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Building Tips and technical articles. => Building techniques => Topic started by: Dave Moritz on August 24, 2019, 11:31:42 AM
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What to do about 'em when building? I see some stunt models are equipped with very simple wing tips consisting of nothing more than just a rib running parallel to the fuselage. Others are tapered down in various fashions and look much better. (I'm not sure of the term, but is this called "wash-out"?) Is there a significant performance difference between the two designs in control line?
Dave Mo...
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No, that is not what "wash out" means! Wash-out means that the wings are twisted so that the tips are pointed slightly downward compared to the roots. It's done one aircraft that need to perform much better flying upright than upside down, and it is either done to avoid tip stalls, or to make a "hershey bar" wing oh so slightly more efficient.
Wash-out is undesirable on a stunt plane.
Tip shape doesn't have a huge impact on flight performance. There's some subtleties with how tip shape makes the plane handle in the wind which, frankly, I can't keep track of. Look at the shapes of tips on airplanes flown in the top 20 at the Nats, pick one you like, and run with it.
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Like Tim said, "wash out" or "washin" are free flight terms for trimming a model to turn in a thermal without stalling or spinning. NOT used in CLPA. Ever. n1
From what I have seen since 1948 and my first model, wing tips are like women, you like what you like. D>K
Washin and washout are full-scale aviation terms, too -- same twist, different reasons (one doesn't often trim a full scale plane for a smokin' hot climb followed by a slow glide, all without pilot input).
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No, that is not what "wash out" means! Wash-out means that the wings are twisted so that the tips are pointed slightly downward compared to the roots.
Wash-out is undesirable on a stunt plane.
Actually, "wash out" is when the trailing edge of the wing is twisted upward at the tip. Often employed on free flight models to delay tip stall. "Wash in" is when the trailing edge at the wing tip is twisted to a higher angle of incidence, promotes tip stalling and generally should be avoided with any kind of airplane, model or full size though wash in might be employed on a free flight model for certain issues with flight trim.
An interesting example of "wash out" is to examine the wing tip of the F-15. The wing tip airfoil is highly undercambered and normally is operating at a noticeable negative angle of attack (wash out). That wing tip does not start lifting until the aircraft is pulling several positive G's, as in a hard turn. It will not help much when pulling any negative G's, which most fighter planes do not try to do.
Like Tim suggested, CL stunt planes should avoid any kind of twist - period.
Keith
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Tim, Ty and Keith:
I like what's written here! So I can forget about another aviation term, and choose a tip design that fancies my eye. Many thanks for such timely responses.
Mo...
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Actually, "wash out" is when the wing is twisted upward at the tip.
Oh dangit, it's that free flighter vs. the rest of the world terminology difference. When you're building a free-flight wing you shim the trailing edge up to get wash-out. But that means that the angle of attack of the tip is down (which is what you find in the full-scale aeronautical texts).
I'm not going to say I'm backwards, here, but if open my mouth at a free-flight field I'll try to get it right...
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Tim, Ty and Keith:
I like what's written here! So I can forget about another aviation term, and choose a tip design that fancies my eye. Many thanks for such timely responses.
Mo...
Yes.
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Oh dangit, it's that free flighter vs. the rest of the world terminology difference. When you're building a free-flight wing you shim the trailing edge up to get wash-out. But that means that the angle of attack of the tip is down (which is what you find in the full-scale aeronautical texts).
I'm not going to say I'm backwards, here, but if open my mouth at a free-flight field I'll try to get it right...
The terms "wash out" and "wash in" apply the same in full size aviation as well as model airplanes, including free flight model airplanes.
Keith
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Wingtips? LL~
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For a while, there was a certain segment of the stunt "guru club" advocating tips which had taper, front to rear, similar to the Flite Streak. No good scientific explanation was given, except that it was "better".
I design wingtips to complement the overall design lines. Some round. Some elliptical, some just squared.
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For a while, there was a certain segment of the stunt "guru club" advocating tips which had taper, front to rear, similar to the Flite Streak. No good scientific explanation was given, except that it was "better".
Which parts of Ted's "Imitation" article are you disputing?
Brett
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"Actually, "wash out" is when the wing is twisted upward at the tip."
To make this as easy as possible to understand,
Washout:
The root airfoil is at a greater angle of attack than the tip airfoil.
So, the root could be designed to be at a positive "2" degrees and the tip could have a positive "1" degree or "0".
Best explanation I can do as a washed up former commercial pilot. n~
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Make your wing tips like the SV 11 or Pathfinder. Randy Smith says it's better.
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Make your wing tips like the SV 11 or Pathfinder. Randy Smith says it's better.
Everything I have designed since 1965 has had swept tips. I have no idea if they are actually better, I just think they are and they look cool.
Ken
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I think "looks cool" is the operative phrase. Just as some like the "jet look", where the canopy is 1/2" behind the propellor. On a real plane, I wouldn't want to be that close to the prop.
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For a while, there was a certain segment of the stunt "guru club" advocating tips which had taper, front to rear, similar to the Flite Streak. No good scientific explanation was given, except that it was "better".
I design wingtips to complement the overall design lines. Some round. Some elliptical, some just squared.
I'm with you Floyd. At our Renolds numbers it doesn't matter...... We need the DRAG in the vertlcal portion of out maneuvers anyway.
Jerry
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Swept back wingtips, like "Flite Streak", were widely discussed on this forum.
I do not attribute this idea to any particular person.