westerman

This image is of a typical 15% symmetrical airfoil used on a ugly stick. 10" chord. The blue profile is the "standard" NACA 0015 airfoil. The white profile has a sharper LE roundness factor. What effect does leading edge shape have on aerobatic performance? Stall speed?



Thanks CL

wellss

The purpose of sharpening the leading edge is to reduce straight line drag, but maximum lift will suffer

If you're playing around with airfoil shapes, it might be worthwhile to try a NACA 0015-64

I'm using VisualFoil, by Hanley Innovations to analyze, and it shows both higher maximum lift and lower drag
Try Javafoil and see what happens?

R8893

My Feedback: (20)

The shape of the model airfoil may relate more to available balsa sizes and the design of the LE construction. Did the original Ugly Stik have a piece of square balsa rotated 45 degrees for the LE?
Chuck

speedracerntrixie

My Feedback: (29)

Chuck, the Jensen Ugly stick did have a 1/4" sq stock LE at a 45. The two LE examples shown will fly no different, there just isn't that much of a change. The only reason I have ever sharpened a LE is to promote better snap/stall characteristics on aerobatic models. My pylon aitplanes have a good radius because good turning characteristics are more important then that additional 1/2 MPH.

soarrich

My Feedback: (98)

I think you'll find the elevator feels softer around neutral on the -63 as opposed to the -33 airfoil.

charlie111

Do you have any suggestions for an (Electric Rotarywing) I am working on.I had to change direction of rotation to Run Stock Rotation on Both Sides.Getting Equal and Most Efficiante Airflow!

BMatthews

Westerman, all else being equal the sharper radius of the 0015-33 option will stall a trifle sooner with a cleaner break.

Which is better for you depends on how you want to fly. If you want to do really tight high G turns and tight fast loops without snapping out of them the -63 nose will do more for you. If you enjoy snaps and want to get into the now popular post stalled 3D style flying where you want the model to stall on command and dump the flying energy fast when going from normal to post stalled maneuvering then the sharper -33 nose will help with that.

Mind you for the 3D stull the current vogue is to go with thinner airfoils than 15%. The idea seems to be to get closer to a flat plate but still keep the airfoil thick enough to contain a decent spar system. It seems like many models of this sort are showing up with 10 to 12% airfoils.

speedracerntrixie

My Feedback: (29)

You will find that as lightly loaded as our models are 99 out of 100 guys would not be able to tell the difference with the 2 examples illistrated. As for the 3D type airplanes having thin airfoils, I have not really seen that. Krill is really the only manufacturer that seems to like really thin airfoils. I have a feeling it leads to cost and weight reduction more then any performance gains.


As far as an auto-gyro goes, a simple flat bottom airfoil works well. No need to get fancy.

Rotaryphile

Old text "Airplane Design" by Warner shows effect of three different leading edge radii for the NACA 0012 symmetrical section.

A knife-edged leading edge reduced peak lift coefficient from 1.4 to 1.03, but produced a very gentle stall. Minimum profile drag was reduced only by a percent or so, and was increased at lift coefficients over 0.2 - definitely a poor trade-off, apart from its friendly stall characteristics.

A very blunt leading edge with radius of about 5% of chord increased maximum lift coefficient to about 1.5, increased minimum profile drag by about 10%, and produced a far more abrupt stall.

The blunt section, with its higher lift and abrupt stall is good for maximum possible lift, clean snap-roll entry, at the cost of tendency to stall and snap-roll. This probably explains the popularity of the so-called ice cream cone sections used on Extras, Edges, and Sukois for all-out aerobatics. Just don't let your airspeed get too low during a landing approach.

speedracerntrixie

My Feedback: (29)

For our IMAC type Extras, Edges, Caps and Sukois with the low wing loading we have the exact opposite is true. This is why one just can't use full scale data on our models and have it work the same.

charlie111

I noticed on the (Airfoil that it was for Aerobatic use.With no Flat Bottom.Looks like it would work as well inverted? Thanks( Roll Over Sigorski!)

MTK

In most models especially aerobatic types, creating more lift means practically nothing. Models are extremely lightly loaded and they don't really much care about the wing creating another couple percent of lift. Maybe slope soaring sailplanes could use that to beter advantage

MTK

SRT hit it on the head regards to model aerobatics. In fact, blunt wing LE takes so much elevator and rudder to partially stall one panel during a snap roll, thatsnaps are often "buried" which makes recovery very difficult and unpredictable. Also, many times initiation suffers since we just can't get enough throw into ele and rud fast enough in radio controlled aerobatic flying. Radios are just too slow compared with a guy sitting in the cockpit.

One can easily do an experiment on thick winged, blunt LE'd aerobats. Add a strip of balsa to the outside 12-15" of wing LE, near the tip. 1/8" thick X 1/2" wide strip is fine. Results will be immediate...

charlie111

I understand completely Have you seen 1st prototype.I had to get some (Bugs) out.Like changing the Direction of Rotation to get equal an Most efficiante Airflow on Both sides.!st prototype had reversed direction and Reverse Prop; on one side to get the Same Airflow.Changing Direction Solved it.I now use Stock rotation and Props. on both sides.Smallest reverse prop I could find was 8 inches. actually to Big for My Prototype.

westerman

My interest is totally in high speed aerobatics.

