downthrust?!?!? righthrust?!?!?

[xoon]

hey guys I heard something about this downthrust and righthrust, and I was wondering what does it means, any major impact on airplane abilities?

[lrsudog]

Downthrust & right thrust are often needed to counteract torque & a thrust line either above or below the wing.

Generally, the more torque the prop applies to the fuse, the more right thrust you may need. Without it, many planes tend to turn or roll to the left when power is applied.

Also generally, the further below the wing the thrust line is, the more down thrust a plane will need. Without it, a plane will usually tend to balloon up when power is applied.

Ideally, you can get the plane to track straight in pitch, yaw, and roll when power is applied or removed if you properly set up the thrust angles.

[JohnC]

It simply means that some airplanes needs the motor to have the propller shaft pointed downward (help to counteract the nose of the plane pitching up when changing the speed of the plane on a flat bottomed wing for example) and to the right to counteract the effects of torque of turning the propeller. Most Pattern airplanes do not use downthrust and right thrust. How ever many sport and old timer type planes with flat bottom airfoil wings for example need down and right thrust. Each kind of airplane needs more or less adjustment according to many factors, airfoils shape, planform and decalage etc.

Let the flame wars begin!

John F. Clarke
AMA 9473

[Kwok_Yu]

You have to keep in mind that you don't alway need down or right thrust. Or in fact you need the opposite. It depends on the plane. For example, I always thought right thrust was needed because the vertical fin was on top of the tail. Most engines spin counter clockwise, causing a vortex that hits the tail on the left side and pushing it to the right. Motor right thrust would counteract this yaw. But if the tail was on the bottom, you would need left thrust. Also if the motor spins clockwise then you would also need left thrust.

[tim hooper]

Off to Modelling Science with this one..........

tim

[xoon]

thks, I'm just beginning to fly

[raptor22]

How do you calculate amount of thrust angle neeeded? Anyone know?

--Alex

[JohnC]

If the plans do not show it! Ask others on the ezone if they had to add any for that model or fly the plane and be prepared to add down and or right thrust.

John F. Clarke
AMA 9473

[raptor22]

For a scratch built model, if you're building a plug, you need to know before you biuld anything; and since its your design, noone else can help you with their experiences on it!

--Alex

[Majortomski]

ARRRRGHH!!!!!!
Come on folks let's get the terms and reasons CORRECT!!!!

Right thrust can not, will not, is physically imposible, to have any effect AT ALL on torque! Right thrust corrects for P-factor and P-factor ONLY!!!

Now surprisingly, down thrust often eliminates most of the p-factor that made you think you needed right thrust in the first place.

Tom

[Fantam]

What is P-factor?

[Chas]

Spitfire pilot's language! Basically the WW2 warbirds were the most extreme example of it because of their taildragger configuration and huge, waffling blades driven by lots of power.

The handbooks referred to it in short as P-factor, but basically when the propeller disc is inclined to the airstream (either positive or negative, torque advocates please note!!) the opposing blades of the prop experience differing angles of attack. This produces a left swing with positive disc inclinations, and a right swing with negative disc inclinations (as, in a dive). The effect is most pronounced at take-off because of the high inclined angle and the near-max thrust application.

As to down and right thrust, it can only ever be compensation for poor design. In any case, it is only ever right at one speed, so why bother?
Downthrust is a hangover from the bad old days when we had no in-flight pitch control. It's a dinosaur, forget it.

Side thrust produces a yaw force. Trying to counteract a roll force, whether from torque or P-factor or anything else, by introducing yet another force in yaw, is at best inefficient and at worst dangerous. Anyway, how does it work when the aircraft is inverted?

How does torque produce a swing with the aircraft firmly on the ground? Or with a trike U/C? Forget the nonsense about extra pressure on the left wheel. Compensate for torque with roll trim.

Chas

[vintage1]

Well actually you do use sidethruist to counteract torque, by inducing a yaw, which, with dihedral, sort of gives you a roll moment.

However its a pig really, because the yaw and roll moment is dependent on speed, whereast torque is dependent on RPM.

Its a crude way basically of getting the model to more or less track straight under variable power. But as anyone who has fliown a high wing model with dihedral and right thrust will tell you, it is at best a bodge, and at worst totally useless. I always end up having to hold right rudder pulling up into a loop and left rudder coming down...

Basically, if you want a precise model, buld it mid wing with zero sidethrust or downthrust..and plenty of wing area and a not too large diametr prop...and ..and..and

However if its a rudder only high wing piper cub sort of thnig, use about 1.5 degrees right thrust to make it more or less fly in straight line most of the time hands off.

Ive platyed around with washers and stuff for hours on those sorts of models, and they nevertrack perfectly under all conditions, but 1.5 degrees menas its as likley to pull left as right more or less :D

Downthrut is also associated with decalage and CG. A forwad CG and more decalage needs more downthrust. Since speed changes under power will tend to make it climb more sharply if trimmed that way.

One model I built for bang bang rudder only needed about 15 degrees of downthrust.

But mostly 2-3 is a good place to start.

Again for sort of sporty and scaleish things, I am tendiing to think that its actually better to mix in a little down with the throttle tho. They look better with the prop pointing in the right direction...

As far as P factor goes, I am dubious it is relevant to our models. But you are correct that sidethrust should be an exact counter to it. However in normal cruise flight the designer should arrabnge for teh aircraft to be flying with a horizontal thrust line anyway.

So no p factor.

If P factor was an issue drooping thrustlines should give more thrust on the LHS of the model anyway. Thius counteracting toruqe. The fact that it doesn't seem to happen would imply to me that P factor is very small compared with torque roll effects. And the fact that most models with downthrust exhibit left rolling tendency at slow speeds and seldom right yaw at high, suggets the same.

Oh, and P factor doesn't prduce a ground loop either.

But a spiralling propwash hitting the top of the fin does just that.

And right thrust will angle that propwash to hit one side of it, effectively counteracting the yaw nicely.

Or you can have lots of fin below the centerline of the motor. That works too.

[robert harik]

[QUOTE=vintage1]Oh, and P factor doesn't prduce a ground loop either.

No, but gyroscopic precession does.(oh no not another one!)

At least in a tail dragger.

On the take off roll When you bring the tail up or it comes up on its own the nose wants to swing left hard ( it really depends on how fast you bring the tail up and how much mass your spinning, like say a heavy metal prop on a light airplane) and if you dont put in lots of right rudder, your goin on around! Wheeee!

This is also very true for model tail traggers.

[Chas]

There's also the point, regarding torque, that it only applies to accelerations and decellerations. My old Ford V8 rocks on its mountings when I step on the gas, but when it reaches a steady speed again the engine settles happily onto its blocks. Torque 0, Spiral Slipsteam 1.

Also, P-factor can not apply at the start of a take-off run, because the aircraft is not moving. Discounting any wind, P-factor can only possibly be an influence when there is a forward movement of the propeller disc, inclined to the plane of that disc. So Robert is quite right, the initial swing is all spiral slipstream (first part) andgyroscopic precession (when the tail comes up). Torque might press a little harder on that left wheel for wet grass!
Chas

[banktoturn]

ARRRRGHH!!!!!!
Come on folks let's get the terms and reasons CORRECT!!!!

Right thrust can not, will not, is physically imposible, to have any effect AT ALL on torque! Right thrust corrects for P-factor and P-factor ONLY!!!

Now surprisingly, down thrust often eliminates most of the p-factor that made you think you needed right thrust in the first place.

Tom

Tom,

Right thrust could be used to compensate for P-factor, but it is not correct to state that it corrects for P-factor only. Right thrust could be used to compensate for any source of yaw torque, of which there are more than one. The yaw caused by the spiral slipstream of the prop impinging on the vertical stabilizer is one, and is probably a bigger problem than P-factor.

banktoturn

[vintage1]

[QUOTE=vintage1]Oh, and P factor doesn't prduce a ground loop either.

No, but gyroscopic precession does.(oh no not another one!)

At least in a tail dragger.

On the take off roll When you bring the tail up or it comes up on its own the nose wants to swing left hard ( it really depends on how fast you bring the tail up and how much mass your spinning, like say a heavy metal prop on a light airplane) and if you dont put in lots of right rudder, your goin on around! Wheeee!

This is also very true for model tail traggers.

Yes. No argument with that one.

[vintage1]

There's also the point, regarding torque, that it only applies to accelerations and decellerations. My old Ford V8 rocks on its mountings when I step on the gas, but when it reaches a steady speed again the engine settles happily onto its blocks. Torque 0, Spiral Slipsteam 1.


