Treefeller wrote:

Yellowbelly wrote:The good old Hersey Bar wing, besides being simple to build, stalls at the wing roots first and progresses outboard and forward as we become more stupid and ignore the buffet. It can fly with the whole center section of the wing stalled and still have the ailerons doing their job.

Is that a function of the chord though? Or the washout that's built into the wing? I think you can build washout into any wing chord profile and achieve the desirable effect of root stalling first, tip stalling later to retain aileron effectiveness. Will the hershey bar have that characteristic on its own without washout?

My original question was mostly in regard to the type of flying we enjoy-- bushplanes. I'd forgotten about the Bushhawk.

I wonder what the actual measurable speed envelope difference is between 3 wings of equivalent span, but each having a different chord profile-- straight, semi tapered, and fully tapered.

You are correct. wash out is usually built into a traditional "Hershey" bar ,constant cord, constant camber. Some designs use stall strips instead of wash out to promote premature stalling of the inboard section. The taper wing modify stall characteristics by way of a sectional progressively increasing aspect ratio (taper). The wider chord inboard section stalls first, where as the shorter cord outboard has less induced drag and stalls at a slower speed. The supposed benefit is higher cruise due to less drag at higher speed. But then there is the old adage for stol performance, and that is,there is no replacement for displacement. That goes for horses as well as wing area. What is meant by the later, is a wing is much like a boat, only that a boat displays static (displacement) buoyancy. The wing in a much rarefied medium depends on dynamic buoyancy and if slow speed and climb is the mission then wing area is the jewel. But at a cost.
Unfortunately physics do not allow one to have the cake and eat it too.

I believe the Cessna tapered wing (170A onward) has washout built into it.
As far as other tapered chord wings, I have seen a DeHavilland Beaver with a custom tapered chord wing. I don't know if it was an attempt for better STOL capabilities, more speed, or just a solution in search of a problem.

Treefeller wrote:................I wonder what the actual measurable speed envelope difference is between 3 wings of equivalent span, but each having a different chord profile-- straight, semi tapered, and fully tapered.

I think the comparison should be between wings of the same area (square footage) with different chords & spans. For example, a Pacer wing & a C150 wing have very simlar areas (160 or so sq ft), but different spans (29' vs 33'). There's even more difference in area & span if the Pacer had short tips like a Cessna instead of the long round tips that add area & span withouth doing much for lift.

One of the most beautiful wings ever built is on the "Gullwing" Stinson...but it's pretty much a slug, especially when compared to any of the "straight wing" Stinsons, such as the SR-5 or SR-6.
I'd say that the ease of building is the biggest factor... look at a straight wing...basically the same rib from root to tip. It doesn't matter if you're homebuilding or production building, one mold/form is much more economical than a whole bunch of different ones.
John

hotrod150 wrote:I believe the Cessna tapered wing (170A onward) has washout built into it.
As far as other tapered chord wings, I have seen a DeHavilland Beaver with a custom tapered chord wing. I don't know if it was an attempt for better STOL capabilities, more speed, or just a solution in search of a problem.

That was likely a Barron wing. Supposedly better turning and stall characteristics. Never flown one, but never had a problem with the stock wing....

MTV

Treefeller wrote:Is that a function of the chord though? Or the washout that's built into the wing? I think you can build washout into any wing chord profile and achieve the desirable effect of root stalling first, tip stalling later to retain aileron effectiveness. Will the hershey bar have that characteristic on its own without washout?

Yeah, the rectangular planform wing has the good stall characteristics intrinsically, without washout. If you taper a wing, or part of it, you are reducing the mean (average) chord length. This increases the aspect ratio of the wing so you get less induced drag, but you screw up the pattern of the stall progression, so you twist in some washout, or change the airfoil section as you move outboard to one that's more favorable. Twisting, blending airfoils, variable rib sizes... it all makes the wing a lot harder to build and the advantages probably end up being minimal at the kind of speeds our bush planes fly.

Even rectangular wings GENERALLY have some washout to ensure good predictable stall characteristics....as in the Cub wing..