[youtube]http://www.youtube.com/watch?v=25GK6s91pzI[/youtube]

[youtube]http://www.youtube.com/watch?v=xHXBho2L1yo[/youtube]

[youtube]http://www.youtube.com/watch?v=_C3Rgk7zeuM[/youtube]

Rotaryphile

To crudely test the effect of sharp leading edge, I taped 45 degree triangular strips of balsa to the inner third of the span of one of my own design aerobatic biplanes. I expected them to act like the stall strips used on some full-scale taper-wing airplanes, causing the inner portion of the wing to stall first, leaving the outer portion of the wing remained unstalled, and keeping the ailerons in business.

The result: I couldn't detect any difference during flight testing.

I then taped the same balsa strips to the outer third of the span, expecting to get more tip stall. Again, I could detect no difference in stall behavior.

The test airplane is pictured here:

http://media.radiocontrolzone.com/ma...aneSecrets.pdf

It appears that Reynolds number may have a large effect on the behavior of wings with sharp leading edges. My model flew at a stall Reynolds number of about 100,000. The figures in Warner's "Airplane Design" appear to have been obtained at a Reynolds number of at least a million, in order to obtain a 1.4 lift coefficient from the NACA 0012 airfoil.

In general, full-scale texts report that airfoils with relatively high maximum lift coefficients tend to stall more abruptly. I tried the same, very blunt, airfoil used on the Edge 540 on a hyperactive aerobatic model I designed a few years ago. It produced excellent lift and clean snap roll entry, but also tended to tip stall.

The flat-plate airfoils used on many small aerobatic "foamies" seem to stall in a very friendly manner, but their maximum lift is poor.

Maybe you can say only one thing for sure about model aerodynamics: It keeps you humble.

Rotaryphile

Here's an interesting discussion on leading edge radius by Don Stackhouse:

http://www.djaerotech.com/dj_askjd/d...lunt_wing.html

Don mentions that sharper leading edges produce a gentler stall, but does not quantify the accompanying reduction of maximum lift, or the effect of a gentle stall on aerobatic performance. A sharp stall break tends to promote cleaner snap roll entry and recovery, I think.

BMatthews

Westerman, if you're going to fly fast like that again the sharper leading edge is what you want. But now you're working the other end of the performance envelope from the near stall and post stall slow speed 3D style. Instead you're going to reduce the drag by using the sharper LE so you can go faster for the same power or go AS fast with less power and run for longer on a tank.

Keep in mind that part of the big high speed zoomy style of flying is to not drag down the speed of the model by pulling high G tight turns and pitch motions where you run the wing up to the high angles of attack where you risk the high speed stall. Instead you keep it moving and use the lower drag middle lift coefficients except where you want to do a snap. Then you park the sticks in the corners and watch the fun. And the sharper airfoil the works in the other zone to give you the sharp and abrupt stall you want compared to the softer nosed option.

rmh

Theory is one thing
The last TOC event had varous style models (as did other TOC events) - -sharp blunt le you name it - actual differences in performances?
not much if any - which indicated LE shape was critical
Our last TOC design- a Bucker with 11% airfoil - very gentle yet would snap easily recover quickly Just a nice 30% high point shape with gentle LE radius- about 3/16"" radius
wing loading- far far more important

MTK

Any wing LE shape within reason can be forced to snap or spin. The larger LE radii require much more elevator to initiate. To me, more throw is not whatI want to produce the same effect

That's the reason I like sharper LE's on the wing. Less throw on the control surfaces is necessary to initiate. Servos are happier, airframe is happier, and lower throw helps exit on line better.

I am looking for something totally different than the sport fliers do. In competition, we perform these aerobatic maneuvers for a score so everything is important. In sport flying, as long as the crate remains intact, anything goes. There is no need to tune the commands for a refined response

da Rock

The never ending problem with aerodynamics is...........

Seldom does one thing control one thing.... like the LE radius isn't the only thing that controls how easy a model is to snap.

rmh

True - a full scale EDGE has a huge rounded leading edge on the wings
Many of the old "textbook" guys don't even know about this shape - it snaps quickly recovers quickly - also spins well recovers on point etc..
After doing more airfoil shapes than I can count - (aerobatic types) I came up with a shape which resolved the issues for me
"make it as thin as you can but still rigid and strong ."
OR make it thinner yet and brace it - either setup works as long as the wing loading is within reasonable limits
For really forgiving but maneuverable flying - a low aspect ratio very thick wing is also good - it is pitch insensitive
The new little VisionAire by Horizon is a prime exampleof this approach.

MTK

What I implied is minimizing the workload of the pilot during competition flying. My implication didn't translate well considering the comments I saw. In my last paragraph above, I think I stated my position...

My original argument stands....as an experiment, one can figure out how much command is required to make a model (with a thick wing and blunt LE) snap roll

Then do the same after taping a sharp LE to the outboard one foot or so of span. The sharp LE isn't elaborate...just a thin 3/32"-1/8" thick strip of balsa, about 1/2" wide. Dick that goes for the Edge wing too, but you may already know that answer

speedracerntrixie

My Feedback: (29)

A fellow club member once did an exact scale ( including airfoil )33% Sukhoi SU29. Great looking model but horrible at R/C aerobatics. It had to be forced to snap and spin. Took lots of elevator throw for the snaps that would kill almost all your airspeed. For the life of me I could not get a snap exit anyehere near the same line as the entry. It also had a wicked yaw to pitch couple. It was however a very tame airplane and the pwner actually used it as a sailplane tug. I once had an Aeroworks kit built Edge 540, the original one with the flat tail. After a conversation with Bill Hemple while building the airplane I was advised to sand the entire leading edge to a 1/16" radius. That was one of the best snapping airplanes I have ever owned. Every IMAC or pattern airplane I have built since then has had sharp leading edges.

rmh

Look at new little VisionAire -it snaps nicely