Fixed rotor head Gyros

[David A Ramsey]

In an attempt to get my first fixed rotor head electric autogyro to fly, I've just about finished my second airframe.

The mast has been set to -12 degrees. The rotor blades are set to -1 degree with an aspect ratio of 8 to 1 (1.25" x 10") for a 24" rotor Dia. The rotation is CW and the rotor has left tilt and can be bent as needed. The motor is set to 5 degrees down thrust. Weight is approx. 7.5 oz.

The motor is a Feigao IPS BL 4000KV mounted in a GWS A drive turning a GWS EP1047 prop. Uses 2s 1040mAh Lipo.

The airfoil photo shows 2 airfoils. The narrow profile was used on Gyro no. 1. It was difficult to wind up unless -2 degrees was set for angle of attack. It also gave poor lift unless the mast was set to -15 degrees.
The wider and thicker profile is for Gyro No. 2. It winds up good in a gentle breeze at a slow run.
Neither of these airfoils would wind up at all well when set to 0 degree angle of attack.

I haven't got great hopes for Gyro No. 2, but I'll give it a try. This will be my last attempt for a fixed rotor head, as John Boren's articulated head Gyro make more sense.

This thread may be a good example of how not to approach an Autogyro.

But then again, maybe not! See post 18, page 2

David

[AustinTatious]

hehe its cool! why dont you hAve much hope for it?

Make sure your blades can flap.... and go with 3 cells!

iF YOU BUILD ANOTHER FIXED HEAD, DESIGN IT SO THAT THE TOP OF THE MAST CAN BE ADJSUTED.

[David A Ramsey]

hehe its cool! why dont you hAve much hope for it?

Make sure your blades can flap.... and go with 3 cells!

iF YOU BUILD ANOTHER FIXED HEAD, DESIGN IT SO THAT THE TOP OF THE MAST CAN BE ADJSUTED.


Dang Austin, this is adjustable. The top of the mast ends with a brass threaded rod and will hold a tilting adjustment. I hear ya!

Blade flap is apparent when running up the head using a 20" box fan. Will use 3S if necessary.

Why don't I have much hope? After the attempts with Gyro 1, I feel it's good to maintain a healthy negative attitude. This way, maybe, it can only get better?

Appreciate your comments.

David

[AustinTatious]

LOL, i knwo what you mean... nothing has ever frustrated me as much as this little gyro of mine. ( sorry about the caps lock in my above post, i was in a hurry out the door on hand being drug by the woman!)

[David A Ramsey]

Hey Austin, you can "caps lock" me anytime. He who has autogyro success is my mentor. Even if he is being drugged around by a woman.

[JWarren]

Looks like a good model to me! My project has taken over a year! I just put it on the back burner and come back to it later. There is so much to these models sometimes a little time to think about whats going on with the model helps. Heres mine.

http://www.rcgroups.com/forums/showthread.php?t=302523

John

[David A Ramsey]

Hey John;

I've read you're historical thread and found it interesting. Hoping to read of future successful flights.

David

[David A Ramsey]

Had a chance to try launching my Autogyro today with the customary results. Good rotor speed on launch followed by half left roll to inverted and Splat! Beginning to feel I need to hand launch this thing upside down and perhaps it will roll upright.

Why does it roll into the advancing blade? I use CW rotation.

Is the left roll due to motor torque?

Is the Disc loading too light?

Maybe right rotor head tilt?

Would a CCW rotor compensate for motor torque?

I would like to learn something from this experience. So, any thoughts?

David

[AustinTatious]

Try launching it with partial power and see if it still rolls and if so does it do it as hard or harder than with full power.

You have the correct rotation for countering prop torque.

in your pic above you do not appear to have any downthrust in your motor. Start with abotu 5 degrees! You may end up at 10.

[David A Ramsey]

Well Austin, I got 5 degrees down thrust and +2 degrees in the stab.

Reduced power? Will try tomorrow.

David

[AustinTatious]

keep in mind, reduced power isnt the solution, just a variable to change to see what causign the problem.. Odd indeed that it rolls into the advancing blade!

You must have GOBS of torque.

[David A Ramsey]

Yesterday there were some pretty strong, 10-15 mph, winds. Too much for flight, but I spent some time watching and feeling the rotor behavior without running the motor. I had prebent the rotor head to the left and could feel a strong pull to the left. I re-bent the rotor straight and still a strong pull to the left. Bending the rotor head to the right helped, but how is this possible? Maybe I should try a launch this way.

Now here's something else that puzzles me: I'd like to build a small Cierva C-19. The 3-views I have are by B. Karlstrum. The plans show a 3 bladed CW rotor tilted to the right as the flying attitude of the rotor. Hey what's this????

There are forces going on I can feel, but don't go along with what I read.

This is tedious Mr. Tatious

David

[David A Ramsey]

Amazing what 5 degrees of right tilt to a rotor will do! To the disappointment of my fellow club members, my little Autogyro did not do a half roll into the ground.

For the first launch, with right rotor tilt, I under proped with an 8" prop to reduce - if any - motor torque effects. The altitude from launch was about 30' followed by a "contollable" desending circle to a perfect landing. This is good.

Second flight was with the GWS EP-1047. With no apparent motor torque effects, she climbed very nice at full power. More important now, since she was flying, was how well she responded to rudder and elevator. For 5 minutes or so I just couldn't believe how beautifully she flew. OHHHH life is good!

So now I need to get comfortable flying her and perhaps get someone to take a flight photo.

Austin: Thanks for coming along with me.

David

[AustinTatious]

hehe congradulations! its feel like you ahve concured somthing ehh!

autos can be a real PITA. I had severaly that never flew. Total bummer.. jsut made the one that worked extra special... The kickback is that you realise all the dumb mistakes you made with the ones that never worked.

[David A Ramsey]

Austin: The problem remains: I'm still not sure what's going on. I understand the forces of the advancing blade before flight RPM is gained. It seams that once autorotation RPM is achieved, there's another set of forces working on the rotor. Seems like such a little thing to bend a little right tilt into a CW rotor and turn a monster into a lovely flyer.

David

[AustinTatious]

Im confused :(

It flies, but the problem remains?

Its so hard to diagnose thru text..

A few q's:

1. Yoru Rotar rotates Clockwise when viewed from the top correct?
2. Your prop rotates clockswise when viewed from the rear correct?
3. How much Can your blades flap?
4. where is your VERTICAL cg?
5. if you hold the craft by the top of the center of the hub, how does it hang?
6. did mast tilt left or right Make it fly?

If it flies, what is the problem and what appears to cause it?

[David A Ramsey]

Im confused :(

It flies, but the problem remains?

The problem is I don't completely understand why it flys so well

Its so hard to diagnose thru text.. YUP

A few q's:

1. Yoru Rotar rotates Clockwise when viewed from the top correct?
YES
2. Your prop rotates clockswise when viewed from the rear correct?
YES
3. How much Can your blades flap?
They sag about 1/4" at tips. Very flexible rotor plate.
4. where is your VERTICAL cg?
With mast at 12 degrees, CG is 1-3/8" behind mast center line at base.
5. if you hold the craft by the top of the center of the hub, how does it hang?
About 5 degrees down.
6. did mast tilt left or right Make it fly?
Tilt right about 5 degrees.
If it flies, what is the problem and what appears to cause it?
See above.

You must have read my last post too fast.

Before making any further judgements, I'd like to get a couple of dozen flights and see how I feel about it.

It isn't good enough that it flys if I'm not sure why.

David

[David A Ramsey]

I've accumulated about 30 minutes flying time now. Knowing it's not going to fall out of the sky has made each flight a pleasure.

