[Nuker]

Fodder and I were talking about this the other day. My Hawk, just ran out of power after just over 1/2 tank. Full throttle didn't even lift the skids.

I figured the engine was too rich. So here was the question. In the plane world, you stand behind the engine, run it up and adjust the needle. This just didn't seem like a viable option with the helis Now I've read on the web where some people attach the heli to a bench, stand below and adjust that way but ......

So what is the best approach to do this? Is it 1-2 clicks on the needle, back away, check the throttle, throttle down and repeat?

Just looking for some opinions on how you do it.

Thanks,

Bob

[JimMcIntyre]

I know a few people who strap their heli to a workmate but, this is only good for intial setup, especially when determining pitch curves.

The answer is Heat....

If the engine is too hot to touch, it's too lean.

It's a bit gross, but many use the spit-sizzle test;
wipe some spit on the engine, if it sizzles, the temp is right, if it evaporates immediately, it's too hot.

Myself, I err a bit on the rich side, get in the air, checking for plenty of smoke, do a couple rapid climbs listening to the engine. If all is well, I fly, if not, I land, check the engine temp, adjust a couple clicks and repeat.

For low speed, I use the pinch test. With the engine warmed up and running at idle (and a firm grip on the head), pinch off the fuel line to restrict fuel to the engine. The engine should continue to idle for 3-4 seconds, and begine to rev up (it'll quit if you keep pinching so let go ). Less than 3 seconds and it's too lean, longer and it's too rich.

As you already know from flying fixed wing, fine adjustments are needed as temp and humidity changes. It's amazing how quickly your ear can become 'tuned' to a well running engine. In fact, I've heard you comment on overly lean sounding fixed wing planes in the air......

[Colin]

hi,

Several ways available to adjust the helicopter engine. First you need the correct throttle/collective relationship. Start at half open carb barrel and 5 degrees collective then tune the needles -basically. These reference points should be at half to 3/4 collective stick displacement. (1/2 for beginners)Watch for smoke and two/four-cycling. You want the engine to drone in the hover or very light on the skids. A rich engine at proper rotor rpm will generally kick the tail abck and forth slightly with the audible 2-4 cycle transition noise. The heli carb design is different and more critical to that of a fixed wing requiring a decent midrange over idle and full power. Once the smoke and drone are in the ball park you can then adjust the throttle curve to maintain an acceptable rotor rpm of 1500-1800. The five degree collective should be set from half stick to 3/4 stick displacement dependant on flying style and skill. If you go too lean the rotor rpm will sage afte getting in the air from overheating. You can run a heli engine pretty rich provided you have the right throttle opening. this is why helicopter radios have a throttle curve, use the mid point on the throttle curve to fine tune rpm once you see the right amount of smoke which is thicker than that of a plank because of lower velocity rotor wash.

Often the pinch test will not work on helis since this area tends to be richer in favour of midrange. Heli engines will often load up at idle and need to be cleared at operating rpm. Not a problem because they operate at a constant speed.


If you strap the heli down do it to a soft surface like grass or carpet to avoid ground resonance. Shove some long sticks/decking etc through the skids and weight down with bricks or something heavy.

Nominally:

You can then adjust the 30 -39 spec engine main needle mixture using up to 9 degrees positive collective. TT39 engines run at 3-3.5 turns out and OS32 run about 1&1/4 on the main. Run the low speed needle to obtain a good reliable idle.

stephen

[Fodder]

Originally Posted by JimMcIntyre

... get in the air, checking for plenty of smoke, do a couple rapid climbs listening to the engine. If all is well, I fly, if not, I land, check the engine temp, adjust a couple clicks and repeat.

Along the same lines. When I was starting engine on Saturday it was "fine", but after say about 20 seconds it died (it was still on the ground). It did this about 3 times, but the forth I leaned it out one click and it was fine - whether that fixed it or not, I don't know. I will admit that I was scared to lift off in case it quite while in the air, but there were no problems. (In hind site, I probably should have let someone else check it out first - I have to start flying on Sunday, but it survived). So, how does one check for that?

[Fodder]

Originally Posted by Colin

A rich engine at proper rotor rpm will generally kick the tail abck and forth slightly with the audible 2-4 cycle transition noise.

I wonder if that is what mine does. It doesn't do it all the time, but every now and then while lifting off it will "wag" quite a bit. If it is excessive, I sit it back down and try it again - usually resulting in no wag. Hmmm

[Colin]

Once in a while wag...Maybe knock the gyro gain down if engine sounds smooth. Flown to the limits all gyros will eventually wag a tad at some point in a flight. It is something you can tweak out but if you go for max gyro gain it does happen once in a while. What you don't want is a steady fast wag in FFF or during FFF turns. (fast forward flight)

Some heli engines are sensitive to glow plug selection. The TT engines 30, 39 and 50 run best with a hangar 9 # HAN3006 super plug. At least that's the best we found with these engines and the OS32SXH so far and they are well priced. I prefer these plugs over the OS and Fox etc. pricing aside. The two cycle super plug element is thicker resembling a four stroke element and holds the heat during less than ideal mixture transients.

stephen

[Nuker]

In hind site, I probably should have let someone else check it out first

Oh sure, but you wanted me to just lean mine out and try it

Thanks Jim and Stephen for the input. I know that both Fodder and I were set up (or in my case resetup) by a local heli guy so our systems were done to hover at 1/2 throttle. If we are to review and modify the throttle curve and collective, I think I'll get some assistance, based on what you said Stephen and my lack of experience and from there I should be able to adjust on my own. Hey, gotta learn somewhere.

I had some tail wag on takeoff that day (which it hadn't done in the past). I know I have an OS #8 plug in the TT .39

I was hovering fine then it just settled down and landed softly; though the throttle was raised to the max by that point. So I shut it down and took it as a sign . The engine is idling nicely though it is rich based on what is coming out of the muffler.

Just curious on the RPM's comment. Would you use a regular (read airplane) tachometer or is there one specifically designed for heli's. I guess I can get Scott aka Fodder to stand below the heli with a tach to measure while I fly Then to assist I'll fly his while he measures it again

Thanks again for the input guys,

Bob

[JimMcIntyre]

Originally Posted by Nuker

I was hovering fine then it just settled down and landed softly; though the throttle was raised to the max by that point. So I shut it down and took it as a sign

Sounds like it was a bit lean and overheated. Was there much smoke while you were flying? Was the day particularly hot/humid?


Headspeed. No the aircraft tach won't work, you need a special tach ... which costs about the same as a governor these days.

I don't use one myself, I figure I'm in the right range when my toes begin to curl with unease. Bob tached it for me once, the toe curl appears to be about 1750rpm.

[Fodder]

The day was fairly hot and humid. At first I had trouble lifting off, but credited to the tall grass around the training aid in our hover area. Once I lifted off it was fine. I know I leaned my engine out a bit last year, but not sure if Nuker has adjusted his yet. When the planes were done, I hovered on the field with not engine problems.

Jim, what time did you say the heli school started.

[JimMcIntyre]

Originally Posted by Fodder

Jim, what time did you say the heli school started.

You're a fixed wing instructor, you know when training times are.... Wed. 6pm - Dusk, Sat 9am - 1pm

If you're asking for extra time, you'll have to negotiate with my wife.