Should the pedals NEVER be used to steer?

[Jonathan Bailey]

I have read some articles on line about using the pedals in a helicopter. They say the pedals should never be used to steer a forward-moving chopper, but only used in a hover.

 

My experience piloting a helicopter has been a Bell Jet Ranger 206B in Microsoft Flight Simulator. Using the cyclic to bank and turn at high speeds works OK when flying out in the open, but when trying to follow a river in a narrow, crooked canyon at speeds under 70 knots, using the cyclic alone to turn sharply is almost impossible; it causes the bird to want to walk sideways like a crab. I found that maneuvering in tight, twisty areas in slow flight works best using both the cyclic and the pedals SLIGHTLY or the pedals only at speeds under 30 knots with sharp turns at corners. The pedals keep the nose pointing along the path I want to follow as a taxiway, road or river.

 

My simulated helicopter never malfunctions, gets damaged or crashes from using slight pedal input to steer at low air-speeds.

 

How does a pilot steer a real helicopter at low speeds and/or in tight turns?

[Eric Hunt]

The Flight Sim program is using a modified version of a Cessna, which has adverse aileron drag requiring a bucketful of rudder to fix it.

 

A real helicopter only needs a nudge into the turn to make it work.

 

All these questions should be on a Great Pretenders MS Flite Sim forum, not somewhere like this, as it doesn't relate to reality

[cherminator]

 

All these questions should be on a Great Pretenders MS Flite Sim forum, not somewhere like this, as it doesn't relate to reality

 

The first and last paragraphs in his post are completely based on reality and he is asking a legitimate question. I'm not a flight instructor or even a commercially rated pilot so I'll let the experts chime in on this one.

[aeroscout]

Jonathan Bailey is trying to learn how to fly helicopters because he is going to buy one when he hits the super lottery.

Then he is going to fly his german shepherd in it up to hypoxia altitudes to catch bigfoot.

Jonathan, do I just about have it all right ?

[Jonathan Bailey]

The Flight Sim program is using a modified version of a Cessna, which has adverse aileron drag requiring a bucketful of rudder to fix it.

 

A real helicopter only needs a nudge into the turn to make it work.

 

All these questions should be on a Great Pretenders MS Flite Sim forum, not somewhere like this, as it doesn't relate to reality

But I did ask how a real helicopter was supposed to be maneuvered out of curiosity. I am not a pilot but an enthusiast. I will probably never enjoy the opportunity fly a genuine aircraft. But the fantasy is still alive. The flight sim from MS probably cannot duplicate real airplane physics accurately. I was assigned to an attack helicopter aviation outfit in the army in the Persian Gulf era (I was stateside) though my MOS was in the field of fleet diesel truck repair as a light wheeled vehicle mechanic. This aviation unit, ironically, had more damn trucks than birds! The birds have to be supported logistically from the ground. Parts, fuel, ammo, tools, shop equipment and armament. Some of the crew chiefs in my outfit explained the basic principles of helicopter design and operation to me. As a soldier, I was a passenger in the gunner's seat of a Cobra and also the passenger of a Huey. The Cobra shook like hell as the warrant officer was slowing the bird down, I remember, and that was scary. I got to look through the gunsight and move it around. Some of the troops were given helicopter rides for fun. This was at Ford Ord, CA in '92. I had wanted to go into warrant officers candidates for flight training as a helicopter pilot but army recruiter said no on account of my glasses. Piloting any real bird is something few will ever enjoy.

[Gomer Pylot]

There is some adverse yaw when banking a helicopter in forward flight without using the pedals. Watch the trim ball when you bank while in trim without moving the pedals, and you'll see the ball go in the opposite direction of the turn for a short time before returning to center. But it's only momentary, and most instructors teach just ignoring it and not using the pedals at all. It's really better to initiate the turn with some pedal input, then removing it, keeping the ball centered at all times, but very few pilots do this. It's much easier to just not make any pedal input, and the results are almost the same. The lower the airspeed, the more adverse yaw affects turns, and at some point you really have to use pedals to make turns. At a hover, the turn is done entirely by pedals, and not by banking, although cyclic input is essential to keep the aircraft over the same spot. However, the only real way to learn the coordinated inputs necessary to fly a helicopter is by flying a helicopter. Even multi-million dollar simulators aren't completely realistic, although they do come close.