With near calm wind conditions she flys very nice on a 2S lipo. Climbs well on full power and sustains altitude at 3/4 power. However my 2S Kokam 1020mAh is only rated at 2C with 4C bursts. At 1/2 power ( on full charge ) the draw is 2A and at full power it's 3.3A. Add cold weather and this battery is marginal for flight times over 4 minutes. A 2S 1200mAh rated at 8C would be a better choice.

Using the Balsa Products Feigao / GWS IPS A Drive charts as a guide, I find I need better than 1:1 weight to thrust for acceptable flight. With a 2S Lipo, Feigao 4000KV, IPS A Drive and EP-1047 prop, the max. thrust is 8.3oz. for a Gyro weight of 6.9oz.

A better power arrangement is using a Kokam 3S 0.340mAh (20C) and EP-0947 Prop. The Balsa Products Chart shows 11.5oz. of thrust for 4A at full power. The difference in performance is amazing. Can't beleive how fast she climbs. I can see a loop in the near future.

The accumulated flight times have shown a decrease in mast rake might be a good idea since i'm using quite a bit of down trim.

At a 100', or so, visibility is no problem, but there are times when she's far out and low, I start to wonder which way she's going.

Turns to the advancing blade are very smooth, while turns to the retreating blade are quicker with attention to minimizing the bank angle, especially in the down wind turn.

David

[JWarren]

Nice going David!

The photos came out really good too! How many controls do you have on that model? Rudder or elevator or just a DC head? Have you practiced rolling landings as well as drop in landings? Have you been able to hover in an on coming wind yet?

Looks like a great bird to get a kick out of!

John

[David A Ramsey]

Thank you John.

Just rudder and elevator. Does a nice roll out landing, but "0" ground roll is more fun. The GWS Pico-Stick wire landing gear is pretty flexible, so for grass field landings "0" ground roll is safer. And yes, she does hover. She's very stable and manoeuvreable, while I do most of the shaking. Still can't beleive how easy it is to fly her.

Hummm, gonna have to giver her a name.

David

[JWarren]

Is the right tilt you added, as looking from the rear or the front of the gyro?

[David A Ramsey]

John:

When viewed from the rear: CW rotation for rotor. About 5 degrees right tilt on rotor hub. ie: the threaded axle shaft cemented into the top of the mast is bent to the right.

David

[JWarren]

Ok, Now I am looking from the rear of the bird as well and understand.

From everything I have read, and I may, still, be wronge here, but I think I got it correct. The blades have it's effecting airfoil on the top of the blade. This creates lift. The retreating blade dose not create lift and is pretty much equaled out due to the headwind. The advancing blade is being pushed down on the left and this is due to it's incedence. An airplane wing is getting lift from both sides of the wing and is equal. A gyro only on one side, thus not equal. Thus the need for trim of 5 degrees to the right. One thing you can try is changing the blades incedence (angle of attack) in 1 degree increments. You can do this by putting a thin shim under the TE of the blade to lift the TE up. I have the same 5 degree trim in my gyro except on the other side as it is a CCW blade spin. I have not tried shimming the blades to get the model flying at zero trim, as of yet. I want to chew and swallow what I have in my mouth, before I take another bite. :) I will let it fly with the trim for now and play with it later. I will also try to change the angle of the motor at some point, to see if the prop tork is causing the situation. I just don't see this solution as logical as the previously mentioned solution. But it will give me the opportunity to study the effects and take notes.

I just need 3 more hours in every day to get it all done. :)

John

[AustinTatious]

You guys shoudl not worry about having to bend your mast to the side.. IMHO this is perfectly acceptable... IF you ahd built a DC head then you woudl have done exactly what you ahve done except you would have used a trim lever on the TX.

You model is flying because everythign is right! Tilting the mast 5 degrees is not really a SMALL change to go from pitfall to Puppydog. IF you ahd 5 degrees positive incidence on one wing of an airplane, what would happen? Would you consider that a small change?

Take notes and when you build your next model you can use what you have learned!! Congrats! Getting a gyro to fly and fly well is no easy task!

[gbarc]

Amen to that!! Very nice model!!

Greg

[David A Ramsey]

Austin:

I accept the fact that I've got the Gyro working. NOW I want to know why?

David

[mnowell129]

Austin:

I accept the fact that I've got the Gyro working. NOW I want to know why?

David
You may want to consider centrifugal force in the equation. My gyro blades are so floppy that when you lift by the blades at mid span you get about a
60 degree cone angle of the blades. In flight the cone angle is about 5 degrees. The effects of the centrifugal force are significant. The retreating blade is generating enough lift to cone up. The blades exert a force on your rotor hub that is both up and out. In effect the gyro copter is suspended between the blades which are being slung out and lifted up. ALthough completely non-sensical to build , if you had tiny rocket motors at the end of string instead of rotor
blades, and the little rockets were set at some small up angle, the "rotor" would spin, cone up and lift your craft. Modifying your shaft angle is changing the pitch of your blades, changing the speed at which it turns. My observataion from all your reports is that your rotor speed was too low, which might be corrected with more negative pitch and a return to an upright shaft position. The retreating rotor blade passes to the front of the gyro in clean air and may get an extra bump of lift. If the rotor speed is too low there is not enough centrifugal force to tame the blade rising 90 degrees later and you get the confusing roll to the advancing blade. My gyro copter does the same thing, changing the pitch settings changes the roll trim.
Just some thoughts...
mickey

[David A Ramsey]

The blades have it's effecting airfoil on the top of the blade. This creates lift. The retreating blade does not create lift and is pretty much equaled out due to the headwind ???. The advancing blade is being pushed down on the left and this is due to it's incedence ???. An airplane wing is getting lift from both sides of the wing and is equal. A gyro only on one side, thus not equal. Thus the need for trim of 5 degrees to the right. One thing you can try is changing the blades incedence (angle of attack) in 1 degree increments. You can do this by putting a thin shim under the TE of the blade to lift the TE up. I have the same 5 degree trim in my gyro except on the other side as it is a CCW blade spin. I have not tried shimming the blades to get the model flying at zero trim, as of yet. I want to chew and swallow what I have in my mouth, before I take another bite. :) I will let it fly with the trim for now and play with it later. I will also try to change the angle of the motor at some point, to see if the prop tork is causing the situation. I just don't see this solution as logical as the previously mentioned solution. But it will give me the opportunity to study the effects and take notes. John

John, I have problems with some of your thoughts and I added bold question marks to your Quote and they are rhetorical as we're both pondering.

At some point in the near future, I'm gonna have to talk with my friend Dr. James Wang about this Rotor phenomenon. Right now I'm trying to understand it by going through the back door.

Here's what I'm chewing on: For now I don't see motor torque (for my Gyro) as an issue.

I look at blade angle of attack in terms of lift, drag and ability to autorotate. Right now I have a small (not measured) negative blade incidence. Wind up in no wind, at a slow run, is rapid. Most of the launches show I have more head speed than necessary. At some point I'll get someone to use my Sky-Tach for a reading of the head spead during flight.

I look at rotor speed in 2 steps: 1. Pre-autorotation and 2. Flight autorotation. During rotor wind up it's very easy to understand why the Gyro will tip toward the retreating blade as the advancing blade's lift overpowers the retreating blade. Once the rotor is in flight capable, sustained autorotation, I feel there are forces that I don't understand. I understand that blade flap dampens forces as the blades rotates between advancing and retreating. I use a single blade bolt to allow the blades to find their lead/lag position.

