Nose down tendency at speed!

Vance

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Thank you my friend!

Thank you my friend!

Thank you Stan,

I am glad to have you along on the adventure.

That is just the point; Mariah Gale is not that far outside the edges and is not going anywhere that no one has gone before.

Your SparrowHawk was one heavy gyroplane. I will remember that next time someone tells me that the Predator is too heavy.

Part of why my adventures succeed is all the friends I have helping along the way.

I never know just where the help will come from or what form it will take.

I do know that whenever I am outside my capabilities, even if I don’t recognize it, my remarkable friends will help out.

Some of my new fixed wing friends have been remarkably supportive and helpful so I don’t have to reinvent things that were figured out long ago.

Thank you, Vance
 

Vance

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There is a question at the bottom Doug.

There is a question at the bottom Doug.

Thank you Doug,

Learning is iterative for me and I know I have been here before.

You, Chuck, Udi, Jim and many others have helped so much with your technical expertise.

The interaction of the forces still seems magical to me.

The multifaceted success of the “new heart” has caused me to imagine I know enough to move forward with Mariah Gale.

I am grateful to have you watching my back.

The lack of funding helps to hold me back from using a TSIO-550 and exploring the edges of my gyroplane knowledge and piloting skills.

I sat in my friend’s Acrosport for a long time and I didn’t like the feeling of being surrounded by aircraft. Then we mocked up a proper canopy and I found that even less desirable.

I went flying and felt like I had escaped captivity. I love the feeling of the wind in my face in the Predator and I don’t want to lose that with Mariah Gale. I love to feel the gusts of wind from the side and smell the strawberries and mustard. I love to feel the sea air against my skin. I have fooled with Bonneville stuff enough to know that an open cockpit is not a stable low drag design.

If speed was the point than she would be a tractor, have a full canopy and a Continental TSIO-550 for a heart.

I am not in a hurry to get anywhere. I am just trying to mitigate the weakness in my personality combined with the anticipated capabilities of Mariah Gale.

How do you feel about bolting on an empennage from a fixed wing and using the elevators for pitch trim?

Thank you, Vance
 
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C. Beaty

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The weather bureau would be technically correct to say that the component of wind out of the east is 10 mph as is the component of wind out of the north. That would confuse more people than to simply say that there is a 14-mph wind out of the northeast.

Resolving rotor thrust into vertical and horizontal components amounts to the same thing.

That’s the rationale of our unenlightened friends when they say: “All gyros will tumble out of the sky when that big drag chute holding the top of the mast back goes away as a result the stick being shoved forward.”
 

Vance

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I am not sure just what you are saying.

I am not sure just what you are saying.

Hello Heron,

I am satisfied with my Sport Copter blades.

I suspect they will go as fast as I want to go.

I do not have the desire or technical expertise to pursue unloading the blades in high speed flight.

At what most consider cruise power, 85% the predator is doing 80kts, 92 miles per hour. In my fantasy that will result in 100kts, 115 miles per hour in Mariah Gale. I find the chaos disquieting in an open aircraft.

I will probably be much happier at 50% power, cruising at 60kts, 69 miles per hour.

Reducing the drag is part of my personality.

This may lead to increased capability in Mariah Gale and combined with my tendency to push could get me into trouble.

Thank you, Vance
 
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Vance

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Thank you Chuck,

Thank you Chuck,

That’s the rationale of our unenlightened friends when they say: “All gyros will tumble out of the sky when that big drag chute holding the top of the mast back goes away as a result the stick being shoved forward.”

I am still unenlightened but I have come to believe speed and disk angle are not the demons that many feel they are.

I love the self regulating rotor rpm and lift of a gyroplane.

I am still struggling with your enforced fuselage pitch.

I would think a small application of elevators as trim would pitch the fuselage regardless of what the rotor is doing.

I would be grateful for your efforts to enlighten me on this relationship of rotor angle to fuselage angle.

Thank you, Vance
 
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C. Beaty

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Think of a gyro as a wrecking ball on the end of a weightless stick; the mast.

Whatever the condition of flight, the rotor thrust line passes through the center of the wrecking ball so long as the line of fuselage drag and line of propeller thrust also pass through the CG.

The angle of attack of the rotor and its line of thrust is set by airspeed; for any given airspeed, the rotor thrust line is fixed in space. It is unaffected by fuselage dangle angle.

Things that produce a moment of torque about the CG swing the wrecking ball and its attached stick relative to the rotor thrust line. Without a horizontal stabilizer, an airspeed increase tilts the airframe nose down. With a horizontal stabilizer, the tilting tendency is opposed because a download is generated that opposes the nose down tilt.

Offsets swing the CG relative to the rotor thrust line for good or ill.

CG aft of the rotor thrust line is an example of ill; no different than is the case for any tail-heavy aircraft.
 

