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Nov 07, 2010, 07:14 AM
RC Group therapist
DeRidder LA.
Joined Nov 2008
1,961 Posts
Quote:
 Originally Posted by Sky-walker Hi mnowell129 I have read most of what you wrote beside my previous knowledge in rotorcraft aerodynamics. But I have a kind of an interesting buggling question that I want to answer; Is the cyclic of an "autogyro" REALLY the same of a "swashplate helicopter" Lets pretend that the swashplate helicopter has no collective, . Let us imagine the heli is fully rigid(yes it is stupid) with no hinges but the feathering. To keep it simple(I hope): the pilot pushes the stick forward, the "net" result of the autogyro rotor in every cycle(the fore and aft blades are at nose and tail), is as if we took a whole rigid(nonteteering) rotor-hub assembly and tilted it forward a few degrees? The "feathering" incidence of the fore/aft blades there, are zero offcourse (there are none but I write for clearence) correct? (I know I am, if you say no, then you misunderstood me already). Now, if it was a rigid heli rotor instead, wouldnt the helicopter rotor head vary its feathering hinges whole the time so the front blade is minimum pitch( after traveling 90 degrees from the left position ) and the aft is maximum in pitch where on a gyrocopter the "front and aft blades" are at "zero feathering incidence". Or wait, are the helicopter blades at zero degrees feathering incidence at the front and aft as well??? Well, I will be guarnteed be misunderstood here, it is very hard to explain, these are very complicated matters and even worse when explaining a question.
Hello Sky
Your question sounds as though you're looking to argue, but I'll try to answer it anyway. You have not been misunderstood, of course you can always use that if you don't like my answer. I'm unsure of what your "previous knowledge in rotorcraft aerodynamics" is, but reading through the material Mickey had posted is always helpful. Everything he posts can be backed up, and isn't just pulled from his like a lot of folks on the forum, in short; he's a credible source of info.

To short answer your question; yes Cyclic feathering occurs in swashplate systems as well as flex plates (like I use in most of my models). There isn't a simple way to illustrate this for you, it would take many drawings and formulas to show what is really occuring. The main difference, as you mentioned; is mechanical feathering Vs. aerodynamic feathering. Many people confuse angle of incidence, and angle of attack. When a blade flaps up or down, the induced flow changes, thereby changing the angle of attack without a mechanical incidence change. Tilt a flexplate gyro hub, and you've in effect just changed the angle of attack with the above mentioned effects. In your example; Obviously the mechanical angle of the blades did not change.....they are rigid, but by changing the induced flow of the "Fixed blades" you change the aerodynamic angle of attack. This is the same end state as mechanical cyclic feathering. The two systems obviously have mechanical differences, but they are performing the same aerodynamic functions. Look into blade element theory; which will show you scalors and vectors for a given rotation cycle and snapshot of a given blade element. Might be a bit more than you are interested in, but a partial understanding of aerodynamics leads to incorrect assumptions most of the time.

Why is a fully rigid rotor system stupid?!? The full scale LUH-72/EC-145 helicopter that I fly on a daily basis has a rigid rotor system without lead/lag/flap bearings or hinges. It only has feathering as you described. I better let Eurocopter know the system won't work right away. In seriousness, all the lead/lag/flapping is done in the blade itself by being extremely flexible at the root.

Are you building a gyro currently, or do you already have one? Autogyros are fun to me because so few people in the RC community have flown them with any real success. If it weren't challanging there would be no point in it for me.

Regards,
-Mike
Nov 07, 2010, 01:16 PM
Registered User
Joined Jun 2005
1,025 Posts
Quote:

I am not arguing with Mickey. what he wrote is correct. It is just that there is one unclear point in my head that I "can not visualize or really understand" and that is iratating me. No more no less.

Yes, I know that helicopters like LUH-72/EC-145 are "hingeless"
but they are really hinged in that they are "flexible" on all axes instead of using bearinghinges. When I said rigid I meant ofcourse absolutely rigid and that is plain stupid in a functional helicopter but I wanted to use that as an analogy!, like the earlier Hiller coaxial(yes its a different case, because coaxials dont rollover because of dissemetry of lift) and yes a fully rigid single rotor wouldnt fly becuze it will tip over as fast as it gets forward speed.

Any way, I discovered that the best way to understand the part I am wondering is to watch a slow motion camera footage of rotating helicopter rotorblades. Nothing would be beter.. hmm, but where to find such footage

"Are you building a gyro currently, or do you already have one? Autogyros are fun to me because so few people in the RC community have flown them with any real success. If it weren't challanging there would be no point in it for me."

BTW Are you wondering if I own or flew a real gyrocopter?

Kalle
Nov 07, 2010, 02:58 PM
Registered User
Joined Mar 2010
4 Posts
Hi!

Quote:
 Originally Posted by Sky-walker ... Or wait, are the helicopter blades at zero degrees feathering incidence at the front and aft as well??? ...
Yes, they are.
Look at this picture:

I hope this helps.

