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Author Topic: Why right circles when they naturaly want to go in left circles?  (Read 903 times)
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chevy43
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« on: April 16, 2017, 10:58:53 AM »

Why try to make the plane go right under power?  Is it because you cant get it to circle right after power if you don't?


Thanks,
T.
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calgoddard
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« Reply #1 on: April 16, 2017, 11:30:55 AM »

The two usual flight patterns for outdoor rubber powered free flight model airplanes that I am familiar with are right - right and right - left.  

My outdoor models that have fixed props are usually trimmed to climb in circles to the right, and glide in right handed circles. They have some right thrust to help pull the model through what might otherwise be a series of stalls during the initial burst of power. Down thrust is used to avoid power stalls but too much down thrust undesirably suppresses the climb.  Right thrust can also help prevent the model from rolling to the left, into the ground, shortly after being launched.  At that time launch torque can be extremely high on a model, such as a P-30, for example.

I am told that a free wheeling right-hand prop (typical) tends to make the model glide right, so why fight this in your trim?

F1G (coupe) is a different story.  I have my coupes climb right, and then glide left when the prop folds.  The fin on one of my coupes has an airfoil configuration set up to make the model glide in left handed circles.  I fine tune with stab tilt as needed to control the size of the left hand glide circle.

Indoor rubber powered stick models (e.g. Penny Plane, A-6, F1D, etc.) usually circle left, due to about 1 - 3 degrees of built in left thrust.  They take advantage of the torque roll to induce left hand circles.

I have seen built-up indoor models like Embyros and Bostonians trimmed to circle right.  I never do this with my indoor models but people have success with right hand circling indoor models.

Hopefully the experts will chime in and correct any of my misunderstandings.  That really helps me progress in this hobby.  

« Last Edit: April 16, 2017, 11:42:32 AM by calgoddard » Logged
chevy43
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« Reply #2 on: April 16, 2017, 11:51:10 AM »

Outdoor rubber free flight - yes.  

I've been reading about right - right and right - left but it hasn't been explained why. If prop torque wants to turn it left why fight that?  So a gentle left under power to a gentle right glide might work?



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calgoddard
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« Reply #3 on: April 16, 2017, 12:36:32 PM »

I have never heard of using a left - right flight pattern with outdoor rubber powered free flight models.

As I said, right thrust helps prevent stalling during the climb and also helps preclude the model from torquing into the ground at high launch torque. Right thrust naturally produces a right circling climb.

A right-handed fixed prop (most props) produces a right handed glide.

A propeller that turns clockwise to produce forward thrust, when viewed from aft, is called right-handed. One that turns counter-clockwise, when viewed from aft,  is said to be left-handed.  The vast majority of propellers used on model airplanes are right-handed. Therefore, the rubber motor, and the winder, are wound clockwise viewed from the front.
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calgoddard
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« Reply #4 on: April 16, 2017, 07:25:42 PM »

Don Ross, in his book entitled "Rubber Powered Model Airplanes", says  that many low wing WWII and racer scale models are usually trimmed to climb left and glide right.  However, he goes on to warn that since the model is turning with the torque, extreme care is necessary in gradually working up to maximum power "to avoid a left spin."

And of course I should have said above that a right-handed FREE WHEELING PROP produces a right glide when free wheeling.  If the prop doesn't free wheel, you have a crude DT, in other words, the glide is ruined.  

Free wheel means that the prop is free to spin in response to the oncoming air during the glide.  

You probably are familiar with the many types of free-wheeler mechanisms used in our hobby.  The simplest (to use in your model airplane) and most reliable free-wheeler mechanism is the one included in the GizmoGeezer prop assembly.  It's not simple in construction, but it comes fully assembled when you buy it, and it has never failed me.  

I hope this helps.
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Warhawk
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« Reply #5 on: April 17, 2017, 12:05:05 AM »

Conventional wisdom is that high-wing airplanes do best on a right-right or a right-left flight pattern.  Low wing models do better on a left-left or left-right pattern.  Twins often wander a bit, and I wonder if the F6F shouldn't fly straight Grin   

I've had high-wing airplanes that like to fly left under power, and I let them.  I'm not certain why, but I suspect that I built in enough warp-age that it had to go left.  I've tried to correct a couple of them, but it took too much adjustment to change it and usually resulted in lower flight times. 

I believe that Mike Midkiff stated once that he trims for a straight flight under high to maximum power, and lets the model choose which way it turns after that.

Justin
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chevy43
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« Reply #6 on: April 17, 2017, 12:39:44 AM »

Thanks for the replys.  Thinking about all this is one of things that makes Free flight rubber challenging and interesting.