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Heron

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Vance
I heard somewhere that our rotors can go 150 mph as they are. I will be happy with 100/120 mph cruise, very atainable nowadays.
SportCopeter blades are the finest for all accounts given.
Some guys are trying to go over 200 mph cruise and that will involve wings.
I have a feeling you will be happy soon enough.
I remember back in 2000 talking about this and gettin people all aroused and telling me I was crazy. Time told differently . . .
thanks
Heron
 

Vance

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Thank you Chuck.

Thank you Chuck.

I feel confused on a higher level now.

I tried to explain it to my hangar mate today and it is clear I still don’t understand it.

I understand the concept of tail heavy.

I don’t know how far the rotor thrust vector can be ahead of the center of gravity before it is bad.

I don’t know exactly what bad is.

I don’t know how to mitigate the bad from the rotor thrust vector being ahead of the center of gravity other than not allowing that.

I would be grateful for any light shed on the darkness.

I will build a model.

Thank you, Vance
 

Vance

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I am already happy.

I am already happy.

Hello Heron,

I will be happy with a 90kt cruise.

I will be happy with a 300 nautical mile range.

I will be happy if it is hard to make a big mistake.

I am hoping for less stick shake.

I am hoping for better ability to trim for airspeed.

I want to able to manage a vertical descent.

I want to be able to land and takeoff at places other than an airport.

I would like a better GPS and a radio that can listen to two stations at once.

I am sure it will be fun to try to accomplish these things.

Thank you, Vance
 

C. Beaty

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You are certainly demanding…

Tail heavy is bad because it results in angle of attack instability, something that applies to most all vehicles. With rotor thrust line ahead of CG, hit an upgoing bump and the nose is jerked upward, increasing magnitude of upward bump. Same as with tail heavy cars, go into a turn, the tail end swings outward, tightening the turn until it goes through the fence tail first. AKA oversteer.

Moderate nose heavy is good because it provides angle of attack stability, generating pitch force that keeps rotor headed into the relative wind. Too much nose heavy is bad because it increases pitch stiffness and can lead to high frequency pitch oscillation. It’s like a spring keeping the machine on course; when the spring is too stiff, a high frequency bobble can result.
 

RotoPlane

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Thanks for post #28 Vance.....I literally laughed till I cried! You sure have a way with words. Now I can hit the sack happy....
 

Vance

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I am sorry if I seem demanding.

I am sorry if I seem demanding.

Thank you Chuck,

I apologize if I seem demanding; I am trying to ask these questions in a casual way.

I am struggling mightily to grasp what to you are simple concepts as far as how things relate to each other.

Would you please quantify how much tail heavy it takes to be bad as far as the cg being behind the rotor thrust vector?

Would you please quantify moderately nose heavy, enough to be good as far as the cg being ahead of the rotor thrust vector?

This brings me back to a horizontal with adjustable trim.

How much down load for a horizontal stabilizer is good?

Does it vary with airspeed?

Thank you, Vance
 

Vance

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I was not trying to be funny.

I was not trying to be funny.

Hello Ed,

I am glad you liked post #28.

Learning is ab iterative process for me so as I learn I become confused on a higher level.

I seldom imagine I understand something.

I have found if I understand something I can explain it.

A changing angle of attack is something fixed wing people understand.

A rotor thrust vector is not.

On his Acrosport the entire horizontal is tilted for trim and the elevators are used to change the angle of attack of the wing.

The discussion became helplessly muddled with an inability to agree on which direction was which. This indicated to me I was confused on a low level.

I left John with the feeling that gyroplane people don’t understand the particulars of a wandering rotor thrust vector. I was a poor representative of the gyroplane community because most of the gyroplane people I talk too claim to understand this well. I would like to be confused on a level that would allow me to imagine I understand it.

Thank you, Vance
 
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C. Beaty

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How unstable is too unstable?
How stable is too stable?

How fast is too fast?
How slow is too slow?

How high is too high?
How low is too low?

How hot is too hot?
How cold is too cold?

You should address those questions to your spiritualist. With the appropriate degree of harmony, a séance might provide you with the answers you seek.
 

Friendly

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Alan_Cheatham

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How unstable is too unstable?
How stable is too stable?

How fast is too fast?
How slow is too slow?

How high is too high?
How low is too low?

How hot is too hot?
How cold is too cold?

You should address those questions to your spiritualist. With the appropriate degree of harmony, a séance might provide you with the answers you seek.


What we need here is some rigidly defined areas of doubt and uncertainty.

.
 

Doug Riley

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"How much HS download" is the start of a good question... but it's actually two questions, with two different answers.

