Left Turn, Right Turn which is more stable at 60*

[dragonflyerthom]

I have observed that a left turn seems to be more stable on my machine. I am thinking this is because of the direction of rotation on my Gyro. It turns clockwise if you look up. Wouldn't it be the opposite if it turned the other way?

[OzyRuss]

I've found over the yrs, "most" pilots are LH turners, seems to just happin.
Stick a newbie into the seat, commence training, sure enough they tend to turn left each time.
No big deal, then after a few hrs etc, i get em to turn RH only.........that's when things can go pear shaped a tad............usually rudder balance is all gone, ............interesting tho

Same when gettin em to fly using left hand on the stick...........interesting reactions by some..........geez russ, bugger this left hand stuff.

As to the mechanics of stability etc, right verses left turns ?????????
turn whatever way.........just deal with it

[birdy]

The biggest difference between left and right turns in gyros is the effect of the props gyroscopic resistance. One way it unloads the rotor and the other it loads it.
If you dout it, then climb to a safe alt and chop the power to idle [ next to no prop gyroscopic effect] and youll find theres no difference left or right.

My rotaxs mean its 'harder' to turn left than right, because the rotor has to counter the props force as well as pull you round the turn, right turns are easy, if the taps open. If i have to turn hard to the left, ill chop it, rip it round and fly off, easy. The tighter the turn the more youll notice it, coz your tryn to change the prop blades flight path faster, meaning they will resist more.

[C. Beaty]

You would find, Mr. Bird, that if you had a full span vertical tail, it would make no difference which way you turned.

When the prop disc is rapidly yawed, its gyroscopic precession creates either nose up or down reaction as you know from having played with a spinning bicycle wheel.

[StanFoster]

I have noticed that a hard left rudder on my SparrowHawk or my RAF would cause the nose to pitch down....and pitch up with a hard right rudder.

This goes exactly with what Chuck B just posted. Both props turn ccw looking from the rear....so a hard left yaw....looking from the rear of the prop is pulling it back at the 9 o'clock position. Gyroscopic precession makes it react 90 degree later...or like its being pulled back at the 6 o'clock position. This causes a nose down moment.

A hard right rudder input...again looking at the rear of the prop...causes the prop to be "pulled" at the 3 o'clock position...and once again our faithful gyroscopic precession law has the reaction 90 degrees later in the direction of the prop rotation...and the action noticed is the prop path being pulled at the 12 o'clock position. This pulls the nose up.

Stan

[Vance]

Hello Stan,

Your vocabulary and delivery is progressing toward the technically astute.

Thank you, Vance

[Heron]

I do have probelms turning to land right handed!
I will have to pull a little stronger and keep it a little longer to find the correct alignment.
Left hand is ok. NOw I need some more air time and emergency procedures to go solo! :D
Heron

[automan1223]

The prop may have something to do with turns but I thought that the ROTOR was flying the machine and control inputs had a lot to do with the ease of turns.

Gyroscopic precession is a major force of course as it is applied to the rotor when it is loaded in turns. At least for myself it is easier to pull back on the stick and level out in a left hand turn than to push forward slightly on a right hand turn to keep the nose down.

Most students are taught left hand turns from the start because they are easier to perform and human nature always takes the path of......plus most patterns are left hand.

If that is in fact what we are talking about.

Jonathan

[StanFoster]

Chuck or some of the other think tanks.... I have a router that turns at 30,000 rpm. Talk about a hand held gyroscope. Its neat to try to roll it on say the x axis quickly only to have it hopelessly rotate on the y axis.

I have never really ever read or heard the exact explanation of why this reaction occurs 90 degrees later in the direction of rotation. But I will type here what I have deduced is the reason why this happens. Please correct me if I am wrong...or add whatever you can.

If a disc is spinning ccw looking down from above.....and you appy pressure at the 3 o'clock position...it will of course react by going down 90 degrees later at the 12 o'clock position.

My feelings on why this occurs is that when you are applying pressure at 3 o'clock....that point has the highest velocity relative to your finger...and it instead "starts" deflecting its tilt there...and just simple geometry has it moving its greatest deflection at 12 0'clock where the speed relative to the pressure being applied at 3 o'clock is least.

Chuck or Al or Doug,or Udi......is this a fair assessment? My pea size brain burned a lot of calories coming to that simple explanation. I would like your input either correcting me or adding to it.

Thanks

[C. Beaty]

Astute, Vance, is an adjective. If you need a noun, you might try astuteness.