 

PC flight simulators have little to do with reality, because they were developed by programmers, not pilots, and with low cost as the primary factor. Just know that MS Flight Simulator and the real world have little to do with each other, and have fun playing video games.

[WolftalonID]

I came into flying helicopters after first flying fixed wings. My instructor always gave me crap about my love of the pedals in flight!!! One day he made me fly the whole hour with my feet on the floor, as it was a rather calm day and we didnt need them much at all.

 

Pedals are used to control the tail rotor or nozzle in a NOTAR design. The tail rotor has one purpose, that is to counter the torque made by the main rotor.

 

In a hover the main rotor is spinning and that momentum gets transferred to the fuselage(body) of the helicopter. Just like when your in the mall walking and a person runs past you, bumps you, and your body takes that energy and spins away from that bump? The helicopter wants to do the same thing.

 

So we have pedals that will change how much air the blades can bite at one time. In a hover we need more teeth back there, so we use more pedal input.

 

Once we start moving forward, the fuselage becomes like a lawn dart in the air. The wind helps it keep straight by flowing aerodynamically around it and down the tail cone, across the tail fins, both the vertical and horizontal fins. The Vertical fin is the one that does most of the work. It takes on the roll of pointing us in the right direction with the flow of air across of it. The faster we fly, the better job it can do.

 

Just like putting your hand out the car window at a red light. Yep its out there....but unless you move it up and down, it doesn't do much without much more muscle use.

 

Now do the same task on the freeway, and with very little muscle use, the wind will move your whole arm up or down as the wind flows over your hand.

 

The main rotor is supporting the helicopter from one point. We control its direction with the cyclic stick, and it pulls the helicopter along in that direction. If we tip the disk to our side(left or right), the helicopter will follow. The wind pushes against the fuselage and tail cone, the fuselage spins out of the way, just like your body did at the mall when the guy ran into you as he ran past, and then that vertical fin, called the vertical stabilizer btw, takes over and we are now pointed forward as we turn.

 

Some pedal is used to keep the aircraft in "trim" but thats just a very small amount. We also use pedal to overcome that main rotor torque in flight if we change how much power we are using.

 

Up Collective, more pedal, down collective less pedal, same with throttle settings. More or less pedal is used to describe it over right and left pedal, because, it is different dependent on which way the main rotor turns. They vary from one make and model to another.

 

One last thought. While hovering in windy conditions, the pedals can be used a ton to overcome the wind trying to point us in a direction we don't want to point. We can still move over the ground in the direction we want to go though, regardless of which way the nose is pointed, its just not as easy to see where we are going!!!

 

 

Hope that helps the real helicopter part some.

[superstallion6113]

There's got to be some program out there to add wookies and bigfoot into the forested terrain in the maps. Could be great training for doing some actual squatch hunting in a 206. That's the one thing a sim like MS Flight Sim is good for, learning and practicing procedures and checklists.

[aeroscout]

There's got to be some program out there to add wookies and bigfoot into the forested terrain in the maps. Could be great training for doing some actual squatch hunting in a 206. That's the one thing a sim like MS Flight Sim is good for, learning and practicing procedures and checklists.

You are right of course, but you are leaving out ewoks. Are you ewokist ?

[Jonathan Bailey]

There's got to be some program out there to add wookies and bigfoot into the forested terrain in the maps. Could be great training for doing some actual squatch hunting in a 206. That's the one thing a sim like MS Flight Sim is good for, learning and practicing procedures and checklists.

Hopefully, PC sims will get more realistic. Yes, moving animals, people and crypto-creatures would make a nice addition to flight sim scenery.

[Jonathan Bailey]

You are right of course, but you are leaving out ewoks. Are you ewokist ?

I have not even spotted one Morlock in flight sim.

