CEF Profile Scale Speed 2015!

[/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 .  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  You see what I'm saying?  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  What effect will weight have on speed and handling weighing in at say 9 oz?  7 oz?  5 oz?  I know what the Cox 5x3 will do with a 4.6 oz plane  and now an APC 5.7x3  but what about a Master Airscrew 6x4?  Experimenting is Fun!!  

Jim

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

Jim

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)!

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

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..

I read through the rules and decided I'd try this, especially since it meets the AMA calling for GSUMP   .  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 .  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 ! Oh well, one more variable to take into consideration  
https://servimg.com/view/19201836/47  

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

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.

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!

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? They can swing bigger props.

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

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.

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.