This is what I don't understand: Why does the rotor disc need to be tilted toward the retreating blade (in forward flight) to keep the Gyro from rolling toward the advancing blade? I would think the advancing blade would naturally cause the Gyro to tilt to the retreating blade side and therefore need to be tilted toward the advancing blade.

If you could maintain autorotation without external power or relative air movement, (in a vacuum) the forces through rotation should be balanced and each blade would be only advancing, or retreating.

I'm trying to understand the forces on the rotating disc as gravity, gyroscopic action and moving through the air take effect.

I'm leaning now to beleive it's the Gyroscopic force that demands the oposite tilt to the rotor. Humm, I think that's it. Have to think on it some more.

For now, like you John, I'm gonna just enjoy flying the little Gyro.

David

[JWarren]

Austin,

I do have a DC head on my gyro. I never said I had to bend my shaft. I never mentioned anything about changing the incidence of a wing on a plane either. I am however trying to help David in his quest to understand why he had to bend the shaft to get the 5 degrees he needed to get his model flying.

I am glad you got your autogyro flying, Austin. Which gyro did you say you have again?

Just, saying don't worry about it, is not an acceptable answer for me. I have the need to know more. Thats what makes me tick! Why would you come on to a thread where someone is asking a question, make comments and offer up absolutely zero usable information? I'm guessing thats just what makes you tick. I'll just take note of that.

John

[David A Ramsey]

Austin-John-Mickey:

I gained quite a large amount of information from the RC Model Autogyro web page, however the exchange of ideas from you has been even more thought provoking. Whether the Gyro is fixed or Direct controlled, the forces on the rotor disc are the same. I feel these forces require greater attention and understanding for a fixed rotor as the rotor angles need to be pre-set.

I find it interesting that each of us has a working Gyro, however we all have a slightly different way of wording the way we discribe our approach.

I truly appreciate your explanations and the time you take to comment.

David

[JWarren]

David,

The retreating blade does not create lift and is pretty much equaled out due to the headwind ???.

This is known as "Retreating Blade Stall".

Aerodynamic stalling of a rotor blade as it turns from nose to tail. This is caused when the forward speed of the aircraft is high enough that when this air speed is subtracted from the air speed caused by the rotation of the blade, the relative wind speed on the retreating side is so low that not enough lift is created on that side of the aircraft. The aircraft will roll to the retreating blade side; Pitch up or both.

The advancing blade is being pushed down on the left and this is due to it's incedence ???.

In normal flight, the forward speed of the autogyro adds to the airspeed passing over the advancing blades and subtracts from the air speed that the retreating blades move in. As the blades advance the increased air speed causes the blade to climb or "flap". As it does, it decreases its angle of attack. This action effectively equalizes the lift on each side of the rotor disc and permits the autogyro to fly level in forward flight instead of rolling because of the unbalance of lift accross the rotor disc.

On the autogyros produced by Pitcairn and Kellett, the rotating mast of the rotor was inclined toward the retreating side and also inclined toward the rear, in that way, encouraging the blades to flap. To take care of the differences in lift that might be caused by this offset when the autogyro was descending vertically, a lead weight was bolted in side the tip of the right wing on a gyro which had a CCW rotation.

When the angle of attack of the blade on the oncoming wind is increased it also increases its drag. Lift is increased also, but not at the same rate as the drag. Knowing this, it may be possible to change the angle of attack slightly in 1 degree increments to eliminate the need for the 5 degree offset of the rotor.

To be more correct or precise in my second sentence I sould have said the blade MAY be pulled down by drag insted of pushed down. Although the drag may be slight, it may be causing the situation.

I have heard of the gyroscopic effect which may play a role in the gyros flight characteristics and I must admit, it is thought worthy! I would be very interested in hearing what your freind Dr. Wang has to say about it.

One thing is for sure the main objective is to get the gyro flying! Now that you have, little changes will show what causes what. It's quite a learning experience!

[David A Ramsey]

By golly John, you put a lot of effort into the above post 31. Will need to read that 5 or 6 times before commenting. Please keep in mind I can be very dense till I grasp the "WHY" of a problem.

In the mean time I've got a dialog going with James. His first response was:

"Did you design that autogyro or is it from plan? Very
nice, only 6.5 oz. Actually the advancing side will
encounter more air volicity for the airfoil, and then
the rotor flap 90 degrees later due to precession,
which means the rotor will flap backward, That is why
helicopter and autogyro all tends to pitch up in
forward flight. Not sure why your roll to the left. "

I'll send him some pictures of my rotor head with some additional details to see if I can nail down a reason.

David

[David A Ramsey]

Regarding my questions to James Wang, these are 4 photos I've sent him as reference.

David

[JWarren]

Hi David!

Thanks for posting those photos here! I did notice that you do not need a bottom stop on your blade mount. The rigity of the hinge may be causing your need for the 5 degree offset as the blades may not be able to freely rise and fall as with a pinned hinge. Just something I noticed.

I was thinking earlier today, that you may be wondering where I get my information on autogiros. I have refered to Jim Baxters web site as well a book which I obtained off the internet. I started a thread on the book so others who may be interested can contact the people selling it. I thought I would put a link to the thread here for you as well.

http://www.rcgroups.com/forums/showthread.php?p=3000367

Talk to ya later!

John

[mnowell129]

Have you tried lowering the pitch slightly?
Your right tilt is effectively lowering the pitch of the blade that's out front, it shows clearly in the photo. I believe that if you lower the pitch of all
the blades the need for trim will go away proportionately.
mickey

[David A Ramsey]

John; I've watched the behavior of the rotor dics in a 10mph wind and in front of a 20" box fan. The box fan provides a more turbulant air flow. It's very easy to see the up flap, but I've never noticed down flap. Whether or not down flap could be a problem in flight remains to be seen. The disc has very little coning angle. My blades are also tip weighted.

I too have gone through Jim Baxter's Web site - couple of times and have printed out much of the technical material. I have reread many times looking for answers to my roll phenomenon. Have to check out the Hanna book.

Been going back and forth with emails to James and he is puzzled. Right now he suggests:

"I think you have to bring that gyro to the doctor and
get it diagnoised!"

In the mean time I'll just fly it and hope it's easier to see with an orange nose.

David

[David A Ramsey]

Have you tried lowering the pitch slightly?
Your right tilt is effectively lowering the pitch of the blade that's out front, it shows clearly in the photo. I believe that if you lower the pitch of all
the blades the need for trim will go away proportionately.
mickey

You make an interesting point. I've started making up another set of blades for that purpose. But after going through the left roll syndrome, I'm not looking forward to possible right rolls!

Right now the rotor is so easy to bring into autorotation and generates so much lift, I am reluctant to change anything.

Appreciate your observation.

David

[David A Ramsey]

Have you tried lowering the pitch slightly?
Your right tilt is effectively lowering the pitch of the blade that's out front, it shows clearly in the photo. I believe that if you lower the pitch of all
the blades the need for trim will go away proportionately.
mickey

Just read your idea a few more times and: As I have negative blade pitch, do you mean that I should lower the blade pitch even further. In my photo that shows the right tilt of the rotor, you can also see the negative blade pitch as compared to the rotor hub. I have not measured it, but is in the -2 degree area.

In my first response to your observation, I was thinking of raising the pitch, although I don't need additional lift.

David

[mnowell129]

Just read your idea a few more times and: As I have negative blade pitch, do you mean that I should lower the blade pitch even further. In my photo that shows the right tilt of the rotor, you can also see the negative blade pitch as compared to the rotor hub. I have not measured it, but is in the -2 degree area.

