The leading edge is not a circle. Its radius is as specified only at point zero on the X. The curve has a constantly changing radius away from 0, which a circle or arc does not. It's a pity MoI does not have a curvature radius display then it would be more obvious what I am talking about. An ellipse is a better approximation than a circle. Indeed it is suggested that a tilted ellipse is the way to get the first section of the aerofoil. You do not want tangent connections either. They must be G2 curvature continous at the very least.
everything I have seen from naca shows the le as a circle, including the blue Bible. do you have naca documents or experience regarding your assertions. I have worked for two different propeller manufacturers and the le was a circle tangent to the rest of the data. I'm not interested in noncontructive information. Your free to model things however you like. I enjoy the same frerdom. Frankly I'm tired of responding to your posts.
Anthony, would you please confirm the AFXTAB and AFYTAB data, in particular, the last 6 points, in each array, as follows:
"X & Y" Elements 24: Leading Edge "tangent" point, end of arc radius, and also the starting control point, of the curve "spline".
"X & Y" Elements 25: Trailing Edge "tangent" point, end of arc radius, and also the ending control point, of the curve "spline".
"X & Y" Elements 26: Leading Edge "uppermost arc radius start" point.
"X & Y" Elements 27: Leading Edge "arc radius center" point.
"X & Y" Elements 28: Trailing Edge "lowermost arc radius start" point.
"X & Y" Elements 29: Trailing Edge "arc radius center" point.
I will enter the first and last points of the "spline", again, (a second time, in the order to be selected for spline), to simplify point selection in the for loop.
I read over the articles you are referencing. They state that the original definition contained circles:
"The values of leading-edge radius of the derived airfoils, published in references 9 to 12, were initially determined by plotting
the ordinates to a large scale and fairing in the best circle fit by hand."
I know from many documents and experience that the le and te are based on circles of a specified radius, made tagent to the rest of the airfoil definition. Perhaps you are confusing what some NASA engineers are doing in a Fortran code 50 years later to what the original designers specified. I am using the original NACA 65A009 definition. I am not going to recode this NACA Fortran code you are referencing. It offers me no benefit. There already exist many NACA airfoil plotting codes for one thing. I recommend Hanley Innovations VisualFoil Plus. You can not only plot the airfoil but get data for it at transonic speeds. I don't have $700 dollars to spend on it. Thus I am using the NACA definition and data.
I appreciate people trying to help. However, what you have been doing I do not perceive as help. Thus my frustration at this point. I am a retired engineer who has designed and worked on a number of real aircraft propellers. I am well aware of what I am doing. You can take that as hard heading if you like. When someone is insisting I am doing something wrong, I don't know how you would like me to take it. Plus, not showing how to do it supposedly right, until I request it. I have worked with a number of people that think being a road block is an accomplishment, that is how you are coming off to me.
No one needs to use this script if they don't want to. Nor develop it for that matter. I could care less. I thought it would be useful to people, thus the request. If you think its wrong, fine don't use it. But enough already. You are beating a dead horse.
Are you seeing something wrong with them? I ran two examples with them and they work out pretty could. I still think my original method is better, because there is no round-off error when you do it inside MoI. The points I added were determined using my original method. However, there is some round-off error. Visually, when I made the models to check the new points, I could not see anything horrible. As far as ripples or lumps.
The last four points are for the circles. The two points preceding the last for are the new tangent points. You can place them in any order you need.
Points X = 0.0D0, Y = 0.0D0 and X = 100.0D0, Y = 0.0D0 aren't really needed anymore. I left them there, they could be helpful. But you can make the arcs now without them. If you wanted it may be simplest to just make the airfoil arc from everything but the last six points. Then mirror that curve. The only thing left is the arcs and MoI may be able to do it without a center point. I haven't tried it that way, but want to next. If you wanted to leave the center points in, then I know you can definitely do it that way.
There is nothing wrong with your data, as far as I can tell. (except maybe the tangent points, see below :-( ) I just wanted to confirm that I had identified the points correctly.
I believe that the spline needs to start and end on the "tangent" points, which is why I put an extra copy of them back in the array, in the order in which the spline is created. So the "tangent" points have a dual purpose.
Attached is an updated Prop_DesignGeo, which incorporates your data as of 12/29/2011,
also creates and shows the control points for the rails.
To see the control points for the Airfoil, do "show points."
The control point spline runs from upper "tangent" point, to lower "tangent" point.
The user still needs to add the two arc radii.
Unfortunately, it appears that the two "tangent" points are just a little bit off, the arc radii do not quite intersect them...(zoom in).
(Or maybe I've made a mistake somewhere...)
(I've read how to calculate the tangent points manually, using either arctangents, or simple algebra, as a right triangle is created.)
