Turboprops Need Warmups Why Not Jets?

william · Wed Sep 02, 2009 9:47 pm

We all know the first flight out on a turboprop they go out onto the apron and do the obligatory 5-10 minute warmup. SInce a turboprop is a jet geared down why do jets (737,A320 et al) not have to warmup first flight out ?

Max Q · Wed Sep 02, 2009 10:41 pm

Well, they do, most jet engines need a few minutes to stabilise and for the oil temperature to be 'in the green'

Normally, unless in extreme cold temperatures, however these few minutes will be absorbed during the taxi to the runway.

Goldenshield · Wed Sep 02, 2009 11:36 pm

Turboprops also have an auto-feather system, and that needs to be tested, among other things, and that may be what you are thinking of as the "warmup." When they test them, the RPMs drop, and then rise again, they will sound akin to testing of the magnetos on a 4-stroke airplane engine, but it is not the engine; rather, it is the props taking a bigger bite of air, and dropping in RPM.

[Edited 2009-09-02 16:40:05]

thegreatchecko · Thu Sep 03, 2009 2:49 am

I've never done a warmup on the megawhacker....

So not all turboprops need a warmup.

pilotpip · Thu Sep 03, 2009 2:53 am

Turbofan engines usually have a 2-5 minute warmup and other parameters must be met as well.

How's it going checko? I don't have anything on the schedule for Sept yet but if I end up in DEN I'll call you.

DashTrash · Thu Sep 03, 2009 3:04 am

Don't have to warm up the engines exactly.

In the Dash you had to let the oil temp rise to a certain temp (don't remember the value) before you could take the props out of feather. It might take a minute or two to get there if it's real cold, but turbines make a lot of heat fast.

KELPkid · Thu Sep 03, 2009 3:58 am

Quoting Goldenshield (Reply 2):
Turboprops also have an auto-feather system, and that needs to be tested, among other things, and that may be what you are thinking of as the "warmup." When they test them, the RPMs drop, and then rise again, they will sound akin to testing of the magnetos on a 4-stroke airplane engine, but it is not the engine; rather, it is the props taking a bigger bite of air, and dropping in RPM.

When I used to work as a lineboy at LRU, back in the early 90's, YV used to cycle the props through to the beta range on their Beech 1900's three tiimes before takeoff...a far cooler sound than any piston aircraft checking the prop govenor Cool

Quoting Max Q (Reply 1):
Well, they do, most jet engines need a few minutes to stabilise and for the oil temperature to be 'in the green'

At ELP, WN has a gate that probably has a 400'-500' taxi to the threshhold of RWY 8R....however, before departing that gate to 8R, the aicraft usually sits there on the ground for about 2-3 min. after disconnecting from the pushback tug...I'm guessing it's so that the engines are run for the manufacturer's minimum run time before flight.

thegreatchecko · Thu Sep 03, 2009 4:02 am

Quoting DashTrash (Reply 5):
In the Dash you had to let the oil temp rise to a certain temp (don't remember the value) before you could take the props out of feather. It might take a minute or two to get there if it's real cold, but turbines make a lot of heat fast.

Okay, so I forgot about the days when the temperature is at 40 below.

Those days are no fun. cold

Checko

DashTrash · Thu Sep 03, 2009 3:15 pm

Quoting TheGreatChecko (Reply 7):
Okay, so I forgot about the days when the temperature is at 40 below.

Those days are no fun. cold

You're not kidding!!

soon7x7 · Fri Sep 04, 2009 2:51 am

As I fly WN much , first flights out, I notice that during the taxi each engine is spooled up for 30 seconds to get the oil thinned and circulating while we are taxiing...j

Flighty · Fri Sep 04, 2009 4:16 am

Quoting TheGreatChecko (Reply 7):
Okay, so I forgot about the days when the temperature is at 40 below.

How about extreme cold? Airline ops never seem to cancel due to subzero temps in Moscow or Fargo. Is any warmup time required there, or can turbines just shake it off relatively fast, on the way to the runway?

DashTrash · Fri Sep 04, 2009 3:31 pm

Quoting Flighty (Reply 10):
How about extreme cold? Airline ops never seem to cancel due to subzero temps in Moscow or Fargo. Is any warmup time required there, or can turbines just shake it off relatively fast, on the way to the runway?

All airplanes have a minimum temperature they can operate in. It's damn cold though.

Engine oil doesn't take long at all to warm up. Turbines make lots of heat, rapidly.