[Jonathan Bailey]

I came into flying helicopters after first flying fixed wings. My instructor always gave me crap about my love of the pedals in flight!!! One day he made me fly the whole hour with my feet on the floor, as it was a rather calm day and we didnt need them much at all.

 

Pedals are used to control the tail rotor or nozzle in a NOTAR design. The tail rotor has one purpose, that is to counter the torque made by the main rotor.

 

In a hover the main rotor is spinning and that momentum gets transferred to the fuselage(body) of the helicopter. Just like when your in the mall walking and a person runs past you, bumps you, and your body takes that energy and spins away from that bump? The helicopter wants to do the same thing.

 

So we have pedals that will change how much air the blades can bite at one time. In a hover we need more teeth back there, so we use more pedal input.

 

Once we start moving forward, the fuselage becomes like a lawn dart in the air. The wind helps it keep straight by flowing aerodynamically around it and down the tail cone, across the tail fins, both the vertical and horizontal fins. The Vertical fin is the one that does most of the work. It takes on the roll of pointing us in the right direction with the flow of air across of it. The faster we fly, the better job it can do.

 

Just like putting your hand out the car window at a red light. Yep its out there....but unless you move it up and down, it doesn't do much without much more muscle use.

 

Now do the same task on the freeway, and with very little muscle use, the wind will move your whole arm up or down as the wind flows over your hand.

 

The main rotor is supporting the helicopter from one point. We control its direction with the cyclic stick, and it pulls the helicopter along in that direction. If we tip the disk to our side(left or right), the helicopter will follow. The wind pushes against the fuselage and tail cone, the fuselage spins out of the way, just like your body did at the mall when the guy ran into you as he ran past, and then that vertical fin, called the vertical stabilizer btw, takes over and we are now pointed forward as we turn.

 

Some pedal is used to keep the aircraft in "trim" but thats just a very small amount. We also use pedal to overcome that main rotor torque in flight if we change how much power we are using.

 

Up Collective, more pedal, down collective less pedal, same with throttle settings. More or less pedal is used to describe it over right and left pedal, because, it is different dependent on which way the main rotor turns. They vary from one make and model to another.

 

One last thought. While hovering in windy conditions, the pedals can be used a ton to overcome the wind trying to point us in a direction we don't want to point. We can still move over the ground in the direction we want to go though, regardless of which way the nose is pointed, its just not as easy to see where we are going!!!

 

 

Hope that helps the real helicopter part some.

 

 

Yes, but it is the devil to try to follow a crooked river or twisty narrow canyon at 25-45 knots with no pedal input. I like to keep the path I am following dead in front of my eyes for the most part.

 

I was just wondering if using pedal at forward velocity was dangerous in a real flying machine.

 

I used to ride motorcycles. This is a good analogy. One has to lean (cyclic in heli) into turns at high speeds but using the handlebar (pedals in heli) to steer is more effective at low speeds. The rudder in an airplane, however, has almost no power to steer at any speed. I use my ailerons exclusively to steer my flight-sim fixed-wing craft.

[ridethisbike]

You have to remember that you are also on a computer that offers very little visibility.

 

Think about driving around in your car... You look where you want to go, correct? It's the same way in a helicopter. The problem is that your computer program quite literally shows you what is directly in front of you. Next time you're in a car (as a passenger), lock your head in the direction that the car is pointing so that you are looking directly out over the hood. Don't move your head through the turn. This view is exactly what the computer is giving you.

 

Slow flight like what you are talking about on a computer SIM will REQUIRE you to make some pedal inputs, just for the sake of being able to see where you're going.

[WolftalonID]

In a fixed wing air craft the ailerons do not steer the aircraft. The roll it or bank it left or right on its longitudinal axis. The rudder steers the aircraft. Just like a ship. When those controls are combined it will induce a turn.

 

In a fixed wing, the turn or bank angle is established and the control is brought back to neutral during the turn or bank. In a helicopter the control is held the entire time the turn or bank is desired. Neutralize the control and it levels.

 

Fixed wing aircraft, and helicopters fly due to the same basic principles of flight. They however have some serious differences on how they are controlled while in flight.

