Can Dihedral wing Angle negate the need for Ailerons

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Riggerrob

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My answer is no, not really. Perhaps the question is why would an aircraft want to have no direct means of roll attitude control? I trained as a flying qualities engineer and can't see any reason why a designer would willingly give up the best roll control device we have invented in favour of using the secondary effect of the yaw control!! Although an ultralight might want to save weight, giving up the ability to operate in anything other than pretty calm conditions is a compromise too far for me. Birds just use a different systems, many have swing wings or can vary wing area - we don't have a weight efficient means to do that!! Increasing dihedral angle will make the aircraft want to fly in a straight line, requiring a more and more aggressive yaw to roll the aircraft (or larger and larger ailerons or slower roll rates). Properly designed ailerons just makes any aeroplane much more enjoyable to fly... Why else do we fly recreational aircraft?
Some designers (e.g. Henri Mignet's Flying Fleas) want to build the simplest possible airframe. Simple reduces cost and time of construction. Simple also means fewer controls for a student pilot to learn.
As others have pointed out, as long as you keep wing-loading light and landing speeds slow (e.g. SkyPup), cross-wind landings can easily be converted into diagonal landing on existing grass runways.
 

Lucky Dog

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Lower airspeed is where theory and reality often clash. A reasonably experienced two-axis Quicksilver pilot can fly in buffeting weather. Hang glider pilots must fly in windy conditions with weight-shift alone, which reacts more quickly than hinged flight controls. I've flown both and once you get a feel for your turn entries, it's a no brainer. The standard flight regime where two axis creates a compromise is cross-wind landings, but even that might be solved with spring-loaded castering wheels ala Ercoupe. I've often wondered if splitting the elevator and mixing the "elevons" to augment roll control would be a feasible solution for a short span aircraft. Worth a try?

The only practical dihedral/two-axis benefits I can imagine, though, would be very simple, quick-detachable wings - and, provided that you had trimmed your elevator, if you fell asleep at the controls, your airplane could fly itself until nap time was over. Dihedral might be aviation's least expensive autopilot. :cool:
 
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Gregory Perkins

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I know if you were in a deep stall in a high dihedral 2 axis plane that you could initiate some twirling behavior
( spin? ) by kicking in full rudder but it likely would straighten out by itself if you let go of the controls.
A deep stall in a weedhopper was much like parachuting down and it was extremely easy to keep the wings
level ie. "do nothing" . I am trying to recall if there were any dangerous circumstances... I would think
a high speed hi banked departure stall while kicking in a lot of inappropriate rudder would be attention
getting but it all might level out by just letting go of the controls. I dont know. I never assumed my
plane was aerobatic.
 

Aesquire

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And then there's the other version of 2 axis control used by weight shift trikes/hang gliders, with weight shift for pitch, and weight shift initiating wing warping for roll control. Yaw is "automatic" by sweep and lift distribution.

The downside of that is you don't have separate yaw control, so you don't sideslip in a relatively straight line for glidepath control. And zero & negative Gs are a Problem.

And then there's the Other, other version of 2 axis control, with "brakes" on paragliders/ppgs/ram air parachutes, that pull differential "down only" elevon control for roll & yaw... There's some pitch input too, but that mostly gets damped by pendulum effects, to the extent you can pull both brakes on takeoff, to increase camber and lift. ( and drag...TANSTAAFL ) Things get weirdly coupled compared to "regular airplanes" when you do steep turns & wingovers, as the pitch stability and pendulum swing interact. As you bleed energy, the wing "wants to" nose down and recover it. If you use that in a sequence of turns, it can get acrobatic with high G loads. Including loops and barrel rolls.

But not classic 4+ point rolls.... that soft connection with the wing.... And there's some weight shift roll control too.
One major Error you can make in paraglider/etc. types is to stall & swing & make the wing surge ahead, which means you can actually find yourself in a ballistic arc into your own wing which loses tension in the suspension lines, and wraps you in a tangle of high strength synthetic fabric, lines, and the aerodynamics of a rock thrown through a handkerchief. ( and not enough drag to substantially improve the impact )

That's not to say recovering from an inverted stall in a modern hang glider isn't a significant emotional event.

We carry reserve chutes for Reasons.
 

TFF

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First, if everyone should go build an old fashioned Sig Kadet II. Get second wing kit and build one no ailerons and one with. I drag one out once in a while with no ailerons and have a ball. Not my first RE plane for sure, but they will teach you a lot of all around functional flight.

Not rudder only, but the Ercoupe is two control plane with rudder and ailerons linked. Easy to fly but not at the same time. An issue comes about then your reflexes taught three axis is limited to two. Normal Crosswind landings have you cross the controls to go straight. Ailerons turn into the wind usually and rudder to compensate and make it not a turn. Net direction is down the runway for a cross wind landing. Two controls leave you without compensation. Lots of Ercoupe landings accidents because the right frame of mind is not applied that you can’t do it standard. Plane not bad, that way to fly is not standard.
 

