Re: COX engine throttles

**RknRusty** Wed Feb 13, 2013 2:26 am

mx862 wrote:Question for you folks...

Higher nitro content will increase combustion temp correct? i still haven't received my fuel.. so i cancelled my order

Ive been running one year old 20% rc car fuel, (odonell racing fuel) with extra 25% drug store castor, and it still works pretty well considering i kept it in my bathroom for the whole time with the cap not tightly sealed, it could have absorbed some water, the engine runs much better with a glow driver attached, and can burn the fuel off immediately, im thinking with better fuel, higher nitro content = higher temps = better combustion= better throttle response and more power... Am i thinking along the correct lines here?

Thanks

You're right about higher nitro running hotter as it has a higher flame temp than alcohol. Your fuel may very well be moisture soaked, or the volatiles have evaporated. Or possibly a platinum deficient glow plug is the reason it runs better with the battery attached.

You've done an impressive job of working out your throttle, MX. Good skills and even better patience.

Surfer_kris Wed Feb 13, 2013 3:33 am

A better running with the battery attached indicates a rich setting. What you have made is a choke (as you correctly describe it too), it is not a carburator, so you should not expect it to run well/lean at lower revs. The choke solution was a simple add-on on cl engines to provide a little bit of "throttling", that's all.

**RknRusty** Wed Feb 13, 2013 5:25 am

Surfer_kris wrote:A better running with the battery attached indicates a rich setting. What you have made is a choke (as you correctly describe it too), it is not a carburator, so you should not expect it to run well/lean at lower revs. The choke solution was a simple add-on on cl engines to provide a little bit of "throttling", that's all.

And once again I've learned the obvious. Of course. That's why RC engines use hot plugs.

John Goddard Wed Feb 13, 2013 5:32 am

RknRusty wrote:
Surfer_kris wrote:A better running with the battery attached indicates a rich setting. What you have made is a choke (as you correctly describe it too), it is not a carburator, so you should not expect it to run well/lean at lower revs. The choke solution was a simple add-on on cl engines to provide a little bit of "throttling", that's all.

And once again I've learned the obvious. Of course. That's why RC engines use hot plugs.

Only with low(ish) nitro fuel though Rusty

**RknRusty** Wed Feb 13, 2013 11:21 am

John Goddard wrote:
RknRusty wrote:And once again I've learned the obvious. Of course. That's why RC engines use hot plugs.

Only with low(ish) nitro fuel though Rusty

Quite right you are, ol' chap. Thanks for tacking that on.

Do y'all still say "chap?"

mx862 Wed Feb 13, 2013 1:35 pm

Big Al wrote:
The 5-40 is a standard UNC thread. Taps and dies are readily available from any industrial supply. Check MSC for example for a wide assortment.
Al

Standard measurements might as well be in chinese, i did not know it would be abbreviated as 5-40, when i was asking for 0.125-40, i got some strange looks, im a child of the metric system.

thanks.

RknRusty wrote:You're right about higher nitro running hotter as it has a higher flame temp than alcohol. Your fuel may very well be moisture soaked, or the volatiles have evaporated. Or possibly a platinum deficient glow plug is the reason it runs better with the battery attached.

You've done an impressive job of working out your throttle, MX. Good skills and even better patience.

Thanks, the plug is fine, i have 3 and they all work the same, my hope is increasing nitro will provide a crisper response.

Surfer_kris wrote:A better running with the battery attached indicates a rich setting. What you have made is a choke (as you correctly describe it too), it is not a carburator, so you should not expect it to run well/lean at lower revs. The choke solution was a simple add-on on cl engines to provide a little bit of "throttling", that's all.

Yes i know the difference between a carb and a choke device( im a motorcycle mechanic), and thats not what im going for here, the question was, will higher nitro, burn better and produce a crisper throttle response, this issue also plagues my exhaust throttle.

Obviously an on board glow driver is out of the question due to size and weight restrictions, so im hoping higher nitro content will produce the result im after.

Just out of curiosity.. what engines used a choke device for a throttle? ive never seen or heard of such a thing, Jared was the first person ive seen that tried anything similar.

Thanks.

Will source some higher nitro fuel, and see what happens.

Thanks for your help folks, much appreciated Cool

John Goddard Wed Feb 13, 2013 1:56 pm

Yo Mx
Higher should should make it less needle
Critical in my experience.
Don't forget though higher needs a larger
N/v Opening mine runs 6.5 turns out on 30%
Again in my experience a silicon fuel tube
Sleeve is critical to stop them thar air leaks.

Throttle rings were I think originally on the
Medallion R/c's.
That's what I nicked the one on my Extreme off.
Very Happy

Surfer_kris Wed Feb 13, 2013 2:22 pm

mx862 wrote:Just out of curiosity.. what engines used a choke device for a throttle? ive never seen or heard of such a thing, Jared was the first person ive seen that tried anything similar.