 

Your PC is controlled by...... Ahhhh never mind, I use a MAC that actually works!!!!

 

The point I am making is what was already stated above. Programers are often not pilots...so we have no way to explain why your SIM flies the way it does. But those of us who are pilots, and CFI's can explain how real aircraft fly.

[bqmassey]

In a fixed wing air craft the ailerons do not steer the aircraft. The roll it or bank it left or right on its longitudinal axis. The rudder steers the aircraft. Just like a ship.

 

Not quite But I just watched another forums argue for 180 replies about what turns an airplane.

[aeroscout]

 

Not quite But I just watched another forums argue for 180 replies about what turns an airplane.

There is more than one way to complete a turn in an aircraft, and that includes helicopters.

[bqmassey]

There is more than one way to complete a turn in an aircraft, and that includes helicopters.

 

Maybe in an aerobatic routine or something, but in any typical regime of flight the rudder isn't where the turning force comes from.

[iChris]

I have read some articles on line about using the pedals in a helicopter. They say the pedals should never be used to steer a forward-moving chopper, but only used in a hover.

 

My experience piloting a helicopter has been a Bell Jet Ranger 206B in Microsoft Flight Simulator. Using the cyclic to bank and turn at high speeds works OK when flying out in the open, but when trying to follow a river in a narrow, crooked canyon at speeds under 70 knots, using the cyclic alone to turn sharply is almost impossible; it causes the bird to want to walk sideways like a crab. I found that maneuvering in tight, twisty areas in slow flight works best using both the cyclic and the pedals SLIGHTLY or the pedals only at speeds under 30 knots with sharp turns at corners. The pedals keep the nose pointing along the path I want to follow as a taxiway, road or river.

 

To hold a steady coordinated turn often requires both pedal and lateral stick displacements; however, you have the option of making single control turns using only pedals or only lateral stick motion.

 

As an example, in the first case, you make a pedal only turn to the right, which produces an initial sideslip to the left. Dihedral effect will generate a roll moment to the right and the helicopter will enter a right turn. Once the turn is established, the bank angle can be held with pedal alone-although some sideslip will exist (the larger the side force and dihedral effects, the smaller the sideslip angle).

 

The other option is to make a pedal-fixed turn using only lateral stick. When the stick is displaced, the helicopter rolls and starts sliding toward the low side. Directional stability then makes it weathervane into the direction of flight (this effect is reduced at low airspeeds (≤40 knots) making it necessary for you to aid the turn with pedal). After the desired bank angle is achieved, the stick is returned to the initial trim position-or nearly so, since to hold it would result in a continuous roll rate. In this case, the sideslip is minimized by strong side force and directional stability characteristics.

 

During the initial roll into the turn, the yaw may first be in the wrong direction due to a condition known as adverse yaw which is similar to an airplane for example, during a right roll that tilts the lift on the left wing aft and lift on the right wing forward to pro­duce a yawing moment to the left.

 

The same effect also works on the advancing and retreating blades of a rotor, trying to speed it up for right roll rates and slow it down for roll to the left. For a turbine helicopter with a governed engine, the fuel control will respond to these speed changes by increasing engine torque in left rolls and decreasing it in right rolls, for American rotation.

 

Helicopters tend to roll away from the approaching wind. This is the same characteristic found on airplanes with dihedral, both wings slanted up. It’s known as “positive dihedral effect” on rotors though the source is different.

 

Pitch-roll coupling is still another nonsymmetrical result of rolling into a turn that can be noticed in the pitch-down when rolling left and the pitch-up when rolling right. This difference is caused by the way the rotor flaps during turns.

 

In a fixed wing, the turn or bank angle is established and the control is brought back to neutral during the turn or bank. In a helicopter the control is held the entire time the turn or bank is desired. Neutralize the control and it levels.

 

When you tilt the disk with respect to the helicopter, it will generate a roll rate and the helicopter will continue to roll while you hold the cyclic stick displaced from its initial trim position. After the desired bank angle is achieved, the stick is returned to the initial trim position. In order to level the helicopter, the cyclic must be displaced laterally, opposite the turn, thereby rolling the helicopter level then returning the cyclic to its initial trim position, technically lateral cyclic stick commands roll rate.

