Why no Flying Wings at a TD contest

[atjurhs]

Hello all,

I just flew in my very first TD contest yesterday, and had a great time. There were all sorts of planes there from my OLY2 all the way up to $1800 exotic birds, but no flying wings.

I do know about planes like the Yoda, but I didn't see any there, and I've never heard of someone flying TD with a Flying Wing type of plane, so I have to wonder why?

Is it just complexity of the build? Surely not, there are several folks here that like to build as much as they like to fly, me included. So there must be some aerodynamic reason, but I can't think of what it is. Can you tell me?

[schrederman]

It's because TD as we know it is basically a landing contest. Flying wings are not too easy to land accurately. Just my honest opinion.

Flame away... Happy Memorial Day...

Jack Womack

[xtc]

in my opinion ,flying wings only perform well on paper! ,by that i mean ;; the stats are good for flying wings but there darn hard to thermal well

xtc

[atjurhs]

So if the contest rules were say to land within a 25foot radius circle (all or nothing on the landing points) then they would fare well? Your answer implies that in the air, the flying wings could be just as competitive as those that I saw at the contest, that they have no aerodynamic difficencies?

[mlee8249]

Flying wings have a couple of things going against them. First, they have no real means of pure yaw motion, because they don't have a trailing tail. As mentioned Jack, most of these events are a landing contest, and without a really good yaw axis to use, you won't be very good at landing on target. Secondly, not too many of them launch really well on a winch. Not that they don't...they do launch from a winch, but to get the type of launch a conventional bird does will require much more tweaking on the plane to get it right.

The real bottom line is that the conventional birds do such a good job of performing the task, there is little reason to use anything else. So, most of us go with the flow and flying wings fall by the wayside. On the other hand, you won't see too many conventional aircraft mixing it up in full contact slope combat!!!!

Mike Lee

[atjurhs]

Thanks all, I think that pretty much answers the question.

[rscarawa]

I also wonder how well a Wing will signal lift when there is not extended tail to be moved. With a tail two feet behind the wing, you can see when the plane has been disturbed by the fuse angle. I wonder if you would notice this in a wing?

[Ollie]

Flying wing airfoils have only about ~80% of maximum coefficient of lift compared to tailed planes. For low air speed, flying wing needs about ~80% wing loading compared to tailed planes. A sweep back flying wing with about 20 to 25 degrees has about ~10 times torque loading compared to tailed planes. A sweep back flying wing with bending load couples into twist too. With a fast launch under towing, like winch or two person towing manual, puts very high G loads. Therefore, the flying wing structure needs to be much stiffer than tailed planes. It's a big design, with low weight and high stiffness, structure problem.

[pocket rocket]

if you're interested in soaring flying wings then you should check out the RC Soaring Digest web site

the webzine always has stuff about flying wings and this month is a flight report

Philip

[TLyttle]

Many years ago, there was (is?) a prolific designer of thermal-worthy wings, many different sizes. He had a rudder at the end of a short fuselage (dealing with yaw problems), and the design I wanted to build was the Blackhawk for handlaunch. He claimed (I have no reason to doubt him) that the advantage to wings was the quick recovery from a stall (low pitch inertia). There is a time and place for everything !

Hmmmm... maybe I should build the Backhawk next winter...

[djklein21]

No one has mentioned that there is no trailing edge ( camber-reflex) control on a wing. In fact, on the winch, when you pull up elevater, the wing gets reflexed, lowering the CL of the wing.

[djklein21]

Flying wing airfoils have only about ~80% of maximum coefficient of lift compared to tailed planes. For low air speed, flying wing needs about ~80% wing loading compared to tailed planes. A sweep back flying wing with about 20 to 25 degrees has about ~10 times torque loading compared to tailed planes. A sweep back flying wing with bending load couples into twist too. With a fast launch under towing, like winch or two person towing manual, puts very high G loads. Therefore, the flying wing structure needs to be much stiffer than tailed planes. It's a big design, with low weight and high stiffness, structure problem.