Riggerrob

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"
... I've often wondered if splitting the elevator and mixing the "elevons" to augment roll control would be a feasible solution for a short span aircarft. Worth a try? ...
"

I have worked on an airplane that used differential elevators to supplement roll control. Mind you, CF-18 has vastly more thrust and hydraulic power than typical light airplanes. CF-18 elevons are half the span of the main wing. They are so huge because the tail moment arm is severly shortened to satisfy supersonic aerodynamics.
While both the F-16 and F-18 have fly-by wire systems an F-16 loses control when his (triple-redundant or quadruple-redundant) electronics quit.
OTOH If all three FBW channels fail on an F-18, it reverts to stick-only hydraulic control and that only manipulates the huge, full-flying elevons. So a hydraulics-only F-18 pilot can still change pitch with elevons and roll by applying differential elevons. Theoretically this allows the poor pilot to recover with only hydraulics. Rumor has it that only a single Canadian pilot has landed a CF-18 with failed electronics. Keep in mind that the runway at Canadian Forces Base Cold Lake is 11,000 feet long.
 

wanttobuild

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Such fond memories of Cold Lake!
I loaded a heat exchanger in North Carolina destined for cold lake, enroute I loaded a generator in Danville, ky destined for Vancouver, bc.
delivered the generator, over the Canadian rockies to cold lake, unloaded the heat exchanger.
Loaded 2 Air Force blazers in cold lake destined to Las Vegas. $22,000
 

bmcj

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On the theory that no one should be flying ultralights if there is any significant wind.
I’ve successfully flown 2-axis Quicksilvers during Santa Ana winds. The solution to crosswind was simply to land across the runway into the wind.
My answer is no, not really. Perhaps the question is why would an aircraft want to have no direct means of roll attitude control?
I agree with you, but 2-axis can work and it’s simple and light. Also remember that while a rudder can impart roll, ailerons can impart some yaw too. I have flown some 3-axis ultralights with ailerons, but the ailerons were not designed well. At the slow speeds the ultralights fly, I have found that dihedral and a big rudder can sometimes be more effective than ailerons.
 

Eddie Clark

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Back in 1995 or 96, I headed up an RC, high wing scaled up version of an old free flight model called a Quaker. when the radio tec. allowed for small servos, guys stated to fly them with rudder, aileron only. they were very easy to fly, and made great RC trainers. We decided to build a times 5 replica with a half VW engine in it like used in some small aircraft. It looks similar to a Cub. the model has about 5Deg. dihedral. Due to the size, we decided to go with 3. It weighed 406
LB's and was very easy to fly. We could do loops, roles, spins and slow roles with it with no problem. But, response time was, 1-2-3-4 5 and wait. If you have ever been to Triple Tree Aerodrome. It hangs in the main hanger. It is still flyable. Many non pilots from all over the world have flown it in the air. Eddie Clark.
 

Dav-h12

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I don't think the bird example is directly relevant to an airplane without ailerons. Birds warp their wings differentially to produce roll. One wing then has higher camber and lift, so the bird rolls. Some airplanes (including early ones built by the Wright brothers) also used this wing warping to produce roll. Now, most planes use ailerons instead to produce different camber and lift, because it is simpler, but it achieves the same thing as avian wing warping.
Just a reference of dihedral angle…that birds can change at will.
 

Dav-h12

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The post was due to my curiosity watching birds (change dihedral across their wings) and seen one ultralight some years ago with no ailerons and some pilots were real up nosed about it while other pilots thought it to be interesting.
The bird photo referenced inflight dihedral changes and tactile feedback that they feel and adjust for. There has been more the one engineer/pilots who perished after their design failed… the Bonney Gull specifically….an engineer/pilot trained by the Wright brothers who designed his own plane after bird wings and lawn darted the plane (lost control) and died on the first flight. The wing tips could adjust the forward/aft(slightly) and the rear elevator shaped like a birds tail feathers.
 

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Dav-h12

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The Bonney Gull had ailerons, but the rear elevator seemed to be one gull/dove tail shape. Most of us have seen birds and they roll their tail feathers on the longitudinal axis; flare their tail feathers out wide and draw their tail feathers close in.
I suppose the interest of Bonney was supremely controlling the airplane while feeling completely “wired in” to the airframe. Yet his elevator doesn’t appear to flare out at all semi- parallel to the Y axis.
 

