RE: Props-More Myths Busted  
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RE: Props-More Myths Busted - 3/25/2007 6:37:41 AM   
Flyboy Dave



Posts: 13460
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: online 		....I see another two weeks (or should I say two weak) has passed and nobody has
a report....or a single clue about the big bad APC props are superior to the common
Master Airscrew or the old fashioned wooden Zinger propellers.

FBD.



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An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
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RE: Props-More Myths Busted - 3/25/2007 8:21:28 AM   
TCrafty



Posts: 450
Joined: 2/25/2006
From: Lakeland, FL, USA
Status: online 		Quick question (maybe I should make a new post?) but with those offset-boring your APC props to true them up, how do you do it with precision? I've got a reamer but it's not selective on which side it takes material from. Do you put it in a drill press? If so, how do you know that YOU are dead on?

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Club Saito Member #521

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RE: Props-More Myths Busted - 3/25/2007 3:17:13 PM   
bob27s



Posts: 4831
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		What I do is open up the "Shaft" hole slightly over size.

Then, I use a metal centering spacer (Similar to what is used on the Tru-Turn spinner backplates). This is inserted into the counter-bore on the back side of the hub - that is indeed tooled and true.

The bushings are something common for the Q-500 and QM40 crowd, so 5/16 and 1/4" sizes are not hard to get.
http://www.darrolcady.com/Propellers/propellers.htm


If you have any concerns about centering the prop, this is how to correct the situation.

Bob


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Jett Engineering - Engine Mfg Support Forum Host

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       Post #: 228

RE: Props-More Myths Busted - 3/25/2007 4:59:01 PM   
rc-sport



Posts: 2901
Joined: 4/15/2002
From: Highwood, IL, USA
Status: offline 		I have been a big fan of APC props ever since I put one on my Rascal 40. It had a Saito 56 in it and I always had a Zinger prop on it (I do like the look of a wood prop). After I installed the APC I noticed a big increase in performance, more speed, more pull through loops etc. From then on I have always used APC except on my Stinson, you can't put APC on that beauty, has to be wood. Recently I replaced an 15-6 APC prop on my Skybolt/Saito 120 with a Graupner 14-8 3 blade. I did this for 2 reasons, 1 to get more ground clearance and more important to me, slow the plane down. I always heard 3 blades are less efficient blah blah blah. So can someone tell me why my Skybolt is now even faster, not just a little but alot faster. What happened to the loss of efficiency? The motor had many hours on it already, the fuel is the same, the only difference is the prop and of course the spinner. I have since been using Graupner 2 and 3 blade props on my planes because the look a lot better than the APC's.

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Damn gravity!!!

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       Post #: 229

RE: Props-More Myths Busted - 3/25/2007 5:41:06 PM   
gkamysz


 

Posts: 1590
Joined: 6/24/2003
From: Crystal Lake, IL, USA
Status: offline 		You went from a 6" pitch to an 8" pitch. Theoretically it could go 30% faster. Look up some info on pitch speed. I wouldn't go less than 6" pitch. It will waste a lot of fuel. Just throttle back.

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Greg

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RE: Props-More Myths Busted - 3/25/2007 5:46:19 PM   
rc-sport



Posts: 2901
Joined: 4/15/2002
From: Highwood, IL, USA
Status: offline 		Actually I meant 14-7. Rule of thumb with three blades is you go down 1 in prop diameter and up 1 in pitch, so that's what I did.

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Damn gravity!!!

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       Post #: 231

RE: Props-More Myths Busted - 3/25/2007 6:16:48 PM   
DarZeelon



Posts: 7096
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline 		RC-Sport,


There is no such thing as gravity.

It is just that the Earth sucks...

--------------------

That rule-of-thumb doesn't really work as a rule... It only applies to a small prop range of about 11" in diameter.
And it is either reduce 1" from the diameter, or reduce 2" from the pitch...

Use the Reivers PropPower calculator. You can use it freely, or download it from the MVVS NL web site. Go to 'Propellers'.

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MVVS - Jett - Nelson - Bolly - Mejzlik

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       Post #: 232

RE: Props-More Myths Busted - 3/25/2007 7:58:52 PM   
rc-sport



Posts: 2901
Joined: 4/15/2002
From: Highwood, IL, USA
Status: offline 		Ahhhhhhh....now I get it

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Damn gravity!!!