I think this is a mute point, since flying wings have a much lower AR than a conventional sailplane. They also have a much larger root cord, so structure is actually not a problem at all.

[Ollie]

djklein21,

Thanks!

I downloaded RCSD from 1/06 to 6/06 and Peter Wicks on Planks and I read them. I now interstand his great articles. I'm dropping my comments and dropping my design with sweep back thermal soarers and redo mydesign thermal soaring flying wing with a plank around a PW106 airfoil.

[rdwoebke]

I also wonder how well a Wing will signal lift when there is not extended tail to be moved. With a tail two feet behind the wing, you can see when the plane has been disturbed by the fuse angle. I wonder if you would notice this in a wing?

They signal lift well. I used to fly a lot of hand launch wings (Red Herring type).

I keep reading the RCSD articles by B Squared and think I need to build one of those models!

But then, I am kind of a non conformist. I flew my Gentle Lady in F3J.

Ryan

[Kai@UCSB]

TD contest is landing contest.
How about flying wing for Cross Conutry contest (low cost) or some other format ? :D

-Kai

[Buran]

I’ve built and flown a couple Klingberg 2-m built-up wings. They fly great. I think they would be competitive in contests but the landing task might be difficult; it’s no lawn dart. This is coming from a guy who thinks the use of skegs should be illegal. Anyway, these are great flying wings. It’s too bad Future Flight went out of business years ago. They show on ebay at times and I believe there is a Klingberg for sale in the sailplane sale forum on this site. I don’t know if it is the build-up or foam version.

[rdwoebke]

How about flying wing for Cross Conutry contest

Do you read RCSD? B Squared has what they call an "XC" Blackbird. It is about 100 inches in span, but due to the aspect ratio of that beast it has over 2000 sq inches of wing area. I'd expect you could see that model quite well far away.


Ryan

[Wind Shadow]

I for one, LOVE flying wings.... :D
Am an "old" hang glider pilot, nothing thrills like seeing a clean, high performance wing in the air, be it slope or TD.

But, IMHO you want to know why we REALLY see so few wings in TD comps? Not due to performance...Not even due to lack of yaw control(some wings I have seen with tip rudders would yaw nicely)....The main reason is the darn things are so hard to SEE! :eek:

Try thermaling your 3+ meter F3J ship from 500 yards away...it may be 'kinda hard(depending on your eyes) but very doable.

Now imagine trying to thermal that same ship with no fuse, no tail, probably less dihedral(maybe, humor me for a min)....It ain't no cakewalk folks!

From a side view, you only have a wee sliver of shape to see, and control.

I once was driving home after work one day, out of the corner of my eye, I see "SOMETHING" go hurtling by a couple of miles away...I thought for a couple of seconds I had SEEN THE MOTHER SHIP!! :censored:

Turns out, a well known military air show was taking place about 20 miles away, and I saw a side view of a real, honest to goodness B-2 Bomber.
I could barely get a bead on it, just a little sliver of dark color going by, no real shape, just a dark line.

And THAT dear friends, is why you do not, and probably will not, see much in the way of TD flying wings at comps...you understand? :)


Wind Shadow

[ChuckA]

:cool: Flying wings are invisible at normal thermaling distance. That's called stealth. Nice if you are trying to keep from being shot down but bad news if you need to see it. :)

[GLIDERGIDER]

Todd,
My opinion is that winching is more difficult to get correct due lack of yaw control. Plus the elevator is so closely coupled with the wing, as someone mentioned, when you use the elevator, you effectivley loose a chunk of the wings lifting ability.

Second reason is the landing task. I'm sure its been done, but the crow required to spot land would be a challenge to work out.

Keep in mind that my opinion is based on winch launching some 48 inch foamys, so forget what I just wrote.
Dave

[OVSS Boss]

Everyone is forgetting the Taborca, huge flying wing by EMS in Germany, a friend has one and it is cool, but would hate to program the radio to any degree of first flight certainty. Not like we have a main frame to try out the software first.

