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Old Jun 01, 2010, 07:00 PM
ajbaker is offline
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Quote:
Originally Posted by henkvdw View Post
5x3 means 5" diameter and 3" forward travel per revolution if no slip occurs.
Me, too
AJ
Last edited by ajbaker; Jun 01, 2010 at 08:37 PM.
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Old Jun 01, 2010, 07:19 PM
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Thanks AJ. Typo corrected.
Old Jun 01, 2010, 08:36 PM
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Prop Stuff


Quote:
Originally Posted by ajbaker View Post
I got this post on another forum. I do not know whether I agree with it or not. I have not tested the statement yet. Maybe some of you folks have. If so, let us all know.

My plan is to take a 2409-12t motor which should handle the amperage draw easily for the following tests with a WattsUp meter and my thrust stand.
5x3
6x3
7x3
Then:
6x4
7x4
8x4
I use these because I have all of them in stock. I would have preferred a 5x4. 6x4, and 7x4. But, I do not have a 5x4 (only a 5x4.3). So, any guesses anyone on what the thrust comparison will show?
AJ
I ended up using a 2409-12D motor (rated at 25A max) and got the following results:
......Ap..Wp..Vm.......Thrust-oz.
5x3 7.5.....88.4..11.79...8.7
6x3 12.39 142.2 11.30 17.0 APC
7x3 21.40 253.4 10.91 25.0

Then:
6x4 14.18 161.5 11.16 15.5 APC
7x4 22.85 253.4 10.75 25.5
8x4 30.78 325.0 10.18 32.7

Then:
6x5 13.16 153.9 11.49 17.5
7x5 18.99 214.9 10.96 26.10
8x5 - exceeds Amp rating of motor

All props used (except as noted) were "real" TGS props and appeared to be identical except for the pitch on the first props and the diameter on the second and third props.
Conclusion- A smaller pitch prop (keeping the diameter the same) on a given motor might produce more instantaneous thrust. However, after ~.5 to 2 seconds the static thrust will be greater as the pitch of the prop increases. This is where I dislike the 1st gear analogy comparison. 1st gear in a car does not slip like the air does over a prop. But, anytime I reduce the pitch in an airplane prop, it does reduce the top speed.
AJ
Last edited by ajbaker; Jun 02, 2010 at 02:51 AM. Reason: fix Decimals
Old Jun 01, 2010, 09:25 PM
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Quote:
Originally Posted by henkvdw View Post
5x3 means 5" diameter and 3" forward travel per revolution if no slip occurs.
does that mean that the plane you have the prop attached
to will move forward 3" per revolution.
Old Jun 01, 2010, 10:57 PM
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Quote:
Originally Posted by jonnyd View Post
does that mean that the plane you have the prop attached
to will move forward 3" per revolution.
Yes . . . if there's no slippage. It's like a screw thread.
Old Jun 01, 2010, 11:24 PM
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Quote:
Originally Posted by jonnyd View Post
does that mean that the plane you have the prop attached
to will move forward 3" per revolution.
Since the prop is spinning in air and there is slippage, the plane will not be moving forward at the 3" rate.
This is just a way of specifying the pitch. Not what happens when the prop is spinning in air.
Like the previous member said, the specification of pitch is similar to what is used in bolts/screws and nuts. There is no slippage.
Old Jun 02, 2010, 07:35 AM
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Quote:
Originally Posted by Greywing View Post
Yes . . . if there's no slippage. It's like a screw thread.
Quote:
Originally Posted by henkvdw View Post
Since the prop is spinning in air and there is slippage, the plane will not be moving forward at the 3" rate.
This is just a way of specifying the pitch. Not what happens when the prop is spinning in air.
Like the previous member said, the specification of pitch is similar to what is used in bolts/screws and nuts. There is no slippage.
ok i got it now. thanks for the clarification. so the higher the second number the more aggressive the pitch and ideally more thrust right?
Old Jun 02, 2010, 07:37 AM
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yes correct + more amp draw...
Old Jun 02, 2010, 03:57 PM
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what is an appropriate cg for a first time flier. where do you measure from. how do you check for cg.
Old Jun 02, 2010, 04:14 PM
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Quote:
Originally Posted by jonnyd View Post
what is an appropriate cg for a first time flier. where do you measure from. how do you check for cg.
The CG should be 72mm from the LE of the wing. Make a CG jig by putting two 1/4" rods about 6" apart into a board and balance the plane on them. OR Buy THIS.
AJ
Old Jun 02, 2010, 06:03 PM
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Originally Posted by ajbaker View Post
The CG should be 72mm from the LE of the wing. Make a CG jig by putting two 1/4" rods about 6" apart into a board and balance the plane on them. OR Buy THIS.
AJ
is this cg measurement specific to the sky surfer. i have ordered a dynam hawk sky as well which i expect to receive first so i would like to know the cg for that plane as well.
Old Jun 02, 2010, 06:27 PM
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yes.. each plane has it's own CG that should be mentioned in the manual. sometimes planes have two (one on each side) circles shaped underneath usually on the main wings that show the CG point...
Old Jun 02, 2010, 08:05 PM
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Originally Posted by jonnyd View Post
is this cg measurement specific to the sky surfer. i have ordered a dynam hawk sky as well which i expect to receive first so i would like to know the cg for that plane as well.
Hawk Sky CG - 60mm from LE of wing. I am anxious to find out which plane you prefer to fly. They are both excellent planes, IMO. For me, I prefer the SkyS. Please share vids and pics when you build/fly them.
AJ
Last edited by ajbaker; Jun 03, 2010 at 12:42 AM. Reason: Add comment
Old Jun 03, 2010, 12:43 AM
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Another Clone


Anyone fly the Clouds Fly/Floater Jet from HK? How do you like it compared to the SkyS?
AJ
Old Jun 03, 2010, 03:24 AM
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Quote:
Originally Posted by ajbaker View Post
Anyone fly the Clouds Fly/Floater Jet from HK? How do you like it compared to the SkyS?
AJ
AJ, I have been following this tread with interest.
As I know you fly both the CF and SS (plus many others), I'm interested to hear your views.
The CF is my first and (so far) only plane.
From what I've read here, the SS may suit me better due to availability of parts.
I have a trendency to crash a lot.
Having said that, Banana Hobbies seems to discriminate against Indonesia - the last time I checked they wouldn't ship to me.
I'd be interested to know if the SS (or clone) and parts, are available elsewhere.
Cheers, Peter


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