You wouldn’t say Stan is approaching lovely, but you might say he is approaching loveliness.

There; you have my English lesson for the day.:rolleyes:

[Vance]

Thank you Chuck! I stand corected!

[C. Beaty]

Stan, I wish I could give a simple, concise explanation of precession but I can’t.

Gyroscopic precession is an extremely complex phenomenon for which there is no simple explanation. College level physics textbooks offer no 10 word explanation. First year physics texts often give “simplified” explanations with vectors of wheel angular velocity pictured as either right or left handed screws depending upon direction of rotation and vectors of precessing torques added at oblique angles. They go on to state you’ll have to wait for your senior year before fully comprehending precession.

All things that are resonant display an equivalent phenomenon; displacement lags force by 90º, whether mechanical or electrical resonance.

[Al_Hammer]

Stan, I gave it a shot. The attached diagram is my attempt at an explanation.
It shows precession as a side effect of having an object in a circular "orbit" relative to another circle which is used as a reference point to define which way is up and down. The paths will cross and up changes to down 90 degrees later from the point of maximum up velocity(where the input is aplied).

[ckurz7000]

Well, here is an intuitive explanation of gyroscopic precession which I came up with for a high school physics course I once taught:

Imagine yourself tying a good sized potato to a piece of string and whirling it around your head ccw looking from above (don't try this at home, folks, where you can be seen by your neighbors). Now, at the 3 o'clock position the velocity of the potato will point straight forward. If you nudged the potatoe a bit downward at this point, you'd change the velocity at that point so that now the potato is moving straight forward as well as a bit downward. Remember, you haven't displaced the potatoe itself, only changed the direction in which it is moving! If the potato is moving forward and slightly downward at the 3 o'clock position, it will have reached its lowest point at the 12 o'clock position. So there you are! You pushed down at 3 o'clock (changing the potato's direction of flight) and the potato actually reached its lowest point at the 12 o'clock position (which is 90° later).

Here is an illustration (counting for a 1000 words):
32118
The potato is shown at the 3 o'clock position following initially the red trajectory. Then the nudge from above tilts its velocity downward (grey) and hence it now follows the grey trajectory. Note that the potato's new flight path has its lowest point at the 12 o'clock position -- which is those magic 90° later!

Hope that helps, -- Chris.

[Al_Hammer]

I like it. Very concise, Chris.

I should have used a potato. Our diagrams are quite similar, but you made it very clear that the direction is changed by the nudge where I only showed that for the case of linear motion. Acceleration can be a change in direction or a change in displacement.
In the case of the rotor blade, it gets its direction changed(pilot input accelerates blade), just as the potato gets nudged and changes its direction and plane of motion.

[Douglas Riley]

The rotor blowback effect is different in turns with the rotor and against it. I didn't think so until I did the arithmetic; once you do, it's as obvious as why $5 is only 5% of 100 but 10% of $50. "Duh" on me.

Assume a rotor that turns CCW viewed from above. Do two turns with equal airspeeds and tunring radii; one left and one right.

When you turn right (against the rotor), both blades have less airspeed than they do in straight flight at the same airspeed. The retreating blade, however, loses MORE airspeed than the advancing blade does because the retreater is on the outside. Therefore, the difference in airspeed between the two gets larger. The teeter hinge reacts to this increased difference by allowing the rotor disk to flap black relative to the spindle. This, in turn, move the rotor's thrustline forward relative to the CG -- an unstable direction for it to move.

In a left turn, everything's reversed. The advancing blade picks up the same number of MPH of airspeed that the retreating blade LOST in the right turn. The retreating blade actually gains airspeed, too, compared to straight flight. It picks up the same number of mph that the advancing blade LOST when you turned right.

(The key to understanding this is recognizing that increases in forward airspeed actually DECREASE the retreating blade's airspeed. Putting the retreating blade on the outside of a turn -- where the forward airspeed is higher -- costs the retreating blade dearly. The retreating blade is happier on the inside of a turn, where it loses less airspeed that it would in straight flight. This is quite different from fixed-wing experience, where the "inside" wing loses lift and airspeed no matter which direction you turn.)

As a result, in a left turn, the teeter hinge faces a situation of greater "blade equality." The hinge reacts by allowing the rotor disk to fly more nearly square to the spindle. This moves the rotor thrustline aft relative to the CG -- a stable reaction.