In my first response to your observation, I was thinking of raising the pitch, although I don't need additional lift.

David
Yes, I would try lowering the blade pitch with respect to the hub.
Your -2 degrees is geometric pitch, that is the pitch measured from
leading edge to trailing edge. The true pitch is measured against
an imaginary line drawn level when the blade is making no lift. This line
goes from the trailing edge to some point above the leading edge for this
type of airfoil. I think, but dont have the data in front of me, that this line is 4 degrees above the
geometric pitch line for a "clark-y" type flat bottom airfoil. So
your -2 geometric pitch may in fact be 2 or more degrees positive.
I believe that increasing your rotor speed by putting in some more negative will reduce the need for right tilt.
I think raising the pitch will just slow your rotor down and increase the need
for right trim. Your best gyrocopter performance is when your blade is
operating at its' best lift/drag ratio and this is at a much lower angle of
attack than the high lift, close to stall, angle.
Because you have an aft tilt on the mast ( I assume around 15 degrees) and
you have +2 true angle of attack on the blade, your advancing blade is
seeing +17 degrees of pitch angle. This is probably right at the stall setting
for this airfoil at this size.
If your blade pitch was set at a geometric -6, or true -2, when you add the
mast tilt of 15 the net true pitch the advancing blade will see is +13 degrees which is at a much more efficient L/D setting.
I have ignored the component of rotor rotational velocity for the time being but what that does is lowers the effective angle of attack. I can make a diagram and upload it if you would like to see it.The retreating blade is really not stalled as one would come to believe. Retreating blade stall is a real condition in rotor craft but occurs at speeds where the backward velocity of the inboard retreating blade is close to the same as the aircraft forward velocity and occurs at very high speeds, it is what effectively limits the top speed of a helicopter. Its not a low speed problem because the rotor rpm is usually much higher than the forward speed of the aircraft.
The bottom line is that with the aft tilt angle a geometric pitch setting of several negative degrees could be appropriate, the blade is still at quite a positive pitch with respect to the airflow and is still in fact "autorotating".
My model is 30" span, 13 ounces, flies about 5 mph, hovers in a headwind
and has the trailing edge 4mm higher than the leading edge on a 1.5" blade.

The reason you don't see negative pitch on full sized gyros is that the L/D of airfoils at that scale is different and they don't need as much negative to reach the optimum L/D of the blade. Further the tip speed is much higher than models, this effectively lowering the "real" angle of attack that the blade "sees".

Here's a thought to keep in mind, the lift of a blade is proportional to the
angle of attack, the size of the blade, but proportional to the square of
the tip speed. If you make the blade 10% bigger you get 10% more lift.
If you make the angle of attack 10% better you get 10% more lift. But if
you increase the rotor speed by 10% you get 21% more lift. (1.10 *1.10 =
1.21). So if you decrease the angle of attack effect by 10% you get 90% of the lift, but if this increases your rotor speed by 10% you end up with 9% more lift (0.9 * 1.1 * 1.1 = 1.09). This does seem to make good common sense but it's true. This only goes so far obviously because you reach a point where the blade is making no lift at very high rpm, but there is a point at which total lift is optimized.
I think you will find it lower than where you are now.
Big post, sorry about the size. The mechanics of these rotor systems are fairly well understood in engineering math terms, just hard to communicate in written words.. hope I'm making some sense...

mickey

[David A Ramsey]

/
Big post, sorry about the size. The mechanics of these rotor systems are fairly well understood in engineering math terms, just hard to communicate in written words.. hope I'm making some sense... mickey

Yup you've made sense! Let me say I have a great deal of respect for your conveyed knowledge and I've taken note of your Autogyro Project.

So, if the mathematics of rotor systems is fairly well understood, Why would I roll toward the advancing blade??? It's easy for me to understand a roll into the retreating blade. Must be some sort of magic in my fixed rotor plate hub. Right now my mast and rotor angle looks a lot like the 1932 Cierva C-19.

I understand your blade angle of attack explination as related to a true Clark Y. If you look closely at my airfoil, at best, it might have +1 degree when considering the the rounded leading edge. My Robbe/Schluter Whopper has a fairly true Clark Y airfoil and when measured shows +1-1/2 degrees.

I agree with you about communicating with words. My gyro needs some "hands on" evaluation and I'm hoping to get together with James Wang in January.

You spent a good deal of time on your post! Thank you.

David

[JWarren]

Seems to me there is a clear prossesion of things that need to be done to trim out the rotor. In steps (i.e. 1,2,3).

balance blades
mount blades
fly and trim with transmitter
adjust angles to bring rotor back to zero, etc.....

Mickey,

I just kinda spit that out there. Basically as an example. Trying to think of a way to put the rotor setup in some form of instruction manual (if you will) in steps, so newbies won't be so frustrated and quit. Getting the gyro in the air seems to be the major challenge, all due to the rotor and its complexity. Once flying everything else is a matter of tweeking things out. Do you think this is possible or are there too many variables?

Great post by the way!

John

[mnowell129]

Yup you've made sense! Let me say I have a great deal of respect for your conveyed knowledge and I've taken note of your Autogyro Project.

So, if the mathematics of rotor systems is fairly well understood, Why would I roll toward the advancing blade??? It's easy for me to understand a roll into the retreating blade. Must be some sort of magic in my fixed rotor plate hub. Right now my mast and rotor angle looks a lot like the 1932 Cierva C-19.

I understand your blade angle of attack explination as related to a true Clark Y. If you look closely at my airfoil, at best, it might have +1 degree when considering the the rounded leading edge. My Robbe/Schluter Whopper has a fairly true Clark Y airfoil and when measured shows +1-1/2 degrees.

I agree with you about communicating with words. My gyro needs some "hands on" evaluation and I'm hoping to get together with James Wang in January.

You spent a good deal of time on your post! Thank you.

David
"the book of mickey" is funny... :)
Your whopper is big ( no pun intended). An often overlooked but very important quantity is Reynolds Number. You may or may not know what this is so forgive the redundant explanation. Reynolds number is the ratio of inertial forces to viscous forces in air. In lay speak it is a measure of how
much air behaves like a bunch of particles with individual inertia versus how
much it behaves like a viscous fluid like syrup. I'm not going to bore you with the calculation of reynolds numbers, but give you the simple result. Bigger airplanes fly better, more efficiently, etc. etc. Your whopper can sustain a postive AOA 1) because it has a prespin mechanism and 2) THe blades are
bigger chord, longer and spin faster. It is a infuriating fact that the flight
mechanics of a piper cub are not the same as an indoor rubber airplane and those are not the same as a bumble bee.
The L/D performance of an airfoil is very dependant on reynolds number (Rn), the lower the reynolds number (smaller chord at lower speed = lower reynolds nubmer) the worse the L/D performance.
I did some calculations on my 30 sized helicopter versus my 60 sized helicopter to find out why the 60 autorotated MUCH better than the 30.
It turns out that the reynolds number on the 30 machine was right on
the cusp of hitting really bad reynolds numbers. So in an autorotation when
you pulled in pitch to flare, the blades slowed down, hit a magic Rn and the lift went to (*&(*& and the heli piled in.
Most model gyrocopters are flying in a reynolds number range thats lower than that and need significantly lower pitch to maintain autorotation. The difference between your whopper and something smaller is enourmous, way out or proportion to the actual relative sizes.
Your roll to the advancing blade..
THis is what I believe is happening:
1) Your rotor RPM is low, thus the airflow on the rotor from airspeed is
significant.
2) The rotor blade at the aft position is flying in dirty turbulent air, because
it is in the prop blast and behind the mast.
3) the blade over the nose is flying in clean air.
4) The aft blade gets very little lift, in fact loses lift as it passes to the back of the aircraft. 90 degrees later the gyroscopic precession takes place and this blade (the advancing one) tilts DOWN, i.e. left roll into the advancing blade.
5) The blade in clean air gets a lift increase, 90 degrees later, precesses UP, thus adding to the LEFT roll (into the advancing blade).

