons for it either working or not working could be explained (the maths is always right, you just might not have asked the right question!!). It just probably isn't worth the effort or expense to figure it out!

James

There are the published findings on certain airfoils, designs, etc that are available too. Most of this has already been done, wind tunnel tested, and documented. Tapered, double tapered, wingtip dihedrals, AOA, etc all have predictable properties. I don't have the links anymore to the NASA databases where you could read about all of airfoil properties, stability findings, etc. Then, there are the books. Getting in the ballpark for a given pattern design wouldn't be all that difficult if some research was done first to get the fundamentals. I think the fine tuning aspect would be where some trial and error would be involved if one was looking for what they considered to be their ideal pattern plane.

Marcelo Columbo of CA Models has mentioned a little of his process to refine the Widebody design when he came out with the Epsilon. He was after better snaps and knife edges. It is interesting to see the evolution of his designs when he tells his goals.

It was mentioned that pattern has evolved to a certain stage of performance and stays there because it is good enough. I don't really agree with that. I think that the vanes people are calling side force generators has been overlooked for decades. Now, Hangar 9 has a plane using that along with the gaudy advertising. A guy gave me a banged up Somethin Extra where he had found that a little fin (or vane) on the landing gear helped knife edges. Same principle. Also, I think that fuselage bottoms are a victim of looks instead of functionality. Some things have been written about improving knife edges by modifying this shape. These are only a couple of things that are probably ignored for better precision flight. But, significant improvements in pattern design would probably mean significant styling changes too.