You'll need more aft stick in a left turn that in a right one. Saying the same thing another way, you're a little more likely to lose speed and mush out of a right turn than a left one. A gyro with good airframe stability with respect to airspeed and angle of attack will compensate for the differences in turn direction.

The effect becomes less and less as bank angle steepens. It's zero at the Stan Foster bank angle: 90 deg.

[ckurz7000]

Astute, Vance, is an adjective. If you need a noun, you might try astuteness.

You wouldn’t say Stan is approaching lovely, but you might say he is approaching loveliness.f

Sorry guys and gals, but since English isn't my mother tongue either, I'm in dire need to clarify this (lest I can't sleep tonight).

@Chuck: I think Vance had it right: "Your vocabulary and delivery is progressing toward the technically astute." Reason being that "the technically astute" is a group of words that stand in for a noun (as evidenced by the definite article).

There are two ways to say it:

(1) He progresses toward THE TECHNICALLY ASTUTE.

Or

(2) He progresses toward TECHNICAL ASTUTENESS.

Both are correct in my understanding. And don't come down flogging me all at once, please! There's got to be an English teacher flying gyros somewhere on this forum....:help:

-- Chris.

[Al_Hammer]

Sorry, not an english teacher, but "the technically astute" would be a group of people, wouldn't it? They are those that are technically astute.

One can progress towards becoming technically astute, but vocabulary and delivery are not people, so I think you would say your usage of vocabulary is progressing towards becoming more astute, but your vocabulary itself cannot be astute.

Oh, forget it, we're all likely to join Vance in his "higher level of confusion."

==================================================
The rotor blowback effect is different in turns with the rotor and against it. I didn't think so until I did the arithmetic; once you do, it's as obvious as why $5 is only 5% of 100 but 10% of $50. "Duh" on me.

Doug, are you sure??? I tried working the numbers and I get no difference in total flapping left or right.

[Harry_S.]

EXACTLY.


Cheers :)

[Fl90]

In Chuck's defese, English is an illogical language with rules and structures a soap opera would be proud of. Not that Chuck B. needs me to defend him.

Back to topic.

Doug, the difference in blade speed and craft airspeed seems, to me, to be great enough not to be affected to the point of noticability. I've not had a conflict of turn performance to get my attention. I'll think on it, then fly a while...

[C. Beaty]

According to Random House dictionary, astute is always an adjective.

as·tute (Ã stÁtÆ, Ã styÁtÆ), adj.
1. of keen penetration or discernment; sagacious: an astute analysis.
2. clever; cunning; ingenious; shrewd: an astute merchandising program; an astute manipulation of facts.
[1605–15; < L asttus shrewd, sly, cunning, equiv. to ast- (s. of astus) cleverness + -tus adj. suffix]
—as·tutely, adv.
—as·tuteness, n.
—Syn.1. smart, quick, perceptive. 2. artful, crafty, wily, sly.

Turns: We are concerned about the ratio of rotor peripheral speed to translational airspeed. The ratio does of course change in a turn but if you look at the numbers, the outside blade isn’t going so much faster than the inside blade that the ratio (μ) is significantly affected. And the speed differential is reduced by the cosine of the bank angle and by the square root of the load factor.

[StanFoster]

Chris: Your potato example is a good one....but its basically what I mentioned in post #9...where I mentioned that the the disc "starts" to deflect where you apply the force...mainly because its at is highest velocity there. The potato is easier to visualize.


Doug...that was a most easy to understand explanation of rotors during a left and right turn.


Stan

[birdy]

You would find, Mr. Bird, that if you had a full span vertical tail, it would make no difference which way you turned.
?????????
Where in my post did i say anythn bout prop torque Chuck? [ a full span tail only counters prop torque, not the gyroscopic thingy]
I never mentioned prop torque, coz i know it makes no difference, i was talkn bout gyroscopic resistance from the prop.

[C. Beaty]

A full span tail, Birdy, also eliminates the throttle/yaw coupling. The bottom half of the spiraling propeller slipstream yaws a half height tail in whichever way it’s going.

A full span tail eliminates both torque roll and throttle/yaw coupling, reducing trim drag in the process. There may even be some thrust recovery from straightening out the slipstream.

Typically, some 10% of the available power is wasted needlessly whirling the slipstream.

[ckurz7000]

Methinks a full span tail would just convert the yaw moment into a roll moment. Not so?

-- Chris.

[gyromike]

Methinks a full span tail would just convert the yaw moment into a roll moment. Not so?

-- Chris.

It will, but it will be in the opposite direction that the prop is trying to roll the frame.