My gyrocopter will do exactly the same thing on takeoff if I try to horse it
off with too low a rotor speed, If I wait one more second for the rotor to spool up, it takes right off with neutral trim.

It is what's happening at the front and back of your rotor disk that is causing the roll, not at the sides.
When you reduce the pitch what you do is increase the rotor speed. Because the rotor speed is now faster the airflow due to the forward motion of the aircraft is less a factor and thus the difference between the lift on the back blade and the front blade is less and thus there is less roll 90 degrees later.
What is fairly well accepted in models is that the lift difference in advancing/retreating blades leads to the "flap back" due to precession. This roll trim is the same effect turned 90 degrees (but largely ignored), aggrevated by too low a rotor speed. If your blade tip speed is 20 mph and flight speed is 10 mph then the effect of flight speed on the blade is large. If your tip speed is 40 mph and flight speed is 10 the effect of flight speed is 1/2 the first case. Increasing the rotor speed diminishes the affect caused by the clean/dirty air problem because the flight speed is less of a factor overall.
A final note. use of cyclic pitch, whereby the blade angle changes around the circle, by either a tilting shaft (so called direct control) or by a swashplate has the effect of trimming out these local differences around the rotor without having to reduce the overall pitch. What you are doing by applying rotor tilt is putting in a fixed amount of cyclic pitch as a correction.
You can do it this way, or reduce the overall pitch, your choice. The reduced pitch choice may vibrate less as you are not constantly, in effect, holding in some right aileron control as you are by tilting the shaft.
If you observe carefully your rotor is probably flying level with respect to the body. If you hold the tips of your rotor level and move one blade all the around and watch the pitch of the blade with respect to the body, you will see that it is doing cyclic pitch to obtain the roll trim setting you so desire.
howzat?
mickey

[David A Ramsey]

Your roll to the advancing blade..
THis is what I believe is happening:
1) Your rotor RPM is low, thus the airflow on the rotor from airspeed is
significant.
2) The rotor blade at the aft position is flying in dirty turbulent air, because
it is in the prop blast and behind the mast.
3) the blade over the nose is flying in clean air.
4) The aft blade gets very little lift, in fact loses lift as it passes to the back of the aircraft. 90 degrees later the gyroscopic precession takes place and this blade (the advancing one) tilts DOWN, i.e. left roll into the advancing blade.
5) The blade in clean air gets a lift increase, 90 degrees later, precesses UP, thus adding to the LEFT roll (into the advancing blade).

howzat?
mickey

WOW, zat's good stuff! What a dissertation. I'm indebted and low on cash.

Will need to read your posts many more times for absorption and will take awile, but has a logical ring to it.

I think a duplicate model is in order as I'd like to experiment with reduced mast and blade angles.

Please hold off on Chapter III from the Book of Mickey for awile till I catch up.

David

[David A Ramsey]

Just thinking we outa talk to Mr. Cierva so he can straighten out his C-19

[David A Ramsey]

At some point I'd like build this. Balsa and SoLite.

[mnowell129]

WOW, zat's good stuff! What a dissertation. I'm indebted and low on cash.

Will need to read your posts many more times for absorption and will take awile, but has a logical ring to it.

I think a duplicate model is in order as I'd like to experiment with reduced mast and blade angles.

Please hold off on Chapter III from the Book of Mickey for awile till I catch up.

David
Awaiting your questions my master.

[David A Ramsey]

Awaiting your questions my master.

Oh good Lord! Don't worry, I'll come up with another hair brained question for you.

I emailed your 5 point theory on my roll Phenomenon to James for his thoughts. I just received his reply:

"The correct solution is to articulate each blade, put
a hinge on it and with a droop stop so the blades can
not come down too low to hit the tail."

Even with that in mind Mickey, I think your Book I and II is going to be part of that equation.

Options, options, and more options. Amazed that mine flys! Scary.

John had suggested an instruction manual, but the options are endless due to so many variables. The Mechanics of a rotor systems, as you mentioned, follow established rules, but just the choice of construction materials can affect the outcome. You've provided so much information. I hope those who are interested in Autogyros will take the time to read.

David

[mnowell129]

I]"The correct solution is to articulate each blade, put
a hinge on it and with a droop stop so the blades can
not come down too low to hit the tail."[/I]


This does not provide a solution, freeing the blade to flap does not
make the force that caused it to flap to go away. The out front blade
is still getting a lift boost from some source, still tries to precess 90 degrees later, but now because you've allowed the blade to flap, it actually will flap higher. Mr Wang's analysis may not be completely thought through at this point. The fact remains that there is a force trying to make your blade flap up on the retreating side, and that ultimately has to be dealt with. You either put in cyclic or mitigate the fore/aft lift differences.
I believe that if you take his advice, make your blade free to flap, that if you don't change any other variables such as blade pitch and rotor speed you will still need right tilt to be trimmed.
The solutions being presented to you all lead to the DC, control delta three hinged, articulated rotor designs currently available. I'm suggesting an alternative solution.
Definition : Insanity : Repeating the same experiment over and over and expecting something different to happen each time.
If you want the same results other people get, do what they did, if you want different results do something else....
The point is that there are a lot of people on these forums that have done all the trial and error work on the head designs and they have them working to their satisfaction. Reproducing one of these designs makes sense. I'm suggesting that there may be another way to skin a cat.
mickey

[David A Ramsey]

The fact remains that there is a force trying to make your blade flap up on the retreating side, and that ultimately has to be dealt with. You either put in cyclic or mitigate the fore/aft lift differences.
I believe that if you take his advice, make your blade free to flap, that if you don't change any other variables such as blade pitch and rotor speed you will still need right tilt to be trimmed. I go along with this.

Definition : Insanity : Repeating the same experiment over and over and expecting something different to happen each time. Sounds like Government work.

I'm suggesting that there may be another way to skin a cat.
mickey. And I'm beginning to grasp them.


Mickey, It isn't my intention to get between a he said, you said. Both of you have offered ideas that are pretty much in parallel. I feel very lucky to have two dependable minds to draw from.

For this Autogyro, my intention was to design a simple working model at minimal cost - If you don't consider hanging $190.00 off a bit of foam and basswood. The design failed due to rolling on launch. Ok, how do I fix it. At this point I was looking for a simple fix, if there was one, without going through an elaborate thought process. Well there was and it worked very well. And now I have a simple, successful Autogyro. With that out of the way, I was interested in why. A reading from the Book of Mickey and the Book of James has brought me into the light. Well almost there.

In any case, seeking to understand the forces acting on this particular rotor system is a great help in accepting what was required to make it work.

With my "little" Whopper, size, weight and Reynolds numbers aside, there was ONE important criteria; Head spead at lift off!!! And a 20 mph head wind was your friend. Without head speed, the roll to the retreating blade was easy to understand. (The Whopper was the first model I've ever flown that clearly showed the flight degrading performance as a result of 100F degree temperature and 100% humidity in a no wind condition.) However when my little electric Autogyro rolled to the Advancing blade, with head speed, well that was curious.

Ya know Mickey, I've got the parts list for your Autogyro, however I'm thinking 3 bladed, flybarless.