CanadianNorth · Fri Sep 04, 2009 6:30 pm

Quoting Flighty (Reply 10):
How about extreme cold? Airline ops never seem to cancel due to subzero temps in Moscow or Fargo. Is any warmup time required there, or can turbines just shake it off relatively fast, on the way to the runway?

As far as I know every aircraft has a minimum temperature which it can operate it. Some airplanes (I've been told on the CRJ for example) it's around -40, where as others (like the 737) it's well below that. So for some aircraft you do have to keep the limits in mind during colder parts of the year, but on many aircraft by the time it gets cold enough to hit that limit everyone probably would have up and gone home anyway.

As for warmup as everyone is saying it's pretty standard issue to have to meet certain oil temps and whatnot, but as said turbines make a lot of heat in a hurry so even on cold days it still only takes a couple minutes.

CanadianNorth

Fabo · Fri Sep 04, 2009 6:48 pm

Dunno how it is in western cold ops, but there is a talk of Aeroflot sending then-new 767 somewhere to Siberia, Irkutsk perhaps, for an overnight in November, and not being to fly it out until mid-spring. No idea on credibility though.

Bartonsayswhat · Fri Sep 04, 2009 8:45 pm

I heard once in one of our training classes for winter ops that if it gets below -45 overnight we're supposed to put the CRJs in a hanger because once in YXY or somewhere they went to open the door and the handle broke off. I'm not sure if the trainer was serious or not, he may have just been having a laugh with us, as a very mild winter station, we'll believe anything.

Woodreau · Mon Sep 07, 2009 6:41 am

Quoting William (Thread starter):
We all know the first flight out on a turboprop they go out onto the apron and do the obligatory 5-10 minute warmup. SInce a turboprop is a jet geared down why do jets (737,A320 et al) not have to warmup first flight out ?

As others have said, the turboprop isn't warming up - it's most likely doing something called First Flight Checks - checking autofeather, the beta range. Our company discouraged having any pax onboard when doing the first flight checks - so it required the crew to show up and before boarding starting up the aircraft and doing the checks, shutting down then boarding.

Since (doing those checks in the company preferred manner - without boarding pax) that meant the flight crew wasn't paid for the first flight checks, so a lot of crews elected to do those checks during the taxi out on the first flight with the pax on board.

Other than the uniquely turboprop checks - they have the same warmup limitations as turbofans. As long as all the indications are in the green - it's good to go usually after 2 minutes. The only time it became a problem was when it was a short taxi - like 30 seconds from the terminal to end of runway to takeoff (like at DUJ, JBR, SLN, or JLN) then you had to wait the extra 90 seconds to get the minimum warm up time for takeoff.

747classic · Mon Sep 07, 2009 9:06 am

On most jet engines there is a minimum idle time (between 3-5 minutes) before T/O thrust is set. Slightly above idle is permitted for break away thrust (also max N1 or EPR limits in force) Additional there are limits for minimum oil pressure (or max. oil pressure in sub zero temps). Before T/O all indications have to be in the "green band".
This is all required for thermal stabilization of all components in the engine. Also the clearances between rotating and stationary parts are optimized during this stabilization time.
After a quick turn around (30 minutes) you need the stabilization time sometimes for thermal reasons. During this relative short engine shut down time the upper side of the engine is becoming hotter than the lower side (residual heat) After starting engine vibration (high speed rotor) is higher than normal, causes by a "bowed rotor". After a few minutes stabilization time the vibration returns to normal values.

Problems faced by very low outside temps are EGT indicators showing flags, so engine starts without EGT indications have to be performed, very high oil pressures, etc.

DocLightning · Tue Sep 08, 2009 4:23 pm

Quoting CanadianNorth (Reply 12):

As far as I know every aircraft has a minimum temperature which it can operate it. Some airplanes (I've been told on the CRJ for example) it's around -40,

But the temperature at cruise can be far colder than that...

Goldenshield · Tue Sep 08, 2009 5:31 pm

Quoting DocLightning (Reply 17):
But the temperature at cruise can be far colder than that...

Yes, it can; however, the crew cannot take the plane to temperatures colder than allowed by the manufacturer, which generally means a lower cruising altitude.

747classic · Tue Sep 08, 2009 5:59 pm

Quoting DocLightning (Reply 17):
But the temperature at cruise can be far colder than that...

Quoting Goldenshield (Reply 18):
Yes, it can; however, the crew cannot take the plane to temperatures colder than allowed by the manufacturer, which generally means a lower cruising altitude

Boys, this thread, we are still on the ground ( and starting our engines).
At cruising altitude there is no temperature limitation for the engine start, so far I know. And if you have to start immediately your engines at cruising altitude, you don't mind the extra engine wear.
The only altitude limitation for engine operation is the fuel temperature.

