Side-by-Side Little Wing Build

[Vance]

Miranda is building a gyroplane with fixed pitch.

Miranda is building a gyroplane with fixed pitch.

In the hundreds of turning autos I did to the ground during my Army training, and in the dozens of turning autos I did in my civilian training to a 3 foot hovering power recovery...

...The ONLY reason that was ever discussed for having to add pitch to avoid the rotor overspeeding, was the change in the angle that the resultant relative wind enters the rotor system. A slight amount of aft cyclic to cause the turn causes a slight change in the entry angle of the relative wind...which adds a tremendous amount of rotational force to the blades.

Now I do admit that the most recently FAA Published Advisory Circular says the reason for RPM increase is the increased load on the rotor.

Flying the two place tandem gyroplane I fly it is not unusual for the rotor rpm to increase from a little over three hundred rotor rpm in level flight to a little over four hundred rotor rpm in a steep banked turn.

I feel this increase in rotor rpm is from the increased load in a turn.

In all the gyroplanes I have flown it is my observation flying nose high (aft cyclic) will reduce the rotor rpm.

I feel this is because of the reduced indicated air speed.

In all the gyroplanes I have flown it is my observation that the flair to land (aft cyclic, raising the nose) will increase rotor rpm, reduce airspeed and arrest the descent.

Please don’t get off track Brian, Miranda was asking something very specific about gyroplanes.

Thank you, Vance

 

[Brent_Brown]

Piper colt is a good start.

 

[Alan_Cheatham]

In all the gyroplanes I have flown it is my observation flying nose high (aft cyclic) will reduce the rotor rpm.

I feel this is because of the reduced indicated air speed.

In a nose high attitude propeller thrust is carrying part of the aircraft weight and reducing the load on the rotor.

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[Miranda]

I much appreciate everyone's contribution to this discussion. It has been both interesting and very helpful. And thanks for the links to the NACA reports and Franklin Harris's books, Juergen. (If I could find the umlaut command on my computer keyboard I would spell your name properlyhwell

One thing I could not find when I read NACA Report 523 "The Influence Of Wing Setting On The Wing Load and Rotor Speed Of A PCA-2 Autogiro As Determined In Flight" is any mention of the airfoil used in the PCA-2 stub wings. I have not been able to find that out through other means, either. It would be interesting to know what airfoil the PCA-2 wing uses, even if only for comparison purposes.

I did locate a very helpful NACA report, No. 331 "Collection Of Wind-Tunnel Data On Commonly Used Wing Sections", as I was looking for input on flat-bottom (or nearly flat-bottom) airfoils to consider for my stub wings. I was looking for airfoil sections that provide higher lift at the lower speeds of gyros in general and that also possess a nice fat thickness in which to contain my fuel tanks. The report is especially helpful because it covers some very common airfoils that are all candidates for use in my design: the Clark Y-15, Gottingen (minus umlaut ) 387 and 398, Navy N-22, and USA35A. I have only skimmed through the data so far. I will have to review all of these airfoils for their performance at varying angles of attack and at various speeds. Whatever I choose will have to have the ability to provide lift at the slowest speeds and highest angles of attack and, at the same time, not develop so much lift that they unload the rotor system below 60-percent at VNE.

One thing is clear from Report 523: It will be exceptionally important to get the angle of attack correct. Although I hesitate to do anything that might unnecessarily complicate the design, it just occurred to me that I might end up making the angle of attack adjustable to account for changes in takeoff weight depending on whether the gyro is being flown with one or two people. The idea would be (based on the data from Report 523) to decrease the wing angle setting when flying single seat/lightly loaded to avoid generating too much lift at higher cruise speeds. Conversely, the wing angle setting would be set to its maximum efficient setting when flying closer to maximum weight.

Once I have decided on an airfoil I will have to address induced drag at the stub wing tips and decide whether - and which - kind of winglet or wingtip fence to use. I'll be the first to admit that I don't yet have much knowledge about low-aspect-ratio wings. It just seems to me that the stub wings will likely suffer from a higher level of inefficiency (compared to high-aspect-ratio wings) from induced drag if I don't address the problem in advance.