Edited March 10, 2014 by iChris

[Rosco99]

If you are looking for a bit more of an "accurate" sim, you may want to use X-Plane, and fly the helicopters there. It will show you better principles than Microsoft (IMHO), but nothing substitutes the real thing.

 

I know the Army said no, but flying civilian may be an option for you. Do you still have the GI Bill?

[aussiecop]

I have experience in both RW and sim, and have to agree with the guys here. MSFS is severly lacking in certain realism factors. I make helicopter addons for the simulator and there is constant frustration at the lack of availability to model certain helicopter charachteristics in the sim P3D (the lockheed variation of MSFS) has added some functionality, but it still has a long was to go to be at the same par as xplane for realistic flight charachteristics. That being said, there is one addon out there that gets close for MSFS and thats the Dodosim 206, that is as close as you will get inside a microsoft framework to flying a 206 with realistic startup shutdown and emergency procedures.

[Wally]

I've done full motion simulators at Flight Safety and Eurocopter, and neither fly like the real thing. I don't use MS FS helos as I need to learn to "fly the sim" instead of the aircraft more than it seems I do airplanes.

 

In the real world you do whatever needs doing to make it happen most efficiently with the least wear on the aircraft. Different aircraft types react to the yaw trim changes differently... Generally, you do keep the trim ball/slip indicator centered, but I will use the pedals to skid or slip if I need to, especially useful to correct a couple, three degrees in heading.

Edited March 10, 2014 by Wally

[Nearly Retired]

iChris:

Helicopters tend to roll away from the approaching wind. This is the same characteristic found on airplanes with dihedral, both wings slanted up. It’s known as “positive dihedral effect” on rotors though the source is different.

 

 

Hate to disagree with you, old man, but I've found the exact opposite to be true: Helicopters (at least 206-type helicopters) do not exhibit positive dihedral effect in real life - only in theory.

 

My fixed-wing experience is that if you are in stable, straight and level flight and you add some right pedal, an airplane will naturally bank to the right. A helicopter will bank to the left. I know this sounds "wrong" but it's true.

 

I like to demonstrate this in the 206. (You need a fairly calm day.)

 

I have the pilot friction the cyclic down enough so that it will not move if he takes his hand off. This doesn't take much friction - just enough to add some drag to the stick (you don't want it too stiff or "ratchety"). Then I have the pilot fold his arms across his chest, sit back and relax. As we cruise along, if the ship banks to the left, I demonstrate that a little *left* pedal pressure can bring it back to wings-level. Pressure, not movement. Same for a right bank - pedal *into* the bank. If you get the fore/aft cyclic pitch trim set right, you can happily fly for long periods of time without touching the cyclic by just using slight pedal pressures to maintain hands-off straight and level flight.

 

I discovered this out in the Gulf of Mexico when I worked for PHI. I'd get one of their LongRangers up at 2,500 feet on a calm day, friction the cyclic down and just cruise along while eating a sausage biscuit and using tiny pedal pressures to maintain S&L. (I usually only did this when I had no pax. Usually.) As a fixed-wing pilot I was surprised to see that the pedals react differently in flight - in fact they react the opposite of an airplane! Other pilots disagree with me, mostly because they've never tried it. Helicopter pilots are just too paranoid to take their hands off the controls for *any* length of time.

 

Other airplane pilots are quite puzzled by this. Helicopter pilots know it intuitively but spout the opposite nonsense when you ask them the theory. Helicopters are supposed to have positive dihedral effect, right? (Not really.) Fact is, they don't. At least two-blade helicopters don't. I haven't really screwed around in multi-blade helicopters much...like the Bo105...probably because that piece of junk had *ZERO* stability in any flight regime...or the S-55, which maybe I'll mess with this summer when I go back up to Washington. And obviously I cannot speak for teeny-tiny ships like the H-300 or R-22.

 

I'm no aeronautical engineer, but I have a cockamamie idea as to why the 206 behaves like this.