That not true either. If you had that engine under load it WOULD be producing torque and would cant the engine over...and a propellor is a load.

In your case the temporary load is provided by the inertia of teh flywheel carmnk etc. It takes atorwue to accelerate them.

But when driving along with no hood, at high power that engine will be visibly rocked over on its mountings just the same...or haven't you done that? :D

The effects of torque are easily seen in the hover, where the model will rotate against the prop torque.

[globemaster3c17]

There's also the point, regarding torque, that it only applies to accelerations and decellerations. My old Ford V8 rocks on its mountings when I step on the gas, but when it reaches a steady speed again the engine settles happily onto its blocks. Torque 0, Spiral Slipsteam 1.
If that were true for flying, then helicoptors would need a tail rotor only part of the time. The torque talked about with flying an airplane deals with spinning the prop. Any time the prop is spinning, there is torque being applied in the opposite direction of rotation. That is because any time a prop is spinning, it is generating drag. If you were spinning the prop in a vacuum, then what you mentioned would be correct. But, what would be the point of having a prop inside a vacuum?

[Andy W]

What happens when you turn an airplane upside down?

..a

[Chas]

Sorry guys, you're confusing torque with drag. Torque applies in a vacuum, of course, and will be nought at a constant speed. Drag reaction from a spinning prop or rotor is, of course, a constant factor, and is why helicopters need tail rotors.

Vintage,
If it's under load it's accelerating. If it's steady state, there is no load. Let's not start this again!

Banktoturn
Yaw torque? That's a new one! Let's get the terms right guys.

Chas

[Chas]

Andy,
Exactly! The right-thrusters would have you believe that right thrust still counteracts torque even with the aircraft inverted - but of course right thrust is then left thrust. Go figure!

Chas

[Andy W]

I have an awful lot of torque and thrust in an F5B model, pushing 1000W+ thru a 15 or 16" prop. There is no hint of torque roll or yaw when the model is launched and flown at safe speeds. So I'm inclined to think it's really only needed for sport models where pilots don't want the hassle of using a touch of rudder to correct for the p-factor on takeoff. If I want straight and true tracking in flight, I want no offset in the mount..

.. but that's just my inexperienced opinion.. I'm hoping the real experts in aerobatic flying will chime in at some point..
..a

[raptor22]

My questrion still remains; can I calculate amounts of DOWNTHRUST needed for something like a plank w/ a high wing or a pylon racer like the stinger that also has a high wing?

--Alex

[Chas]

Alex,
You don't need downthrust. Therefore you don't need to calculate it.
Downthrust is only an attempt to compensate for a displacement of the thrustline vis-a-vis the centre of resistance, namely drag.
It was only ever "invented" because the early days of radio, or the free-flight era, meant that you had no pitch control. Therefore the designers had to find some setting at which "power on" flight would not utterly discomnabulate the glide.
So, they set up the airframe to glide properly, but then had to put the engine at ridiculous "downthrust" angles to get it to fly under power without looping back into the ground. In some cases (eg Sharkface radio, or most contest power freeflights) these angles were 15 degrees!!

It's totally unnecessary now. You have pitch control, and pitch trim. These are the ways in which you should be handling power variations.

Asking how to calculate downthrust is like asking how to hide the unsightliness of your whalebone corset. Answer: "Don't".

Chas

[banktoturn]

Sorry guys, you're confusing torque with drag. Torque applies in a vacuum, of course, and will be nought at a constant speed. Drag reaction from a spinning prop or rotor is, of course, a constant factor, and is why helicopters need tail rotors.

Vintage,
If it's under load it's accelerating. If it's steady state, there is no load. Let's not start this again!

Banktoturn
Yaw torque? That's a new one! Let's get the terms right guys.

Chas

Chas,

In order to describe a torque, you must specify the axis in which it acts. The torque which has been referred to most frequently in this thread would be roll torque, which would be a torque which tends to cause the plane to roll. I am describing torque in the yaw axis, and want to make sure it is not mistaken for torque in the roll axis. What's the problem?

banktoturn

[Majortomski]

My questrion still remains; can I calculate amounts of DOWNTHRUST needed for something like a plank w/ a high wing or a pylon racer like the stinger that also has a high wing?

--Alex

You could run a lot of math to determine your down thrust. Again, as lost in the above posts, downthrust primarily is a way to cheat at not re trimming your model with each and every power change. To empirically find out how much down thrust you need, fly your model at 1/3 throttle, and trim it to hold that attitude. now go to full throttle if the airplane goes into any form of climb, land add one small washer between the engine mount flange and the engine mount itself under the rear two bolts. Then tighten the front bolts and then rear bolts and go fly again. If the plane still climbs, land and add another washer.

Why this works. For most aircraft there is only one airspeed at which the natural downward pitching moment of the wing is in ballanc with the down thrust on the stabilizer. For 1:1 aircraft that cruise at one speed for long times it isn't much of a problem to retrim for a power change. In our case the increas in airspeed ususally causes more stabilizer down force which causes the airplane to nose up. We're using the bit of down thrust to pull the nose back down at the higher speed. A negative side effect of this cheating is if you're boaring around at full throttle and then suddenly chop the throtlle t he plane will pitch up becasue the down force from the down thrust is now gone and the stabilizer will do its designed job.

And I could rant for hours on the myth of slipstream spiral.

Tom

[raptor22]

In a high wing plank flying wing, the center of pressure is above the thrustline due to wing being up there, and will induce an upward pitch when power is applied.

The airplane will be trimmed for gliding flight (where it will spend most of its time as an electrified sloper type of thing), so trim designed to hold the nose down will screw me up in most situations.

The way to counter this is downthrust, since my problem will not be aerodynamic but will be due to motor power and exactly variable to the power being applied.

See my point? Downthrust is a more elegant solution than just pushing down at high power settings, although it is not "required".

--Alex

P.S., as a plank I don't worry about stabilizers; my pitching moment in nearly zero for the airfoil (.00001 or something similar).

[banktoturn]

Alex,
You don't need downthrust. Therefore you don't need to calculate it.
Downthrust is only an attempt to compensate for a displacement of the thrustline vis-a-vis the centre of resistance, namely drag.
It was only ever "invented" because the early days of radio, or the free-flight era, meant that you had no pitch control. Therefore the designers had to find some setting at which "power on" flight would not utterly discomnabulate the glide.
So, they set up the airframe to glide properly, but then had to put the engine at ridiculous "downthrust" angles to get it to fly under power without looping back into the ground. In some cases (eg Sharkface radio, or most contest power freeflights) these angles were 15 degrees!!

It's totally unnecessary now. You have pitch control, and pitch trim. These are the ways in which you should be handling power variations.

Asking how to calculate downthrust is like asking how to hide the unsightliness of your whalebone corset. Answer: "Don't".

Chas

Chas,

You are being a bit too general. Downthrust is often used on a plane like a trainer, which typically has a wing with a lot of camber, and hence tends to generate high coefficient of lift. Since the wing is at positive incidence, it will make a lot of lift as the airspeed goes up, and would require a lot of trim change for different speeds. Downthrust is used to reduce the amount of trim adjustment required.

banktoturn

[globemaster3c17]

Sorry guys, you're confusing torque with drag. Torque applies in a vacuum, of course, and will be nought at a constant speed. Drag reaction from a spinning prop or rotor is, of course, a constant factor, and is why helicopters need tail rotors.

Vintage,
If it's under load it's accelerating. If it's steady state, there is no load. Let's not start this again!
Chas
Yes, what you are talking about really is a result of drag. But since the drag from the prop spinning tries to roll the plane the opposite direction, it is called the torque effect. This is a lot like induced drag. Induced drag really isn't drag, its just a rearward component of the lift vector. Don't believe me about the torque? Grab a pilot manual and take a look at the section covering left turning tendencies. Ever thought of why a torque roll is called a "torque" roll? The same force is there any time the prop is spinning.
The only time there is no load on an engine is when it is not running, or there is nothing connected to the crankshaft.

[vintage1]

Andy,
Exactly! The right-thrusters would have you believe that right thrust still counteracts torque even with the aircraft inverted - but of course right thrust is then left thrust. Go figure!

Chas

It does actually, because when upside down dihedral becones anhedral..

Aren't you the guy with the 400% efficient motor by the way?


:D

[vintage1]

To take up Andy's point and resist the trolls....

A properly designed aerobat needs nothing: But our lanes are often trimmed for more stability (decalage and dihedral) and carry much larger power to weight ratios than full size. In order to have a more or less hands off straight flying aeroplane, that is loosely modelled on a full size, downthrust and right thrust will prevent the pilot having to hold excessive down under power, and a little right stick as well.

