I justed wasted an hour carefully tracing the rib drawing only to discover that the dimensions that are supposed to be held closely are pretty far off in the printed plans, and the bottom rib is not nearly a straight line. I am sure many of you have had similar experience... At this point I'd just as soon manually draw the airfoil from the numbers (I have no CAD experience or access). Unfortunately, I am not sure where to find them. I searched past posts, but no luck. (I am not confident I am getting access to everything I should be - pilot error most likely.)

Does anybody have an excel/ascii/word file of the airfoil ordinates (for the EROS). I'm sure I can come closer by hand than the reprinted plans offer... Thanks!

Tony

Tony,  A lot of us had this problem.  What I did was start with a straight line on a large sheet of paper, mark off all the fixed points from the plans.  I then had photocopys made of the rib drawing, cut them up and pieced them together on my new layout.  It should come out close with all the critical points where they need to be.  Then just adjust the top curve to a smooth curve that estimates the original.  As long as all your ribs are the same and your spars are in the correct place it will be fine.

Yeah, I had similar issues with the rib drawing and asked the same questions.  I ended up just making sure that the "hard points" were correct such as straight on the bottom, and spars perpendicular to the bottom, etc and used the drawing as an approximation.  Like Randy said, as long as your ribs are all the same that is the main thing.  They need to match each other in order to get a nice square wing assembly.

Pete

One time I asked Wayne what airfoil he used. He answered "LP 10". I said "LP 10?"  "Lead pencil 10th try". He replyed.

    "Bat Cave" Dave

Ok fair enough. I'm not worried about it flying if I am off a bit with the airfoil. But not having a real sophisticated understanding of aerodynamics I was only concerned that changing the airfoil a bit might alter some of the subtle flying characteristics of the wing such as how the center of pressure moved at various angles of attack, or stall characteristics, etc. But I'm willing to go with LP 10.tp or whatever... I saw earlier that some folks created rib drawings with CAD, so I assumed someone must have the ordinates. Maybe if I had said I was going to create CAD drawings someone would have offered them?... No big deal really. It'll fly... Thanks for your insights. If it is good enough for you guys, I am sure it will work for me... Hope to get my jig done before the weekend... - Tony

When I got My Plans, they came with a two piece full size rib drawing. The instruction said hold this length and gave a measurement, and make the bottom stright. Do they not send this anymore. I would be glad to loan, but right now I am building another and need my rib jig. charlie

Hi Tony,

I am in the same boat as you for the actual dimensions. I have a .dxf that Ari shared with me, I can pull some measurements for you but I can't verify them (the reason I didn't share earlier). It seems that Team or JDT were a little shy on information and counted on full scale prints to actually build with unless I missed something.

Ari, if you are monitoring this thread, how did you come up with the .dxf's and do you mind me sharing?

Dennis

Dennis:
Thank you for your offer. I wasn't meaning to criticize anyone for not sharing. And I do appreciate both your hesitancy to share info you can not verify, and your willingness to share what you have. I'll gladly accept your offer of measurements if it doesn't require a whole lot of effort on your part. Thank you... I too am curious as to where folks arrived at numbers for .dxf if JDT/TEAM hasn't provided them.

I don't expect my airfoil to be perfect. My construction skills are not that refined. But my ribs will all be the same, and I'd just like to be as close as I can within reason. If we knew closest airfoil model we could probably find coordinates on the Web.

This certainly isn't a huge issue from my perspective. But I am a little surprised it hasn't been resolved more precisely during the last 12 years.  That is not a criticism of JDT or Eros builders in any way. Just my naiive perspective... Thanks again for everyone's replies.

Tony

I kept going back and forth about my DXF drawing, whether I should talk about it here or not. Tony was very specific that he didn't want to deal with CAD, and I didn't want to offer him something he didn't want. I can understand not wanting to learn yet another technology. It took me years to give in and learn CAD, and it always annoyed me that people would post DXFs in forums like this one and I couldn't read them. This said, I'm happy to post the file here if anyone finds it useful.