-=Stevie=-
 Nov 07, 2010, 03:49 PM Registered User Joined Jun 2005 1,025 Posts Hi Stevie, so if the rotorblades are ultrastiff and if there are no flap hinges at all and no "o-rings in a RC model case," the helicopter wont move anywere to aplied cyclics?
 Nov 08, 2010, 02:05 PM Registered User Joined Jun 2005 1,025 Posts It is a real shame, that real helicopters use ultra complicated swashplates when they could use the very simple teetering hinge. Ofcourse the only reason for the swashplates is the collective. If we would fly at very low altitudes, we really dont need collectives as much and a teetering hinge would work perfectly. introducing a collective mechanism to a teetering hingle is as complicated as installing a full swashplate and therefore they introduced the swashplate as the key of the future. IMHO, a swashplate is delicate and complicated. I would rather ride in a teetering hinge heli-craft(not many helis got that) with a new solution to autorotations. I am having a hard time finding any helicopters using a tilthub. The only one I found was the BJ "schramm" I think it is called
 Nov 08, 2010, 03:20 PM 1.21 gigawatts Fort.lauderdale Florida Joined Jul 2006 724 Posts Mickey Thank you so much for this thread it has help Me understand rotor aircraft to a great extend never knew how important all this info is till now Looking forward for more Eddie
Nov 09, 2010, 05:48 PM
Registered User
Joined Mar 2010
4 Posts
Quote:
 Originally Posted by Sky-walker I am having a hard time finding any helicopters using a tilthub. The only one I found was the BJ "schramm" I think it is called
Do you talk about the Helicycle?
 Aero-TV: Helicycles Aloft -- BJ Schramm's Legacy (9 min 25 sec)

Although it has tilthub, it also has swashplate.
Like most of UL helicopters.
For example: R-22, Mini 500, Mosquito Air, etc.
The Bell JetRanger has tilthub too.

ps: sorry for my english, I don't speak it too well.
 Nov 09, 2010, 06:19 PM Registered User Sydney, Australia Joined Mar 2006 1,315 Posts Thanks for the video. There is a nice view of the teeter-head at 2:02.
 Nov 09, 2010, 08:55 PM Mickey from Orlando. Really. Joined Nov 2004 3,813 Posts This thread seems to be confusing the teetering head with the tilting spindle/hub. The helicycle does not have a tilting hub. It does have a teetering head. Collective is not the only reason for using a swashplate. The tilting spindle mechanism has it's own set of problems.
Nov 10, 2010, 05:37 AM
Registered User
Joined Mar 2010
4 Posts
Quote:
 Originally Posted by mnowell129 This thread seems to be confusing the teetering head with the tilting spindle/hub. The helicycle does not have a tilting hub. It does have a teetering head. Collective is not the only reason for using a swashplate. The tilting spindle mechanism has it's own set of problems.
You are right, I confused the two different things. Sorry for my mistake.
As I said, I don't speak english well.
Online dictionary is not enough help to understand such technical language clearly.

Regards.
 Nov 10, 2010, 07:23 PM Registered User Joined Jun 2005 1,025 Posts Stevie, no, it is not the helicycle which is a standard typical swashplate non-tilt helicopter I made some search but it is hard to find which "heli version" is the tilt-hub. I think it is Here and is called Scorpion 2 by rotorway and sometimes called by B.J schramm, so confusing could be either this http://www.aviastar.org/helicopters_...orpion_too.php or http://www.aviastar.org/helicopters_eng/scorpion.php You can clearly see it doesnt have the typical swashplate, but has only a seperate "push-link" to the collective
 Dec 08, 2010, 06:39 AM Winging it Ò> Joined May 2006 10,076 Posts stability vs controllability in rotors Here is something that's been on my mind; stability vs controllability. 1) If I define stability as the propensity for a rotor to return to level flight, and I define control-ability as the speed that the rotor responds to controls; faster response equaling more controllable. (I know that a "too fast" responding rotor seems uncontrollable;maybe a better term is unflyable; but that is because the pilot is too slow, not because the rotor is not controllable). Based on these definitions, what forces and what design techniques can improve stability? It seems that some of the things one can do to make a rotor slower responding so that the pilot can keep up, will also reduce stability. For instance by making the flapping hinges stiffer, the rotor will become slower responding for the pilot, but it will also be slower responding to the pendulum forces of the autogyro trying to level the rotor.
Dec 08, 2010, 02:06 PM
Registered User
Joined Mar 2010
4 Posts
Quote:
 Originally Posted by Sky-walker Stevie, no, it is not the helicycle which is a standard typical swashplate non-tilt helicopter I made some search but it is hard to find which "heli version" is the tilt-hub. I think it is Here and is called Scorpion 2 by rotorway and sometimes called by B.J schramm, so confusing could be either this http://www.aviastar.org/helicopters_...orpion_too.php or http://www.aviastar.org/helicopters_eng/scorpion.php You can clearly see it doesnt have the typical swashplate, but has only a seperate "push-link" to the collective
In fact, the pictures (on the links you gave) show it's NOT a tilt-spindle helicopter.
It has a "normal" swashplate for cyclic control.

Look these closer pics:

I think these are what you were looking for:
 Nick's Ultra-Lite Heli Rotor Head 0001 (1 min 56 sec)
 Nick's Micro Heli Rotor Test 2 (5 min 35 sec)

 AirScooter (0 min 53 sec)

These do have tilting spindle.

Regards.
Dec 09, 2010, 07:20 AM
Winging it Ò>
Joined May 2006
10,076 Posts
more on stability/control-ablity

Below are three examples of rotor craft with different stability/control-ability characteristics. I should note that I'm directing this topic at pitch and roll axis only.

1) the 450 helicopter has a 90 degree flybar, very rigid blades (no flapping). It is very controllable but it is unstable. Adding weights to the flybar will make it less unstable but also slows the control response. This helicopter never returns to level on it's own.

2) the Blade SR 120 (best small heli I've ever flown) has a 45 degree flybar, no flap, is very stable and has pretty good control-abilty. At high forward speed I have to put in some left aileron to keep it level; assymetric lift?

3) Mr. Twister has flapping hinge blades. It is very controllable and very stable. No assymetric lift.

Here is where I am going with all of this. I want to make the 450 more stable to make it easier to fly. So far I think I have two choices. 1) Add a flapping function to the blades and 2) change the flybar angle.

I may experiment with both. I was thinking of modifying the head so that I could ground adjust the flybar to any angle to see what effect it has.

I would appreciate thoughts and suggestions from the rotor scholars/experts.