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Jun 15, 2013, 03:21 PM
Launchpad McQuack
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Discussion

New foils 2014: Ultima


Inspired by the great success of Geralds' Zonev2 airfoils, I've been wanting to design my own DLG foil family for years. About 1 year ago I started a project to find a new airfoil family that beats ZoneV2 in every possible way...

An ambitious project. I soon discovered just how good Zonev2 really is, and how little the current software algorithms allow performance progress.

But I had a plan.

After weeks of nightly analysis I've created hundreds of genuine new DLG airfoils using a software program named "Edgar 3.0". http://www.evolutiondesigns.eu/

Software input consists of the desired airfoil performance priorities at prescribed operating points. Airfoil geometry can be defined by specifying certain constraints on thickness/camber/nose radius etc. The results weren't good enough, so I started combining foils, and kept the ones that seemed to deliver better performance than ZoneV2 did. It was hard to find a foil that performed better in all three operating points "speed", "cruise" and "float". Sometimes a good foil was found, only to discover that it seemed impossible to design a decent foil family for a wing planform from it.

Here's what I have so far. It's a very thin airfoil, likely to give all kinds of trouble with servo installation, wing bending strength/stiffness and torsional stiffness. Planform is still bog standard (but very good) original ZoneV2. (higher AR wings proposal will follow soon)



Geometric comparison between ZoneV260 and Ultima 8. (Root foils)


As you'll notice, there's a clear similarity between the two. Ultima is noticeable thinner, but relative nose radius is much larger. Camber is slightly lower.

Speed (no flap):








Cruise (Flap 2):









Float (Flap 4):








Float (Flap 6):





Download the complete XFLR5 project (V6.09.05 Beta) & Ultima airfoils (.DAT & .DXF) below.

Comments are welcome.

Regards,

Vincent

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EDIT 12th July: new files to be found in post 38
https://www.rcgroups.com/forums/show...5&postcount=38
Last edited by Prop-er; Jul 11, 2013 at 05:44 PM.
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Jun 15, 2013, 04:43 PM
ThomasLee's Avatar
Hi Vincent, very interesting product and it looks great. Once I get time I'll play with it a bit on some of my planforms too and see how it stacks up against the ZV2.
Jun 15, 2013, 05:15 PM
Registered User
Very cool! Good to see some more folks diving into foil design! It's surprising how time consuming it really is. Sure makes one appreciate the tremendous amount of work Gerald has already put into advancing our sport without asking for so much as a penny in return. I look forward to seeing prototypes and hearing flight reports! I'm waist deep in my own projects right now or I'd consider building one myself. I'd be curious to build a lower AR DLG using these foils. There are a couple of manufacturers building low AR wings with very thin foils these days (Brko and Twister 3). Thanks for making these available!

B
Jun 16, 2013, 12:31 AM
G_T
G_T
Registered User
I put a lot of work into various foils to try to get the performance I could while keeping them thick enough in the wing and at the hingeline so that people would be willing to give them a try! Particularly at the tips I gave up going below 5% thinking nobody would try it. Perhaps now though since people have become used to somewhat thin wings they would be willing to try thinner.

With a full carbon skin I think your wing should be buildable.

I won't get a chance to look this over in any detail until after next weekend at the earliest. I'm too swamped getting ready for URRF. But afterwards I shall certainly check this out!

Gerald
Jun 16, 2013, 12:46 AM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Vincent, great to see some more guys keen to put the time and effort into advancing our sport/hobby.

Gerald, it is amazing how many ZoneV2 foiled models there are out there, and making it available to the masses is a truly selfless act that deserves some form of award

I am yet to try a Zv2 foiled model, and am very keen to try one.

The Ultima sounds like the start of the next big thing too. With the small current trend of "all in the pod" and full carbon wings, also with new materials becoming available, makes a thinner foil more likely to become a success IMO

Really keen to follow this...
Jun 16, 2013, 03:31 AM
tau
tau
Registered User
Hi Vincent,

definitely a nice project! I'd be interested in seeing how you defined your optimization goal within Edgar?!

Unfortunately i can't seem to load your XFLR5 project zip.... Nope i managed to d/l it now!
Jun 16, 2013, 05:21 AM
Launchpad McQuack
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Thread OP
Thanks all for the compliments.