The OS PET is one, the webra another, I don't know who was first (the ones on OS PET where available in the late 50-ties). These where simply add-ons onto regular cl engines to give them a bit of throttling (or rpm variation) without having to change anything else. The chokes where soon replaced by proper carbs in combinations with a variable exhaust restriction (e.g. Veco .19) and later when the mufflers arrived, the variable the exhaust restriction was dropped.

COX engine throttles - Page 5 A4004858-17-OS-Pet%5B1%5D

COX engine throttles - Page 5 A4004858-17-OS-Pet%5B1%5D

COX engine throttles - Page 5 Osm-1959-pet-ii-099rc

Surfer_kris Wed Feb 13, 2013 2:44 pm

mx862 wrote:
Yes i know the difference between a carb and a choke device( im a motorcycle mechanic), and thats not what im going for here, the question was, will higher nitro, burn better and produce a crisper throttle response, this issue also plagues my exhaust throttle.

Nitro is only a fuel additive to me, and it is closely linked to the compression ratio. If the compression ratio is a little too low for zero nitro, then adding 5-10% will make the engine run better and cooler, and it will then also be a little less sensitive on the needle. Increasing the Nitro level even further will require a reduction of the compression ratio, but the sensitivity of the needle can be seen as a need to optimise the compression ratio. When the fuel and compression ratio are well matching then the engine will be less sensitive on the needle, without the need for nitro. So more Nitro is not the solution to everything...

If you know motorcycles, then try to run that on full throttle and then use the choke only to regulate the speed, and you'll see where the problem is. I think you are simply asking to much from your engine and set-up, you cannot get a proper metering of the fuel without using a proper carburator. More Nitro cannot fix an inherent design problem with the fuel metering.

Jaspur_x Wed Feb 13, 2013 2:56 pm

Big Al wrote:>I was informed by Matt, in the other thread, its 0.125-40, im not familiar with any of these sizes, i being helped trying to locate one.
>
The 5-40 is a standard UNC thread. Taps and dies are readily available from any industrial supply. Check MSC for example for a wide assortment.
Al

ebay, can find individual parts/pieces/tools on ebay quite often once you find the exact description of the suplies you are looking for

mx862 Wed Feb 13, 2013 2:58 pm

Kris, thanks, you learn something new everyday, i never thought a choke could be used to "throttle" thats why i though this will never work. Then i saw Jared's vid.. and since i already had the the aluminum blanks.. i thought i would give it a try. And was quite surprised with the result.

I will be building a carb after i figure out how im going to feed the fuel into it, the carb drawing i posted a few pages back, has a simple system, but i dont like it as the the fuel nipple rotates with the barrel.

I have a few rc carbs, that i think could be simplified and replicated at this scale, but i dont know how efficient they would be, everything i read about carbs on the 010 was always negative.

And again im more than aware that a choke is not a throttle, and im aware of the effect on bikes.

My hope was more nitro would improve the burn, this is more of a problem using an exhaust throttle.

My fuel is already suspect, so better fuel could only improve things.

Jaspur_x Wed Feb 13, 2013 3:52 pm

Surfer_kris wrote:
mx862 wrote:Just out of curiosity.. what engines used a choke device for a throttle? ive never seen or heard of such a thing, Jared was the first person ive seen that tried anything similar.

The OS PET is one, the webra another, I don't know who was first (the ones on OS PET where available in the late 50-ties). These where simply add-ons onto regular cl engines to give them a bit of throttling (or rpm variation) without having to change anything else. The chokes where soon replaced by proper carbs in combinations with a variable exhaust restriction (e.g. Veco .19) and later when the mufflers arrived, the variable the exhaust restriction was dropped.

I have one of those old buggers in my collection,I bought it used in questionable condition back in the 1980`s ,i never did get it to run though. the guy I got it from tuned engines like he was a gorilla escaped from the zoo Rolling Eyes

so I figured it was 50/50 chance enine was shot or it was just that engines are more complex than bananna`s Reading

Jaspur_x Wed Feb 13, 2013 3:56 pm

mx862 wrote:Kris, thanks, you learn something new everyday, i never thought a choke could be used to "throttle" thats why i though this will never work. Then i saw Jared's vid.. and since i already had the the aluminum blanks.. i thought i would give it a try. And was quite surprised with the result.

I will be building a carb after i figure out how im going to feed the fuel into it, the carb drawing i posted a few pages back, has a simple system, but i dont like it as the the fuel nipple rotates with the barrel.

I have a few rc carbs, that i think could be simplified and replicated at this scale, but i dont know how efficient they would be, everything i read about carbs on the 010 was always negative.

And again im more than aware that a choke is not a throttle, and im aware of the effect on bikes.

My hope was more nitro would improve the burn, this is more of a problem using an exhaust throttle.

I do believe Bernie and Matt both sell intake choke style throttles for the surestart 049`s,and ACE made them for the reed vave COX 049`s I believe in the 1970`s or 80`s I`m not sure which but a similar item is on my drawing board when I manage to get to that little item

My fuel is already suspect, so better fuel could only improve things.

mx862 Wed Feb 13, 2013 10:38 pm

Oh yeah i forgot about those, never really looked at them closely, since i dont have an 049.

