TD .049 for Stunt?

Not very much. The problem I always had was on the intake end of the system. Take a box-stock TD on suction and it's very errratic and a real pain to try to get repeatable flights. Take the exact same motor, remove the black plastic carb mount, and the rest of the intake (remove the thrust washer, unscrew the ring that holds it on, slip the whole thing off) and replace it with a stock Medallion cast venturi/spraybar, and it's all of a sudden a sweetheart. Even with the trumpet glow head and no shims.

Or, buy a PAW 1b (1 ball-bearing) .049 and swing a 6x4 Master Airscrew prop at about 16,400 rpm. 3-blade Tornado 6x4 went at 13,200. Rev-up 7x4 ran 11,300. That's POWER!

Proceed cautiously, taking Brett's advice and Larry's suggestion most seriously.

Did anyone ever build those 3 or 4 kits I sold online three or four years back?

Someone above mentioned that the author was trying to get good throttle sleeve response which is true, but I have built engines using his suggestions for CL stunt that were excellent.

The basic concepts that you have to take from the article and apply to the stunt engine are the lowering of compression, and the reduction of the venturi ID. As TD's go, they have always been overcompressed and had comparitively huge venturis- both factors which make the engines harder to needle and more inconsistent in a stunt run.

The setup that I have used based on his info was a TD with a standard head, 3-4 head shims, and the reduced venturi with a KK needlevalve assembly. The one difference I introduced was to run backplate pressure. With a 1oz tank and a cox black 6-3, I get good runs.

As for power difference- there is most definitely a difference when compared to my TD's on 45%nitro, huge venturis and bladders, but those are little beasts (frustrating). The power difference between a standard TD and one modified per the article is not that great.

BTW, I believe you are essentially achieving the same thing as reducing the TD venturi dia by installing the medallion body with its smaller venturi ID. I have one new in the box out in the shop, and I will try to measure it and verify that.....

I defer to Larry. I merely wanted to point out that adding head gaskets really doesn't really help when it's an intake problem. Additionally, the reflexive tendency to "add head gaskets for stunt run" is a pet peeve.

Hmm, interesting thought. I had just assumed adjusting head gaskets would be for timing. If I make it breathe better at lower RPM I expect to use a larger prop (~ 6x3) for more disc area. Of course you could still crank it up with a 6x2.

Are you saying that someone would try to make it 4-2-4 or just decrease power?

What size props have you guys who have tried 1/2A stunt been using?

Actually, perhaps this rework could be used on later Norvel .049s to provide better suction also.

The PAW runs perfectly on a simple vent tank with the vent pointed into the airstream. As seen at the Golden State Championships, the run is flawless.

I am finally getting a handle on running the Norvel, I have seriously loosened up the crankshaft fit, and am running backplate pressure into a uniflo tank. The engine will finally run just where you set it through the entire tank. I did find (I think) that the engine can not handle the retained heat of the muffler. It also requires some sort of pressure feed, thus the backplate pressure. Unlike the Tee Dee, the needle on the Norvels is very fine thread, and thus, easy to set well. I sincerely believe that my problems with Norvels have all been due to overheating.

The MP-Jet is currently running on a simply vented tank, driving a 7x5 Rev-Up prop. I don't recall the rpm, but the lap times on 50' lines are very comfortable, while the line tension is consistent. I plan to try a uniflo tank. I do find the fuel draw of the MP is not very good, and may yet put in a muffler tap to try that out. For some reason, despite the poor fuel draw in starting, the run in the air is consistent. Go figure?

As far as 4-2-4 is concerned in 1/2A, I think you are better off maximizing the power, using a lower pitch prop, and flying a larger model on longer lines. But whatever flips YOUR prop is OK if you are willing to make it work.

Brett

Agreed. Back when I was flying a lot of RC, I would frequently comment it was my view that changing the needle setting ought involve a lot more work than merely a short reach and a big twist. Make changing the needle setting as difficult as, say, changing head clearance and then maybe people would first look for the real reason their perfect needle from previous flight of a sudden is now two turns lean.

It was only when beginning to fly CL Stunt that I saw the flaw in my argument, as it seemed people were tossing head shims in their engines with approximately the same amount of thought and hopefulness as goes into furiously dialing the needle when it's the fuel filter which needs attention.

