Go Back  RCU Forums > RC Airplanes > "1/2 A" & "1/8 A" airplanes
Reload this Page >

Throttlability of 1/2A Cox (and Norvel too) engines

Notices
"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

Throttlability of 1/2A Cox (and Norvel too) engines

Old 01-15-2005, 08:52 PM
  #1  
meowy84
Thread Starter
 
Join Date: Oct 2004
Location: , IN
Posts: 1,061
Received 2 Likes on 2 Posts
Default Throttlability of 1/2A Cox (and Norvel too) engines

Ok, ok, I know this subject has been beat to death already in other posts but i STILL have more questions and comments so I thought I'd throw them out there for the guru's. As some may know I'm 'researching info' on building some carbed/exhaust throttled Cox engines (both reedie and TD) in the single configuration and also in the flat twin configuration and eventually if all looks good to culminate in a Cox 5 cylinder radial. My ramblings may be disjointed so bare with me.

Here's what I learned and what I still wanna know. As a few of you have commented, building a r/c carbed Cox reedie (or TD) is not as simple as it may sound (especially compared to the larger engines). Some mentioned that a combination of throttling methods might give better results so I have decided to give the engine (Cox reedie ot TD) as many advantages as possible and use a combination of an r/c carb (one from an AERO/AME .049 engine that I just happen to have) and an exhaust throttle. Also, for best results Wink mentioned that the reed valve should be as close as posible to the end of the crank to essentially minimize the crankcase volume, thereby allowing better inflow of fuel charge when the reed valve finally opens.

Anyways, while I'm trying to concentrate on Cox engines at this point I also have a NIB Norvel .061 Revlite r/c engine and a NIB Norvel Cmax .061 engine with the muffler rod-throttle setup. I haven't ran either of these engines as of yet but was wondering if those who've ran either of the Norvels could fill me in on the general idle rpm of these engines? What do these engines idle at? I recall 7,000 rpm being thrown around as the idle of a lot of the 1/2A engines. Is it possible to reduce this any further (to the level of .10-.15 r/c engines which I assume idle at around 4,000 rpm or so?)? Again, someone suggested that I use the r/c Revlite with the t-shaped throttled muffler from the Cmax to further reduce the idle rpm and improve the response throughout the rpm range. This leads me to another question. How does the idle rpm of the r/c Revlite compare to the idle rpm of an exhaust throttled Cox .049 reedie or Cox TD? I realize that these (Norvel and reedie Cox) are two different engine designs but let's assume all other things being equal and comapre just the lowest reliable idle rpm figures.

Also, what about the progression and responsiveness? With 1/2A engines should I expect better throttling qualities with an r/c carb (as in the Norvel or others of course like AP, etc.) or with an exhaust throttle ring type of device?

To summarize my main questions then: (1)idle rpm of Cox engines? (2)idle rpm of Norvels? (3)responsiveness with carb vs. responsiveness with exhaust throttle?
Old 01-15-2005, 10:17 PM
  #2  
SST
Senior Member
My Feedback: (2)
 
Join Date: Jun 2002
Location: Mt. Morris, MI
Posts: 1,151
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Just my opinion, but after 30 years of Cox engines, since Norvel came along, I wouldn't use a Cox for ballast weight...
Old 01-15-2005, 10:34 PM
  #3  
CafeenMan
Senior Member
 
Join Date: Jan 2003
Location: Spring Hill, FL
Posts: 4,734
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

I don't tach my engines so I can't give specific numbers. I have a Norvel Big Mig .061 R/C in my [link=http://airfieldmodels.com/gallery_of_models/rc/jgrc_aggressor/index.htm]JGRC Aggressor[/link] and it throttles well. Late in the video you almost stop hearing the engine. I thought the engine quit, but the pilot, my friend Mike, had simply throttled back. I find it idles well.

The only problem I had with the Norvel was it took about 5 tanks before it would keep running below half-throttle. Part of the problem was a sensitive needle and I'm sure part of the problem was lack of break in. I have to say that the engine throttles much better than I would have thought.

Now I just want it to gain about double its current RPM. The Aggressor isn't as fast as I want it to be.

As far as the Cox goes, it's been a long time since I've run one. I ran Cox engines almost exclusively as a kid and owned maybe 30 or more of them. I still have several. One of my control line planes came with the exhaust throttle. It was set to be high or low but it killed the overall power and the plane wouldn't stay airborne at low.