Goldenshield · Tue Sep 08, 2009 6:08 pm

Quoting 747classic (Reply 19):
Boys, this thread, we are still on the ground ( and starting our engines).

It's not my thread deviation. Wink

Quoting 747classic (Reply 19):
And if you have to start immediately your engines at cruising altitude, you don't mind the extra engine wear.

Depends on the aircraft, and engine, and whether your engine is not locked up. duck

grandtheftaero · Tue Sep 08, 2009 9:20 pm

The #2 engine on GE-powered DC-10s use to be susceptible to ejecting their turbine rear frame bearings because pilots failed to warm up the engines. As the story goes, the airlines were trying to save fuel (and possibly brake pads) so they would taxi out to the runway using only the #1 and #3 engines then start up the #2 engine right before take-off and gun the power levers. The bearing housings did not respond well to the heat shock.

Sasha · Wed Sep 09, 2009 12:08 am

At our local airport with -50C temps happening in Dec-Jan, Boeing 757-200s are doing fine Smile

So are the An-24s and L-410s. They all need prior warm up by a vehicle which feeds hot air into the cabin, etc after a cold night. Procedures are said to start at 5am for a scheduled 8am take off!

Not sure about the 757s, their procedures may be different like leaving APU/GPU running all night to feed heating (if there's any internal mechanism for that).

Also, had a chance to flip through an Annex manual for A-310 certified for Cold Ground Ops. There it stated that engine warm up during taxi time is sufficient.

Viscount724 · Wed Sep 09, 2009 1:35 am

Two years ago, in January 2008, AC had to cancel all their flights to/from Yellowknife (YZF) , capital of Canada's Northwest Territories, for several days when temperatures dropped below -40C which is apparently the lowest ground temperature the CRJ used on those routes is certified for. I think it's related to the lowest oil temperature for engine starts. Some AC CRJ and Embraer flights to/from YEG were also cancelled for the same reason.

AC's competitors to YZF, First Air and Canadian North, both operating 737-200 Combis, maintained normal operations. The 732 has been operating for decades in that part of Canada where winter temperatures sometimes go below -50C.

A couple of related news items re the above.
http://www.cbc.ca/canada/north/story/2008/01/29/cold-jazz.html
http://network.nationalpost.com/np/b...ncelled-due-to-chilly-weather.aspx

T prop · Wed Sep 09, 2009 2:57 am

Quoting DashTrash (Reply 5):
In the Dash you had to let the oil temp rise to a certain temp
[quote=747classic,reply=19]
Boys, this thread, we are still on the ground ( and starting our engines).
At cruising altitude there is no temperature limitation for the engine start, so far I know. And if you have to start immediately your engines at cruising altitude, you don't mind the extra engine wear.
The only altitude limitation for engine operation is the fuel temperature.

I don't know about the large turbines, but on smaller ones there is a limitation for shutdown and restarts in flight. Recall the Pinacle CRJ accident where the pilots screwing around stalled the engines. They ended up with both engines corelocked and we read about them in the newspapers. On a turboprop like Dash 8 there is a specific warning about shutting an engine down in flight for longer than 10 minutes (pilot training) and then restarting when ambient is lower than -40c.

DashTrash · Wed Sep 09, 2009 3:03 am

Quoting T prop (Reply 24):
On a turboprop like Dash 8 there is a specific warning about shutting an engine down in flight for longer than 10 minutes (pilot training) and then restarting when ambient is lower than -40c.

Never saw that limitation, but we didn't have a re-light procedure for in flight. Once you shut it down, it stayed off. We did all our training in the sim, so it just didn't matter to us.

DocLightning · Wed Sep 09, 2009 5:42 pm

Quoting 747classic (Reply 19):
And if you have to start immediately your engines at cruising altitude, you don't mind the extra engine wear.

This is true. I suppose gliding into the ground puts a lot more wear-and-tear on an engine than starting it in-flight, huh?

Quoting Viscount724 (Reply 23):
Two years ago, in January 2008, AC had to cancel all their flights to/from Yellowknife (YZF) , capital of Canada's Northwest Territories, for several days when temperatures dropped below -40C which is apparently the lowest ground temperature the CRJ used on those routes is certified for. I think it's related to the lowest oil temperature for engine starts.

So cars have this issue, too. This is why in places like Minnesota and Alaska, cars often come equipped with engine block warmers to keep the oil and coolant from freezing. Why couldn't this be included as an option for aircraft that are expected to cold soak?

