How I plan to kick your butt next season ;-)

So you got a hot plane, eh? Tell us why you think you're gonna be Top Gun this year!

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gsjames
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How I plan to kick your butt next season ;-)

Post by gsjames »

Here is a printout of computerized "wind tunnel" results of some of the most popular airfoil sections in use by RC Combat fliers along with a new section that I have developed. If you know what you are looking at you should be shaking in fear[:D] If you don't know what all this means, don't worry... I'll SHOW YOU next season[:0]

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RC Combat is F-U-N!!! I'm having a blast in my first year doing this stuff!

See ya' next season.
Bruce B
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Post by Bruce B »

I dont know what the green line is, but i think you might need a plan B
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Ed Kettler
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Post by Ed Kettler »

First, I have to show you how to post pictures. You posted the thumbnail, not the full picture.
Image

Double click on the thumbnail so that the gallery goes to the full picture, then use the same method you used to post the thumbnail.
gsjames
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Post by gsjames »

Thanks Ed! I reviewed and noted the difference in the link addresses between the thumbnail and the full-size and now I understand how to do it. Thanks!
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boiler
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Post by boiler »

For us that can read a graph but don't understand what the coordinates are, can you help.
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Post by gsjames »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by boiler</i>
<br />For us that can read a graph but don't understand what the coordinates are, can you help.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Sure Bob, I'd be glad to, especially since this is 'mostly' tongue-in-cheek and an attempt to bait people and start a smack-talk war on my part[:)]

The graph on the left is a plot of the 2D 'lift-curves' of several common airfoils used on our airplanes. The calculations were done at 'scale speeds and sizes' (Reynolds number for those of you who know what I mean) and with the assumption that the boundary layer airflow is almost entirely turbulent. This is almost assured by the sticky stuff on our leading edges and all the dents that they pick up. The x-axis of the graph (alpha)is the angle of attack of the airfoil in degrees above and below zero and the y-axis (Cl) is the lift coefficient. The lift coefficient is just a non-dimensional way of looking at the lift being produced. By looking at the graph we can see what the lift behavior of the airfoil section is as a function of angle of attack. The higher up the line goes before it 'bends over', the more lift the section is producing. The 'bending over' is the stall. We see that all of our airfoils produce some lift at zero angle of attack, which is what we would expect since all of them have some camber to them. If we used a symmetrical airfoil, it's line would pass through the 0,0, point of the graph showing that it produces no lift at zero angle of attack. The Eppler 203 has the most camber and produces a lift coefficient of approximately 0.3 at zero angle. Now I know that the graph is a little small but what I see with the E203 is that it has a "flat stall". In other words, it starts stalling at about 9 degrees and the lift essentially goes 'flat' for awhile until it really starts dropping off at about 15 degrees. This 'may' not be all that bad. What it means is that although the maximum lift is not very high, the section has a gentle stall and is rather insensitive to really yanking it around. It would not be prone to "snapping out". The S8036 has a very shallow lift curve, which tells me that airflow separation starts early but progresses fairly slowly. It has low maximum lift but is also very gentle in the stall and would not be prone to snap. The other sections exhibit a variety of behaviors. My new section, the one in light green, has a significantly higher maximum lift while still maintaining a relatively benign stall (but not as benign as the E203). What this means is that for an airplane of the same size and weight, the one with the new airfoil will turn about 13% tighter than the best of the others. What it gives up is an extremely benign stall. It's not clear whether this would be a good 'trade' or not. It may be that the new wing would have a greater tendency to snap out. I won't know until I get a chance to test fly it and compare. You can always modify the stall behavior of an actual 3D wing by adding 'washout' to the wing panel.

The right hand graph is called a 'drag polar' and is a plot of the coefficient of drag (Cd)as a function of the angle of attack. There's not all that much to see here except to note that all of the sections have similar drag (not enough difference to be important) at low angles (low lift) and that as the angle of attack increases, the S8036 and my 2 new sections have lower drag as you really yank it around. That means that airplanes built with those wings should not lose as much speed in hard maneuvering. The SD6060 is really bad all the way around, high drag and low max lift. Not a good choice.