Anyway, I think it is progress :-)
With the help Michael gave a few posts back, I think the "tangent" points can be created in the scripts, using either your "point line tangent to circle" method, or else the Thales method....
Being how we are not alone in the forum, I like to jump in and paticipate whether needed or requested.. It's how I learn stuff. It is not intended to direct anybody. It may be usful for someone reading the thread..
Here's how I have done airfoil curves using Conic sections:
Sometimes I use the blend tool also, when I want to use G2 and G3 Curvature.
I stuck the 0.75 and 0.835 points back in, and reran the tangent line and thales arc, which produce the blue
point on the attached png. The adjoining red point is your point. (I think this is correct....)
The two points are very close together...
Hi Brian,
Where the last scripts curve ends, an arc wont fit. An easy check is to use the arc-cont tool between the 2 points. The last 2 points of that arc should be planar. I wonder if the blue point would create one.
yes if they are off some it is probably round off error. i added them to try and help you. but if you can do it another way that is better. i previously tried adding them about a year ago and found it was problematic due to round-off error. so feel free to take them out if you don't need them. you are right that they perform double duty and are intended to be the start and end of the spline. i didn't realize you needed them in a certain order. so if you do keep them and need to move them that is fine.
should i try out the script you just posted or do you want me to wait until you settle on a method. i'm fine with whatever works for you.
that is helpful. i don't personally have an issue with changing the leading edge in order to keep the points straight. what i have been saying is the ler and data do not agree and something has to change. since for me it is pretty obvious what the ler and ter mean, i have been changing the data points. the difference is minimal. one thing to keep in mind is that the airfoil points you were working with have one point removed, because it was way out there. i can try just giving you something with the exact data points and see how the ler you are doing works out. this whole thing is rather silly to me. but its not a big deal to try out what you are doing. thanks for actually showing a working example.
the airfoil info is ancient, done before computers, most likely with slide rules. so a little bit of an issue with comparing computer generated data to the old data is no surprise to me.
Hey Anthony,
Here's a quick shot of it for Brian. Using an Arc is just slightly off where he was at, but his new blue point looked like it may relate.. Showing a quick tool to see it. Maybe he can make the points make sense with this info...
Here is an update removing the tangent points and adding the point I previously omitted on purpose. The ler and ter definition points are still the last four. I tried burrman's method and it works fine. In this case you can use all the naca points and the ter definition but ignore the ler definition. I don't really care which way you go here. I am keeping the ler and ter and loosening the data point definition. The difference I have been allowing is small. However, if you want to redefine the ler, its fine by mean. Comparing the leading edge you get with burrman's method and using the naca defined radius, the difference is small. I'll let brian and whoever else works on the actual script to decide how they want to do it. I don't plan on using this myself. I just wanted it for others. I have finished all my work on PROP_DESIGN, this was just a loose end I thought could be improved. Either way you go, its about the same for all intensive purposes. The data points, as defined now, should allow you to create the airfoil spline however you like. The main thing is to create a blade that transitions smoothly and follows the naca file i'm referencing as close as possible, since PROP_DESIGN utilizes the performance data for this specific airfoil.
Edit; Latest version is available in a later post.
I tried out your latest update. Very nice. I see the error you found and can duplicate it. I determined it is indeed round-off error. Here are the arrays including the tangent points with as much precision as I can have with the tools available to me:
They do not have the one point I take off to have the curve fit work out. So at this point you have a couple of options you can follow. I compared what burrman did to what I did and the difference is small. I am fine with either one. They both make a nice solid with no ripples or any other distortions. Both deviate from the naca definition to make everything work out, as the naca definition contains some error. I am keeping the le and te radius definitions and relaxing the data points by using a curve fit. With burrmans method you can keep the data points using a control point spline and then modify the le definition. The te definition is fine as is.
Thank you Anthony.
I'll try out the new numbers.
(I previously used the MoI distance script on the two close points, for Y and Z difference, and tried to reverse calculate, and got two multidecimal numbers, but must have messed up the math...)
Also it is possible to drag the spline "tangent" control point, over a tiny bit to meet the arc radius...
Currently trying to script a couple of 3 point arcs, for an intersection. I think "ring circle" script has the techniques to assign a frame, and script enter the
3 points, or two points and an angle.
I'm using this code:
var arcfactory1 = moi.command.createFactory( 'arccenter' );
// angle of +/- _ degrees.
var angleinput = 180.0 ;
arcfactory1.setInput( 0, pt_leArccenter );
arcfactory1.setInput( 1, pt_leArcStart );
arcfactory1.setInput( 3, angleinput );
arcfactory1.update();
arcfactory1.commit();
(repeat for second arc.)
It does not draw anything on the screen. I think the "frame" has to be set?
Next step to create the tangent point, maybe something like this: ?
Leading edge.jpg