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1/2A Size Dumas Boat Club

Old 11-18-2009, 12:22 AM
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Default RE: 1/2A Size Boat Club

when my boat is done i wil make a video and post it on youtube.
[youtube]http://www.youtube.com/watch?v=qOlWYx3H2VQ[/youtube]
Old 11-18-2009, 12:25 AM
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Default RE: 1/2A Size Boat Club

ORIGINAL: robot797

my rc ring fiberates and leakes on evry side.
so the trottle cant be still on 1 speed.

what can that be



Robot that would be great we would all love to see it.

I forgot you mentioned having trouble with your throttle ring.

Have you had your cylinder off of the motor yet? If you have look to see or try and remember if the wall by the exhaust openings is all smooth and straight all the way down from the bottom fin to the end of the cylinder where the threads are.

A throttle ring will not work on a cylinder that is cut small around the exhaust openings. Some cylinders are made that way, and people dont know that they are and try and fit the rc ring to it. It does slip over and fit but it wont work with those kind of cylinders. The exhaust gas goes right around the cylinder to the rc ring opening. It never really closes the exhaust ports. Maybe this is what you have?
Old 11-18-2009, 12:33 AM
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Default RE: 1/2A Size Boat Club

well it leakes at the bottem and the upper side bit when i fully close the exhaust
the motor shuts down.

so i think it is good  



does this count as 1/2A

[youtube]http://www.youtube.com/watch?v=zQ_Mi2V1B9M[/youtube]
Old 11-18-2009, 04:52 PM
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Default RE: 1/2A Size Boat Club

I think it quailifies as a 1/2 ounce boat......wheres the motor on that little thing?
Old 11-18-2009, 11:53 PM
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Default RE: 1/2A Size Boat Club

above the flame.

it is a small steam boat
Old 11-24-2009, 12:49 AM
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Default RE: 1/2A Size Boat Club

I have found a Tee Dee .020 on ebay took a few tries to win one at a reasonable price. Iended up snaggin one for 43.00. Istuck in the fly wheel problem as there is nothing on the market for this size motor. It only weighs 21g. 23k .055 bhp and read they can run happy at 26k without over stressing them. So here's a pic of the lil guy and the rigger waiting for the lil gem. Imay try and make a fly wheel out of two sizes of washers stackedto create a groove in the middle for a belt starter. The rigger now was laser tach at 31,607rpm unloaded getting max ride height prop actually runs slightly above its hub. I hope to get 20k at the prop on the water with the cox td 020; the tub on this rigger is 12in long. The lite rigger is a perfect choice for lower rpms as it will still ride on the hub at 20k. The previous owner of this Tee Dee used a flood off tube mounted thru the venturi what a shame, I have dug for a replacement no luck. Ijust didnt want to have to epoxy the hole up but oh well. Other then that it appears to be ok im holding my breath till it gets here.
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Old 11-24-2009, 01:04 AM
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Default RE: 1/2A Size Boat Club

I think it would be awesome to get 31,000 RPM from a Tee-Dee .049....But i suppose its not possible? I heard somewhere about a aftermarket supercharger??? for a Cox engine??? or was that the beer talking again....
I've been upgrading my Babe Bee's a bit, heres a pic of what I have done so far, I have a total of 8 Cox engines, Babe bees and a medallions .049 & .09and a Tee-Dee .051 in my arsenal...
I replaced the crankcase's and got the dual port cylinders & new pistons...New glow plugs too. I rebuilt the Bee's tanks also and polished them up with 000 steel wool...Only thing I can think of is some Galbreath heads....I'm hoping to get at least 20,000 something RPM at the prop for my Atlas thats almost done....

On your homemade flywheel, using steel washers may work, I would suggest balancing the flywheel when your finished with it....