 

When you make a pedal input in an airplane, the whole aircraft yaws...wings, fuselage...everything. Let's say that you make a right pedal input in a Bell 206 helicopter (with no corresponding cyclic input), the nose yaws to the right but the rotor (i.e. the "wings") stays put, driving along just like normal. But now the relative wind is hitting the side of the fuselage. Increased drag on the left side of the fuselage will cause it to lean over to the left because it's hinged up at the top, at the rotor hub. Try it!

 

I know, I know what the books say helicopters are supposed to do. I know. But they don't. At least, the 206 and FH1100 don't. Somebody once told me that the Bell 212 exhibited such poor positive dihedral effect that back in the 1970s Bell had to stick a big "shark fin" stabilizer on the roof of the cabin in front of the mast to get the thing certified for IFR, where all aircraft have to demonstrate positive dihedral effect. (Oh, and a spinning rotor doesn't exhibit any "dihedral effect" at all - one way or the other. If it gets upset from its "trimmed" position, it will continue to fall off in the direction of the upset until corrected by the pilot.)

 

Call me crazy, but I've been flying for a long time and this is what I've experienced. And helicopters like the JetRanger and LongRanger do not exhibit positive dihedral effect.

[Wally]

My observations coincide with Nearly Retired, except that rate and duration of pedal application affect outcome. My recollection is that an aircraft with a "low' tail rotor (206, 350/355) will roll away from a moderate pedal initially, but the pitch attitude will diverge depending on which pedal is applied and then it will roll into the pedal... or farther out of trim. Long days flying in the GoM...

 

Harder to say with smaller aircraft. The 269's canted horizontal had a really strong effect on out-of-trim flight, hence the infamous autorotational tuck.

Edited March 10, 2014 by Wally

[iChris]

iChris:

 

Hate to disagree with you, old man, but I've found the exact opposite to be true: Helicopters (at least 206-type helicopters) do not exhibit positive dihedral effect in real life - only in theory.

 

Call me crazy, but I've been flying for a long time and this is what I've experienced. And helicopters like the JetRanger and LongRanger do not exhibit positive dihedral effect.

 

Most all helicopters have some degree of positive dihedral. In fact, only a slight negative dihedral is allowed under certain certification conditions.

 

A moderate amount of positive effective dihedral is needed for good flying qualities, meaning if a helicopter is flying straight and level runs into a gust that rolls it over slightly, the force resulting in a sideslip. Dihedral effect generates a rolling moment proportional to the sideslip angle in the direction of the yaw, damping roll toward the sideslip.

 

In the case of a helicopter most of the dihedral effect comes from the flapping of the rotor; however, some of the effect comes from the airframe components. Any vertical surface located above the center of gravity increases the dihedral effect while any low surface reduces it. In other words the rotor flaps back away from gust, causing a restoring moment against the rolling moment caused by the sideslip.

 

It’s the dynamics of flapping and it was accounted for in the design of the helicopter. There’s lots of dynamics you’re not aware of that the designers took care of long before you set foot on the pedals.

 

 

Static Lateral Directional Stability

 

(ii) Dihedral requirements may be more difficult to assess. For those rotorcraft which do not meet the position and force gradient requirements for the conventional, cross-controlled sideslips, there are alternative tests which may be used to determine acceptable characteristics. If directional pedals are utilized in steady sideslips, the resultant rolling tendency is the sum of (1) the aircraft’s roll due to sideslip tendency (dihedral), and (2) the aircraft’s roll due to directional control input. If the rotorcraft has a tail rotor which is excessively high or low in relation to the rotorcraft’s vertical CG, application of tail rotor thrust will introduce a significant rolling moment. The basic intent of dihedral stability testing is to determine the rotorcraft response to sideslip exclusive of directional control input. In general, if a tail rotor configuration is involved and the tail rotor is above the vertical CG of the rotorcraft, the effect of pedal input upon dihedral effect is destabilizing during conventional, control-induced sideslips.

 

(iii) There are two alternate methods which, for small angles of sideslip, can give an indication of the basic dihedral stability of the rotorcraft. Both methods involve freezing the directional controls while artificially creating sideslip by other means.