In practice a couple of degrees is all it takes usually. One liitle plane I had I omitted it, and had to mix in down and righht on the stick to make it track more or less straight under power. It wasn't a total solution - under some powre levels it wanders left, under others right, but it ws a lot better than nothing..

On my almost-aerobat, there is none of either. Engine ,wings and tail feathers are all in a line, and symmetrical in section. There is no dihedral.

The fueselage side area is large, there is almost as much of it before the wings as behind, and the fin extends well below the centerline.

With a fairly rearward C of G there is very little climb under power tendency, and of ther is any roll under power, its well controlled with a touch of right aileron. It has of course a massive wing area for its weight.

If you are building a scale model then arguably mixing is a better way to get tracking true, since props hanging off at bent angles look odd.

But ona simple 3 channel model of the cub style, with no mixing available, you relly do need it unless you are good enough to fly with constant stick pressure.

[Chas]

Bank
There is only "roll" torque, as you term it.

Torque can not possibly act in the yaw axis. If a yaw results, it's only because of the aerodynamic setup of a particular airframe (eg its yaw/roll couple, for one), and this will not apply to many airframes . Some have virtually no yaw/roll couple, as some "rudder-only" designers found out.

"Yaw torque" does not exist, and therefore is only going to screw up any discussion if we introduce it into an already foggy picture.

For example, Majortomski says that downthrust "pulls the nose back down". Downthrust does no such thing; it simply alters the pitch trim of the aeroplane, which settles onto the new trim and flies along straight and level. If downthrust were "pulling the nose down", the aircraft would just perform a continual outside loop.

As to the torque, it only applies during power change. Globemaster mentioned a helicopter in a vacuum - good example! Assuming the mass of the rotor and fuselage to be the same, they would both be rotating at equal speed, in opposite directions of course due to torque. But there would be no torque once equilibrium had been reached, and you could not measure any at the bearing. Furthermore they would continue to spin, ad infinitum, until something else changed.

Also, Globemaster does not differentiate between "torque" and "torque effect". You should! That's why there are so many lop-sided notions floating around. Torque is a negligible and transient force. Yet people are believing in it like some sort of sacred cow, and altering their model designs to compensate for it!
If I buy a Station Wagon like Mr. Griswold with "wood effect" side panels, how smart would I be to sand them down and revarnish the vinyl? Same with "torque effect" - it ain't torque!

I think a lot of the problems arise because of the car-drivers notion that you increase power to go faster. In aeroplane driving, it's different - the throttle is a device for controlling ALTITUDE. The elevators (and their associated trim) are devices for controlling AIRSPEED.

Vintage

You are introducing spurious terms, as usual. Who said anything about dihedral? If you introduce dihedral you are bringing in a whole new raft of aerodynamic implications which conveniently result in effects which support your "downthrust" belief.

There's no escaping the fact that in an inverted airframe "right" thrust becomes "left" thrust. Torque doesn't change. For a level playing field, assume a level wing. Now, how does sidethrust work again?

My motors are not even 100% efficient. I miss the point of your remark entirely, sorry. I dare say you are trying to rubbish my previous posts, but that's not what we're supposed to be here for, and exhibits a lack of objectivity which you purport to endorse. Could you be a bit more specific about which contributor you regard as a troll?

Chas

[Chas]

Vintage,
I have just noticed that you said a club trainer needs to fly with "constant stick pressure". This is the concrete mindset which we need to break if we are to avoid inefficient and over-complicated models, perpetuating this 19th century fallacy into the future.Save our aeromodelling children!

If you have to hold constant stick pressure your TRIM is WRONG. You need less wing incidence, or more tail incidence, or a more rearward CG, or whatever. Trying to get it to fly right by messing about with the thrustline is futile, and in any case will only EVER be right at ONE speed.

Of course, some aeroplanes need more trim variation with power changes than others. If they're grossly over-reactive to power changes, the design is c***, which is what I said at the start.

Chas

[banktoturn]

Bank
There is only "roll" torque, as you term it.

Torque can not possibly act in the yaw axis. If a yaw results, it's only because of the aerodynamic setup of a particular airframe (eg its yaw/roll couple, for one), and this will not apply to many airframes . Some have virtually no yaw/roll couple, as some "rudder-only" designers found out.

"Yaw torque" does not exist, and therefore is only going to screw up any discussion if we introduce it into an already foggy picture.

For example, Majortomski says that downthrust "pulls the nose back down". Downthrust does no such thing; it simply alters the pitch trim of the aeroplane, which settles onto the new trim and flies along straight and level. If downthrust were "pulling the nose down", the aircraft would just perform a continual outside loop.

As to the torque, it only applies during power change. Globemaster mentioned a helicopter in a vacuum - good example! Assuming the mass of the rotor and fuselage to be the same, they would both be rotating at equal speed, in opposite directions of course due to torque. But there would be no torque once equilibrium had been reached, and you could not measure any at the bearing. Furthermore they would continue to spin, ad infinitum, until something else changed.

Also, Globemaster does not differentiate between "torque" and "torque effect". You should! That's why there are so many lop-sided notions floating around. Torque is a negligible and transient force. Yet people are believing in it like some sort of sacred cow, and altering their model designs to compensate for it!
If I buy a Station Wagon like Mr. Griswold with "wood effect" side panels, how smart would I be to sand them down and revarnish the vinyl? Same with "torque effect" - it ain't torque!

I think a lot of the problems arise because of the car-drivers notion that you increase power to go faster. In aeroplane driving, it's different - the throttle is a device for controlling ALTITUDE. The elevators (and their associated trim) are devices for controlling AIRSPEED.

Vintage

You are introducing spurious terms, as usual. Who said anything about dihedral? If you introduce dihedral you are bringing in a whole new raft of aerodynamic implications which conveniently result in effects which support your "downthrust" belief.

There's no escaping the fact that in an inverted airframe "right" thrust becomes "left" thrust. Torque doesn't change. For a level playing field, assume a level wing. Now, how does sidethrust work again?

My motors are not even 100% efficient. I miss the point of your remark entirely, sorry. I dare say you are trying to rubbish my previous posts, but that's not what we're supposed to be here for, and exhibits a lack of objectivity which you purport to endorse. Could you be a bit more specific about which contributor you regard as a troll?

Chas

Chas,

I think you've now demonstrated that you should not be the guy in charge of terms. Torque can act in any axis. Consider looking up the definition of the word before you post again. When a rudder is deflected, or a spiral slipstream impinges on the vertical stabilizer, torque is being exerted in the yaw axis, which is what causes the plane to yaw. Any rotation of the plane is caused by torque acting in the corresponding axis. The fact that you declare torque to exist only in the roll axis is really amazingly silly. Could you please tell me why you think this is true?

Downthrust definitely tends to pull the nose down. You can describe the situation in terms of trim if you like, but it doesn't change that fact. On a plane which needs it, the increasing downthrust as the throttle is opened is intended to counteract the increasing lift generated by a wing operating at a higher airspeed. In level flight, the plane will definitely fly faster when the throttle is opened, regardless of the conventional wisdom that throttle is used to control altitude. Throttle is a perfectly valid and effective way to control airspeed.

Torque, in the roll axis, is being exerted when the engine is running, whether the power level is being changed or not. The prop exerts torque on the air, and it must be balanced by the airframe. When the throttle is opened, there is a transient increase in torque as the propeller is accelerated, but torque definitely does not go down to zero after the prop reaches constant speed again. If it did, you could shut off the engine once you get the prop to the desired speed. Where are you getting this stuff? You seem to think that torque can only result from the engine accelerating the prop. Is that it? The rest of the world uses the word 'torque' to the full extent of its definition. If you insist on restricting its definition in your favorite way, you will probably have a lot of these kinds of discussions.

banktoturn

[Chas]

Bank
We were discussing the torque as it is applied to the propeller. That is, the torque transmitted via the engine crankshaft. This can only, ever, be a force acting in roll. If you want to talk about spiral slipstream and rudder deflections causing a rotation in the yaw plane, start a new thread, because that's a different subject.

You say "the prop exerts torque on the air". What utter nonsense!
Engine torque is the rotating force applied to the crankshaft. Period. It works in a vacuum. The "equal and opposite" roll reaction to engine torque would be exactly the same in a vacuum, assuming your engine would run. Do you think there is no torque in a vacuum? Like I said above, you're confusing prop drag reaction with torque.

Downthrust does not pull the nose down. If it did, what would stop it from pulling the nose down all the way around an outside loop? Downthrust causes a nose-down pitch, which with a pre-existing level flight trim situation where nothing else is altered, results in a balance (ie., equilibrium) being achieved at a lower alpha. The nose down pitch is not a pulling down of the nose, and if you think it is you'd better check your own dictionary.

