Bob - I understood your post, better than I understood 777's comments and graphs... 777 probably knows his stuff pretty well, at least it appears that way to an uninformed novice like myself... However, it is human nature, at least for some of us, to utilize and put confidence in information we feel we can comprehend, more than that which is just presented as fact, even by an authority or expert. I suspect there is a wealth of insight in the graphs 777 posted. But for those of us who have not studied aerodynamics, interpretation of that information might be enhanced if it were supplemented by a cogent explanation. Of course, I suspect there are some builders here for whom the graphs made perfect sense at first glance. However, I assure you, you were not the only one who didn't "get it." (at least there are two of us ...)
777 - I guess my point is, that depending on your objective, and your target audience, you might want to assume a little less technical training/knowledge of some of us. It sounds like you have some good insight to offer. But remember, some of us chose to build a 'max design because of its apparent simplicity, and its reputation as a reasonably stable, dependable homebuilt design. I do think most of us are open to learning and improving our understanding of most issues related to the process... But some us will require a little edification along the way ...
just my opinion though. Thanks for your insights. - Tony
Why focus on proving how great you are, when you could focus on becoming better?...
I have been doing this airfoil stuff for 60 years, believe me, 777 has a good point but MY openion is us mortals cant tell the difference in the speed regime of the maxi's. flat bottom, curved top not to pointie of leading edge and the wingy will produce lift at an angle of attack. even if it is flat on top it will lift at an angle of attack. the science part will predict the exact performance but most any foil will make lift. Also wings make drag. too much drag is bad.
I suspect there is a wealth of insight in the graphs 777 posted. But for those of us who have not studied aerodynamics, interpretation of that information might be enhanced if it were supplemented by a cogent explanation.
777 - I guess my point is, that depending on your objective, and your target audience, you might want to assume a little less technical training/knowledge of some of us. It sounds like you have some good insight to offer. But remember, some of us chose to build a 'max design because of its apparent simplicity, and its reputation as a reasonably stable, dependable homebuilt design. I do think most of us are open to learning and improving our understanding of most issues related to the process... But some us will require a little edification along the way ...
just my opinion though. Thanks for your insights. - Tony
ОК, Tony , let`s talk about one more issue on the P-II graphs.
You may ask people who flown Maxes, they will tell you one thing- all of them have to keep forward pressure on the stick immedeately after take off so that not allow aircraft nose went up too much, not loose speed not spin.... down at last. Did one of them ask why this happening? Because no one knows how centre of pressue of original airfoil migrates depending of angle of attack.
I do not say a word about good o worse specs for original airfoil. Anyway it works and works pretty fine.... Mr. Ison did a perfect design work and his planes a best around all similar (otherwise I would be in another BBS ). But!!!!!!!!!!!!!! They could be a bit better . This will not harm not to planes not to Mr. Ison`s reputation (last one without questions at all).
Look at the polars. You may see the curves Mz- that is a moments (not about time , but about forces). Mz does not change it`s value from zero to above angle of attack- that means centre of pressure for this airfoil remans constant and not migrates depending of how up goes aircraft nose. There are no forces to pull nose up. That means you need to be less cousious about possibility loose climb speed and do not need keep under control forward pressure on the stick. That is all- you have less chances to spin
777 - I think we are discussing two different issues here. Not a single post in this thread has questioned your opinion about the flying qualities of the P-II. In fact, the person who has years of experience with airfoils agrees with your points. However, we don't all speak your language (not country , but technical). Speaking for myself, your last post was the most helpful because you offered a reasonably cogent explanation of one way the two airfoils differ. I.e. a static center of pressure, regardless of angle of attack. Based on your explanation, even I get it . So, thank you.
Again, I am not arguing your technical opinion. (after all, less chance to spin might be considered a good thing by some ..) I am only suggesting that some of us can appreciate your insight more when it is offered in a format and with terms that are at least partially familiar to us.
Maybe others here already know, but I am curious, what model minimax are you building, or already flying? And, are you building/flying with wings based on the P-II airfoil that you are enamored with?