David

[mnowell129]

I have parts on the way for 4 bladed, flybarless, with collective.
I think the three bladed flybarless will work if you weight the blades
correctly. They need to be CG adjusted and heavier than normal.
There are many flybarless r/c heli's flying, the solution always involves
tip weight to get the rotor response down low enough to by flyable by a human.

BTW I have been flying my gyro under the streetlight at night. When
I can figure out how to video this I'll tape it.

Thanks for the prompting, I enjoy the interchange.
mickey

[mnowell129]

BTW, I'm "this" close to doing short kits for G3PO....
Just need to see if I can break even at it.

[David A Ramsey]

I think the three bladed flybarless will work if you weight the blades correctly. They need to be CG adjusted and heavier than normal.
mickey

I got a pretty good handle on blade balancing. I made a mini Schulter Blade Balance to handle the small stuff, but in the end I find I still have to balance the rotor as a whole. In the next set of small blades I was thinking of running a 1/16" dia. solder along and forming the leading edge. Oughta move the CG ahead. The Whopper used 1/8" music wire. I did most of my wood helicopter blades that way also. They weren't the best for acrobatics, but neither am I.

Was at Balsa Products this afternoon and checked out the Dragonfly parts to see what I might scrounge for a three bladed head. Unless there's a small three bladed helicopter available, and I haven't checked, I would need to make some parts. For awile I'll leave it on the "one day" list.

I'm enjoying the interchange also!

David

[David A Ramsey]

BTW, I'm "this" close to doing short kits for G3PO....
Just need to see if I can break even at it.

Yes, yes, yes, a short kit! Pretty sure the IRS will leave you alone on that one. Think it's a good idea.

Was thinking of a construction article for mine.

[mnowell129]

Impressive blade balancer, I don't have the patience.
I just weigh them on a .1 gram scale, then add scotch tape
if there is any shake left. I'm a KISS principle builder.
I put solder in for weights on my latest round of gyros, 3" of
.062 1/8" back from the LE on 1.5" aerobalsa blades. Seemed to do the trick.
Check out centuryheli.com and look at the hummingbird elite collective pitch
parts. They have some nifty ball bearing blade holders and a neat little 120 degree swashplate. A three sided delrin head block and you're in business, no muss no fuss. Or a double plate fiberglass star with threaded blocks between the arms with a center block. I think I could make that in an hour or so. Even easier cross drill and thread some of those steel threaded computer standoffs for the blade holder bolts. Then just screw the mess together with screws.
Hmmm... in can see only having to make the FG plates and using off the
shelf parts for the rest.
Best part about these chinese helicopters is that now you can get all the heli bits for little $.

Kit income will get reported, I'm self employed and don't want the IRS in my house, so I pay em what I owe em with no games.
mickey

[David A Ramsey]

Mickey - post 52.

By gosh, now I owe you for research! Didn't realise the Book of Mickey had a Hardware Index. Goooood ideas!

For the 1/16" dia. solder weights, I like the rosin core solder. If I have the tip weights extended to the blade tips I can use the core as a center finder, for removing bits of weight with a 1/16" drill to fine tune the balance.

I'm selfemployed also. I use, strategically placed, IRS sensitive land mines.

David

[JWarren]

David,

Thats a nice little counter scale you have there. Is the counter weights on an threaded rod or just plain ol music wire?

John

[David A Ramsey]

Thanks John;
I used a piece of 6-32 threaded rod, with old fashioned Thumb Nuts as counter weights. The dark gray parts are rigid PVC. The pivot is ball Bearing supported.

David

[JWarren]

I put a bolt through the mount hole on two blades and used two glasses to balance them on. Brought the blades to the same weight as the heaviest one of the set. Worked out pretty good. I then balanced the hub with everything but the blades, with my prop balancer. Once the blades and hub where balanced I put the entire rotor on my prop balancer and found the complete rotor to be perfect. One thing I did note when balancing the complete rotor. If the blades are not perfectly streight, it will seem to be out of balance.

John

[David A Ramsey]

Hey John;

I made a major error in my second set of blades as I didn't weigh the blanks first. Amazing what the weight difference can be in one strip of hard balsa, 3' long, cut into three equal pieces. The main reason I use a pivoting blade axle bolt is the blade finds it's flight position easily during rotation. Run the rotor up, snug up the bolts and balance the rotor. Doing this a couple of times makes for a smooth turning rotor. Another reason for single blade axles is survival.

Your comment about having the blades (2, 3, or 4) in their proper position on the hub is true for my counter balance.

Perhaps a Blade/Rotor Balancing Thread might help this Trial Forum.

David

[mnowell129]

Mickey - post 52.

By gosh, now I owe you for research! Didn't realise the Book of Mickey had a Hardware Index. Goooood ideas!

For the 1/16" dia. solder weights, I like the rosin core solder. If I have the tip weights extended to the blade tips I can use the core as a center finder, for removing bits of weight with a 1/16" drill to fine tune the balance.

I'm selfemployed also. I use, strategically placed, IRS sensitive land mines.

David
Flattery gets you everywhere, but seriously, the BoM has many chapters born of frustration trying to acccomplish some outlandish scheme. One day I'll write about my design evolution of foam airplanes with real airfoiled wings. It's something else I will probably kit...
Good idea on the solder. I never go to the tips since in the gas days we could sling the weights out, which ain't pretty.
What kind of work ? Email if you prefer.. mnowell129@earthlink.net
I'm an embedded software engineer ( this got started doing microprocessor controlled supersonic wind tunnel controls, Ask me about laser doppler velecity measurement sometime when you need to get some sleep ).

[David A Ramsey]

OK Mickey, now we get into the biography section of this thread. For the last 32 years I've been building industrial models. One man shop. These models include Trade Show support models, new product prototypes, medical models and body parts. The computer age has taken a toll on my business, but if I had another 30 years ahead of me, I'd love to learn the technology and buy the tools. Love tools! I have a Web Page at www.ramseymodeldesign.com

Have enyoyed building model airplanes for 48, Ugh, years or so. Flew helicopters, all Schluter, for 10 years, not much lately. Last couple of years I've been playing with GWS EDF 50s. Did a Learjet for Flying Models and presently I'm trying to finish a Boeing 727 for publication.

Good to know you're around when I need to understand the "why" of things.

David

[mnowell129]

NOW I understand the beautiful blade balancer. I'd probably wet my pants to see the tools you have available.
You are welcome to all the "why" I have. This hobby is complicated and often misunderstood from a theoretical perspective. I benefit from an undergraduate degree in aerospace engineering, so the full scope of the aeronautical research ( now mostly on the web, how convenient) is at my fingertips. The challenge is how to translate what looks clear in math terms to a seat of the pants description for non aerodynamically trained folk. I've kinda adopted this as a mission, hopefully to keep aerodynamics a science and not a religion.....
The math makes many things clear to me, here's two:
1) The airfoil of tiny gyrocopters is not a big deal, surface finish is
much more important than airfoil selection.
2) The smaller the gyro the more negative pitch is needed to operate
at the maximum L/D, and thus optimum performance.

maybe this will kick us out of bio's back into giro's....
mickey

[mnowell129]

Small world, I bought the FM issue to get Your lear jet issue.
Beautiful model, no time. Your design is wonderful.
I was going to try to reproduce in minimum time with
bent 2mm depron... eventually...

[David A Ramsey]

The challenge is how to translate what looks clear in math terms to a seat of the pants description for non aerodynamically trained folk. I've kinda adopted this as a mission, hopefully to keep aerodynamics a science and not a religion.....