Chas

[banktoturn]

Bank
We were discussing the torque as it is applied to the propeller. That is, the torque transmitted via the engine crankshaft. This can only, ever, be a force acting in roll. If you want to talk about spiral slipstream and rudder deflections causing a rotation in the yaw plane, start a new thread, because that's a different subject.

You say "the prop exerts torque on the air". What utter nonsense!
Engine torque is the rotating force applied to the crankshaft. Period. It works in a vacuum. The "equal and opposite" roll reaction to engine torque would be exactly the same in a vacuum, assuming your engine would run. Do you think there is no torque in a vacuum? Like I said above, you're confusing prop drag reaction with torque.

Downthrust does not pull the nose down. If it did, what would stop it from pulling the nose down all the way around an outside loop? Downthrust causes a nose-down pitch, which with a pre-existing level flight trim situation where nothing else is altered, results in a balance (ie., equilibrium) being achieved at a lower alpha. The nose down pitch is not a pulling down of the nose, and if you think it is you'd better check your own dictionary.

Chas

Chas,

You seem to be confusing what YOU were discussing with what WE were discussing. If you go back to the beginning of the thread, you will see that it is titled: "downthrust?!?!? righthrust?!?!?". Downthrust would affect pitch, and rightthrust would affect yaw. Interestingly, the only torque you are interested in would affect only roll, which was not part of the original topic at all. My use of your private word, 'torque', caused you to assume that I was referring to torque exerted by the engine, which I was not.

There is definitely some nonsense in the vicinity. Let me ask you, if you exert torque on the shaft, and it is connected to the propeller, what is the propeller exerting torque on? What you want to exclusively call 'drag' is simply the mechanism by which a propeller exerts torque on the air. Yeah, there can be torque in a vacuum. There can also be torque without any angular acceleration, due to the drag forces acting on the propeller at a distance from the crankshaft. Hint: prop drag and torque are not exclusive.

Downthrust certainly does pull the nose down. This is true even at equilibrium, in which case that force is being balanced by other forces, not the least of which is the lift generated by the wing, which is the whole point of using downthrust in the first place.

banktoturn

[Chas]

No, torque came in at Post No. 2.

You're fixated on observable effects in a whole real aeroplane, and don't seem able to narrow the concepts down to the specifics of the discussed terms. Take torque for example.

Torque is the rotational force applied to a shaft, or at least a body capable of rotation, like a nut or a screw. Air is a three-dimensional fluid medium, and there is no way you can apply torque to it.

As for your idea of the nose being pulled down, and how I'm saying this is NOT the same as a nose-down pitch, ok let's try one more time. It's not being pedantic or semantic, it's NECESSARY to understand the discussion with any precision.

OK you're flying along straight and level and your tailwheel drops off. You experience a nose-down pitch. Agreed? Has the nose been pulled down? No.

The single channel flyers in the fifties used motor control in "normally" trimmed airframes instead of elevator. They opened the taps and looped. Ask any pilot, open the throttle and you will climb, but at the same speed. That is, if you leave everything else alone. This is basic flight school stuff.

Using downthrust to counter-act the "lift of the wing" as you call it, is surely one half-assed way to fly. Spoil the lift by using extra power? Why not put the prop on backwards or tie bricks to the thing and be done with it?

Chas

[banktoturn]

No, torque came in at Post No. 2.

You're fixated on observable effects in a whole real aeroplane, and don't seem able to narrow the concepts down to the specifics of the discussed terms. Take torque for example.

Torque is the rotational force applied to a shaft, or at least a body capable of rotation, like a nut or a screw. Air is a three-dimensional fluid medium, and there is no way you can apply torque to it.

As for your idea of the nose being pulled down, and how I'm saying this is NOT the same as a nose-down pitch, ok let's try one more time. It's not being pedantic or semantic, it's NECESSARY to understand the discussion with any precision.

OK you're flying along straight and level and your tailwheel drops off. You experience a nose-down pitch. Agreed? Has the nose been pulled down? No.

The single channel flyers in the fifties used motor control in "normally" trimmed airframes instead of elevator. They opened the taps and looped. Ask any pilot, open the throttle and you will climb, but at the same speed. That is, if you leave everything else alone. This is basic flight school stuff.

Using downthrust to counter-act the "lift of the wing" as you call it, is surely one half-assed way to fly. Spoil the lift by using extra power? Why not put the prop on backwards or tie bricks to the thing and be done with it?

Chas

Chas,

You are simply wrong about torque. No shaft needs to be involved for torque to be exerted, nor does anything need to rotate. If you exert a force at a distance from an axis, then you are exerting a torque about that axis. The rudder exerts torque about the yaw axis. A propeller, by virtue of the drag force it exerts on the air along its span, exerts torque on the air.

If a force is exerted on an object in a particular direction, it is reasonable to say that the object is pulled in that direction. An engine mounted on the nose of a plane with a small downward angle in the thrustline will simply pull down on the nose. You can compensate for the force, if you like, to maintain equilibrium, but the force doesn't disappear.

You can disparage the use of downthrust if you like, but this is exactly why it is designed into some planes. If it really bothers you, try decaf.

banktoturn

[globemaster3c17]

I think a lot of the problems arise because of the car-drivers notion that you increase power to go faster. In aeroplane driving, it's different - the throttle is a device for controlling ALTITUDE. The elevators (and their associated trim) are devices for controlling AIRSPEED.


Chas, we could probably go around and around on the torque subject. But, I have to agree quite a bit with what I quoted from you. I've been thinking about posting info on that for a while, but just haven't got everything pulled together so I can explain everything. The best way to say what you are talking about is using the phrase "pitch plus power equals performance". Since it is way off subject from the original topic, I won't write more on that until I write that post I've been planning on doing.

[Chas]

Chas,

A propeller, by virtue of the drag force it exerts on the air along its span, exerts torque on the air.


banktoturn

Hmm, where to start? Please don't take this wrongly Bank, but I just think you are confusing the drag reactive force of a propeller, with torque.

Look, a propeller doesn't exert a drag force on the air. If anything, the drag which the air exerts upon the propeller may be observed at the prop hub as a force in contra-rotation to the direction of rotation, but this is NOT torque!!

There must be a shaft for torque. You can't have torque about an invisible axis, like the vertical (yaw) axis of an aeroplane. It's an imaginary point; how can you torque it? You can't exert forces on imaginary points, any more than you can thin air.

My problem is not caffeine.

[Chas]

Globie,
Thanks, it seems pretty reasonable to me at least - amazingly silly or simply wrong as I may be! So I guess I'll stop the going round and round on it and shut up, the basic notions are there for anyone to read.

I'd love to hear some cohesive ideas on the power/trim situation, please do break a bottle on a new thread. I promise to read-only!
Cheers
Chas

[globemaster3c17]

Thanks Chaos, I hopefully will get that typed up here in a few days. I'm trying to see if I can try to debunk a lot of flying myths I've seen R/C pilots throw around.
But just so you know, it really is torque we are talking about. Take a look in a dictionary. The following are definitions from Webster.com
Main Entry: 2torque
Function: noun
Etymology: Latin torquEre to twist
1 : a force that produces or tends to produce rotation or torsion <an automobile engine delivers torque to the drive shaft>; also : a measure of the effectiveness of such a force that consists of the product of the force and the perpendicular distance from the line of action of the force to the axis of rotation
2 : a turning or twisting force
Main Entry: 3torque
Function: transitive verb
Inflected Form(s): torqued; torqu·ing
: to impart torque to : cause to twist (as about an axis)
- torqu·er noun

[Chas]

Fine. But you can't have torque without a physical object as the axis.
I think everyone knows that engine torque was the subject of this thread.

Chaos

[banktoturn]

Fine. But you can't have torque without a physical object as the axis.
I think everyone knows that engine torque was the subject of this thread.

Chaos

Chas,

We seem to have zeroed in on the disconnect. It is simply not the case that an obvious physical axis, such as a crankshaft, is needed for torque to be exerted. If you exert a force on an object, we could choose to specify an arbitrary axis, inside or outside of the object, and then calculate the torque corresponding to that force, around that axis. If you exert a force on an object, you impart momentum. Analagously, if you exert a torqe on an object, you impart angular momentum. This is true even if the 'object' is a region of air in the atmosphere, and it doesn't require the existence of anything that is recognizable as an axis. It is also true if the torque is exerted in an axis other than the roll axis of an aircraft. It is also true that torque is exerted by things that aren't aircraft engines, such as control surfaces.