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Old 11-24-2009, 01:54 AM
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Default RE: 1/2A Size Boat Club

Those motors look nice in clean on 20%nitro I read they can do 17k with a prop so with a fly wheel you may see over 20k if the prop is running loose on the water. I worked ona TD 051 Sunday night put a water cooling coil on the motor and ran it on 25% nitro it seems ok at this level I know Castor oil is a must with these and even more so in boats. One thing to mention with glow head adapters a standard glow plug responds better to a sub C 1.2v battery better then the original cox glow elements .. the nichrome wire was meant to be used with standard 1.5v dry cell batteries and needs the extra voltage to glow well on start up .. this only has me using adapters more so in a pinch they will still light up in the field after a few hours into your day.I use a small bit of heat shrink tubing on the fly wheels retaining bolt as they fly wheel's hole is over sized. This is a must as over the course of a few runs you can waller out the crank case housing in the front. Another is add another thrust washer between the engines front prop plate and crank case to help absorb the thrust loads from the prop. Here's the lil motor pic from ebay hope it looks like this when it shows up. Yea not sure about the fly wheel issue what do yetmay find some scrap iron and make my own. Another trick is to isolate the fly wheel from the engineand use bearings to support its weight. I have made a gear driven hydro with a TD back in the day Iliked the fly wheel on the spur gear end supported very well and no chance of wear on the engine crank case.
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Old 11-24-2009, 02:06 AM
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Default RE: 1/2A Size Boat Club

What is your plan to throttle the Bee?  I have seen simple K&S tube used for a throttle sleeve.  Also think you should use the big gas tank. You will be thankful for the extra run time on days that took alot of needle tweekin. You can use no screen and slighty bore out the carb throat a hair. And then theres always 30% nitro with 20% castor. There is a guy in houston that will custom blend his fuel for the hobby shops. Ritch's Brew 713.661.5458  I mostly use 25% nitro and his castor/synthetic blend. His quarts sell localy for 8.49 not too bad.
Old 11-24-2009, 03:51 PM
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Default RE: 1/2A Size Boat Club

I was thinking about a flywheel today and i remembered that some of those push cars that you can wind up by pulling the car backwards then releasing it...they have little inertia motors in them and I took one apart to see what makes it tick, and they have a little machined steel "flywheel". You know what I'm talking about?
Maybe that would make for a .049 flywheel as well?

As far as throttle....I have a few new medallions .049 and a .09 both with a throttle ring....I beleive the ring can also be used on other cox engines as well....Up to this point I may just run my Atlas with just the Bee engine pictured above with no throttle....But its still a work in progress...I'm waiting for some couplers to come in the mail so I can use .098 flex cable and I picked up some Pine car decals for a stock car....bunch of small penziol and champion decals that will fit nicely on the cowl just like the rear atlas....

My Short Stuff that I'm starting on next will get the R/c .09 medallion...I hope with the .09 it should run well....What do you think about stuffing a .09 Tee-Dee in your smallest rigger?
Old 11-24-2009, 08:03 PM
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Default RE: 1/2A Size Boat Club

I do have two fly wheels from dumas for my 1/2A's. I thought I could buy another and have it milled down from 1in dia to 3/4 for the TD 020 which has the same power/watt output as a bee 049.I will have a look for those push cars n see whats possible. You could use a fuel shut off/pinch lever on the feed line and servo operated to at least be able to shut it downwhenin trouble.The lil rigger I have must use a TD020 as theTD 051 isaround 108watts of shake rattle n roll. The rigger is built lite and could handle smooth 100w from a motor but not from a engine of the same output. The same rigger could be built more robust with 1/16 th ply sheet stock. Here's a nice way to water cool your 1/2A easy n cheap the up side is you have a cooler engine that will take in more air fuel for more power. The other pic shows a TD 051 for fit comparison with the lil rigger. I have posted a pic with the slightly larger rigger made with 1/16th ply further back in the thread. I have a TD 09 RC its a power house rated for 185 watts. And it does fit in the other rigger, the speeds would be in the low 40's with a X427. Also I have used the dumas fly wheel on the queen bee 074 and found it to work well I think the TD 09 would juuuuuuuust manage to be enough mass to protect the engine.
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Old 11-24-2009, 10:41 PM
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Default RE: 1/2A Size Boat Club

