The best throttle options for cox engines

This video tests three throttle options for Cox engines applicable to both reed valve and rotary (Tee Dee) engines. The main variable of interest is which throttle allows for the lowest and most stable idling, without compromising full throttle performance of the engine. The three throttles tested include 1) air intake valve, 2) exhaust port valve (i.e. throttle ring) and 3) the combination of both used concurrently. Link mentioned in this video • DIY Throttle for Cox T...

[@terryunkert5237]

The air intake valve is really a choke since the spray bar is downstream of it. This richens the mixture as it restricts flow since the spray bar essentially "sees more vacuum" and thus flows more fuel per the amount of air entering. When the engine finally dies due to closing the valve it becomes flooded, hence hard to start. The exhaust ring by itself primarily restricts the flow thru the engine without affecting the air/fuel ratio directly but only due to the retention of some of the exhaust gas. Using the two together somewhat mitigates the air/fuel ratio disturbance at the spray bar caused by a high vacuum (restricted intake) by adding back pressure. 45 years as aerospace engineer with fluids, thermo, combustion background and ex contol line kid from 50's-60's.

[@ronaldgreen5292]

Wow!😮A very nice and professional explanation of the little engine in the video!!❤💯💯👍👍

[@ronaldgreen5292]

Just as, he kinda had a, sort of dual throttle setup. The one on the back of the engine, was more of an traditional carburetor and the throttle ring, would restrict the exhaust flow, thus, slowing the rpms down. The funny thing is that the propeller is the flywheel!!

[@patrickpendergast898]

This video has given me hope of making a tiny gas/electric generator for a small 7-10in quadcopter. Thanks for the explanation on why it’s best to use both a throttle and exhaust ring for engine speed management. Will help me control voltage coming out of the electric motor.

[@VintageTechFan]

If you look at vintage RC engines, often from the 1960s before muffles became pretty much mandatory, they almost always had that coupled system. A relatively simple carb, and a butterfly valve over the exhaust. The first OS mufflers (the early "Jetstream" types) even had that valve in the muffler still.

[@user-oe8vv8cb1t]

I had many .049 engines in the 1970s and the exhaust restricter is the best way I found to alter the speed.

[@francoisrivard893]

Nice video! For actual flying situations, the throttle ring is slow enough for reasonable ground handling and landing. The real plus is that the acceleration is instantaneous, which can help bail you out of a botched landing approach or a sudden gust of wind on the final leg. I have both .049 and .09 versions of the 60's style slide exhaust restrictor / intake flap combination. Although they perform really well in terms of engine speed control they are very fragile, fiddly, and the large slide area can easily get contaminated with dirt and dust and start sticking. I can see why Cox abandoned it a long time ago and instead relied on the more elegantly simple throttle ring implementation.

[@gordinir7]

Nice video, first of all I want to say that with 6000rpm on a Cox engine you can perfectly land a Q tee since at those "low" rpm Cox prop produce very limited thrust so there is no really need to go that low. Now in my case I have a tee dee with a carburettor and a throttle ring that work together. Ring helps the engine stay hot at those low rpm and idle perfect at 6000. For a standard 049 like black widow or golden bee I would choose the ring only since it can reduce revs very satisfactory as in your video.

[@homienat3374]

I think the ring does the job just fine I'm going for that option I think once dialled in should be fine fingers crossed, good luck all

[@tenlittleindians]

I still got my baby bee with it's throttle ring. I got it new on a Plastic P-40 Warhawk line control in the late 60's. The plastic control handle had a slide control for your index finger and a third line allowed take offs and landings when a friend wasn't availible. The engine throttle control was perfectly acceptable because anything less than full throttle meant you were landing as those Cox airplanes were almost too heavy to fly! I still think it would make a great rc engine in a balsa or foam model.

[@lukewashburn9639]

Loved the video! Thanks for this high quality content

[@j.d.farmer6164]

I will toss my two cents into the wind: 1. The exhaust restrictor comes with a rectangular opening. This makes the closing crtical. If you use a small file and change the closed-off side of the rectangular opening to a "V" notch, you get a slower, gentler cutoff which improves control of the exhaust restriction. 2. You need to watch the arrangement of the control rod as it goes to the restrictor. If you don't get a good (nearly square) angle betwwen the rod and restrictor plate as it closes, the restrictor closing becomes "twitchy" and causes problems. Also, since the engines have screw-on cylinders, keeping this arrangement requires some fiddling after putting the cylinder onto the engine after removal for maintenance. 3. The stock needle valve assembly on TD engines generally leaks air and makes settings difficult. First fix is to put a small piece of silicon fuel line tubing over the needle valve. The tubing needs to go from the venturi shoulder where the needle valve enters, and back to the shoulder on the needle valve where the threads stop. This makes a gasket which stops air leaks. Better fix is to get a Kirn Kraft needle valve assembly and put a length of tubing on its needle valve. I have no idea how long ago Kirn Kraft stopped production.

[@johnbuttery1171]

Very interesting, thanks for sharing. I'm now eyeing up my old 049s. My understanding is that an inlet throttle needs to restrict the airflow upstream and downstream of the needle valve to maintain the same fuel air mixture. The engine seems smoother with the exhaust throttle.

[@kh40yr]

The best fix for the throttle body and exhaust rings and Tarno carbs low rpm woe's, is 35% Nitro 15-18% oil. Extra nitro content will keep the glow plug lit at low rpms, without the methanol dowsing the coil once it sets at low rpm for a bit. A tick less oil did allow that to happen easier and the motor lived just fine. The rings and bodys are just airflow shunts which cause the micromotors to go extra rich. Extra nitro content carries extra oxygen molecules, by it's own self. THE next best low speed throttle control I seen for the Cox motors was the OEM Cox/Maples throttle body for the 1/12 GTP Nissan R/C onroad. Those Maples throttles, when set right even outshined the Tarno adjustable lowspeed needle carbs, for the flight .049's. The caveat emptor, was that the Maples would goop up pretty quick and needed attention often. You can usually find Boat fuel or Heli fuel that is 35/10. It's what I use. You could also use 30/10. Grab some Sig or Klotz or Novarossi Castor and bump the oil in the jug to at least 15%, BEFORE you take ANY out of the Gallon jug.