MTV

Seems like for ease of building, a flat wing with no washout would be the way to go. For proper stalling sequence, add stall strips at the root end and/or VG's or leading edge device(s) in front of the ailerons.

It's just as easy to build a wing with wash as it is without. Just takes a jig or table, which is necessary for a flat wing anyway.

MTV

mtv wrote:It's just as easy to build a wing with wash as it is without. Just takes a jig or table, which is necessary for a flat wing anyway.

MTV

It's actually far more practical to build a wing with washout than it is to build one without washout.

Imagine your angle tolerance is +/- 1/10 of a degree on the twist (a reasonable tolerance band) for a wing that doesn't incorporate twist, and you end up with the left wing twisted positive 1/10 degree from root to tip and right wing negative 1/10 degree from root to tip, your airplane will be inclined to stall from the tip inboard on the left wing and the right wing will stall from root to tip. This is a very unfavorable situation.

If you have the same deviations from nominal in a wing with 1/2 degree washout, though one wing will stall slightly ahead of the other in a coordinated wings level stall, both wings will stall from root to tip, allowing roll control through the stall.

Having worked in building construction all my life, I think it is way easier & quicker to build just about anything flat straight and/or level than to build the same thing twisted curved or otherwise out of whack.

Sidebar: How is washout measured when rigging a rag and tube wing? Distance/altitude above a level surface? A jig? The washout is held by tensioned X-cables, right? I've never had the opportunity to look inside a rag wing.

The ultralights that I have helped build in the past had a king post with cables radiating out to various points on top of the wing, and the same underneath the wing. These cables were tensioned like spokes in a bicycle wheel to rig the wing.

The Cessna wing (looks cooler than any other wing in my opinion) has its washout fixed in, it cannot be altered. The only thing that can be adjusted is the eccentric bushing at the trailing edge carrythrough spar attach point, which lets one rig the root AOI, but nothing in the wing itself can be adjusted except for the neutral droop of the ailerons.

Zzz wrote:Sidebar: How is washout measured when rigging a rag and tube wing? Distance/altitude above a level surface? A jig? The washout is held by tensioned X-cables, right? I've never had the opportunity to look inside a rag wing.

The ultralights that I have helped build in the past had a king post with cables radiating out to various points on top of the wing, and the same underneath the wing. These cables were tensioned like spokes in a bicycle wheel to rig the wing.

The Cessna wing (looks cooler than any other wing in my opinion) has its washout fixed in, it cannot be altered. The only thing that can be adjusted is the eccentric bushing at the trailing edge carrythrough spar attach point, which lets one rig the root AOI, but nothing in the wing itself can be adjusted except for the neutral droop of the ailerons.

The twist is typically built in to the wing jig. Once holes are match drilled and rivets are driven in an all-metal wing, it's practically impossible to alter the twist of the riveted assembly.

With rag-wings, the torque cell formed by the leading edge skin and the ribs is usually stiff enough in torsion to retain a lot of the dimensional stability introduced in the jigging, but with independently adjustable forward and aft lift struts, you can tweak the twist some after the wing is installed.

On either the rag and tube or the metal winged planes that have two struts, the rear strut is used to adjust the washout and the front strut adjusted only when changing the dihedral. Normally the fuselage is leveled at the cabin floor or lower door frame or other reference point, depending on manufacturer's recommendation. The level can then be moved to the outer most wing rib and laid from front spar to rear spar while measuring the gap from the point of level to the bottom of the wing at the rear spar. The gap is adjusted by lengthening or shortening the length of the rear strut clevis at the fuselage/strut attachment point. Specifically, on my Tundra, with one degree of washout an 11/16 inch block can just be slid between the trailing end of the level and bottom of the wing at the outer rib at the rear spar. It should then read level from the front spar to the rear spar. The rear spar of the wing at the outer rib ends up being 11/16 inch higher than at the front spar making for a flatter angle and delayed stall for the tip.
The CNC punched holes are pre located in the wing skin to include the washout of one degree but fine tuning of hands off flight may call for this adjustment if there is a slight roll to be adjusted out.