@Gerald: I'm really keen on your opinions.

Quote:
Originally Posted by tau
definitely a nice project! I'd be interested in seeing how you defined your optimization goal within Edgar?!!
Good question!

It took some time to get any meaningful results. Please note that Edgar is far from being a finished program. It crashed all the time.
To get an idea of airfoil parameters I just investigated all well known DLG foils:





I calculated the data of the three operating points.

Design Point 1: thermal

Cl = 0.55
Re = 60k
re.sqrt(Cl) = 60k / sqrt (1/0.55) = 44,5k

Design Point 2: cruise

Cl = 0.15
Re = 120k
re.sqrt(Cl) = 120k / sqrt (1/0.15) = 46,5k

Design Point 3: start / speed

Cl = 0.025
Re = 400k
re.sqrt(Cl) = 400k / sqrt (1/0.025) = 63k

Through the course of several weeks, several inputs were tried. One of them is shown here:








Result example:


Output foil example:


Output from Edgar was compared to existing foil data:



Edgar (it's a commercial program) allows point file export, but thickness is scaled by a certain value to prevent free use.

It's however quite easy to import the point data in Rhino, and scale it back to original thickness. By using Excel, suitable DAT files were created from the Rhino point cloud files.



From here, manual optimization starts....

Jun 17, 2013, 09:04 AM
Registered User
TDM30076's Avatar
I am so happy to see new people pitching in to improve and to try to make our hobby more enjoyable.
So far so good and it looks like a great start. I see one little issue here. It is tough to fit a Hyperion in a Zone V2 wing but with an even thinner airfoil we will be forced to go to MKS or D47 and the like to put them in the wing. Then it comes to material selection and with a foil so thin it is pretty much all carbon wings. What I am trying to say is to think about buildability.
As for me my new Evolution 3 allows me to use a wing that is half as thick as the V2 without problems and as stated with 4 in the pod the thickness of the wing does not have much play. Other than that we may run in to problems. I could use your current foil in my DLG right now.
I am not ann aerodynamicist but doesn’t the CL/CD give the ideal slope for that configuration and if that is true then it looks that you have better CL/CD at 4degrees. That make me think if the cruise set should be at 4 degrees and float at 6 degrees of more. But that is just from someone who never did something like this and or does not see the whole picture.
Jun 17, 2013, 09:31 AM
Aurora Builder
Vincent,

Nice work, I will need to look at these when I have time, possibly in August.

Traian,

Servos may be a limiting constraint in some regards but don't forget as you go thinner it becomes difficult to build a wing with sufficient torsional and structural rigidity. For example, your beautiful glass disser wings would likely experience flutter if these foils were used and a strong thrower was launching. Hence, you'd need an all-carbon wing, which has a number of issues to contend with, not the least of which is material cost. At some point even full carbon skins are insufficient.

Regards,
Sam
Jun 17, 2013, 10:29 AM
Launchpad McQuack
Prop-er's Avatar
Thread OP
Quote:
Originally Posted by Traian
I am not ann aerodynamicist but doesn’t the CL/CD give the ideal slope for that configuration and if that is true then it looks that you have better CL/CD at 4degrees. That make me think if the cruise set should be at 4 degrees and float at 6 degrees of more. But that is just from someone who never did something like this and or does not see the whole picture.
Best Cl/Cd reached is 22,7 @ 7 m/s using 0 flaps.
Lower speeds require flaps to keep Cl/Cd optimal.

Performance comparison in real numbers: (Green = best value)


Quite depressing to see the small performance gains. (+0,5%)

The real performance upgrade should be launch height.
Does anybody have an example of an aerodynamic launch height calculation?

P.S.: data is wing only.
P.S.2: glijhoek = glide angle
Last edited by Prop-er; Jun 17, 2013 at 02:22 PM.
Jun 17, 2013, 11:47 AM
Registered User
TDM30076's Avatar
Quote:
Originally Posted by samc99us
Vincent,

Nice work, I will need to look at these when I have time, possibly in August.

Traian,

Hence, you'd need an all-carbon wing, which has a number of issues to contend with, not the least of which is material cost. At some point even full carbon skins are insufficient.