Engine torque is not the subject of this thread. The subject of the thread is the purpose and effects of right thrust and down thrust. Irsudog, in the second post, made the incorrect observation that right thrust and down thrust are used to counteract the effect of torque, and he did seem to be referring to engine torque, but that doesn't make it the subject of the thread.

banktoturn

[John O'Sullivan]

I think it's time to back off from a gaggle of self styled pseudo experts monopolizing this discussion. They are egotistic self-proclaimed experts, whose expertise is based more on egotism than fact.
Get real and get out and fly. Models don't believe in BS!

[Chas]

Thanks for the BS John. Great input!

Bank
There must definitely be a physical object for torque to exist. It is a force. You can't exert a force on an imaginary object, like a yaw axis. There are points about which forces are "considered to act", like the CG for example, but that's not torque.

There is a disconnect, and it's the sloppy description of torque I referred to earlier. I didn't understand at first why Globie provided us with a definition of torque, because nobody seems to be disputing it, but then I realised that he isn't differentiating between torque, and torque reaction. They are literally diametric opposites.

Globie seems keen on his Funk and Wagnall, but
I have consulted The Bible, and St. Simons says, speaking of propellers:-

"Drag forces resist the rotary motion, producing a torque reaction against the drive shaft. The aeroplane experiences this torque as a force tending to cause it to roll one way or the other, depending on the direction of propeller rotation. (Some aileron trim is required to counteract this).

When the drag-torque reaction equals the shaft torque from the engine, the maximum rate of rotation is reached for the particular set of conditions.".

Chaos

[John O'Sullivan]

Do you guys actually fly models or waffle on indefinitely about it?
Remember flying models were not around when they wrote the bible so it has no knowledge of aerodynamics

[Chas]

Flew models since 1960 John, and I know that I'm no expert. But this is a "discussion", which has clearly illustrated that there are several points of view about apparently "settled" issues. That's one of the beauties of human discourse, and one of the attractions of a review, with an open mind, of our old prejudices.

If you don't find it interesting, go fly your planes.

The Bible referred to was "Model Aircraft Aerodynamics" by Martin Simons, and he has been observed by independent witnesses to emerge from his academic cloister and actually lay hands upon aeroplanes.

By the way, watch your syntax! Books, Bibles or not, are incapable of knowing anything.

Anyway, there were some pretty advanced machineries around in Biblical times. Haven't you ever heard of "the roar of Moses' Triumph"?

Chaos

[robert harik]

This thread is good, because it made me get out my old books and look stuff up.
I did not realise how much I had forgoten.

[John O'Sullivan]

1960 was the year I flew in my first FF Power World Championships at Cranfield, GB. Beat the Brits too!
I have also for many years been familiar with Martin Simons publications and find him less pontificating than Chas.

John O'Sullivan

[Chas]

Then if you have any light to shed upon this subject, from your great store of experience, please do. Otherwise, there can be little greater "ego" or "pontificating" than that shown by someone who butts into a thread with no input whatsoever other than
a rude and insulting commentary upon the personalities involved.

Chaos

[robert harik]

Instead cutting someone down with insults , use arguments on the subject at hand.
Rob

[Kwok_Yu]

This thread pops up in my email all the time. I replyed way back in post#4, but since then it has been a lot of bickering about nothing. Well, a few good point were made. It seems to me that there are alot of arguement about force, torque, and axis. So I would like to bring up this point. In engineering, they use a tool called a "free body diagram". It's just a picture of the object. Forces are represented by arrows. Torque is refered to as moments, which are represented by curved arrows around the axis they act on. So lets take a prop and put it is space and draw its freebody diagram. The are not forces on it, no gravity and no friction. So our picture is just a prop with no arrows. Let's say we spin it with our finger. What would the diagram look like now? It would be a picture of the prop with an arrow at the prop tip. So did we apply a force or a moment? Is there a moment? If so why isn't it on the diagram.

The answer is that a force and a moment is basically the same thing. You can redraw the free body diagram to show a moment. It would be a moment around the prop shaft axis and a force also acting at the center in the prop plane. With this second diagram it easy to see what happen when we flipped the prop. The moment spins the prop and the force of the finger flick caused the entire prop to move off in a straight line.

In fact you can draw this diagram in infinitely different ways. With hundreds of moments and forces acting anywhere you like, for this simple prop flick. Look how much time it takes me to present such a simple point. It would be almost impossible to argue anything complicated in is forum and to have it make sense. Just say your point and move on. Well, that's my thoughts for today.

{Edit}
Oh, forgot something. If two people argued to the death, one using diag#1 (just a force) and one using diag#2 (moment,force & axis). What would be the point? They are eqivalent. Ok that's really the end. Bye.

[Chas]

Much as I hate to be driven into this interminable definitions game, I can't help but resort to a dictionary if you say that force and moment are the same thing. The following is from the dictionary, not from me:-

"FORCE, in physics, influence that moves something; a physical influence that tends to change the position of an object with mass, equal to the rate of change in momentum of the object. Symbol F."

And a very good symbol too.

Force is clearly then, a physical entity with real, material application. Not arrows on paper representing it.

Chas

[Chas]

{Edit}
Oh, forgot something. If two people argued to the death, one using diag#1 (just a force) and one using diag#2 (moment,force & axis). What would be the point? They are eqivalent. Ok that's really the end. Bye.[/QUOTE]


So why did you post a few hundred words to argue the toss? :D

Chas

[1705493]

To every action, there's an equal and opposite REACTION. In all of this discussion, aren't we referring to torque REACTION and how it relates to trimming an aircraft? If that's been covered somewhere and I missed it, I apologize.

I think that true torque reaction is only significant when increasing or decreasing rpm rapidly. I suspect that the drag of the propeller, (or rotor blades) has a greater effect on the need for a counterbalancing force, such as that provided by a tail rotor in a heli or right thrust as in an airplane. Yes, right thrust implies that it acts on the yaw component but all I know is that in free flight, peeling off (roll) to the left (and into the ground) is easily trimmed out by adding right thrust. It shouldn't work but it does. How is the question, I guess. I'm sure that the Wrights gave this problem great attention and handily solved it by using twin, counterrotating props.

I have an exact scale 1/2A Tsunami that has no right OR downthrust and it flys great. Knife edges, right or left with no pitching either way. I suspect that the low thrust line is a major factor. There IS a small pitching trim change between high and low throttle but I usually trim for full throttle and put a little back pressure on the stick when coming in to land. JMTCW

Now, about that downwind turn,,,, uh, never mind.

[Kwok_Yu]

I said a moment and force is equivalent, not the same but basically the same. Otherwise their definition would be the same.

http://www.hancockjoist.com/glossary.htm#M
One definition of a Moment:
"The tendency of a force to cause a rotation about a point or axis which in turn produces bending stresses"
By definition, you can't have a moment without a force.


Forces are always represented by vectors because they have a magnitude and a direction.

Force is clearly then, a physical entity with real, material application. Not arrows on paper representing it.
Chas

[vintage1]

Torque is present at all times with a spining propellor, the wtorque is basically a function of blade drag (force) integrated over the blade radius.

It does of coure change sharply and dramatically in magnitude when e.g. opening te throttle, as extra torque is required to accelerate the mass of the blades and motor rotor up to the new RPM. This will probably be most noticeable on outrunner motors.

As far as this statement goes

Force is clearly then, a physical entity with real, material application. Not arrows on paper representing it. you have to go right to the limits of the philsophy of science to discover that the above statement is pretty much meaningless.

Everything in the world that we know of its 'arrows in the mind' so to speak representing what may, or in fact may not be, 'phsyical entities'.

We cannot in fact, prove that the physical world exists at all. Howoever it seems conveninet to assume it does for the purposes of stuffing burgers down our throats and flying toy airplanes :D

[Chas]

I agree Vintage. But we were talking about real, live, actual model airplanes, and real, live torque. There's no need to bring in Wittgenstein. The descent into hair-splitting definition was necessary because people were applying simple terms like "torque" to inappropriate phenomena, like for example rudder yaw. Correcting a term like "yaw torque" is not philosophy - I'm sure you especially would try to put that right!

1705493

Post 41, first paragraph; Post 47, second paragraph to Bank - and elsewhere.

As to right thrust, there is no denying it has an effect, but with radio it's totally unecessary. You mentioned free=flight - yes, it's handy there, because you have to trim for two conditions (power on at launch and power off at the end) without having in-flight control. You can set up the glide to perfection, but with engine on the trim is hopelessly upset again, especially in high-power models, by the torque (and P-factor, and gyroscopic precession, etc), so that right thrust is a simple and effective fix.

