Proper mixture leaning HOWTO

[jagipson]

What is the proper way to lean the mixture on the DC-3? There is no EGT, which is what I was taught to use for mixture leaning.

[Goran_M]

For some reason, the photos we used of the engine gauges, don't have an EGT gauge.

You're definitely correct and we found some other photos that do have an EGT gauge.

Seeing as it's needed to adjust mixture, we'll make an EGT gauge and have it in an update soon.

[jagipson]

Oh, I wasn't necessarily requesting an EGT -- I assume many planes in this vintage don't have them. I was just wondering if there is an alternate way to lean the mixture w/o EGT. I've been doing it by leaning back until the engine MP drops off (and it drops of very fast when you get to that threshold, because the engine is starving at that point) and enriching about 10% from that point.

[Goran_M]

After just going through some of my documentation, I can definitely say that not all DC-3's have EGT gauges. Apparently, pilots used to go by, as you said, engine RPM and MP indications, and if fitted, CHT temperature indications. The EGT gauge allowed for more accurate and faster mixture leaning, but it definitely was not essential to setting the fuel mixture.

[jagipson]

Now, I definitely not asking you to modernize the DC-3 (My opinion, anyway). I just would like to learn the proper procedure for engine leaning with MP and RPM...

[Goran_M]

As you get higher, and if the mixture is on full rich, the CHT will get slightly cooler, and the engine RPM will gradually slow down (because of the gradual carburetor flooding) along with the Manifold Pressure dropping. Bring the mixture back until there is a SLIGHT increase in engine RPM (maybe about 50RPM increase). Bringing it back further than this will cause fuel starvation and the engines will run very rough. Push it back up until you get smooth engine running. IIRC, you'll need to check this about every 1000 feet on climb AND decent.

[Ntr09]

The main reason that there were no EGT gauges was because you didn't have to lean it. It had "Auto Rich" and "Auto Lean" settings that you pulled the mixture levers to. There was no need to lean them manually. It would be nice if you included this feature.

-NR

[Goran_M]

We're looking into Auto Rich and Auto Lean for an update somewhere in the next few weeks.

If we can add it, we will.

Edited April 8, 2012 by Goran_M

[PWJT8D]

I have been leaning by the means of what the original poster had mentioned. As you climb, your manifold pressure and RPMs begin to drop and I will ease back on the mixture slightly until there is an increase in the RPM's and keep cross checking this until at cruise. Once at cruise, I will slowly ease back the mixture until the engines begin to run rough and then advance the mixture about 10% and leave it until it's time to descend. It works for me and I have no problem with it.

Edited April 8, 2012 by PWJT8D

[Ntr09]

We're looking into Auto Rich and Auto Lean for an update somewhere in the next few weeks.

If we can add it, we will.

Thanks!

I have been leaning by the means of what the original poster had mentioned. As you climb, your manifold pressure and RPMs begin to drop and I will ease back on the mixture slightly until there is an increase in the RPM's and keep cross checking this until at cruise. Once at cruise, I will slowly ease back the mixture until the engines begin to run rough and then advance the mixture about 10% and leave it until it's time to descend. It works for me and I have no problem with it.

Which works fine, as you said. But isn't the way the real one works.

[philipp]

Quoting John Deakin from avweb.com, 65.000hr pilot and vintage/radial engine specialist:

In the big old radials, where we can often watch the exhaust at night, we can see directly what is happening. At full rich (takeoff and climb), the exhaust is a bright yellow, with visible flames licking (slowly, relatively speaking) back along the cowling. Lean it out, and the flame turns blue, becomes shorter, and burns more intensely (quicker). Keep on leaning, and it turns white with a noticeable loss in power. If you lean it far enough, the fire goes out and the engine quits. In the early days of the big radials, it was easy enough to learn how to lean the engine by sight at night, develop a "feel," and duplicate it closely enough in the daytime.

(from http://www.avweb.com...n/182084-1.html, emphasis mine).

You can of course try retrofitting the DC-3 with my modern engine monitor, though it shows only 6 cylinders: http://forums.x-plan...&showfile=12206 It also does kind-of the auto-rich and auto-lean functionality.

Edited April 8, 2012 by philipp

[Paraffin]

We're looking into Auto Rich and Auto Lean for an update somewhere in the next few weeks.

If we can add it, we will.

My $.02 opinion, is that this would be the best way to handle it, instead of adding a modern EGT gauge that wouldn't look right in the old-style panel.

This would be similar (or the same) as what Hydroz is doing with their recent PBY Catalina model. If you add this control, then please make sure you do what they did, and allow mapping joystick buttons (or keys) to the carb settings, so they can be quickly adjusted without using a mouse to manipulate the controls in the cockpit.

[Ntr09]

My $.02 opinion, is that this would be the best way to handle it, instead of adding a modern EGT gauge that wouldn't look right in the old-style panel.

This would be similar (or the same) as what Hydroz is doing with their recent PBY Catalina model. If you add this control, then please make sure you do what they did, and allow mapping joystick buttons (or keys) to the carb settings, so they can be quickly adjusted without using a mouse to manipulate the controls in the cockpit.

Couldn't we just use our mixture levers? If you have them that is. If you don't, go get a CH quadrant. Money well spent.

-NR

Edited April 8, 2012 by Ntr09

[Paraffin]

Couldn't we just use our mixture levers? If you have them that is. If you don't, go get a CH quadrant. Money well spent.

I have a mixture controller (analog "Incr" wheel on the Warthog throttle quadrant set up for mixture). But it's a continuous control setup. That won't work here, because if I understand this correctly, it's a discrete switch with different states -- "Off," "Auto-Rich" and "Auto-Lean." It's not a continuous control like normal mixture. You'd need a 2-way momentary or three-position button to control it from a joystick or throttle quadrant.

Take a look at how they do this in the Hydroz PBY Catalina model for X-Plane. I assume this is the same thing, from the same era in radial engine planes. Here's the .org forum post where they added a fix for controlling it with a joystick button:

http://forums.x-plan...showtopic=57550

Edited April 9, 2012 by Paraffin

[Ntr09]

Ah I see. I figured one could get it to work by holding the lever position (in the model) when your physical levers passed over that detent in the virtual throttle quadrant.