Roll trimm

[birdy]

but I have never delved this deeply into it.
I never woulda even bothered either Leigh, but thats the way the thread has headed, so im follown along.
Mind you, the end result aint worth 2 knobs of nanny goat cr@p in real life, wotever the result is, but iv started now, and my curiosity wont let me stop.
[ how would we be without the likes of Mr. Beaty?]
No dout he'll have an instant answer thatll shoot me down ina fire ball.

Birdy, I think the effect is not doubled. It was canceled.
JC, id imagin youd have as much trouble understandn me as i you, so you have my simpathys.
But, with wot im on about, youv gota ditinguish and seperate between the internal inertia of the disc, external inertia of the disc, lift, drag and the effects of gravity, coz they are all pulln different ways, while at the same time, balanced.

energy to mount the blade is provided by the blade that descends. And it produces a bending bar hub in the vertical plane.
Im assuming you mean move, where youv got mount.
If the lifting blade was lifted through the axis of the teeter bolt by the decending opposit blade, your hub bar wouldnt last 5 seconds. They EQUALY compensate for differing airspeds at the same time, so the seesaw is powered airodynamicaly, not each blade leavering the other.

 

[Jean Claude]

Yes Birdy, but I just want to mention the potential energy of the blades. Suppose a rapidly rotating propeller (horizontal axis) Replace the blades by two inert masses. Where does the energy to lift the mass lifting? Where energy escapes to the mass descending ?
Jean Claude

 

[C. Beaty]

Pay attention to what JC says, Birdy, he understands rotor physics.

As the rotor rotates, its total energy remains constant. Even viewing a rotor blade in isolation with its axis horizontal, the relative force is ~5000 lb. from centrifugal acceleration and ~20 lb. from gravity.

Your mental block comes from not being able to accept that the rotor is effectively on a universal joint and is connected to the rest of the machine only by cyclic pitch and rotor thrust.

I imagine you’ve flown a kite. If it flies with the string at an angle of 45º and pulls on the string with a force of 14 lb., then the lift is 10 lb. as is the drag. If you had additional strings for operating elevator and ailerons, you could make it fly at some different angle; the equivalent of cyclic pitch control.

I’ve attached a drawing of the Doman helicopter rotor. There are 4 blades rigidly connected to the hub except for feathering bearings with the complete assembly connected to the helicopter by a gimbal. It can point in any direction necessary to establish equilibrium, same as the kite on a string.

There is no fundamental difference between a Doman rotor and a seesaw rotor; only the way that cyclic pitch is applied differs.

 

[RotoPlane]

Originally Posted by birdy
Correct me if im rong, but i recon i read sumwhere ere that one of the first attempts at a gyro was with a fixed spindle rotor mounted atop an old FW.
First thing that happened wen forward speed was added to the disc was it tryed to ROLL LEFT [ or away from the advancing side]. IOW, no teeter hinge ment the greater lift on the advancing side tryed to tip the machine over.

Originally Posted by Chuck Beaty
Rolling over sideways is straight from the imagination of historians and journalists without the foggiest notion of the laws of gyroscopic precession. A rigid rotor would have pitched nose up.

What David said is what I thought would happen with a rigid head; the ship would roll left. Now I can see a teetering head pitching the nose up as speed is increased, but I thought a rigid head would act differently….because it can't teeter. Am I to understand that dissymmetry of lift is handled the same way by both teetering and rigid head rotors....with the same cyclic displacement? Oh yeah....I am really confused....

 

[C. Beaty]

Gyroscopic precession is what it is; displacement lags force by 90º, always. It is a resonant phenomenon; each particle of mass in a gyro wheel is resonant at the frequency of rotation.

If you have a wrecking ball suspended by a cable from the ceiling beams of a blimp hangar, you have a pendulum that can be used for a clock. Set it swinging and its swing remains fixed in space as the Earth rotates. You can paint a clock dial of the hangar floor.

A 300-ft pendulum requires 19.2 seconds to complete a cycle so it’s not moving very fast. Aerodynamic drag doesn’t amount to much and if your wrecking ball weighs 500 LB, there’s a lot of stored energy. It should run for several days before needing rewinding.

But setting your clock might be a bit of a puzzle. Give it a westward push at the center of its swing as it heads south, say, and it responds 90º later by moving ever so slightly to the west at the southern limit of its swing. Behaves just like a gyroscope.

As previously mentioned, Cierva was well aware of the law of gyroscopic precession and of dissymmetry of lift. His first two attempts at a solution weren’t successful but to say his machines rolled over sideways because of more lift on the advancing blade is incorrect and denigrates Cierva’s ability as an engineer.

 

[birdy]

Am I to understand that dissymmetry of lift is handled the same way by both teetering and rigid head rotors....with the same cyclic displacement?
Yes.
Its just handled a different way.
the teetering one seesaws ona fee hinge, the ridged by cyclic input from the swash.

