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Old Jan 02, 2012, 10:08 AM
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Vernon Hunt's Avatar
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Practical experience with a certain wing style helps alot. Each wing has it's own certain sweep, twist, and anhedral, or not. I consider every wing I make an experiment, but with plenty of years making wings, I have finally gotten more comfortable with that first test flight.

Vern
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Old Jan 02, 2012, 02:17 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
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It's just that I want to understand the issues relating to the design of tailless aeroplanes and then write myself an Exel based design utility. From the Panknin formula, I already have the twist side sorted but the sweep / dihedral / winglet height interplay still needs work.

Getting back to the article in question, it would've been useful if the worked example at the end had the calculations as well as just the results. Oh well....
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Old Jan 02, 2012, 02:51 PM
less is more
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United States, CA, Marina
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Quote:
Originally Posted by Shedofdread View Post
It's just that I want to understand the issues relating to the design of tailless aeroplanes and then write myself an Exel based design utility. From the Panknin formula, I already have the twist side sorted but the sweep / dihedral / winglet height interplay still needs work.
There are a few such spreadsheets floating around the web. But Panknin formula provides total twist only and does not address BSLD, thus it's linear twist approach will have a significant lift flat spot in the middle of the wing. Do you really want to do that?

My early flying wings had enough twist thanks to the application of the Pankin formula, but were hardly good performers.

Kent
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Old Jan 02, 2012, 03:01 PM
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Originally Posted by Shedofdread View Post
Would someone be so kind as to run that calc themselves and see what they get. It's driving me nuts.

Many thanks (he said, off to somewhere quiet...)
I'm afraid that I won't be any help with the math but maybe I can offer some conceptual help on dihedral effect and ways to fine tune the skid/yaw and skid/roll moments. These two moments have to be coordinated for stable flight. Both moments are created by a swept wing but, unfortunately, one is proportional to CL and the other to CL² so, in the absence of any tricks, a swept wing will only have well behaved flight characteristics at one speed. I've writen a lot about this stuff in other threads so instead of redoing all that typing I'll just point to them:

This one mentions the type of canted winglets that Burt Rutan used on the LongEZ. There's a link in that post that leads to a post in another thread with more discussion and another link... ad infinitum

Here's another one that covers the same stuff as the previous link but is part of a very long and rambling thread that goes into many aspects of directional stability of tailless aircraft.

Here's my conceptual understanding of how BSLD can produce favorable yaw moments. Nobody has given me any significant criticism of it yet so I think it's not too far off. Of course just designing the wing for a BSLD won't work by itself: You have to balance it accordingly

--Norm
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Old Jan 02, 2012, 03:50 PM
Deniable plausibility
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Derbyshire, UK
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Kent - as you know, I'm not a Horten 'believer' so I don't need BLSD (and arguably, neither did they....). My interest is in platforms more like the Co series (ie fins and a sensible C/G location). Interestingly, Unverferth applies the applies the washout (a similar amount to that suggested by Panknin) progressively with 0 across the first third, a little in the second third and the bulk in the last. My feeling is that this distribution is NOT calculated. I intend to go down a similar route. My approach to the required anhedral is currently anticipated to be to give it about 1deg and say "to *heck* with it*.

Norm - as ever, thank you for your kind and thorough posts. I'll be sure to read all that you've linked to (couldn't open the homebuilt forum one - will try again later) and endeavour to understand it.

It would've been good to have figured out whether I was missing something or if there was a typo in the effective sweep doc as that would've tied up another loose end but that may have to remain one of life's little mysteries.

While we're on matters technical, when a published airfoil quotes a Pitching moment coefficient, how are they measuring it? OK, it has to be at Cl=0 but Cmo varies with Re so what value are they using?

Thanks again,

S
who may well, eventually build a tailless design...
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Old Jan 02, 2012, 06:08 PM
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Originally Posted by Shedofdread View Post
Unverferth applies the applies the washout (a similar amount to that suggested by Panknin) progressively with 0 across the first third, a little in the second third and the bulk in the last. My feeling is that this distribution is NOT calculated. I intend to go down a similar route.
S
I would suggest that the progressive twist you have described is a version of BSLD that may have very well been created for the sole purpose of creating a simplified BSLD for use in foam cut wings.

Kent
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Old Jan 02, 2012, 06:37 PM
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Originally Posted by Shedofdread View Post
Kent - as you know, I'm not a Horten 'believer' so I don't need BLSD (and arguably, neither did they....).
Hhhhhhhrrggggg BLASPHEMER I'm a Philistine myself Who cares about what's technically superior? It's a hobby, dammit! If you want to see Snoopy fly make him fly We know dogs don't make good vehicles: that's not the point. The point is to do something satisfying regardless of the utility of the result. I happen to find elegance satisfying but a 300 watt per pound Snoopy could also amuse me for a while.

Quote:
I'll be sure to read all that you've linked to (couldn't open the homebuilt forum one - will try again later) and endeavor to understand it.
I think his server is having trouble. We've been seeing time-outs during replies too for a couple of days. You can find that post by going to the site home page and typing "skid/yaw" into the embedded google search box. Here's another deep link to a page on HBA just to test your patience some more it concerns diffuser tips.
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Old Jan 02, 2012, 06:49 PM
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Hhhhhhhrrggggg BLASPHEMER I'm a Philistine myself Who cares about what's technically superior? ...
I gotta be honest with you Norm. I didn't follow this at all. I don't see how you read all of that into Shed's comment.