That's why I said right at the start that down and side thrust were hang-overs from the free-flight or single-channel radio days.

Nowadays, they're just a waste of power and building fuss.

Kwok
I never once mentioned moments. They don't apply to what I'm saying. I was talking about torque, on the engine shaft, which is precisely what affects the roll behaviour of the model (although as I said, it is transient and negligible). lrsu dog did not erroneously post, he was spot on.

Chas

[banktoturn]

I agree Vintage. But we were talking about real, live, actual model airplanes, and real, live torque. There's no need to bring in Wittgenstein. The descent into hair-splitting definition was necessary because people were applying simple terms like "torque" to inappropriate phenomena, like for example rudder yaw. Correcting a term like "yaw torque" is not philosophy - I'm sure you especially would try to put that right!

1705493

Post 41, first paragraph; Post 47, second paragraph to Bank - and elsewhere.

As to right thrust, there is no denying it has an effect, but with radio it's totally unecessary. You mentioned free=flight - yes, it's handy there, because you have to trim for two conditions (power on at launch and power off at the end) without having in-flight control. You can set up the glide to perfection, but with engine on the trim is hopelessly upset again, especially in high-power models, by the torque (and P-factor, and gyroscopic precession, etc), so that right thrust is a simple and effective fix.

That's why I said right at the start that down and side thrust were hang-overs from the free-flight or single-channel radio days.

Nowadays, they're just a waste of power and building fuss.

Kwok
I never once mentioned moments. They don't apply to what I'm saying. I was talking about torque, on the engine shaft, which is precisely what affects the roll behaviour of the model (although as I said, it is transient and negligible). lrsu dog did not erroneously post, he was spot on.

Chas

Chas,

Yaw torque is a perfectly valid, unambiguous term. In discussing the forces and torques which affect an aircraft, one must be able to do so in all three axes. There are most definitely torques (same thing as moments, by the way) acting in all three axes, and they are pertinent to this thread. YOU may have been discussing engine torque, since it seems to be the only thing you consider to be willing to use the word 'torque' for, but I was not.

The trimming that most people do with their radios does not take the place of right thrust, since the torque being counteracted by right thrust depends on the throttle setting. You could perhaps mix throttle and rudder, but right thrust is just as good a solution, probably better.

Neither right thrust or down thrust are useful to counteract undesirable effects of engine torque. That particular statement in Ursudog's post is inaccurate. In fact, engine torque is in the only axis which is irrelevant to the question in the original post.

banktoturn

[Sparky Paul]

P-factor causes our usual left-turn problems.
Engine torque operates along the longitudinal axix of the plane.
Twin-engine planes don't have torque problems, but they do have p-factor problems.
The p-factor -also- operates around the YAW axis.
It has to! It's ahead and offset from the YAW axis!

[Chas]

Chas,


The trimming that most people do with their radios does not take the place of right thrust, since the torque being counteracted by right thrust depends on the throttle setting.

banktoturn

Absolutely, unequivocally, incorrect. So does your right thrust alter in flight when you throttle up or down? That's one of the main problems with right thrust. It's FIXED. Even if it "works", it's only correct at one speed.

See Martin Simons' post above. You correct for torque with aileron. Torque is a ROLL force so you use ROLL trim to correct for it.

Yaw torque? Do we have to keep going over this same fallacy? The yaw axis of an aeroplane is a notional, imaginary line. You can not have a real thing, a real force, acting on an imaginary line. What you're talking about with regard to rudder deflection etc is a moment about a point.

The real, live, genuine McCoy force known as torque requires a physical object to be torque'd.

Again, I made no claims about torque and moments being the same. I said FORCE and MOMENTS are different things. Entirely.

Chas

[banktoturn]

Absolutely, unequivocally, incorrect. So does your right thrust alter in flight when you throttle up or down? That's one of the main problems with right thrust. It's FIXED. Even if it "works", it's only correct at one speed.

See Martin Simons' post above. You correct for torque with aileron. Torque is a ROLL force so you use ROLL trim to correct for it.

Yaw torque? Do we have to keep going over this same fallacy? The yaw axis of an aeroplane is a notional, imaginary line. You can not have a real thing, a real force, acting on an imaginary line. What you're talking about with regard to rudder deflection etc is a moment about a point.

The real, live, genuine McCoy force known as torque requires a physical object to be torque'd.

Again, I made no claims about torque and moments being the same. I said FORCE and MOMENTS are different things. Entirely.

Chas

Chas,

Yes, right thrust does vary with throttle setting, because it simply directs a portion of the thrust to the right. This portion of the thrust increases and decreases with the throttle setting. That's what makes it a good solution to the problem.

A moment about a point IS torque. Moment and torque are synonyms. The aircraft IS a physical object, torque can be exerted on it in all three axes, and any number of forces exert torque on it in the yaw axis. The absence of a shaft whose recognized purpose is to transmit torque in no way eliminates the possibility of exerting torque. You are simply completely mistaken on this point. Go and look up all these words, and try to find the word 'shaft' in any of them.

banktoturn

[Chas]

xxxx

[Chas]

I have already given, under duress, a definition of "torque" above. Note the emphasis which the definition attempts to give to an actual, physical entity (a physical influence....the position of an object with mass). How much clearer could it be?

Here's "moment" -

"In Physics, the tendency to produce rotation; a product of the force times distance; the product of a quantity, for example, force, multiplied by its perpendicular distance from a given point.".

Just as clearly, this is a NOTIONAL concept, which is used to compute, explain or describe the action of force in turning environments.

Now, quite honestly if you cannot accept these very different definitions, we can't talk about the basic concepts at all. If you say that "moment and torque are synonyms", and "a moment about a point IS torque", well no wonder we get into such a conflab.


Chas

[Kwok_Yu]

Kwok
I never once mentioned moments. They don't apply to what I'm saying. I was talking about torque, on the engine shaft, which is precisely what affects the roll behaviour of the model (although as I said, it is transient and negligible). lrsu dog did not erroneously post, he was spot on.
Chas

http://www.wordiq.com/definition/Torque
The definition of torque:
"The concept of torque in physics, also called moment or couple, originated with the work of Archimedes on levers. Informally, torque can be thought of as "rotational force" .....etc"

[Chas]

Kwok
Your own definition says " the concept of torque".
The concept of torque is akin to moment; actual torque is what we encounter in the real world, and on engine shafts.
Chas

[Chas]

The rudder exerts torque about the yaw axis.

banktoturn

This is the disconnect. You can not exert actual torque about an imaginary point. You can have a moment acting upon this imaginary axis, but not actual torque.

Think of it with straight logic;

1. Torque is a FORCE.
2. Moment is not a FORCE, it is an IDEA.
3. Ergo, because of these differences, Torque and Moment can not be the same thing.

If this is not the case, I will join Colin Powell in Baghdad on the opening of his Village People Extravaganza Night.

[Kwok_Yu]

Chas:
Even in your real world. It all begins in the engine cylinder with an explosion of fuel. A force pushes the piston down. Your "torque" migrates out through the motor shaft and into the prop deforming every piece of it. Also imparting momentum to the air. Likewise doing the explosion, the engine cylinder is pushed up, torqueing the entire structure of the aircraft. It is felt everywhere, throughout the entire structure. At every point, you can describe it as a moment, a force or a combination ot both. It would be incorrect to pick one point, say the engine shaft. Then give it a pet name and say everyone elses concept is wrong. Especially based on supposed names not being correct. That's why I introduced the concept of scientifically representing forces and moments, with a diagram. And the idea, that they came be conbined and rearranged to understand what is going on. Even by your definition, "actual torque is what we encounter in the real world", is not real or exist in the real world. It is just the paticular model in your head, that you use to comprehend the forces action on an airplane (system).

[banktoturn]

This is the disconnect. You can not exert torque about an imaginary point. You can have a moment acting upon this imaginary axis, but not torque.

If this is not the case, I will join Colin Powell in Baghdad on the opening of his Village People Extravaganza Night.

Chas,

This 'imaginary point' thing is so bizarre that I almost can't figure out a way to respond to it. Where did you learn about this distinction between torque and moment? I've never heard about torque being the 'real' one and moment being the 'imaginary' one. Please tell me where I can read all about it. Please send me some specific references, so that I can carefully read them, and be prepared to post more intelligently. You are so clear about this distinction that I am sure you didn't just fabricate it, it must have come from one of your engineering textbooks, or some other authoritative source. I'm very anxious to start reading, so please let me know right away where to start.

