1/2A Throttling
08-20-2016, 11:10 AM
#1
1/2A Throttling
Wondering about throttling comparison/contrast between these various means...
Only one I've really had any experience with so far is the ultra-simple Ace system which is simply a tapered needle that is moved in or out of the reed orifice and thus is restricted to reed valve engines only. Thought it worked quite well but the application at the time didn't use it well - that being a Cox Sportavia (motor glider) that needed every bit of the power to get to as high an altitude as possible lest the flight would be very short.
I remember putting in a flight on a neighborhood kid's C/L plastic P-51 a long time ago that I believe was equipped with an exhaust throttle sleeve: IIRC, a quick snap of the wrist down would give a preset low throttle position and likewise a snap of "up" would go to full throttle.
What little I saw about the Tarno carb sounds like low throttle position is not so great and vaguely remember that it may have required CC pressure to run properly?
Only one I've really had any experience with so far is the ultra-simple Ace system which is simply a tapered needle that is moved in or out of the reed orifice and thus is restricted to reed valve engines only. Thought it worked quite well but the application at the time didn't use it well - that being a Cox Sportavia (motor glider) that needed every bit of the power to get to as high an altitude as possible lest the flight would be very short.
I remember putting in a flight on a neighborhood kid's C/L plastic P-51 a long time ago that I believe was equipped with an exhaust throttle sleeve: IIRC, a quick snap of the wrist down would give a preset low throttle position and likewise a snap of "up" would go to full throttle.
What little I saw about the Tarno carb sounds like low throttle position is not so great and vaguely remember that it may have required CC pressure to run properly?
08-20-2016, 12:27 PM
#2
The Tarno works best with a muffler for better idle and pressure tap helps when you bang it open to full throttle.
I like the open throttle sleeves no fuss they simply work with no set up issues.
The reed valve needle airflow / fuel restrictor has you dealing with a hole in the firewall to access the pin with
a servo. Eliminates the screen and restricts airflow some when drawn out by the servo as some of the pin
is still in the venturi. Throttle sleeve is the best solution for minimal power loss with reed engines.
I like the open throttle sleeves no fuss they simply work with no set up issues.
The reed valve needle airflow / fuel restrictor has you dealing with a hole in the firewall to access the pin with
a servo. Eliminates the screen and restricts airflow some when drawn out by the servo as some of the pin
is still in the venturi. Throttle sleeve is the best solution for minimal power loss with reed engines.
08-24-2016, 10:42 PM
#3
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Cox made a cylinder for their .049 engine that was machined to accept a movable ported sleeve to throttle the engine. The sleeve had a C clamp type connection with a arm sticking out to move the sleeve to open and close exhaust port for throttle. You could adjust sleeve to any position in relation to the arm.
08-30-2016, 07:07 AM
#5
I just ordered one of these last night. There was a write up in r/c flyer (if memory serves me correct) about these.
http://coxengines.ca/cox-.049-rc-flyer-engine.html
http://coxengines.ca/cox-.049-rc-flyer-engine.html
11-17-2016, 09:22 AM
#7
I just ordered one of these last night. There was a write up in r/c flyer (if memory serves me correct) about these.
http://coxengines.ca/cox-.049-rc-flyer-engine.html
http://coxengines.ca/cox-.049-rc-flyer-engine.html
Would be interested to know what throttle types can also shut the engine down when commanded to do so. Will this type do it?
Last edited by H5606; 11-17-2016 at 09:26 AM.
11-17-2016, 10:03 AM
#8
That Tarno Carb is meant for the "TD" versions and none of the TD's idled like you would exspect a larger engine does. I have used Sleeves of various makes, with some success, that other thing from Ace I have never tried, looks like it is meant for the reedy engines.
11-18-2016, 05:36 AM
#11
Don't forget the Ace style throttle. It is pretty much the same thing but for the tank mount. Cheaper too.(sorry, less expensive) http://coxengines.ca/throttle-for-co...bee-style.html I think they are very rich on the low end, but any of the reedies will fall out of the air at 7,000 rpm anyway, as the propellers are not very efficient at those speeds.
11-18-2016, 06:21 AM
#12
Here's a couple of videos I made in 2011 when I was experimenting and playing around the Cox .049 Sure Start.
https://www.youtube.com/watch?v=pdnC55uOhfk and https://www.youtube.com/watch?v=pvpmLy0ToYE
I was impressed with how well it worked although I haven't flown it.
https://www.youtube.com/watch?v=pdnC55uOhfk and https://www.youtube.com/watch?v=pvpmLy0ToYE
I was impressed with how well it worked although I haven't flown it.
