Cox .051 Un-numbered Cylinder/ Tarno Air Bleed

I bought a used teedee015 off of ebay,it too has no number on the cylinder,original or not I can`t say. Thats the engine on my modded littlest stick in my crash video
I put a carb from Bernie on mine too,never tach`d it yet though,no need to concern about those details on this little airframe,26" wing just to help her be flying @ managable speeds and it still seems a tad much

My used,tarno carbed TD049 is on its way for comparison sake,but the bernies carb works,slightly modded after that crash. The fuel nipple got broken by the impact so I modded the teedee nbv to fit over the fuel nipple sleeve that was on the carb,that brass fuel nipple will be less likely to break

But now that I have a teedee05r/c I will probably swap the 051 off that plane anyway.

Your ace wizzard is a great plane for a teedee049/051/05r/c,she will be a load of fun with that engine on there,mine hangs over my desk lol

Mine is un-numbered as well. I'll have to look at the piston though, haven't had it apart yet.

PV Pilot: The links will get you to 3 pictures of how I made the adjustable air bleed
on my Tarno carb. The details are as follows to a disassembled carb.:

1. Original air bleed hole enlarged to appx. twice the original size and de-burred both inside and out.

2. Carefully flatten face of carb. using #400 wet /dry sand paper on a flat glass surface.

3. Drill and tap a hole on flat face of carb. for 2 x 56 screw. Not a thru hole but appx. 3/16" deep. Requires two tap styles. One a plug tap and finished with a bottoming tap. Exact position not measured, but positioned by eye.

4. A small sliding "door" was fabricated from a scrap piece of aluminum, appx.3/32"x1/4"x3/8". One end was rounded and drilled for a tight 2x56 clearance hole. The mating face of this little widget was carefully flattened using #400 on a glass surface. This was done to insure a good seal against the carb. face.

5. A 1/4" long 2x56 Pan Head Phillips screw and a lock washer secure the widget to the carb. and allow adjustment by slicing the bleed hole very precisely. This whole setup must have a low profile to avoid being hit by the prop. Unfortunately it can not be adjusted with the engine running.

[b][u]Result: 7k to 18K at 5800' ASL. Good enough for 1/2A RC with 5x3 Rubber Duckie.


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Thank you, but those links are lisited as "image doesn't exist"

I'll give the picture posting another try??

https://servimg.com/view/17167917/36
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Follow these instructions and they will help you post the image in the topic.

Those links worked,,thank you for posting those.. Nice work on that ajustable bleed.

I'm doing some thinking about why an adjustable Air Bleed works particularly on a Tarno carburetor. Very dangerous! Once I come up with some logical ideas, I will post them here as some food for thought if anyone is interested. I am also soliciting any thoughts anyone else may have.

A little too much time spurred me on to do a little rambling about the theory behind my modified Tarno Carb and it’s adjustable air bleed that does work.

I think that unmodified “Antique” Tarno Carbs. are probably not worth the money or tinkering time because their stock performance has a lot to be desired. They are quite heavy to boot. Other Carbs. and setups work as well as or better which I mentioned in my original post. Examples include: latter day COX TD05 RC Carbs. and throttle ringed/venturi necked “Dickybirded” TD 049/051 setups work very well. “Dickybird” TD setups work best for me due to their simplicity/reliability, light weight, and good performance. (≈5.5-6K to 19+K RPM)

For me, modifying a Tarno is another story. Tinkering presents challenges that my retired and atrophying engineering brain needs to keep its 65 YO clock wound. Take note, most of what I say concerning the reasons for my enhanced Tarno Carb.’s performance is opinion which is not thoroughly analyzed or provable. My experimentation did however result in a useable carburetor. (I’m thinking about using the previously shown modified Tarno TD.051 engine on an Air Boat rather than a 1/2A Plane because a boat won’t crash if the engine quits). I have a TD 049 that is “Dickybirded” and will work fine for the ACE Whizard I am building. (≈5.5-6K to 19K RPM)

This particular Carburetor running at 5800 ASL after being modified, has smooth transition, fairly high Idle speeds, (≈7K RPM but slow enough for bringing an RC plane down), and lower High-end, (≈18K, again, high enough to fly most 1/2A RC planes). The unmodified carb., ran at (≈ 10K idle to ≈18K high end, with ragged transition).

I don’t know whether the throat has a larger opening than an exit. I never paid attention or measured it. That would seem to be backward and not according to “Hoyl” or “Murphy”. I do think that when the barrel is closed the pressure around the fuel bar gets lower. This causes more fuel to be sucked resulting in a richer mixture that is out of the ideal combustion range (steicometric** [spell??] ratio). The volume of intake air is also reduced adding to the rich mixture like a choke on an old time car. This results in very poor performance, loading up of the engine, and eventual engine stoppage. This is contrary to what you want to have happen in an RC carburetor. A relatively constant fuel/air **ratio throughout the carb’s. range of operation and a little rich at idle is the ideal in my opinion. A slightly rich idle will facilitate a smoother transition to full throttle. Without being able to control this pressure in a stock Tarno carburetor, performance is significantly compromised. I think the pressure at the fuel nozzle gets lower as the barrel is closed due to higher acceleration of the air in the carb. throat. (Bernoulli’s principal) Try the experiment shown below and do some ancillary thinking while blowing on the spool. Think about acceleration and air pressure and why a venturi or any other airfoil works. Consider why the piece of cardboard doesn’t just blow out of the spool when you blow harder.

To counteract the much richer mixture at idle, and the lowered pressure in the carb. throat, as well as higher suction at the fuel nozzle, the air into the carburetor must be better controlled. A closed Air Bleed creates a richer mixture—Open Air Bleed causes leaner mixture. This is done by providing an air bleed opening which results in increased carb. throat pressure and a leaner mixture due to less fuel being drawn thru the fuel bar. Getting the sweet spot for any given carburetor requires adjustability. “Voila” the adjustable air bleed.

Getting the sweet spot for any given carburetor requires adjustability. “Voila” the adjustable air bleed.

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I think you are right on the money Astronomer 1. Since most smallish air engine manufacturer's only think in the high speed realm and dont give proper attention to low speed or drop dead idle performance, one has to think outside the box.

I have several off road engines that use a 3 needle carb (high,mid,low), plus a idle air gap needle. I looked for the smallest 3+1 needle carb I could find, and the only thing I could find (at this time) was one for a 15 sized offroad engine. Basically the mid range adjustment is just repositioning the outlet jet orifice in a different spot in the airstream and it is a range of from the side of the carb bore and then out to near the middle of the whole bore,,or more centered in the body/airstream. when you adjusted the mid range needle or jet position, it also moved the high speed needle assembly in turn. very tunable and you can get the top end, transition, low speed mix, idle, pretty much perfect. But then again, it is offroad stuff.

PV Pilot: Thanks for the feedback. Sometimes thinking out of the box gets a different perspective on things. Compiling ones thoughts in writing tends to serve as kind of a "Fact Checking" exercise. I was in the process of adding my Bernoulli's demo diagram while you were responding.

Someone with other ideas will probably show up who will hopefully shed a different light on my VERBOSE dissertation.