I tried it on an R/C plane once but again, it really robbed all the power and the throttle capabilities weren't all that great either. I don't know what other type of exhaust throttles are available, but the one I have isn't worth bothering with. It is an original Cox part btw.
Old 01-15-2005, 10:34 PM
  #4  
Andrew
 
Join Date: Feb 2003
Location: Murray, KY
Posts: 3,201
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

ORIGINAL: SST

Just my opinion, but after 30 years of Cox engines, since Norvel came along, I wouldn't use a Cox for ballast weight...

Aw, come on Doug, don't hold back -- say what you feel.

Come to think of it, DickeyBird could melt down a few of his COX engines and cast another cannon -- call it his COX POPPER.
Old 01-16-2005, 08:11 AM
  #5  
DICKEYBIRD
Senior Member
 
DICKEYBIRD's Avatar
 
Join Date: Apr 2002
Location: Collierville, TN
Posts: 2,749
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Oh c'mon guys, stop the trash talk.....I don't have time for another full-blown "OK you Norvelites have gone too far" thread! Besides, I need all the self-confidence I can muster; my Design Contest entry has a Pee Wee .020 on it. Those little fellers will bring the most diligent of tinkerers to their knees!

Meowy, a nice snug-fitting exhaust throttle sleeve on a non-SPI cylinder equipped Tee Dee will get you down to 4500 - 5000 rpm. It will require lowering the compression and reducing the venturi ID as well.
Old 01-16-2005, 05:11 PM
  #6  
meowy84
Thread Starter
 
Join Date: Oct 2004
Location: , IN
Posts: 1,061
Received 2 Likes on 2 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

McClintock told me that he has three different types of Cox throttles...all original Cox throttles I think. I have one that came on the Cox cars I believe that has the 3 detents and a little side plate that's attached to the crankcase. Since I never have any time I haven't run it yet to see how it performs. But my question is this: are these throttles really an on-off proposition with not much inbetween? And if so then why is that? I assumed that if I removed the detent I could set the throttle up for a smooth progression and so would hope for a correspondingly smooth rpm gain.

Dickeybird, that's good news...4500-5000 is not bad at all as far as I'm concerned. What can I expect without the compression and venturi modifications that you mentioned? Also, excuse my ignorance but what is SPI?

So as far as throttling (be it an exhaust throttle or otherwise) am I to assume that because of their design, the TD engines have a lower idle and smoother transition than the reed valve engines?

CafeenMan, so after the break-in period the throttling improved significantly?
Old 01-16-2005, 05:25 PM
  #7  
CafeenMan
Senior Member
 
Join Date: Jan 2003
Location: Spring Hill, FL
Posts: 4,734
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

ORIGINAL: meowy84
CafeenMan, so after the break-in period the throttling improved significantly?
Yes.
Old 01-19-2005, 08:20 PM
  #8  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Meowy84,

Dig up my articles on throttling 1/2As for the lowdown on the subject. I've had TDs, Norvels and VAs down to 4K with excellent transition to the top after prolonged idling. On a 6 X 3 black Tornado, the TDs could do 17 to 18K, the Norvels 19K, and the VAMK2 a solid 18.5K. I've had the VA MK1 down to 2.5K on occasion, on a 5.5 X 2 APC prop, transitioning cleanly up to 22K. These figures are the best I can remember off the top of my head. They can vary due to temps and humidity, fuel freshness and plug type and condition.

Quite often while playing with engines, I get them purring at 3K on a 6" prop and its fun to watch. However, the least disturbance, such as moving the stand, or touching the fuel tubing takes them out of some sort of zone and they crap out. Anything below 5K on a 6" prop is just extra insurance. Often I try for 4.5K just to be sure she'll keep running at 6K in the air. And, 6K is all you need. Depends on the plane, some will land at 7 to 8K, and that's fine.

The TDs are notorious for being hard to throttle at the intake. For various reasons, they throttle better at the exhaust, but many engines will do that, as I found and the articles describe. The Lite Machine's heli is one of them. On a Cox Texaco, I tried an exhaust throttle of my own design along with a muffler and at idle, it was so quiet, you could hear the reed vibrating. Waiting to be tested is a diesel version. To get the TD to throttle well, I had to cut new timing numbers and bypasses into a blank Cox cylinder. Shape of the bypasses was also a factor.

