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CEF Profile Scale Speed 2015!

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Re: CEF Profile Scale Speed 2015!

Post  roddie on Mon Sep 21, 2015 8:31 am

Hi Jim, Have you thought of using a little less fuel? How many cc's is getting you 23 laps? The leaning-out (speeding-up) of the engine will come sooner in the flight; preferably (I would think..) toward the last few laps. Personally.. I'd rather turn 16 or 17 laps at 50+ mph.. than 23!
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Re: CEF Profile Scale Speed 2015!

Post  modelbuilder49 on Mon Sep 21, 2015 10:13 am

roddie wrote:Hi Jim, Have you thought of using a little less fuel? How many cc's is getting you 23 laps? The leaning-out (speeding-up) of the engine will come sooner in the flight; preferably (I would think..) toward the last few laps. Personally.. I'd rather turn 16 or 17 laps at 50+ mph.. than 23!
Greetings Roddie!  For the purpose of the example, I was using a Black Widow with its stock tank and just filling it up Smile.  As silly as this may sound, I honestly never thought about that, short tanking, that is  Huh... !!  It's a great idea!  Thanks, I'll give a shot Very Happy !!

Jim
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Re: CEF Profile Scale Speed 2015!

Post  roddie on Mon Sep 21, 2015 10:42 am

modelbuilder49 wrote:
roddie wrote:Hi Jim, Have you thought of using a little less fuel? How many cc's is getting you 23 laps? The leaning-out (speeding-up) of the engine will come sooner in the flight; preferably (I would think..) toward the last few laps. Personally.. I'd rather turn 16 or 17 laps at 50+ mph.. than 23!
Greetings Roddie!  For the purpose of the example, I was using a Black Widow with its stock tank and just filling it up Smile.  As silly as this may sound, I honestly never thought about that, short tanking, that is  Huh... !!  It's a great idea!  Thanks, I'll give a shot Very Happy !!

Jim

If you don't already have one Jim; a cc-graduated syringe for fueling is very helpful. I believe that some contestants were easily getting their laps in on 5cc's. (Babe Bee tank) with laps to spare.. The APC 4" props add instant performance.. I bought (x3) 4.75" x 4's from Tower Hobbies. I didn't get tach #'s.. but there was a marked gain in rpm's over a Cox black 5 x 4 using Sig's 1/2A 25% nitro blend. If you haven't tried that prop yet, you could see a lot more speed at less laps on a full tank. Your Black Widow would like that prop!
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Re: CEF Profile Scale Speed 2015!

Post  modelbuilder49 on Mon Sep 21, 2015 5:45 pm

[/quote]If you don't already have one Jim; a cc-graduated syringe for fueling is very helpful. I believe that some contestants were easily getting their laps in on 5cc's. (Babe Bee tank) with laps to spare. The APC 4" props add instant performance.. I bought (x3) 4.75" x 4's from Tower Hobbies. I didn't get tach #'s.. but there was a marked gain in rpm's over a Cox black 5 x 4 using Sig's 1/2A 25% nitro blend. If you haven't tried that prop yet, you could see a lot more speed at less laps on a full tank. Your Black Widow would like that prop!  [/quote]

I have a syringe but it's a 2oz so I may have to invest in getting a smaller one from somewhere Neutral .  Well, I bought a selection of the APC props, but I didn't try the 4.75's yet because while the engine would definitely increase rpm I was concerned about the overall thrust and speed deteriorating Huh...  You see what I'm saying? Huh...  For example, a 2" or 3" dia prop with say 3" pitch would probably rev like crazy but would there be sufficient thrust for a plane with a 15" wingspan Huh...  What effect will weight have on speed and handling weighing in at say 9 oz? Huh...  7 oz? Huh...  5 oz? Huh...  I know what the Cox 5x3 will do with a 4.6 oz plane Neutral  and now an APC 5.7x3 Smile  but what about a Master Airscrew 6x4? Huh...  Experimenting is Fun!!  Very Happy

Jim
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Re: CEF Profile Scale Speed 2015!

Post  JPvelo on Mon Sep 21, 2015 5:57 pm

You want an apc 4.75x4, the fastest prop I've found by far.

Jim
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Re: CEF Profile Scale Speed 2015!

Post  ARUP on Mon Sep 21, 2015 7:17 pm

Roddie- we were using 35' lines (handle to ~center of model) and standard 2 bladed black Cox props. The lines are green fishing line. Can't remember exactly but mine are braided DuPont 'Iron Line(?)' 10lb test or some such. They are pretty draggy. You really see them bow due to air pressure. I'll have to find a way to get videos for the races!
Thanks for compliment, Getback (Eric)!
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Re: CEF Profile Scale Speed 2015!

Post  roddie on Mon Sep 21, 2015 8:08 pm

ARUP wrote:Roddie- we were using 35' lines (handle to ~center of model) and standard 2 bladed black Cox props. The lines are green fishing line. Can't remember exactly but mine are braided DuPont 'Iron Line(?)' 10lb test or some such. They are pretty draggy. You really see them bow due to air pressure. I'll have to find a way to get videos for the races!
Thanks for compliment, Getback (Eric)!

Yea.. I've heard about line-drag with synthetic braid. Apparently it gets worse if they become oil soaked. I bought 30# SpiderWire EZBraid for the 1st CEF contest. I never got the plane airborne to see how the 42' set felt. Since then I bought 15# test.. which I plan on making a 35' set with.



The 30# is .3mm dia. (.0118") and the 15# is .2mm dia. (.0079"). The 30# test was definitely overkill.. Laughing
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Re: CEF Profile Scale Speed 2015!

