Angle of Bank and G loading

[Vance]

I am trying to understand angle of bank and G loading on a gyroplane.

How many Gs are required to get a gyroplane to maintain 80 degrees of bank?

I have seen and believed explanations about why it is not 4 Gs. I found I was not able to articulate and defend the explanation.

I seem to be confused on a low level.

The question that I couldn’t answer well was “how much pull would be on a string that had a one pound ball attached for the string to get to an angle of 80 degrees from the horizontal?”

Thank you, Vance

 

[brett s]

If you maintained altitude & airspeed during that 80 degree banked turn it would be near 6 g's (5.76?) - but you can't do that in a gyro even if you wanted, not enough power or lift available.

If you're not maintaining altitude you're using less load factor.

 

[StanFoster]

Vance- My mind is overwhelmed right now...but if you take the cosine of the bank angle...and divide 1 by that...thats the G load. 60 degrees...the cosine is .5 divide that into 1 and you get 2G's.

70 degrees the cosine is .342 divide that into 1 and you get 2.92 G's

80 degrees the cosine is .1736 divide that into 1 and you get 5.75 G's


Stan

 

[PW_Plack]

...The question that I couldn’t answer well was “how much pull would be on a string that had a one pound ball attached for the string to get to an angle of 80 degrees from the horizontal?”

If the other end of the string is being held in a fixed location, you get one answer, but if whatever is holding the string at the center of the arc is free to move in space, (like a heavily loaded rotor,) it will be pulled out of place by the ball, so you'll never reach that theoretical G number.

If you were to watch a gyroplane with a smoke system doing a series of barrel rolls, the smoke would draw a corkscrew with a fairly large radius, not the tight, "braided rope" look of a Pitts doing the same thing. The higher the blade loading, the bigger the circle.

Kinda like trying to do a thrust test by chaining your gyro to a kid on a skateboard.

 

[Vance]

Still confused!

Still confused!

Thank you Brett,

Yours is the explanation I was parroting without understanding and I came up with the same figure.

Thank you Stan,

That is the number I came up with.

Thank you Paul,

Your explanation is just what got me into trouble.

The particular event that brought this up happened the second day of the air show. I was headed toward the crowd at 95kts indicated airspeed and began my 70 degree bank to keep from passing the 500 foot air show box line. I had a tail wind and it looked like I was going to get blown over the line so I increased my bank. I was losing airspeed but maintaining altitude. Ed got a picture of the gyroplane moving away from her so that would have been close to 90 degrees of turn past where I feel we achieved the steepest bank and we measured the bank at more than 80 degrees. My best guess based on where we were in the air box when we began the turn is the turn had less than a 400 foot radius. Based on what I imagine I know about gyroplanes this is not possible so my observations must be in error.

Jims question was; how much load should we design for? My response was 3.5 Gs but it was not backed up with understanding.

I did not note my rotor speed.

I am still confused and the skate board example doesn’t work for me.

Thank you, Vance

 

[brett s]

I can see the turn being less than 400' radius as you were bleeding off lots of airspeed during the maneuver.

I'd see some pretty steep pitch & bank angles doing ag work occasionally but minimal g loading because of the airspeed and/or altitude changes going on at the same time.

 

[PW_Plack]

Vance, regarding the skateboard example, the pounds of force measured on the cable will equal static thrust if it's anchored to a tie-down on the airport apron. If you instead hand it to a kid on a skateboard, you can produce the same static thrust, but the pull on the cable will be much less while the kid on the skateboard is being accelerated by the towline.

In Europe, where some regulators require testing gyroplane airframes at 3G loads, developers have to do it on the ground, because it cannot be achieved in flight. If you tie a gyro down to a trailer, you can tow it with a truck and lift 3G, but only using rotor RPM way above what you'd get (or would have the HP to sustain) in flight, and a powerful (relative to the gyro) tow vehicle is required to overcome the resulting inefficiencies.

If you could borrow a recording G-meter, (scroll down from the link and click on the GF-1,) it would be interesting to fly your maneuvers in the Predator, and see what they actually produce. This might be worth doing before you lock down assumptions for Mariah Gale, and might help Jim greatly.

 

[Walter]

Now I am confused. If the turn is a coordinated one, the 1/cosine rule must hold, in my view. This applies for powered (level and no acceleration) as well as for non-powered flight, e.g., in a glider. I do not see how the deterioration of the glide angle due to high loading would decrease the g load in a coordinated, steady turn.

 

[RotoPlane]

I agree with Walter. As long as a Turn & Bank instrument is indicating a coordinated turn, the 1/cosine rule is valid. The amount of bank angle obtainable while maintaining coordination and altitude, will depend upon the rotor area and solidity-ratio....in relation to the gyro flying weight.

 

[WaspAir]

Now I am confused. If the turn is a coordinated one, the 1/cosine rule must hold, in my view. This applies for powered (level and no acceleration) as well as for non-powered flight, e.g., in a glider. I do not see how the deterioration of the glide angle due to high loading would decrease the g load in a coordinated, steady turn.

Hmmm - I may not understand your question fully, but here goes.

