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Old Aug 19, 2010, 11:29 PM
Master of the Wind
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United States, CA, San Jose
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Wow this is massively tedious. I have a new respect for the masters of this art, and I see why a lot of the designs are proprietary. I have to thank JW for sending me down this path. I never would have learned all this had he just dropped a good design in my lap. There are enough good planes locally that I can afford a year to try and do better. I highly recommend anyone who is contemplating a design to dive in and learn, if you have the time.
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Old Aug 22, 2010, 11:54 PM
Master of the Wind
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United States, CA, San Jose
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Hn-217

Took at shot at the HN-217. A bit risky because it is a bit higher camber, but in section the L/D is the highest of the group I am looking at. Went through the exercise of optimizing the airfoil at each break to match up the peak in L/D by changing thickness, camber, and the high points. This puts me up a bit on the learning curve, the problem is everytime you add a trick to the bag, you have to use it, and burn even more time. The airfoil responds well to this treatment and the end result would be a really nice flying plane to thermal around in but it just misses against some of the faster planes on course. My guess is the slightly higher camber results in too much kink at the flap break when you reflex enough to get it to move out.

It looks like one really important parameter to look at is how the L/D responds off center in the reflex mode, say between 18 and 22 m/s. It would be worth it to give up a little max L/D in order to flatten out that curve so that L/D does not suffer at STF. This plus the polar around min sink in camber as JW mentioned, if it is too peaky the plane will not be forgiving to fly, though I am wondering how much of this can be compensated for by using snap flap in thermal mode.

Looks like the next step is to sort through the short list again and find the best candidate based on how it tails off at higher speed, and see how fast we can get between thermals without compromising the climbout.

And the lucky winner is HN-990 F3B, this week's time sink hole.
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Old Aug 24, 2010, 11:47 AM
yyz
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Any plans to test the newer HQ sections?
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Old Aug 24, 2010, 02:29 PM
Master of the Wind
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I looked at the DS sections he published. They looked interesting in 2D but I couldn't make them work as a wing. I've learned a bit more since so I could take another crack at it. I also thought about some of the older ones since people seem happy with the Zenith but that is lower on the list.

Getting faster, if the short time mafia does not hit me today I'll have a decision on the HN-990. At first glance it looked a little peaky with camber but that may be the price to pay for going faster.
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Old Aug 24, 2010, 03:38 PM
yyz
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This would be a pretty lengthy and involved exercise, but it would be interesting to see how each of the airfoils that you're examining hold up, aerodynamically, to hangar/car/field/landing rash. In other words, how "ding sensitive" they are.

Mike



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Originally Posted by G Norsworthy View Post
I looked at the DS sections he published. They looked interesting in 2D but I couldn't make them work as a wing. I've learned a bit more since so I could take another crack at it. I also thought about some of the older ones since people seem happy with the Zenith but that is lower on the list.

Getting faster, if the short time mafia does not hit me today I'll have a decision on the HN-990. At first glance it looked a little peaky with camber but that may be the price to pay for going faster.
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Old Aug 25, 2010, 09:40 AM
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By changing the NCrit value you can have an idea of how each wing section works in different quality airflow (from dirty to very clean). This is not the same than analyzing surface roughness but it will tell you how sensitive (or not) the sections are to the quality of the flow and/or how "forgiving" they are. One thing for sure is the sensitivity of ANY section to LE damage. But the bigger the LE radius, the less sensitive for any "ding" it is in general.
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Old Aug 25, 2010, 12:02 PM
yyz
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Interesting. Thanks for the thorough response. Is bug contamination an issue in the more humid parts of the world or do the low Re numbers and lower probabilities of hitting swarms of bugs make this a non-issue?

I've never seen any mention of bug strikes on the leading edge of a fin or stabilizer on a f/s ship (most similar to our Re) being a concern.

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By changing the NCrit value you can have an idea of how each wing section works in different quality airflow (from dirty to very clean). This is not the same than analyzing surface roughness but it will tell you how sensitive (or not) the sections are to the quality of the flow and/or how "forgiving" they are. One thing for sure is the sensitivity of ANY section to LE damage. But the bigger the LE radius, the less sensitive for any "ding" it is in general.
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Old Aug 26, 2010, 12:02 AM
Master of the Wind
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Short time mafia got me.

Now I'm having a problem with the HN-990 F3B foil. I'm trying various thin and decamber, move the hi point forward modifications and it will not converge. I tried over a range of values and reasonable Re and it still does not converge. I tried the HN-354 quick since it is on my list also, and it also failed to converge. No problem with the higher camber F3J foils from NH, and just as a sanity check I stuck the DS19 back in and tried it and it converges no problem. Anybody know what is going on here? Physically looking at the foils they look reasonable and I know if I built a wing out of them they would at least fly. Thinning to a point is fine but moving the hi point fwd a few percent seems to be what it does not like.
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Old Aug 26, 2010, 07:02 PM
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[QUOTE=yyz;15882661].....Is bug contamination an issue in the more humid parts of the world ..........

I was at Oshkosh when Voyager landed after it's flight from Mojave. John Roncz whom designed the airfoils ran up to it with a ruler and counted the number of bugs per foot on the leading edge. The concern was the loss of laminar flow in those areas which would increase drag and fuel consumption.

So yes to some it's an issue of concern. On a 2 to 4 hour flight for us, I suspect much less so.

MikeN
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Old Aug 26, 2010, 07:21 PM
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Profili smoothing

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Now....... I'm having a problem with the HN-990 F3B foil. I'm trying various thin and decamber, move the hi point forward modifications and it will not converge.
I've had a little success at solving that problem in Profili by using the "Smoothing" option. Yes it modifies your airfoil some but there's four increasingly different amounts available to choose from. It's an Xfoil option so I don't know if it's available in Xflr5 too. If not and you don't have Profili, feel free to send me any .dat files that you'd like me to try to get to run for you.

MikeN
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Old Aug 27, 2010, 02:44 PM
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Mike,

Thanks for the tip. I did not find a smoothing function in XFLR5 but if you increase the #points from 101 to 151 it works.

Greg
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Old Aug 29, 2010, 11:43 PM
Twisted and Confused
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Greg

did you ever consider the SD7003? I built a 100" pitcheron with RG14mod (to work with SD7003) changing to SD7003 at the tip and AR of 15. At a wingloading of around 20oz/sq' it had excellent low speed handling - something I've not really experienced from pitcherons before and has a great turn of speed. It has also been used before in F3B planes as I'm sure you're aware.

Enjoying reading the process, keep up the great work.

Steve
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Old Aug 30, 2010, 05:17 AM
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yyz, full scale gliders do have some devices to clean their leading edges IN flight... Only the very high performances ones and only the very competitive pilots, but they do exist and work!
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Old Aug 30, 2010, 09:15 AM
Master of the Wind
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Steve,

I think that was what was on the Fletcher. Somewhere there is a nice design study published on that plane. It is a bit dated but since I am going after the faster design space I should look at it.

Almost done with the HN-990 and it looks interesting but I got a little sidetracked with repairs.

Greg
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Old Aug 30, 2010, 04:52 PM
Twisted and Confused
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Greg

that article is here.
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