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Apr 07, 2006, 01:59 AM
Striving to Rip the Bring
raptor22's Avatar
Quote:
Originally Posted by EdSoars
The beautiful composite 3+ meter Taborca wing is in a different category of aerodyne entirely! There is actually no aerodynamic reason for a tapered swept wing, Neil tells me, since the lift distribution is completely different than for an unswept wing. The mysteries of fluid dynamics elude me: a digital watch in the next room is enough math exposure. I suspect the 3M wing's taper is a matter of controlling flutter.

ed
While it is true that a swept wing has a different lift distribution, saying that "there is no aerodynamic reason for a tapered swept wing" is a pretty large generalization.

If you want to look at things in a little more detail, try downloading XFLR5 (FREE) and doing a vortex lattice calculation. You can use it to compute the optimum planform much more accurately than any rule of thumb.

--Alex
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Apr 07, 2006, 06:57 AM
Registered User
Aio_1's Avatar
Quote:
Originally Posted by EdSoars
....Concerning washout and tip stalls: as I mentioned, the Talus prototypes have no washout...flat bottomed all the way. Easy to build true. Yes, there must be SOME twist, but it required only about 1/8" up elevon for the first flights. This will be reduced as the CG gets tuned....
Ahh but the slight up elevon is the same as washout if the control surfaces are on the outer portion of the wings! You can either reflex the entire trailing edge a little (same as a plank) or the just the outer portion (but a little more reflex) which will almost certainly be more efficient. Unless you move the CG aft of 25% MAC you'll never eliminate that reflex and if you move the CG aft of 25% MAC the wing will become unstable.
The real question is not whether you need reflex and/or washout but rather whether it's best to add that reflex/washout with the control surfaces or by using the aerofoil as designed but twisting the wing. If you are using a MH44 aerofoil and reflex the control surface then the aerofoil is no longer an MH44. I'm not saying that there's anythig wrong with that approach. It may be the most practical way to do it. I'm just pointing out that picking an aerofoil based on data such as the Cm and then reflexing the trailing edge is a bit deceptive because that data is no longer applicable.

Quote:
Originally Posted by EdSoars
....Swept wings are inherently stable in turns.......This stability makes the plane feel like you're flying in a grooved track: put it in a bank and it just stays there, no falloff, no pullout. Almost weird except that it's so nice. VERY different from anything I've yet flown.....
The swept flying wing planform always introduces spiral stability which is one of the nice things about the format.
Quote:
Originally Posted by EdSoars
....There is actually no aerodynamic reason for a tapered swept wing, Neil tells me, since the lift distribution is completely different than for an unswept wing......
The amount of taper that can be tolerated without harming the lift distribution varies with sweep angle but for a moderately swept wing of around 20 to 25 degrees at 1/4 chord a taper of up to ~70% is fine and can still permit an elliptical distribution. The primary advantages of taper are that you reduce spar strength requirements significantly which allows you reduce weight (alternatively leave the spars as they are and have a wing that flexes less in the air both torsionally and spanwise) and you remove mass from the extremities which improves control response.

Aidan
Last edited by Aio_1; Apr 07, 2006 at 07:03 AM.
Apr 07, 2006, 09:09 AM
Registered User
EdSoars's Avatar
Alex: Yes, a slight taper would be a bit more aerodynamically efficient, but the "optimum planform" has to include consideration for manufacturing limitations and ease of construction as well as "vortex lattice" calculations. Aio, that's why the MH-44 is modified. Gaining a wee bit of efficiency from a full-wing twist relative to a slightly reflexed control surface is INEFFICIENT when ease of construction is included in the equation. Try cutting that concave upper TE surface of the true airfoil in balsa, and keeping it in one piece, without going to a molded construction. See what I mean?

As you say, the big advantage of taper is stress and mass distribution. But without much of a fuselage, and the batteries in the wing, the load distribution is pretty evenly distributed. All this goes out the window with ballast on the keel, of course. For now, if I can get away with an un-tapered planform, I'll keep at it. After all, some very high-performance swept wings have no taper. If structural considerations force a taper on me, I'll go that way, but it will require some more airfoil modifications to accomodate the balsa TE at the tip, which must be proportionately thicker to maintain strength.

Every part of a new design MUST include consideration for the targeted builder and the target cost of the kit; not just the aerodynamic efficiencies. Everything's a compromise. Hateful, but true.

Ed
Apr 07, 2006, 11:09 AM
Striving to Rip the Bring
raptor22's Avatar
Since when is a single tapered wing with washout difficult to build? Virtually every flying wing on the market uses taper and washout.

All you have to do is cover it in the core beds to make sure it's straight.

--Alex
Apr 07, 2006, 12:08 PM
Needs brain lubrication
biber's Avatar
One of my favorite reasons for tapered wings is the improved mass distribution.
Wings do fly way nicer if masses are centralised and thus rotational inertia is minimum possible.
Too heavy wingtips can make wings to be a horror to fly.
I have made that mistake before and will never do that again.

Imagine:
-little yaw damping
-winglets and wingtips inducing lift/alpha on each other
-gusts and overall rough air on a slope
-you do a hard turn with that wing
...may end in a sudden snap, wich is spectacular, but not exactly the desired manouver to be performed.

Now that eats up performance!


