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The Care and Feeding of Glow Engines

by

Richard Lindberg



 

Assumptions:

1. You are starting with fresh, or recently used, glow fuel appropriate for your engine.

2. The glow plug is also new, or relatively so. Just because it glows is no indication that it is good! Generally, if there seems to be a white cast to the filament, get a new one!

3. You have mounted the appropriate propeller on the engine, and the prop nut is tight.

4. Your fuel system has relatively new, tight hoses, a filter on the feed line, and a pressure tap appropriate for your engine.

4. If your engine is new, you’ve read the instructions and set the engine accordingly. If your engine is not so new, but you have the instructions, see the preceding. If you don’t have the instructions, don’t worry; we’ll get it running right anyway!

Procedure:

1. Open the high-speed needle valve approximately three turns. If your carburetor is an air-bleed carburetor, close the air-bleed screw and then open it approximately one turn. If your carburetor has a low-speed needle valve, close it and then open it approximately two turns. What we are going to do is start from a rich setting, both low and high, and lean the engine. This protects the engine from that dreaded ‘lean run’ we’ve all heard so much about.

2. Set the throttle to a high idle setting, apply power to the plug, and start your engine. At this point, it should be running pretty rough; if you attempt to take off the plug power, it might die. Keep the plug hot by leaving the power on for a bit!

3. Now WAIT for a while! Let the engine warm up for at least 30 seconds, or slightly longer. Then gradually increase the throttle and listen to the engine. If it ‘gurgles’ and dies, it’s probably too rich (!), so turn the high-speed needle in about 1/4 turn and try again. (Go back to step 2.) If it speeds up and seems to be "rarin’ to go", shut it down and open the high-speed needle about 1/2 turn. We want to start on the rich side, remember! If the engine doesn’t die, then gradually turn the high-speed needle in to increase the RPMs. Be careful—that prop is dangerous! Listen to the engine! When the engine peaks, then back out the high-speed needle until the RPMs drop about 3-400 rpm. This is a good starting high-speed setting. We’ll refine this later.

4. Now we will set the idle. You want the idle speed to be approximately 1800-2100 rpm for most .25-.61 glow engines; a little higher for smaller ones; not much lower for bigger ones. We will refine this later, as well. Now, cut the throttle and listen to the engine. If it dies because the RPMs are too low, adjust the linkage (or the throws in your radio) accordingly. If it’s idling too fast, see the preceding. Now run the engine at full throttle for a few seconds to ‘clear it out’, and go to step 5.

5. From full RPMs, cut the throttle to idle and listen to the engine. What we are attempting to achieve is a response that is smooth and uniform—a transition from full throttle to idle, with no ‘blips’ in between, and a uniform, steady idle; a smooth run-up from idle to full throttle with no ‘blips’ or hesitations or gurgles in between. If the engine reaches idle speed, then speeds up, it’s too lean! Shut it down, and turn the low-speed needle out another 1/2 turn, or turn the air-bleed screw in another 1/2 turn, and try again. If the engine reaches idle speed, then gradually slows down, it’s too rich (good). Check this by trying to run-up to full throttle—it will probably hesitate, or gradually increase its speed. Shut it down and turn the low speed adjust about 1/4 turn (in for needle; out for air-bleed). As you get closer to the correct setting, you should reduce the adjustment to 1/8 turn or less.

6. Start the engine again, and go to full throttle for approximately ten seconds or so. We want to clear out the engine of any fuel residue from that rich idle setting! Now go to step 5, and repeat this procedure until the engine performs properly. The engine should idle for at least 30 seconds, not gaining or losing but a few rpm, and should IMMEDIATELY reach for full RPMs when you advance the stick, with NO hesitations. REALLY! This process will take perhaps 20-30 iterations to get it right, and perhaps nearly a tank of fuel, but once you’ve set the engine properly, you shouldn’t have to change the needles until the weather changes, and even then you won’t have to change them very much.

7. Now let’s refine these settings for proper flying. Get the engine started; then at high throttle, point the nose of the aircraft straight up. The engine shouldn’t sag or die. If it does, then richen the high-speed mixture until it doesn’t. (If you can’t achieve this, change your prop, your fuel setup, or your engine. It’s NOT a needle problem!) It should hold its RPMs for at least 20-30 seconds. Now cut the speed to idle, and place the airplane on the ground. A good idle speed is that which doesn’t allow the airplane to "creep". If it does, reduce the RPMs slightly until it doesn’t. If the engine size is the correct one for the airplane, this should be achievable. If not, see above.

8. This procedure works for all normally aspirated glow engines. Enjoy!