Those bird wings

[HELModels]

You know the birds, firebird, aerobird, fighterbird, any bird like v-tail pushers. Some are better than others. My question is about the wings: Are most of these just a camber with almost no thickness, or do some have an actual aerodynamic thickness distribution around a mean camber? Or, do they just mold the top of some wing and call it good?

The slow stick is another example of what I believe are camber only wings, but not sure if they are or not.

I'm asking these questions beause I bought a clearance wing from LHS and stuck it on my v-tail pusher pod boom. I initially had too much incidence but adjusted that and the thrust angle and got some very good results. The bird wing is an increase in wing area and span, so my loading went down and the AR went up. My initial design used a polyhedral wing which was very responsive to rudder, almost too responsive. This bird wing has dihedral but alot less than my initial design and has taper. Rudder sensitivity went down with the new wing, but stability is a bit better. Does a LE taper lke these wings have provide a dihedral effect, so they dont need as much as a straight taper wing?

[JetPlaneFlyer]

In answer to your last point... Wing sweep back does have a dihedral like effect. Very roughly 5 degrees of sweep would be similar to 1 degree of dihedral. Sweep should be measured on the mean chord line, not on the LE, but a wing with a 'straight' TE and a 'swept' LE will have a little overall sweep back. Probably it would be worth no more than a degree of dihedral.

[HELModels]

Thanks, when I look at the wing I can see that the highpoint on the wing sweeps back, quite a bit more than 5 degrees. There seems to be some thought behind these aerobird wings and short of making a mold of it, I would like to make use of it's good points. The planform is nice looking.

[HELModels]

In answer to your last point... Wing sweep back does have a dihedral like effect. Very roughly 5 degrees of sweep would be similar to 1 degree of dihedral. Sweep should be measured on the mean chord line, not on the LE, but a wing with a 'straight' TE and a 'swept' LE will have a little overall sweep back. Probably it would be worth no more than a degree of dihedral.

These aerobirds and mine also have V-tails, do swept wings have any effect on adverse yaw or is the lack of adverse yaw because of the v-tail? I'm trying to figure where are the improvements over my original wing.

So far, the difference is higher AR, more span, swept LE, seemingly less dihedral, reduced wing loading for same weight. Neither configuration has adverse yaw.

[JetPlaneFlyer]

What do you mean by adverse yaw?...

Adverse yaw (http://en.wikipedia.org/wiki/Adverse_yaw) is something that occurs on aircraft with Ailerons whereby the downgoing aileron creates extra drag which yaws the aircraft in the opposite direction to the intended turn.... I get the feeling this is not what you are talking about? If this is what you are referring to then either a ‘V’ tail or swept wings should have much influence on it.

[HELModels]

I actually mean uncoordinated turns, not adverse yaw, I guess. If you dont have enough dihedral and try to turn, you only get a skid with no bank. You might see the same thing on a plane with ailerons if you try to turn without using the ailerons. I tried a third wing a while ago and it definitely was too flat an trying to turn was ugly.

Anyway, neither configuration has any trouble making a smooth turn. I had it out flying about an hour ago and also noticed it had no tip stall tendencies even without washout. I caught some small lift and banked it steep and slow and nothing but goodness resulted.

I want to know what makes this wing good.

[HELModels]

This is somewhat funny actually. I read up on the aerobird and found some specs like wing loading, length, weight, etc. I also watched video of a real aerobird in flight. They push these planes as being great for begginers and with a wingloading of 14 oz./sq ft as they are sold, this could be a handful. In the video you can see a factory bird swooping and diving and generally fighting to stay airborn. My version has a wingloading of 8 oz./sq ft. and is probably more what that wing designer had in mind.

[HELModels]

The thing about this wing that is amusing is that for $10.00 I got a good flying plane and had I paid $150.00 for the real thing, I would have had an overloaded pig.

The original intent of this thread was to try to get some learned analysis of an aerobird wing to try to understand it's features. So, I will restate the question:

From an aerodynamic perspective, what is good about the aerobird wing?

[JetPlaneFlyer]

I don’t think that there is anything 'magical' about the aerobird wing design. I guess it's good flying characteristics come from the high aspect ratio plus thin wing section (very thin section with moderate camber is best for models of this type operating as they are at low Reynolds numbers)... You will see generally similar designs on most 'hi efficiency' model wings.

[Murocflyer]

In answer to your last point... Wing sweep back does have a dihedral like effect. Very roughly 5 degrees of sweep would be similar to 1 degree of dihedral. Sweep should be measured on the mean chord line, not on the LE, but a wing with a 'straight' TE and a 'swept' LE will have a little overall sweep back. Probably it would be worth no more than a degree of dihedral.

This is good to know. Thanks.

I'm thinking 5 degrees to get 1 degree, would the 1 degree really amount to much?

Frank

[JetPlaneFlyer]

This is good to know. Thanks.

I'm thinking 5 degrees to get 1 degree, would the 1 degree really amount to much?

Frank

No, 5 degrees of sweep giving about one degree of 'dihedral effect' is not really significant... Where it really does start to show is in swept wing jets that have 30 - 45 degree sweep. You quite often see full size swept wing jets with anhedral to prevent them from being too stable due to the dihedral effect of all that the wing sweep.

