Scratch Single-Rotor 23" 6.5 Ounces - Page 30 - RC Groups
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Sep 17, 2017, 02:10 PM
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Quote:
Originally Posted by rus1
Now, if you have the time I encourage you to make some airfoil foam blades. This doesn't take very long, under 1 hour for all three. Just be ready for the CG to move forward with airfoil blades. You will be amazed at how much better your gyro will fly and you may even get longer flight times.
Meanwhile I built new blades with an airfoil that "looks about right", roughly copying the airfoil of the HK blades from my Auto-G-MK1. However, I kept the dimensions of the blades unchanged (300mm x 45mm) to allow a direct comparison to my flat blades.

The flight time increased from about 6 min. (flat blades) to about 7 min (airfoiled blades). Wow!
The CG had to be moved a lot forward. I moved the battery as far forward as possible and had to add additional weight to the nose.

Can somebody please explain to me, why such airfoiled blades need this forward CG ? Or give me a link where it is explained?
Can this be corrected by a different mast angle? Smaller or larger?
Last edited by Ralf W.; Sep 17, 2017 at 02:20 PM.
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Sep 18, 2017, 11:51 AM
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Ralf,
Congratulations on your upgrade to airfoiled blades! Your rotor with airfoiled blades produces much more lift than before. Your rotor thrust has increased.

Since the mast is angled back, the increased rotor thrust is acting vertical and aft. The aft force is rotating your gyro around its horizontal CG so the nose wants to lift and the tail wants to drop. You compensated by moving the horizontal CG forward by adding weight to the nose. You have another option. In your tractor gyro, you could offset the nose up tendency by adding more downthrust on your motor to offset the increased aft rotor thrust vector.

Adding weight is not generally desirable, so your best solution is to add motor downthrust and move the battery forward if necessary. You will need to experiment some to find the sweet spot, but when you do I think you will be very happy with the results.

Good Luck!

Cheers,
Russ
Last edited by rus1; Sep 18, 2017 at 12:09 PM.
Sep 18, 2017, 12:35 PM
Registered User
Thanks, Russ!
Will change the down thrust of the motor and maybe mount the rotor mast a bit backwards to get a longer fuselage in front of it.
Sep 18, 2017, 01:56 PM
Registered User
Move the mast back toward the tail if you need to, but don't change the angle.
Sep 19, 2017, 06:21 AM
I'm not as bad as they say.
Put a little more negative shim in the blades. It's likely this will make it spin up faster and you may not have to change the geometry at all.
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Sep 19, 2017, 01:41 PM
Registered User
Quote:
Originally Posted by mnowell129
Put a little more negative shim in the blades. It's likely this will make it spin up faster and you may not have to change the geometry at all.
Thanks! I still have to read and learn a lot, before I will understand how these machines do function.


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