Tony
Why focus on proving how great you are, when you could focus on becoming better?...
these lines represent swift air moving through my own head... some have suggested to me there is not a lot inside to slow it down or cause turbulence... but no need to reply based on evidence gathered on this forum folks ...
Why focus on proving how great you are, when you could focus on becoming better?...
Hi Bob; Do a search for ieSpell. I asked the same question many months ago and someone told me how to get this program. it is free and works great. It works with anything. Either r click or you can find it in the tool menu (after installation). You might try the Internet with a search of ieSpell. I wish I could tell you how to get it. Fly safe, Bob Hoskins
777 brings back a memory I had not thought about in some long time. Back in the day when airplanes were just starting to become popular. designers tried to find ways to go faster. removing one wing helped. removing all those flying and drag wires helped more. BUT, wings started to come off. they did not brake but twisted off the fuselage. the torgue due to the lift center shifting caused unexpected loads. the naca later nasa began a long series of wind tunnel testing to produce a series of airfoils the 230XX shaped that tried to avoid the pressure shift with airspeed. They in fact succeded and things like DC_3's became common place. the only drawback to these foils is the bad manners at the stall. The brake can be sudden and unpredicted.
777 - what model minimax are you building, or already flying? And, are you building/flying with wings based on the P-II airfoil that you are enamored with?
Tony
No flying now, Tony (everything in the past so far... from rags to jets). Just designing and building ...... Chick-Max (she must look like a chick, isn`t it?)... and another interesting thing... if the others will be agree to this name .... and defintely with P-II airfoil
777 your original Design looks a little bit like the Proto of the Rans Stinger or here in Europe more known C22 and X-AIR!
Why did you chose the over the nose engine configuration and not the config where an engine belongs to, the nose and not the forehead? Just my personal idea, same rounded design but engine in the nose and cantilever wing and a Taildragger, yeahaaa.....!
The next time you fly your minimax watch how the fabric balloons up between the wing ribs. You can actually see the top of the wing distort the airfoil as you change air speed and angle of attack. Is this thing we call flight grand or what.
Here is P-II 16% (the best thickness for this airfoil) done for Minimax/Himax 54 inch chord in natural size, could be printed on the B0 paper format 1400mm x 1000mm . In addition for alluminium airbike drawings (posted above in a thread within a link) the same airfoil with chord 1300 mm
Thanks Arthur, but I think I'll pass. If I can live to be old enough maybe I'll have time to creat my own design. "NOT" !!!! LOL But seriously, that's a lot of info you got there. Bob
I did a project when I was in an aviation class in high school at a skills center that was pretty fun. We got to pick out coordinates out of a book and us a drafting board to draw the airfoil using drafting tools. Then we photo copied the drawing and reduced it from a 12" chord to a 6 inch chord. Then we made two aluminum sheetmetal templates using the photo copy for a pattern. The two templates were then glued to a block of pink foam insulation and we used a hot wire cutter to make a 6" wide "wing" section of our airfoil. We had a simple wind tunnel about 4 feet long and maybe 18" in diameter. The foam wing section was mounted in the wind tunnel and it had a way to measure the lift using a simple digital scale that read out in grams. We then "flew" the airfoil in the wind tunnel at different angles of attack and recorded the results. All in high school!
post, better than I understood 777's comments and graphs... 777 probably knows his stuff pretty well, at least it appears that way to an uninformed novice like myself... However, it is human nature, at least for some of us, to utilize and put confidence in information we feel we can comprehend, more than that which is just presented as fact, even by an authority or expert. I suspect there is a wealth of insight in the graphs 777 posted. But for those of us who have not studied aerodynamics, interpretation of that information might be enhanced if it were supplemented by a cogent explanation. Of course, I suspect there are some builders here for whom the graphs made perfect sense at first glance. However, I assure you, you were not the only one who didn't "get it." (at least there are two of us 
...)
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Logged
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"If in doubt, Chicken out." 