The way I came up with the ordinates was not very scientific. I tried to build my rib jig around the full-size drawing, which as we all know by now, is impossible. So I scrapped the first jig and started with a clean piece of paper (literally) on which I drew the dimensions I was supposed to hold. This wasn't difficult, just frustrating because I had to adjust my expectations about plans quality. This was before I decided to go CAD. You can see photos of all this on page 1 of my build log thread (http://www.lonesomebuzzards.com/cgi-bin/forum/Blah.pl?m-1185574047/s-0/)

After I built all my ribs, I needed to cut plywood sides for root and tip ribs, and by then I'd decided to use CAD and CNC. But now I was stuck with 24 ribs that were based not on any kind of airfoil ordinates but on a freehand approximation of the "hold this" dimensions. I should have gone CAD from the start! If I had, I could have taken NACA 23012 coordinates and worked from them, but now I was stuck with "reverse-engineering" my completed ribs. So I traced one of the ribs, drew verticals every inch and measured their heights.

All said and done, the rib outline is the least useful part of my CAD effort. With that in mind, if anyone wants to use it for any purpose, I have no objections.

Ari.

IANAL:
    This drawing is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

I can start to appreciate Mr. Ison's plight (legal issues only, I can't even approach his level of genius).

Dennis

Quoted from iter

I kept going back and forth about my DXF drawing, whether I should talk about it here or not. Tony was very specific that he didn't want to deal with CAD, and I didn't want to offer him something he didn't want. I can understand not wanting to learn yet another technology. It took me years to give in and learn CAD, and it always annoyed me that people would post DXFs in forums like this one and I couldn't read them. This said, I'm happy to post the file here if anyone finds it useful.

The way I came up with the ordinates was not very scientific. I tried to build my rib jig around the full-size drawing, which as we all know by now, is impossible. So I scrapped the first jig and started with a clean piece of paper (literally) on which I drew the dimensions I was supposed to hold. This wasn't difficult, just frustrating because I had to adjust my expectations about plans quality. This was before I decided to go CAD. You can see photos of all this on page 1 of my build log thread (http://www.lonesomebuzzards.com/cgi-bin/forum/Blah.pl?m-1185574047/s-0/)

After I built all my ribs, I needed to cut plywood sides for root and tip ribs, and by then I'd decided to use CAD and CNC. But now I was stuck with 24 ribs that were based not on any kind of airfoil ordinates but on a freehand approximation of the "hold this" dimensions. I should have gone CAD from the start! If I had, I could have taken NACA 23012 coordinates and worked from them, but now I was stuck with "reverse-engineering" my completed ribs. So I traced one of the ribs, drew verticals every inch and measured their heights.

All said and done, the rib outline is the least useful part of my CAD effort. With that in mind, if anyone wants to use it for any purpose, I have no objections.

Ari.

IANAL:
    This drawing is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

why not just use the published naca 23012 data? besides at minimax speeds the exact airfoil shape is not as important as having the spar be the correct height etc.  between the ribs what is the airfoil shape?

Quoted from CFBTB

why not just use the published naca 23012 data?  as having the spar be the correct height etc.

14% thickness

Wow. Again, I really appreciate everyone's interest, comments and responses... Be assured, I have nothing at all against CAD. In fact, I really respect and admire those of you who have gone to the effort of creating CAD drawings, and especially of moving to laser cutting parts. Under different life circumstances, or if I had easy access to CAD and laser cutting technology it might seem worth it for me to take time to learn CAD now. However, thats not my current situation, or really where my current intrinsic interests lie in regards to this project.  For now, I'm happy relying on my relatively low-tech aircraft building skill-set.

I only mentioned CAD because I suspected that CAD drawings must be based on actual ordinate numbers(or relative transformations thereof), and if I had those numbers I could hand draw an airfoil that would be plenty close enough. Apparently my assumption was wrong. I now understand that those of you, or at least Ari, who have DXF drawing for the ribs had to reverse engineer your own manual efforts at working with the original drawings.

All that said, now that I know the airfoil is close to published 23012.  As "bear" suggested, I'll just look those up and go from there. Thats all I was requesting really.

Again, thanks to everyone. I don't want to steal anyone's hard work. I just assumed the ordinates must be floating around for a 12-year old design of interest to a cooperative and collaborative group of folks that max builders seem to be. It was only meant to be a simple request to learn from those ahead of me. -Tony

I'd be very careful about those statements "I'm not worried about the airfoil being off a little bit." Pretty soon one might not worry about that glue joint, seems about right, it's only an airplane. Catch the drift?

