Aerodynamics Discuss the concepts of aerodynamics here

I really don't understand wing shape.

Old 03-05-2015, 10:16 PM
  #26  
theapplepi3.14
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Originally Posted by JetPlaneFlyer View Post
Washout can be seen on many WWI and earlier aircraft.

To be honest 3D planes don't really brake any 'rules'. They are just lighter, have better thrust/weight ratio and have much larger control surfaces than the typical aerobatic model. You wouldn't find washout used on 3D models just because they need to fly well inverted. There again you wouldn't find washout on a traditional aerobatic pattern model either (for the same reason).
They also are designed to not really have a side that is "up" so that they handle the same in all orientations right?. You can also control them even well beyond "stall"(it is a lie!)
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Old 03-05-2015, 11:01 PM
  #27  
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Originally Posted by theapplepi3.14 View Post
They also are designed to not really have a side that is "up" so that they handle the same in all orientations right?. You can also control them even well beyond "stall"(it is a lie!)
That's all true, you can control them beyond a stall. But they don't use any special 'tricks' to do it... just large control surfaces, lots of thrust and light wing loading.

Pretty much all 'full house' aerobatic models are designed to fly the same upright and inverted, that's nothing special or unique to 3D models.
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Old 03-05-2015, 11:04 PM
  #28  
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Some washout was used by the Wright Brothers. They figured that trick out using their kite-prototype models."
You can get an aerodynamic washout effect that works upright and inverted by changing the wing rib from root to tip.
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Old 03-05-2015, 11:11 PM
  #29  
JetPlaneFlyer
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Originally Posted by fhhuber View Post
You can get an aerodynamic washout effect that works upright and inverted by changing the wing rib from root to tip.
That (decreasing camber toward the tip) still only works the normal way up.

You can use a sharp leading edge near the root and a more rounded leading edge near the tip to help prevent tip stall, not really the same as washout but it does work, and that does work either way up.
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Old 03-05-2015, 11:15 PM
  #30  
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That only warns you of one cause of stall
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Old 03-05-2015, 11:57 PM
  #31  
fhhuber
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Change the thickness % of a symmetrical airfoil and you can get aerodynamic washout with a symmetrical airfoil.

A really quick proof is the change of stall characteristic just by changing the leading edge. Round it more at the tips and have it come to a sharp edge at the root and you will have it stall first at the root.
Works every time. This is a fix for the bad stall characteristic of a few old aircraft that didn't use washout.
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Old 03-06-2015, 12:10 AM
  #32  
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I think by studying the Boeing 787 Dreamliner's wing we could find out the answer to any wing based question we ever had! lol! It is so complicated!
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Old 03-06-2015, 12:24 AM
  #33  
fhhuber
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Actually... no.

The Dreamliner wing is purpose built for payload and efficiency in passenger/cargo carrying over long distances above 18,000 ft.

There are better wings for speed or heavy lift at low altitude or aerobatics....
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Old 03-06-2015, 01:03 AM
  #34  
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I didn't mean you should copy the airfoil! Sorry. I should have been more specific. I meant that they use so many techniques that if you understood the rational behind everything they did to make the wing you could use that knowlege to design really great wings. Basically I was saying that the wing is a hard copy of knowlege (if you know how to use it). I agree with you. The specifics of the wing are not useful for Rc, just the design principals. Lol. Sorry about the confusion!
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Old 03-06-2015, 02:18 AM
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Originally Posted by theapplepi3.14 View Post
I think by studying the Boeing 787 Dreamliner's wing we could find out the answer to any wing based question we ever had! lol! It is so complicated!
Sure, and we could all spend our time here trying to "out-think" the room too..........
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Old 03-06-2015, 03:45 AM
  #36  
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Originally Posted by pizzano View Post
Sure, and we could all spend our time here trying to "out-think" the room too..........
lol?
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Old 03-06-2015, 06:47 AM
  #37  
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Originally Posted by fhhuber View Post
Change the thickness % of a symmetrical airfoil and you can get aerodynamic washout with a symmetrical airfoil.
No you don't really. Washout is when you change the lift coefficient distribution along a wing (reducing to the tip). Changing the thickness of a symmetrical airfoil doesn't do that because the lift slope gradient remains unchanged due to thickness so the lift coefficient is the same.

What this can do (and more rounded vs sharper leading edges) is alter the critical AoA of the wing causing the root to stall first, thus avoiding tip stall, but it's not washout.
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Old 03-06-2015, 06:49 AM
  #38  
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Originally Posted by theapplepi3.14 View Post
That only warns you of one cause of stall
No, it doesn't 'warn you' it helps prevent a stall starting at the tips, which was what we were talking about.

Stall horns and stick shakers 'warn you'.
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Old 03-06-2015, 11:41 AM
  #39  
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I wonder how many of the 'features' of a Dreamliner's wing (or any other modern airliner come to that) actually work in the same way (or to the same degree) at model sizes?
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Old 03-06-2015, 12:33 PM
  #40  
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Originally Posted by quorneng View Post
I wonder how many of the 'features' of a Dreamliner's wing (or any other modern airliner come to that) actually work in the same way (or to the same degree) at model sizes?

Very few.

There are significant factors of scale and related to the desired airspeed range of the aircraft.

Dreamliner stalls above the top speed of most of our models.
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Old 03-06-2015, 07:00 PM
  #41  
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Originally Posted by JetPlaneFlyer View Post
No, it doesn't 'warn you' it helps prevent a stall starting at the tips, which was what we were talking about.

Stall horns and stick shakers 'warn you'.
I was not referring to the wing design you had talked about, I was referring to the gps ground speed stall indicator.
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Old 03-06-2015, 07:57 PM
  #42  
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GPS ground speed has little to nothing to do with predicting stall unless you are in level flight and there's no wind.

If there's 10 mph tailwind that GPS is possibly going to say you are fine all the way into the dirt.
If you put the plane into a common "gentle" banked turn you might be pulling 2 to 4 G. (there's rarely anything gentle about how we fly our planes) As G goes up so does the airspeed required to prevent stall.

The Pitot tube based airspeed indicators would be better...but would still need the pilot to understand that any stall speed warning setting is going to only be good for while in level flight or doing the gentlest of maneuvers.

Full scale stall sensors work based on sensing the airflow starting to break up... and they can fail to give warning if you make a sudden maneuver.
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Old 03-06-2015, 08:46 PM
  #43  
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I know this. I did not agree with the gps idea! you are right. the best way is to sense air breakup, not to predict it.
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Old 03-06-2015, 10:37 PM
  #44  
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Wow. This thread is back from the dead with a vengeance!
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