Sports Aerobatic Wing Section

[Stephen Bennett]

Hi,

I'm in the process of designing a low wing sports aerobatic model of around 44" wingspan, which will be electric powered.
What would be a good wing section to use to enable good aerobatics (not out and out 3D).
I've been looking at the NACA 2415 which is not fully symmetrical but am clutching at straws really.
Would a fully symmetrical section be better for the job.
Any help would be appreciated.

Steve.

[Brandano]

The wing section on full size acrobatic planes is a really interesting feature: it's plain ugly. It's highly inefficient, and very draggy. The issue is that these planes aren't meant to cruise. They are supposed to fly just as well upside-down than right side up, they are meant to stall in a benign way, but sharply to allow entering intentional spins, and they are supposed to have plenty of drag in a dive to avoid exceeding VNE in a large loop, on the assumption that if you really need speed you just put a bigger engine on the plane. If you want to do the standard aerobatic routine (8 point roll etc) but still have a sport flier any decent semi-symmetrical section with decent stall characteristics will do just fine.

[Al M]

The 24XX series works well and I didn't find any nasty surprises yet.

[macboffin]

The wing section on full size acrobatic planes is a really interesting feature: it's plain ugly. It's highly inefficient, and very draggy. The issue is that these planes aren't meant to cruise. They are supposed to fly just as well upside-down than right side up, they are meant to stall in a benign way, but sharply to allow entering intentional spins, and they are supposed to have plenty of drag in a dive to avoid exceeding VNE in a large loop, on the assumption that if you really need speed you just put a bigger engine on the plane. If you want to do the standard aerobatic routine (8 point roll etc) but still have a sport flier any decent semi-symmetrical section with decent stall characteristics will do just fine. Please can I have a SCREAM!!!! There are no semi-sym sections. They are either symmetrical, or they are not! We don't talk about "semi-flat bottomed" sections, or "Semi-running engines" either. So please ; lifting sections, flat plate, or symmetrical.

[BMatthews]

Just go for the symetrical section. For any model that will spend considerable time upside down even if it's only about 1/4 of the time there is NO other choice that makes any sense at all.

Those oddball sections you see on those planes is done for a purpose. It's actually highly stall resistant but when it does let go it' does what it needs to do.

A few buddies locally used the Eppler 474 on some control line fast combat models when the old Granderson airfoil was high speed stalling in the turns and coming in on them. I talked them into trying the brand name airfoil and they ended up using it for the rest of their combat time on probalby 100 models. It both turned tighter and at the same time lost less speed than what they called the Granderpig airfoil.

But it is a rather draggy choice. For you I'd suggest a Selig 8020. It's true use was supposed to be as a high alpha tolerant all flying sailplane airfoil. But the same charactaristics that make it a winner for that use would be good on an electric aerobat. I can't find out how thick it is at the moment since I'm not on my home computer but if needed thicken it to 12 to 13% thick for your use.

If you don't have it already download and install Profili2 from www.profili2.com .

[Brandano]

There are no semi-sym sections. They are either symmetrical, or they are not!
Aye, you are right. However, in my defense, the language isn't made by those who define it, but by those who speak it, and semi-symmetrical is nowadays in the common use. http://images.google.com/images?q=semi-symmetrical+wing+section :)

[Lon Enloe]

I use the Eppler 168, 12.5% thick, fully symmetric, on all my aerobatic ships (four successful designs so far). They are pattern planes, not 3-D ships. Besides exhibiting good aerobatic performance with no nasty stall tendencies, they all slow down nicely for landings, and if you implement flaperons, will land in a very short space.

[mnowell129]

As an engineer, airfoils are either cambered or not (symmetrical if you will). That plus the thickness distribution is about all you need to describe an airfoil.
"flat bottom", "lifting section", are modeling terms or terms out of old out of date books, not current engineering terms.
I'd hope that in a forum called Modeling Science the real terms for things would be used.

How come this forum doesn't have a glossary sticky for things like airfoil, wing section, AC, NP, CG, chord, tail volume, lateral stability, longitudonal stability, aspect ratio, static stability, dynamic stability, trim, L/D, Cl, Cd, Cm, non-dimensional coefficients, reynolds number, boundary layer, kutta condition, parasite drag, profile drag, form drag, induced drag, (Cl ^ (3/2))/(Cd), etc. etc. ...??

I enjoy the topics anyway.

[Stephen Bennett]

Thankyou,

For your input people, much appreciated

Steve.

[PabloM]

How come this forum doesn't have a glossary sticky for things like airfoil, wing section, AC, NP, CG, chord, tail volume, lateral stability, longitudonal stability, aspect ratio, static stability, dynamic stability, trim, L/D, Cl, Cd, Cm, non-dimensional coefficients, reynolds number, boundary layer, kutta condition, parasite drag, profile drag, form drag, induced drag, (Cl ^ (3/2))/(Cd), etc. etc. ...??

I enjoy the topics anyway.

Start one!!!

[MCarlton]

As an engineer, airfoils are either cambered or not (symmetrical if you will). That plus the thickness distribution is about all you need to describe an airfoil.
"flat bottom", "lifting section", are modeling terms or terms out of old out of date books, not current engineering terms.
I'd hope that in a forum called Modeling Science the real terms for things would be used.

How come this forum doesn't have a glossary sticky for things like airfoil, wing section, AC, NP, CG, chord, tail volume, lateral stability, longitudonal stability, aspect ratio, static stability, dynamic stability, trim, L/D, Cl, Cd, Cm, non-dimensional coefficients, reynolds number, boundary layer, kutta condition, parasite drag, profile drag, form drag, induced drag, (Cl ^ (3/2))/(Cd), etc. etc. ...??

Because for most of us, those things are pretty much irrelevant and whilst its very nice to be able to trot out technical terms and to look impressive doing so, what would be more impressive would be able to engineer an aircraft at model scale accurately enough to be able to make use of those things.

Also, given that this is a modelling forum, I would have thought that modelling terms would have been ok, I refer to a flat bottom section as such because there's no gaps under it when I put it on a building board. I call a symmetrical section that because it doesn't matter which way up it is, it's the same. I can, and do, understand bits of aerodynamic theory where I need to, but the fact that we don't all talk about these things in precise engineering terms does not make us irrelevant dinosaurs.

I should also perhaps say that terms like camber, LD, drag coefficient and so on are not engineering terms, they are aerodynamics terms and exist as theories before they ever see an engineer.