Bob, with all respect, I think you are making a big leap regarding my statement... The purpose of my original post, and the nature of the entire thread was that my aim was to come as close is as reasonably possible to the desired airfoil, (otherwise, why did I even bother posting request for correct ordinates once I realized the plans drawing was off?) recognizing that, if it requires doing the best I can to work with the imperfect plans, I would. The very next sentence in the post you quoted explicitly states that my concern is that I did not want to alter flying characteristics of the wing. In my opinion, your implication is based on quoting me out of context...

now off to buy some Elmer's glue for those joints  

Tony

Ari - I have a question about how you determined your revised rib jig dimensions. It sounds like your plans were same as mine, i.e., bottom rib not flat and stated dimensions to be held not precise. Like you described, it is easy enough to start from scratch with the specific dimensions that plans say to hold. But then, did you still fit the curvature on the original drawing to your new jig, or did you attempt to adjust for the apparent stretching of the plans some way?... My confusion/concern is that if we can assume the non-straight bottom line and inaccurate dimensions of the plans are due to printing stretch/distortion, then shouldn't we also assume the top curvature of the airfoil on the original plans is likely different from what was originally intended?  

I agree with your comment in your log, either an accurate full size drawing, or an accurate scaled drawing, or just the ordinates would be much less confusing. As the plans are, the specific shape of the airfoil seems up to builder interpretation...  To what extent it matters, who knows. I don't have the expertise to say... But there does not appear an obvious way to "get it right" without knowing the specific ordinates of the originally intended airfoil?

Tony

Quoted from CFBTB

why not just use the published naca 23012 data?

Wane used a modified [sic] section. For one thing, NACA sections don't have flat bottoms the way the MiniMAX plans do. The top line is probably fairly close, but again, the LP-10 is afar better description than NACA 23012.

Quoted from 457

14% thickness

You're absolutely correct, I got the thickness wrong, and I think I got the series wrong, too. It seems the correct airfoil is 4414--thanks making me check.

Quoted from RedBird

Under different life circumstances, or if I had easy access to CAD and laser cutting technology it might seem worth it for me to take time to learn CAD now.

CAD was easier to learn than I thought. If you change your mind, I can tell you that I use a free program called QCAD (http://www.qcad.org). Even if you don't want to learn CAD, you can use this program to print out my drawing at Kinko's. Actually, if you want it, I can mail you my paper drawing, or even the whole rib jig--I'm done building ribs.

Also, I can laser-cut the parts for you--PM me if you're interested.

Quoted from RedBird

I don't want to steal anyone's hard work.

Not at all, I'll be happy if you find it useful. "He who receives a file from me receives instruction himself without lessening mine—as he who lights his taper at mine, receives light without darkening me."

Ari.

Hello Ari,
Appears we were posting to each other simultaneously.... Its not that I don't want to learn CAD, and I could probably blunder my way through it ok, but, my original post was just looking for a quick way to get the airfoil correct, given that I've never bothered to learn CAD, and don't currently have it at my disposal... However, after the discussion here, I realize that what I was looking for probably doesn't exist. I.e. a set of specific ordinates for the original Eros airfoil. Anything out there was likely reverse engineered, along the lines of your efforts.

At this point I'll probably look up a couple airfoils that appear closest (thanks for the revised NACA section), keep the hard points specified in the plans, plot a full sized drawing, and go from there. Just for the sake of it, I might post the ordinates I decide upon, with all disclaimers of course...

Thanks for your offers. I'll give the laser cutting some thought.

Tony

No problem Tony. I understand where you're coming from, is why I hesitated to post the file in the first place.

I don't think the airfoil matters that much. I'm not building a laminar supersonic record-breaking anything. Imperfections in wood grain and my workmanship will have an effect, and the way fabric stretches over ribs means you can only maintain the airfoil over ribs, anything between them is only an approximation anyway.

I agree however that it's very disappointing to see such sloppy reproduction in the plans. It was a big turnoff for me. The good news is that we both overcame this disappointment. The bad news is that, if my experience is any guide, you'll have more disappointments to overcome as you work through the plans and drawings. You're right, it doesn't have to be this way, and in fact I own other plans by Ison that are much better in all these respects. But nothing can beat the community here, and imperfections in the plans, angering as I find them at times, have always been resolved when I asked about them here.

Good luck with your project. I'm sure that with the care you're giving it it will be a wonderful airplane. I'm looking forward to watching your progress!

Ari.

