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Cox .049 max RPM?

Old 02-14-2013, 09:03 PM
  #26  
combatpigg
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Default RE: Cox .049 max RPM?

APC usually doesn't make a "specialty" prop that doesn't have any real world application.
The 4.2x4 doesn't really fit into competition anywhere, except for maybe some 1/2A control line racing event.
It's not enough prop for AMA 1/2A pylon planes.
It's just about the perfect prop if you build small, thin & light enough for RC speed. I hope these props never go away, but I sure don't see much evidence that they're even getting used much by the guys at this forum.
Jeremy Chinn is the guy who built the most serious and "pure" 1/2A Cox TD.049 speed project that I know of.
He called it "Caliente" and it did something like 123 mph. It had a high aspect wing with swoopy tips IIRC...might have been a V-tail or T-tail too..?
IIRC it was piped....[well, it HAD to be piped to be able to hit 123 mph if I had to guess how he did it].
That's all I remember about it...but that effort has to be a prime example of what mick1404 was looking for in this thread.
I think you could block off 1 of the exhaust ports and turn it into a transfer port. Raise the other exhaust port to acheive 180 degrees of exhaust duration and adapt a G&Z .061 full wave pipe.
Begin testing with a cut down 4.2x4 prop and 30% oil and the lowest compression that will allow it to run and hit resonance without getting hot. Gradually increase compression and load until you see severe plug damage, pitting on the piston and head ....of course you'll probably blow out moving parts regardless of how careful you try to be..but that's how I'll wager you get a Cox TD engine to survive as a piped speed engine long enough to make some recorded passes.
Jeremy would be the guy to ask about how he did it though.
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Old 02-15-2013, 05:59 AM
  #27  
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Default RE: Cox .049 max RPM?

They are using the APC electric 4.75-4.75" prop for the mouse race reedy motors.  They would likely burst in your face on a TD or better.  Apparently they are faster and give more laps than more conventional props.  Maybe a fiberglass copy would be ok for a TD or Norvel or even Fora for a speed plane.
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Old 02-15-2013, 11:39 AM
  #28  
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Default RE: Cox .049 max RPM?

I'll bet they are efficient props, no doubt.

Mouse racers are more draggy than a pure CL speed design and both are far more draggy than a clean RC design due to the lines. So the 4.75x4.75 might be a good prop for some applications in RC but it looks like too much shaft load to me for all out speed, especially for the Cyclon/Profi engine crowd, those engines are timed for peak power in the 35-36k range. A 4.125x5 prop dragged my Profi .061 down to 32k static, although it still went like a raped ape in the air. In general, a clean RC speed design on the same motor as a much smaller CL speed model should be able to handle a little less diameter and more pitch due to the absence of line drag which is enormous (hence the long funny wings on F2A models..).

Evidence of this can be found by comparing the AMA 1/2A CL speed records to some of sport speed 1/2A numbers we've seen. The best numbers I've seen for 1/2A Cl speed are 135-140mph - that is for top competitors running the engines hard, tweaking props, bla bla bla, and on a good day. Whereas most of us could screw a Cyclon/Fora/Profi .049 to the front of a small clean RC speed model and achieve these speeds daily with relatively little effort no tuned pipes, broken engines etc. Okay, it's not a total cake walk but it is easily within grasp.

Same for D speed - 10cc RC models have topped 240mph, but you'll never see that from a .65 ukie speed model.
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Old 02-15-2013, 12:19 PM
  #29  
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Default RE: Cox .049 max RPM?

As soon as a control line model record hits 200 mph, the AMA changes the line sizes to slow them down and presumably to make them safer. A high pitch prop may not rev up on the ground but will unload muuuch more in the air.  Combat planes always use a low pitch prop for good acceleration and so the motors don't overheat.  For speed high pitch is usually the way to go.  A square dia/pitch like 5-5 , 6-6, 8-8 etc. usually gives the best speed on a clean plane.
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Old 02-15-2013, 12:48 PM
  #30  
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Default RE: Cox .049 max RPM?

The E speed props that I've found a use for work on some small engines real good. They are so thin that making them out of carbon would take some skill I'll bet. They look like a lot of work to copy.
In order to get the piped G&Z .061 to run best I used to scrape the blades of the 4.2x4 down to what you would call "E prop" thickness. There is a very fine line you can not cross [load wise] with high timed engines or they just wont perform. Right on the invisible line and they will burn themselves up. It's always better to be 1/2 step below the line [in terms of load] if you just want to have fun
I just tried to look up the AMA 1/2A speed record..but got nowhere with my slow dial up.
For years a guy named Bob Fogg held 1/2A records, then maybe 6 years ago a guy named Carl Dodge grabbed the record.
I believe it is over 150 mph now.
The FAI [world] record is for .061s and it would be interesting to know where it stands now, too.
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Old 02-15-2013, 01:22 PM
  #31  
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Default RE: Cox .049 max RPM?