Malmi18 · Wed Sep 09, 2009 5:53 pm

> Our company discouraged having any pax onboard when doing the first flight checks - so it required the crew to show up and before boarding starting up the aircraft and doing the checks, shutting down then boarding.

Why? Makes passengers scared that something may not be alright or what?
I'd be more scared if I suspected that the plane has NOT been checked.

Woodreau · Wed Sep 09, 2009 8:39 pm

Quoting Malmi18 (Reply 27):
Why? Makes passengers scared that something may not be alright or what?
I'd be more scared if I suspected that the plane has NOT been checked.

Most of your pax have absolutely no interest in aviation other than it gets you from point A to point B - and are very skittish about flying in a "small" turboprop - an airplane they already regard as "dangerous" and "outdated" - no matter how safe a turboprop is.

If it's out of sight it's out of mind (i.e. the first flight checks.) They assume you've already done everything to get the airplane to fly.

On a turboprop I flew, the first flight checks - I guess would be the piston equivilent of doing "Magneto Checks" - involved testing the overspeed governor, autofeather and some other noisy items - that most pax don't really care to go through, especially if it's really hot out. A prop is noisy already, but the checks add shudders/violent shaking to the "din and mayhem" on a flight that most pax can't wait to get off of. It can take an experienced crew about 2-3 minutes to do the first flight checks, but a new captain can take 10-15 minutes to run through the checks. The cabin cooling works only in the air and not very well at all on the ground.

So that's why the company prefers not have any pax boarded when doing the checks.

Plus if you did find something wrong (rare but it happens more often than you think), now you have to deplane the pax.

I think the only people who have any interest in seeing first flight checks on a turboprop are (a) not pilots and (b) are into aviation.

The original poster asked why turboprops "warmed up" and jets didn't. In my very limited three years of turboprop flying, I've never had to "warm" up the engines other than the 2 minute limitation from engine start before applying takeoff power, or I imagine the jets have the same kind of limitation.

[Edited 2009-09-09 13:45:59]

rwessel · Thu Sep 10, 2009 5:42 am

Quoting DocLightning (Reply 26):
So cars have this issue, too. This is why in places like Minnesota and Alaska, cars often come equipped with engine block warmers to keep the oil and coolant from freezing. Why couldn't this be included as an option for aircraft that are expected to cold soak?

Probably because even in places like Yellowknife, -40C (or -40F, for that matter) days are pretty rare. And it's probably just a matter of demand not being high enough to certify to lower temps (or to make the required mods). Also, it's not just the engines that are an issue.

A similar problem exists at extremely high temps - on many aircraft the standard performance documents have an upper limit, and from time to time you hear of flights being canceled in places Australia or Phoenix because the temperature is off the charts. Some aircraft have supplemental charts available (for a price, of course), that expands the envelope at the high end. It's certainly plausible that a manufacturer could make additional operating envelope available on the low end as well (either by expend certification or adding extra equipment), but it's clearly something that needs to be paid for somehow.

william · Sun Sep 13, 2009 9:19 pm

Thanks for the replies folks. So please explain in laymen terms just what is being accomplished when on the first flight out one goes to the farthest part of the tarmac and runup begins? How does running up the props test the autofeathering?

And the pilot who posted two threads back is correct, when one is sitting in a turboprop in the early morning darkness, and you have SAAB 340 or ATR seemingly feeling like its going to shake itself to apart and generate decibels that have Bose QC2s crying uncle, its disconcerting.

Viscount724 · Mon Sep 14, 2009 3:49 am

Quoting Rwessel (Reply 29):
Probably because even in places like Yellowknife, -40C (or -40F, for that matter) days are pretty rare. And it's probably just a matter of demand not being high enough to certify to lower temps (or to make the required mods). Also, it's not just the engines that are an issue.

Following Canadian government data for a few of the colder AC Jazz destinations served by CRJs for the period December-March for the past two winters. Number of days where the lowest temperature was below -40C and -35C, and the lowest recorded temperature during the period.

Dec-Mar 2008-2009
Yellowknife (YZF): -40C 11 days, -35C 34 days, lowest recorded -44.6C
Whitehorse (YXY): -40C 2 days, -35C 10 days, lowest recorded -40.9C
Edmonton (YEG): -40C 2 days, -35C 9 days, lowest recorded -42.7C

Dec-Mar 2007-2008
Yellowknife (YZF): -40C 14 days, -35C 27 day, lowest recorded -45.8C
Whitehorse (YXY): -40C 6 days, -35C 12 days, lowest recorded -44.6C
Edmonton (YEG): -40C 1 day, -35C 3 days, lowest recorded -44.4C

DashTrash · Mon Sep 14, 2009 5:06 am

Quoting William (Reply 30):
Thanks for the replies folks. So please explain in laymen terms just what is being accomplished when on the first flight out one goes to the farthest part of the tarmac and runup begins? How does running up the props test the autofeathering?

