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Old Mar 23, 2013, 01:41 PM
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Greg_E's Avatar
Durbanville, South Africa
Joined Oct 2006
67 Posts
Help!
HK Cierva keeps nosing up when I fly

HI All

I have had the HK Cierva for a few years now. After the "CD like" clear bendy rotor center piece broke, I replaced it with 2mm polycarbonate that worked well for a year and then it broke in flight - It wasn't pretty.

I have now replaced the rotor center with pc board. I have had the problem of the Cierva nosing up ever since. I thought this might have something to do with the pc board being too stiff causing the advancing blade reaching it's uppermost point before it reaches the front of the disc rotation, and the following nose up gyroscopic progression. I removed the pc board material so that it is now only 7mm wide near the blue rotor disc center piece.

She still noses up.

The motor has got extra downthrust, 25g of lead in front and I fly with a 2200mAh, 3S lipo.

Any suggestions as to what can be causing the problem?

Greg
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Old Mar 23, 2013, 05:57 PM
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Tom Wright's Avatar
Joined Feb 2012
877 Posts
Hi Greg.

As the model has only had the nose up problem since using a stiffer material ,it's a fair bet that,a more flexible material is needed .
0.4 woven glass fibre sheet should do the job and be more robust than the original material .This uk based supplier is very reasonable on cost and postage .

http://hobbyplastic.co.uk/index.php?...ex&cPath=52_54

Tom.
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Old Mar 24, 2013, 04:26 AM
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Durbanville, South Africa
Joined Oct 2006
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Hi Tom

Thanks for the link. I will see if I can get any epoxy glass sheet in South Africa. If not I will import from the UK.

Cheers

Greg
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Old Mar 25, 2013, 06:10 PM
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Trailer Down By The River
Joined Sep 2004
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Hey guys ,,I read the thread and remember reading here on this forum alot of guys use tuperware for the flex part of the rotor head with success on various autogyros. I fly the HK Cierva also but used polycarbonate which seems stronger than the original flex part but I am also using longer ,wider and heavier rotor blades I made myself.
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Old Mar 26, 2013, 06:04 AM
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Durbanville, South Africa
Joined Oct 2006
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Quote:
Originally Posted by TURBOOMNI View Post
Hey guys ,,I read the thread and remember reading here on this forum alot of guys use tuperware for the flex part of the rotor head with success on various autogyros. I fly the HK Cierva also but used polycarbonate which seems stronger than the original flex part but I am also using longer ,wider and heavier rotor blades I made myself.
I flew with 2mm polycarbonate and one day I lost a rotorblade mid flight. It wasn't pretty. Surprisingly the damage was only minor. The Cierva ia a tough little gyro.

The tupperware part sounds interesting.

What size/length blades are you using?

Greg
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Old Apr 01, 2013, 03:39 PM
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Trailer Down By The River
Joined Sep 2004
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I made blades that are about 1 inch longer but 1/3 wider than the stock blades. I flew it with the stock blades and had to fly too fast to keep it in the air. It flys much slower with my home made blades which is what I wanted.
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Old Apr 15, 2013, 02:14 AM
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Durbanville, South Africa
Joined Oct 2006
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Finally some positive feedback!

I got the 0.4mm epoxyglass plate from a local supplier. I changed my "pc" board head back to the orignal type head set up.

The first launch was the 2nd worst crash I have ever had with a gyro. I think It travelld around 2.5m forward before connecting with the ground hard, despite full up elevator. OUCH!

I repaired the gyro and removed the 0.5mm shims I have put under the blades to give me more negative pitch with the old pc board head. This time I found some long grass and retested.... What do you know the gyro fly out of my hand the way it was supposed to. What a non-event and no more nosing up tendancy!

Thanks for the advice Tom. It was nice to have a decent flying gyro once again.
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Old Apr 15, 2013, 09:19 PM
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Glad to hear you got it worked out. So are you saying you had too much negative pitch and that was your problem?
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Old Apr 16, 2013, 08:44 AM
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Durbanville, South Africa
Joined Oct 2006
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Well, yes and no...

The thin negative pitch spacers were needed on the previous head type set up to get the blades rotating and there was enought lift to fly.

Moving back to the original head set up, the blade gets more negative pitch input as the blade lifts due to the angle of the "hinge" point, so it simply did not produce enough lift.

I took out the shims, I had in and then she flew off perfectly. No other adjustments were made.

Thanks again to everyone for their input.

Greg
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