I think Carl went about 140 this year with a CS.  It was pretty hot out. Carl won the FAI F2A class at the World Champs a few years ago.
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Old 02-15-2013, 02:10 PM
  #32  
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Default RE: Cox .049 max RPM?

All I could find were regional records on the NASS site - 140.6 by Carl Dodge:

DIV. 3 - MIDWEST (Wisconsin, Illinois, Michigan,
Indiana, Ohio, Kentucky, Ontario)
½ A Speed 140.63 Carl Dodge Dayton, OH 9/11/05

Not sure what the all time record is.

I'll bet he worked wayyyy harder to achieve this and can do so less consistently than achieving the same on a hot open exhaust .049 on an RC model. I think 150 is achievable and maybe a bit more.

The guys flying FAI straight line RC speed overseas run way more than square props - 7.5x13, 8x12, that sort of thing on 10cc, or up to 9x10 on the slightly slower models (as in 175-200 or so..).

Check out the props f3d uses on his Profi .40 twin speed model: (!)

"Doppelprinz speed airplane with 2x 6,5ccm MB Profi pylon engines, speed 240 mph, propeller 6.2x9.5; 2200 gramm weight, wingspan 112 cm ; 30100 rpm on the ground"

Watch it on Youtube - the engine note must drill holes through the eardrums.

You can get away with more "oversquareness" on a clean RC design because the lower drag without lines allows higher airspeed thus you can "gear up" more - less disc area/more pitch. All depends on your peak hp rpm and the limiting speed for the hp and drag.
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Old 02-15-2013, 04:03 PM
  #33  
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Default RE: Cox .049 max RPM?

[link]http://home.earthlink.net/~lloydfour/speed.htm#1/2a speed[/link]

1/2 A Speed engine size .05 ci AMA record speed 156.42 mph

This class allows unrestricted airplane designs. They are full-bodied and streamlined to reduce drag. The model design may be a conventional or an asymmetrical design. The current trend is to build asymmetrical models. Speed models do not have landing gear to eliminate drag. They use a takeoff dolly and land on the belly of the fuselage. Flight control is usually via a mono line system.
The engine of choice for 1/2A at the moment is the CS .049. Visit the CS web site for the engine specs. 1/2A Speed is one of the speed classes that allows unrestricted exhausted systems. That means you can use a full wave tune pipe. Fuel is also unrestricted. Think of it, 80% nitromethane and 20 % oil. It's quite exciting!

Here's a picture of Charlie Leggs' 1/2A Speed models, then and now. 1953 - 1998. The speed has climbed from 90 mph on 35 foot lines to 155 mph on 47 foot lines.
top

[This is news to me...156 mph..!][X(]
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Old 02-15-2013, 05:24 PM
  #34  
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Default RE: Cox .049 max RPM?


ORIGINAL: aspeed

They are using the APC electric 4.75-4.75'' prop for the mouse race reedy motors. They would likely burst in your face on a TD or better. Apparently they are faster and give more laps than more conventional props. Maybe a fiberglass copy would be ok for a TD or Norvel or even Fora for a speed plane.
The aforementioned Caliente made a big jump in speed when Jeremy switched to APC electric props and rotated the cylinder to be in front of the wing fillet. He and I talked about it on the phone while he was building the 2nd Caliente and I was happy the suggestions worked.

APC offers a lot of choices in 4 and 5" props, enough that just about any 1/2 engine can be made to work where it is at it's best.

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Old 02-15-2013, 05:55 PM
  #35  
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Default RE: Cox .049 max RPM?

I think they are limited to 10% nitro in 1/2A now, just recently.  Don't quote me on it. Charlie makes his own motors.
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Old 11-25-2019, 04:11 AM
  #36  
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Update

NANO X / Tee Dee .051 / Profi .8cc Tuned Pipe 25" span / 75 sq. in. / 8.2oz RTF
Peak 33,100 rpm / 141 mph pitch speed reached.
HQ carbon 4x4.5 prop Idle prior to launch idle 7,016 rpm
Static peak 25.8k rpm / 106w / 7.4oz thrust / 110 mph pitch speed
Profi Tune Pipe used MRP set at 7.5"

Last edited by Pond Skipper; 11-25-2019 at 04:15 AM.
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