Yeah I was trying to think of what toy vehicles would have that but its a interia driven flywheel. You hold the car on the floor, pull it back, and release it and it takes off....I took one apart years ago, and they have the most neatest little milled steel flywheel....I remember spinning it like a top, and it would go on for at least 3 minutes or so!
Down here where I live it gets pretty hot during summer, about '96 or more is an average day, so water cooling is probably a good idea, I do have a Cox buggy heatsink. The rudder that I decided on for my Atlas build is the "head of the rivers" micro rudder with built in water pickup. Its a really well made piece...I can always run a small dia tube up the side going into the engine well, its no big deal to do it....
Now the Dumas water heatsink I have is a bit on the heavy side and I like the idea of wraping the tube around the cylinder like you have pictured...
Silly question, but I dont have too many tools, do I need something special to get the brass tube wrapped around, or did you do it by hand?

I was just fooling around and I found this site.....How about microturbo jet engines in our boats? I'm not really serious but, is it possible to use one of these in a micro rigger?
www.waoline.com/detente/hobby/HobbyTurbines.htm
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Old 11-25-2009, 03:34 AM
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Default RE: 1/2A Size Boat Club

I used aluminum tube and no tools needed just go to the K&S rack. If you go nice n easy as you wrap the cylinder it wont kink. And I agree the dumas water cooling clamp is a paper weight at best. Dont buy brass its not going to absorb the heat as well. Any idea how much the boat weighs now that its painted? I have some doppler software now if you can video the boat when its ready I can give you some mph figures. I want to buy radar for in the field next. Im not sure the support gear that tags along with the jet engine all adds weight. My guess the lil one you posted could fare well in a 26in rigger.
Old 11-25-2009, 12:31 PM
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Default RE: 1/2A Size Boat Club

I thought about weighing the boat as it is right now...I will have to pick up a cheap scale or kitchen scale to use, I'm curious myself. I'm sure I saved some weight with all the cutouts made....I thought I saw a jet engine powered model boat on You tube, I dont think theres any advantage to using one.
Old 12-01-2009, 12:23 AM
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Default RE: 1/2A Size Boat Club

I made a new isolation mount fora TD051. Iaddeda aluminum carb body from ebay. Itdidn't fit without some filing, Iwas not impressed with the extra work I had to do to make it fit well.The nextstep is to drill ntap the aluminum sidemounts for nylon bolts. I will use rubbertube to isolate the nylon from the plysides of thethe tub.Imay opt to takeoffthe rubber pads and join the engine metal to metal and take advantage of the heat transfer to the engine mount. I'm also counting on the carb body helping. The idea is to max out the coolingandallow more fuel n airto pick up some extrarpmbefore it starts tolean out.
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Old 12-01-2009, 01:19 AM
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Default RE: 1/2A Size Boat Club



I had mentioned a long drive line here's the result with 12in x 2.5mmand setin oilet bushings and thick walled aluminum tube. The result was thankfully litethe entire engine combo is 4.47oz, I still plan to drill n tape a grease fill tube to collect in the lower half for water repelling. The friction is minimal compared to just brass tube as long as you don't dry run the engine into high rpms the top bushing should last with only its impregnation. I may opt out and go with a top bearing with the stuffing boxgrease protecting it from water.</p>
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Old 12-01-2009, 12:06 PM
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Default RE: 1/2A Size Boat Club

I put a few of my Medallions up on ebay, The rpm &amp; power is pretty close to what my hopped up Golden bee's put out and I'm stocked up w/ rebuild kits and replacement parts for Bee's for the next 5yrs anyways.
The thing thatslimits the reed engines to around 17,500RPMIbelieve is the restrictionsto the flow around the reed valve....I wonder if machining out the venturi which is 3/32 I think on the bee'sto a larger diameter would allow more air/fuel flow?
What I've done with my bee's was to replace the old cylinders with new ones with dual ports and new pistons, and galbreath heads....should be close to 20,000rpm
I do have a few Tee-dee .051's &amp; .049. The .051 is going in my Thriftway......I screwed up putting on the original decks, they were a pain trying to tape down without popping up in areas, I even stacked books over the decks....Theres not alot of area for tacks to grab onto either....I would suggest readers out there to consider using Weldwoods contact cement....I used it before without any problems and my deck on another boat has held up 4 yrs now...Just spread the stuff on the underside of the deck, then apply a bead on top of all frames. let it sit for about 10-15 minutes, then CAREFULLY put the deck on, once it touches, its ON, and will not allow you the chance to reposition....
I went out and picked up some 1/32 birch ply, and thankfully I traced the parts out before I built it...and reinstaled the decks, using my lil' trick....
Heres a pic of Thriftway, its not pretty now, but no one will know onces its all sanded/filled and painted....I plan on using a Tee-dee .051 to a 1/8 drive. short stuffing box and the small brass dumas strut will support it towards the stern.....
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Old 12-01-2009, 06:34 PM
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Default RE: 1/2A Size Boat Club

