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RE: Props-More Myths Busted - 12/30/2006 3:47:33 AM   
RVM


 

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Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		How do you modify it?

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       Post #: 101

RE: Props-More Myths Busted - 12/30/2006 4:14:11 AM   
blw



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From: Auburn, AL, USA
Status: offline 		Myway,

You may be right most of the time, but not always. If you don't add the aerodynamics of the plane behind the prop you will run the chance of being wrong. Mostly, it is the cowl/cheek shapes that have effect. For instance, I pushed a buddy of mine to use an APC prop on his Great Planes RV-4 kit. He did and also used a MA prop. It flew much better with the MA. That RV-4 has a large and unusual shaped cowl, and that is probably what changed things on that plane. I had watched that same engine fly another plane using APC props and just assumed that it was what he needed on his new kit. I was wrong.

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       Post #: 102

RE: Props-More Myths Busted - 12/30/2006 6:56:16 AM   
Flyboy Dave



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quote:

ORIGINAL: RVM

How do you modify it?


Most wood props do not have the super sharp (and dangerous) edges the plastic cast
props have. The thickness of the edges of the wood props add to the durability, strength,
and longivity of the wood props, not to mention cracking and warping from blades that
are too thin at the edges.

Wood props are very strong when it comes to centrifical forces, but will be damaged with
even a minimal prop strike. This is another reason extra material is left on the edges of
most wooden props.

You can modify wood props by sharpening the edges, and extra performance can be extracted
from them in this manner. When the wood Zingers were used in pylon racing, it was the modeler
who best modified his prop that won the race.

The tips of wood props can be modified as well. Keep in mind....the total of aero-modelers
that are involved in serious racing are probably about 1% of total r/c fliers. This is why the
comparisons between racing propellors and sport propellors are just about the same as the
difference between outboard motorboat users. Out of a hundred motorboaters, you would be
hard pressed to find a single one that could name a performance propellor, much less tell you
anything about them.

FBD.



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       Post #: 103

RE: Props-More Myths Busted - 12/30/2006 2:33:30 PM   
downunder



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quote:

ORIGINAL: Flyboy Dave
Wood props are very strong when it comes to centrifical forces, but will be damaged with
even a minimal prop strike.

The only prop I use for CL stunt with my larger (51-61) engines is the Zinger 12x5 and the engines are set for about 8000 revs on launch. A couple of times I've tried for a slightly too much downwind launch and the wind has lifted the tail up on release. Naturally the prop hit the ground (grass field) but all it did was stop the engine. No damage whatsoever to the prop. I was quite amazed . I can only guess it was because there was no forward speed to bend the prop backwards.


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       Post #: 104

RE: Props-More Myths Busted - 12/30/2006 2:45:17 PM   
buzzard bait


 

Posts: 1018
Joined: 1/1/2003
From: Ithaca, NY, USA
Status: offline 		My impression is that there is some useful room between super sharp and the school-ruler edges on the Zingers. I'll be playing with some modified props next summer.

I have noticed that Rev-Ups break easily with a chicken stick--their edges are not as sharp as APCs, but much sharper than Zingers, so you are pushing on a thin piece of wood. Now I either use an electric starter or a gloved hand with Rev-Ups. I'm sure I'll have to do the same with modified Zingers. Also, I think it's much more important to thin toward the tips than closer to the root, because of course the blades move a lot faster there. I'm inclined to thin only the outer 1/2 of the blade to keep it strong nearer the root.

Yes, prop strikes are a no-no. I test new planes with MAs.

Jim

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       Post #: 105

RE: Props-More Myths Busted - 12/30/2006 3:14:35 PM   
DarZeelon



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quote:

ORIGINAL: buzzard bait

I have noticed that Rev-Ups break easily with a chicken stick



Jim,


This is why I don't own, or use a 'chicken stick'... I have an electric Sullivan starter, but only lend it out...

I hand start all my engines, by back-flipping against compression.
My fingers are out of the blade's way when it flies back under power.

That way, even if it is a 'meat-grinder' APC, I only touch the round (I clean the props to remove the 'deadly' casting slag) leading edge and never the sharp trailing edge.


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       Post #: 106

RE: Props-More Myths Busted - 12/31/2006 6:31:36 PM   
Flyboy Dave



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From: San Bernardino County, CA, USA
Status: online 		Anyone that thinks APC props sre so superior to say, the regular Zingers can do this
simple test....take a 60 size plane/engine combo and fly it with a 12-6 Zinger, and then
with a 12-6 APC....

....you'll find out in a hurry that the APC is not better than the Zinger in any way, shape, or form.