The small engines on this japanese page.. also show a choke type throttle... http://homepage2.nifty.com/tachino/engine6.html...

Then theres this guy on youtube... i thought for some reason it was a carb.. but also appears to be a choke device. https://www.youtube.com/watch?v=mV90e3wcBww

Hmm not as uncommon as i once thought.

mx862 Fri Mar 01, 2013 10:40 pm

Ok finally some rpm numbers, i bought one of those cheap laser tach's of ebay, the one with the reflective tape, one piece facing the tach, the other on the back side of the other blade to balance things out...

Original engine: (worn out)

MF exhaust throttle copy.

Idle rpm: 8000 give or take.. anything below it wont sustain.

Max rpm 21230.

Choke device throttle.

Idle rpm around 7200

Max rpm 19855.

Second engine: (new)

MF exhaust throttle copy. (throttle doesnt fit)

No data.

Choke device throttle.

Idle rpm: 7567

Max rpm: 25780.

So both perform quite well, the exhaust throttle is much less finicky.

I just found out that the OD of the 010 cylinders is different, so i cant test it on the new engine, i have to make a second one custom fit to the cylinder.

Jaspur_x Fri Mar 01, 2013 10:57 pm

Probably due to the different production runs just like in the TD 049`s etc, may be a factor in the value/reliability of them;COX had several designs for most of their more popular engines for various reasons including these

mx862 Fri Mar 01, 2013 11:01 pm

Looks like i will be purchasing later models due to the thicker cylinders, as ive been informed in the other thread i started, the later ones are the thickest.

Jaspur_x Sat Mar 02, 2013 3:13 am

mx862 wrote:Looks like i will be purchasing later models due to the thicker cylinders, as ive been informed in the other thread i started, the later ones are the thickest.=as is generally the tendancy of most of the COX engines so the 010`s are no huge suprise, but I never checked mine comparatively

mx862 Sun Mar 24, 2013 12:00 am

I went ahead and drilled out the choke throttle body, to 2mm up until the venturi bore, that stays the same, throttle response still sucks but its no where near as sensitive to needle settings as before, 4 turns out and the throttle response is the same as when running lean with the old bore od.

I went ahead and mounted the engine in the plane.. should be done within a month, so i can then test it...

I installed the new piston in the old engine... i guess i lapped it too much.. slight increase in comp, but still leaking around the sides. Looks like i will be getting another motor or a new cylinder in the future.

Rpm is close to 22000 on with the new piston, not good enough.

No time left to build a proper carb, will probably try next winter, for the time being i think i got what i need for my current plane with the two throttles.

Jaspur_x Sun Mar 24, 2013 12:28 pm

Persistance pays off,you`ll get it the way you want it eventually. Perhaps you did lap it too much,or perhaps the bore is just that worn;they don`t always wear evenly throughout the bore.
Throttle response can varry a lot when the engine is weak,it may be a great throttle but fuel draw is affected by the performance so it performs like an imperfect throttle if you see where I`m going with this.

mx862 Sun Mar 24, 2013 1:28 pm

Im at the point where i think i got what i need, 2 engines with 2 different throttles.

The one with the mf exhaust throttle copy is the worn out one, the good one has the thinner cylinder and is running with the choke throttle.

My biggest concern now it the plane its going in... too heavy of a build, and the tiny prop barely clears the cowl... the 020 prop cut down is better but the engine wont throttle with it.

Jaspur_x Mon Mar 25, 2013 4:33 pm

Yes prop clearance is necessary for thrust lol I havn`t tried 020 props on my 010`s yet, could be a rotating mass complication for throttling,not sure.
I have problems with heavy builds myself, havn`t gotten a plane to fly well on 010 power in years but that will soon change.

mx862 Mon Mar 25, 2013 5:12 pm

Thats what im thinking also... the 020 prop is lighter than the 010, even cut down to the same size, it just doesnt rev up.. so it must be the weight, the pitch is different but cant see it making that big of a difference.

Jaspur_x Wed Mar 27, 2013 6:06 pm

It would be possible,several vriable to consider there, pitch can load on an engine if its severe enough pitch to affect heavy load. swap prop[s back to stock 010 to see if its a remedy or not

mx862 Wed Mar 27, 2013 10:52 pm

Jaspur_x wrote:It would be possible,several vriable to consider there, pitch can load on an engine if its severe enough pitch to affect heavy load. swap prop[s back to stock 010 to see if its a remedy or not

Stock props work just fine, pitch isnt dramatically different... oh well, will just use the stock prop.. or get rid of the throttle and run the 020 prop.

Looks like the plane will come in under 5 ounces, but still too heavy,I went a bit overboard.. steerable nose wheel, landing/navigation lights, heavy epoxy fuel proofing, wheel pants.. all that stuff was unnecessary. I may ditch the cowl.. like the one guy on youtube with his 010 powered guillows piper cub.

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