I hope that I helped explain it, at least a little bit.

I'm going to build a couple of test wings to see if any of this is actually worth a damn when translated into real hardware.
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Post by Bruce B »

Dont forget about plan B.just in case[;)]
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Post by gsjames »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Bruce B</i>
<br />Dont forget about plan B.just in case[;)]
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Yep... plan B is where my "stock" Battle Axe STILL eats Helldiver streamers...[:D]
Hey Bruce, if you and David get together for a little informal practice, drop me a line via email and if I'm home, I'll try to come up and play.
Bruce B
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Post by Bruce B »

yep, eats helldiver streamers[;)].(and fuel nipples)[B)]
I am always ready for some combat flying informal or otherwise.let me know when you think you will have a weekend day and maybe we can get some people together.i've got $5 with your name on it.

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boiler
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Post by boiler »

My 203 and YH look pretty competitive. Thanks for the explanation.
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Post by Dr. Kamakaze »

I remember back to my days of flying free-flight and competing in hand-launched gliders as a kid. One of the guys who had designed his own glider was asked what kind of airfoil he was using and he replied with the "FCR" airfoil. When asked what kind of an airfoil that was his reply was "French Curve and a Ruler". I've also heard that the side of a shoe works quite well too...sometimes the KISS method works best! Interesting charts though...Waaaay beyond me!
Dr. Andy Runte aka "Dr. Kamakaze"
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gsjames
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Post by gsjames »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Dr. Kamakaze</i>
<br />When asked what kind of an airfoil that was his reply was "French Curve and a Ruler". I've also heard that the side of a shoe works quite well too...<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Yep, you are absolutely right. But it's VERY important to use the right shoe... for example should one use a Nike, or a New Balance? If you were flying combat in Germany should you use an Adidas? And do we want a size 9D or a 13A...Decisions, decisions...[:D]

All seriousness aside, all of this makes VERY little difference. As we all know, a skilled pilot can take just about any plane and make it fly circles around us mere "mortals". But, still, it's something to do, and it keeps me out of the topless bars on layovers...[;)]
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Ed Kettler
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Post by Ed Kettler »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by gsjames</i>
<br /><blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Dr. Kamakaze</i>
<br />When asked what kind of an airfoil that was his reply was "French Curve and a Ruler". I've also heard that the side of a shoe works quite well too...<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

And do we want a size 9D or a 13A...Decisions, decisions...[:D]

<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Depends on whether you are doing the root or the tip!
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Post by Hat Trick »

Want to share the killer airfoil? The E203 was a major improvement over the early airfoils we used. Which were tennis shoe airfoils! The SD 6060 was maybe a slight improvement although I'm not totally sure! I'm a bit afraid the more abrupt stall characteristics ofyour airfoil may outweigh the improved lift but only testing will tell!
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Post by gsjames »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Hat Trick</i>
<br />Want to share the killer airfoil? ...but only testing will tell!
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Dr. Evil: Yes, I'll share it eventually after I do some actual flight testing to see if it's worth a damn. I'm pretty good with airfoil design using computers, I had the privilege of taking a course in airfoil design from Dr. Richard Eppler himself, but I DON'T believe any of it until I see results in real hardware. These computerized "wind tunnels" are very useful, but like CFD (computational fluid dynamics) you must be careful interpreting the results. The mathematical models are "perfectly smooth", etc. and of course real hardware isn't. Many a young aero-engineer has been unpleasantly surprised when the drag numbers of the hardware was 15% higher than his "model". It is apparent to me that tactics are MUCH more important than aircraft turning performance. This is true in REAL air-to-air combat just as it is true in model airplane combat.

The turning performance of any airplane is related to only two factors, wing loading and CLmax of the wing. You can only increase the CLmax about 10% at best without using variable wing flaps (which by the way would be easily "do-able" on any conventional tailed airplane with dual aileron servos) (oops, shouldn't have told you that...), and you can "easily" decrease the wing loading by that amount by increasing the wing area while minimizing the increase in weight of the wing.

I'll cut some cores over the winter and see if they work well.
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