So, if I have an airplane in my hands, and cause it to start rotating about its vertical axis, are there any circumstances under which you would admit that I exerted torque on it? What if it rotates such that one point, say the CG, does not move, and the whole plane rotates around it. Would you let me define the axis of rotation as the vertical line through that point, and thus say that I exerted torque on the airplane? If not, please explain in detail why not.

banktoturn

[Chas]

Kwok
I'm sorry but I find your description of the forces at work incomprehensible. "The engine cylinder is pushed up, torqueing the entire structure of the aircraft"? Really I am not being disparaging, I just see no logic in it. Especially the "is not real or exist in the real world" part. So tonight I'll go out and fly my planes using the concept of torque? I'd better watch my idealistic fingers!

Bank
I haven't time to send a reading list. Just look at the two dictionary definitions I gave for "torque" and "moment"; if you can't see any difference, well then what matter, just arrange for three degrees right on that engine plate and keep on flying.

Chas

[banktoturn]

Kwok
I'm sorry but I find your description of the forces at work incomprehensible. "The engine cylinder is pushed up, torqueing the entire structure of the aircraft"? Really I am not being disparaging, I just see no logic in it. Especially the "is not real or exist in the real world" part. So tonight I'll go out and fly my planes using the concept of torque? I'd better watch my idealistic fingers!

Bank
I haven't time to send a reading list. Just look at the two dictionary definitions I gave for "torque" and "moment"; if you can't see any difference, well then what matter, just arrange for three degrees right on that engine plate and keep on flying.

Chas

Thought so.

[Chas]

Ok, try this -

moment:
tendency or measure of tendency to produce motion esp. about a point or axis

(Webster)

Try to fly your 3D on a tendency, or measure of tendency!

torque:
something which produces or tends to produce rotation or torsion

Webster

Now that's more like it. Something in the real world.

We don't need to go to a PhD to understand simple words like these and their use in real life model aeroplane behaviour. Torque is what you feel and moment is a model to think about it.

A border is what you cross in the real world but it doesn't really exist. Same thing with your yaw axis - you can no more torque a yaw axis than you can break a border. Nuts, you can torque.

Chas

[banktoturn]

Ok, try this -

moment:
tendency or measure of tendency to produce motion esp. about a point or axis

(Webster)

Try to fly your 3D on a tendency, or measure of tendency!

torque:
something which produces or tends to produce rotation or torsion

Webster

Now that's more like it. Something in the real world.

We don't need to go to a PhD to understand simple words like these and their use in real life model aeroplane behaviour. Torque is what you feel and moment is a model to think about it.

A border is what you cross in the real world but it doesn't really exist. Same thing with your yaw axis - you can no more torque a yaw axis than you can break a border. Nuts, you can torque.

Chas

That is unmitigated nonsense, but it reminds me of a useful piece of advice:

"Don't wrestle a pig; you can't win, and it annoys the pig"

[Chas]

What's nonsense about it? Don't you like the Webster definitions? Why are they (and the others I posted) incorrect?

Very good on quaint, homespun insults. Not so good on rational argument.

Chas

[Sparky Paul]

...
A border is what you cross in the real world but it doesn't really exist. Same thing with your yaw axis - you can no more torque a yaw axis than you can break a border. Nuts, you can torque.

Chas
.
A nut, you can't "torque" unless you exert a force around its longitudinal axis, or, its "yaw axis" in this instance.
A rudder produces a "torque" around the "yaw axis", the same as the elevator produces a "torque" around the pitch axis, etc.
Such axes are "imaginary", yet the forces operate around them by convention.
.
"torque:
something which produces or tends to produce rotation or torsion"
.
This something... how about a force at a distance perpendicular to an axis... can also be termed a moment.
Resistance to rotation is a better term... the ever popular "Prony Brake" resists "torque".. with a force at a distance.

[Chas]

Sparky
You are absolutely correct. The point I am trying to make is that the yaw axis of an aeroplane, although it can be imagined as a point for the action of torque, can not be used as justification for a term like "yaw torque", which pre-supposed the argument which was in dispute in this thread.

The everyday use of the words was what I originally intended. It has been corrupted by semantics, as usual.

How many 5 Series would BMW sell if they advertised it as having "Plenty of moment to get you through those tough driving situations.". Torque is what gets you to work.

Chas

[Chas]

Chas,



So, if I have an airplane in my hands, and cause it to start rotating about its vertical axis, are there any circumstances under which you would admit that I exerted torque on it? What if it rotates such that one point, say the CG, does not move, and the whole plane rotates around it. Would you let me define the axis of rotation as the vertical line through that point, and thus say that I exerted torque on the airplane? If not, please explain in detail why not.

banktoturn

You can have your aeroplane rotating like a dervish around its axis if you like. Torque is a measurable force; so, please measure the torque at the yaw axis. You can't, of course, because it is just a parcel of thin air in the cabin area. It is an entirely imaginary line about which the aircraft "is said" to rotate.

You might as well try to measure the torque at the centre of a spinning balloon.

Engine torque is an actual, measurable force, an output which you can feel yourself if you care to try to stop it.

In any case, we are a million miles from the original statements about engine torque and its relationship (if any) with sidethrust. The "yaw torque" debate was a total waste of time and I still don't see any relevance of "yaw torque" :confused: to the sidethrust issue.

Chas

[raptor22]

What's nonsense about it? Don't you like the Webster definitions? Why are they (and the others I posted) incorrect?
Chas

Websters defines a boomerang as a curved stick made by australians to return. The true definition of a boomerang by the competitions and those who are interested in it is something made tor return when thrown.

Websters dictionary refers to words in terms usually thought of by the uneducated public; it can have many errors in its scientific or similar meaning.

Due to this, I think the other definitions offered would be far more accurate than those made by websters.

--Alex

[raptor22]

1. The moment of a force; the measure of a force's tendency to produce torsion and rotation about an axis, equal to the vector product of the radius vector from the axis of rotation to the point of application of the force and the force vector

Main Entry: 1torque
Pronunciation: 'tork
Function: noun
: a force that produces or tends to produce rotation or torsion; also : a measure of the effectiveness of such a force that consists of the product of the force and the perpendicular distance from the line of action of the force to the axis of rotation

torque (tôrk)
n.

A turning or twisting force.

all from dictionary.com

my point is made; it is any turning or twisting force, usually about an axis

--Alex

[raptor22]

You can have your aeroplane rotating like a dervish around its axis if you like. Torque is a measurable force; so, please measure the torque at the yaw axis. You can't, of course, because it is just a parcel of thin air in the cabin area. It is an entirely imaginary line about which the aircraft "is said" to rotate.

You might as well try to measure the torque at the centre of a spinning balloon.

Engine torque is an actual, measurable force, an output which you can feel yourself if you care to try to stop it.

In any case, we are a million miles from the original statements about engine torque and its relationship (if any) with sidethrust. The "yaw torque" debate was a total waste of time and I still don't see any relevance of "yaw torque" :confused: to the sidethrust issue.

Chas


Wanna bet? It can be extrapolated by measuring the yaw forces and calculating the moment at the cg ("torque: the moment of a force"). That isn't a MEASUREMENT, per say, but neither is tourque as you describe it a direct measurement; it has to be extrapolated as well. Why do you think it is referred to as oz/ins?!? The two units refer to something that was not measured, but extrapolated.

Oh, and you can feel torque around the yaw axis if you try to stop it! If you try manually to stop an aircraft's turning you will feel it. Possibly you could try this in a wind tunnel to actually experience it without the plane rushing past you. Anyways, its possible.

--Alex

[Chas]

Raptor

I don't know how many times we have to go over this. Webster's is fine by me; but if you don't agree with it (!!!) then let's use the definitions you have yourself provided:-

"The moment of a force..." ie., NOT a Force. It is the moment OF a Force. A cerebral representation, or notion, of the Force's action.

"torque...
a FORCE that produces.....

Your point is indeed made. Torque is an actual Force and Moment is an idealised description of it. Why do you think it's referred to in oz/in? It's because it's a palpable and real effect.

I am repeating myself but try this simple test - it's "logically necessary" -

1. Torque is a Force
2. Moment is an Idea
3. Ergo Torque and Moment can not be the same thing.

A horse is similar to a donkey, but a horse is not the same as a donkey. That's why we have the two different words "horse" and "donkey". Similarly with Torque and Moment.

Extrapolated forces won't turn a 10x6. The actual force itself does that. Sure, calculate the extrapolated force and call it moment' that's closer to the truth.

Chas

[Chas]

Websters defines a boomerang as a curved stick made by australians to return. The true definition of a boomerang by the competitions and those who are interested in it is something made tor return when thrown.