The Black Widow Backplate and Tank, along with the plastic Killer Bee backplate, both sport larger venturi's. I would have to dig through the 1/8A & 1/2A Airplane Forum here to find it. You can and people have modified the venturi size just using a fresh drill bit and a pin vise. You loose a little bit of the taper of the venturi by doing it but guess it doesn't hurt!

I found when I opened up a backplate and tank it did run a bit better. You can tell it's choked down when you do it. I kept stepping up sizes until it would not draw fuel, then took a mental note of it thinking I would always remember but 40 years later that doesn't happen. I believe the right size people agree on is a number size drill, not a fractional. It's good to have both types of sets handy even if they are cheap ones just for this kind of thing. The number sizes are ranged much closer together than fractional sizes.

A bit of thinking on opening that venturi up. I remember as I got larger where it seemed to not matter in rpm's to go larger, I started to pop the reed out of the retainer. I think using the stainless or the four star reed is the best bet. I have teflon and mylar types that are shaped like a flat oval where I think they would have trouble staying behind the spring.

Have I got a deal for you. I just bought some Ribbon Sepele veneer you could sheet that deck with if you want. 18 inches out of a 1/4 mile of what I bought won't break me, and you'll have one spectacular looking deck and if you do it right I think you can buy a relaxer agent or make your own using laundry soap and water to soften the veneering (.022" thick) and sheet the whole thing in one piece without a deck seam.

Where did you get the charts??? Excellent stuff! Wonder if thier dyno stayed the same across the years.

Air Mover has the goods on making hardware. It's great to see hard core happening here! [sm=shades_smile.gif][sm=thumbup.gif]
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Old 12-01-2009, 09:15 PM
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Default RE: 1/2A Size Boat Club

Hey JP,
Here check out this website, very good info on Cox engines, this is where I found the charts...www.mh-aerotools.de/airfoils/cox_frameset.htm
I know that if you remove the mesh screen on the back of the backplate helps. Also the Golden bee's vented tank has a larger venturi than the babe bee's along with the engines you mentioned..I'm looking forward in firing my engines up....
When I recieve a .049 from ebay, first thing I do is disasemble it and inspect &amp; clean/polish with 000 steel wool.....Then I install a new pistion &amp; dual port cylinder....Replace all gaskets, venturi O-ring, backplate screws....et...I've been using the oval shaped metal reeds....I've got a stockpile of new cox parts for my bee's....I've been bidding on the lesser priced babe bee's and golden bee's....and getting my parts from xenalook...they have a bunch of anodized crankcases too, many colors to chose from, really COOL! [img]file:///C:/Users/Ron/Pictures/rock1.gif[/img][img]file:///C:/Users/Ron/Pictures/rock1.gif[/img][img]file:///C:/Users/Ron/Pictures/rock1.gif[/img]

Now my Thriftway is going along well, Built differently than the Atlas. I would like to weigh the Atlas,because its noticably less than the Thriftway....I'm tempted to take my medallion .09 and stick it in the thriftway....I think with an .09 I may get away with using 27-30mm props....like an octura X427? What do you think? .051 Tee-dee or .09?

Old 12-01-2009, 09:50 PM
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Default RE: 1/2A Size Boat Club

An .09 tether model, picture that one. Those can fly. The tether takes some of the weight off the hull and makes gravity go sideways instead of down in the water.