Oh, and not really a design for slopeing but just for the nice pics, take a look at that thread:
http://www.rc-network.de/forum/showthread.php?t=40280

biber
Apr 07, 2006, 01:05 PM
My hangar is,... "almost" full
No Step's Avatar
Charge on you guys! I hope this endevor is successfull. I've come to dislike "Zagi style" wings completely. How Boring! Something new is very welcomed. Hmmm, I wonder if a powered version would still have that terrible whine a "pusher wing" usually has? Good luck with your testing.
Apr 07, 2006, 01:11 PM
Registered User
EdSoars's Avatar
biber: yes, that Yoda is a gorgeous piece of woodwork. Nice airframe for electric! It isn't at all difficult to make the tips lighter than the roots, even on a straight planform.

raptor 22: You talk about gross generalizations... Of all those tapered foam wing planforms, how many have tapered elevons? I've built a bunch, and every single one, both conventional and tailless, has straight, box-stock control surfaces. Of all those tapered foam wing planforms, how many use custom machined control surfaces to minimize airfoil distortion? Of all those tapered wing planforms, how many have aspect ratios above 7? The Talus is over 10. Trust me, there is a difference, in L/D and in difficulty in getting warps out in construction.

I'll have to get the "Project Aerodynamicist", Neil Pollock (a professional aeronautical engineer, BTW) to reply to the straight vs. tapered lift distribution issue. Hey, I don't care, as long as it kits, builds, flies and repairs great.

Greg, thanks so much for the post! Who would have thought it would have sparked this much criticism and debate? If we ever get past the development stage, it ought to be a winner!

Ed
Apr 07, 2006, 01:57 PM
Registered User
Aio_1's Avatar
Ed,

You seem to be getting a little annoyed about people pointing out possible weaknesses in the design. I just want to make clear that I for one am not trying to ridicule the design in any way. It looks good and will undoubtedly fly pretty well too. There are always compromises to be made and I appreciate that. My comments were just in response to claims that weren't quite accurate which I felt could be clarified such as the potential advantages of taper and washout.

It's good to see a proper flying wing with a decent aspect ratio for a change.

Aidan
Apr 07, 2006, 03:17 PM
Needs brain lubrication
biber's Avatar
Quote:
Originally Posted by No Step
I've come to dislike "Zagi style" wings completely. How Boring!
Quote:
Originally Posted by Aio_1
It's good to see a proper flying wing with a decent aspect ratio for a change.
That seems to summ it up perfectly for me.

Neither did I intend to spoil anything.
You know, that's why I said: Dooooo eeeet!

Taper is not that important for good performance in this case, I think going without is fully appropriate.
Especially if it eases the building accuracy, it's quite reasonable, I think.
It's just, that it looks better (I mean way better ) and does possibly(!) give you the last few available percents of performance,
if everything is tuned decently on the particular design.
I mean all the little details, like ... well, taper e.g...

Now, can somebody tell me why I constanly placing those 's all over my posting? Duuh!

biber

P.S.: Since the official wings' forum section is an all around boring place,
I think it is indeed adequate that this thread is located in the slopers' realm,
wich is anything but boring. Thanks Ed for posting it here,
because otherwise I would have missed it.
Apr 07, 2006, 03:29 PM
Registered User
Aio_1's Avatar
Quote:
Originally Posted by biber
....P.S.: Since the official wings' forum section is an all around boring place,
I think it is indeed adequate that this thread is located in the slopers' realm,
wich is anything but boring. Thanks Ed for posting it here....
Very true - it was always going to happen which is why I was against it being called "Flying Wings". It should never have been called that as it was pretty clear from day one that it was a forum for slope and electric foamies of the Zagi persuasion in which anything else would get lost. I really like flying wings (I did my undergraduate thesis on the subject!) but I never bother looking in that forum.....Oh well!

Not saying I'll never fly a Zagi type wing myself - it's just that they're not normally terribly interesting to talk about!

Aidan
Apr 07, 2006, 04:02 PM
Needs brain lubrication
biber's Avatar
Singing the Zagi Blues...

Who's next to chime in?

biber
Apr 07, 2006, 05:11 PM
Registered User
EdSoars's Avatar
No problems, gents! If I didn't want the criticism (and I use the word in the sense of "critique", not "put-down"), I wouldn't have posted the thread. I've emailed Neil to ask him to respond to the taper issue, but since he's down under in Oz, it'll be tomorrow at least before he gets back. If you haven't read his 2-part article in Quiet Flyer, it's a good place to get some background on swept wings, that isn't in German!

One of the difficulties of putting out a kit like this is the very small expected sale numbers. With the expectation of selling only a hundred or so Talus kits, there's no way to produce the kits cheaply unless we stay with some pretty limited manufacturing methods. No CNC-machined molds, no bulk discounts on materials, et cetera.

If I can give North County Flying Machines a nip at the heels in the performance and building ease, I'll consider the Talus a HUGE success. Derek Choice and his team really set a high standard for performance and quality. Then there's Windrider, in Hong Kong, with the Bee and Bat. Amazing performance, so easily buildable! How does he afford the molds?

And finally, there's what you're all doing right now, which can only help. And to get an idea of what goes into my kit designs, go to the Laserarts website, or search the Slope and DLG forums for the Spinner.

I gotta get back to the shop....
ed
Apr 07, 2006, 05:36 PM
altitude adjustment
thumbhead's Avatar
I currently have an Arrow 60 from Skycraft on order. Well, I haven't sent the money yet, but am expecting an email telling me the kits are ready to ship. It's been a couple of months now but Noel assures me he's almost there and he'll let me know as soon as they're ready. I've always liked the constant cord, swept wing layout. Can't wait to see the final version of the Talus.

mark
Apr 07, 2006, 06:04 PM
Needs brain lubrication
biber's Avatar
One design that did quite well for me, was that on the picture below.

For specifications see https://www.rcgroups.com/forums/show...8&page=4&pp=15

biber
Last edited by biber; Apr 09, 2006 at 08:54 AM.


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