We have to be a little careful about terms here. A turn is by nature an accelerating maneuver (that's what the g-load is all about, a g-meter being a form of accelerometer), so what people usually have in mind is constant indicated airspeed (tangential to the turn) rather than "no acceleration". Changing direction and changing speed are both ways to "accelerate" and change velocity.

The secant of the bank angle will give the perceived load in g units only if you really can hold that coordinated turn, and all aircraft are limited in their ability to do that as bank increases. Eventually, as the pilot commands more bank / more load the lifting device can't generate the centripetal acceleration necessary to pull the aircraft steadily toward the center of the turn as desired. In a fixed wing aircraft, you will exceed the stall angle of attack at some point before you get to really high g force (one hopes, anyway -- one prefers a stall over bending the spars and breaking things, and that's one reason there's a maneuvering speed given for planes, so that stall precedes damage and failure). In a gyro, the rotor ultimately can't produce enough lift to do all you are asking of it, and that happens at a relatively low g-load. It doesn't "stall" in the same fashion as a fixed wing, but it will reach a maximum load and refuse to increase beyond that.

 

[Fl90]

the rotor flies at 9 degrees, straight and level. so what's the g loading at straight and level?

You can't use the 1/cosine rule since the gyro is falling through the turn. It's not really a coordinated turn.

Do turns on a point, as tight as you can, while maintaing altitude.....then do the math, it'll be a lot closer to the rule.

Falling through the turn is easy to see at low altitude and high cruise. Doing a 90 degree turn without power change and heavy stick and rudder will stand it on it's nose where you can see the ground slide by.

phil

 

[Mayfield]

Do turns on a point, as tight as you can, while maintaing altitude.....then do the math, it'll be a lot closer to the rule.
phil

But only if the airspeed and angle of bank also remains constant.

Jim

 

[C. Beaty]

Try this:............

 

[JEFF TIPTON]

Check this web site.

https://www.aerospaceweb.org/question/performance/q0146.shtml

 

[Mayfield]

Check this web site.

https://www.aerospaceweb.org/question/performance/q0146.shtml

Thanks Jeff,

Of course. Makes perfect sense.

I left out the decreasing radius constant G scenario.

Jim

 

[Lspav8r]

I think I just used up about 5 million brain cells just reading all you guys posts regarding g loads I am glad there are people like you guys that understand all this stuff cause if it was a requirement to know this and understand it to be able to fly gyros, I think a lot of us would still be looking up at the sky wondering what it feels like to fly.

Thank God there are people like you guys to figure all this stuff out for people like me, allowing me to use the few brain cells I do have left to do the easy part. FLY!

 

[Redbaron]

I've heard gyros will only pull so many g and the gee will "spill off" the rotors but my mind doesn't comprehend how gees can spill off! yet when I bank my bee into a hard 60 degree bank I don't feel many gees, there would definatelly be some feel in a plane! my mind is boggled lol

 

[Vance]

I feel confused on a higher level.

I feel confused on a higher level.

Thank you Brett,

Observations often make more sense to me than theory.

Thank you Paul,

John is going to loan me his G meter. I will report what I find.

Thank you Walter,

I am glad that I am not the only one confused.

Thank you Ed,

Perhaps we have confusion consensus.

Thank you J.R.

That is part of the path that led to the confusion.

Thank you Phil,

I did the math on my observations and it came out to three Gs so I am still confused because that is not supposed to be possible according to many of the books I have read.

Thank you Jim,

It was not constant.

Thank you Chuck,

Those numbers are exactly what confused me. They did not align with my observations.

Thank you Jeff,

That was very helpful, I feel confused on a higher level now.

Thank you Jim,

I wish it made perfect sense to me.

Thank you Jim S,

I understand your trepidation about complex theory. Because I am on the outer edge of my knowledge and understand I am trying to grasp how strong to build Mariah Gale. I am grateful for the people who are trying to help.

Thank you for your input Jeff, our confusion seems to be aligned.

I will learn more with the G meter and report what I find.

It will probably be after the Ken Brock Freedom Fly In.

Thank you, Vance

 

[Walter]

"We have to be a little careful about terms here. A turn is by nature an accelerating maneuver (that's what the g-load is all about, a g-meter being a form of accelerometer), so what people usually have in mind is constant indicated airspeed (tangential to the turn) rather than "no acceleration". Changing direction and changing speed are both ways to "accelerate" and change velocity."

Thanks for the clarification, and a good example of words causing confusion. I did not use acceleration right, since I meant only no change in speed.

But as long as the turn is constant and coordinated, the 1/cosine law applies. Lets see what Vance measures.

 

[RotoPlane]

I take your last post Vance....that you are still somewhat confused . Don't blame ya! It has been hard for me to imagine more than 2.5G in a smooth entry into a high bank because it seems to me that the speed would bleed off before the G's could go higher. Now an abrupt pull-up I feel is a different story and I can see perhaps 3.5G. I'm stressing for 5G and load testing for 4G. But that's for me, a place where I feel somewhat comfortable....and flying conservatively .

I like your idea of G-meter testing with the Predator.....