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This thread is privately moderated by mnowell129, who may elect to delete unwanted replies.
Sep 27, 2016, 02:19 PM
I'm not as bad as they say.
Quote:
Originally Posted by ssrobzoom
Mickey on some of your first AutoGyro I saw you had flybars.

On some of the Autogyros I see heads running a flybar and heads with two and three blades.

Why does some gyros have flybars and some not? If you elect to run with out a flybar, what special designs or requirements come in play?

Will you have to run a flybarless unit similar helis?
Lots of factors at play here. I used flybars so I could use a two bladed semi-rigid head. Otherwise the controls would be too sensitive. Most use 3 bladed heads because this serves to desensitize the controls some. Others have done two bladed heads and dealt with control sensitivity by tip weight or other aerodynamic surfaces. Small two bladed rotors can be very tricky.
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Oct 05, 2016, 03:15 PM
Registered User
If I wanted to do away with the flybar on your Begi what do you suggest with only using two blades?
Oct 06, 2016, 08:52 AM
I'm not as bad as they say.
Quote:
Originally Posted by ssrobzoom
If I wanted to do away with the flybar on your Begi what do you suggest with only using two blades?
I would probably use one of the many working three blade heads first, with some tip weight. Then once I had that sorted out I'd make a two bladed version using the same construction. Begi was very short coupled, with no stab and depended on the rotor being stable by itself, hence the flybar. If you are going to keep the general layout then you probably want to make the rotor pretty stable by itself.
Latest blog entry: AIrcraft I've built.
Jan 26, 2017, 05:47 AM
Registered User
Does having a propeller behind the rotor axis affects the flight in some way compared to having it forward of the rotor? I thought that if it's on a greater distance before the rotor & the prop axis is slightly leaning down, then it would be trying to stabilize the horizontal flight as the rotor is dragged behind. While if it the prop is behind the rotor then the model would tend to fly with a hanging tail unless I make the tail stabilizer divert the prop's flow a little down to balance the model. Is such correct?
Looks like the rotor for a model must have either zero or negative incidence - how such affects the lift & rotating speed? Maybe then the model flies not cause of the spinning rotor providing a lift, but a drag like if it's an ubrella there?
I have a design of an autogyro with a 2 blades rotor, & a ducted prop behind the rotor - or would it be better without the duct & with some 3-4 blades?

Also, what I have is a RC from micro toy car - engine on/off & steering left/right controls only - would that be enough for an autogyro model? It would mean the rotor is fixed (unless I can make it self-adjustable for a stabilized flight), fixed horizontal stabilizer (unless it can be adjusted before the flight) & controlable rudder for left-right steering.

Another thing is, I read the real autogyro rotor should have self-adjustable blades, especially when it's a sigle rotor, yet I see many models have a solid rotor & fly quite good withou getting tilted to the side & falling.
Jan 29, 2017, 05:19 AM
BigTradioman's Avatar
I think it depends on the thrust lines relationship to the cg. Measuring the cg with pushers is done by hanging from the mast and the nose. Refer to the RPG Gyro build log.


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Aug 27, 2017, 03:02 PM
Registered User

If it isn't Broken, Don't Fix It


We had a great flying pusher gyro. Recently, we discovered the correct motor position above the CG. See: https://www.rcgroups.com/forums/show...shers-Oh-My%21

The blade spin up was satisfactory, but in the desire to improve things, we used a newly constructed rotor plate that is identical to the original with one exception: it provides a slight (2 degree) negative pitch to all 3 blades.

The test flight revealed the spin up is really fast and easy, but instead of being able to ROG, the model noses over. Holding the model for a simulated hand launch sees a powerful nose down moment when power is applied. Bottom line is that no flights were possible.

At the field we scraped away the 3 small (1/32 inch) ply strips that were 3/4 inch behind the blade leading edge to give negative pitch. Now once again the rotor plate is flat and blade incidence is zero. Low and behold, she flies wonderfully again. So why?

Currently we think that the negative pitch reduced the rotor thrust enough that the motor thrust now overcomes it, causing the push over. A possible solution would be to revisit the motors position above the CG (lower the motor) to once again balance rotor thrust with motor thrust for level flight. Q: Do we correctly understand what is going on, and is our possible solution a reasonable one?

Thanks in advance for your thoughts!

Russ
Aug 28, 2017, 06:36 AM
I'm not as bad as they say.
Hard to tell without watching, but it' s possible that with lower blade settings the rotor was operating much more efficiently, that is making plenty of lift without as much drag. This can happen with a faster rotor speed. If this is the case, the high motor position is too much for the less draggy rotor and you might have the behavior you describe.
A quick test is to put a little more up rotor in, hand launch with a spinning rotor and a little run, and much less motor application. You might be able to feel this out on a windy day without even letting go. If it appears that you can retrim and fly level with less motor input, then indeed you are getting the rotor to operate with less drag and you an adjust the motor position to correct. Probably you will need less power to fly at the new configuration.
All this is theory, so proceed with caution.
All of mine flew with some negative incidence after experimenting. I had metal straps where I could adjust the pitch and refly quickly, so I arrived at the correct pitch pretty quickly to get the most efficient operation. It was always negative.
Latest blog entry: AIrcraft I've built.
Aug 30, 2017, 04:02 AM
BigTradioman's Avatar
Too much negative pitch on the blades will severely reduce the lift but increase head speed. Depending on your blade profile it is possible that you will not need any shims to achieve a good lift at a reasonable head speed. I use a reformed Clarke Y with a very sharp leading edge and rarely if ever need shims.
Aug 30, 2017, 07:14 PM
Registered User
Thank you Mickey and Big T,

In this case, the hot wire cut foam blades covered with Tyvek and containing tip weights and constructed with a 2mm carbon rod on the front of the foam cores under the Tyvek are the same dimensions and airfoil shape as the wooden blades used on Flying Balsa's "Scout" gyro.

We found they spin up fine with zero incidence, but noted that the "Scout" has 1/32 " strips placed on the rotor plate 3/4" back from the blade's leading edge for negative blade incidence and that is why we wanted to see if we could improve on the spin up by adding this feature to our gyro.

I think one of the lessons learned is that every rotor is different, you are flying the rotor, and gyros are very picky when it comes to their rotors, each rotor requiring its own tuning and trimming for optimum performance. We have even seen this when replacing a damaged blade with a new one on an otherwise happily performing rotor. The pusher configuration seems to be the most picky.

Russ
Aug 31, 2017, 02:17 AM
BigTradioman's Avatar
To quote one Rich Harris " it's all in the blades". I found Airobalsa blades too soft, too floaty and too expensive so made my own using the Rich Harris method. Much more forgiving profile and much easier to predict and tune.


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