On the Dash 8, you get both engines running. The captain will check the ECU enrichment solenoid by selecting the ECU switchlights to manual, watch for an engine RPM drop, then back to normal. While he is doing that, the FO will check the PTU. That makes a pretty loud "thunk" in the back. The captain will then bring the props out of feather, and the FO will do the autofeather / power uptrim test. This simulates an engine failure to the engine opposite being tested. The engine being tested will feather its prop, while the "good" engine will increase its torque. Repeat for the other side, run the after start checklist (along with the other non-first flight items), and call for taxi.

The props feathering is what gets peoples attention in the back. We always did it with them on board. Never heard anyone make a comment about it, but I did get a comment about the PTU check once.

Northwest727 · Mon Sep 14, 2009 9:28 pm

I am also making a guess, that because the propellers on turboprops (or most other constant speed props, including piston powered aircraft) need oil-usually engine oil, to change the pitch of the blades, its a good idea to use warm oil which is better flowing, but also helps extend the life of the seals inside the hub assembly.

Having never flown a turboprop, but regularly flying pistons with constant speed propellers, this is my reasoning, in addition to what others have said above.

DashTrash · Tue Sep 15, 2009 1:24 pm

Quoting Northwest727 (Reply 33):
I am also making a guess, that because the propellers on turboprops (or most other constant speed props, including piston powered aircraft) need oil-usually engine oil, to change the pitch of the blades, its a good idea to use warm oil which is better flowing, but also helps extend the life of the seals inside the hub assembly.

Yep. That's why the oil temp has to be above 0 before you take the prop out of feather. We didn't have to cycle the props like on a piston though since the blade pitch is continually moving throughout the taxi.

FlyASAGuy2005 · Tue Sep 15, 2009 3:08 pm

I love props.

I was on an ATR in 2007 on D in ATL when they had just chanhed the oil, or did something with the engine. The Mec asked me to secure the boarding door and he ran up both engines. Kind of fun to hear the distinguished woosh and low roar sound when you raise and lower the RPM and change the pitch on the blades. Planes was also bouncing around pretty good.

Arrow · Tue Sep 15, 2009 6:18 pm

This trip was prominently displayed in the news in 2001(?) when it took place. I have a recollection that the Twotter pilots claimed a record for a cold start for the PT6 on their return, but I couldn't dig that up anywhere to confirm it.

This is an excerpt from a science blog -- gives you an idea what goes into planning for cold weather operations.

"NSF officials noted that several factors, all of them weather-related, argued in favor of employing the Twin Otters instead of the much larger Hercules. The extreme temperatures at the Pole are less likely to affect the Twin Otter landing gear, which is less reliant on hydraulic fluids than are the Hercules. Also, it is considerably easier to bring the smaller quantities of fuel needed to power the Twin Otter to an operating temperature by moving into a heated area of the station.

The decision to use the smaller planes was made chiefly on the basis of their rated temperature range. The four-engine turboprop LC-130, the veteran workhorse of the Antarctic program, is rated safe down to -55 Celsius (-67 Fahrenheit). The Twin Otter is rated to -75 Celsius (-103 Fahrenheit). In addition, the large military aircraft would not have been able to attempt the flight to the Pole after April 22, when it becomes too dark and too cold to conduct the mission safely.

The Borek Twin Otters, however, have repeatedly flown the route from South America to the Pole. Moreover, the small aircraft can be completely refueled with only 1,000 gallons. That amount is available at a fuel "dump" between Rothera and the Pole.

Full article:

http://www.scienceblog.com/community/older/archives/C/archsf161.html

CX Flyboy · Sun Sep 20, 2009 2:23 pm

On the 777 the GE90 needs a 3 minute 'warm up' prior to setting take-off thrust. Thrust higher than idle is permitted for taxi. Similarly there is a 3 minute cool-down period as well after landing before engines are shut down.

The Trent 800 we are told needs 5 minutes before setting take-off thrust although there was never this restriction for us until GE informed us of their restriction for our new 777-300ERs. I suspect it was only then that someone asked RR whether there was a similar thing for the Trent800 and was told 'yes'. For the 12 years of operations before that though, there was no such restriction that we knew of! Whoops!

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