GOOD MISSION! I like "SEAT OF THE PANTS".

The math makes many things clear to me, here's two:
1) The airfoil of tiny gyrocopters is not a big deal, surface finish is
much more important than airfoil selection.
2) The smaller the gyro the more negative pitch is needed to operate
at the maximum L/D, and thus optimum performance.


RE: Point 1 - Blade finishes for the anal! For small blades, Solite is a great covering material, especially for weight considerations. The surface of Solite, however, has a tacky feel (surface tension), but wiping with a rag, sprayed with silicone, makes for a slick surface.

Another method is to finish the blade with thin CA. Remove all dust. Spread on a thin coat, let dry. Sand lightly with 320 grit paper, Apply second coat, sand lightly. Use a single edge razor blade to scrape any ridges. Buff blade to mirror finish and wipe with silicone. Butchers wax is also good. Note: When spreading CA, you may want to wrap your finger with thin Polyethylene, as in zip lock bags, but not suran wrap as it's too thin and can stick.

RE: Point 2 - Negitive Pitch. This is interesting as most information leans toward zero to positive pitch for blades. Even for my Gyro it had been suggested that I remove the negative pitch I felt was necessary. The performance of the rotor with negative pitch as compared to zero pitch, could'nt be ignored.

[David A Ramsey]

Mickey, post 63:

Thank you.

[mnowell129]

RE: Point 2 - Negitive Pitch. This is interesting as most information leans toward zero to positive pitch for blades. Even for my Gyro it had been suggested that I remove the negative pitch I felt was necessary. The performance of the rotor with negative pitch as compared to zero pitch, could'nt be ignored.

Was the performance BETTER with negative pitch or WORSE with
negative pitch?
The encouragement for positive pitch is rooted in the fact that full
sized autogyros have positive pitch. The ongoing issue is that models
operate at vastly smaller reynolds numbers, hence the L/D of the airfoils
is many times worse than full sized. As the L/D worsens the pitch must
be reduced to maintain autorotation.
Full sized helicopters routinely autorotate with only positive pitch. Model sized helicopters routinely need negative pitch. This is due in large part
to the drastically different reynolds numbers involved.
Based on my model experience I went straight to -10 degrees pitch on mine and flew it right off. I then added pitch and reduced power to get to the minimum power required. Still at about -4 degrees (geometric) on a 32 inch rotor.


Thanks for the tips. What kind of silicone?

[David A Ramsey]

Negative pitch: Initially at zero, blades flat. rotor acted dead in the wind and prespinning the rotor was no help. Added negative pitch using 0.010, 1/16" wide strip of styrene at rear of blade holder and away the rotor went. This was true for my, higher aspect, first blades. Although I don't work with actual Reynolds numbers, I can see the principle.

I'm developing some questions about your Autogyro - Mast rake and blade pitch - which I will put to you soon. Read your thread a couple of times. Liked the flybar bit.

Silicone in spray cans was available at Home Depot. I use Sprayon by Sherwin Williams, No. 206 all purpose silicone lube. As there's only 5% silicone, with the remainder propellent, it's cleaner to spray the stuff in a rag to avoid overspray.

[AustinTatious]

Was the performance BETTER with negative pitch or WORSE with
negative pitch?
The encouragement for positive pitch is rooted in the fact that full
sized autogyros have positive pitch. The ongoing issue is that models
operate at vastly smaller reynolds numbers, hence the L/D of the airfoils
is many times worse than full sized. As the L/D worsens the pitch must
be reduced to maintain autorotation.
Full sized helicopters routinely autorotate with only positive pitch. Model sized helicopters routinely need negative pitch. This is due in large part
to the drastically different reynolds numbers involved.
Based on my model experience I went straight to -10 degrees pitch on mine and flew it right off. I then added pitch and reduced power to get to the minimum power required. Still at about -4 degrees (geometric) on a 32 inch rotor.


Thanks for the tips. What kind of silicone?

being that not all models are created equal, I find it hard to simply say that you need more negative pitch the smaller you get. My small gyro woks great at 0 pitch. its a little harder to get spooled up , but a good flick and a walking pace works nicely.

-4 degrees is an aweful lot for a gyro that size. I think we all know that there are a million variables on these gyros and having negative pitch Could likely be covering up other "issues" that if corrected would allow for flatter pitch.

I think a good experiment would be to make a gryo with full collective adjustability and then you could adjsut the pitch in flight and find where you get the best performance. I suspect the setting would be different for different modes of flight: high alfa slow, high speed, fast climb and so on.

[mnowell129]

being that not all models are created equal, I find it hard to simply say that you need more negative pitch the smaller you get. My small gyro woks great at 0 pitch. its a little harder to get spooled up , but a good flick and a walking pace works nicely.

-4 degrees is an aweful lot for a gyro that size. I think we all know that there are a million variables on these gyros and having negative pitch Could likely be covering up other "issues" that if corrected would allow for flatter pitch.

I think a good experiment would be to make a gryo with full collective adjustability and then you could adjsut the pitch in flight and find where you get the best performance. I suspect the setting would be different for different modes of flight: high alfa slow, high speed, fast climb and so on.
I need to clarify the statement. Assuming all other things equal if were to magically take a working gyrocopter and scale it down, you would have to reduce the blade pitch to make it autorotate the same, and further due to the lower reynolds number you would get poorer relative performance.
I know that I am at the right pitch because at slightly higher pitch it will not self start. Also recall that my blades are at -4 GEOMETRIC pitch. The true angle with this airfoil is 0, because the zero lift angle for these blades is -4.
I have performed the angle adjustment you indicate. I made the blade holders from thin straps of steel specifically to accomplish this goal.
At very negative pitch you get quick spin up, and faster minimum airspeeds and better aerobatic performance. You need more power.
At less and less negative pitch you get slower spin up, slower minimum speeds and the aerobatic performance starts to produce rotor stoppages. Less power is required to fly level.
I am working on a full collective version that will vary in flight.

Here is another "mind picture" about L/D. An airfoil makes a force in reaction to the air its moving in. The force is tilted back slightly from 90 degrees from the airflow direction. We mentally resolve this into two parts, lift and drag. Lift being 90 degrees to airflow, drag being parallel. Think of it differently however, think of it as a single force, leaned back slightly from 90. THe amount it leans back is the angle L/D. With a very high L/D the tilt back from 90 is tiny, so a small amount of forward tilt is enough to make the airfoil move forward, whether glider wing, or rotor blade. Once the force vector crosses vertical with respect to the shaft axis the blade will turn. It will accelerate until the drag reaches the component of force of the blade in the forward direction. THen you have reached steady state rpm. In full sized autogyros the L/D is high and the angles such that the rotor force vector can be tilted forward, with respect to the rotor shaft, while the airfoil is rigged at postive angle with respect to the rotor shaft.
If the L/D is poor, the forward tilt (more negative) has to be more to finally get the force vector leaning enough to make the blade move forward.
The same airfoil scaled down experiences a loss in L/D just due to scaling. This scaling (reynolds number) is significant and largely ignored. At an L/D of 50:1 the back tilt angle from 90 degrees is 1 degree. At 20:1 the back tilt angle is 6 degrees. This is the difference between flying at reynolds number of 150000 down to 60000. The exact same gyrocopter at 48" rotor span with 0 pitch will take 5 degrees in the negative direction to autorotate when scaled down to 20" span, all other things being equal (speed, loading etc).
Look at the reynolds number table at
http://www.rcuniverse.com/forum/Reply_to_Suzonka/m_2427933/tm.htm
For an idea about what size rotors and rpms generate what reynolds numbers.
Note that at any reynolds number < 100000 things start to go badly very quickly with L/D.

