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Any Danger At Running Props Full Power?  
User currently offlineTriebwerk From United States of America, joined Sep 2008, 126 posts, RR: 0
Posted (5 years 7 months 3 weeks 2 days 9 hours ago) and read 3984 times:

[In terms of "power," I'm talking about the throttle, not the mixer.]

I'm quite the geek when it comes to civil aviation, but quite the newbie when it comes to flying planes in general. The only experience I have is some dozen hours in Flight Simulator X. (Not that that counts to begin with.)

Here's my question. Knowing that it's damaging and potentially dangerous to run a turbojet (Triebwerk) at full power, does the same apply to props? Should I worry about giving my simulated Skyhawk 100% throttle?

Thanks in advance for helping out an aviation newcomer.  Smile

18 replies: All unread, jump to last
 
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (5 years 7 months 3 weeks 2 days 8 hours ago) and read 3960 times:



Quoting Triebwerk (Thread starter):
Knowing that it's damaging and potentially dangerous to run a turbojet (Triebwerk) at full power

Err...why? That should happen during every (non-derated) takeoff.

Tom.


User currently offlineTriebwerk From United States of America, joined Sep 2008, 126 posts, RR: 0
Reply 2, posted (5 years 7 months 3 weeks 2 days 7 hours ago) and read 3945 times:

Well, if I'm not mistaken, pushing the throttle stack on an airliner as far as it can go (e.g. the throttle won't move forward any more) is not a position you want to be in for more than a few seconds. (Is this only the case with heavies?)

[Edited 2008-09-02 21:18:13]

User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 3, posted (5 years 7 months 3 weeks 2 days 7 hours ago) and read 3940 times:

Nearly all turbojet and turbofan engines have a time limit to be operated at full thrust.
They also have an MCT thrust rating (maximum continuous thrust) for which there is no time limit.

Most large radial piston engines have a time limit for which full power is available.
This time limit is usually two minutes.
These engines also have a METO (maximum except takeoff) power rating, and there is no time limitation, with METO power.

Most (but not all) small GA piston engines can be operated at full throttle, developing max rated horsepower, without any time limit.


User currently offlineDukeofDashes From , joined Dec 1969, posts, RR:
Reply 4, posted (5 years 7 months 3 weeks 2 days 7 hours ago) and read 3940 times:



Quoting Tdscanuck (Reply 1):
Err...why? That should happen during every (non-derated) takeoff.

Not really. Most take offs I'm aware of occur with the thrust setting around 90% - 91% of N1. To run a reduced power take off, the power setting is usually around 86-87% N1


User currently offlineKELPkid From United States of America, joined Nov 2005, 6267 posts, RR: 4
Reply 5, posted (5 years 7 months 3 weeks 2 days 7 hours ago) and read 3940 times:



Quoting Triebwerk (Thread starter):
Here's my question. Knowing that it's damaging and potentially dangerous to run a turbojet (Triebwerk) at full power, does the same apply to props?

You don't want to continuously run the engine at 100% power, no...you want to throttle back to about 2400-2500 RPM once you're at altitude. Keeping it at WOT (Wide Open Throttle) is hard on the engine.

Quoting Triebwerk (Thread starter):
Should I worry about giving my simulated Skyhawk 100% throttle?

Heh, it's a simulator, you won't hurt anything  Wink You should take off at 100% throttle and climb up to altitude at that throttle setting, but then you would throttle back for cruise or maneuvering. In the real plane, you would want to pay attention to the cylinder head temperature and oil temperature. These will climb when you're abusing the engine. Prolonged periods of high power with a low airspeed (like spending too long in slow flight  Wink ) are your engine's enemy. Remember, it's air cooled...

Quoting Tdscanuck (Reply 1):

Quoting Triebwerk (Thread starter):
Knowing that it's damaging and potentially dangerous to run a turbojet (Triebwerk) at full power

Err...why? That should happen during every (non-derated) takeoff.

I've noticed in flight sim that if you're flying something that doesn't have FADEC protecting you, and you ham fistedly jam the throttles to the firewall, you will exceed SOMETHING, usually N1 and one or two of the temperature parameters...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineTriebwerk From United States of America, joined Sep 2008, 126 posts, RR: 0
Reply 6, posted (5 years 7 months 3 weeks 2 days 6 hours ago) and read 3919 times:

Thanks for the info! I'll be sure not to overheat any simulated oil.

