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flying a correct coordinated turn


newbie2k

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Wow,

 

this was a hot discussion, none the less, some posters here call to out rule Newton's Laws:

 

Things you should know and remember whenever looking at mass in motion, regardless of if it is your Sim Heli, your R/C Heli ( yes, I had more than a bunch and I built and programmed the FM myself, as all R/C Pilots need to do...and had to read a few books and ask fellow club mates too ) or if you call yourself a RL Helicopter Pilot or if you simply think of, HOW DOES A bicycle perform a turn, it is ALL basically the same and directly related to:

 

Newton's 3rd Law "Lex Tertia" F_A->B = -F_B->A

 

To trun a bike you have to steer into the opposite direction a LITTLE bit ( most don't notice this despite they might be great riders ) so Lex Tertia lets your bike "fall" into the desired direction of turn and then, and only after this fall, you can steer into the direction of the wanted and anticipated turn. Don't focus on this bike thing, just an example of how universal this Law is for masses in motion and how to move them and what comes with it naturally.

 

Helicopter:

 

There is only ONE motor for main rotor and tail rotor and that implies a whole chain of correlations throughout ANY and EVERY move you make with your swashplate, be it cyclic, collective or tail rotor.

 

With ANY move it makes from a given state of stable and straight flight/movement ( Newtons 1st Law, Lex Prima, Inertial Law in english, Trägheitsgesetz in german ) it directly implies Newton's 3rd Law and falls under the ultimate law of physics which is Energy Preserving.

Let me explain in detail what causes what:

 

The mass of the heli in level flight follows #1 Law, Inertial Law, and tries to stays UNDER ALL CIRCUMSTANCES in that condition. Drag and Natural G-Force force you to inert some a static amount of energy to overcome those 2 static forces, in space and far away relative to a large mass you wouldn't need this, but here on earth you need to compensate those 2 forces.

 

Following the need to apply force, done by the main rotor spinning, introduces Newtons 3rd Law into the game. The force applied by a sprocket teething ( right term ? ) into another sprocket somewhere in the gearbox, driveshaft, wherever, its irrelevant where actually,

induces a force of the same vector ( power of this force ) in the opposite direction which would let the frame/fuselage spin in the opposite direction relative to the rotor ( or propeller in fixed wing ).

To compensate this STATIONARY yaw force ( we are not turning yet, still going a straight line ) you need to counteract to keep it straight. This is done by the tail rotor. The tail rotor itself is also driven by the same motor and partly by the same gearbox at some degree. As long as you keep flying straight it stays fairly simple and I hope you all could follow that far.

 

Things get complex when you interact by moving the swashplate, regardless, ABSOLUTELY regardless in which direction, up/down ( collective ) or or tilt ( cyclic ). BOTH ways of moving the swashplate result in a CHANGE of force, call it torque if you like, the name does not play a role, to is a FORCE and Newton's 3rd Law GRABS your full attention now because of the many things changing now:

 

By changing the swashplate's attitude, you change the amount of energy and thus force directed into the main rotor, this , at the SAME moment results in a change of DYNAMIC yaw compensation needed as 3rd Law implies the tail rotor now having to little or too much force applied.

You then need to adjust tail rotor pitch +/- to keep the desired attitude of your fuselage ( Z-Axis ).

 

Now it gets even trickier, now that you apply + or - to the tail rotor, you again mess with the 3rd Law and again, corrections are needed, minor, but the effect is there without any doubt.

 

It really means, you cannot move one without all others, it is IMPOSSIBLE by nature. Whoever says something else either has no clue about the basics of Newton's Physics ( I did my Abitur, or College Degree in your world in Physics, and I wasn't that bad ) OR flies with computer aided controls and does not recognize the small inputs done by servos and gyroscopes and FM-CPU.

 

When you build your own Heli ( and I think the 1 guy with the Photo of the R/C swash plate does )

and also have to program your Helicopter in the Computer Controlled Radio with tons of mixers and compensators, does know, must know about it.

 

Any good R/C TX has special programs for Helicopters and all of them, if they are good ( JR, Futaba, Multiplex, Spectrum etc. ) have AT LEAST two sets of pre-configured Torque Compensators, one for static compensation ( the force you normally have to fight in static conditions, relative to your throttle and pitch position ) and second, the dynamic torque compensation that comes into play when you move either cyclic or collective or both at the same time.

 

In the R/C world, we are FAR beyond the RL Helicopter development at this point, computer's have made things possible you couldn't dream of 10-15 years ago and the 2 mentioned compensations are nowadays incorporated in any "flybarless" control system which is a fully stabilizing system with at least 3 Gyros, 1 for each axis, and usually a GPS and or Barometer and a fast CPU that measures any movement of the Helicopter, reads your control inputs and THEN decides what it does do, according to what you wanted to do, you can call it a fly-by-wire system as you have no more direct control of the cyclic and pitch anymore in the full scale.