None of this has anything to do with one model versus another. It is simply the way airfoils scale down.

Reynolds number scaling is fundamentally important to model gyrocopters. All other things being equal, when you scale down you must use less pitch to achieve autorotation.
The flying fields are littered with exact scale bensens that won't fly, probably due in part to not considering the full impact of scaling effects.

The reason reynolds number doesn't bite the fixed wing crowd is that a GWS pico stick flying 20 mph is still at a reynolds number of 100000. So is your
gentle lady sailplane and an 0.049 sized airplane.
THe indoor/micro model guys have reynolds number as an issue, thus you see different construction/airfoils and lower wing loadings than would be expected from just shrinking in size alone. Small reynolds numbers are the issue.

(ooops, another chapter in BOM...sorry david)
BTW, got an improved answer on the roll to the advancing blade. Will put that up later (back to work).

[David A Ramsey]

(ooops, another chapter in BOM...sorry david)
BTW, got an improved answer on the roll to the advancing blade. Will put that up later (back to work).

That's OK, I was waiting for it! Look forward to more enlightenment.

[David A Ramsey]

Finally had some nice weather to fly this gyro again and, son of a gun, does it do nice loops! An autogyro doesn't have to be complicated to fly well.

David

[mnowell129]

Finally had some nice weather to fly this gyro again and, son of a gun, does it do nice loops! An autogyro doesn't have to be complicated to fly well.

David
Congratulations. It's neat when it finally flies.

What's the final configuration?

As an aside, was what I wrote of any help with this model?
If so, what was it and can we generalize the advice?
mick

[David A Ramsey]

Congratulations. It's neat when it finally flies.

What's the final configuration?

As an aside, was what I wrote of any help with this model?
If so, what was it and can we generalize the advice?
mick

The configuration is the same as when I started the thread. Once I bent the rotor axel (approx. 3-5 degrees) to the right to compensate for the left roll to achieve a level flight attitude, I haven't done any additional trim changes. Your input came after I had made this adjustment. But, every bit of information you supplied made it possible for me to understand the "WHY" of this seemingly little change.

Due to our wonderful weather, I haven't flown the gyro for almost two months.
Yesterday evening I flew for about 15 minutes. Much of the time was watching roll differences through different rotorspeeds, plus finding out how tight, turns could be made....pretty tight. Also played around with power off, high angle of attack, blade slowing situations and recovery. While flying at a fairly good altitude I added full power and did a loop. Worked so well, did another.

I would generalize by saying; For a fixed head, non controllable, rotor, you can expect to make some angle change of the rotor axel, in relation to the mast, to achieve a level flight attitude at a certain rotorspeed that maintains level flight. Once this is found, the rudder, if addiquate, will provide sufficient yaw corrections for changes in rotorspeed during a flight.

How's that sound?

[mnowell129]

Sounds good. It is nice to have some data points.

[GWS4CEO]

At some point I'd like build this. Balsa and SoLite.How about that we use a GWS Funny Park to convert to an autogyro? :p

[GWS4CEO]

I got a pretty good handle on blade balancing. I made a mini Schulter Blade Balance to handle the small stuff, but in the end I find I still have to balance the rotor as a whole. In the next set of small blades I was thinking of running a 1/16" dia. solder along and forming the leading edge. Oughta move the CG ahead. The Whopper used 1/8" music wire. I did most of my wood helicopter blades that way also. They weren't the best for acrobatics, but neither am I.

Was at Balsa Products this afternoon and checked out the Dragonfly parts to see what I might scrounge for a three bladed head. Unless there's a small three bladed helicopter available, and I haven't checked, I would need to make some parts. For awile I'll leave it on the "one day" list.

I'm enjoying the interchange also!

DavidGreat ideal!

[David A Ramsey]

How about that we use a GWS Funny Park to convert to an autogyro? :p

Dear Mr. Lin. Do you ever sleep???

I could see GWS making 2 Autogyros.

1. A simple fixed head autogyro using either the IPS, or 400 size Slow Sticks.

2. A complex Autogyro using the Dragonfly head parts that has been so well done by Mickey Nowell. I think the Funny Park Fuselage would make a very appealing Autogyro base.

Will you be attending the WRAM SHOW this coming weekend, Feb. 25, 26 & 27 ? I plan to be there Friday the 25th.

Best regards, David

[mnowell129]

How about that we use a GWS Funny Park to convert to an autogyro? :p

I have successfully used GWS Dragonfly helicopter parts to make a very nice gyro. You can see it fly at www.mickeynowell.com/id9.html.
Contact me if you want details and/or want to apply this design to one of your fuselages. The PT17 would be appropriate with a slightly longer set of blades.
mickey

[cnc_dude1]

I have managed to put together a scratch built fixed gyro and was wondering how fast the rotor should spin when just doing a static test using only the motor for the power source(no head wind)?

And buy the way,
Mickey,
I'd love to get more details on your model using the dragonfly parts!

Thanks in advance!
Jeff

[mnowell129]

I have managed to put together a scratch built fixed gyro and was wondering how fast the rotor should spin when just doing a static test using only the motor for the power source(no head wind)?

And buy the way,
Mickey,
I'd love to get more details on your model using the dragonfly parts!

Thanks in advance!
Jeff
Couple hundred rpm.

There's a complete build thread on G3PO at :
http://www.rcuniverse.com/forum/How_to_build_G3PO/m_2380064/tm.htm

[soarrich]

David

I was wondering, if you built a CCW rotating rotor and you still need right tilt, would that eliminate the advancing retreating blade for the problem. If you needed left tilt it would confirm it?

I'm going to put a tach on my PT's rotor to get the rpm to see how big the difference is between the advancing blade's airspeed and the retreating blade's airspeed. In hover it should be very small, yet your gyro stays trimmed in roll at forward speeds and hover, odd.

[David A Ramsey]

Rich; I'm pretty sure, well yes I'm sure, If I was turning CCW, the resulting forces would require a mast tilt to the left.

Does my gyro stay trimmed??? NO! With the mast tilt I have, my Gyro is only in trim if the rotor and forward speed stay close to the same. This trim will change at more or less forward speed and rotor speed. If I speed up, I need more right rudder for straight flight. As for hovering, I can't unless I've got a bit of a head wind, or I loose R/E control. Can't do a full stop touch down LDG either for the same reason. Plus without some head wind, with power down, the head speed changes which needs to be trimmed for, but I can't. Gotta keep this gyro moving forward.

I feel the power I have available is the key to this gyro's manoeuvring ability. It keeps the R/E alive through air, ground and rotor speed changes.

David

[soarrich]

FWIW
I checked my rotor's RPMs today, when it started getting light it was at about 500 rpm, at 550 it had enough lift to fly. I would say that while its flying it's turning around 600 rpms, high Gs raise the rpms to maybe 800 rpm max.

The rpms work out to about 55 mph tip speed on a PT Gyro.

[David A Ramsey]

Rich;

Not sure how I'd approach actual RPMs on my little gyro. I know on a hand launch and a slow run I can get way more head speed than I need. It can really whistle. If it sounds to fast I let it go with less motor power. With a gyro this small it's difficult to feel much lift, so I generally launch when the rotor speed sounds right.

[David A Ramsey]

Rich;

Not sure about the actual RPMs on my little gyro. I know on a hand launch and a slow run I can get way more head speed than I need. It can really whistle. If it sounds to fast I let it go with less motor power. With a gyro this small it's difficult to feel much lift, so I generally launch when the rotor speed sounds right.