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       Post #: 233

RE: Props-More Myths Busted - 3/26/2007 2:56:11 AM   
blw



Posts: 4569
Joined: 3/15/2004
From: Auburn, AL, USA
Status: offline 		Rc-sport- You will find that some people say that any prop other than a 2 bladed one is more inefficient. Period. This is generally an untrue assumption for many reasons. The biggest reason is that there are too many other variables to consider, and a blanket statement like that is wrong most of the time. True, you can select an inefficient 3 bladed prop, but people do that a lot with 2 bladed ones too and never realize it. The braking action of a 3 bladed prop is nice to have at times.

Just looking at the tips of Zinger and Master Airscrew props shows a basic inefficiency of the design over more elliptically shaped props. These props will suffer various amounts of tip vortices and may have undesirable tip stall characteristics. The most efficient tip shape is close to elliptical most of the time which is in contrast to the Zingers and MAs.

By the way, I got to look over a carbon fiber Bolly 3 bladed prop the other day. The size was something like 32x12. I was impressed with the undercamber near the root, and twist down the span. It looked like excellent work.

editted for grammar

< Message edited by blw -- 3/26/2007 2:57:24 AM >

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RE: Props-More Myths Busted - 3/28/2007 3:13:17 AM   
Flyboy Dave



Posts: 13460
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: online
quote:

ORIGINAL: blw

Just looking at the tips of Zinger and Master Airscrew props shows a basic inefficiency of the design over more elliptically shaped props. These props will suffer various amounts of tip vortices and may have undesirable tip stall characteristics. The most efficient tip shape is close to elliptical most of the time which is in contrast to the Zingers and MAs.



blw.....you just created another Internet myth....

FBD.


_____________________________

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 #: 235

RE: Props-More Myths Busted - 3/28/2007 3:19:40 AM   
blw



Posts: 4569
Joined: 3/15/2004
From: Auburn, AL, USA
Status: offline 		Nah, not me.



editted for grammar


< Message edited by blw -- 3/28/2007 3:20:23 AM >

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The ultimate responsibility of pilots is to fulfill the dreams of the countless millions who can only stare skyward...and wish.

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       Post #: 236

RE: Props-More Myths Busted - 3/28/2007 11:52:05 AM   
speedster 1919



Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		GO GET HIM FLYBOY DAVE _ HE JUST BLASTED OUR BELOVED MAS AND ZINGER PROPS.

The only thing I will give the 3 balde nay-sayers is the 3 blade selection is narrow and will not cover every size of prop. 3D being the main one.

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Hey Buddy -That was the most spectacular crash I've ever seen , That rolling cart wheel with parts slinging out was cool...

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       Post #: 237

RE: Props-More Myths Busted - 3/28/2007 1:43:06 PM   
Flyboy Dave



Posts: 13460
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: online 		I going to assume our friend blw is dropping this load on purpose....heh heh.

Propeller vortices are caused by condensation of the water in the air around fast moving
propeller tips in high moisture (humidity) areas like jungles and around aircraft carriers
at sea, and have nothing to do with the efficiency of the propeller.

"Tip stalls" concern wings....not propellers....so this is a non-issue.

The tips of the APC props are designed for less "lift" (thrust) which produces less noise.
They are quieter, but not more effecient at the tips than a standard propeller.

Let the myth busting continue.....

FBD.

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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.

(in reply to speedster 1919)
       Post #: 238

RE: Props-More Myths Busted - 3/28/2007 3:35:07 PM   
Sport_Pilot



Posts: 7727
Joined: 1/21/2002
From: Acworth, GA, USA
Status: offline 		Tip stall? On a prop? Not aware that round tips are better than square ones. Full scale props are usually squared off.

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RE: Props-More Myths Busted - 3/28/2007 6:50:18 PM   
Cyberwolf



Posts: 1045
Joined: 1/10/2004
From: Blackfoot , ID, USA
Status: offline 		I sat here all morning and read this whole thread and I too want to see the results Jett comes up with ,but myself I have a good Idea of what they will be.The APC will win hands down .
As far as pusher props go I don't know a thing about them in daves case maybe the APC, pusher props are not as good as the zingers .But as far as pull props go I have done my own testing and in the air is what counts and the zingers won't stay with the APC's .
The former owner of the LHS did some testing wasn't nothing fancy but he thought the wood props was the best thing since sex becuase they would pull