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Stechiometer title in modern helicopters


Chewberta

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Im looking for information from more seasoned pilots. How long has it been since you could actually adjust the stechiometric title whilst flying like its done in planes that enrich or lean as required. I seem to recall it being doable in piston ships but cant recall when we stopped.

Can anyone shed some light.

Thanks a million

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Only piston choppers I flew were the R22 and the (barfff!) Enstrom, neither of which allowed the mixture to be fiddled with. No propellor to keep it turning if you accidentally went too lean.

 

Planes were a different matter, but this is not the forum for'em.

 

And it is "stoichiometric" by the way.

Edited by Eric Hunt
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I flew the TH55 in '68, '70 and '71. Full rich for all normal operations.

Hughes 269/300 B & C models '81 - '83, also full rich. I'd have to get the RFM out, but I believe that full rich for all normal operations.

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You would have to be extremely careless to accidentally lean the mixture far enough to kill the engine. In practice, it just takes a few turns on the mixture control in either direction and a glance at exhaust temps on the Graphic Engine Monitor (GEM) to confirm the desired effect. Verify around 1500°F in the hover, lean to ~1590 in cruise flight for best economy, enrich to 1500 prior to landing. The mixture changes and scanning the GEM for proper temps becomes second nature and really lets you optimize the performance of the machine for best power or economy. I used to fly a 280C that would do 10.5 gph leaned out in cruise at 100kts.

It's been a few years since I've been in the piston Enstroms but if I remember correctly, normal fuel mixture adjustments only take place in less than 20% the full range of travel of the vernier mixture control (within a centimeter of full rich). You would have to go well beyond 50% of the full range of travel before the engine starts running rough and overheating and probably 75% or more before killing the engine. In other words, you'd have to be very inattentive or very stupid to let it happen.

Edited by 280fxColorado
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Im sure that the Enstrom system is a great tool and in the right hands is advantageous. My objection is that in terms of fuel savings and spark plug cleanliness (we toss them every few hours anyway) the benefits do not outwit and outweigh the results of the human factor which is way too common and of great cost in lives. More so since, other than flight schools, piston helicopters are in use by low hour pilots or private users in general. I mean to say that those pilots who would make good use of the mixture control probably do not fly piston ships

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