 

(iv) The first method is only applicable for rotorcraft with single main rotor systems. To utilize this method, the rotorcraft is stabilized in a given flight condition and small collective (torque) changes are applied in each direction (e.g., ±5 percent and ±10 percent) while holding pedals fixed. Sideslip angle, lateral control position, and lateral control force may be measured and plotted for small torque changes from trim. This technique will not work for aircraft which have collective to pedal or collective to lateral control couplings.

 

(v) In the second method, the rotorcraft is stabilized in a trimmed flight condition with a small amount of bank (5°-10°). The rotorcraft is then rolled to an approximately equal angle of bank in the opposite direction holding the pedals fixed. The change in direction of bank results in a small change in sideslip angle and again sideslip angle may be plotted versus lateral control position and/or force. This test should be conducted in both directions and the results averaged. This method can give reasonably accurate results for small perturbations. Other factors contribute to the results of either of these two methods. It is always important to assess the roll due to sideslip tendency with pedal induced sideslips to assure lateral control forces are reasonable and in a proper direction for directional out-of-trim conditions, and to assure the pilot has adequate sideslip cues.

 

(vi) Wording of the dihedral requirement is intended to allow slightly negative dihedral stability at critical loading conditions. This will ordinarily result in positive dihedral stability throughout a great majority of the approved loading envelope. The test for maximum allowable negative dihedral effect would involve stabilization at a required flight condition, inducing a sideslip up to ±10° from trim, then assessing lateral cyclic friction/deadband to determine if roll is restrained while remaining in the control system friction/deadband so that the control may be released without resulting in the aircraft rolling in the adverse direction. When testing for this condition, lateral cyclic friction should be adjusted to the minimum value.

 

Ref: AC -27-1B CERTIFICATION OF NORMAL CATEGORY ROTORCRAFT

 

Edited March 15, 2014 by iChris

[iChris]

(Oh, and a spinning rotor doesn't exhibit any "dihedral effect" at all - one way or the other. If it gets upset from its "trimmed" position, it will continue to fall off in the direction of the upset until corrected by the pilot.)

 

Call me crazy, but I've been flying for a long time and this is what I've experienced. And helicopters like the JetRanger and LongRanger do not exhibit positive dihedral effect.

 

"Most rotors try to "back flap" when a speed or wind increase is imposed on them. That is due to the fact that the blade that sweeps into the increasing wind gets more lift (from its increased speed) so it flaps upward. The full effect is felt approximately 90 degrees later, so the rotor disk tends to flap away from the speed increase. That is one of the contributers to the dihedral I mentioned for the last two posts.

 

Actually, we use the term dihedral to describe the effect (when a yaw makes a roll) and can be measured on airplanes, helicopters and even ships! the paper describes wings but the effect is the same.

 

For helicopters, lost of stuff happens in the rotor, as you describe, like flapping and stuff. The rotor disk is also coned just like an airplane's wing, so there is a contribution there as well.

 

But, helicopters generally have strong dihedral due to the way the rotor behaves when we impose a new wind direction on it. If you can, picture the rotor having been trimmed with the cyclic forward at high speed, so that the disk is level and the nose is down to trim at that speed. Then simply rotate that helicopter a bit to the right, like a right yaw would do. If you look at the rotor from the wind's perspective, where the air meets the disk as the new forward, you can see that the cyclic is now trimmed to the right relative to the airflow, so it has a small roll input, this makes the aircraft roll in the direction of yaw, so-called positive dihedral.

 

the problem with helicopters is that they fly at very low speeds. By the time you slow to 50 or 40 knots, the small effect I describe above is lost in the mud, and there is little dihedral for small angles of yaw. This is often the problem that sets the low speed Vmimi limit for helicopters. that big fin on the rook probably helps get some traction at low speed to add some roll, and perhaps gets the dihedral effect back at 40 or 50 knots, allowing Vmimi to be set lower. VFR aircraft don't need it, of course, since that dihedral requirement is an instrument thing."

 

REF: NickLappos PPRuNe

Edited March 11, 2014 by iChris