This site doesn't have a 4414, but here is link with 4415 ordinates. Not sure how close will be to Eros airfoil, but I'll probably check just for fun...

http://www.pdas.com/sections45.htm

Quoted from RedBird

This site doesn't have a 4414, but here is link with 4415 ordinates.

Same thing. One is 14% thickness, the other 15%, just scale appropriately.

Everyting you ever wanted to know about NACA airfoil numbers: http://en.wikipedia.org/wiki/NACA_airfoil

Quoted Text

The NACA four-digit wing sections define the profile by:
   1. One digit describing maximum camber as percentage of the chord.
   2. One digit describing the distance of maximum camber from the airfoil leading edge in tens of percents of the chord.
   3. Two digits describing maximum thickness of the airfoil as percent of the chord.

Ari.

Attached is a csv file (tab delimited) of ordinates based on NACA 4415 with max thickness reduced to 14% of chord length. If I have done this correctly that should make it a NACA 4414. However please note the following disclaimer:

I know absolutely nothing about airfoils or aerodynamics or aeronautical engineering or even building aircraft!, Nor do I have any idea if my calculations are correct, nor how close this airfoil represents the original airfoil designed for the Eros.  For all I know, an airfoil based on these ordinates might fall out of the sky, if it ever became airborne in the first place... With those realities firmly in mind, enjoy, modify, use to your heart's content...

Tony

Quoted from RedBird

Attached is a csv file (tab delimited) of ordinates based on NACA 4415 with max thickness reduced to 14% of chord length. If I have done this correctly that should make it a NACA 4414. However please note the following disclaimer:



Tony

That is one of the high lift airfoil. The only drawback: it has very high Reynold`d numbers (2 500 000- 4 500 000 depending of speed and other factors). For the Ison`s planes more than enough and will work better not exceeding Re=800 000-1000 000

Get one below with Re=810 000 high lift airfoil for slow aircraft and you will not be sorry

777:
Thanks for your insight. To be real candid, I'm not in a position to judge the aerodynamic plots you have graciously provided. As stated in my disclaimer, I have no knowledge of aerodynamics. I scaled to NACA 4414 only because it was identified as being the basis of the original Eros airfoil.

I am sure someone with genuine detailed understanding of airfoil characteristics and curves etc can make lots of cogent arguments for a particular choice. But I can't. I just was looking for a way to reasonably plot the airfoil originally intended so I could start working on my rib jig... I.e., I am not looking to "improve" the original design, just to accurately implement it.

Thanks again for your thoughts.

Tony

Quoted from RedBird

I am not looking to "improve" the original design, just to accurately implement it.

Thanks again for your thoughts.

Tony

Just take in account one thing- the Ison`s handly drawn airfoil has no any data at all. The Maxes are flying but no one knows how better or worse should it be.
The airfoil provided is the best one from TsAGI comes from 30-th for ragwing aircraft with speds not exceeding 170 km/h (100 mph roughly) and thousand and thousand airplanes flown and flying with one. For example An-2 (Antonov-2 biplane) with this airfoil  it`s wing lift with fully applied mechanisation is 3.5 (Cy=3.5)

?
Bob

Quoted from flybob13

?
Bob

Could you specify your question?

777,
I was just expressing my inability to comprehend all of this technical stuff. This is the best site I have found for builders and I REALLY appreciate everything that is discussed here. It's just that I'm kinda "low" tech. I think it's wonderful that there are people on this site that "know" this stuff and are willing to share. I personally just want to build and fly. My aerodynamic knowledge is basic at best, push the stick foward, the houses get bigger, pull the stick back, the houses get smaller. I was really just trying to be funny, you know, like when a dog hears a strange sound and cocks his head. Sorry, keep up the good work and info everybody, I'll go back and sit in the corner.  
Bob
P.S. I still haven't found the spell check.

Unless you keep pulling back----Then they get big again  REAL FAST!! Charlie

OK, for those who did not realize the polars of the P-II airfoil. Look at the curve Cy (alpha) where one crossing Cx (at Cy alpha) and project this cross point to angle of attack (some 25 degrees) than read data what is lift  coefficient at this point. This point shows non stall regime for this angle of attack. Could anybody say something similar or KNOWN about original Max`s airfoil? This airfoil is the result of TsAGI`s  work with their scientiests, equipment, wind tunels and so on.