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Old Sep 28, 2014, 11:52 PM
G_T
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Foils and wing - SynerJ

Hello everyone,

Last year to honor a request I spent the summer generating a new wing for this past F3J WC. Unfortunately due to long delays in mould generation, and the moulds not being usable when they were finally available, the plane has not yet flown. I generated another wing design for an independent request for a smaller span electric using the outer portion of the new wing series; it also has not yet flown though it is close to being ready.

This foil series has not previously been named. I put out a request for suggestions on the K forum in one of my threads. It seems that SynerJ is not likely to be confused with anything that has flown so unless there are objections that will be the name.

Hopefully I'll get it all published this week. Since the work was completed last October this is long overdue! Consider this post a teaser.

I'll have to change the foil names from my normal naming convention now that a name is established. For those not familiar with my work, those funky names in the picture are a date, the Type-II Reynolds number for which the foil is optimized, and the flaperon deflection relative to speed mode. +2, for example, is 2 degrees down and could be considered a candidate flap and flaperon setting for cruise. I use this sort of naming convention because I've quite literally created thousands of foils.

Gerald

PS - The zip file is a little avi showing the transition point behavior modeled in XFLR5. It seems I can no longer post videos on rcgroups so I had to zip it up.

PPS - I forgot to mention - Free to use, commercial or otherwise. I would like to hear about projects using it or modified versions of it so that I have data for any future work. I'd also like to get credit when it is used.

PPPS - Foils on post #16, wing design on post #28.
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Old Sep 29, 2014, 07:39 AM
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Fantastic.
At 1360g (47 oz) isn't the plane mass a bit low for a 3.8m plane?

Terry
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Old Sep 29, 2014, 07:42 AM
Hugh Blackburn
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Melbourne, Australia
Joined Jun 2005
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Hi Gerald,

That's nice work. Could you tell me why the XFLR5 analysis is sometimes apparently giving a span efficiency greater than unity? Is it a mis-match between projected/reference areas and spans?

Hugh
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Old Sep 29, 2014, 09:47 AM
G_T
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Quote:
Originally Posted by Chuchuf View Post
Fantastic.
At 1360g (47 oz) isn't the plane mass a bit low for a 3.8m plane?

Terry
It should be structurally do-able. Think short tow and low sink rate.

One can always add ballast if necessary. My designs generally have a fairly wide speed range compared to the work of others so it might not need quite as much wing or span loading for equivalent conditions. I've only seen a few J designs though as most won't publish their work. I'd like to start changing that...

Anyway that was the target design weight, so think of it as a suggested weight to aim for. If it is heavier, within sanity, it should still be just fine. It will just fly a little faster and of course come down slightly faster - just like any other J design.

One can of course use the foil series to design one's own wing. But I would like to discourage that for those without a lot of experience doing the aero design. It is a lot of work to make a J plane. My experience from seeing designs produced for K models off my foils is that more often than not they are a little deficient in one or more aspects of flight. But if one knows what one is doing, and particularly if one has different design goals, go for it!

Gerald
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Old Sep 29, 2014, 10:50 AM
G_T
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Quote:
Originally Posted by floquet View Post
Hi Gerald,

That's nice work. Could you tell me why the XFLR5 analysis is sometimes apparently giving a span efficiency greater than unity? Is it a mis-match between projected/reference areas and spans?

Hugh
To my understanding, it is a ratio of numeric values computed through two different methods. One being simple lifting line theory assuming elliptic lift distribution to determine the minimum induced drag under that assumption. The other is some method of estimating the induced drag of the wing.

Honestly it doesn't concern me at all. I don't use the values as absolute anyway, and I ignore that particular value completely. I use XFLR5 for relative comparisons of very similar designs for optimization purposes.

The subject has been in posts many times. Please refer to those.

In any event, strictly minimizing induced drag will not produce the minimum drag, due to viscous effects which scale rather badly with Reynolds number. Our wings, particularly towards the tips, are too small and flying too slowly.

