AndyW

My Feedback: (1)

Yes, the slightest amount of leakage will affect how low you can go with a sleeve type throttle. Milton (Dickeybird) Dickey's excellent article in Flying Models last year gives the lowdown on throttle sleeves for Cox engines. Again, it works real well IF you can get a combo with an excellent fit. Good is not good enough and that's why adding a stock throttle barrel style was developed. The fit of the exhaust restrictor can be precisely controlled if its independent of manufacturing tolerances of the cylinder.


Bob,

Can't find your Hiscott post. Can you help?

Tom @ Buzzard Bluff

Andy wrote:
< Bob, Can't find your Hiscott post. Can you help?>

Nor could I and I tried pulling up a list of his last 100 posts. I suspect it isn't in the post title or I would have jumped on it the 1st time around since I am interested in them.
For meowy84s benefit:
<Bob, what engine are you using the Hiscott carb on?>

The Hiscott throttling system is much more than a carb. Stated a different way it's not even a carb at all in the tradional sense. It is a very odd-shaped rotating spraybar that replaces the Cox item in the Medallion front housing. The rotating spraybar has an actuator arm that controls it's position through a servo. After about the first half of the rotation of the spraybar the upper end of the arm makes contact with a sliding bar in the exhaust collector that gradually restricts the exhaust as it simultaneously completes the rotation of the spraybar. It is much harder to verbalize well than it is to understand when seen in action. Essentially the spraybar rotation serves the purpose of a low speed circuit in the initial portion of it's movement while the mixed action of spraybar and exhaust restriction working in concert over the last portion of their movement is the high speed circuit if that will help the viualization process. It is a unique system that depends on both spraybar and exhaust restriction working together to effect the desired result. Some very original non-linear thinking went into developing the system and the designer has my admiration. HTH, Tom

meowy84

AndyW, in re. to your latest pics of the TD with the throttle-in-muffler I assume that this is the setup that you also mention worked very well on the Cox .049 reedy, where at idle the most dramatic noise was the vibration of the reed? Also, I'm curious as to the effectiveness of this setup since in one of the articles you mention that the preferred setup (as on the Litemachines Norvel Cmax with the t-shaped muffler) is to have the exhaust governor/restrictor/butterfly situated AFTER the muffler, while in the TD setup in the pics the butterfly valve is BEFORE the exhaust enters the actual muffler. Any comments on the advantages/disadvantages on each setup and how much would this depend on the engine? In particular I was wondering which setup might work better with the reedy: the Alton brothers Litemachines setup or the setup as in your latest pics of the TD? Also, what is the purpose of that partially screwed in allen screw in the top of the exhaust manifold on that TD? Is it some kind of a stop screw for the butterfly valve?

Another issue I wanted to touch on is the volume of the muffler itself. There was an article on muffling in an older issue of M.A.N. where it stated that the ideal muffler size (in terms of breathing, power and noise) for a 2 stroke is one that has a volume either 10 or 40 times (can't recall which) the displacement of the engine. Of course the shape has a lot to do with the power and scavenging and so forth but the volume it was said was a primary factor.

Tom, I assume that the carb had no other purpose other than as a variable exhaust restrictor? If so then this principle is often used in r/c boats and if said to give better acceleration and deceleration that a carb alone.

meowy84

Tom, in my above post (from 2/2/2005 6:56:02 PM) I was referring to your 'po boy' setup (I see it might have been ambiguous in light of your Hiscott post which you posted while I was typing my post). In re. to the Hiscott system, I assume the travel in the spraybar would have been very tiny?

AndyW

My Feedback: (1)

Yes, WITH THE NORVEL, it worked out that exhaust restriction worked better, aftermuffler. Why? Not sure. With the Cox, it just worked but keep in mind that with my set up, as with the Hiscott, there's an exhaust collector that allows some expansion of the exhaust gases as opposed to the sleeve style which traps exhaust gases directly against the cylinder. This is likely the reason SPI is detrimental to exhaust throttling with an exhaust sleeve.

Also, it may be that the style of exhaust restriction has an effect in some way. I do know that Dave Arlton said that the shape of the plug was critical in their patented exhaust throttle. Apparently, a flat ended plug didn't work. The bullet shape works and why is a very good question.


Either type will work as I discovered with the two TD .010 throttles I made. Both worked well on a TD and I can't think of a reason why both wouldn't work on a reedie.