Marc

[BMatthews]

:cool: Flying wings are invisible at normal thermaling distance. That's called stealth. Nice if you are trying to keep from being shot down but bad news if you need to see it. :)

Not true. The generally wider chords make up for the lack of fuselage and they are just as visible at range as a regular model. Of course they still suffer when facing head on to the pilot but all designs do that.

GLiderguider, I'm not sure if you have flown any flying wings but the Windfreak of my buddy did not suffer from any of these ills. It was responsive and nice to fly both on the winch and in the air.

There's a trick you can do with the wings to avoid requireing up elevator while on the line. Move the hook back to the point that you do not require elevator at all or only a little down trim for the first part of the launch. That will avoid the need for up elevator and the added reflex. This is a commonly used trick for conventional models as well.

Like any design plank wings require that you trim and adjust to suit the model. They are different but they can do the job if you're willing to find the answers to what they require for trim and tricks. Regular models need the same attention to get the best out of them. It's just that we know what is needed for them since they are so common.

Most of the negatives seem to be coming from folks that have not flown a plank wing or that may have seen badly designed or badly trimmed ones fly. But there are some very effective flying wings out there. All they lack is someone with good flying skills to adopt them and make them win.

[screamin' eagle]

I fly a lot of slope and just had my eyes checked yesterday after my first trip to the TD field in years. I've gotten my 3m ships thermalling high up and far away on the slopes and have had trouble with orientation into the sun. I have a few planks/flying wing designs and orientation on those becomes nearly impossible when they're much closer in than that.

[rdwoebke]

I have a few planks/flying wing designs and orientation on those becomes nearly impossible when they're much closer in than that.

Do your planks/flying wings have the same wing area as your TD ships?

[screamin' eagle]

The planks likely have less wing area but the problem is when the ships are viewed in profile, where wing area doesn't matter. It's the lack of a boom and real tail that makes it very difficult. The wingspans are definitely smaller, and I noted that they disappear much further in - even compared to conventional ships of the same wingspan. This notion seems to be very widely accepted in the slope crowd.

[mdennis]

I recently built a large flying wing plane called a Mothership. It has an 82" wing span, (about 2M), and a massive wing area (1,440 sq in I think). I did not build it to be winch launched, but did make it so I could put a removable motor and battery pod on it.

http://www.rcgroups.com/forums/showthread.php?t=457992&highlight=mother+ship

It thermals very well. Lift signals are different than a conventional plane, but you can tell , (feel?), when it is going up. It kind of just elevates. It is very hard to see when in profile or edge on, but so are conventional planes. Sometimes you have to trust that it is still going the direction you aimed it and then bank the wings or pull up on the nose so you can see it. (Just like normal plane). I don't fly it any further out than I would a 2 meter plane though.

Like was suggested earlier. Go to RCSD online and look through past issues. The articles on flying wings are great and are as technical as you could ever want.

Mark

[Aio_1]

I think this is a mute point, since flying wings have a much lower AR than a conventional sailplane. They also have a much larger root cord, so structure is actually not a problem at all.
Thermal duration flying wings typically have similar aspect ratios to their conventional counterparts. They also tend to have very low taper ratios and in many cases have no taper at all. This is in order to maintain an elliptic lift distribution. So generally the root will be similar in chord to that of a conventional plane.

[Aio_1]

No one has mentioned that there is no trailing edge ( camber-reflex) control on a wing. In fact, on the winch, when you pull up elevater, the wing gets reflexed, lowering the CL of the wing.
There is no reason why you can't use flaps on a flying wing. You just have to design them a little more carefully since you'll want them pretty pitch neutral. Obviously an unswept wing can't have pitch neutral flaps but a swept wing can. Typically the aspect ratio would be over 10 and the sweep would be in the region of 20 degrees. This means that the trailing edge straddles the neutral point and so careful positioning of the flaps will cause them to have no effect in pitch. Ideally you want to have multiple control surfaces to mix flap/spoiler, elevator and aileron functions as efficiently as possible across the span.