Suppose a rapidly rotating propeller (horizontal axis) Replace the blades by two inert masses.
JC, your missn me point.
The 2 forces im talkn bout are directly opposit each other, so any imbalance will created cyclic vibration.
Gravity and a horisontal rotors THRUST are at 90* to each other, so they dont effect each other.

Pay attention to what JC says, Birdy, he understands rotor physics.
I dont discount anyones comments CB, im only a SCG tryn to figure.
Its me point thats getn missed.

As the rotor rotates, its total energy remains constant. Even viewing a rotor blade in isolation with its axis horizontal, the relative force is ~5000 lb. from centrifugal acceleration and ~20 lb. from gravity.
Forget bout centrifical force and internal inertia Chuck, think airflow direction, autorotation and gravity.

Your mental block comes from not being able to accept that the rotor is effectively on a universal joint and is connected to the rest of the machine only by cyclic pitch and rotor thrust.
I understand that Chuck [ cept the mental block bit].
Yes, the rotor is coupled to the machine through a uni joint, BUT, the rotor is connected to the rotor bolt through ONLY ONE HINGE. [ the teeter] One hinge on its own cannot do the same asa uni joint. The stick is RIDGEDLY connected to the spindle, and theres only one hinge between it and the rotor.

There is no fundamental difference between a Doman rotor and a seesaw rotor; only the way that cyclic pitch is applied differs.
Clear as crystal.

[ At least im not blown outa the water................. yet. ]

If, as you say CB, the RTV is at 90* to the tip plain, why then is there no lateral feed back through the stick in blustery conditions wen you can see the tips at 3 oclock divergn 18" or more?
Surely, if the tips are moven that much in relation to the stick, and the RTV followeds the tip plain, thered be massive feed back through the stick.
If your cruisen in calm air, and try to make the tips diverge that much with the stick, it takes considerable effort.

 

[RotoPlane]

Al Hammer - When you have disssymmetry of lift, the disc (tip path plane) tilts but NOT the rotorhead (the teetering hinge makes this possible), so the blades do not "point" in the same direction as the disc when they are at the side position. This changes the angle of attack.

The thumbnails and the rest of the post is here: https://www.rotaryforum.com/forum/showpost.php?p=95082&postcount=18

I can understand the gyroscopic precession (which I had discounted for a rigid head)....but a rigid head cannot do what Al said happens with a teetering head. So in my head I think there would need to be different stick movements for the different head types to keep from climbing as speed increases.....

 

[C. Beaty]

Birdy, here’s a Cardan joint, Hookes joint, U joint or whatever you want to call it. Whatever the name, it’s the same.

A seesaw rotor is the same thing with the upper yoke missing.

If, as you say CB, the RTV is at 90* to the tip plain, why then is there no lateral feed back through the stick in blustery conditions wen you can see the tips at 3 oclock divergn 18" or more?
Surely, if the tips are moven that much in relation to the stick, and the RTV followeds the tip plain, thered be massive feed back through the stick.
If your cruisen in calm air, and try to make the tips diverge that much with the stick, it takes considerable effort.

What you’re seeing is blade flexing; the rotor disc is not flopping around that much.

 

[C. Beaty]

The thumbnails and the rest of the post is here: https://www.rotaryforum.com/forum/showpost.php?p=95082&postcount=18

I can understand the gyroscopic precession (which I had discounted for a rigid head)....but a rigid head cannot do what Al said happens with a teetering head. So in my head I think there would need to be different stick movements for the different head types to keep from climbing as speed increases.....

Flap hinges provide a method for the application of cyclic pitch by means of head tilt. The hinges form a universal joint that permits rotation of a blade about its feathering axis simply by tilting the rotor head.

A rigid rotor must have feathering bearings and swash plate for cyclic pitch.

The control phase is about the same in both.

 

[RotoPlane]

"The control phase is about the same in both." Okay....thank you Chuck! I am so glad that you put-up with us/me.

 

[Mark E]

On the original question: the tendency to roll with the longer blades:

....dumb question time

are these the only possibilities?

1. The lift vector is always offset - birdy just happens to have it perfectly trimmed out with the shorter blades.?

2. Different hub bar? The teeter bearing friction may differ?

3. Blade dissymmetry? eg - perhaps the blades are not quite on the same angle of attack (or profile) for one of the sets, creating more lift for one blade (retreating or advancing) than the other (ie ideal for the particular airspeed one of the blades encounters?):noidea: (can that happen? or is that self canceling?)

 

[C. Beaty]

Although I wouldn’t rule out teeter pivot friction as the cause of Birdy’s disconcertion, it is more likely the byproduct of coning angle.

With an out of track rotor, everything goes in a circle that equalizes things side to side. An out of track condition is too obvious to be ignored; it stirs the stick in a 1/rev circle and causes a vertical lope.

Blades having different curvature of the mean line may have less shake when deliberately thrown out of track but that is extremely rare. Out of more than 2,000 sets of rotors delivered, Ernie (Dragon Wings) has only had to scrap one blade for that reason.

 

[birdy]

Birdy, here’s a Cardan joint, Hookes joint, U joint or whatever you want to call it. Whatever the name, it’s the same.