Post  modelbuilder49 on Tue Sep 22, 2015 9:00 am

JPvelo wrote:You want an apc 4.75x4, the fastest prop I've found by far.

Jim
Thanks for the heads up! I'll order a few!

Jim
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Re: CEF Profile Scale Speed 2015!

Post  modelbuilder49 on Tue Sep 22, 2015 9:18 am

ARUP wrote:
Yea.. I've heard about line-drag with synthetic braid. Apparently it gets worse if they become oil soaked. I bought 30# SpiderWire EZBraid for the 1st CEF contest. I never got the plane airborne to see how the 42' set felt. Since then I bought 15# test.. which I plan on making a 35' set with. The 30# is .3mm dia. (.0118") and the 15# is .2mm dia. (.0079"). The 30# test was definitely overkill.. Laughing

I read through the rules and decided I'd try this, especially since it meets the AMA calling for GSUMP  Tired w/ Coffee Read .  I miked it at several points and it averaged .0115 diameter.  I made up a set at 35' c/l to c/l and gotten in about a half dozen flights so far Smile .  It certainly is tough and I don't think it was any more draggy than my .008" cables but I haven't made a directed speed comparison as yet, either Huh...! Oh well, one more variable to take into consideration  Rolling Eyes
https://servimg.com/view/19201836/47  Very Happy


Last edited by modelbuilder49 on Tue Sep 22, 2015 9:22 am; edited 1 time in total (Reason for editing : Didn't know what I was doing with posting the image!!)
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Re: CEF Profile Scale Speed 2015!

Post  getback on Tue Sep 22, 2015 11:09 am

do the props from towers fit on the cox 049 engines or do they need an adaptor ? http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHMK2&P=7 Thanks , Eric
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Re: CEF Profile Scale Speed 2015!

Post  roddie on Tue Sep 22, 2015 2:34 pm

getback wrote:do the props from towers fit on the cox 049 engines or do they need an adaptor ?   http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHMK2&P=7 Thanks , Eric

They need a bushing to fit the Cox .049's 5-40 prop-screw Eric. I believe that Ken Cook knows where to find them.
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Re: CEF Profile Scale Speed 2015!

Post  Ken Cook on Tue Sep 22, 2015 3:58 pm

I made the adapter over a friends house. I passed my adapter onto Mike Parkin who made them a lot faster and in more quantity then I could produce them. Mike was responsible for the aluminum TD carb bodies that he was making and selling on Ebay. Mike went under the name I believe which was Ridenfligh. I haven't seen anything from Mike listed on Ebay in months. I really need to get in touch with him. Not all APC props have the same relief in the back of the prop. However, I designed the adapter to work with the plastic bushing that comes with the props. They're a direct fit without the plastic bushing for several and from memory: 5x3 6x2 5.5x2 . The plastic bushing is required when you get into the 4.4x2 4.25 x 3.75 4.2 x 4 and so on. If you use a short piece of tubing and place it on the thread of the screw, you can screw the prop screw into the prop and spin the entire assembly onto the engine. I did it for years and still do it. It works fine. The only reason I designed the bushing was to not only and 100% center the prop but for the ease of swapping a prop in 1/2A combat. Every second your plane is airborne is 1 point. It's critical not to be futzing with your equipment and having a fast pitman. That's where my son comes into play.
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Re: CEF Profile Scale Speed 2015!

Post  ARUP on Tue Sep 22, 2015 9:57 pm

I started drawing plans for a new racer! It is the Lawrence Institute of Technology's 1949 G-1. The reason I picked it is it is a 'pusher' design and it has twin booms for the tail. Now, when the engine quits I won't worry about broken prop when landing in grass! This racer has tandem wheels so that will be less 'draggy' than the tricycle gear set-up the next year. So far the dimensions are 15" wingspan and 16 5/8" length.
Question: does Cox make a reverse rotation spring starter? Hand flipping is a good way to get them running 'the wrong way' but if the special spring is available that would be great! Thnx!
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Re: CEF Profile Scale Speed 2015!

Post  JPvelo on Tue Sep 22, 2015 10:50 pm

ARUP wrote:
Question:  does Cox make a reverse rotation spring starter? Hand flipping is a good way to get them running 'the wrong way' but if the special spring is available that would be great! Thnx!

http://coxengines.ca/cox-.049-snap-starter-spring-cam-hex-lh.html
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Re: CEF Profile Scale Speed 2015!

Post  ARUP on Thu Sep 24, 2015 7:02 am

Thanks for the link! I made my purchase(s). I bought a few props and a couple of engines. Anybody know where to source diesel fuel? Are diesel-ized Cox engines legal? Popcorn They can swing bigger props.
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Re: CEF Profile Scale Speed 2015!

Post  getback on Thu Sep 24, 2015 7:58 am

Check out this thread and there are others here too https://www.coxengineforum.com/t7726-diesel-or-glow-head?highlight=diesel+fuel
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Re: CEF Profile Scale Speed 2015!

Post  ARUP on Fri Sep 25, 2015 7:20 pm

Thanks for the link! If the Teflon disc heads are no good then are the MECOA ones good to use? I would like to try diesel at least once before I pass into oblivion or Heaven... whichever comes first. lol!
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Re: CEF Profile Scale Speed 2015!

Post  Oldenginerod on Fri Sep 25, 2015 10:35 pm

Diesels can be fun but can also be really frustrating. I've used plenty of them but never a Cox diesel conversion, so I can't vouch for the different heads which are available, but weighing up the stories I've heard about the ones with the Teflon disc, I'd be trying the MECOA (RJL) unit.

Rod.
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Re: CEF Profile Scale Speed 2015!

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