I'm a "born again" BSLD believer and from what I gather, Shed has never bought into the concept.... that's fine with me.

Kent
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Old Jan 02, 2012, 07:13 PM
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Originally Posted by Knoll53 View Post
I gotta be honest with you Norm.
I thought the second half of that paragraph
Quote:
The point is to do something satisfying regardless of the utility of the result. I happen to find elegance satisfying but a 300 watt per pound Snoopy could also amuse me for a while.
clarified my point of view adequately but apparently I needed to use a few more words, so here they are: Doing a job with a minimum of parts is elegant. Monoplanes are more elegant than biplanes, 'wings with tip fins are more elegant than monoplanes with tails, 'wings without verticals are more elegant that 'wings with fins
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Old Jan 02, 2012, 10:33 PM
Just call me crash for short
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Joined Jan 2011
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At the risk of detracting from the current line of discussion, while staying on the topic of Thermal Wings, I have a question for you all.

Is anyone using a high start or winch to launch their wings? I'v seen lot's of slopers and electric assist, but I can't say that I have seen a TD type wing being launched by high start. In doing some research with the old timer designs, I see launch assist devices like the JASCO Sailwing 50 uses to get it up the line. Then there is the "Rolling Bobbin" type of setup that has been used and for some reason, fallen out of favor, from what I can see anyway.

I have had my eye on the Paoli type of design that I have been wanting to try, but coming up with a good way to get it "up there" has been holding me back a bit. I am thinking that I might try a 1.8m - 2m build (the size will match my currently working high start) and use the rolling bobbin setup. Just need to figure out where, in relation to the CG, the hooks should go. I guess I could just go for it and if all else fails, I will get a brief moment of entertainment with the cool looking balsa confetti at the end of a short ride. Any of you here have any thoughts on what would be the best way to high start / winch launch a Thermal Wing?

Anyway, I thought this forum, Nurflügel, would be the best place to ask this rather than the other wing forum that is far more concerned with EPP and getting little wings to go fast. I for one am happy I stumbled into this forum. I'm over on the Vintage & Old-Timer Designs forum a bit and jumped up one level and saw it. Thanks guys for starting this.

Mark
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Old Jan 03, 2012, 12:35 AM
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Peter V's Avatar
Joined Nov 2008
132 Posts
Thermal wing

hello all,

happy new year in good health to you all.

Mark, is this what you mean?
I use - and as far as I know, do others too - an elastic cord (used for rolling up sails on sailboats) - which is streched to its limits (about 10kg of pulling power) and of you go.

Peter
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Old Jan 03, 2012, 12:59 AM
Just call me crash for short
Quick61's Avatar
United States, OH, The Plains
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Quote:
Originally Posted by Peter V View Post
hello all,

happy new year in good health to you all.

Mark, is this what you mean?
I use - and as far as I know, do others too - an elastic cord (used for rolling up sails on sailboats) - which is streched to its limits (about 10kg of pulling power) and of you go.

Peter
No, not really. I'm talking about a regular high start, 100 feet of surgical tubing, 300 - 400 feet of line launch you glider 400+ feet into the air, or a powered winch like this - http://www.rcgroups.com/forums/showt...ighlight=winch or even an FPW like the OneWinch The pics there are showing what I would call a Zip Line that helps get the motor glider moving. What I am talking about is launching an unpowered wing 200 - 500 feet up like the tailed TD ships get launched. Is that making any sense? it's not about getting it moving forward, it's about pulling it UP, and when doing that, I've seen more than one tailed glider stall out / go unstable and crash. Which is why the rolling bobbin was used, as it aided in controlling the yaw on the way up with it's Y connection to the wing.

Nice pics and great looking wing BTW. Some day my wings will grow up to be Hortens.

Mark
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Old Jan 03, 2012, 01:53 AM
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Originally Posted by Quick61 View Post
Is anyone using a high start or winch to launch their wings? I'v seen lot's of slopers and electric assist, but I can't say that I have seen a TD type wing being launched by high start.
This video was attached to the last post in CloudyIFR's build log of his Tinamou. The URL he gave, in the second post, for that nifty implementation of the Panknin spreadsheet was his old address the new one is in his user ID right above the site sponsor button.
Tinamou Compilation (1 min 45 sec)
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Old Jan 03, 2012, 02:22 AM
Just call me crash for short
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Yes, that is what I am talking about. Thanks for that. I'll have to read through that thread in the next few days and see what he says about tow hook location. That is the first video I've seen of a wing going up the line on a high start. Very smooth, but them again, Curtis is an accomplished builder so that is of little surprise. I had seen that wing in an article in Radio Control Soaring Digest but never the launching of it. Looking at the number of views and posts in this thread, there seems to be a bit more than a passing interest in thermalling wings. Maybe this is an aspect of soaring that is starting to open up a little? I might just have to sneak a wing build in between my other projects. Thanks again for posting the video.

Mark
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Old Jan 03, 2012, 04:17 AM
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Florida
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Mark,

I've launched my skinny wings hundreds of times and it goes up like any sailplane. At the glider end of the bungee I use a bridle, that attaches to 2 hooks outboard on the wing just ahead of the CG. Works great.

Vern
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