SPI is sub-piston induction, a misnomer, in my opinion. What occurs is that at top dead center, the bottom of the piston rises above the bottom edge of the exhaust port. This does hinder good throttling on Cox engines but does not do the bad deed on Norvels and VAs (the ones that have it). Why that is so, is speculative, but I think it may have something to do with the fact that Cox has true schneurle porting, (two exhaust ports) while the others have one exhaust port and three by-passes.

Throttling improves after break in because as you run in the engine, your main needle setting is changed as you progress and this also affects your mixture at idle. A rich needle at full bore and the engine will keep running. A rich setting at idle is a killer.

There are two engine that, so far, have defeated me in the way of perfect throttling. One is the VA .020, which never made it to market in a meaningful way. It was non-throttled so I added a G-Mark .03 throttle to it and that had added to it an adjustable airbleed. One of the issues with the VA .020 was the plug they gave you and the fact that it was far undercompressed. Playing with .010, .020 and .049 plugs, I came up with a modified .049 plug that gave me a good 18K (as I recall) on the stock grey prop. However, despite having an adjustable airbleed, this one will idle all right, but transition is erratic.

The other is the TD .020. Coincidence? Don't know. After successfully throttling the .010 with an exhaust throttle, I made one up for the .020 expecting the same result but that was not to be. So, I tried a small throttle made in Czechoslovakia that already came with an adjustable airbleed. Like the VA, this did not work well either. So, I connected the exhaust valve to the intake throttle and while there was an improvement, perfection is still out of reach.

Successful throttling has nothing to do with keeping the glow plug lit. It has everything to do with maintaining the proper fuel mixture at all speeds. Don't even think of throttling at the intake without some sort of adjustable airbleed, or other means to adjust the idle.

MP Jets makes an exquisitely made, two needle throttle and VA makes an equally well made, adjustable airbleed unit. Start with either one of those and you'll have a tremendous head start.
Attached Thumbnails Click image for larger version

Name:	Fd90859.jpg
Views:	14
Size:	129.2 KB
ID:	217695   Click image for larger version

Name:	Hc91548.jpg
Views:	10
Size:	118.5 KB
ID:	217696   Click image for larger version

Name:	Sx62540.jpg
Views:	13
Size:	166.6 KB
ID:	217697   Click image for larger version

Name:	Lj23048.jpg
Views:	10
Size:	125.4 KB
ID:	217698  
Old 01-19-2005, 08:34 PM
  #9  
rrragmanliam
Senior Member
My Feedback: (1)
 
Join Date: Oct 2003
Location: Arvada, CO
Posts: 1,228
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Mr. W,

WOW

I am so glad you are feeling better and contributing to this fourm. You sir are a veritable encyclopieda of knowlage in all aspects of this hobby we love so much. I cannot get enough of your post's. Thanks for all the info I appreciate it!

Darren
Old 01-19-2005, 08:44 PM
  #10  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Thanks Darren,

You certainly are welcome and yes, things are looking up. Your appreciation is most heart warming and I hope that any information or advice I give, is useful to any and all.
Old 01-20-2005, 07:13 PM
  #11  
meowy84
Thread Starter
 
Join Date: Oct 2004
Location: , IN
Posts: 1,061
Received 2 Likes on 2 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

1705493-Andy, thank you for sharing your knowgedle with me (us). Here's some questions: You said that "The TDs are notorious for being hard to throttle at the intake. For various reasons, they throttle better at the exhaust, but many engines will do that, as I found and the articles describe. The Lite Machine's heli is one of them."...You mean the Norvel .061 Cmax in the helis is better throttled at the exhaust than with an r/c carb? Does that mean that the Cmax throttles better than the Revlite r/c .061? What are your thoughts on using a Revlite .061 r/c and adding the T-shaped-rod-throttled muffler from the Cmax?

Also, where can I dig up some of your atricles on throttling 1/2A engines? (I'm afraid my search skills aren't quite up to par).

You also say that to throttle at the intake you must have an adjustable air-bleed. I don't have my engine in front of me so I can't check right now but is one present on the Norvel Revlite .061 carb?

