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December-2018
Dave P.'s

"RC Tee Dee 049"



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seeking teedee 0.049 wisdom to get me sorted

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seeking teedee 0.049 wisdom to get me sorted

Post  layback209 on Sun Jul 29, 2018 1:47 am

Hey folks, I have a really good running teedee however a few nuances keep popping up that cost $s to keep fixing and have been ending flying days early. Wondering if there is anything simple i can do to improve the situation. Im using a balanced apc 6x2, sig 25% 1/2a fuel, 2 head shims, the engine is easy to tune.

It appears the vibration of the engine keeps causing the venturi and or the glow head to loosen off, cause a lean condition and wreck glow heads and or end a flight early. I have been checking and tightening these components after every flight when required as a mitigation but it is not helping much.

I dont understand why the glow head is backing off i put it on there good... my black widow / other non teedee engines don't do this (loosen off). The venturi being held in with plastic threads is one issue, if i crank it down much more it will certainly strip out. Anyone try Teflon tape to keep the venturi+nva from backing off? was also thinking of coating the glow head threads with automotive cylinder head gasket sealer (the copper stuff) or use lock tight blue....

Unfortunately getting one of the aluminum plastic replacement venturi bodies is pretty cost prohibitive once shipping + duty gets added in. maybey i should just epoxy the venturi in there..

any advice would be appreciated. I currently have the motor torn down to reset the piston ball socket.
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Re: seeking teedee 0.049 wisdom to get me sorted

Post  1/2A Nut on Sun Jul 29, 2018 7:34 am

Yessa on the plumbers teflone tape, if everything else is perfect with no other resolution.

Reducing engine vibration:
The prop Is it getting a good centering? Try a harden black oxide hex bolt rather than the
soft all thread bolt (they can flex when the spinner shifts).
Get one that has the threads stopping mid way so you spinner is not so loose.
Or buy a bullet spinner from Cox International out of Canada it centers the prop very well:
https://coxengines.ca/cox-.049-aluminium-spinner-valentine.html

You can insert fuel tube into the bored prop so you get a tight fit when the prop bolt goes
through insuring your prop is centered to reduce vibrations.

You can not use epoxy, as over time castor build up around the venturi where the
fuel flows could clog up one of the 3 small holes or particle etc.

If your ball socket is loose use a reset tool to tighten up the slop. Note if your piston
is hitting the glow plug it will cause the apparent vibrations that are rattling your
engine apart. Add a extra head gasket could help with clearance.

Small Cox Logo RC Plane Small Cox Logo July-27
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Re: seeking teedee 0.049 wisdom to get me sorted

Post  Cribbs74 on Sun Jul 29, 2018 8:14 am

Loosening heads is a sign of work hardened copper gaskets. Replace with a brand new one.

As far as vibrations go, the engine will vibrate, how is the mount and structure around it?

Mounts need to be rock solid! Prop balanced of course...
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Re: seeking teedee 0.049 wisdom to get me sorted

Post  Ken Cook on Sun Jul 29, 2018 9:36 am

I have repaired cracked carb bodies many times. I use a piece of brass tubing. I can't recall, but I believe 5/16" tubing. This provides a nice tight fit. I fit the tubing to the neck of the body. This requires a conical radius on the bottom and a bit of filing on the top. This is easier done with a lengthy piece of tubing due to being able to hold it and file it. Once it's fit as tightly as possible to the lower section of the body, make two scribe marks and cut it off filing the top. It's much better to have the neck of the tubing slightly below the factory plastic as this will allow the needle valve assembly to sit on the plastic. I then soak the part in alcohol, rough up the outside with sandpaper and apply epoxy on the outside. Hit it with heat and allow the epoxy to flow into the cracks. Press the ring on and let it sit. I then chase the threads with a 1/4-32 tap when done. It's better than new as the tubing really pinches the plastic tightly allowing you to tighten the venturi tight.