Juergen, I see you are in Duesseldorf. I lived in Germany for 3 years (1980-1983) and was stationed at Katterbach Army Heliport, near Ansbach. Unfortunately, all of our flying was done in and around southern Germany and I never got that far north or west. In my entire 3 years in Germany we never left the country for sightseeing or touring, preferring instead to do as much in country as possible. We absolutely loved our time in Germany and would have stayed longer if it had been possible. We are seriously considering coming back to tour Germany on our bicycles in a couple of years or so. First, though, we have to take care of some major tasks, such as selling our home, building another, and relocating. Oh, and completing my gyro build as well.

 

[bryancobb]

In a nose high attitude propeller thrust is carrying part of the aircraft weight and reducing the load on the rotor.

.

I'll buy that if propeller thrust is available. Suppose your gyro's engine is dead and you are descending and raise the nose...then what?

 

[twistair]

At roughly $25k new the Rotax models are about 3 times as much as I can afford.

You may want to consider buying used 80 hp Rotax and upgrading it with a turbocharger like it's used in Xenon gyros. This would give ca.120 honest hp at a very reasonable price. The upgrade itself is not that complex.

For a side-by-side gyro 80-85 hp is... well, it simply is too little to make a gyro just a little frisky.

Good luck with this interesting project.

 

[Alan_Cheatham]

One thing I could not find when I read NACA Report 523 "The Influence Of Wing Setting On The Wing Load and Rotor Speed Of A PCA-2 Autogiro As Determined In Flight" is any mention of the airfoil used in the PCA-2 stub wings. I have not been able to find that out through other means, either. It would be interesting to know what airfoil the PCA-2 wing uses, even if only for comparison purposes.

Check out these reports, wing section was a modified M3.

https://naca.central.cranfield.ac.uk/reports/1935/naca-report-475.pdf

https://naca.central.cranfield.ac.uk/reports/1933/naca-report-434.pdf

.

 

[Alan_Cheatham]

You may also find these patents informative.

1947901
1958444
2098230

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[Miranda]

You may want to consider buying used 80 hp Rotax and upgrading it with a turcocharger like it's used in Xenon gyros. This would give ca.120 honest hp at a very reasonable price. The upgrade itself is not that complex.

For a side-by-side gyro 80-85 hp is... well, it simply is too little to make a gyro just a little frisky.

Good luck with this interesting project.

I agree that 80-85 HP is insufficient to give a 2-place gyro adequate performance. I have pretty well settled on doing one of the Yamaha Genesis conversions, but if I have difficulty finding an engine to convert (when the time is right) I will also consider the 80 HP Rotax with turbo upgrade.

Thanks for the suggestion and encouragement.

Miranda

 

[kolibri282]

We absolutely loved our time in Germany and would have stayed longer if it had been possible. We are seriously considering coming back to tour Germany on our bicycles in a couple of years or so. First, though, we have to take care of some major tasks, such as selling our home, building another, and relocating. Oh, and completing my gyro build as well.

Great to hear that you had a good time in Germany, Miranda, though your task list before another visit sounds pretty substantial...;-), hope you'll make good progress with all of your projects!

There is another report (of course by the indefatigable Harris) with a considerable amount of information on the PCA-2. https://www.rotaryforum.com/forum/showthread.php?t=35865 I am rather posting the links to the "Technical Papers, Books and Publications" section since I want to encourage people to rummage a bit through our pretty comprehensive collection of rotorcraft links. It's easier to find papers there than to search the web and sift through thousands of useless hits.

Saving time actually was the reason why I had proposed to use my program since it would take quite some time to calculate the trim solutions for a winged autogyro, especially if you want to include such things as rotor downwash, which depends on rotor load which depends on wing load which in turn depends on rotor downwash.

I'm sure your project will be a lot of fun, no matter how you start working on it.

Cheers,
Juergen

PS: Below is one of my favourite pictures of a Pitcairn gyro, from here:
https://www.stuffinder.com/autogiro.htm