Cox TD .049 Stunt

Plane is going to be a 170 sq. in. (scaled up) Swordsman.

What's a good engine set up for stunting the Cox .049 TD?

Should I use the #1702 that comes with it or, a low compression head?

I was thinking on a 6-3 Tornado black magnum for the prop or, a black plastic Cox 6-3.

Do I go for a 2-4 break or just run a fat 2 stroke?

Fuel?

I want to run a (Cox) muffler on it, for the neighbors, will the free porting make it run bad?

Thanks,
Giffy

You may want to go larger, say 200 Sq. in. if your still building. 2 stroke only. Use the high comp head; 5.5X3 or 5.7X3 apc; bladder pressure; 25 nitro, 25 caster. The muffler, you're on your own.

Maybe even a little bigger, say 215-225. I run backplate pressure with one-way valve. Agree with Mark on other points. Also like Master Airscrew 6 x 3 cut down to 5.5. No experience with mufler.

In my opinion, for stunt, you are better off running a Cox Medallion .049. More consistent runs, and almost as powerful. Good fuel draw, too. And you may not need the high comp head.

And don't overlook a well broken in Black Widow.

>In my opinion, for stunt, you are better off running a Cox
>Medallion .049. More consistent runs, and almost as
>powerful. Good fuel draw, too. And you may not need the high
>comp head.
>
>And don't overlook a well broken in Black Widow.
>
>Currell

Currell speak with straight tongue....Other gooder choice is replace
T.D. with PAW .049 single bearing diesel; benefits are best fuel
draw and 40% less fuel requirement. Also can run 6"x4" prop for more
speed on longer lines...T.D. not pull such a prop.....make plane
model fly good in breeze...
Tony

I agree with the consensus that it is too small. I would suggest maybe as much as 270 - 300 sq. in. I used a Cox black 6x3 with the old Tatone muffler and 30% nitro/25% castor. A Kirn Kraft needle assembly is a great help.

OK, now I will get in on this. The ones we have designed and flown had around 32 inch wing spans with scaled down moments (except for the nose which needs to be a little longer). Weight was 10 to 14 ounces. The 14 ounce ship is a foam wing critter and flies good, even at that weight. You get a little more pull on the lines.

The TD will work fine as-is, although some in the past have used the Madalion or a TD with a one port sleeve. The muffler will work fine. There is no such thing as trying to run these things with a 4-2 break or in a rich stunt run. They are designed to run flat out and will not produce any power if slowed down. Turn the biggest low pitch prop you can.

Ironically, on the fuel, we used 5% nitro on the TD. The last half-A contest Matt entered with the TD, there was another contestant with the "hot" set-up. He was talking how his 25% nitro gave much more consistent runs. He flew first. His engine sagged. He crashed on his first fliight. Matt was the only one who made it through the entire pattern. Sometimes low tech is OK.

Thanks to all who responded.

This prodject is a trip down memory lane as well as something fun to fly in the back yard. My dad had a Swordsman and, later I built one and taught my wife to fly.

I wanted this one to be as big as an all sheet model can practically be so, I'm basing the size on the all sheet 1/2a models of Dick Sarpolus (170 sq. in.). I hear they are good fliers. I'm hoping the tapered planform of the Swordsman will help reduce wing flexing.

I've had good luck running Cox engines on spec racing fuel which is 10% nitro 20% castor. It might fly a little fast fully tweeked but, I can make a smaller venturi to reduce power. Stock is .116" so, maybe .093" to start?

Giffy

Hi guys, brand new member, 1st time post so be gentle!

I've been experimenting with Tee Dees for years and came up with a combo that works very well for r/c sport use with an exhaust sleeve throttle. I'm sure some of the mods will work as well for a u/c stunt powerplant.

I reduce the stock venturi I.D. to .096" by bonding in a short piece of K&S 1/8" O.D. alum. tubing with JB Weld and reshaping it to a smooth curve from the entry down to just a hair above the annular fuel holes. This one mod broadens the needle, (don't need the fine thread gizmo anymore!) increases the fuel draw immensely and just makes it an all-around happier engine.

The late style "Sure-Start" product engine comes with a great cylinder that has a twin bypass cylinder plus 2 extra ports but doesn't have free-porting. They work GREAT with sleeve throttles so I'm sure a muffler would work as well.

At my altitude (300-400 ft.) the lower compression Babe Bee or "product" head works great with about 4-5 gaskets on 25-35% nitro and a black 5x3 prop. A 6x3 black would probably work OK but as you know, the load on a 1/2A engine is critical. I find that a 5x3 turns up more, is less needle sensitive and at the resulting higher revs, puts out about the same (if not more) thrust as the 6x3.

I also have a "John Deere" engine which is a b@$tardized Medallion with a Tee Dee ft. end and a throttle sleeve. This allows a venturi to be fitted to the Med. with a bushed down (.063") venturi. With a Texaco head and 5 gskts., it pulls a 7x3.5 a hair over 11000 rpm. It will also 4-2-4 on a good engine day. I have it on a big, (305 sq. in) light 4 channel r/c plane but would like to try it on a big, calm air u/c plane one of these days.

No question, 170 sq.in. is WAY too small. The Pinto is about right at 220 sq.in. and should weigh in about 10 ounces. The Norvels can go out to the size of the Baby Pathfinder at 235 sq.in. if you keep it under 12 ounces.