They should cancel each other out.

[ckurz7000]

It will, but it will be in the opposite direction that the prop is trying to roll the frame.

They should cancel each other out.

They will at least be opposite to each other, which helps. -- Chris.

[C. Beaty]

For anyone who would like to play with the numbers, the radius of a circle flown at constant bank angle and airspeed is:

Radius = V²/(tanθ*g)

Radius of circle, feet.

V = airspeed, ft/sec

Θ = bank angle, degrees

g = acceleration of gravity, 32 ft/sec²

Thus, a gyro flying at 50 mph and a 30º bank angle flies in circles of 585’ diameter. At least, its CG does. The horizontal distance between blade tips is rotor diameter x cosine of bank angle.

The load factor with a 30º bank angle is only 1.15 Gs (1/cos30º) so the rotor RPM doesn’t increase very much; ~7.5%.

Perhaps some older versions of MS’s browser scramble Greek letters, etc. I use Firefox, so can’t tell.

[Joe Pires]

You wouldn’t say Stan is approaching lovely, but you might say he is approaching loveliness.



I think Chuck has a crush. :lol:

[Dean_Dolph]

Hey, Al, any chance you can divide the drawing and repost as two separate ones? How do you expect me to fit both drawings into your autobiography when they won't fit on one printed page?:D :D

[Al_Hammer]

Sorry, Dean. I never check the print size, since I don't have a printer at the moment. Post #13 is edited and the precession diagram is now split into 2 attachments. Let me know when that book comes out :D

[dragonflyerthom]

So

As I understand it there is little to no difference in a 60 degree turn left or right.

But some slight difference in a under 30 degree turn.

[Doug Riley]

Al, don't lead Dean on. You know you already sold your exclusive story to the tabloids months ago. Pretty racy stuff, too, I hear.

I look forward to reading it all as I wait to check out my groceries.

[Al_Hammer]

Doug, I'm still trying to figure out how Dean is going to write my autobiography. :rolleyes:

[Vance]

Hello Al,

I believe Dean would use a word processor with spell check.

Thank you, Vance

[Al_Hammer]

Thank you Vance, but the fact remains that if you're writing about another person, it's a biography. If its about you, then its an autobiography. Or did I miss some subtle Vance Breese humor here?

[Vance]

Sorry Al,

I misunderstood the question.

In my experience, the subject of the autobiography often does not write their autobiography.

No humor here!

Thank you, Vance

[Al_Hammer]

Technically, an autobigraphy can only be written by the person who is the subject of the autobiography, though they may choose to have someone help them write it down. That's why its called an AUTObiography.

[Vance]

Thank you for clearing that up,

Vance

[Harry_S.]

Technically, an autobigraphy can only be written by the person who is the subject of the autobiography, though they may choose to have someone help them write it down. That's why its called an AUTObiography.



Maybe the definition need be changed to..."The story of a persons life written or dictated to another, by one's self."


Cheers :)

[Dean_Dolph]

Other than the fact I got what I wanted I wish I hadn't brought this up; shame on me! And just for being picky Al, you are going to have to do the rest of the writing, so there!

[magilla]

OK, I'm following most of the aerodynamics lessons here closely, and chalk up the difference in my experience with helos to the NACA airfoil on a gyro versus a helicopter.

In my UH-60, 80 KIAS, in autorotation (falling like a bloody brick at 2400fpm), in trim, blades turning CCW as viewed from above. 75 degrees, and standard weight, rotors are tuned to about 103% (337 rpm)

If I turn hard right (greater than 30 up to 60 degrees) my rotor will climb through the roof.

If I turn left, my rotor RPM decreases.

This has to do with the AoA on the "Driving" region of the blade in a right turn versus a left turn.

We are always taught in power management to make a hard right turn as opposed to a left turn. Didn't believe it until I started instructing and test flying....

Anyway...is the difference because of the airfoil type?

[Doug Riley]

Spencer, gyros and helos can use the same airfoils. The real difference is that gyro spanwise twist is opposite. Helo blades wash OUT while gyro blades wash IN, root to tip. The Florida gyro crew used to use discarded Hughes 269 and 300 blades on their gyros. These airfoils are symmetrical (0015 or 0018?) They just flipped them over and spun them CW so the twist would be correct for a gyro.

Helo blades are twisted wrong for good autos. This leads to a larger-than-normal inboard stalled area, as well as areas just outboard of the stalled area that are just about to stall during unbanked auto flight.