When comparing a flying wing with a conventional plane you need to consider the entire plane not just the primary lifting surface. Remember that a standard configuration aeroplane has a tailplane to control pitch. This is additional area is included in the flying wing which offsets the wingloading effects mentioned earlier in the thread. Also the tailplane produces a downward force to pitch the glider nose-up which is comparable to the reduction of lift coefficient of a flying wing when a portion of the trailing edge is reflexed for the same purpose. The force tends to be higher for a swept wing since the moment-arm tends to be shorter however it's important to realise that there are comparable compromises for conventional configurations when looking at the plane as a whole.

Aidan

[jrgospod]

atjurhs,

Now that you have the design info of why you don’t see wings at TD contests, I will give you the other prospective on your original question.

The overwhelming majority people that fly TD are in it to score and not to enjoy the relaxed type of thermal flying you may associate with soaring. They are a very competitive group. That is why they most always use the MOM format. They want to even the field within a very narrow set of rules. They then try to push the letter of the rules to the extreme, This tends to make the contest a landing contest and a technology contest.

The skill of reading the indicators of lift to know when to launch is no longer a developed skill needed by the pilot because all pilots launch at the same time and in the same air. Being able to control the plane and have it come to rest on a spot landing is being diminished by the use of landing sags and composite designs that let you “spear” a landing. It is also no longer necessary to control the energy of the plane to the extent that you bring it to a stop (not spear) on a landing tape. Being able to read lift is also under fire by the use of onboard telemetry that will tell you if you are in lift (this is currently being reevaluated but I believe it is still allowed in most contests and at the NATS). To the credit of OVSSBOSS I think that OVSS is working to eliminate onboard lift sensor telemetry.

In that environment flying-wings are just not going to score well and hence you will not see them used much, if at all, at TD contests. The only people that you will see flying them are the ones that enjoy the design and flying something different. They are the pilots that don’t care about competition and winning. They enjoy a different aspect of the sport and are in most cases non-conformists.

John

[rdwoebke]

The skill of reading the indicators of lift to know when to launch is no longer a developed skill needed by the pilot because all pilots launch at the same time and in the same air.

At the most recent contest I attended (OVSS1 a MOM contest) I saw a number instances where pilots could have bettered thier scores had they been paying attention to pre-launch lift indicators. They would have went down wind right after launch rather than fooling around on field/up wind. So from that perspective, reading the air before launch is still an important skill.

I was also guilty of not minding the river of air on one or two instances. Life is a constant battle of learning and relearning old lessons.

Now to go re-read Buzzard and meditate...


Ryan

[GLIDERGIDER]

jrgospod:
Just last week we flew the Tullahoma TN contest. The landing circle was an "in-out" 25 point target. It was a 50 foot diameter. Even a GL can land in that size circle. It was fun.

The reason the flying wing is not widely embraced in the TD environment is because it's just not efficent. The weight of the fuse, using todays building materials, is nothing, but the long moment arm gives the pilot so much more control. Yes it helps greatly with the landing task, particularly because of the crow, which changes the pitch response of the airplane.

One of the reasons I like flying wings is because they are so robust, and that strength makes them perfect for the slope. If you made a TD flying wing using carbon, kevlar and fiberglass like an Icon, it would be plenty strong enough to withstand the spear type of landing. What it wouldn't have is the pitch control to negotiate a steep decent with flaps and ailerons hanging in all directions to slow it down.

There is nothing prettier then seeing an Icon on final decent in a 20 degree dive just crawling to its landing.

Speaking of efficency, look around at all of todays aircraft, the number of flying wings in full sized craft are so few that they don't even number a single percentage point. Only recently because of stealth, do we have the B2.

Bottom line, the efficency gained by a flying wing is not enough to make a builder give up the large tail moment for control authority. Unless of course you are on a slope, and there with unlimited lift, a flying wing is perfect.

[rdwoebke]

Speaking of efficency, look around at all of todays aircraft, the number of flying wings in full sized craft are so few that they don't even number a single percentage point. Only recently because of stealth, do we have the B2.