11-26-2016, 09:06 AM
#13
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Long long ago I cobbled up a workable throttle with some tubing and washers:
http://www.rcuniverse.com/forum/1-2-...-throttle.html
This may inspire someones creative juices and improve apon it. One thing I would do differently is make the whole exhaust assembly about 1/2 the length shown in these old pictures.
Dave
http://www.rcuniverse.com/forum/1-2-...-throttle.html
This may inspire someones creative juices and improve apon it. One thing I would do differently is make the whole exhaust assembly about 1/2 the length shown in these old pictures.
Dave
Last edited by fritzke; 11-26-2016 at 09:12 AM.
03-05-2017, 11:38 PM
#15
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I read this thread only last week, with interest as I always have 4-5 engines in bits and carbs here and there to tinker with.
Saturday I went out to the hanger to meet my buddies and do some winter work on the Moth. As usual, 1-2 people drop by during the day to say hi and keep us from making any progress by talking for hours. One of the fellow owns the house and property to the north, has a PA-12 there and taxis in through the back of his yard to use the runways, He dropped in around 2pm and as I had some model stuff strewn around, we startted chatting and I learned the had flown some c/l and r/c in the past and was interested in getting back at it. Mentioned he would like to go electric.. bla bla..
Then he mentioned he had flown a such-and-such, ACE something.. with a 3 channel radio and TD .049.
"Whizard"?
"Yeah, the Whizard, that's it.. and the engine had one of those carbs you could order for it, what was that now?
"Tarno?" I suggested..
"That's it!... you know, I still have engine back in a box at the house. If you're interested, I could pop over and grab it."
"Sure.."
10 minutes later he was back, "Yup, found it. I think it's in pretty good shape.. think you can get it to run again?"
"Oh, probably, it's worth a try. Thanks."
I have one of these exhaust throttles in the collection.. it's from a Medallion .049 and was coupled to doohickey on the intake as well. I put it on the Space Hopper just to look at it. I don't have the .049 it came from.
Saturday I went out to the hanger to meet my buddies and do some winter work on the Moth. As usual, 1-2 people drop by during the day to say hi and keep us from making any progress by talking for hours. One of the fellow owns the house and property to the north, has a PA-12 there and taxis in through the back of his yard to use the runways, He dropped in around 2pm and as I had some model stuff strewn around, we startted chatting and I learned the had flown some c/l and r/c in the past and was interested in getting back at it. Mentioned he would like to go electric.. bla bla..
Then he mentioned he had flown a such-and-such, ACE something.. with a 3 channel radio and TD .049.
"Whizard"?
"Yeah, the Whizard, that's it.. and the engine had one of those carbs you could order for it, what was that now?
"Tarno?" I suggested..
"That's it!... you know, I still have engine back in a box at the house. If you're interested, I could pop over and grab it."
"Sure.."
10 minutes later he was back, "Yup, found it. I think it's in pretty good shape.. think you can get it to run again?"
"Oh, probably, it's worth a try. Thanks."
I have one of these exhaust throttles in the collection.. it's from a Medallion .049 and was coupled to doohickey on the intake as well. I put it on the Space Hopper just to look at it. I don't have the .049 it came from.
03-06-2017, 08:52 AM
#16
Its nice to have airport buddies like that. 
Is the picture taken on the paper towel possibly what was referred to in the quote from post #3? ...Something they used in their surface vehicles?
Cox made a cylinder for their .049 engine that was machined to accept a movable ported sleeve to throttle the engine. The sleeve had a C clamp type connection with a arm sticking out to move the sleeve to open and close exhaust port for throttle. You could adjust sleeve to any position in relation to the arm.
03-06-2017, 11:20 AM
#17
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Have you poked around this site? http://www.mh-aerotools.de/airfoils/cox_frameset.htm
03-06-2017, 11:24 AM
#18
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Yeah no kidding! There is a bit of a pattern, I've run into enough private pilots with old Cox stuff at home that I wonder if I ought to start posting want ads on the bulletin boards at all the local airports..
"Top dollar for used Cox engines - $5, maybe $10 depending on condition! Contact me for honest and generous appraisal."