Gerald
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Old Sep 29, 2014, 11:52 AM
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United States, VA, Falls Church
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Thank you Gerald, for all your hard work. The design isn't dead, just drug out longer than I'd hoped. The masters I rec'd are unusable, and I'm deciding how to proceed to get some usuable tools.

If anyone has access to a large CNC table, please contact me offline and we'll get this thing moving. I'm currently reaching out amongst some of my UAV connections to see if anyone can help for less than retail machining costs, although at this point, the model just needs to be done - I need it for next year's TS.

Gerald's work on this is quite amazing. There is no doubt that this will be the next generation of J designs.
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Old Sep 29, 2014, 12:20 PM
G_T
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It took Daryl and Phil Barnes a bit of arm twisting and persuasion to get me to do this design... If I'd done it the first time Daryl requested, he'd have had about 6 more months to get the plane built.

Gerald
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Old Sep 29, 2014, 12:47 PM
Aurora Builder
United States, MD, Lusby
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Quote:
Originally Posted by Daryl Perkins View Post
Thank you Gerald, for all your hard work. The design isn't dead, just drug out longer than I'd hoped. The masters I rec'd are unusable, and I'm deciding how to proceed to get some usuable tools.

If anyone has access to a large CNC table, please contact me offline and we'll get this thing moving. I'm currently reaching out amongst some of my UAV connections to see if anyone can help for less than retail machining costs, although at this point, the model just needs to be done - I need it for next year's TS.

Gerald's work on this is quite amazing. There is no doubt that this will be the next generation of J designs.
Daryl,

PM sent. Have in-house capability along with connections in the professional machining world. HAAS time is still HAAS time unfortunately.

Best,
Sam
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Old Sep 29, 2014, 03:00 PM
RIP MC
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Awesome Gerald,
I'd be very curious to get your thoughts regarding the thickness of your root section and how you got there.

Based on a molded spar and latest construction techniques, for 19 A/R on a 3.8-4.0m wing, I couldn't come up with a section less than 8.25% and still have a strong enough wing strength (200lbs lift), yet be light enough not to give up much in the launch.

It's the single hardest point of the equation and even with plenty of math, there's still some guess work involve because even if I am confident in the spar strength, the "flutterability" has huge question marks.

Since the launch in my opinion, is the single biggest performance differentiating point in J among models, I started with the mass as the 1st design element. Then from there going with the thinnest airfoil that can scale ( A/R wise) to adequate strength.

I also settled on an A/R of 19 for a 4M as most practical, but my scaled mass is no where near what yours will be.

I would love to hear you spell it out as how you did in the DLG forums!!!!

Thanks a billion for doing this!
TL
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Old Sep 29, 2014, 03:32 PM
G_T
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Honestly I don't mind putting a bit of a structural challenge to the builders. When I first started designing for f3k there were plenty of comments along the lines of can't be done. Now it is no big deal. Biased spread tow carbon skins for torsional stiffness, for instance, with layers and thickness appropriate for the load. I wanted to go a little thinner actually, but Daryl didn't want to go solid core, so... Anyway I kept the wing much thicker than I'd otherwise likely have done.

For spar, I'd consider a multi-layer structure such that HM carbon is near the shear web and lower modulus near the surface of the wing, with IM in between. That will distribute stress more uniformly through the mass of the spar caps.

Gerald

PS - The design had dimensional constraints spelled out by Daryl, to which I conformed. He had specific goals in mind. He wasn't concerned about flying it in high wind for instance where the spar is most highly stressed as he didn't figure to fly it then! In any event, I think it can be done. However I do intend to leave the structural work to those who choose to make the wing. Perhaps sometime in the future I'll design a wing without consideration of structural issues, and then everyone can have real fun building!
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Old Sep 29, 2014, 05:13 PM
RIP MC
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Are you at liberty to elaborate at all on the foil thicknesses? One of the problems that surfaced for me with such light planes is the large difference between inside and outside wing speed when in a tighter circle, while bank angle is not as high.
The inside mid/tip panel foil at this point does not like to be thinned too much at all.
I'll share my root- mid-tip foil thickness progression in hopes that you can comment too see if I'm way off the reservation.
I know there is a lot more to it than that, but this at least gives me something to compare too for now.