Swept forward wings on the other hand have a negative dihedral (anhedral)effect.

[Murocflyer]

I see, thanks.

Frank

[HELModels]

I've been flying and studying this wing some more. It needs a bit more dihedral in wind, does great in no wind. As soon as it gets gusty, I yearn for the excessive polyhedral the old wing had.

I say I've been studying the wing and it seems some of it's features are a result of manufacturing. The trailing edge is thin but there is a thickening right before the edge, so the shape there doesnt seem optimum.

I might just go ahead and pick a really thin foil and see what I can build. Any recommendations on a camber and thickness to rival an aerobird style wing?

[HELModels]

I take it back, just flew in 17 MPH winds gusting to 20. This wing does fine in wind, it is the motor that needs more ummph. Full power and I was hovering in one spot and the rudder was completely authoritative. I did find myself pumping alot of down elevator as the wind would gust. I would find a comfortable spot and just kind of oscillate left right and then bam a gust would hit and I needed lots of down or it would shoot up vertical. I let it do that a few times just for altitude and kicks.

Anyway, any complaints about the aerobird family not having enough control authority are not because of the wing itself. That should be obvious and is, my version is an improvement, nonetheless.

Still, if I were to build my own wing, I would probably pick an airfoil with about 7% camber. To get the thickness right would be tough without using the same material and equipment.

Anyone, recommendations?

[Ollie]

The problem is structural. With these wings, with high aspect ratio, they need bending stiffness and bending strength. The simple answer is a sandwich the foam with 0.003" carbon, top and bottom.
See:
http://www.deltronix.net/cgi/acp_display.exe
CLX--, !.5" width at the root and tapered to zero at the tip.

[HELModels]

The problem is structural. With these wings, with high aspect ratio, they need bending stiffness and bending strength. .

You dont know how right you are about that Ollie, so I will tell you.

I went out today wind about 10-14 MPH but was from due west, same as the sun. I figured I could get up and then fly to avoid the fire ball...The last I saw of it was flying straight and level and then I was blind and could only hear the RPM's picking up. I cut throttle and heard the pop. I was so blinded by the sun that I could not find all the parts like the motor. Nothing but swirls of yellow burned into my eyes. As my retinal response returned to normal I managed to find the motor and the 2 pieces of wing and made the walk.

Actually, smacking into the ground is tough on most structures. It did give me a look at the wing profile and it looks very much like a NACA 73xx mean line. If I had to guess, I would guess the xx part is less than 4 % and more than 2%.

[HELModels]

I decided a picture would say it all.

[HELModels]

Gorilla Glue to the rescue. Literally stronger than new.

[HELModels]

This thing is begging for a good slope and some strong wind, but I dont know where to take it around here. Anyway, I like the way it flies now and I've added two wing bolts, so the rubber bands are only to hold the motor on. The plan is to make a mount which will bolt to the wing. This will reduce drag further and probably make the motor and prop more effective.

The question now is mainly ethetic, but there might be more aerodynamic reasons for the shape I am using. Maybe someone can answer.

I dont like the aerobird tail, besides not having one to use, because the movable surface is too small. Some modify that tail so that the surface is full span. What I dont like about that and it is quite common to see, is that the moving surface goes into the vortex. Mine is semi elliptical and only a very small part of the elevator might touch the vortex.

So, here is the question:

Is an elliptical tail, where the elevator portion doesnt go right out to edge of the tail, less draggy? You can see the shape in one picture above.

[HELModels]

I guess it doesnt matter when the wind is 25 gusting to 30, as it was today. I should have quit when I was ahead. The hill I fly on gets some wind driven lift and I took it there today and was doing fine and even gained some altitude at zero throttle...then the monster gust hit. I went from 0 ground speed to about 80 and was headed for the highway. I managed to get the nose into the wind and then it got tossed again, so I just forced it into the ground. This broke the tail off the boom and threw the motor into the mud. If I could have kept the nose into the wind then I would have flown through the gust and hopefully had the judgement to land.

So, aerodynamically clean tail shape or not, 25-30 mph is beyond this plane and pilot. 15 mph is fun when not directly into el sol.

[HELModels]

Sorry, this has become a blog, but what a difference a day makes. Winds were WNW 10 and very easy to handle, plus lots of lift. Winter doesnt mean no lift even while snowing, as it did today.


Anyway, I'm going to use my own ideas on tip shapes and save my posts for the blog area.

[JetPlaneFlyer]

So, here is the question:

Is an elliptical tail, where the elevator portion doesnt go right out to edge of the tail, less draggy? You can see the shape in one picture above.

Theoretically an elliptical planform wing (or tail) is most efficient... However in the 'real world' the difference would be so slight over a conventional tapered planform, that it is undetectable. Also for use on a wing the elliptical planform can result in undesirable stall characteristics. For the tail, stall behaviour is not really an issue, so if you think elliptical looks nice then go for it, but don’t expect any performance change.

Stopping the control surfaces short of the tip is i believe primarily to avoid control surface flutter which can be a problem on some fast flying models, though in my experience it's a problem with Ailerons, not elevators. There would be no significant reduction in drag by stopping short of the tip.