Roll trimm

?????????????
Well there ya go, lerarn sumthn new every day.

If thats the case, why do i need roll trimm on only one set of blades?
 
Birdy, in flying straight the sum of all torques is balanced. Motor + rotor + H. S. + twisted construction + Trim = 0. A different cone angle requires a different trim.
Jean Claude
 
But why dose one blade need sum, and the other need nun?
 
But why dose one blade need sum, and the other need nun?

Probably cone different: Pitch different? mass different? Airfoil different? diameter different? chord different?
 
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But if ALL rotors fly as CB says, then why dose only one of mine need trimm?
 
Birdy, you probably have one of those gawdawful automobile starter motors offset to one side that takes care of trim with the short rotor. With the long rotor, even that lump of iron isn’t enough.
 
For a start you old goat, i upgraded from them lead weight prespinners long ago, and agin your rite, i never even thought of the spinner cable. :)
Wot the hell would we do without the old goats.;)
You catch me out so easy and often its embarrassing. :(
 
What about the 2 odd % that the disk is offset to left. would this be the same for both sets or woulnt it need to change for a larger disk.
Just wondering?
 
Offsetting the rotor sideways compensates for propeller torque roll.

Cierva tinkered with sideways offset but chose differential tailplane incidence as the better option since it more nearly compensates for changing power settings.

The sideways tilt of the airframe due to lateral flapping of the rotor is miniscule; typically less than one degree.

Even Birdy’s sensitive hind quarters wouldn’t set off alarm bells with less than 1º of tilt.
 
The sideways tilt of the airframe due to lateral flapping
Sorry CB, the more i think bout this, the less i can understand how the rotor, flyn streight, can force any sideways tilt on the machine.
Gess ill just have to live with the fact that bricks are think, and have other uses. :(
 
It’s really quite simple Mr. Bird, when you stop to think about it.

Even with lateral flapping, to fly straight, the rotor thrust vector must point straight up. To make it do this, you have to hold a bit of opposite stick that tilts the rotorhead over a bit.

The aircraft CG hangs directly in line with the rotor thrust vector but the rotorhead has been tilted slightly which means the top of the mast is offset a hair.

The fuselage isn’t tilted very much; well under a degree in most cases. It depends upon the amount of lateral flapping and the distance from teeter bolt to roll pivot.

Now wasn’t that simple?
 
If the sideways tilt is worrisome, I suppose it would give piece of mind.

I prefer aerodynamic compensation as was done by Cierva with differential tailplane incidence. Cierva actually used cambered airfoils on the tailplane with the airfoil inverted on one side.

Ron Herron compensated the LittleWing by placing the main wheels on scales and adjusting tailplane incidence to provide equal readings with the tail tied to a tree.

Addressing propeller torque, not lateral flapping.
 
Ron Herron compensated the LittleWing by placing the main wheels on scales and adjusting tailplane incidence to provide equal readings with the tail tied to a tree. Addressing propeller torque.
In my opinion, the audit of the compensation of torque with a scale under the wheels is very vague. It is correct if the propeller thrust is perfectly axial. But an error of only 2 ° produce (4 feet above the scale) an equivalent to 30% engine torque of the scales.
Jean Claude
 
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Now wasn’t that simple?
No.

Ill never be able to fly confidently ever agin.:(
 
Sorry to jump in the middle here. Does all this mean that when in a vertical descent, a properly trimmed machine will most likely drift right (small amount)? Unless the compensation is entirely made in the tail.
 
If a gyro had correctly balanced counter rotating props, there would be no rotation of the propeller slipstream and no torque roll.

Similarly, if aerodynamic vanes in the propeller slipstream removed the swirl, there would be no torque roll. The counter torque exerted against the vanes would balance prop torque.

In a vertical descent with the engine switched off, everything would be vertical. If the machine was trimmed to resist torque roll in normal forward flight, some sideward stick pressure would be necessary to counter the trim springs.

An idling propeller still produces a bit of thrust and exerts a bit of torque against the airframe. The rotor thrust vector must be tilted slightly aft to resist thrust and slightly in the direction of propeller rotation to resist torque in a vertical descent.

And of course, a ½ height vertical tail is yawed in whichever way the bottom of the propeller is moving, requiring some rudder input to correct.

The Dominator cruciform tail does a good job of straightening the propeller slipstream, making it an easier machine for beginners. No rudder pedal dance during the takeoff roll.
 
In a vertical descent with the engine switched off, everything would be vertical. If the machine was trimmed to resist torque roll in normal forward flight, some sideward stick pressure would be necessary to counter the trim springs.