Now I just need to build one that is aloft long enough to wory about what pattern it flys.

Thanks,
T.
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Prosper
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« Reply #7 on: April 17, 2017, 03:54:11 AM »

Happy Easter everyone.

 
Quote from: chevy43
. . .but it hasn't been explained why. If prop torque wants to turn it left why fight that?
Exactly. Thanks for asking the question chevy43. I've asked the same question at least twice on this site and never got an answer. I mean an answer that explains in aerodynamic terms why right should be better than left.  

I take the point calgoddard raises from Don Ross's book that as power increases, the more careful you have to be during the trimming process, but I'da thought if flying in a limited area, that applies to right turns as well as left. You could trim for a right turn up to a certain torque - and then at full torque see your model do a beeline towards the industrial estate, then commence nice right turns down onto the roof of a giant warehouse. If in an unlimited area I would try Mike Midkiff's straight-flight-under-high-power method. Otherwise, for me it's left (i.e. not fighting the torque so hard), until someone can provide a technical explanation of why that's the less good option.

Stephen.
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Hepcat
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« Reply #8 on: April 17, 2017, 06:34:08 PM »

This subject came up recently in the thread about Peter Fardell’s Caudron and I put some thoughts on there about why it was so common to circle left whilst flying Indoors and I have repeated those comments below in the next couple of paragraphs:
I have pondered this matter of why indoor models are often flown left for many years.  Considering duration models first. The Americans got the use of large buildings for indoor flying back in the late 1920s I think and I would guess that modellers instinctively built light versions of outdoor models, launched them, noticed that they turned left because of torque and thought that was fine because it kept them away from the walls.  As models rapidly got much lighter the torque had a greater effect and started to bank the models too much to the left so they did the obvious thing of moving the wing over to the left giving more wing area and lift on the left wing to keep the models level.  This set-up continued for quite a while but as models got lighter and lighter it was found that the motor stick was being twisted by the torque of the rubber which moved the wing posts and this changed the incidences on the wings in such a way that the change in wing lift counteracted the effect of torque.
I am not going to say much about why indoor scale models are often flown left because I don’t know much.  I remember some top scale flyers did give some comments a year or so ago, here on Hip Pocket.  I think one consideration was the qualification rules.  Something like flying fast and banked at that start reduced the climb and kept the model off the ceiling and as the power died off the model levelled out for a landing.
I further  historical point about circling left is that in the early days of ‘gas’ models the propellers were usually large and heavy and it was thought that the upwards gyroscopic precession force when turning left was more beneficial than the downward force when turning right.
Turning now (unintentional but brilliant witticism!) to outdoor duration models; these are usually flown to the right under power. One reason, often advanced and easy to understand, is that the torque is trying to depress the port wing and in a right turn the port wing is travelling faster than the starboard wing so is trying to lift the port wing.  We appear to have a balance of forces but there is no evidence that the forces are at all similar in magnitude so that is not a conclusive answer. We are back again to the fact that adjusting rubber duration models is a matter of balancing forces by experience.  Some like thrust and torque will depend on the motor, aerodynamic ones may vary with speed and offset thrust and auto surfaced add to the mix.  Good trim often seems to favour opposites.  If you turn the rudder you oppose it with some wash-in on the wing, you oppose more downthrust with some negative on the talplane and in he extreme case of a right/left pattern for climb/glide you oppose big thruust line offsets with large aerodynamic offsets.  Anyway, although I can’t produce a single equation to back my case I still believe that it is safer and more efficient to fly in circles that oppose the torque.

John
John
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chevy43
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« Reply #9 on: April 18, 2017, 01:42:21 PM »

I'm starting to see many fantastic left circle rubber flights on youtube so I guess anything can work:

https://m.youtube.com/watch?v=xlbrx10EOZY
« Last Edit: April 18, 2017, 02:07:34 PM by chevy43 » Logged
Prosper
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« Reply #10 on: April 20, 2017, 03:39:30 AM »

Quote from: chevy43
I'm starting to see many fantastic left circle rubber flights on youtube so I guess anything can work:
Yes - if there is a definite difference between the two patterns, I'd guess it would be slight, otherwise it would have become obvious donkeys' years ago and noone wanting duration outdoors would even consider flying left.

Quote from: Hepcat
. . .the propellers were usually large and heavy and it was thought that the upwards gyroscopic precession force when turning left was more beneficial than the downward force when turning right. . .

Quote
. . .One reason, often advanced and easy to understand, is that the torque is trying to depress the port wing and in a right turn the port wing is travelling faster than the starboard wing so is trying to lift the port wing. . .