On the VA MK2, I've run an older Norvel muffler and also a custom muffler that has near three times the volume. Also, an original muffler made for the TD was HUGE compared to what you see today. In my experience, muffler volume is a small factor in top end power. And that would be another interesting experiment. Make up a LONG muffler with a trombone type sealed piston that you could run back and forth while the engine is running. One might find that there's an optimum volume that gives an rpm boost. You never know. Also important to consider is the muffler stem diameter. The smaller this is, the quieter and the greater power loss, all other things being equal.


If I may be allowed, yes, in the old days, (premuffler) exhaust baffles connected to intake throttles were used to great effectiveness. In some instances, just exhaust restriction works well, as we see with 1/2A engines.
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>>EDIT _ Altered HTML coding. wr.

Tom @ Buzzard Bluff

The movement of the spraybar approaches 90 degrees. Only in @ the last third of it's arc does it affect the exhaust. I had to go to the shop and dig out the engine that has it installed, a converted TD with an RJL diesel conversion head. I'll not have time for anything else this next season if I conduct proper tests of all the engines that I have ready for sundry tests.

Moving to your last post on the .09 thread I think you yourself are a candidate for 'dieselizing' by your stated preferences in the type of power you seek. As George (gcb) noted in one of his replys diesels are the torquers in the model engine family. The adjustable compression is, in reality, adjustable ignition timing, allowing a very wide range to tune for torque with the big, efficient, scale-like props yoyu need to turn. The Brits have long used them for scasle for all the reasons mentioned and more. See some of Andys posts on diesels. He is now a 'believer'.
BTW, a few years ago I was diving South, leaving the hills of the Ozarks for some reason. Along the 2 lane hiway on my route I did a classic double-take. There, in a hangar on a private airstrip sat a Wilga. In the Ozarks? Yup. Dunno if it's still there as I haven't seen it recently, but I go that way infrequently.
BTW #2. I was happy to see that you understood what I have been trying to convey in your .09 thread. Tom

Tom @ Buzzard Bluff

Afterthought dept.
Diesels have the added advantage for scale of the 'right' sound compared to glow engines. A throatier, deeper sound that isn't reminiscent of a mosquito with his privates stuck in his zipper. As a scale buff (if not a scale builder) I am intolerant of Cubs that sound like a bee on steroids flown at scale speeds of modern fighter/bombers aircraft doing things that no lightplane has ever done nor can be even remotely considered capable of doing.
The adjustable timing provided by the compression lever means that you needn't jump thru hoops changing head gaskets, nitro levels and needle each time the temperature or humidity vary a few degrees either. Just twist the lever to compensate and fly. As easy as setting up for different prop loads.
Don't allow the different operating technique scare you away from the advatanges offered by diesel for scale. Learning new things can be half the fun of the hobby.

AndyW

My Feedback: (1)

Yes, that's quite perceptive of you. It IS a stop screw. A better arrangement would have come in at the side allowing for adjustment of the low end stop. This, however, is only useful on the stand. In practise, you NEVER want the stop screw to act as your bottom end limiter when installed in an aircraft. All you do is stall your servo and drain your batteries unnecessarily.

meowy84

Tom, ah the Wilga....a very nice plane indeed if somewhat oddly shaped. Although it perhaps doesn't have the immediate beauty of say the Piper or Beaver to most but it's something that definitely grows on you. If I wasn't more into WWI and II military planes it's something that I'd build I think. As for diesels, yes it seems I've been avoiding them...perhaps because of the fuel issue most of all and my lack of experience with them (you know, old dogs and old tricks sort of thing). Plus, I'm still in the process of working out the details on building my first plane so I thought that I'd do the glow thing first and see what results. After I get some more experience modifying and tuning 1/2A engines if I still don't get the results I'm after then I'll lilkely venture into dieselizing.

AndyW, thanks for the good info on the factor of allowing some gas expansion before the gasses hit the restroctor/throttle. One last question and then I promise to leave you alone: In yout pics of that TD it looks like the pre-muffler collector is aluminum. Is that the case and if so what method do you use of sealing it against the cylinder in light of what was mentioned that aluminum expands at a higher rate than iron/steel.

meowy84

Tom, I was concerned about the diesel fuel as well. In fact since I haven't seen any in my LHS and was met with a deer-caught-in-headlights look when I once asked about it was perhaps my biggest deterrent in thinking about model diesel and I assumed that it was relegated to the fringes of the alchemistry crowd. I have visions of crusty modelers bent over cauldrons mixing up their special concotion of model diesel fuel worth its weight in gold.