And on sum machines [ the ones with dunny door sized HSs] youd also need sum back stick, to hold the nose up. ;)

Iv lerned alot for you over the years CB, but this thing bout roll trimm to counter sumthn you say is comen from the rotor aint sinkn in. :(
Iv been assup for abit with the flue, so iv had plenty of thinkn time, but still no go.
Was thinkn bout the similarity between our rotors and our blackfellas bent sticks [ boomerangs]. But it still didnt help.
If our rotors took off without us [ rotor bolt let go] theyd follow the same parth as the bent stick, ie; theyd turn back, to the left. [ if spun in the same direction as our rotors].
The higher AS on the advancing blade of the rotor [ and the bent stick] will mean it wants to fly in circuls.
This would imply that theres a cyclic input all the time for us to hold our streight flight parth, which we all know is the teeter action.
But, the teeter action only allows for each blade to balance eachothers different ASs by changing their AOA, which balances the lift, so we can fly streight.
Teetering acts lateraly, and so dose the teeter hinge, so how the hell can it force anythn through the stick?

Even with lateral flapping, to fly straight, the rotor thrust vector must point straight up.
Thats logical.

To make it do this, you have to hold a bit of opposite stick that tilts the rotorhead over a bit.
Why?
I thought the teeter was do'n it for us.
In a machine with a ridged rotor and swashplate i could understand why youd have to counter it with stick position, but we have a teeter hinge to do it for us.

Sorry CB for my dumness, but i cant grasp where this [ margional] force is comen from. :(
 
I need to sort you out on a couple of things, Birdy.

First of all, if the teeter bolt let go, the rotor would more than likely tumble and go nowhere but down. The bent stick has gyroscopic stability because it is bent. With a rotor, you’d need 3 blades to obtain gyroscopic stability.

If the 3-blade rotor let go, it would do a normal inside loop.

When I was a little bitty bugger, we used a lot of mineralized roll roofing. This stuff came in 100 ft² rolls with frisbee like protective metal end caps. They made great toys for a 6 year old boy. They sailed nicely when given a spin.

I used to cut a series of radial slits around the rim with tin snips and twist them for lift. Sail them with a spin and they’d loop.

At age 6, I didn’t know why they looped. Only later did I begin to understand the rules of gyroscopic precession.

A boomerang behaves in the same way. Flung with the spin axis vertical, they’ll do an inside loop. To make one return, the spin axis has to be horizontal or nearly so.

Surely you understand the rotor cone presents the appearance of blowback in forward flight. That’s cyclic flapping.

If you were riding the rotorhead axis, it would look very much like flapping. If you were riding the tip plane axis, you would see no cyclic flapping; only cyclic feathering. Cyclic flapping and cyclic feathering are one and the same; it all depends on where you’re looking.

Gyroscopic precession means that that displacement lags force by 90º. The advancing blade of a rotor would develop greater lift than the retreating blade but for flapping. As the advancing blade flaps upward, the rotor disc tilts nose up relative to the rotorhead or you could say the rotorhead is tilted down relative to the rotor disc. This lowers the pitch on the advancing blade, raises pitch on the retreating blade and equalizes lift side to side.

Tilting the rotorhead in a gyro does exactly the same thing as tilting the swashplate in a helicopter; the rotorhead is in fact the swashplate.

And just in case you thought I was yanking your string about sideways flapping, here’s a page from Gessow & Myers about that very thing:
 

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My bumness is realy startn to p1ss me off now. :(

And it coz all of this;
If you were riding the rotorhead axis, it would look very much like flapping. If you were riding the tip plane axis, you would see no cyclic flapping; only cyclic feathering. Cyclic flapping and cyclic feathering are one and the same; it all depends on where you’re looking.

Gyroscopic precession means that that displacement lags force by 90º. The advancing blade of a rotor would develop greater lift than the retreating blade but for flapping. As the advancing blade flaps upward, the rotor disc tilts nose up relative to the rotorhead or you could say the rotorhead is tilted down relative to the rotor disc. This lowers the pitch on the advancing blade, raises pitch on the retreating blade and equalizes lift side to side.

Tilting the rotorhead in a gyro does exactly the same thing as tilting the swashplate in a helicopter; the rotorhead is in fact the swashplate.

i understand clearly.
So, wot dont i get?



Surely you understand the rotor cone presents the appearance of blowback in forward flight. That’s cyclic flapping.
This ones got me puzzled tho.
Isnt the disc still coned ina virtical decent?
Corse it is, so wheres the link?
I would have said you can see cyclic flapn wen you look left then rite.
Advancing is higher than retreatn.
Sure, the frunt is alot higher n the back, but thats coz we need air flown in under the disc + the result of flapn.

To my way of thinkn, gyroscopic precession dont exist in a rotor that is flyn S/L.
Its happily spin'n and nuthns tryn to change anythn. Its only wen you put in abit of cyclic pitch, precesion has an effect, and its controled by cyclic airodynamic forces.
 
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