Ah now that's more like it - something I can think about. Thanks John.

Stephen.
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OZPAF
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« Reply #11 on: April 20, 2017, 05:02:23 AM »

Quote
Good trim often seems to favour opposites.  If you turn the rudder you oppose it with some wash-in on the wing, you oppose more downthrust with some negative on the talplane and in he extreme case of a right/left pattern for climb/glide you oppose big thruust line offsets with large aerodynamic offsets.  Anyway, although I can’t produce a single equation to back my case I still believe that it is safer and more efficient to fly in circles that oppose the torque.

My small amount of experience with outdoor sports duration models leads me to agree with John. I have been flying small 300mm wingspan models of around 8gm weight with 5.5 ' dia props running on a single loop of 1/8" rubber(not tan SS or similar though). I am achieving a climb to around 80-100' or more in something like 10-11 secs or so of motor run.

With this high power/weight ratio - a left climb trim has not worked for me. I trim for a fast steep right climb by balancing a small amount of right rudder against the inboard right wing wash in. If necessary I add a slight bit more right thrust to maintain a slight right turn in the cruise. The advantage of working rudder against wash in is that it appears to provide a consistent stable balance of forces that is controllable in small steps.

I accept that with lower power/weight ratios and scale subjects with low wings/low dihedral then it is easier to power trim for a climb to the left  or pro torque but I'm convinced that climbing to the right is best for efficiency.

John
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Hepcat
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« Reply #12 on: April 20, 2017, 09:46:37 PM »

There is something I deliberately left out of my last post because it seemed like a criticism of scale models but common sense tells me we are looking at reasons for the difference between right and left turns so it should be considered.
It is bad for efficiency if an aeroplane banks because the lift is no longer vertically upwards so the aeroplane must fly faster for the vertical component to equal the weight.  Flying faster needs more energy and increases drag.  Scale models usually have higher wing loadings than duration models and consequently fly faster.  If they are flying faster in a circle then centrifugal force will attempt to push the CG outwards.  I am not going to attempt to list all the forces acting on a model trying to fly sideways but obviously dihedral will try to roll the model into a bank.  If the model is turning left with torque then the right wing will be travelling faster, generating more lift, and trying to make the model bank more.  If the model banks more it flies faster and I am back to where this paragraph started.
That is what I thought I saw in the video that Chevy43 mentioned, although that was outdoors. There was a smart climb in well Banked tight left hand circles but I liked it when the power ran down, the bank and the turn disappeared, the speed reduced and the glide seemed to go on forever.
John 
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RalphS
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« Reply #13 on: April 25, 2017, 10:58:43 AM »

Have a look at this video at about 2 and half minutes. https://youtu.be/CMY6AyyDyxA

This shows what happens if you try to put too much power into a left turning model. 
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Prosper
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« Reply #14 on: April 26, 2017, 08:58:08 AM »

From what you're all saying (and illustrating, in Ralph's case) I wonder if this all boils down to staying as far away from a left-hand torque roll as possible. If that's the answer then a right turning pattern is "better" in terms of safety, but perhaps not duration.

It looks as if these duration models can have such a power burst that they must turn to avoid huge power stalls or loopa de loopa type antics. As calgoddard says up the thread, right thrust can help to tame power stalls. I presume the right thrust induces a bank, and it's this bank/turn which suppresses the stalling. However if you let the model turn left to fulfil that same requirement to suppress power stalls, then the model would be far too close to a deadly torque roll, as the video clip Ralph links to suggests. Other means of taming the power burst will impact cruise duration as calgoddard also says. So could it be that certain models or classes of model can only safely turn right?

If the above makes sense, okay, but both Johns say right is more efficient too, and I'm still struggling to see why. I like Hepcat's right turn "torque pushes left wing down but its faster speed lifts it up" balance, because it's the only thing I've read that might imply less-than-expected control deflection, and therefore less trim drag. However I suspect that there is already more trim drag caused by forcing the thing to fight the torque in a right turn, so I'm not sure if there's an overall benefit.

Quote from: Hepcat
If the model is turning left with torque then the right wing will be travelling faster, generating more lift, and trying to make the model bank more.  If the model banks more it flies faster and I am back to where this paragraph started.
I wonder how a trimmed FF model elects to fly faster? To do that wouldn't it need a reduction in drag or a pitch trim change? I would expect the model to continue at its preset trim speed in a banked turn, with the sideways lift component countering centrifugal force. As the faster wingtip lifts up, the bank causes a loss in vertical lift; the model sideslips and dihedral will lift the lower wing, until an equilibrium (balanced turn) is established. I reckon any loss of vertical lift due to banking is experienced simply as a loss of flight duration. This loss of flight duration would be the same either right or left, I'd have thought.