User currently offlineSashA From Russia, joined May 1999, 861 posts, RR: 0
Reply 7, posted (5 years 7 months 3 weeks 1 day 23 hours ago) and read 3824 times:

In a sim environment I learnt to throttle back the jet aircraft the hard way - kept getting Overspeed warnings shortly after levelling out for cruise  Smile So, that was taken care of. However on turboprop aircraft rarely getting Overspeed indication unless diving, so I just intuitively reduced power anyway...

Now back to the real world. To the turboprops -> AFAIK when it comes to modern planes ranging from C-130 , Dash 8, CASA, ATR, Fokker 50/27 - their engines are said to feature constant speed propellors. I was wondering if this suggested what I assumed it was - i.e. the thrust lever didn;t add the rotations as such but changed the propellors pitch (angle) as well thus increasing and decreasing horizontal power, while keeping the rotation speed steady?



An2/24/28,Yak42,Tu154/134,IL18/62/96,B737/757/767,A310/320/319,F100,BAe146,EMB-145,CRJ,A340-600,B747-400,A-330-300,A-340
User currently offlineCanadianNorth From Canada, joined Aug 2002, 3388 posts, RR: 9
Reply 8, posted (5 years 7 months 3 weeks 1 day 22 hours ago) and read 3805 times:



Quoting SashA (Reply 7):
I was wondering if this suggested what I assumed it was - i.e. the thrust lever didn;t add the rotations as such but changed the propellors pitch (angle) as well thus increasing and decreasing horizontal power, while keeping the rotation speed steady?

Something like that. There is still a normal throttle, which adds/subtracts power from the engine, but aircraft with an adjustable pitch propeller will also have a propeller RPM lever (generally right along side with the throttle and the mixture controls). In this setup it is the RPM lever that is used to control the RPM of the engine. Fancier aircraft will also have a constant speed propeller, which is just an adjustable pitch prop with a special governor so that if you set the engine to say (pulling a number out of my ass here) 2000rpm and then you pull up, the engine will go "underspeed", the governor would kick in and change the prop blades to a finer pitch, which would thus return the engine to an "on-speed" condition. Then if the engine tries to go "overspeed", the governor will send the pressurized oil in the opposite direction, thus changing the blades to a coarser pitch, which will again return the engine to an on-speed condition.


CanadianNorth



What could possibly go wrong?
User currently offlineFr8mech From United States of America, joined Sep 2005, 5098 posts, RR: 12
Reply 9, posted (5 years 7 months 3 weeks 1 day 21 hours ago) and read 3780 times:

Quoting DukeofDashes (Reply 4):
Not really. Most take offs I'm aware of occur with the thrust setting around 90% - 91% of N1. To run a reduced power take off, the power setting is usually around 86-87% N1

Max power has very little to do with the max rotational speed of the engine (jet). The proper term for max power should be max power for the day or to be even more correct, for the given moment.

Power from a jet engine depends on altitude, temperature (ambient) and barometric pressure. Thus, an engine that develops maximum power at 91% N1 at any given time, may require 95% N1 at some other point in time.

The maximum rotational speeds of the various spools are the physical limits allowed by the manufacturer. Above these speeds, after some margin of error, the engine may come apart.

It is quite possible to reach the max N1 without achieving maximum power (on EPR engines); this engine would be N1 limited and is rare. Same with N2/N3 (not as rare) and EGT (common).

And no, there is no real danger to running a reciprocating engine at its maximum RPM for any length of time. Any recip I've run, from A&P training through flight training, has had the redline (max RPM) at the top of the green bar. Just keep an eye on your temps.

[Edited 2008-09-03 07:20:02]


When seconds count...the police are minutes away. Never leave your cave without your club.
User currently offlineBE77 From Canada, joined Nov 2007, 455 posts, RR: 0
Reply 10, posted (5 years 7 months 3 weeks 1 day 21 hours ago) and read 3755 times:

This will repeat a few things already mentioned, so I apologise for the plagerism in advance (just trying to keep it all flowing).
"Full Power" in a simple piston such as a 172 with a fixed pitch prop is not simply Wide open throttle (WOT).