Regards,
Sam
And that is the edge I would like to see explored. Maybe Evo4 dream is already forming. Or just new set of wings for Evo3
Jun 17, 2013, 11:49 AM
G_T
G_T
Registered User
Launch height effects from the wing will be:

Drag at nearly zero lift coefficient, best seen with Type-1 polars. Look for a little tolerance +/- as well so results would be more consistent.

If that criteria is good then the pull-up drag will be fine as well for any foil family suited for DLG use.

Low drag over a range of alpha +/- at pull-up lift coefficient. As the wing yaws, one wing gets +, the other -, and then a moment later this reverses. If drag goes high for either of these cases, launch height will suffer. But, this is unlikely to be an issue.

Dihedral angle... less dihedral --> less yaw->roll coupling. So reduced dihedral reduces energy loss here.

Sweep... Sweep also behaves like dihedral with respect to yaw, altering the relative length of the lever for the left and right wings. Sweep also increases the fuselage masking of the trailing wing in a yaw. So sweep may get the throwing blade in a more advantageous position but it also may result in some loss of energy in the yaw excursions as they couple a bit more strongly to the roll axis.

[Having much sweep also causes handling issues in terms of stall behavior in very tight turns (where it is more likely to occur). If the inner tip stalls then the CP migrates forwards leading to a deep stall. These two reasons are why my designs don't have much sweep. Plus, in tight turns one gets changes in freestream direction based on span-wise location on the wing and distance to turning center, and sweep angle. This has the effect of changing the chord, thickness percentage, and Reynolds numbers. It is more complex.]

Taper ratio - the greater the taper ratio the lighter the tips can be provided the tips are not so thin that extra skin material or other reinforcing is required. Lighter tips reduce yaw inertia on the throw so less energy is wasted cancelling the yaw rate.

One can go too far with taper ratio and end up with tips which have too much of a Reynolds number disadvantage and require structural reinforcement (mass per unit area well above average for the wing, defeating the purpose of narrow tips). I have tried many times in the past to design a wing with pointier tips which I though could be made with tips light enough, without giving up performance, and without giving up handling characteristics. I've always had to give up something for pointy tips - more than I want to give up. I think Synergy is as pointy as I've managed in practice without notable performance loss.

Gerald

PS - Note that shorter noses on fuselages reduce masking of wing center in yaw.
Last edited by G_T; Jun 17, 2013 at 02:00 PM.
Jun 17, 2013, 11:59 AM
G_T
G_T
Registered User
At a glance, the upper surface curvature of this foil family is reduced compared to Zone-V2. That puts it more similar to Edge in some ways (Edge has higher L/D than Zone-V2 by my recollection, and probably higher max lift coefficient, and better min sink. But it is not as forgiving and has higher drag at rather high speeds and has a launch penalty. It also has a mid-wing foil which isn't quite as good as the rest of the wing, unfortunately. It is a blending problem...). Now Edge suffers a bit when the turbulence is high. The shallow upper surface curvature results in less stability in the location of the transition point. The location of the transition point drives the flow behavior on the upper surface of the wing (the reverse, really, but easier to assume the transition point drives the flow behavior and then design to control the transition point behavior) and is one determinant for the lift coefficient produced. As a consequence, in turbulence, the wing will deviate more frequently from the ideal lift distribution so induced drag is a touch higher. The greater reactivity to turbulence means more energy will be wasted in roll reactions, and in pilot inputs to control same.

IMHO, one should also particularly look out for sensitivity of transition point with respect to pitch increasing as one goes from the root to the tip in a series. This pretty much requires broadening and unloading the tips to compensate, or the wing would be too reactive in turbulence.

Gerald
Last edited by G_T; Jun 17, 2013 at 02:03 PM.
Jun 19, 2013, 01:33 AM
Launchpad McQuack
Prop-er's Avatar
Thread OP
Thanks for these insights, Gerald.

Do you run turbulence sensibility simulation at a different Ncrit number?
(Using Ncrit 9 now)
Jun 19, 2013, 06:15 AM
Launchpad McQuack
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Another question: who knows the typical DLG frontal area?


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