And finally, what types of carbs are those in your pics? Is any one of them the Tarno carb?
Old 01-20-2005, 08:15 PM
  #12  
Andrew
 
Join Date: Feb 2003
Location: Murray, KY
Posts: 3,201
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

ORIGINAL: meowy84

You also say that to throttle at the intake you must have an adjustable air-bleed. I don't have my engine in front of me so I can't check right now but is one present on the Norvel Revlite .061 carb?
The NORVEL has an extremely rudimentary air bleed -- it can be modified, but is not in any way adjustable in the manner that Andy is referring to. With the screen removed, you will notice a notch in the back of the venturi. As the barrel is rotated closed, this notch allows for additional airflow into the engine. You can open this notch with a file, but obviously this is a one way trip. Open the notch too much and your idle will be too lean -- with the only remedy being to buy another carb body. You can also change the taper on the needle -- the way the carb is constructed, as the throttle is moved toward idle, the barrel also moves inward, toward the end of the spray bar. There is quite a bit of inward movement -- open the throttle fully and turn the needle in until it seats lightly. back off 1/4 turn and move the throttle to full idle. When you lightly seat the needle again, it will take less than a quarter turn. The overall effect is to lean the mixture as the engine throttles back.

Some of the guys here have drilled thru the carb body at the base of the idle stop screw and used this screw as an adjustable air bleed.

Bipe Flyer had one of the best ideas of managing the mixture. Use a remote needle to set the high end and use the standard needle to set the low end.

OTOH, I tend to fly WOT until empty and deadstick it.

BTW, never ever mention idle speed in any thread that CombatPigg is participating in -- I understand that he gets a rash any time his engines drop below 26K.
Old 01-21-2005, 02:10 PM
  #13  
meowy84
Thread Starter
 
Join Date: Oct 2004
Location: , IN
Posts: 1,061
Received 2 Likes on 2 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Andrew, thanks for that info....I certainly wouldn't want to have to buy a replacement Norvel carb. Since I plan on keeping the Norvel in one piece (maybe even just to display) I think most of my experimenting will be done with a .049 AERO/AME carb that I have lying around. That one unfortunately doesn't have an air bleed screw either, unless it has something rudimentary on the lines of the Norvel. I'll have to grab my magnifying glass and have a closer look at the innards. Either that or maybe a better approach would be to try and make my own carb...I don't think it should be all that complicated to whip something together using some left over brass/alum stock...that way I can play around with the size and shape of the venturi, etc...
Old 01-29-2005, 11:35 PM
  #14  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

M84,

Sorry for the late reply. For some reason, RCU isn't informing me every time a new post is made on a thread I've participated in. I get maybe one out of four. Perhaps the moderator can look into this for me?

To answer your questions.

Yes, it has been my experience that the heli engine, with the exhaust throttle, throttles better than the stock engine with intake throttle. Many disagree with this assessment but I can't account for that as most times when I ask for tach numbers and prop sizes, I rarely get a reply. Yes, I've rigged up the heli throttle to a stock Revlite and it works quite well. Idle is down to some 6K, (as I recall) and transition is excellent. A heli just HAS to have good throttling and the Arlton brothers have done brilliant work in this regard. I have a Lite Machines heli and the quality of parts and performance is excellent. They've upgraded to an .074 retaining their exhaust throttle and I have no doubt it works just as well as their .061 version.

Notable is that Norvel's .074 uses the same throttle as the .061 except with a larger bore in the barrel. Despite NOT having an adjustable airbleed, the .074 throttles very well. Idle is low and transition is excellent. Why and how it works is probably the Rosetta Stone of good throttling. The trick to it is to understand that the .074 has a very broad needle valve response. Once hitting near peak rpm, dialling in the needle produces little effect, at full bore, for nearly a full turn. This characteristic is used to set the idle. With the top end set, throttle back and take the airplane up to a good height. Idle back and just before the airplane touches down, hit full throttle. If it craps out, land and tweak in the high speed needle an eighth of a turn and repeat. At some point the idle mixture will be exactly right without going overlean at full bore. Amazing, but it works.

Andrew is correct that the airbleed slot can be opened up to affect the mixture at idle but this is only useful if your idle is going rich, which it likely is, most times. And, as he says, you can't go back if you go too far. If some of the guys are drilling though the idle stop arrangement to allow an idle bleed adjustment, I honestly can't see how that would work. At any throttle setting, such a hole is completely blocked off by the barrel. Adjusting the taper on the needle can work, but only if you're very close, by chance, to a good idle setting. This can happen due to manufacturing tolerances.