AndyW, thanks for solving the screw mystery.

AndyW

My Feedback: (1)

M84,

My exhaust collectors have a lip at the bottom that is pinched between the cylinder and the case. The Hiscott is done this way (as I recall ) but the lip is very thin to minimize alterations to the timing and compression. I use a thicker lip and I mill down the case to compensate.

meowy84

Here's some pictures of the carb I plan on using....this is the one I was saying has very little meat for the air bleed screw in my opinion. I apologize for the quality of the pics but this is the best my digital camera (and me) can do. Once again this carb came off an older AERO .049 r/c engine.

meowy84

This is another pic of the carb.

AndyW

My Feedback: (1)

M84,

Looks about right. Now we see what you mean. That is one carb I'm not familiar with. Can you show us the Aero .049 it came off of?

meowy84

AndyW, I'll try posting a pic of the engine sometime this weekend. BTW, the engine is essentially a Norvel...probably an early Norvel or AME (?). It says AERO (in Russian) on the crankcase and there's a logo of a letter V with a circle between the forks of the V. You can just see a bit of the engine in the second pic. The muffler on that engine is identical to the one on my Revlite .061 and the engine has the same design (meaning the cylinder fins are integral with the liner and come out as one piece just like on the current Norvels.)

Tom @ Buzzard Bluff

The body of the carb you posted bears a striking family resemblence to the pics of the older series of VA carbs that Andy and I posted in posts 24, 25 & 30. There's probably one shop buried in a Moscow back alley turning out ALL of the carbs for Russian-built model engines. I seem to recall reading that all of the Russian 1/2A size engines are the result of an incestuos process and the carbs seem to bear that out.
At any rate the method I pictured in post # 30 of adding an airbleed circuit should work just fine.

meowy84

Tom, you're absolutely right....a lot of the Russian engines are definitely very similar to each other in design and dimensions.

boberos

To Andy & Meowy,

I used a Cox Medallion for my Hiscott throttle.
I could not find the pic either. Must have sent to ajc as a PM.
I'll try to attach a pic here but I am sure it the same as others.

Bob

meowy84

Here's two pictures of the AERO (AME?) .049 engine that I was talking about next to a Cox reedie.

meowy84

The second picture of the other side.

meowy84

Oops, sorry, that was the wrong pic. Here's the other side (hopefully)!

meowy84

Bob, ah now I see what this mysterious Hiscott throttle is like. By the way is the muffler assembly part of the Hiscott setup as sold originally or is it some other manufacturer's muffler?

boberos

Meowy,

Yes the whole thing came complete in a blister pack for $16.95

It consists of a brass barrel that fits the existing Medallion red plastic carb body, & has abrass throttle arm soldered to it.

There is also a aluminummanifold that fits the cylinder perfectly. The muffler is attached with a screw into the manifold.

Look closely & see the brass rod sticking out the front of the manifold This is the exhaust restrictor & is pushed shut by the throttle arm. Almost ingenious. There is a little spring at the dead end of the restrictor that pushes the brass rod foreward or open when the throttle arm moves foreward or open as well. There is a1/16 dia. roll pin that holds the resrictor in place so it cannot fall out. Barely visible in the close up.

Someone with a lathe & small mill could make a few up of these units. Hint. Not much material in them but quite a bit of labour is involved.

Lot of words here, but I hope I have described it OK. It really is a neat device.

Next time I run the motor I will check to see how effective the restrictor alone is. Perhaps the throttle will not be needed. That way, this device could be attached to any straight barrelled Cox 049 cylinder.

Good luck,
Bob G

meowy84

Bob, that's a neat setup. The restrictor rod looks to be very similar to the restroctor on the Litemachines Norvel .061 Cmax (but in the Cmax of course the rod restricts the gasses post-muffler whereas in the Hiscot it seems to be pre-muffler).

cap10b

All,
My vote is still for the Tarno on pressure, with Charlies RC head adapter running KB RC idle bar plug on sig 25% fuel.
That combo gave me TD performance with a 3000 rpm idle. Not quite able to sit still on a run way but most certainly in grass.
and still ROG if you can hold your tounge right and keep it straight long enough to get some air under your wings.

Sorry for the quality of the pics I was experimenting and just happen to use that plane as the subject.

jds
Webmaster
114th RC Aero Squadron