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Old Oct 05, 2009, 08:22 AM
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madmike43613's Avatar
toledo ohio
Joined Jun 2006
526 Posts
Gene,
The bolt pulled out. That's the one part I didn't find. Like I said the outer few threads look like it pulled right out. Also I really don't see any evidence of thread lock on that end. The other end has a lot though. The feathering shaft didn't bend so it happened pretty fast.

Mike
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Old Oct 05, 2009, 11:11 AM
I Can Fly An FP Inverted!
Hal_The_Hacker's Avatar
Teddington, Middlesex, UK
Joined Jun 2008
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hmm, just as I suspected - soft feathering shaft, I will be ordering a pack of those before my maiden then
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Old Oct 05, 2009, 12:05 PM
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Lake City, PA USA
Joined Sep 1999
328 Posts
Thanks Mike,

When I put mine back together I really tightened the daylights out of it to see if it would hold. It seemed to. I will be dialing down the head speed anyway just to make sure.

I suspect it is not so much soft as it is the tolerences. If the hole in the shaft is a little too big then the threads are not deep enough to grab the screw.

There are plenty of posts cropping up where they are flying fine so hopefully this is an isolated incident and thankfully nobody got hurt.

It does reinforce the need for extra diligence when working on an unproven heli. Align says their head should not be run over 4500 and I suspect the failure point on the plastic HK is a lot less....

Gene
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Old Oct 05, 2009, 04:02 PM
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toledo ohio
Joined Jun 2006
526 Posts
Hal,
I'm not so sure about a soft feathering shaft. I'm thinking maybe it was loctited and only screwed in about 3 turns. So when I checked for tightness it felt tight because of the loctite. This would also keep the blade holder from sliding out until it saw pressure. I am going to check hardness Tuesday at work (I work for a commercial heat treat). I'll report the results.

Mike
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Old Oct 05, 2009, 04:10 PM
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morgantown, wv
Joined Mar 2004
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Your not going to re-use the feathering shaft again are you? That is just asking for trouble if you are.
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Old Oct 05, 2009, 04:13 PM
What package dear?
Hellysmack's Avatar
USA ILLINOIS
Joined Nov 2002
2,066 Posts
Quote:
Originally Posted by madmike43613
Hal,
I'm not so sure about a soft feathering shaft. I'm thinking maybe it was loctited and only screwed in about 3 turns. So when I checked for tightness it felt tight because of the loctite. This would also keep the blade holder from sliding out until it saw pressure. I am going to check hardness Tuesday at work (I work for a commercial heat treat). I'll report the results.

Mike
Cool professional testing
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Old Oct 05, 2009, 05:17 PM
I Can Fly An FP Inverted!
Hal_The_Hacker's Avatar
Teddington, Middlesex, UK
Joined Jun 2008
1,536 Posts
for piece of mind, i just ordered a pack of two align feathering shafts, which include the feathering bolts.
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Old Oct 05, 2009, 07:59 PM
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toledo ohio
Joined Jun 2006
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No, I won't be using that shaft again. If I'm not happy with the hardness test. It will be split down the middle and put under the microscope to look at the threads and the microstructure. I do have an Align one that will be tested also.

Mike
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Old Oct 06, 2009, 12:24 PM
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toledo ohio
Joined Jun 2006
526 Posts
Feathering Shaft Hardness

The shaft is too small for a direct Rc reading so I used the R15n scale and converted to Rockwell C scale.
HK feathering shaft 29 Rc
Align feathering shaft 44 Rc
For those not familiar with Rockwell c hardness a file is usually 63 Rc plus. A spring is usually in the 40 to 48 range. Annealled (soft steel wire) runs below 22
This is a significant differance. 29Rc is just a little better than annealed. 44 Rc would be typical for hardened and tempered stock. This is right in the spring hardness range. If I were heat treating my own this is close to what I would shoot for.
The 29 should still work just fine if the threads are good, it's just going to bend easily.