Most of this has been related in posts going back to last summer. Just click on my "handle/pseudonym" and you'll get a list of all my posts to tickle your brain for a few hours.

As far as my articles are concerned, I'll try to attach them to the next couple of posts. It must be kept in mind that some of the information and opinion will be dated. I continue to experiment with throttling, lately with diesel conversions. Case in point is an exception to my rule that Cox engines throttle better at the exhaust than at the intake. That exception is the TD .09 on to which I installed an MVVS .09 throttle along with a custom muffler. It's been run as glow and diesel and throttling is excellent. Don't recall performance numbers but it flew my sport test bed as well as my stock Norvel .074. Picture attached.

If your AERO/AME throttle is the round bodied one, there's enough meat in the body to install an adjustable airbleed. Let me know and I can rig up an adjustable airbleed. The current Norvel design makes it extremely difficult to make it adjustable. It CAN be done, I did one for Randy Randolph but it was a nightmare. You can see it in his column, in the Sept 2000 issue of Flying Models. Or see the pics attached.
Attached Thumbnails Click image for larger version

Name:	Yw68261.jpg
Views:	15
Size:	43.6 KB
ID:	222477   Click image for larger version

Name:	Bw72678.jpg
Views:	11
Size:	69.2 KB
ID:	222478   Click image for larger version

Name:	Zx69937.jpg
Views:	13
Size:	39.2 KB
ID:	222479  
Old 01-29-2005, 11:44 PM
  #15  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

My first article in the May 97 issue of Flying Models.
Attached Thumbnails Click image for larger version

Name:	Ig12336.jpg
Views:	12
Size:	139.3 KB
ID:	222486   Click image for larger version

Name:	Xs58998.jpg
Views:	10
Size:	121.5 KB
ID:	222487   Click image for larger version

Name:	Zx70186.jpg
Views:	10
Size:	458.9 KB
ID:	222488   Click image for larger version

Name:	Fb87751.jpg
Views:	16
Size:	140.8 KB
ID:	222489  
Old 01-29-2005, 11:51 PM
  #16  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

My second article on throttling in the August 2001 issue. Hmm, can't upload, something about BMP not being supported. Moderator?

OK, if you're freezing, with the white stuff on the ground, maybe my article on skis might be of some interest.
Attached Thumbnails Click image for larger version

Name:	Zx71716.jpg
Views:	10
Size:	455.1 KB
ID:	222493   Click image for larger version

Name:	Zu64652.jpg
Views:	7
Size:	513.4 KB
ID:	222494   Click image for larger version

Name:	Fd93321.jpg
Views:	15
Size:	410.2 KB
ID:	222495   Click image for larger version

Name:	Oj27284.jpg
Views:	10
Size:	182.3 KB
ID:	222496  
Old 01-30-2005, 12:10 AM
  #17  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Well, third try to post my second engine article to no avail.

At any rate, regarding the Tarno throttle, I had mixed results with the unit. It's a very well made little throttle with unique features and a different approach in subtle ways. Unfortunately, it didn't do all that well on my TDs or other engines. Even adding an adjustable airbleed didn't help. I think I understand Ben's (Tarnofsky) approach to the problem of throttling the TD engines but despite my best efforts, I couldn't get it to do what I needed.

In the end, for most engines, some means to adjust the fuel mixture at all throttle settings is a must. There are notable exceptions like the OS MAX .10 and the aforementioned Norvel .074. Some engines won't respond even to an adjustable airbleed and my experimentation has convinced me that timing, compression and even bypass port design, all have an effect as to whether an engine can be made to throttle properly.
Old 01-30-2005, 12:21 AM
  #18  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Missed the full gist of your last question.

The TD .020 has a custom made exhaust throttle with muffler coupled to a John ( that's the make) throttle off of a John .020 diesel. Note that "John" also agrees that an adjustable airbleed is required and he provides one on his throttle. Saved me a bit of work.

The second engine is a TD .010 with a custom made exhaust throttle.

The third is a VA .020 and includes a G-Mark .03 throttle. This one needed to have the adjustable airbleed added.