I have to ask why the 2 pitch prop? That prop is offering very little sending the engine into some fairly high rpm's which more than likely has the engine running above it's maximum torque curve. That in itself is going to cause vibrations. The TD does prefer a little load just not a overload. As Brad stated, if the piston socket has excessive play using that prop could possibly offer contact with the head.
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Re: seeking teedee 0.049 wisdom to get me sorted

Post  1/2A Nut on Sun Jul 29, 2018 12:26 pm

The APC FF prop has a well designed airfoil and makes good work of the air.
The prop is a bit beefy so the 2 pitch helps to keep the rpm up to a reasonable
level is why the FF folks like them, less torque issues on launch too. It really is
a good prop for steady fuel flow rpm kept up insures a good run. Folks should
try them more often with low weight speed planes the flight can be thrilling as
thrust is near constant through out the flight.

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Re: seeking teedee 0.049 wisdom to get me sorted

Post  fredvon4 on Sun Jul 29, 2018 2:19 pm

I have a few (9) Teedee 049/051 and always DECK the Glow heads on a granite block with 600 grit and light oil..NOW flat..I use brand new copper gaskets from Ex or Bernie...Cox or Galbreath heads NEVER loosen on my engines...Ever

I have a few of the aluminum carb bodies but find the replacement Plastic version more compliant with fewer air leaks...I like the metal versions but the nylon and rubber gaskets are iffy..IMO...too easy to distort.... I do not use any gaskets or O rings for the Plastic carb body...but I do pay strict attention to torquing the assy in place

IMO small 1/2a engines need to be squeaky clean and AIR TIGHT!...then anything for %25 to %65 Nitro with at least 20% oil
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Re: seeking teedee 0.049 wisdom to get me sorted

Post  layback209 on Mon Jul 30, 2018 12:38 pm



Looks like my piston may have been contactong the head, there was some significant slop. Depending how much I run this motor I end up re-setting it periodically. Will use some new head gaskets and possibly sand the head using a mirror I'll keep my eye out for a small slab of granite. I did that for a past glow head that had some corrosion and would not seal. It looks like the cox international ones have a machined surface to help with sealing, I can see parallel ring on it.

Wow Ken I'll have to use this tubing solution for sure on a new to me 0.09 I'm going fix up. It has a crack in the usual place. Thanks for describing the procedure. I'll use this on some of the cracked venturi bodies in my part pile to. I heard some guys were wrapping fishing line and coating with epoxy to accomplish the same goal.

Hi Cribs, the engine is mounted to a scratch build beam mount skyray I made. It seems pretty solid but the wood did squash a bit. I may need to make some thin aluminum plates at some point.
https://www.coxengineforum.com/t11381-scratch-build-skyray-with-beam-mount-for-0-049-teedee

I'm more experimenting with the prop pitch, our local guru recommended the 6x2 which echoed 1/2a nut's basis. I fly at 3500ft above sea level, so far this realy seems to help get the motor in the powerband for a good high speed flight with nice string tension. But I've only made one flight so far, my opinion may change.

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Re: seeking teedee 0.049 wisdom to get me sorted

Post  Cribbs74 on Mon Jul 30, 2018 1:29 pm

A piece of glass is a good surface to lap the head on.
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Re: seeking teedee 0.049 wisdom to get me sorted

Post  fredvon4 on Mon Jul 30, 2018 1:36 pm

Flat glass...mirror will be fine... or any fairly flat surface...600~800 grit a a bit of oil...aluminum does NOT need much working to get flat

Over kill and relatively expensive I have a 12x12x3 granite surface that is certified to .001...BUT I have only ever used to to lap crank cases and heads

http://www.grizzly.com/search/?q=(granite+AND+surface+AND+plate)+OR+(granite+OR+surface+OR+plate)
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Re: seeking teedee 0.049 wisdom to get me sorted

Post  layback209 on Mon Jul 30, 2018 10:31 pm

Hey Fredvon4, thanks for the link. They have some awesome stuff. This would also be super handy for knife making and for general machining work to. I'll have to add to my wish list.

Yah i here yah does not take much to remove material from those little glow heads. Does not need a guerillas touch that's for sure.
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Re: seeking teedee 0.049 wisdom to get me sorted

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