But there are several flying wing sailplanes, right? Like the Monarch, Pioneer, I think one called the Genesis. There have been articles on our flying wing full scale cousins in RCSD from time to time.

Ryan

[BMatthews]

But there are several flying wing sailplanes, right? Like the Monarch, Pioneer, I think one called the Genesis. There have been articles on our flying wing full scale cousins in RCSD from time to time.

Ryan

I'm afraid that for the most part I have to agree with GLIDERGIDER. The flying wing needs some serious work if it's to be more efficient than a conventional layout. The planes you mentioned are all homebuilts or close to it. None of them can match the L/D's of the super slippery latest standards.

[GLIDERGIDER]

Exploring this subject further, one can ask, why don't we see more Canard winged airplanes in real life and TD?

Canards with the forward mounted stabilizer in theory are more efficient then a conventional airplane.

It’s theoretical efficiency because both the wing and stab have lifting airfoils. Conversely, a conventional airplane's stabilizer has a downward acting wing load. That downward load just makes the airplane heavier. A heavy airplane has more drag.



So why don't we see the Canard airframe used more often? The answer again is efficiency. It turns out that the lifting vortex off a canards leading stabilizer disturbs the air over the main wing. That disturbance reduces the effectiveness of the wing and thus, the design community says it’s not worth it. The Wright Brothers tried it but finally gave up.

So, what looks good in theory doesn't always pan out in practice. Burt Rutan designed and kitted a canard airplane, but it too is no longer popular.

[jrgospod]

For all that are interested in the future look here!

The Shape of Wings to Come
Inspired by nature, aerospace engineers are striving for a more fluid way to control aircraft.

By Carl Hoffman | September 2003

__________________________________________________ __________


Here is the link to the POP-SI article:

http://www.popsci.com/popsci/aviationspace/7bed5b4a1db84010vgnvcm1000004eecbccdrcrd.html


John

P.S. Link updated, should be good now.

[Ollie]

I'd could put to work with 10 JR DS368 Premium Digital Servos at $70 each and a PCM 10X radio at $1250. Program the whole trailing edge for any flying task. Too, bad I can't budet $ or program the plane to work with test flying before risk.

[rpage53]

Canards with the forward mounted stabilizer in theory are more efficient then a conventional airplane.
Canards aren't more efficient. They mess up the air and kill lift on the main wing. They have other benefits though.
Conventional design isn't due to some conspiracy against innovation -- its the planform that works the best. Martin Hepperle did extensive work with flying wings but couldn't come up with one that was a winning design.
http://www.mh-aerotools.de/airfoils/foil_flyingwings.htm

Don Stackhouse also discusses canards and flying wings in detail. This is the most comprehensive of his posts.
http://www.djaerotech.com/dj_askjd/dj_questions/flywingtheory.html

If you like innovation, a flying wing in a contest will be fun and generate a lot of attention.

Rick.

[biber]

Right on, Rick, Canards aren't that what most people think they are.
And conventional models aren't either.
It's a big misunderstanding when everyone thinks the stab hast to downlift all the time,
in slow thermaling flight mode it does lift on close to every current model.
And that has nothing to do with the particular airfoil used on the stab.
From a flight dynamics standpoint there is no real difference between canard designs and conventional.
Merely the ratio of forward lifting surface to backward lifting surface is different.
For most applications the conventional ratio is definately better suited.

For tailless TD ships look here:
http://www.zanonia.de/aurora_evo.php

and here:
http://www.zanonia.de/thehump.php

biber

[RobinBennett]

Our club has a friendly duration competition for people who don't normally fly gliders. There's no requirement to land on time or at a specific point - just to fly for at least 20 minutes, using a cheap speed 400 and even cheaper batteries. We don't even have to fly on any particular day, just score 5 good flights over the season.

Could a flying wing be competitive? I don't expect to win and could sacrifice some performance for an easy build (and possibly storage, transport and setting up in the field )

I started a thread in the flying wings forum, but didn't get much interest:
http://www.rcgroups.com/forums/showthread.php?t=525959