I imagine that you get an extra dose of blowback in a right turn because so much of the retreating blade's inboard section stalls out. Extra blowback should rev up the rotor -- which of course is just what you need to help overcome each blade's loss of airspeed in a right turn.

[C. Beaty]

In autorotation, Spencer, the tail rotor is sucking power out of the main rotor, trying to yaw it left, so you have to hold some right pedal.

I wonder if the power consumption of the tail rotor, RH vs. LH turn has anything to do with it? Anything that drains power out of the main rotor will make it come down faster.

Does your UH-60 have a cambered tail fin to assist torque compensation in normal forward flight? That would affect rate of descent depending upon turn direction; more tail rotor thrust being required in one direction than in the other.

I’m only speculating, never having seen a UH-60 up close.

[Al_Hammer]

Spencer, I see no reason to to doubt your theory, or whoever's theory it is, that its the increased driving force in a right turn that speeds up the rotor and diminished driving force/area in a left turn that slows it down.

In a right turn, the outside blade has a higher than normal angle of attack and the driving region grows as a result. (The inside blade has less AOA , but the change is greater on the outside, so it wins.) Profile drag must decrease on the retreating blade due to the reduced tip speed and this may raise rpm's too.

The twist of the blade may make autorotation occur at a higher rpm, or more negative collective setting, but I don't quite see it causing the left/right rpm variation. Since the TR is using so much less power in an auto than in powered flight, I having trouble seeing it as being a factor in this case.

The fact that a helo rotor is usually shorter and turning faster than in a gyro may also exacerbate the changes in rpm in the turn, but I refuse to think about this any more!

[reelmule]

Thanks Al, Cris, Chuck, this is all very helpful info!

[birdy]

A full span tail, Birdy, also eliminates the throttle/yaw coupling.

Sorry i havnt been back to this thread for a while, i had a 3000 odd km blap in me wasa.

But BTT, I think i'm missing sumthn here.
Chuck, i know how a full span tail will almost iliminate torque roll, but wots this bout yaw?
Is it related to gyroscopic resistance or a different duck altogether?

[C. Beaty]

As you know, Birdy, the propeller slipstream looks like a giant corkscrew.

If your vertical tail catches just the lower half, it gets shoved in whichever way the lower ½ of the propeller is moving. During the takeoff roll, for example, you have to coordinate rudder with throttle to keep going straight.

A full span vertical tail eliminates the rudder pedal toe dance. A Dominator can takeoff with feet off the rudder pedals if the wheels are properly aligned.

Throttle/rudder coordination is something that primarily bothers low time pilots. Experienced pilots don’t even notice after a while.

[rustynance]

Got to be careful jumping in this creek full of gators. Spencer, as you probably know, in powered flight the helicopter has transverse flow on the rotor at all speeds greater than 0 up to VNE. It is this transverse flow which causes the transient torque conditions associated with left and right turns (again powered flight only). The rear of the helicopter rotor disk has a higher induced flow due to transverse flow. When we make a left turn the blades over the nose and tail are the ones changing pitch most. With more induced flow over the rear we also have more induced drag. When the blade over the tail increases pitch it generates more lift and a disproportionate amount of drag compared to a blade over the nose, the blade over the nose is obviously decreasing pitch resulting in less lift and less drag. This results in torgue increasing during a left cyclic turn. The opposite is true during a right cyclic turn. The effect is hardly noticeable at low speeds and during gentle maneuvering but can be very pronounced at higher speeds and more aggressive applications of the cyclic. The UH-60 mixing unit probably tries to elimiate some of the torgue deviations, unfortunately in the AH-64 our mixing unit is not as complex and does not correct for this at all. During aggressive maneuvering it is common to see a 40% TQ change when moving the cyclic either left or right.
Not certain, but I think Doug is probably correct on the reason for rpm changes in autorotation left or right turns (outside of the normal increase in rpm due to g-loading forcing us into the windmill brake state). It may be possible for transverse flow to play some factor in this as well but haven't thought that part through enough to seriously consider it.

Rusty

[birdy]

Thanx for clearing that up Chuck, i know wot your sayn. Is that wot they call the P facter?

So, wot i was sayn bout the props gyroscopic resistance effect wen your tunring is still valid, and has nuthn to do with the tail setup.
Its this resistance that makes gyros hrader to turn one way and easier the other, depending on the props rotation.
If you think this is crap, turn your machine hard both ways with WOT, you'll feel the resistance in one direction and not the other. Then do the same move with the throttle closed.
With the prop spining at idle rpms, theres much less resistance.