Stock Tee Dees do like the nitro, but you need to add a couple of head gaskets if you use 25% or more for the long stunt runs. Plan on 1-1/8 ounces of fuel to get through the pattern. Make the tank long and narrow to minimize pressure change with speed, and use a uniflo vent system. Backplate pressure with a check valve can be good, and when working right allows drilling out the venturi for more power.

20% oil, at least half castor! When in doubt, add oil. I like Sig fuels, I have some belief that they are honest about their content. Of course Aerodyne is top-notch if you have the time to order it, or a source to buy it directly.

The gray 6x3 C*x prop is a good one, as is the 5.7 x 3 APC.

Try for lap times at about 4.8 to 5 seconds if you can. Use 45' or more of .008 solid or cable. Be sure to use at least a 3" bellcrank, none of that 2 inch "1/2A bellcrank" garbage. Handle spacing is probably going to be almost 1:1 compared to the bellcrank.

Good luck, and keep us posted.

Fox .049, 1st gen design. Just had to throw this one into the mix. Nearly 19K on a 5-3 and only 15% go juice. Bone stock. Currell

>The late style "Sure-Start" product engine comes with a
>great cylinder that has a twin bypass cylinder plus 2 extra
>ports but doesn't have free-porting. They work GREAT with
>sleeve throttles so I'm sure a muffler would work as well.

Need some help here. What is "free porting"? And what are "Sure-Start" engines? And what/how are the two extra ports? All needed to add to my engine education.

Free-porting is when the bottom of the piston clears the bottom of the exhaust port at the top of the stroke. This admits a little extra air. I never have figured out why this is better than drilling out the venturi a bit, but it smooths out the run on C*x engines, at least.

However, if you are running a muffler, you are pumping exhaust into the crankcase instead of fresh air, and you lose rpm in a hurry.

Sure-Start is the current name for the C*x ready-to-fly engine with a big tube out the back that lets you choke the engine easily. Works like a charm. Mike Dorffler designed the add-on piece, I think.

O.K., thanks Larry R. (message 13) and Dickeybird (message 14). Free porting is what we call Sub Piston Induction, (spi), and I recognise the two extra ports from the original Olympic. As for Sure Starts, they sound like a Sure Thing, I'll look out for one at swap meet. I do have a TD049 with a free ported cyl. and Cox silencer for use in a stunter One day. Thanks guys,

I feel a little foolish responding to Larry who knows more about these engines than anyone else, but I always felt that sub-piston induction allows a smaller venturi opening, which should give a better fuel draw. I also assume that the needle is open a little bit more to provide a somewhat rich mixture. Now when the piston skirt moves past the cylinder exhaust port, that extra puff of fresh air can enter the crankcase (which is probably sitting in a slight vacuum), bringing the mixture into the correct range. So net result is more fuel-air mixture to burn.

Well, sounds good to me!

>>The late style "Sure-Start" product engine comes with a
>>great cylinder that has a twin bypass cylinder plus 2 extra
>>ports but doesn't have free-porting. They work GREAT with
>>sleeve throttles so I'm sure a muffler would work as well.
>
>Need some help here. What is "free porting"? And what are
>"Sure-Start" engines? And what/how are the two extra ports?
>All needed to add to my engine education.
The 2 extra ports I was referring to are the additional small "flutes" milled alongside the main bypass ports; 1 extra small port per each bypass port. This allows more flow and more power. The older Tee Dee cyls. had 2 extra "flutes" per transfer and free porting; very powerful! The later Tee Dees have only 1 extra "flute" and have free porting as well.

I like the late product engine cyls. because they have the best of both worlds for my use. Unfortunately, the pistons are heavier than the Tee Dees but I grind the I.D. of the piston skirt and lighten them back down to 2.8 gms. like the Tee Dee. I grind away the bridge between the "twin-slit" exhaust ports as well for best power. The reason for all this (admittedly tedious) extra work is to give me a Tee Dee that will idle down (with a throttle sleeve)to 5000-5500 rpm reliably, instant throttle response and a top end of 18000-19000 on a black 5x3.

Yup, I could just go buy a Big Mig, but where's the challenge in that?

>Plane is going to be a 170 sq. in. (scaled up) Swordsman.
>

Giffy,

The Swordsman tracings I promised were mailed today, USPS Priority. You should have them this week.

Be sure and post some pictures of this new creation!

Got the prints today, thanks. Wow, that Swordsman is alot smaller than I remember (86 sq. in.). I guess I was smaller back then too. It might fly good with my Cox .020 on 35 ft. lines if I lenghten the nose to keep the balance right.

For the TD .049 version I multiplied all dimensions by 1.6 to get 170 sq. in. wing. It didn't look quite right so, had to give it more aspect ratio. I found some real light 3/16" sheet for the wing. Should be able to carve a little shape into it.

Having fun,
Giffy

>Got the prints today, thanks. Wow, that Swordsman is alot
>smaller than I remember (86 sq. in.). I guess I was smaller
>back then too. It might fly good with my Cox .020 on 35 ft.
>lines if I lenghten the nose to keep the balance right.
>
>For the TD .049 version I multiplied all dimensions by 1.6
>to get 170 sq. in. wing. It didn't look quite right so, had
>to give it more aspect ratio. I found some real light 3/16"
>sheet for the wing. Should be able to carve a little shape
>into it.
>
>Having fun,
>Giffy

Giff,

Just got back from vacation. Glad to hear it is going well. Yes, I've always thought that a really light Swordsman with a Pee Wee 020 would be great back yard fare. You can dye it red with Rit dye and use a clear finish to save weight.