--Alex

So the competitors definition of a boomerang, the correct one according to you, also covers a Coke bottle. :eek:

Chas

[victor hull]

Aw shucks guys,
An overpowered high pylon contest free flight requires left and down thrust position of the engine. These models have a very high and forward center of lateral area. The theory is the prop wash strikes the pylon on the left side causing a right bank, thus left thrust of the engine. Down thrust of the engine is required because the over powered model is pulling the higher lift airfoil very fast through the air generating too much lift during the power phase, but is needed during the glide. A lifting tail can reduce the down thrust needed.
So, what I see is the rearward and low center of lateral area in our standard configured sports Rc models allows the engine torque to take effect to the left.
By the way, the CG of a contest free flight is normaly 75% to trailing edge balance with a lifting tail, where our Rc sports models balance about 25% to 33% of the chord without a lifting tail. I don't think this "P" factor is relevant.
So if your model is slightly or highly over powered you will have to control the torque or looping tendencies by the engine thrust angles, flying surfaces trim, and or fiddeling with the angle of attack of the wing in relationship to the stab and thrust line.
Anyway, thats my story, and I'm sticking to it. Have fun. Vj

[raptor22]

So the competitors definition of a boomerang, the correct one according to you, also covers a Coke bottle. :eek:

Chas

Yep. It wouildn't be too interesting of one though. In fact, boring.

--Alex

[Bill Mixon]

This thread sure got long in a hurry. :)

I think some of you might be looking at this a little too "deep". The posts about torque in a vacuum and all that stuff did nothing but confuse people reading this. I couldn't even figure out what part of torque you guys were discussing. So I'm going to post a little and see what you guys have to say.

Thrust setting depends heavily on the plane itself and how it will be flown.

1) Torque from the motor /prop /air or however you want to look at it causes a rolling action, and nothing else provided that the spinning mass (the prop) is not moved in pitch or yaw axis. In other words if the plane is sitting still torque is only working on the roll axis. Now if you move the plane in pitch or yaw, torque is applied due to gyroscopic procession. Yawing will cause a pitching reaction and vise versa.

2) Spiral slipstream is probably the strongest force that causes a plane to yaw and it's typically to the left. Build a plane with the same amount of rudder and stab above and below the thrust line and there will be little or no slipstream effect to cause yaw. Motor can be set at 0 and aircraft will fly straight with the exception of P-factor.

3) P-factor causes yaw, but on most model aircraft it is minimal. A counter clockwise rotating prop (when viewed from the front) will cause p-factor to yaw the plane to the left while upright. It will cause a RIGHT yaw (relative the aircraft not the ground) while inverted.

Ok, now lets hear why my 3 statements are wrong. :D

Bill

[victor hull]

Well "XOON" I guess we confused you enough.
In answer to your question. "YES"

[banktoturn]

This thread sure got long in a hurry. :)

I think some of you might be looking at this a little too "deep". The posts about torque in a vacuum and all that stuff did nothing but confuse people reading this. I couldn't even figure out what part of torque you guys were discussing. So I'm going to post a little and see what you guys have to say.

Thrust setting depends heavily on the plane itself and how it will be flown.

1) Torque from the motor /prop /air or however you want to look at it causes a rolling action, and nothing else provided that the spinning mass (the prop) is not moved in pitch or yaw axis. In other words if the plane is sitting still torque is only working on the roll axis. Now if you move the plane in pitch or yaw, torque is applied due to gyroscopic procession. Yawing will cause a pitching reaction and vise versa.

2) Spiral slipstream is probably the strongest force that causes a plane to yaw and it's typically to the left. Build a plane with the same amount of rudder and stab above and below the thrust line and there will be little or no slipstream effect to cause yaw. Motor can be set at 0 and aircraft will fly straight with the exception of P-factor.

3) P-factor causes yaw, but on most model aircraft it is minimal. A counter clockwise rotating prop (when viewed from the front) will cause p-factor to yaw the plane to the left while upright. It will cause a RIGHT yaw (relative the aircraft not the ground) while inverted.

Ok, now lets hear why my 3 statements are wrong. :D

Bill

Bill,

I think you are spot on, particularly regarding the spiral slipstream and the significance of P-factor.

banktoturn

[Chas]

Bill,
Sounds great to me! Particularly your "Torque from the motor/prop/air or however you want to look at it causes a rolling action, and nothing else...". Maybe if I had just said something like that instead of highlighting "yaw torque" we wouldn't have descended into the Poindexter dictionary fight.

Victor, I think XOON is looonng gone! :-0

Chas

[Chas]

Websters dictionary refers to words in terms usually thought of by the uneducated public;

--Alex

Alex,
I know that you do not include yourself in the unfortunate group to whom you refer, but you may still approach Websters with profit. It may, for example, enlighten you as to the correct spelling of "per se", or "torque".

This is why I am disinclined to argue hair-splitting definitions with you, lifted from dictionary.com.

Chas

[vintage1]

May I suggest that Torque Roll be contracted to Troll so we all know what we are dealing with here.

I guess the summer holidays are nearly over..:D

[Chas]

May I suggest that Torque Roll be contracted to Troll so we all know what we are dealing with here.



Vintage,
This is the second time that you have made these vague, snivelling types of suggestion after my posts. If you think I'm trolling come out and say so.

Actually my first post to this thread was in direct response to the question "What's P-factor". There was no trolling in it, just a response to the question.

My post was followed immediately by yours, wherein you raised a lot of definitive claptrap about the words used, etc etc. There are other occasions too where you have been unable to resist picking nits about definition, and thereby starting off these pointless semantic debates. Who's trolling, Vintage?

Chas

[lookes]

So....... Which way should I twist my motor??

[Chas]

Glad you asked! Well, the way I see it is........

[raptor22]

The way I see it is....


....unimportant!

Maybe you should finich your sentences......;):p

BTW, the spelling errors are typos; I can spell.

--Alex

[Bill Mixon]

So....... Which way should I twist my motor??
It's hard to say without knowing the plane, and even then trying to calculate the amount of thrust offset for a particular plane would be very complex. You typically get in the ballpark and then adjust as needed.
If you have a good understanding of the points I brought up in post #87 it's pretty easy to make an educated guess just by looking at the plane.
When it comes right down to it, you fly the plane and see if it needs or you want a thrust line adjustment. :)

Bill

[Chas]

finich

I can spell.

--Alex :D Yeah.

[banktoturn]

You can have your aeroplane rotating like a dervish around its axis if you like. Torque is a measurable force; so, please measure the torque at the yaw axis. You can't, of course, because it is just a parcel of thin air in the cabin area. It is an entirely imaginary line about which the aircraft "is said" to rotate.

You might as well try to measure the torque at the centre of a spinning balloon.

Engine torque is an actual, measurable force, an output which you can feel yourself if you care to try to stop it.

In any case, we are a million miles from the original statements about engine torque and its relationship (if any) with sidethrust. The "yaw torque" debate was a total waste of time and I still don't see any relevance of "yaw torque" :confused: to the sidethrust issue.

Chas

Chas,

I happened upon the following website in a different thread. It is written by someone who really knows his stuff. You should take a look:

www.av8n.com/how/htm/motion.html#sec-intro-torque

You'll find the relevant part in section 19.7.

If you don't want to bother looking at the site, I'll paste the interesting portion here:

__________________________________________________ ____________
Just as Newton’s first law says that to start an object moving you have to apply a force, there is a corresponding law that says to start an object turning you need to apply a torque.

You may have heard of the word “torque” in conjunction with left-turning tendency on takeoff, and you may have heard of the word “moment” in conjunction with weight & balance problems. In a deep sense, the two words are two names for the same thing. In particular,
A rolling moment is a torque in the roll-wise direction.
A pitching moment is a torque in the pitch-wise direction.
A yawing moment is a torque in the yaw-wise direction.
A familiar example: fuel and cargo cause a pitching moment, depending on how far forward or aft they are loaded. By the same token, they will cause a rolling moment if they are loaded asymmetrically left or right.

Another familiar example: gyroscopic effects are known for causing yaw-wise torques. By the same token, they can cause pitch-wise torques as well.

I will use the terms “torque” and “moment” interchangeably.
__________________________________________________ _____________

banktoturn

[Chas]

Yes, very interesting. He makes a great deal of substituting terms earlier in the piece, saying that old books are not to be relied upon for modern clarity of expression.

He has a point when he mentions that torque is not solely a force, but that it is a force applied by a lever, ie. at a distance from some other location. This is not what we were talking about. We were talking about engine output torque. Your introduction of torque or moment produced by a rudder brought in the whole issue of moments etc that have been soporifically explored above.

Engine output torque produces a roll. Only.

Chas