The fourth is the only 1/2A engine I know of that has an adjustable airbleed. After over a decade of effort on my part, along with Larry Driskill's help, VA FINALLY came up with a proper throttle for their excellent ABC .049 engine. A real keeper and everybody should own one just to see what good throttling in a 1/2A could be like. JMO, as always.
Old 01-30-2005, 04:02 AM
  #19  
William Robison
Senior Member
My Feedback: (3)
 
Join Date: Nov 2002
Location: Mary Esther, Florida, FL
Posts: 20,205
Likes: 0
Received 8 Likes on 8 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

AndyW:

The early version of the TeeDee RC engines had what several have told me is a dead ringer for the Tarno carb, as you said, no air bleed adjustment. See the center engine in the first picture. This version also had only the exhaust collector with a single stack. There was a movable spring band to vary the exhaust restriction. I never got this one to idle with any consistency.

The second version had the collector ring with what looked like a proper muffler attached, and it did have an adjustable air bleed. The two engines on the side in the first picture are this later type.

I have three of these, only one is in service, it has SPI and will idle consistently in the 6K range.

The other two are still NIB, they do not have SPI, hope I might be able to get them down to 4500 or so when they go on their twin.

Two pictures are the later version Cox carb, you can see the air bleed and its adjuster. Fourth is another view of both version engines.

Bill.
Attached Thumbnails Click image for larger version

Name:	Lj21882.jpg
Views:	13
Size:	68.0 KB
ID:	222582   Click image for larger version

Name:	Lg16328.jpg
Views:	15
Size:	94.0 KB
ID:	222583   Click image for larger version

Name:	Ej14223.jpg
Views:	8
Size:	90.6 KB
ID:	222584   Click image for larger version

Name:	Yr47564.jpg
Views:	15
Size:	71.4 KB
ID:	222585  
Old 01-30-2005, 04:24 AM
  #20  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Hi Bill,

Yes, you're right. The Cox RC .05 DID have a throttle with adjustable airbleed. Much wisdom on Larry Renger's part. I suppose what I meant was that currently, no other 1/2A engine offers a throttle with adjustable airbleed. FWIW, after my first article, Randy Randolph installed a Cox throttle on to his VA .049 MK1 and it worked as well as my G-Mark throttled version.

The Tarno was the first, as far as I know, intake throttle for the TD. A valiant effort and some have told me that theirs worked well. Sometimes throttling appears to be more voodoo than science. But only sometimes.

Unfairly overlooked in all of this discussion is the MP Jets .061 available from Ed Carlson. Originally designed as a diesel, the glow conversion runs well and is bulletproof. Hardened steel liner, massive conrod bushed at the business end, and a cast iron piston with the pin held in place by honest to gosh circlips. Plus, it has a remarkably sophisticated, two needle throttle that really works well.
Old 01-30-2005, 05:11 PM
  #21  
meowy84
Thread Starter
 
Join Date: Oct 2004
Location: , IN
Posts: 1,061
Received 2 Likes on 2 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

AndyW, once again, thanks for sharing your wealth of info. BTW, how would you rig up an adjustable air screw on my carb? As to your question, yes my AERO/AME carb is of the round body design but I just don't see where a bleed screw can be put in as the carb body itself is only slightly larger than the venturi opening. The carb does not have a nice square body with a step for positioning the bleed screw like some of the carbs in the pics posted in this thread.

Also, thank you for the articles but unfortunately I cannot read them...the print is too small when I click on them. Is there a way to obtain copies of them or at least be able to read the text somewhere?
Old 01-30-2005, 08:37 PM
  #22  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

M84,

If you wait a moment and you get a small box on the bottom right hand corner of the image, you can left click on that and the image will enlarge enough to read the text.

Re adding an adjustable airbleed to the round body carb, see the pic attached. This one is adapted to mount to a VA MK1. If that's the style of throttle you have, then its relatively simple to do if you have the tools. If you have something entirely different, such as the cast, square body currently available on the Norvels, then its a little more involved. If its something else altogether, a picture would help a lot.

