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Old Dec 17, 2010, 09:24 AM
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Do you think this may be a viable explanation of my 'left roll' problem?

Jochen
Yes.

I'm not certain which way the prop is turning. From the rear view, does the prop turn CW or CCW ? But the effect of the prop as a spinning top is completely valid.

Either way I think you have an explanation. Because of all the rotating machinery left and right will be different.
One solution would be to add a moveable rudder and keep the turns coordinated Or make the rudder large enough that it keeps things coordinated (but then it might become spirally unstable!).
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Old Dec 18, 2010, 05:54 AM
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John,

I, too, noticed all those remarks about left-handers being easier to fly than right-handers. This seems to be independent of wether the gyro is a tractor or pusher. Even my very old Minimum, still equipped with a cw rotor, is flying left-handers better than right-handers. But that one gyro has no statistical significance.

As one of my favourite questions is 'Why?', I'm trying to find out the reason for this behaviour.

With all my gyros (no rudder on these things) left-hand turns are sort of automatic: I bank the gyro and pull a little bit of pitch and then I just have to use some - more or less constant - roll to the right to keep the gyro at the desired bank angle. Right-handers start out the same, but once pitch is pulled, I have to sort of balance the gyro in roll as well as in pitch all the time to fly a flat turn with a constant radius.


John, Mickey,

when I wrote post #419 I had to convert some diagrams about the effects of precession to fit what I had on my gyro. Unfortunately I got the prop spin direction wrong when doing that. The effects of precession I wrote about in that post are therefore only valid for a pusher prop, i.e. a prop turning ccw seen from behind. Of course, as all of us with electric powered gyros, I'm actually using a normal prop that turns cw when seen from behind. For a prop like this the precession effects are just opposite. Which means that precession will yaw my gyro to the right and not to the left.


Mickey,

rudder as an afterthought is not an option on a 85 gram gyro. But first tests showed a noticeable improvement in right-hand turn handling by using very flappy flapping hinges and some more lead in the tips to keep the rotor as flat as before.

Jochen
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Old Dec 18, 2010, 08:21 AM
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rudder as an afterthought is not an option on a 85 gram gyro.
Understood. I was just prodding you a bit
Quote:
Originally Posted by JochenK View Post
...very flappy flapping hinges
This keeps the rotors response close to 90 degrees, reducing cross coupled control. If the rotor were stiff I can see some odd response to control happening.
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Originally Posted by JochenK View Post
... some more lead in the tips to keep the rotor as flat as before.
This also is beneficial, for all the reasons previously discussed.
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Old Dec 30, 2010, 08:55 AM
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mnowell129, so if we build a full scale one man carrying ultralight 33ft rotor helicopter that is based on a simple teeter hinge(like autogyros), how would the flight be like? uncontrollable? stable?

Kalle
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Old Dec 30, 2010, 01:27 PM
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mnowell129, so if we build a full scale one man carrying ultralight 33ft rotor helicopter that is based on a simple teeter hinge(like autogyros), how would the flight be like? uncontrollable? stable?

Kalle
This is kind of an open ended question with lots of variables.
Questions for you:
1) "Simple teeter hinge" is a rotor flapping mechanism, not a control mechanism. Are you planning tilting spindle or a swashplate?
2) Do you have any rough numbers about power, disk loading, etc?

My guess is there are ultralight homebuilt helicopter forums out there where almost everything has been tried.....
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Old Dec 30, 2010, 01:50 PM
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This is kind of an open ended question with lots of variables.
Questions for you:
1) "Simple teeter hinge" is a rotor flapping mechanism, not a control mechanism. Are you planning tilting spindle or a swashplate?
2) Do you have any rough numbers about power, disk loading, etc?

My guess is there are ultralight homebuilt helicopter forums out there where almost everything has been tried.....

tilting spindle or direct control ala gyrocopters rotorheads. i.e. no swashplates. This heli is to be a non-collective one. It will be a ground effect machine.

-Takeoff weight: 160-200kg
-Rotor diameter : 33ft
-rotor rpm: around 200-230rpm
-No collective pitch
-Power 25hp
-anti torque to be discussed someother place

Lift is calculated and in theory it will fly. What eats me and what not even full scale flyers couldnt answer me is how the handleing will be. Will the following rate for instance be like 15 seconds due to the low rpm and the low discloading?. The Rotor rigidity is going to be a little bit higher then normal. In other words the chord is going to be thick, around 20inches for simpler contruction and less overall stress. So how will the handling be on this one. It should be stable enough since it is light? but will it be too un-responsive? I wanted to build a precise 1/3 scale model but realised that I would waste money and time because rotrocrafts differ so much with scaling up.


Oobs. 999th post!
Regards
Kalles
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Old Dec 31, 2010, 12:13 PM
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What eats me and what not even full scale flyers couldnt answer me is how the handleing will be. Will the following rate for instance be like 15 seconds due to the low rpm and the low discloading?.
i don't think disc loading is a factor. RPM, rotor mass and blade aerodynamics are the factors. You can go back in this thread and run the calculations to get the numbers.
My gut feel is that the controls are going to be sluggish. Gyroplanes in this rotor diameter are higher RPM? (I think in the 350 400 range, but I'd be happy to be corrected). Seems like the challenge will be lack of control and/or PIO.
With the un-damped teetering rotor, is suspect PIO may be the big issue, especially while wallowing around on a ground effect bubble...
Can I come watch?
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Old Dec 31, 2010, 08:14 PM
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You are more than welcome to watch it when it is built . I am not sure if its gonna be built though, first it would be a 1/3 scale but since scaling change everything in rotorcrafts I skipped it. And yeah I also feel it is going to be onaslugish side. I have heared from a real teeter hinge helicopter pilot(of a Scorpion Too that use direct tilt) that there was a control delay. When I asked him how much in seconds, he said about 2 seconds! its diamter was less than 33ft and weight is way more than 200kg since it uses a 75-100hp. so the future for my G.E craft is a little bit unknown and dark right now.

