RE: Props-More Myths Busted  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> RE: Props-More Myths Busted
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RE: Props-More Myths Busted - 8/23/2007 11:29:18 AM   
speedster 1919



Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		Well I ordered a 9x6 4 blade APC for further testing this weekend. I hope it shows up in time. This should overprop a 45 Super Dupper Tigre. (smallest they make)----Oh but wait--- this prop should be so grossly inefficent the 45 Tigre shouldn't even know its bolted up !!!!!!!!!!!!!

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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...

(in reply to jaka)
       Post #: 401

RE: Props-More Myths Busted - 8/23/2007 12:53:29 PM   
gkamysz


 

Posts: 1603
Joined: 6/24/2003
From: Crystal Lake, IL, USA
Status: offline
quote:

ORIGINAL: speedster 1919

Well I ordered a 9x6 4 blade APC for further testing this weekend. I hope it shows up in time. This should overprop a 45 Super Dupper Tigre. (smallest they make)----Oh but wait--- this prop should be so grossly inefficent the 45 Tigre shouldn't even know its bolted up !!!!!!!!!!!!!


Trust me your engine will know it's bolted up. The airplane will know it too. Efficiency is thrust power out over shaft power in. It really has nothing to do with how it loads the engine.

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Greg

(in reply to speedster 1919)
       Post #: 402

RE: Props-More Myths Busted - 10/19/2007 4:55:55 AM   
Flyboy Dave



Posts: 13468
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: offline 		....It looks like the APC "victory parade" is not in the near forseeable future.

....no surprise, huh ?

FBD.

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An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
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(in reply to gkamysz)
       Post #: 403

RE: Props-More Myths Busted - 10/21/2007 4:59:44 AM   
bigben2k


 

Posts: 18
Joined: 10/18/2007
From: Tomball, TX, USA
Status: offline 		Quite a fabulous debate, just finished reading it!

I'm building a PBY Catalina, 1:10 scale , and a 3 blade prop is a must: 2 blade isn't even a consideration.

The hardest part to understand, for those struggling to follow, is how different props can be best for different applications. The hardest part to explain otherwise, is how a static test is different that a dynamic one, and why it makes a difference.

For the first, I'll throw in a car analogy: if you ran your car with small wheels, you'd have great acceleration, for the first little bit, then later as speed increases, just about any other car would overtake you. On the other hand, if you setup your car with unusually large wheels, you'd loose the acceleration, but you'd be able to get to that higher up speed. If you want to run (and win) short races, use small wheels. I figure that the same applies to propellers.

As for static versus dynamic, I'll defer to others more knowledgeable than me.

Building a Catalina at this scale, I'm ending up with a 14 inch propeller, with 3 blade. This is scale, and I don't care how it runs, sluggish would actually be good! As it turns out though, a Master Airscrew 14x7 3-Blade G/F Nylon Propeller will probably work very nicely with the engines I'll end up with (a couple of either .61 or .90 two stroke, once I've completely ruled out going electric).

I'm learning more about propellers in this thread than I could ever pick up any other way.

< Message edited by bigben2k -- 10/21/2007 5:03:04 AM >

(in reply to Flyboy Dave)
       Post #: 404

RE: Props-More Myths Busted - 10/21/2007 5:06:24 AM   
w8ye



Posts: 17500
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: offline 		a 90 or 91 would be better with that prop

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(in reply to bigben2k)
       Post #: 405

RE: Props-More Myths Busted - 10/21/2007 6:27:03 AM   
DarZeelon



Posts: 7109
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: online
quote:

ORIGINAL: bigben2k

The hardest part to understand, for those struggling to follow, is how different props can be best for different applications. The hardest part to explain otherwise, is how a static test is different that a dynamic one, and why it makes a difference.



Big Ben,


A static thrust test is quite easy to perform... All you have to do is to connect a fish/laundry hook-scale to your plane's tail, run the engine full-bore and read the scale.

A dynamic test requires a wind tunnel...

...Or it can be done by flying your plane and subjectively seeing how it pulls at various flight speeds.


The point is the static thrust provided by the prop is realized only while the plane is in a static flight condition, or at a very low speed.

One such condition is while your 3-D model is hovering. Another is at the beginning of the take-off run.



It is very possible for a prop to pull like an ox a very low speeds, but to run out of oomph at 15 mph and to stay that way.
Another prop, with the same pitch and diameter, might seem to pull less strongly in static conditions, but as speed is gained, it accelerates the model like a drag racer.


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(in reply to bigben2k)
       Post #: 406

RE: Props-More Myths Busted - 10/21/2007 1:13:41 PM   
speedster 1919



Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		Bigben I set out too prove 3 blades aren't that inefficent and just because a prop is stamped
??x? doesn't mean it is the same performance from mft. to mft. Things like this prop will idle faster than another the same size. Static RPM is the sure test for 3D and hovering. You can throw the radar gun away. Since you have already decided your prop size you need an engine to run it comfortably. Bogged down with cause heat problems and deadsticks. Your now looking at what will run a 15x7 or 15x8 good . That rules out all .61's and .91's for the most part. Saito 100's for weight and fuel economy now start to fill the ticket fill the ticket. Better fuel economy means smaller tank and smaller size and weight. I don't think APC are as good as touted to be.