There is no problem with running a 172 at full rated power (Other than fuel burn and general wear and tear which is it's own controversy - my own experience in paying for stuff encourages me to go to cruise power as soon as level, but some claim no engine wear difference between hi-cruise and full power in most light planes)

Usually if you run WOT at sea level, as mentioned, you are going to go over limit on something - probably rpm, which usually means exceeding full rated power with a fixed pitch prop, especially on a cool day with lots of dense air to turn into power. So, low altitude level flight or in descent with WOT will result in problems - overspeed is definitely not good, and you may go over power in some cases.

GIven the fix pitch and no turbo though, as you climb, things change such that WOT is pretty much the way to go. Basically at altitude, the engine can't make full rated power. (Check out the performance charts, even in FS). A rule of thumb is that 8000' = 75% power. So, level at 8000 feet means WOT can only give you 75% of full rated power anyway. Conveniently, 75% also happens to be a good rule of thumb for cruise.  Smile So generally, WOT at altitude is 75% power which is what you want for normal cruise. (Long range cruise is usually lower power).

Just watch your temps to make sure you aren't cooking something - which would probably only happen on a really warm day anyway (of course, most of my flying is in Canada, with not too many days enough above standard to make a difference, and never enough to not be fixed by running a tad rich to cool things down a bit !).

Of course, adjustable props and turbo's change the entire picture - you can go over rated power almost anywhere, or at least cook things, which if you are very lucky will only cost you money - but you would be taught that before you were rated to fly something with those goodies.

There's always more to the story, for example, things are different for every engine / airframe combination so read the manual, but I hope this cover's your original question.



Tower, Affirmitive, gear is down and welded
User currently offlineAirportSeven From United States of America, joined Feb 2007, 327 posts, RR: 0
Reply 11, posted (5 years 7 months 3 weeks 1 day 20 hours ago) and read 3748 times:

With a constant speed prop, just remember to avoid high manifold pressure/low RPM settings, keep the cowl flaps open during taxi and climb and you and your engine should be fine.

User currently offlineMrChips From Canada, joined Mar 2005, 925 posts, RR: 0
Reply 12, posted (5 years 7 months 3 weeks 1 day 15 hours ago) and read 3659 times:



Quoting Triebwerk (Thread starter):

Here's my question. Knowing that it's damaging and potentially dangerous to run a turbojet (Triebwerk) at full power, does the same apply to props? Should I worry about giving my simulated Skyhawk 100% throttle?

The Cessna 172 is about the only airplane I can think of that I would even consider running with the throttle at the firewall for any prolonged period. This is mostly because it has a very forgiving non-turbocharged engine. Being normally aspirated, a 172 will only produce maximum power in a very narrow range of altitudes and temperatures. At a typical 172 cruising altitude around here, pushing the throttle to the stop will only get you about 75-80% of the engine's rated power. Having said that, if you plan on running a 172 at rental power setting, keep an eye on your oil temperature and your EGT (if equipped).

Now in larger piston engines, which will often have turbochargers and reduction gearboxes, there are limitations as to how long you can run the engine at maximum power. In those cases, there will be a maximum continuous power chart published in the POH. Exceeding these guidelines with a big piston engine can warp cylinder heads, burn pistons, cook turbochargers and do any number of nasty things to reduction gearboxes.

With most turboprop engines, firewalling the power levers is an incredibly bad idea for any length of time. Since most turboprop engines are flat-rated, the gas generator is able to produce much more power than the gearbox can handle, and can do some pretty nasty things if you hamfistedly jam the power levers to the stops. At high altitudes, you'll cook the turbine section if you firewall the power levers.

A bit of background - flat-rating an engine means the manufacturer has deliberately limited the power available from the engine. In a turboprop engine, there are two major maximums to consider regarding an engine's power output. The first is how much power the reduction gearbox is designed to handle. Exceeding this amount will obviously damage the gearbox. The second limitation is the maximum thermodynamic horsepower produced by the gas generator. This is the maximum amount of power that can be produced by the gas generator before it exceeds its temperature limitations. Similarly to a normally aspirated piston engine, the maximum thermodynamic power a gas generator will produce decreases as either ambient temperature or altitude increases.

By fitting a gas generator with the same thermodynamic power as the gearbox can handle, the engine will produce it's maximum rated power only at sea level and ISA conditions. As the aircraft climbs, or the temperature increases, the gas generator will reach it's temperature limitations before the gearbox does, imparting a rather large penalty on aircraft performance. By fitting a much larger gas generator to the same gearbox as before, you have an engine that can produce it's maximum power over a much wider range of temperatures and altitudes, which in turn dramatically increases aircraft performance.