I would think an .09 is better left for something a little wetter like the SK Jr. or the SkeVee 10. Even better the wood or fiberglass DV-10. I bet that would be a good balanced hull with a Cox. Fast enough with good handling.

Putting it in a little mahogany hydro might be a bit much because of it's lift but with a throttle why not? It might want to barrel roll with a larger prop like that though once your really cooking. I would have the XXL rudder handy.
Old 12-01-2009, 10:59 PM
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Default RE: 1/2A Size Boat Club

I agree That the .09 medallion r/c, which I have is the better choice in the DV10. My dv10 "short stuff" is probably gonna be my next project....A 27mm prop is not that big...and would really propel our dumas hydros up to good speed if we hit the rite powerband, something that a cox .049 lacks....Octuras x247 has alot of blade, and for a cox to spin a 27mm blade the blade needs to be narrow like the dumas plastic props are....less tongue, or surface area...The .09 has the torque and rpm to spin an x427 boat to nice speed I'm guessing....
Thing is....I need a .09 wrench, and replacemnt parts have been nearly impossible for me unless someone knows where I can find a new glowhead in case mine goes bad....
Good thing is, my medallion .09 r/c is nearly new and hardly used.....heres a pic of it.....
Has anyone converted their dumas 1/2A boat to electric?
a brushless/lipo combo would be insane on a hull this small.....but fast....
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Old 12-01-2009, 11:16 PM
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Default RE: 1/2A Size Boat Club

On ebay the .09 and parts start to taper off, and the .15's are pricey and rare to find parts for.

Wrenches are pretty common for the .09 and I would get two if you can. Sometimes they are in a bunch of other wrenches and it's hard to tell the size. If you need I can measure one up or you can measure the gap on the head and use that to ask the seller.

RJL at MECOA will have an anodized replacement head that takes a standard plug which is okay. Once you get to the .09's and the .15's a regular plug starts to not hurt performance unlike the smaller .049's. Cox sold the .074 and the .09RC with a standard plug head.
Old 12-03-2009, 07:15 PM
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Default RE: 1/2A Size Boat Club

Well I'm gonna go ahead and do it....

I'm going to put my medallion .09 r/c in my 18" Miss Thriftway.....Its going to have full throttle/rudder control and take advantage of the higher torque &amp; rpm to swing a more appropiate prop....
I'm really happy with how this one came together. Its very rock solid. I replaced the mahagony decks with 1/32 aircraft ply which did lighten it up and gave it more strength...to keep it lite I finally found some k&amp;s 1/8 stainless drill rod and will make a driveshaft from it. I'm going to retain the "Thriftway" theme, but will make a aerodynamic nose piece from either thin balsa or 1/64 ply, instead of the plastic cowl front end, similar to what I've seen on drag n fly type boats and other similar shovel nose hydros, that will go towards the engine...It'l look cool...

For comparison, heres a pic of a babe bee .049 with a plastic dumas prop under it, and to the right is the .09. the nylon plastic prop is a dumas prop made for .09-10 engines, and its slightly larger than the 27mm black props and the red mrp prop that I'l try....

If you guys push me, I may even add a third servo for mixture control on the fly....
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Old 12-03-2009, 07:48 PM
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Default RE: 1/2A Size Boat Club

Are you going to use  a 1/2a fly wheel?  I think the 09 is a perfect choice. Also why not mixture control as micro servos are so lite, it wont be a fuss to do. I have used fuel tube with a plastic control arm. I just slip on the fuel line on once I'm happy with the needle setting each run day.
Old 12-03-2009, 08:11 PM
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Default RE: 1/2A Size Boat Club

My new lil ebay win came in the other day, the TD 020 looks too small for this rigger but would be easy to slap in this10.75in tub. I thinka 09 should perform well on a X427 cut down to 25mm. I know my queen bee only ran stronger with a dumas 1x1 with more stable needle settings but Ididn't feel Ineeded to prop up. The 09 is good for 180 watts, the 05 size brushed motor on 7cellsstart around 150w to 200w with a X427. An 05 has more torque then a 09 thus the thought a 25mm prop with some but less tongue to start.
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