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Dav-h12

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My answer is no, not really. Perhaps the question is why would an aircraft want to have no direct means of roll attitude control? I trained as a flying qualities engineer and can't see any reason why a designer would willingly give up the best roll control device we have invented in favour of using the secondary effect of the yaw control!! Although an ultralight might want to save weight, giving up the ability to operate in anything other than pretty calm conditions is a compromise too far for me. Birds just use a different systems, many have swing wings or can vary wing area - we don't have a weight efficient means to do that!! Increasing dihedral angle will make the aircraft want to fly in a straight line, requiring a more and more aggressive yaw to roll the aircraft (or larger and larger ailerons or slower roll rates). Properly designed ailerons just makes any aeroplane much more enjoyable to fly... Why else do we fly recreational aircraft?
For the unknown of physics. I’m not a pilot/engineer, but designed a handful of UAS for the Army/DoD which is thought to be impossible because infantrymen are supposed to be dumb grunts, but got the attention of the Army/ few aerospace companies, etc, but what I learned is that engineers think in a “Legacy platform” perspective….which is a sound benchmark to follow, yet R&D is out in left field a bit…as is the unknown of physics. What have we not learned as of yet? It’s one of those “keep trying until math and physics prove you wrong”….what impact has the addition of trim tabs made?…and back to the subject of ailerons…a significant impact. Instrumentation/Navigation has had extreme positive changes and impacts(glass cockpits..GPS) It’s the nagging question of “what’s next?” or “is there a better way or some implementation to already existing control “norms” that can make them even better?” Big aerospace companies stay in the comfortable legacy platform frame of mind…Aircraft sales is one thing, yet maintenance parts/cost helps keep the legacy platform perspective. Everyone once thought that the Wright brothers were completely nuts.
 

TFF

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The pioneers of aviation were looking for two things. Fame and money. They would try anything to gain either. A lot of the stuff was to get around the Wright’s patent which they had gone the litigation way and was suing anyone who flew in the US. The US government bought them out because we were falling behind in WW1 in aviation because of it.

Changing dihedral or flapping or anything where moving a big part of the structure is the goal is understood aerodynamically. That’s not the issue. It’s the mechanics and micro mechanics. There is plenty of ideas that want to be tried but they can’t have Caterpillar D10 cylinders on a Cessna 172. That’s the issue. Stuff to control is too heavy. Solve that stuff and the other will flow.
 

cluttonfred

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It's worth reading DESIGN FOR SAFETY by David Thurston for one experienced designer's take on two-axis controls. Thurston underscores that there are significant advantages to two-axis controls in an aircraft designed to be stall- and spin-resistant in eliminating a significant cause of fatal accidents: loss of control at low altitude, most often a stall/spin incident. Numbers from folks like our Ron Wanttaja back that up (source Homebuilt Accidents: Fatal Factors - AVweb):
1629636286268.png
According to Thurston, the major weakness of most two-axis designs is difficulty in controlling the glide path on approach to landing. If a plane has two-axis controls and no flaps (like an Ercoupe), all you can do is slalom to increase your descent rate if too high since you can't sideslip. IIRC, Thurston suggests flaps with high drag settings or spoilers or air brakes (wing or belly) to allow the pilot to manage the glide path with two-axis controls. Interestingly, that is not a problem with a properly configured Flying Flea, as the stick full back puts the plane in a high-drag, high-sink "parachutal descent" without risk or stall or gaining forward speed.

Having spent much of his career working on amphibious aircraft, Thurston also believed that the safety benefits of a pylon-mounted engine in terms of visibility and getting the prop away from the pilot and passengers on entry and exit outweighed any potential danger posed by the engine in a crash. That's a debate for another thread.

For a conventional two-axis type with rudder+elevator controls kept as simple as possible, ideally with tricycle gear, a simple three-position perforated belly brake (flush, 45 degrees, 90 degrees for example) would probably be enough. The result is an aircraft that is not that much simpler or cheaper to build than a traditional three-axis machine, but it is easier and safer to fly for low-time and occasional pilots. Personally, I think something along the lines of a two-place, four-stroke, tri-gear, fully-enclosed Sky Pup would be a lot of fun. I am old enough to remember free-flight and and early RC models and flying around it what looks like a giant model airplane would be a hoot.
1629637381047.png
 
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speedracer

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I’ve successfully flown 2-axis Quicksilvers during Santa Ana winds. The solution to crosswind was simply to land across the runway into the wind.

I agree with you, but 2-axis can work and it’s simple and light. Also remember that while a rudder can impart roll, ailerons can impart some yaw too. I have flown some 3-axis ultralights with ailerons, but the ailerons were not designed well. At the slow speeds the ultralights fly, I have found that dihedral and a big rudder can sometimes be more effective than ailerons.
I do barrel rolls using rudder alone while the ailerons stay in neutral in my Long EZ. The roll takes about eight seconds to complete so I start at around 60 degrees nose up and finish at 60 degrees nose down. It "feels" very weird and I need to get someone to video it to see what it looks like.
 
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