[@christophermacbrian3380]

thanks for posting this. it's quite informative and fun to watch :)

[@ronaldgreen5292]

I had a few of these little marvels of engineering, engines, both for a car, or airplane. How something that small, could actually run!!🤯😳

[@kimtyson9101]

I recall playing with the exhaust restriction ring on a(n) .049 back in the 70s. I could get it to run very-very slowly and sip fuel (for non airplane purposes) by simply adjusting the needle valve while restricting the exhaust. If I remember correctly, making the mixture richer made it run slower. The ring assembly I had fit very tightly on the cylinder and would shut off the engine when fully closed. IE it was full on to full off. I had an extra channel on my MRC and could manage the mixture change with the remote. The mixture lever fit over the needle valve knob after adjustment. (used it on a model pontoon air boat). I still play with the .049s and newer engines - cox engines are still my favourites. Nice discussion, I wasn't even aware of the air intake throttle back then, not sure when it was made available. I would bet that using the needle valve adjustment method you could extend the range of the RPM management with that throttle as well.

[@ronaldgreen5292]

Seems to be happier, around 7,000 rpms @ idle! Pretty amazing that it's able to idle @ 4,000-5,500 rpms 😮😮!

[@larryblanks6765]

That was cool I had to subscribe.

[@collinmccallum]

Liked and subscribed!

[@haroldneely9253]

I agree, good video. I’m going to swap crankshafts from standard to high performance and see what happens. I don’t have a tach so just a test flight.

[@rcsub250g7]

Looking forward to your findings. Thanks.

[@cblount2204]

Pulled mine out of s box yesterday. Last time it ran was 1994. Surprised it still operates. Messing with the mixture screw it got low enough to loop sounding like a low rpm radial. Didn't last long but sounded cool. Can't remember if I had left the 2 d cell batteries attached at the time

[@kuehn1953]

The sure start or snap start spring causes drag on the prop... not much and it varies...which may be why you got some different results.

[@Surestick88]

I wonder how low it could idle if you kept power to the glow plug?

[@homienat3374]

Hi I've just got a babe bee can i adapt a throttle ring to it and if so is it easy to fit live in Dublin lreland no shops sell these adapts any site u could recommend?? Thanks

[@CraftedChannel]

When it quits, it's quitting rich, that is why it takes a long time to start again. Very nice low idle acheived with both. Perhaps setting up some mixing you could get those two servos working in a model very well and reliably.

[@paulbizard3493]

A bit complex for a 1/2A...

[@victormiranda9163]

Overall the exhaust restrictor is the better option... mostly for better operations. The drop from full power to even 3/4 is well below landing speed. If you need ... more range? both are required. The problem for 049 in R/c is a reliable tank pressure system. The carb is more of a spray n pray than a metering system.

[@marcalampi5036]

Big mig .06 and big mig.074 nice little engines. I'm not sure if they are still for sale in America with them being from Russia?

[@marcalampi5036]

I am the very person who developed and researched and made the proto types of the.09 and.05 Cox engine's with the barrel carburetor's with muffler's of which novel finally made their own basic copy with barrel carburetor's with muffler's. Novels being schnurl ported on the sleeves. And having aluminum pistons with wrist pin or piston pins. Novels block designs allowed bigger porting. Aluminum block also cooling better and more fuel efficient and more power and better tunability and stronger lower idle especially on their big mig sport engines. Throttle ring on Cox engines were superior to the barrel carburetor. Also novel start easier.

[@AntiqueQueenz]

What type of cylinder did you use? How many bypass ports did it have and did it have boost ports as well. Also did the piston have SPI? Thanks.

[@rcsub250g7]

Thanks for the question. The engine is a recent a standard SureStart 0.049. Looks to have 2 ports and no SPI. Thanks.

[@christopherknee5756]

Mufflers, silencers, tuned pipes and oil deflectors. How to make a Cox engine quiet.

[@ronaldrose6885]

The tarno carb was the best option.

[@marcalampi5036]

The cox medalian engine's especially the 09 throttled well but we're somewhat under powered

[@marcalampi5036]

Cox medalian engine and black widow were great engine's I myself preferred the medalians. But I felt they needed more power for even a sport or stunt type engine. Queen bee engines were overly compressed but tunable. Ran too hot I felt. Novels 074 was a superior engine to Cox queen bee engines

[@R50_J0]

This is a static test. In-flight with forward airflow over the prop may produce a better, lower idle, no?

[@rcsub250g7]

Good point. It's possible. I have not yet been able to find a place to fly these little noise makers, but when I do I will hopefully have some in flight data to report. Thanks for your comment.

[@R50_J0]

Thanks for the video, BTW.

[@davelowets]

The air intake valve is NOT a carburetor, and is lacking an idle circuit like a true carburetor would have, and is surely leaning out the A/F mixture as it closes off the air supply. The exhaust ring doesn't affect the incoming airflow and the A/F ratio like the intake air valve does, and I'm certain that's why it works better and the engine is more stable at lower RPMs with it.

[@blockhead3654]

Hobby is dying rc field will be shut down withe 10 years. So all you have is junk

[@victormiranda9163]

you miss worded that. the hobby is being murdered.

[@ARockyRock]

lol ok dude

[@davidhaupt7944]

How do I get these carbs I have plenty of blocks heads