 

So, summed up:

 

Whatever you touch in that Heli, be it Huey, Mi-8, Ka-50 implies force in the opposite direction you wanted it to move, resulting in engaging Newton's 3rd Law by trying to fight Newton's 1st Law.

 

No Ying without Yang, no Hell without Heaven, no nice without bad, call it what you want.

 

 

You can, if you call a minor gain/loss in altitude , an increase/decrease of speed of minor value

acceptable, you can say:

 

"I don't need Z-Axis control when I mess with X and Y"

 

but in detail, calculated on paper with algebra and calculus, you cannot say the above as it is simply NOT true.

 

 

Bit


Edited by BitMaster

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In addition:

 

Messing with the tail rotor implies the exact same as described above, also does any other force applied to the Mass-in-motion. Some effects are so minor and unnoticed you don't feel it, some are more severe.

 

When you kick full rudder in the direction the nose does NOT want to turn by itself following the 3rd Law, you REALLY REALLY ask for more engine power as you force the tail rotor to pitch up ( and not let-go, aka pitch down..and let the nose follow the 3rd law b y itself ).

 

When yu kick the other direction, you REALLY REALLY need to lower energy input as your tail rotor now does NOT need that much power anymore as it pitches down and flows with the 3rd law.

 

What does this mean:

 

Opposite direction means--> loose altitude since you bleed of energy ( if not compensated ) in the main rotor since more energy is directed to the tail from a given total amount of energy given to to both.

 

Same direction as 3rd law means you will GAIN altitude since your main rotor now spins UP sine you have left over energy in the system ( if not compensated ).

 

Whenever you have a RPM stabilizer in your system, it means that you have SOME degree of static and dynamic torque compensation BUILT into the system.

 

This may lead some RL Pilots to believe you can do one without the other, simply by not knowing what is actually done under the hood when you do A, B or C. Such a Pilot can safely fly & teach flying...but he could never build one or program one as he has no real clue of whats going on.

 

The big advantage of R/C Pilots that strive for the ultimate is that we DESIGN, BUILD & OPERATE our aircraft in 1 person and thus must know at least the most critical basics of flight and Newtons law, aerodynamics and some other stuff too that is off topic.

 

We have several real life Pilots on our R/C Club, from Jet Airliner Pilots, Luftwaffe and US AirForce Europe Pilots, glider Pilots etc...

 

They all were pretty snobby when they initially came, after a few crashes of their own built models ( some way above the price of a nice Harley ) they agreed to not know it all and rethink, get to the books and get the basics. Lufthansa doesn't teach you everything, neither does the AirForce. They teach you what you have to know to get the job done, not much more.

 

Get a R/C Heli, a KIT, built it yourself, install the servos, engine ( gas ), adjust the carb-curve/pitch relation, adjust the linkage, program the Radio and fly it and then we discuss again.

 

You will be amazed how much you can learn, regardless if you are a RL Heli-Pilot or just a bloddy beginner. Be your own designer, technician and pilot...and most likely your ground repair crew too.

The ladder one makes you learn the fastest, believe me ;)

 

 

Bit

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and to correct one other misleading non-wisdom mentioned earlier in this thread.

 

The 90° offset of reactions resulting from a force/input induced into the spinning system:

 

This is NOT an aerodynamic law in the narrow view, it is a direct relation to physical law

 

and known by mankind ever since we use slings and stones to hunt down prey !!!

 

The reason why you have to input a force at say 270° to have a reaction ( resulting force ) at 360°/0° is the same why the Neanderthaler had to release the sling at 90° offset to where he wanted the stone to be set free. This has absolutely nothing to do with aerodynamics and/or

air resistance, absolutely zero ! ..even it was aerodynamics it would be physics, all aerodynamic laws are physics, but not all physics are aerodynamic laws, don't mix this up.

 

I would have to dig in the books/google to find the corresponding law and its equation and who found this out first and made it a principal.

 

 

Regarding the Heli, there are other offsets of minor degrees involved which are either compensated by asymmetric linkage setup ( older style Helicopters with flybar and no CPU aided FM ) or, on newer systems, computer corrected by a virtual rotation of the swash plate by usually around 2-5°, depending of how many linkages control your swash plate. Common setups involve 3 or 4 control linkages moving the swash plate and it differs by the specific design what direction and value you need to build in physically or dial in digitally in your Flight Computer.

 

There is far more involved than just Newton, Newton is plain algebra.

It really gets complicated when calculus gets involved...thats why there are Computer Aided Flight Systems now that can do curve equations in milliseconds etc...

 

Bit


Edited by BitMaster

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  • 2 months later...

Interesting thread. Just came across it...

 

One thing I have noticed is that the turn coordinator isn't giving you correct std rate turns, 4' std turns as it is supposed to be the case.

 

You can test it with perfectly coordinated or sidesliping turns... Aligning with the left or right 4' marks will not get you a 4' 360 º turn - far from that :-/

Flight Simulation is the Virtual Materialization of a Dream...