Some people use "download" as shorthand for "negative incidence." In casual talk, that's OK. However, since loads are FORCES (measured in pounds, kilos, newtons, etc.) while incidence is an ANGLE (measured in degrees or radians), you can't answer the "how much" question without knowing if you are talking degrees or forces.

This, in turn, gets us into numbers. The numbers will be different for different airframes and rotors.

Say your rotor is five feet above CG. Say the gyro's CG is located on the mast and that prop thrust and fuselage drag are both right through the CG.

Say the rotor makes enough thrust just to hold the gyro up (one G) when the rotor flies at ten degrees AOA (after counting blowback) and 50 mph. Say the airframe is mounted to the mast at an angle that puts the frame perfectly level when the mast is angled back ten degrees to the horizon.

If the HS is mounted so that its AOA is zero when the frame is level, then the HS will generate neither a down-load nor an up-load force at 50 mph -- and that's fine, since the frame is level at that speed anyway.

Now say we speed up until the rotor can make one G at only 5 deg. Recall Chuck's cannonball-on-a-stick. The stick/mast (with the CG at its bottom) will try to adopt an angle of 5 deg. aft instead of ten. If there were no HS, it would succeed in adopting that 5-deg. angle.

At that angle, the frame will ride 5 deg nose-low. What if we don't like that? What if we want the frame level, like it was at 50 mph?

Well, the rotor needs to fly at 5 deg. Any more and the gyro will climb. Therefore, we want the frame now to fly level WITH THE ROTOR THRUSTLINE BEHIND THE CG. Specifically, the mast will ideally be at ten degrees while the rotor thrustline is at five. The rotor thrust will be pulling up on the tail.

Recall that the distance from the rotor down to the CG is five feet. A five-degree "delta" between rotor thrustline angle and mast angle means that, at the CG, the thrustline is about 5" aft of the CG. If the gyro weighs 1000 lb., the tail-up moment as long as the frame flies level is 5000 in.-lb. or 417 ft.-lb.

Therefore, to have the frame fly perfectly level at that higher speed, the HS must create a tail-down moment of 417 ft.-lb. For a 6-foot tail arm, that would mean a download force of 70 lb.

Here's what Vance may be getting at: IF you insist on ZERO change in frame angle with increased speed, a fixed HS can't do it. Our fixed HS will create ZERO download as long as the frame is level. The frame will have to ride a LITTLE nose-lower at high speed in order for the HS to "bite" and limit the nose drop with increased speed.

For example, if the HS is eight sq. ft. on a six-foot arm and our new higher speed is 100 mph, the HS will make roughly 2 lb./sq.ft. of download at -1.5 deg. AOA. 2 x 8 = 16. 16 x 6 = 96 ft.-lb. Meanwhile, the rotor thrust's aft displacement at 1.5 deg nose-down on the frame is .087 foot. At 1000 lbs. rotor thrust, that's 87 ft.-lb.

So, with that particular set of numbers, the gyro will ride a little less than 1.5 deg. MORE nose-down at 100 mph than at 50.

And, yes, you could get rid of that 1.5 with adjustable HS incidence.

If pod drag isn't centered on CG and/or increases exponentially with negative AOA, then you need a powerful HS. A flight-adjustable one would, again, limit the changes in deck angle, but the more important thing is that the pod not be able to over-power the HS, adjustable or not.

Trig buffs will note that I've simplified things here by treating rotor thrust as lift (thrust is actually slightly higher) and arc distances as chord distances. With the small angles we are dealing with, these approximations are pretty accurate, though.
 
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Vance

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Vance

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How unstable is too unstable?
How stable is too stable?

How fast is too fast?
How slow is too slow?

How high is too high?
How low is too low?

How hot is too hot?
How cold is too cold?

You should address those questions to your spiritualist. With the appropriate degree of harmony, a séance might provide you with the answers you seek.

Thank you Mr. Beaty,

I do not have a spiritualist.

I suspect you are making fun of my questions.

I feel there are answers to all those questions.

I have found that any design project is a series of compromises. My more successful projects have manipulated these compromises to where the sum of the compromises aligns with the goals of the project.

I have found that quantifying the compromises and limits is a necessary part of the iterative process for me.

Quantifying things in a measurable way also aids me in the testing and development as I manipulate the variables and measure the change.

The gyroplane I intend to build will not be a particularly large departure from what I am flying now so I shouldn’t get into too much trouble.

I expect it to have a higher top speed and I feel it would be reasonable to expect that will change the stability of the aircraft.

I have a low fear threshold and limited piloting experience so I am trying to limit my design stability errors.

I feel that my rotor disk angle of attack will change more than 30 degrees over the speed range I am contemplating.

In my opinion this suggests I should elevate my confusion about the relationship of rotor thrust vectors to the aircrafts center of gravity as related to stability.

Thank you for trying to help me through my fog, Vance
 
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