[C. Beaty]

I’m not sure just what “P” factor means but I suppose it stands for propeller factor.

There are two forces acting on a propeller; gyroscopic reaction and edgewise movement of a rotor disc that doesn’t have teeter or flap hinges.

Gyroscopic reaction tries to tilt the propeller disc 90º to yaw axis rotation; nose up or nose down, depending on direction. Stomp on a rudder pedal when you’re flying along slowly and you’ll get a nose up or down pitch response.

When flying sideways, you have a rotor disc without flap hinges and the advancing blade gets a bigger bite than the retreating blade, also producing a nose up/down response depending whether the advancing blade is on top or bottom.

I’ve also observed that when flying sideways with the controls really crossed up, you get a judder that can be pretty severe and is stronger in one direction than the other; if you turn around and look at the engine, it looks like it’s trying to jump out of its mounts. I think this comes from gyroscopic vibration and may be more severe with a 2-blade prop than with a 3-blade one.

If you’re spinning while doing a vertical descent, then the machine spins faster in one direction than the other for the reasons outlined above. Plus the spiraling slipstream on a ½ height vertical tail.

[Passin' Thru]

Birdy, P-factor is when your fuel range exceeds your bladder endurance. ;) :D

Seriously, the p-factor is caused by the difference in angle of attack between the ascending and descending blades of a rotating propeller blade when the aircraft is flown at a high angle of attack as at take off and climbing. Specifically, the descending blade has a higher angle of attack, relative to the ascending blade. The propeller prop blade with the higher angle of attack will provide more force, in this case, measured as thrust. With the descending blade providing more thrust than the ascending blade, the center of thrust is moved away from the center and out towards a parallel point somewhere along the descending blade. This effect is not so noticable with pusher gyros because the spiral prop wash is more powerfull and in the opposite direction, canceling it out. It becomes more important with multi-engines and determines “critical engine” performance. Imagine a Piper twin Comanche losing the left engine on take off!:eek:

[birdy]

Birdy, P-factor is when your fuel range exceeds your bladder endurance.
Thats a good one, i never thought o that. :)
[ i seem to always suffer coz of this P facter]

Seriously, the p-factor is caused by the difference in angle of attack between the ascending and descending blades of a rotating propeller blade when the aircraft is flown at a high angle of attack as at take off and climbing.
So, except for at very low ASs, there should be no P facter felt in [stable] gyros, coz the flying surface AOA is not fixed to the machine, and the machine is always allined to the airflow, so theres no difference in airflow to the raising and decending prop blades.
Wen a gyro is in a virtical decent, its the P facter that starts unintended spins, no?


Gyroscopic reaction tries to tilt the propeller disc 90º to yaw axis rotation; nose up or nose down, depending on direction.
So Chuck, i was rite then wen i said,
The biggest difference between left and right turns in gyros is the effect of the props gyroscopic resistance. One way it unloads the rotor and the other it loads it., in my first reply to this thread?

Why are we still on about it then? :( Torque roll and the P facter are small fish compared to the gyroscopic effect, specialy with WOT, low alt, and low performance conditions and only one way to turn. Iv been in several situations where iv had to chop power wen turning low [ <10'] coz the GR was forcing me on the deck.

[birdy]

Gyroscopic reaction tries to tilt the propeller disc 90º to yaw axis rotation; nose up or nose down, depending on direction.
So Chuck, was i rite then wen i said,
The biggest difference between left and right turns in gyros is the effect of the props gyroscopic resistance. One way it unloads the rotor and the other it loads it., in my first reply to this thread?

[C. Beaty]

Birdy, you might be on to something I’d overlooked completely.

In a 60º banked turn, if you have enough power to hold altitude, at 50 mph you fly 195-ft diameter circles in 8 1/3 seconds, precessing the prop at 43º/second. This is a significant precession rate.

Flown in a direction that tilts the airframe nosedown, yes, you do have to hold more back stick to keep the nose up. But I don’t think the gyroscopic moment is the same as adding weight to the nose; it’s like a HTL machine inasmuch as the rotor thrust vector must pass forward of the CG to maintain equilibrium.

If you can give a guestimate of your prop blade weight, blade CG from center and rpm, I can work out the nose down moment.

PS: I don’t really think you’d buy a truckload of cow manure from Dennis; not even the imported sweet smelling French variety.