"Top dollar for used Cox engines - $5, maybe $10 depending on condition! Contact me for honest and generous appraisal."
03-06-2017, 05:09 PM
#19
Good story, MJD. Seems like half of my fellow model club members have given me their old .049s and such when they come across them in the back of their shop drawers. They are usually rundown reedies with broken needle valves, rusty cylinder walls, and dead glow heads. I just keep thanking them and accepting the gifts while showing my appreciation in hopes that some nice mint TDs of any size end up coming my direction. 
03-06-2017, 05:17 PM
#20
As for intake-throttled Surestarts from Cox Int., my experience has been that you can set the engine up for a nice low reliable idle or a nice high rpm ability. If you set it up with higher compression and top end performance, touch and go landings are out of the question. With a lower compression head and a nice low idle, I can only squeeze out about 14k rpm or so. I have the throttles set up on 2 of my planes and have had fun with them regardless of their limitations. And FUN is what it's all about to me.
03-06-2017, 07:45 PM
#21
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The Tarno carbed TD .049 seems to turn a grey 5x3 in the 18,700 range so far. I need to lock the carb down a bit tighter, balance the prop, and screw it to a better test stand, Then I'll get a few tanks through it and see what it;s all about.
So.-o-o easy to make an adjustable airbleed.
So.-o-o easy to make an adjustable airbleed.
03-10-2017, 11:33 AM
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So.-o-o easy to make an adjustable airbleed.
A couple of other things.
- First make sure that both the top and bottom passages close at the same time. It's surprising how many OS carbs I've had which did not do this simple thing. If the top closes early the carb will run hellishly rich regardless of any air bleed. When I ran into this I'd flare out the hole in the barrel so it better matched the intake taper's shape and so that both the intake and downstream ends of the barrel matched up. THEN the air bleed worked well and like it should.
Another option for something like the Tarno with no airbleed is to first ensure that both ends close at the same time. After that file a small "V" notch in the intake side edge of the barrel to act like an air bleed to let a little more air in and suck less on the fuel. Go small and sneak up on a good setting.. Or with the Tarno the body is large enough that it should not be that hard to drill and tap for a 2-56 or 1-72 proper air bleed. Then it's adjustable to account for seasonal variations.
03-10-2017, 12:42 PM
#23
I have not played with my Tarno carb yet. The Queen Bee .074 responded well to an airbleed. It really did not idle at all before the mod. I saw the specs on one of the forums. I drilled the hole a bit smaller than the .062" recommended. I read somewhere that the Norvels needed the base of the carb housing opened up to a bit larger than the top opening like BMatthews mentioned. I have a new .06 that does not idle at all which I may try this on some day. I have since got a few more that work well, so it still sits in the disappointment drawer.
03-10-2017, 05:06 PM
#24
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The scheme I saw was to open the air bleed hole bigger, and add a small tab of shim stock with a machine screw to the front of the carb, pivot it over the hole for the right mixture, and tighten.
Ok not so-o-o easy, but maybe in principle - we're talking a shallow 2-56 tapped hole and fabricating something small from very thin metal - but achievable for the average tinkerer at least. I imagined opening up the hole a bit, then tapping a button head 2-56 into the front tight up beside the air bleeds hole could work - back it out a hair from the surface and go from there. Well maybe the head is still too small, but then that could be dealt with. Anyhow this weekend I'll be able to get some run time on it and figure out how it behaves.
Ok not so-o-o easy, but maybe in principle - we're talking a shallow 2-56 tapped hole and fabricating something small from very thin metal - but achievable for the average tinkerer at least. I imagined opening up the hole a bit, then tapping a button head 2-56 into the front tight up beside the air bleeds hole could work - back it out a hair from the surface and go from there. Well maybe the head is still too small, but then that could be dealt with. Anyhow this weekend I'll be able to get some run time on it and figure out how it behaves.
03-18-2017, 05:22 AM
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I ran a few tanks through the TD/Tarno. Been running 25% fuel, Cox grey 5-3 - best number 18,900 rpm. It throttles okay, but it does have a tendency to load up. Might pick up a couple of number drills and open up the air bleed, or just keep the idle high and live with it, a 5-3 at 5k doesn't do much anyway. I have an old Junior falcon airframe that had rudder only escapement, it is stripped down and pretty much ready for recovering, so I think this would be a fine nostalgic combo, especially since it only needs 5-6 hours more work.