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  • 1 year later...

From Norman Bailey's book:

 

As well as providing a component to balance weight and a force to maintain speed, the total rotor thrust must also supply a further component to change the direction of the helicopter in a balanced turn. Its effect is similar to an increase in all-up weight. In a 30-degree-bank turn, the apparent increase in weight is 15 per cent; in a 60-degree-bank turn, it is 100 per cent.

To maintain height in the turn, more collective pitch is required. Therefore, more power is used, which causes the ‘power required’ curve to move up the graph.

The maximum angle of bank that can be achieved by a helicopter in a level turn is the angle where the airspeed is the speed for maximum rate of climb. If the angle of bank is increased beyond this point, height will be lost and rotor speed will decay.

 

Level Turns

Entering a Turn

To enter a turn from straight and level flight, the cyclic stick should be moved smoothly in the desired direction of the turn. How far the helicopter banks will depend on how much lateral pressure is applied. Since some rotor thrust will have been used in the turn, additional power may have to be applied to maintain altitude.

After the turn has been established, outside visual references should be noted and maintained by using the appropriate control pressures. The nose position will appear different during left and right turns. This is because the pilot sits to one side of the helicopter’s centre-line. Therefore, a point directly on the pilot’s line of sight should be used for reference during turning. The altimeter should be included in the scan to confirm that a constant height is being maintained.

 

Rolling Out from a Turn

Approximately 5–10 degrees before reaching the required heading, the pilot should apply opposite cyclic stick pressure to stop the turn. As the heading is reached, the helicopter should be in straight and level flight at the desired airspeed.


Edited by WildBillKelsoe

AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS

 

Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.

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Very informative... thank you.

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I've been observing some odd behavior in rudder usage recently. On my flight out the slip indicator tells me to add rudder in the direction of turn as what I am accustomed to in fixed wing. On the return trip, the slip indicator tells me to add rudder opposite the direction of turn. What's up with that?

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could be winds

AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS

 

Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.

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  • 3 months later...
I've been observing some odd behavior in rudder usage recently. On my flight out the slip indicator tells me to add rudder in the direction of turn as what I am accustomed to in fixed wing. On the return trip, the slip indicator tells me to add rudder opposite the direction of turn. What's up with that?

 

Bear with me on this wall of text, but I think I can explain it.

 

When you're turning you're unloading lift from one side of the rotor disk whirring above you which will cause you to descend. If you're countering this, you are adding collective and the Huey will be inclined to laterally rotate clockwise (countered with left anti-torque pedal). If you then reduce collective (and RPM), the clockwise inclination will lessen causing you to laterally roll counter-clockwise if you haven't anticipated this (by reducing pressure on the torque pedal).

 

The main problem when you've moved from fixed wing to rotary is the ingrained response of using the pedals. There is no rudder, the pedals purely counter the torque produced by the main rotor. There are far more variables when it comes to flying a chopper.

 

Example: You're in an A10. You turn left, and you apply left rudder to create a smooth turn. Whether you are ascending or descending, adding power or reducing power makes no difference. You apply the pedal for the corresponding turn.

 

You're now in a Huey, and you are turning left with the cyclic. You didn't apply collective and you are now gradually descending. RPM has reduced, and the Huey which is dangling below the rotor starts to rotate counter-clockwise (albeit very slightly. Lower speeds will make this far more pronounced). This will cause you to use right pedal to counter that rotation.

 

You try a second turn to the left. This time you have anticipated the loss of lift on the left side of the rotor disc and have applied collective to maintain a level turn. As you increase the collective to stay level, RPM increases, as does the torque causing the Huey to rotate clockwise so you counter it with the left pedal.

 

I'm not sure what I've written has made any sense, but it's how I understand it.

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As a non-RL helicopter pilot, I tried the technique that Jay43 described and it works fine for me, with a 3kt loss of airspeed in a 10 degree bank turn. I never touched the collective (27 psi) or moved the pedals (the ball stayed centered) and used a bit of back cyclic to maintain altitude. I tried the same technique with 20 and 30 degree banks and lost 5 kts at the most. The small loss in airspeed seems to me like a better option than playing with collective inputs. However, I would make collective adjustments to maintain formation in a turn.


Edited by JimTM
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  • 2 weeks later...
When you're turning you're unloading lift from one side of the rotor disk whirring above you which will cause you to descend. If you're countering this, you are adding collective and the Huey will be inclined to laterally rotate clockwise (countered with left anti-torque pedal). If you then reduce collective (and RPM), the clockwise inclination will lessen causing you to laterally roll counter-clockwise if you haven't anticipated this (by reducing pressure on the torque pedal).

 

To enter/exit a turn you don't lose lift, you transfer transfer lift from one side to the other.

 

Reducing collective will not affect RPM (at least not with a functioning govenor).

 

The reason you lose speed and/or height in an established turn is because a portion of rotor thrust is being used to turn, which is no longer available for maintaining said speed and/or height.

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