Mike
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Old Oct 06, 2009, 01:56 PM
I Can Fly An FP Inverted!
Hal_The_Hacker's Avatar
Teddington, Middlesex, UK
Joined Jun 2008
1,536 Posts
Quote:
Originally Posted by madmike43613
The shaft is too small for a direct Rc reading so I used the R15n scale and converted to Rockwell C scale.
HK feathering shaft 29 Rc
Align feathering shaft 44 Rc
For those not familiar with Rockwell c hardness a file is usually 63 Rc plus. A spring is usually in the 40 to 48 range. Annealled (soft steel wire) runs below 22
This is a significant differance. 29Rc is just a little better than annealed. 44 Rc would be typical for hardened and tempered stock. This is right in the spring hardness range. If I were heat treating my own this is close to what I would shoot for.
The 29 should still work just fine if the threads are good, it's just going to bend easily.

Mike
any chance you might be able to test the tensile strength of the combined HK shaft and stock screws held in place with blue loctite in order to find the save RPM loading?

if you can give me a figure stating at which mass loading (metric please) the stock shaft&screw fails, i should be able to come up with a safe rpm range with the stock blades.
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Old Oct 06, 2009, 03:22 PM
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toledo ohio
Joined Jun 2006
526 Posts
Tensile

Hal,
Interesting problem. I'll see what I can come up with. Our tensile tester is set up to do crush tests only at the moment. I will have to machine some parts to do a pull on it. I'll see what I can do.
The 29 Rc converts to about 134,000 KSI and the 44 converts to about 212,000 KSI. This doesn't tell us what the screws let go at though.

Mike
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Old Oct 07, 2009, 05:24 AM
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East Coast, Australia
Joined Jul 2009
169 Posts
Well mine is done.
Please excuse the photos as they are un-edited and straight off the camera.
Didnt really take any build pics as many many people will be doing that.
Here is basically a before and after series.


The before Kit








HXT900 servos do fit. JUST


I broke the pushrod guide putting it on the boom


Finished


I'm quite happy with the quality of the kit. The frame is Alu and everything else is plastic except the rotating part of the swash, swash mixer arms and the flybar cage is CNC.
I also decided to keep it cheap and used HXT900 and a cheap Telebee instead of the GY520 and S3110's I had planned. Some screws in the head and frame needed tightening but no big deal. I was surprised to see the flybar cage assembled and on the head already with red threadlock used.

Some things that would want replacing with genuine Align parts are as follows:
Main blades - The included nylon blades are too spongy but my two pairs track extremely well.
Feathering shaft - The included one is too soft. I'm not getting any problems with threads either.
Paddles - Stock are too heavy
Tail servo pushrod - Stock is VERY springy
Main rotor housing and swash - I do not trust plastic on 4000+ HS plus my head
had plenty of slop in the swash. Will be replacing soon.
All in all, a very happy camper. For about $160 all up, not a bad heli.

Has anyone had any problems with either of the knight head struts vibrating BADLY?


HK250

Esky 3900KV 15T on 75% Throttle
HXT900 Cyclic
Dynam 30A ESC
Futaba R617FS
Telebee GR302 with INO-LAB HGD 201
Will be using TP Pro Power 910 Batts but for now, jut some Turnigy 1000's.
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Old Oct 07, 2009, 09:35 AM
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USA, IL, Carol Stream
Joined Jan 2009
2,044 Posts
distractor, nice build. Your gyro is on an angle. The base needs to be perpendicular to your main shaft to work effectively.

EDIT* I just double checked and it appears your gyro is also mounted with the wrong side stuck to the gyro shelf too. All my Telebees needed to be mounted with the label on a vertical plane. I checked the part number you listed and it also needs to be mounted this way.

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Old Oct 07, 2009, 09:47 AM
Heli Hooligan
London
Joined Dec 2006
6,057 Posts
Good catch. That would have been an interesting maiden flight, worthy of video
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Old Oct 07, 2009, 11:15 AM
I Can Fly An FP Inverted!
Hal_The_Hacker's Avatar
Teddington, Middlesex, UK
Joined Jun 2008
1,536 Posts
Quote:
Originally Posted by mahbouni
Good catch. That would have been an interesting maiden flight, worthy of video
not really, didnt you hear about it? its the new training feature, when you give a roll command, it automatically mixes in rudder, sure to help n00bs all over the world
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