Producing > Rated Power in a Piston Engine
Thread Starter
Joined: May 2005
Posts: 49
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From: Australia
Producing > Rated Power in a Piston Engine
On a day where the QNH is high and temperature low (ie: a -ve density height) I believe I am correct in saying a piston engine will produce > published rated power.
I can't imagine this being a big problem given the relatively short duration of takeoff power and the actual change in BHP that these conditions might bring about. However would the higher internal pressures / temps cause any problems? TBO affected if this was a regular occurence (eg: cold, sea level climates)?
Taking the example of an engine which is not 'de-rated', are there any allowances in piston engine construction / maintenance for this occurence?
Cheers
I can't imagine this being a big problem given the relatively short duration of takeoff power and the actual change in BHP that these conditions might bring about. However would the higher internal pressures / temps cause any problems? TBO affected if this was a regular occurence (eg: cold, sea level climates)?
Taking the example of an engine which is not 'de-rated', are there any allowances in piston engine construction / maintenance for this occurence?
Cheers
Joined: Mar 2000
Posts: 8,571
Likes: 3
From: Arizona USA
For smaller GA engines, not a problem.
Even the turbosupercharged ones have absolute pressure controllers to regulate the total turbo/engine output...provided of course that the operating pilot is smart enough to have the oil nice and warm before pushing the throttles up.
With large supercharged radial engines, on a very cold day, often times the BMEP will be the limiting factor, rather than manifold pressure.
All the pilot has to do is be able to actually read the gauge accurately.
Even the turbosupercharged ones have absolute pressure controllers to regulate the total turbo/engine output...provided of course that the operating pilot is smart enough to have the oil nice and warm before pushing the throttles up.
With large supercharged radial engines, on a very cold day, often times the BMEP will be the limiting factor, rather than manifold pressure.
All the pilot has to do is be able to actually read the gauge accurately.
Joined: Sep 2001
Aviation Qualifications: CPL
Posts: 2,787
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From: Toronto
I have heard of pilots using carb heat on takeoff in -40C outside conditions to reduce power to within engine limits.
I once did a takeoff in a C150 in about -20C. After a long pre-heat, the mechanic pumped the primer while the apprentice pulled the prop.
When taxiing in a couple days before, I noticed that each a/c in the tiedowns had on a engine blanket and an extension cord coming out. I felt quite naked seeing that
Bearing clearances can go negative in these temperatures; so preheat is vital.
I once did a takeoff in a C150 in about -20C. After a long pre-heat, the mechanic pumped the primer while the apprentice pulled the prop.
When taxiing in a couple days before, I noticed that each a/c in the tiedowns had on a engine blanket and an extension cord coming out. I felt quite naked seeing that
Bearing clearances can go negative in these temperatures; so preheat is vital.
Joined: Jun 2001
Posts: 518
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From: Chicago, IL, USA
Carb heat on takeoff, etc...
I spent 9 years flying in the Alaska bush. Planes like C172, C207, C208, SC7 and eventually a DC6.
I strongly advise against the use of carb heat on takeoff *unless* the manufacturer has a specific recommendation describing the procedure.
On the DC6, I once saw a letter on Pratt and Whitney letterhead describing the use of carb heat on takeoff at temps of -40C. And we performed the procedure a few times, but we had Carb Temp gauges with yellow bands to help us regulate the temp....but even so....it's a *very* workload intensive procedure for the flight engineer to manage the power reductions and related carb temp changes from takeoff power to METO power to climb power: Four throttles, one prop master lever, four cowl flap dials and four carb heat levers and only *two* hands! It's a CRM nightmare that usually calls for the FO to help manage the carb heat.
And by the way, we'd normally reduce the manifold pressure 1"hg for every 10 degrees below standard temp(+15C), while observing BMEP limits.
But, back to carb heat on smaller engines. The problem with using carb heat on say, a Lycoming, when it's so cold outside is that you may be actually warming the air in the throat of the carb to the *perfect* temperature for carb ice!!! (~-20C to 0C).
This is not a good idea without manufacturer recommendations and a Carb Temp gauge.
In fact, for most of the companies I work with in Alaska, we'd set -40C as a cutoff and stop flying the recip aircraft. Everything just gets too brittle at that temperature.
I strongly advise against the use of carb heat on takeoff *unless* the manufacturer has a specific recommendation describing the procedure.
On the DC6, I once saw a letter on Pratt and Whitney letterhead describing the use of carb heat on takeoff at temps of -40C. And we performed the procedure a few times, but we had Carb Temp gauges with yellow bands to help us regulate the temp....but even so....it's a *very* workload intensive procedure for the flight engineer to manage the power reductions and related carb temp changes from takeoff power to METO power to climb power: Four throttles, one prop master lever, four cowl flap dials and four carb heat levers and only *two* hands! It's a CRM nightmare that usually calls for the FO to help manage the carb heat.
And by the way, we'd normally reduce the manifold pressure 1"hg for every 10 degrees below standard temp(+15C), while observing BMEP limits.
But, back to carb heat on smaller engines. The problem with using carb heat on say, a Lycoming, when it's so cold outside is that you may be actually warming the air in the throat of the carb to the *perfect* temperature for carb ice!!! (~-20C to 0C).
This is not a good idea without manufacturer recommendations and a Carb Temp gauge.
In fact, for most of the companies I work with in Alaska, we'd set -40C as a cutoff and stop flying the recip aircraft. Everything just gets too brittle at that temperature.