That will take care of the "APC Internet Myth" in a hurry.

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       Post #: 107

RE: Props-More Myths Busted - 1/1/2007 1:18:03 PM   
speedster 1919



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Status: offline 		Thats a great comparison Dave. I will be going to our numb thumbs Jan 1 st outing at field and Just replaced the prop on Tower 75 from a 12x7 MAS K series to a 12x8 MAS S2 scimitar to see how it will perform on a JOSS STICK 108 that is not underpowered with the Tower 75. I might also slap on a 11x7 and 12x7 3 blade for comparison. Going to be windy............The Tower muffler wouldn't work with wide fuselage so I bolted on a Super Tigre S90 adjustable bullet muffler (not silent type) a little filing and gray RTV sealant. I now call it ---------
SUPER TOWER ENGINE.........

< Message edited by speedster 1919 -- 1/1/2007 1:25:34 PM >

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       Post #: 108

RE: Props-More Myths Busted - 1/6/2007 4:34:39 AM   
Flyboy Dave



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Status: online 		....it's a darned good thing I brought a big lunch....

....it's gonna be awhile till someone shows the "big comparison".

Take another look at this video while your waiting....count how many seconds it takes from
the time he guns the engine (not even full throttle) till the time the plane takes off.
This is with a mediocre 12-6 Zinger....bone stock. This is a fairly good sized plane with a
not very big wing....51".

http://www.rcuvideos.com/view_video.php?viewkey=4175610e5a00c1e221eb

FBD.

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An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
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       Post #: 109

RE: Props-More Myths Busted - 1/6/2007 5:12:02 AM   
blw



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Status: offline 		I dunno Dave. Not trying to argue with you or anybody, but I tried a Zinger, a Master Airscrew, and an APC 11x7 on a plane to see which performed better. It was the APC by a long shot. Like I said earlier, I think it depends on what you put it on, both engine and shape of the airplane. I'm sure that Zingers are good props for a lot of planes/engines but not on that plane of mine.

That was a good video.

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       Post #: 110

RE: Props-More Myths Busted - 1/6/2007 5:52:12 AM   
Flyboy Dave



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Status: online 		....listen closely to the video....he advanced the throttle 5 times. The plane launched in one
second at about just over half throttle.

...I'm impressed.

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       Post #: 111

RE: Props-More Myths Busted - 1/6/2007 7:18:02 PM   
B.L.E.


 

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quote:

ORIGINAL: Flyboy Dave

....listen closely to the video....he advanced the throttle 5 times. The plane launched in one
second at about just over half throttle.

...I'm impressed.


Gee Dave, I got an electric plane that takes off like a flushed quail and then will go verticle to the moon and it has a APC prop on it, and that proves what? If you have any 15x10 Zingers to spare, send them to me and I'll gladly see how they do.

With glow engines, it's not just about prop efficiency, it's the combined efficiency of the whole propulsion system that counts. A prop that is only mediocre in efficiency but lets the engine rev to its power peak may outperform an excellent prop that overloads the engine. Since almost all glow engines direct drive the prop, the best prop is a tradeoff between prop efficiency and the engine's ability to rev high enough to make horsepower.
Just out of curiosity, how did the rpm of the Zinger prop compare to the APC prop while running on the ground. Are they both loading the engine the same? I'm not doubting that the Zinger gave better results but it may not be because the prop is more efficient.

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RE: Props-More Myths Busted - 1/7/2007 2:56:48 AM   
Flyboy Dave



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From: San Bernardino County, CA, USA
Status: online 		....would you like an apple, or an orange with that ?

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An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
"Old Age, and Treachery will overcome youth and skill".
Revver Bro #4.

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       Post #: 113

RE: Props-More Myths Busted - 1/8/2007 2:10:21 AM   
Sport_Pilot



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quote:

ORIGINAL: blw

I dunno Dave. Not trying to argue with you or anybody, but I tried a Zinger, a Master Airscrew, and an APC 11x7 on a plane to see which performed better. It was the APC by a long shot. Like I said earlier, I think it depends on what you put it on, both engine and shape of the airplane. I'm sure that Zingers are good props for a lot of planes/engines but not on that plane of mine.

That was a good video.


You are comparing apples and oranges. APC props are said to the have true pitch (I assume this means that the pitch is compensated for the airfoils zero lift AOA) and the others are pitched to the airfoils center line. That means that for the same designated pitch the APC's would have less pitch. You need to try several prop pitch and size of several brands to be sure of the same one. I recently found that a Top Flite 11-4 is pretty close to an APC 11-5 for an example.

< Message edited by Sport_Pilot -- 1/8/2007 1:16:07 PM >

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