Rc Throttle

I have been using a TTiger pro 46 on a 52" wing span Brodak Tanager. I have been able to adjust the throttle on it as it is adjusted with a rc clevis. As if I need to speed up or slow it down some I just loosen the carb. set screw and turn it one way or the other to adjust the speed. I know it's not what most pro's use on there ships, but I would like to know what's wrong with using this method on your planes vs a none throttle cl engine. It seems with the throttle adjustment it would seem to have some what of an advantage for trimming you planes speed. As you all may know by now that I'm just a excited beginner. I'm learning, that's the fun part of it.

>I have been using a TTiger pro 46 on a 52" wing span Brodak
>Tanager. I have been able to adjust the throttle on it as it
>is adjusted with a rc clevis. As if I need to speed up or
>slow it down some I just loosen the carb. set screw and turn
>it one way or the other to adjust the speed. I know it's not
>what most pro's use on there ships, but I would like to know
>what's wrong with using this method on your planes vs a none
>throttle cl engine. It seems with the throttle adjustment it
>would seem to have some what of an advantage for trimming
>you planes speed. As you all may know by now that I'm just a
>excited beginner. I'm learning, that's the fun part of it.

There are some who are doing what you are doing (especially on the 4-strokes, where this can become, perhaps, more useful). An inverted installation becomes harder to hand choke with the inlet (needle)farther from the crankshaft opening as it is with a carb compared to a venturi. It is somewhat heavier, the venturi (carb) sticks up (or down) more on a cowled installaton. The adjustment of the carb, itself, becomes more of a hassle. Thus, if you get the proper size venturi, all you need is to adjust the needle for your run.

OK, so you want to run the carb as you have it set up. You now have an "adjustable venturi". The carb is, in effect, adjusting the size of the opening of the venturi, so you need to treat it that way.

With the RC engine in an RC installation, you will usually set the needle a couple of clicks richer than full power to compensate for the leaning effect when the engine is pointed up and needs to draw fuel from a farther distance. Then you use the throttle to adjust speed while in flight. With a stunt run, you need the engine to run in a controlled situation where it becomes self adjusting. You can either use a low pitch prop and run the engine in a similar situation, or you can run it richer in level flight, and allow it to lean out when pointed up. In either case you will probably want to run the engine richer than if used in the RC application since you do not have the advantage of using the throttle in flight. You never want it to go full lean (or worse, overlean). And the engine will probably lean out a bit as fuel is used and will lean out further when in maneuvers. The key is to get the characteristic run you want, not just the proper lap speed (although this is important, too.) So when setting the throttle, you will also want to set the needle for the run, making sure you are always on the rich side--even when the engine is pointed up.

>>I have been using a TTiger pro 46 on a 52" wing span Brodak
>>Tanager. I have been able to adjust the throttle on it as it
>>is adjusted with a rc clevis. As if I need to speed up or
>>slow it down some I just loosen the carb. set screw and turn
>>it one way or the other to adjust the speed. I know it's not
>>what most pro's use on there ships, but I would like to know
>>what's wrong with using this method on your planes vs a none
>>throttle cl engine. It seems with the throttle adjustment it
>>would seem to have some what of an advantage for trimming
>>you planes speed. As you all may know by now that I'm just a
>>excited beginner. I'm learning, that's the fun part of it.
>
>There are some who are doing what you are doing (especially
>on the 4-strokes, where this can become, perhaps, more
>useful). An inverted installation becomes harder to hand
>choke with the inlet (needle)farther from the crankshaft
>opening as it is with a carb compared to a venturi. It is
>somewhat heavier, the venturi (carb) sticks up (or down)
>more on a cowled installaton. The adjustment of the carb,
>itself, becomes more of a hassle. Thus, if you get the
>proper size venturi, all you need is to adjust the needle
>for your run.
>
>OK, so you want to run the carb as you have it set up. You
>now have an "adjustable venturi". The carb is, in effect,
>adjusting the size of the opening of the venturi, so you
>need to treat it that way.
>
>With the RC engine in an RC installation, you will usually
>set the needle a couple of clicks richer than full power to
>compensate for the leaning effect when the engine is pointed
>up and needs to draw fuel from a farther distance. Then you
>use the throttle to adjust speed while in flight. With a
>stunt run, you need the engine to run in a controlled
>situation where it becomes self adjusting. You can either
>use a low pitch prop and run the engine in a similar
>situation, or you can run it richer in level flight, and
>allow it to lean out when pointed up. In either case you
>will probably want to run the engine richer than if used in
>the RC application since you do not have the advantage of
>using the throttle in flight. You never want it to go full
>lean (or worse, overlean). And the engine will probably
>lean out a bit as fuel is used and will lean out further
>when in maneuvers. The key is to get the characteristic
>run you want, not just the proper lap speed (although this
>is important, too.) So when setting the throttle, you will
>also want to set the needle for the run, making sure you are
>always on the rich side--even when the engine is pointed up.