I've been informed by Andrew (the other one) how it can be done using the stop screw and the square body design. You drill a hole at a radically upward angle that creates more of a large slot that intersects the open part of the barrel as it rotates. A unique solution and it should work. The concerns are some rather heavy flash to deal with and potential weakening of the carb body at that point. As Andrew points out, most 1/2Aers fly at middle to full bore and don't want or need a super low idle. That's finally dawning on me and I accept that. Its just that I do do touch and goes on the typical grass runway and my aircraft have no problem with take-off and landings on such a surface. The key to taking advantage of super low idle and perfect throttling is a low wing loading in the range of 7 to 8 ounces per square foot. Doable with contest wood, todays coverings and current radio equipment. It's just my style of 1/2A flying and I really enjoy it. I get a LOT more respect from the .40 crowd and that's a neat bonus, not that I really care. We love 1/2A and make no apologies. We just have a greater diversity in our approach to our part of this great hobby.
Old 01-30-2005, 10:02 PM
  #23  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Sorry, the pic refused to attach but here's a few that might be even clearer.

The round body throttle with adjustable air bleed added.

The square body, radically altered to do the same thing. This is actually the third in a series of tries, none of them simple. Andrew's solution is much simpler and doable by the average modeller with a drill press and good aim.

A TD with the MP Jets throttle adapted. Some years ago, Ed Carlson informed me that the Jets folk would probably make up their carb to fit any engine we liked as long as we ordered enough in quantity. I didn't have the guts to take on such a venture so it never happened. Now the Jets guys have more work than they can handle so it's probably too late. A shame because despite the amazing quality and sophistication of this small, two needle throttle, at the time, it was selling for 15 dollars.
Attached Thumbnails Click image for larger version

Name:	Nl28387.jpg
Views:	10
Size:	47.5 KB
ID:	222980   Click image for larger version

Name:	Wh20282.jpg
Views:	10
Size:	51.7 KB
ID:	222981   Click image for larger version

Name:	Ki18414.jpg
Views:	10
Size:	40.7 KB
ID:	222982  
Old 01-31-2005, 11:33 AM
  #24  
Tom @ Buzzard Bluff
Senior Member
 
Join Date: Apr 2004
Location: Mammoth Spring, AR
Posts: 280
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

ORIGINAL: meowy84
I just don't see where a bleed screw can be put in as the carb body itself is only slightly larger than the venturi opening.
Dunno if it will help you or not but here (if this works) is a pic of the way I added an air bleed circuit to the early VA carb following Andy's suggestions almost to the letter.
I drilled & tapped a piece of 1/8" OD aluminum rod for a 2-56 screw and drilled a hole through it that would mate up with the existing air bleed on the carb body. I opened up the hole in the carb body to match the one in the new circuit. Then I filed a groove across the carb body with a 1/8" round file to match the profile of the new air bleed circuit and JB Welded it in place. I used a couple of dental bands at each end of the new circuit to retain it overnight. To prevent it sticking I oiled the shank of the drill bit I had used to open out the air bleed holes in both the new circuit and the original carb body and used it as an alignment tool while the whole mess drird overnight.
Haven't tried it yet but I have every confidence that it will work just as Andy said it would.
Actually I think the VA carb is a good example of what can be done since I don't know of a smaller RC carb. If you will note in the pic the carb body is little bigger than the fuel banjo or the nut holding on the throttle arm. So if an idle circuit can be added to it then anything else should be a cinch. I can hardly imagine drilling and tapping the 1/8" rod without a lathe but I've seen things equally 'fiddly' done 'freehand' so I imagine a pro level tinkerer could do it without anything except a drill bit, tap and a file. HTH, Tom
Attached Thumbnails Click image for larger version

Name:	Om34605.jpg
Views:	12
Size:	45.3 KB
ID:	223185  
Old 01-31-2005, 12:18 PM
  #25  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Throttlability of 1/2A Cox (and Norvel too) engines

Good work Tom,

I'm glad to see that you've sorted it out.


M84, it seems that you've got some sort of throttle that doesn't have enough meat to install the adjustable airbleed. What Tom has done is the solution I came up with for the square body throttle that I did up for Randy. And, it works for the first VA throttle.

A few more pics may help to clarify how it's done. The first is the early VA throttles and the second is their current design.
Attached Thumbnails Click image for larger version

Name:	Ca81662.jpg
Views:	29
Size:	153.0 KB
ID:	223199   Click image for larger version

Name:	Wr53795.jpg
Views:	16
Size:	125.4 KB
ID:	223200  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.