Sometimes, when considering adding a head shim to a CL Stunt motor, I will first take a shim out and fly. You'd be surprised at how many times it doesn't make a lot of difference, indicating the problem might well be further upstream. Or in one of a whole bunch of other variables.

One of my ST 51s was real inconsistent until I increased the compression and decreased the bore size of the venturi.

While I would have to check my notes to be sure, I don't believe either of my two GMA ABC Fox 35s currently being flown in competition, plus the back-up motor in the tool box, have any head shims at all installed under the hemi heads. George and I disagreed about the details of my setup, but y'all can see the good results at any NW contest.

I can't recommend the second version, even though it is maybe 500-1000 rpm stronger. The shaft timing is so agressive that it will run backwards 90% of the time. Reed Coxes are a model of consistency in comparison.

But the first gen ones are sweet little motors. And heads aren't impossible. Yet.

Can't speak to the FAI version for the simple reason that I have yet to own one.

As mentioned in another post above, I wrote the article to share my experiences in coercing Tee Dees into running consistently and throttling well enough with an exhaust sleeve to reliably power sport r/c aircraft. Even though the Tee Dee design is getting "long in the tooth", it CAN be made to accomplish that purpose very well when set up properly. If just a few modelers drag out their ol' Tee Dees, modify them and have as much fun with them as I have, my wish will be fulfilled.

Having said that, I enjoy 1/2A u/c flying as well and intend to do up a relatively large, lightweight u/c sport plane next year using a Tee Dee for power. My plan is to again reduce the venturi I.D. somewhat and reduce the compression (timing) enough to pull a 6x3 consistently. At my geographical location, with the weather conditions we have here and the parts I have on hand, my Tee Dees just plain ain't happy pulling the load of a 6x3. I think the stock venturi I.D. and compression was set by Bill Atwood and friends to pull a smaller prop as fast as possible for competion use. My theory is that at the lower crank speeds obtained with a 6x3, the compression (timing) is too high and the venturi "suction" isn't strong enough to get a relaxed needle setting and a "happy" motor run. Pressure feed helps but I don't want the hassle. IMHO, reducing the venturi I.D. and the compression will give me a consistent running, reasonably powerful u/c engine with 6x3. Hopefully, we'll soon find out!

Milton Dickey

The best totally-stock Tee Dee .049 I ever saw would turn that prop at 19,500. 18,000 was common and the typical, current 17,000 was considered a real loser in those days.

The "new" version of the prop has higher pitch (a true 3",I am told), and has lent some to the image that the engines are worse than they were. The engines won't turn the new prop as fast as the old one.

You can tell if you have a new or old prop by looking at the parting line path on the hub. If it steps all the way down to the bottom of the hub it is an old one. If it steps horizontally through the center of the hub it is the new version.

I still recall repeatedly hearing from one very famous modeler who shall remain nameless, about the fabulous rpms he got with his engines. One day at the field, he was cranking one of these engines up and quoted a ludicrous rpm. Now at the time, I was pretty well tuned by ear, and knew he was wrong. So, I ran and got my freshly calibrated tach, and we compared rpm. His read 8000 rpm high, no, not 800, 8k!!!

I've often wondered about the venturi sizes as production specs. changed through the years. I have a few of the (I assume) early production Tee Dee venturis that have no mesh screen on the inlet and have only a .106" I.D. That's how I got onto the reduced I.D. thing....the engines fitted with those venturis just seemed to handle better and I didn't notice a big reduction in top end. Since you mentioned Bill tuning the Tee Dee originally for the 6x3, do you suppose the .106" was arrived at for that prop and then the I.D. was increased in later versions for smaller props and higher revs?

That's a very interesting factoid on the old/new grey 6x3 props. It absolutely explains why some of my old props were more engine friendly and seemed to hook up better at low speeds! Unfortunately they're all broken and long gone now.

Speaking of having your ear tachometer calibrated, ever noticed how the really good fitting cylinders, whether on reedies or Tee Dees will run ragged/rich at a higher rpm than you're used to hearing when setting the needle, then suddenly burst into a screaming wail WAY higher than you're expecting? A more beautiful sound cannot be heard, in my book! That's the ones you oil up real good and set aside for that special, uhhh, "occasion".

I had a NOS Black Widow do just that on our Lightning Streak. FOUR people walked over and said, "I never knew a Cox could run like that!". It was cooking.

Jay

Been there, done that, no T-shirt!

Sounds like just the prop for that 2m glider I might build with the Norvel on the nose...