The past few times I,ve flown when it ran out of gas It didn't lean out at all. A short spudder and stopped. How come. I will keep in mind to richen it to a slower two cycle. But doesn't it have a tendency to die out prematurely running rich?

Quite a few RC engines will run just fine in CL planes using the throttle, as you've found. Take Len's advice and don't run it too lean and fast. Overheating the motor will ruin it quicker than almost anything else.

The throttle makes it quick and easy to adjust the maximum engine rpm, and horsepower, which needs to be matched to the prop size. At reduced horsepower the motor simply won't turn a given prop as fast, and as several people have posted here before, trying to get a particular rpm on a particular prop just won't work if the motor can't turn it that fast.

So here's what I've done, using the carb on LA engines. Pick a reasonable size prop, something like an 11/4 or 11/5 on the 40 and 46. Start it and richen it up until it is running in a solid 4 cycle. If you're new at this, open and shut the needle valve slowly, until you can recognize the change in the engine sound as it goes from 4cycle to 2 cycle. As you go from 2 to 4 the motor will change to a softer sound and slow up(the 2-4 break). As you keep richening it up it will start to run raggedly and maybe even spit fuel out the exhaust. That is too rich. When it is running a steady 4 cycle, fly it. It should not quit at this setting. If it does there is something wrong with the plug(try a hotter one) or the fuel(old fuel). Experiment with adjusting the setting from one flight to the next and find a setting that works best for that prop and throttle setting.

A CL venturi, with no parts to leak and rattle around, generally will be more reliable than the carb in the long run though. The LA's simple, air-bleed carbs work pretty well. The more complicated, 2 needle carbs are just asking for trouble though.

One thing to remember about an RC carb is that it is a compromise so that the RC engine will both idle slowly, and when goosed,will throttle up for a high speed run. One shouldn't assume that it really does a bang up job in the mid range. What I mean by that is that if you optimise the high end, and then the low end, the run isn't optimised (probably) for the mid-range. The different types of carbs are designed to try and get the mixture nominally ok, once set for the high speed and low speed domains.

For RC use that is neither here nor there, although in certain critical categories (RChelis comes to mind) the mid range is really important. Most RC applications probably could care less if the engine is running a little rich, or a little lean at half throttle. Need more? Throttle it up- Need less, throttle it down.

I think one of the big reasons OS has such a big fan club is that they do a reasonably good job on the carbs.

Now in CL, the RC carb is simply an adjustable venturi. Since I doubt that most users really need the actual adjustable carb in flight (except Windy of course), you can pretty much ignore the air bleed (close it down!) or the idle needle (screw it out!), since once you find your speed, you will simply adjust the (high speed) needle to get the mixture right. Under these conditions, I have a hard time seeing why the RC carb is really less reliable than a simple venturi. Yes it is a bit heavy compared to the venturi, but the flexibility to be able to dial in the power (assuming you don't have to leave it wide open) must be a really nice feature.

Ron B.
F4Fguy

Alan:

The air bleed is the mid range compensation.Changing the main mixture changes the mixture throughout the rev range changing the air bleed changes the slope of the mixture curve,i.e.leaner at the bottom richer at the top of the rev range.Actually,mixture compensation throughout the range is very good if the carb is properly set up(and if there are no leaks other than the intended one).
Also,re an earlier answer to this post,more horsepower won't necessarily turn the large prop faster.It will only do so if the torque is higher than at the lower RPM.For a given displacement,this is unlikely without some serious tuning in the form of porting or pipe changes.
If the engine will turn the large prop comfortably,without overheating and/or running away,and the only problem is lap time,simply change pitch to control speed.
To add yet another truism to the mix,"Accelleration=torque= thrust=torque=prop diameter=torque".There's no substitute for diameter or torque.