Anyway Happy New Year everyone. I also just made the 1,000th post today. Heck, even if I planned this, it would never happen
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Old Jan 01, 2011, 01:50 PM
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A "manned" fixed pitch helicopter?!!?!!:eek:

Hello Sky-walker,

Don't build it. You will get hurt or killed.
Regards,
-Mike
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Old Jan 01, 2011, 07:12 PM
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Hello Sky-walker,

Don't build it. You will get hurt or killed.
Regards,
-Mike
I see Mike, it is so easy to say that and you are right. However,I have been planning this all my and I am very careful by nature, too careful. I cant explain everything in detail but building such thing will happen in many many countless steps. like a test rig, first a remote controlled testrig. Later, a thrust test, after that, a control test etc. When I sit in it I know that it is tested and the craft will be supported by looooong skids. No way to flip over. This is not the problem. Safety is nr 1 offcourse. This machine if ever built will never fly high, its a ground effect machine. The problem is one other thing.

Anyway, I am thinking ahead(as usual )and see my self there trying to control the thing that is responding two years after my commands. Or maybe it is gonna be too sensitive, I dunno. A fixed wing is more dangerous. I know that you wont believe it but the feeling of flying ahead without a brake is scary.
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Old Jan 11, 2011, 12:22 PM
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Hello mnowell 129,

is there with the seesawing head an aerodynamic damping??
Which is determined by the distance B or F.
(see drawing).

How big should the distance be a B in proportion to the rotor diameter?
If there is for it a rule of thumb

A-fulcrum of the seesawing of head
B-distance A to the seesaw
C-rotor sheet screw
D situation of the rotor sheets Statically
E-situation of the rotor sheets in the flight
F- distance CG of the rotor sheets to A in the flight

Or if this is everything far from reality

freya151

Ps. sorry for my bad english
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Old Feb 09, 2011, 05:27 AM
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Disymmetry of Lift

Mickey you are making this way to complicated. What you are describing is the disymmetry of lift due to the difference in airspeed between the advancing and retreating blades. This is compensated for automatically by teetering on a two bladed system and by hinges on a three bladed system. This allows for a change in the angle of attack, reducing the lift of the advancing blade and increasing the lift produced by the retreating blade, compensating perfectly for the disymmetry of lift. Without it the machine would indeed roll over.
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Old Feb 09, 2011, 05:39 AM
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Tetering Rotor

Quote:
Originally Posted by mnowell129 View Post
i don't think disc loading is a factor. RPM, rotor mass and blade aerodynamics are the factors. You can go back in this thread and run the calculations to get the numbers.
My gut feel is that the controls are going to be sluggish. Gyroplanes in this rotor diameter are higher RPM? (I think in the 350 400 range, but I'd be happy to be corrected). Seems like the challenge will be lack of control and/or PIO.
With the un-damped teetering rotor, is suspect PIO may be the big issue, especially while wallowing around on a ground effect bubble...
Can I come watch?
PIO- pilot induced occillation- is produced by the pilot overcompensating for a rocking to and fro fore and aft. The best fix for this is training and centerline thrust. Damping a teetering system is unnecessary. The teetering system takes care of itself. The amount of undersling is the primary adjustment in a two blade teetering system.
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Old Mar 10, 2011, 10:30 PM
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watching this is a little bit like watching someone try various goat saddles on a wild rhinoceros. im gonna ride him if i can find just the right saddle..there are many many many other things u need to do before u check girth sizes,, there are several helos flying with no collective, power only throttle control for altitude, speed,,, that means that u never have access to autorotation.., if u just back off the throttle to go lower altitude and get behind the power band or your engine cold shocks,it stumbles, shudders to a stop and u are the afternoon news,, consider this,,you arebetting your life that your machine will never ever have a power outage for any reason, never run out of fuel, never have an air bubble in your fuel, never a fouled spark plug or wire fall off,,, i will fly almost anything,, well not now,, my doctors said,, but would,,, except weather baloons,,lawn chairs,, shopping bag wings,, and now thanks to the images,,,, no collective helos,, just my 2,,, buck
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Old Jun 17, 2011, 07:57 AM
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There is one thing that screwed my brain lately and I wish to understand: (this is really frieying my brain)

There are teetering rotors that freely flap and hingeless/rigid rotors that hardly flap or flap very little.


Teetering rotor

As we know the blade pitch is made 90 degrees earlier before the desired tilt-plane direction. That is due the gyroscopic preccesion and the softness of the blade and the time it takes to make it flap up(? wrong right? both?).

Rigid/hingeless rotor i.e. rc helicopters
Aaaaah, here comes the madness and confusion. Please bare with me. As I have learned and read, rigid rotors are different from teetering ones. Due to rotor rigidity and lack of hinges, the blade pitch is made less than 90 degrees before the desired tilt-plane. The reason being that the rotorblade flaps up quickly.

So let me put it this way:
In theory if we have absolutely rigid rotors the phase angle should be 0 degrees(ha?!). So in a in a ClockWise rotor seen from above, if we want to fly forward the blade pitch is feathered negatively at the front! right? Why then are the rc helicopters that are fairely rigid made so that the bladefethering occurs 90 degrees earlier? aaah my brain is melting


Thanx
Kalle
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