Riteo, we will call it a Caradn joint so we know wot we are talkn bout.
And a tail shaft universal jiont [ as on your car] is a cardan joint.
It has 2 hinges.
One hinge gives fore n aft movement, the other gives left n rite, and combined, you can move the shafts at any angle you like within the phisical limits of the hinges.
Same as our rotor heads
The spindle can be pointed to an infinite number of angles off the mast, within the phisical limits.
So Wut.
Im not talkn bout any of that.

A seesaw rotor is the same thing with the upper yoke missing.

Our stick is hard linked to the rotor disc through the spindle bolt, and ONE hinge. Thats not a universal joint.
The teeter hinge has only one plane of movement.

I have no idea wot that last pic is sposed to tell me CB.

Although I wouldn’t rule out teeter pivot friction as the cause of Birdy’s disconcertion,
Teeter friction makes it roll left, not rite.

 

[Mark E]

Teeter friction makes it roll left, not rite.

Perhaps there greater friction is in the teeter joint with the shorter blades, and it is trimmed out.

.... but that does not explain why several others are seeing the same thing with longer blades.

(longer blades, outward movement of the average point of lift, more leverage against a sticky teeter joint????) :noidea:

 

[C. Beaty]

Our stick is hard linked to the rotor disc through the spindle bolt, and ONE hinge. Thats not a universal joint.
The teeter hinge has only one plane of movement.

Very perceptive, Birdy. However, that one hinge can only rotate the rotorblades about their feathering axis and exerts no direct control over the orientation of the rotor plane; it is indirect via the mechanism of cyclic pitch control. But there could be an upper yoke and it would always point along the axis of the rotor plane, not the spindle axis.

If you study a Cardan joint running at an angle, the lower yoke with its pivots represents the teeter towers and teeter bolt. The other pair of pivots represent the hub bar and rotor plane. The plane of each pivot is normal to its respective shaft; the planes don’t wobble or flop.

If you were left handed, you wouldn’t have so much difficulty with spatial visualization.

Teeter friction makes it roll left, not rite.

Then I guess you don’t have a left handed rotor either.

 

[birdy]

But there could be an upper yoke and it would always point along the axis of the rotor plane, not the spindle axis.
The phisical axis would, but not the RTV.
Which is my point entierly.
Coz, if you go back to post 95 im sayn why i think the lift isnt equal about the disc.
Unequal lift about the disc would move the RTV, relitive to the tip plane.


If you were left handed, you wouldn’t have so much difficulty with spatial visualization.


Quote:
Teeter friction makes it roll left, not rite.

Then I guess you don’t have a left handed rotor either.
Wot the hells all that mean??????

 

[ckurz7000]

BTW, teeter friction can make it appear to roll to the right. If you have the set of blades with higher teeter friction trimmed out so it flies straight. Then you slap on the set with lower teeter friction, which now makes it want to roll to the right.

-- Chris.

 

[birdy]

Then its the trimm thats rolln it rite Chris, not the friction.
If you had free teeter hinges and it flies streight, then tighten the hinge up, or throw sum dirt into the thrust washers, itll roll left.

 

[C. Beaty]

Spatial visualization is the ability to form and manipulate 3-demensional images in the mind’s eye. Visualizing rotor motion is a good example.

Left handed individuals generally perform better on tests that measure spatial visualization ability.

As much as I hate to admit failure, nothing will ever convince you that rotor thrust is coincident with the rotor tip plane axis rather than the rotorhead axis. You don’t believe me and you don’t believe the people that wrote the book.

In this scan from Gessow & Myers (Aerodynamics of the Helicopter), the control axis is the swash plate axis in a helicopter and the rotorhead axis in a tilt head machine.

 

[birdy]

As much as I hate to admit failure,
Dont give up on me Chuck, you havent failed, i have.

nothing will ever convince you
Not true.
Understandable evidence will every time.

You don’t believe me
Also, not true.
I 'believe everythn you tell me CB, IF i understand it.
Iv never hada blind faith in anyone.
and you don’t believe the people that wrote the book.
and its even less likely ill have faith ina book, no matter who rit it.

Im not discounting wot Gessow & Myers say. Why?
Coz nun of it is relivant to wot im askn.
Yes, we are both talkn bout the RTV and where it is, but thats as far as it goes.
Remember CB, years ago people thought the world was flat, coz all the 'knobs' said so.
I could only ponder wot ridicule the bloke got who first said it was round.

No, im not thinkn for a second that im that bloke, sh1t man, im not that vain.

Im just askn, has the effect of gravity been part of the equasion that they use to determin where the RTV is?

All youd have to do to convince me that gravity has no bearing on the location of the RTV, is explain how a rotor isnt effected in the same way as your rock ona string.

If i can understand that, ill be convinced iv got it rong.
Coz at the moment, its valid in my mind and should be considered.
If im convinced its not, i can easily discount it, which would make it easier for my overloaded greys to grasp wot is.

BTW, im ambidextrous. [ im sure youll be able to sound that one out and correct me spelln ]