[birdy]

Birdy, you might be on to something I’d overlooked completely.
I hope your only jokeing Chuck.

But in case your not, and im interested to know, ill follow along.
In a high power to weight machine like the ferel, holding a greater than 60* bank and alt is easy to do.
It'll do 195' circles at 50mph till the fuel runs out.

But I don’t think the gyroscopic moment is the same as adding weight to the nose; it’s like a HTL machine inasmuch as the rotor thrust vector must pass forward of the CG to maintain equilibrium.
True, its wot i call artificial weight.
But artificialy adding weight or actualy adding weight that causes the nose to pitch down will require the same effort from the rotor to counter it. And the harder the rotor has to work, for wot ever reason, the more power it consumes from the machine.

If you can give a guestimate of your prop blade weight,
Im gessing bout 3lbs each [ conservativly], and iv only got 2 blades onit. This is much less inhibiting than wen i had 3 blades onit.
blade CG from center and rpm
I understand wot rpms are[ at WOT, 5400rpm, the prop would be do'n less than half that coz the reduction is , i think, 2.2/1] , but wot do you mean by 'blade CG from center'? Im gessing your after the leaverage the prop has from the machine's COG.
If its the props plain of flight from the machine's COG, im buggered if i know, but it d be less than 3'.[ go'n by the old double hang pix]

Im greatful for your interest. :)

ps; why the ell would i buy cow sh1t wen i got train loads of it ere. ;) And i bet it smells better n the french stuff, coz it rained ere and this country grows the best cow food in the world. :)

[Jazzenjohn]

Birdy, I think Chuck wants to know, if you took 1 blade off the prop and balanced it on your finger, what would be the distance from the center of the prop shaft to that position on the prop blade? If the prop blades have alot of weight at the tips it would be farther out than if they were heavy at the root. If they're even it would be pretty close to the middle. Using that, plus the weight of the prop blade, and the prop rpm, he can calculate how much gyroscopic force the prop has at that time.

[C. Beaty]

ps; why the ell would i buy cow sh1t wen i got train loads of it ere. ;) And i bet it smells better n the french stuff, coz it rained ere and this country grows the best cow food in the world. :)Because a crackerjack salesman can sell you something whether you need it or not. You've heard the expressions; sell sand to the Arabs, sell snow to the Eskimos, sell cow poop to a SCG.

The CG of the propeller blade is the point where an individual blade would balance and then its distance from the center of rotation. I need that to calculate the moment of inertia of the prop.

But I made some assumptions anyhow.

I assumed your prop is 60” diameter and that blades are uniform in weight over their length. May not be so but in the ballpark.

I also assumed the prop turns at 2800 rpm. Ditto.

That being the case, the torque to precess the prop at 43º/second is 57 ft-lb. This torque gets translated into an equal nose down torque.

So not only does the rotor have to balance that 57 ft-lb of nosedown torque; the engine must supply the precession torque by means of rudder pedal deflection, in addition to whatever is required for a coordinated turn.

[birdy]

Birdy, I think Chuck wants to know........
i thought bout it last nite john, and i recon your rite. :) ill check um out.

Because a crackerjack salesman
He'd have to be bloody good to convince me Chuck. [ even sumone as good as my mate PB couldnt sell me that one. ;)]

Its a 66" Ivo mag.
Itd be do'n less than 2500rpms coz the engine is only do'n 5400 and its got a bout a 2.2/1 reduction.
The effect on the machine i notice more is the roll. of course theres a strong back pressure needed, but its a heavy need for the stick to be held 'out' of a right hand turn. IOW, once your in a steady hard right turn, you need to hold alot of left stick, to stop the props force driving you down sidways, as opposed to needn extra backstick pressure.
Also, wouldnt the distance from the props COM to the RTV be relivent?, coz im thinkn the closer it is, the less leaverage the rotor has over the force, so itd be more noticable in short coupled machines.

And for the argument, ill go check the blades weight and COM.

BTW, is 57 ft/lb alot? Dont sound like much.

[C. Beaty]

Birdy, aviation still lives in the shadow of the Wright Brothers. My speculation –I don’t know; I’ve not researched it- is that the term “P” factor originated with WW I fighter pilots flying SPADs, Fokkers and the like with rotary engines. Rotary engines had the crankshaft bolted to the airframe and the whole engine rotated, producing enormous gyroscopic reactions while maneuvering.

A processional torque of 57 ft-lb, while not insignificant, may not be the source of differences you’ve observed between turning one way vs. the other.