Of course, in some very modern turboprop engines with FADECs, engine handling becomes far simpler, and dare I say it, nearly care-free.



Time...to un-pimp...ze auto!
User currently offline113312 From United States of America, joined Apr 2005, 564 posts, RR: 1
Reply 13, posted (5 years 7 months 3 weeks 1 day 15 hours ago) and read 3644 times:

Your simulated Cessna 172 is made to takeoff and climb at full throttle as is the engine in the real plane. In a normally aspirated (non turbo-charged) reciprocating engine, full rated power is only achieved at sea level, standard conditions, with full throttle and maximum RPM.

With a fixed pitch propeller, you do cannot reduce RPM without reducing power. However, power output will become less as pressure altitude and air density is reduced. Most engine makers recommend cruise with 65-75% power to increase engine life. Engine life isn't a factor in a cyber plane. However, the software usually comes with a representative operator's manual giving recommended power settings and limitations.

To achieve realism in your simulator flying, you should adhere to all of the proscribed limitations and procedures.

Remember that maximum RPM doesn't always relate to maximum power. An analogy is in a car going 60 mph up a steep grade and then maintaining the same speed going downhill. The RPM at the wheels may remain constant but the power changes from maximum to minimum with gas pedal action.


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2532 posts, RR: 24
Reply 14, posted (5 years 7 months 3 weeks 1 day 14 hours ago) and read 3634 times:



Quoting DukeofDashes (Reply 4):
Most take offs I'm aware of occur with the thrust setting around 90% - 91% of N1. To run a reduced power take off, the power setting is usually around 86-87% N1

There are plenty of engines where full rated takeoff power is more than 100% N1. 90%-91% is a very narrow range to consider normal. Even in MSFS.....  Wink

Quoting Triebwerk (Reply 2):
Well, if I'm not mistaken, pushing the throttle stack on an airliner as far as it can go (e.g. the throttle won't move forward any more) is not a position you want to be in for more than a few seconds. (Is this only the case with heavies?)

It depends on the airliner/engine combination. On a FBW Airbus pushing the thrust levers fully forward gives you TOGA thrust, and no more. In complete contrast, many non-FADEC, non-EEC engines, firewalling the throttles will put some or all parameters well over the red line limits.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineFr8mech From United States of America, joined Sep 2005, 5098 posts, RR: 12
Reply 15, posted (5 years 7 months 3 weeks 1 day 14 hours ago) and read 3622 times:

Quoting Fr8mech (Reply 9):
It is quite possible to reach the max N1 without achieving maximum power (on EPR engines);

I've been thinking on this a little and though it is theoretically possible, I don't think it would ever happen in actual practice. The probability is, I'm going to guess, astronomically low.

Quoting Triebwerk (Reply 2):
Well, if I'm not mistaken, pushing the throttle stack on an airliner as far as it can go (e.g. the throttle won't move forward any more) is not a position you want to be in for more than a few seconds.

You are mistaken, at least on modern FADEC engine equipped aicraft. The full forward postion will result in full take-off/go-around (TOGA) power...for the day as calculated by the thrust management system and flight management system. Older airframe/engine combinations will result in some, if not all parameters exceeding the max limit.

Edit: I see Jet beat me to the punch on the firewall.

[Edited 2008-09-03 14:51:52]


When seconds count...the police are minutes away. Never leave your cave without your club.
User currently offlineTriebwerk From United States of America, joined Sep 2008, 126 posts, RR: 0
Reply 16, posted (5 years 7 months 3 weeks 1 day 12 hours ago) and read 3576 times:

Thanks for all the info. It's as if I walked into a roomful of flight instructors and asked this question; you all provided so much detail and content! Greatly appreciate it.

User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Reply 17, posted (5 years 7 months 3 weeks 15 hours ago) and read 3419 times:



Quoting Triebwerk (Reply 16):

Much better than Civil Aviation aye  Wink



What gets measured gets done.
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 18, posted (5 years 7 months 3 weeks 9 hours ago) and read 3353 times:



Quoting 411A (Reply 3):
Most large radial piston engines have a time limit for which full power is available.
This time limit is usually two minutes.
These engines also have a METO (maximum except takeoff) power rating, and there is no time limitation, with METO power.

My old man worked for Curtiss Wright and at that time the acceptance for a military 'type certificate' was...a drum roll.....tttttttttt

150 hours at full power.


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