_____________________________

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

(in reply to bigben2k)
       Post #: 407

RE: Props-More Myths Busted - 10/21/2007 1:31:30 PM   
crashproof


 

Posts: 155
Joined: 1/10/2007
From: , NC, USA
Status: offline 		Hey folks I have read this from the start and have seen all the back and forth and the analysis by would be experts, which I am not. The one thing that does it for me above all else is How does my plane Fly. I have flown planes from Trainers, 4Stars, 60 size Warbirds all the way to what I fly now which is larger Warbirds. I have not tried every prop on the market, Zingers, MA, and APC and in EVERY case the APC has made my plane perform better than the others. Some will flame away with their experiences and formulas but for me that is the true test, and yes I have a box full of APC's. Good luck flying to all with whatever you use. Kevin.

(in reply to speedster 1919)
       Post #: 408

RE: Props-More Myths Busted - 10/21/2007 1:34:49 PM   
w8ye



Posts: 17500
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: offline 		If one starts looking at APC props, they are not all made the same for example compare the 12-5 & 12-6, the 14-6 & 14-8. There are more differences in these props than the pitch.

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Original AMA #31261

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       Post #: 409

RE: Props-More Myths Busted - 10/21/2007 1:47:59 PM   
da Rock



Posts: 6726
Joined: 10/11/2005
From: western, NC, USA
Status: offline
quote:

ORIGINAL: bigben2k

Building a Catalina at this scale, I'm ending up with a 14 inch propeller, with 3 blade. This is scale, and I don't care how it runs, sluggish would actually be good! As it turns out though, a Master Airscrew 14x7 3-Blade G/F Nylon Propeller will probably work very nicely with the engines I'll end up with (a couple of either .61 or .90 two stroke, once I've completely ruled out going electric).

I'm learning more about propellers in this thread than I could ever pick up any other way.


Don't worry a bit about the efficiency BS. Yeah, it's true but it's another thing that's true but of no real consequence, and especially considering what we have available.

I just noticed your mention of the 61 and 91 engines. I've been doing prop tests on an OS61FX and a couple of OS91FXs and have a couple of Master Airscrew 3bladers in the mix.

The 91s have proven to like a number of different props. And they perform equally well with about half of the props tested so far. And the 14x7(3) is one of the "best" props both 91s prefer. As you probably know, MA suggests the 14x7(3) as a prop for 1.5-1.8 engines. I almost didn't test the sucker on the 1st .91 because of that. And it turns out that prop on the 91s pulls like a bull in the air. I use it often on my Sukhoi and like I said, it's one of the best for that aerobatic model. I also use it on a P47 for obvious reasons. And also obvious is that it pulls that airplane as well as any of the favorite 2bladers.

As for the 61 and 3bladers...........
The 14" is too much for mine. It turns the 12x6(3) way too fast. And doesn't fly it's best. The 12x8(3) is a best prop on the Skybolt. And the 13x8(3) hasn't gotten a test yet.

A Catalina was an interesting airplane. I worked with a guy who flew them in WWII. He said they had one speed. It took off at that speed, cruised at that speed, and wouldn't dive much faster either. I read that they tried the airplane with stronger engines and it was only a couple mph faster. Not surprised.



(in reply to bigben2k)
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RE: Props-More Myths Busted - 10/21/2007 1:51:38 PM   
da Rock



Posts: 6726
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		BTW, I've wanted to try Graupner 3bladers but haven't found a place that sells them that I'd buy from. They look somewhat scale and have a couple that might fit in. But so far, the MAs have been so good, there hasn't been a strong desire to make an extra effort.

(in reply to da Rock)
       Post #: 411

RE: Props-More Myths Busted - 10/21/2007 1:57:13 PM   
DarZeelon



Posts: 7109
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: online 		Da Rock,


That speed was 90 mph... It was said to take-off at 90, cruise at 90 and land at 90...

One I saw flying seemed to do better than 90... Maybe there was a strong tail-wind...

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(in reply to da Rock)
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RE: Props-More Myths Busted - 10/21/2007 2:14:14 PM   
speedster 1919



Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline
quote:

If one starts looking at APC props, they are not all made the same for example compare the 12-5 & 12-6, the 14-6 & 14-8. There are more differences in these props than the pitch.

AMEN w8ye That is what I found with the supposedly scientific designed props called APC . 9" look like fat boom-a-rangs . You go down a pitch on a certain size only to find out it boggs down more than the size you came from. It is like they mis stamped the mold size. When I use MAS if I go down a pitch I get it and if I go up a pitch I get it. MAS seems to be a much more linear in size and pitch choices.

_____________________________

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

(in reply to w8ye)
       Post #: 413

RE: Props-More Myths Busted - 10/21/2007 6:47:18 PM   
bigben2k