For me, designing a wing not only involves lots of aero knowledge, there's also 3d puzzle elements to get top/bottom smooth surfaces. I've gotten more gray hair over this than raising my 2 young girls! If I'm asking too much let me know so I won't clutter up your thread so much! Just wished you'd have started this way earlier !! Thanks, again!!!!
Tuan
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Old Sep 29, 2014, 06:19 PM
G_T
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Using a combination of a bit of washout and a bit of extra chord vs elliptic projection one can move the operating point of the outer portions of a wing to a little lower alpha and Cl than would otherwise be the case. This provides a bit of protection for the tips. It also provides other benefits.

One can optimize foils near the tips to be a little lower in drag at reduced alpha vs increased alpha compared to optimal. This reduces the drag of the outer tip and increases the drag of the inner tip in a turn - exactly the direction needed to reduce overall drag (v^2 term) and reduce required rudder deflection for coordinated turns - further reducing drag.

To clarify - In a steady-state turn, the entire plane descends at the same rate. However the outer tip travels much farther than the inner tip, as it travels along a larger circle. If the wing as a whole is flying near optimally, then compared to straight line flight the outer tip is flying at a lower alpha and lift coefficient and the inner tip at a higher alpha and lift coefficient. If the wing design cannot take this condition, the inner tip stalls. If the design is not optimized for this asymmetry, the plane doesn't want to turn as well as it otherwise could.

I can tell you that empirically the approach I use works quite well. I have used it on the last several of my foil series and reference wing designs. The reference designs all turn nicely in tight turns. That is one of the areas where some non-reference designs I've analyzed (and flown) tend to suffer. Many designers do not sufficiently consider turn behavior - which is hopefully what the plane spends most of its time doing!

Smooth transitioning between the numerous foils - yes, that is a bit of a challenge. A collection of otherwise good foils does not necessarily make a good wing.

A tight circle with low bank angle is not something I would generally expect to see in optimal flight. The plane turns most efficiently due to the bank orienting the lift vector towards the center of the turn. A sideslip is not efficient. Neither is flying too slowly which is the other way one can have a tight circle with relatively low bank angle.

I'm not going to have the time to spend on this thread that I usually spend on threads where I present a new design. First off, the design is done. It just needs to be published. So, no thread showing intermediate stages in the development process or carefully laying out all the goals and compromises. Second, honestly I don't have the time. If I can provide short answers lacking in rigor then I will, but that may be the best that my schedule allows. I have quite a number of people waiting for me to finalize Synergy-II for DLGs. That's going to be a popular wing, if the analysis holds any accuracy.

It has been a very busy year.

I'll be providing the foils and wing design over the next few days. Please be patient everyone!

Gerald

PS - I no longer know how to annotate pictures. The picture is from this foil series, each color is a different camber, and each line a different foil in the series.
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Old Sep 29, 2014, 06:44 PM
RIP MC
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Thanks Gerald. Copy all that. My "tight circle" comment was in respect to a heavier design, more in terms of an absolute turn radius, of course lighter = small for a given bank angle.


Can't wait for the foils.


Re: annotating photos, see picture.
T
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Old Sep 29, 2014, 11:16 PM
G_T
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Here's a picture of the root. That should answer some of the thickness questions. Hingeline at 30%.

Gerald
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Old Sep 30, 2014, 02:58 PM
G_T
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I have two tip sections for this design. One is thinner. Anyway these are foil pictures from the thicker series which I developed for Daryl. The difference is the thinner one has a little less drag. I developed the thinner tips for another person for a different project. Sometime in this thread I'll re-generate the wing with the thinner tips and we can see what the performance difference might be. The thicker version was intended to make it easier to use hollow molded construction techniques.

Gerald
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