The roll torque reaction from driving the propeller and the spiraling slipstream that results may be the larger factor.

Torque = (hp x 5252)/rpm

The factor 5252 is a real number; a consolidation of pi and Watt’s drawbar pull of 550 ft-lb/sec per hp.

If you have 100 hp and propeller rpm is 2200, your torque is 239 ft-lb. In order to maintain equilibrium, the rotor thrust line must be offset horizontally from the CG in the opposite direction from propeller rotation. Remove rotor thrust and you become a yo-yo about the roll axis.

Then there’s the spiraling slipstream pushing the vertical tail in whichever way the bottom half of the prop is spinning.

These factors may be the greater cause of differences between RH and LH turns. Shallow turns require less power and torque to maintain altitude so you wouldn’t notice as much difference.

I do believe that if you had a tall tail, most of these quirks would vanish. Would also reduce the number of rollover accidents by neophytes getting the machine crossed up.

[birdy]

Thanx Chuck.
Its definatly linked to the props rpm sumhow, coz if you do the same control inputs at idle, the resistance dissapears.
I have only wrung the neck of one talltail machine, and [from memory] it wasnt as bad, but it was still there.
The t tail would have been countering the airodynamic effects of the prop, but not the gyroscopic. So i spose you could say its the combination of gyroscopic and airodynamic effects that im feeln in the ferel.

[magilla]

What about alignment of the propeller thrustline left/right in relation to the aircraft?

If it's off-center just a little bit, would that not effect the resistance you're feeling turning one way versus the other?

If you were feeling brave, Birdy, you could shim your motor mounts on one side versus the other and see if it makes a difference.

[birdy]

Oh, it makes a difference orrite.
I once had one of the thrust rods [ from the redrive to the mast] attatchment point fail, and the 912 was yaw'n round with throttle adjustments.
No big deal, but i couldnt figure why it suddenly wanted to swap ends wenever i opened the tap? ;)

[Fl90]

I had that happen with a 4 stroke I stuck on the machine. It was my fault for building the mount too light, so I don't bring it up much!

[Shimmy]

Astute, Vance, is an adjective. If you need a noun, you might try astuteness.

You wouldn’t say Stan is approaching lovely, but you might say he is approaching loveliness.

There; you have my English lesson for the day.:rolleyes:


Here's more on grammar so we can roll our eyes some more. Yes, I know this was discussed more! I just wanted to point out how the adjective works. You all can laugh at me when I have to ask questions like what is a *bleep*pit.

Just a reminder, the sentence that is being critiqued is...
"Your vocabulary and delivery is progressing toward the technically astute."

It's true that astute is an adjective and not a noun. The fact is, the example sentence doesn't need a noun. Astute is being used properly as a predicate adjective. Slippery is a good example to use as a predicate adjective. "The rock is slippery."

Changing the sentence structure is fine, you can use astuteness, I merely wanted to point this out. English doesn't have the structure to easily recognize adjectives and nouns. *shrug*

Back to our regularly scheduled program...

[Vance]

Thank you Mr. Weeks.

I am pleased to know that.

That will help with future attempts at communication.

Thank you, Vance

[Doug Riley]

Yup, phrases of the form "the [adjective] did such and such" are very common in other languages and used by good speakers in English, too.

Emma Lazarus has the Statue of Liberty say, "Bring me your tired, your poor..." etc. She could have said "THE tired you've got..." just as well. Not very poetic but OK grammatically.

As for regulation, I'm at the other end of the universe from most aviators politically. Regulation goes with being an urban, technological society; it's much less necessary in a Daniel Boone world.

It IS a shame, though, that the U.S. does such an exceptionally poor job of creating rational laws and regulations. Our political system SEEMS to be cruder and more obviously manipulated by narrow interests than in other "advanced" countries. In that regard (and others), we are sort of a rich third-world country.

Some of the first laws regarding aviation were put there to reverse the stifling effect of the older property law rules. Those rules said (and still say) that a property owner owns a slice of the universe that extends outward from the center of the earth, past the surface and infinitely out into space. Under this rule, every airplane was continually trespassing any time it wasn't flying over public land.

We've come a long way. Private aviation is now viewed by the vast majority of Americans as a nuisance, a threat to their safety and a generally inexcusable fringe activity. Laws that actually PROMOTE it aren't in the cards anymore. I am pretty sure a majority of Americans would vote to ban private flying if asked. Many regulations are put there to toss a bone to this majority.