I'm still stuck at this initial power stage, let alone trying to figger out the ramifications of left-or-right circles on the gliding stage. . .

Stephen.
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Yak 52
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« Reply #15 on: April 26, 2017, 10:22:30 AM »

For a full understanding you need to consider 'P-factor'. This occurs when the prop disc is not aligned to the free stream airflow: https://www.aircraftspruce.com/catalog/pdf/13-09032.pdf (ignore the spiral slipstream bit John  Grin)

Torque effects are largely significant in roll. P-factor can create yaw.

When the model is flying with a high angle of attack ie nose up - the result of P-factor is a left yaw. So at modest power and normal slow flight trim (ie moderately powered indoor scale models) there is an inherent left turning force under power. In fact indoor scale trimming usually means lots of left rudder opposing significant right thrust in a left turn. This is so that as the power bleeds off you don't get an opening turn (wall = ouch) as you lose the P-factor turning effect.

Right thrust creates a downthrust effect due to P-factor. So in the excess power burst of an outdoor duration model right thrust also holds the nose down which helps prevent power stall as Cal said:

... right thrust helps prevent stalling during the climb and also helps preclude the model from torquing into the ground at high launch torque. Right thrust naturally produces a right circling climb.

In some senses downthrust is inefficient but far better than a hugely wasteful power stall.

Left thrust would create an 'upthrust' nose up moment and so would require balancing with plenty of built in downthrust - ie even less efficient.

Bear in mind that when a model is flying in equilibrium (ie not accelerating in any direction or axis) then all the different forces and moments balance each other out. This includes torque effects, P-factor, moments arising from lift and drag, control surface adjustment etc. The 'most efficient' trim state has to consider all of these together. The best overall may mean that you need some compromise in one area. For example a properly coordinated turn needs some aileron deflection (trim drag) but avoids the massive drag arising from a yawed fuselage. So efficiency is a rather woolly concept unless you look at the detail of the aerodynamic task you want to optimise your model for.


Jon
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Prosper
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« Reply #16 on: April 26, 2017, 11:49:48 AM »

Thanks Jon. I hadn't considered p-factor - certainly not as a consequence of sidethrust (duuh. . !).  That's a very useful factor to bear in mind. Personally I  think spiral slipstream may have a part in this too, having observed how changing prop blade pitch requires adjusting rudder and elevator settings. That could be simply because the airspeed of the model is altered by a different prop pitch, but I wouldn't discount trim alteration due to how the differently-pitched propwash impinges on the fuselage and tail surfaces.

Stephen.
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« Reply #17 on: April 26, 2017, 07:44:10 PM »

Quote
I wonder how a trimmed FF model elects to fly faster? To do that wouldn't it need a reduction in drag or a pitch trim change? I would expect the model to continue at its preset trim speed in a banked turn, with the sideways lift component countering centrifugal force.

Stephen I believe the answer here is that the model will need to be trimmed to the higher bank angle to handle the higher torque - it does not alter it's trim in flight. With sufficient dihedral and right thrust, wash in tabs or gurneys then the bank could be reduced, providing more lift for climb but with considerable extra trim drag.

With my small high powered sports models - the climbing turn to the right is at a very shallow bank angle and only needs 1 or at the most 2 turns during the climb which is very steep. The trim settings I find to achieve this are fairly small - slight right thrust, down thrust and a small amount of right rudder to balance some right wash in.

Thus the climb rate in my experience for high powered models is far greater for a right climbing model than for the left trimmed model, which is the efficiency I was referring to. I've confused the issue by not defining what efficiency I was referring to.

As Jon mentions the required task dictates largely the trim in the first place- whether indoor or outdoor particularly with their different power requirements.


John
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Hepcat
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« Reply #18 on: April 26, 2017, 08:46:24 PM »

Just a quick one Stephen because I am sure there is more discussion to come. As I said, when a model is banked the vertical lift is less so the speed must be incereased.  I did not say this could be achieved by trim changes.  Indeed if you do want to fly a model with a lot of bank (as often happens Indoors) it will almost certainly need a bigger rubber motor. Yet more weight and even more speed required!

John
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Prosper
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« Reply #19 on: April 29, 2017, 02:58:13 AM »

It's no good fellers; I'm getting more baffled not less. I'll happily take John and John's word that right is more efficient, at least concerning high power-to-weight ratio duration models - but I'll have to wait for another day to fully grasp why it's so. Thanks again to chevy43 for the OP - I have learned some stuff I didn't know before Smiley.

Stephen.
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