sevenheavy
Posts: 927
Joined: Tue Mar 23, 2004 3:30 am

Pilots: De-rated Take-offs - How Low?

Sun Aug 29, 2004 2:20 pm

Hi,

I guess this question is mainly directed at members with jet flying experience but I would obviusly appreciate comments from anyone who could offer input.

We all know that pilots/airlines use derated engine power settings when conditions permit. What is the minimum (n1/n2) setting that you would use or have used for takeoffs i.e. 92% n1 etc?. I know that the lighter the aircraft and the more runway available means more scope for derated takeoffs but are there any aircraft or company restrictions which dictate minimum settings?.

Once again thanks for all input.

Regards,

SevenHeavy
So long 701, it was nice knowing you.
 
XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

RE: Pilots: De-rated Take-offs - How Low?

Sun Aug 29, 2004 2:26 pm

The CRJ we typically will use a FLEX temp of around 48 C....minimum N1 for takeoff (which this usually gives) is 85% N1.
Chicks dig winglets.
 
wing
Posts: 1357
Joined: Sun Oct 01, 2000 9:10 pm

RE: Pilots: De-rated Take-offs - How Low?

Sun Aug 29, 2004 6:11 pm

As we mostly fly medium range(around 3 1/2 hours flying )full house(mostly charter flights), my experience is mostly we use 24K derate or 26K + asumed temp thrust reduction.Which wil give you roughly around 95-98 % N1.
follow me on my facebook page" captain wing's journey log"
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Pilots: De-rated Take-offs - How Low?

Sun Aug 29, 2004 11:42 pm

Under US regulations thrust reductions exceeding 25% of takeoff thrust are not permitted. Most reductions are far less than this as the highest temperatures and the highest centrifugal loads are reached in the last two or three percent. It is just not necessary to make cutbacks that deep. Also should not see a reduced takeoff thrust that is going to be lower than normal climb thrust at accel height. In other words, the plane should not take off, climb to a thousand feet and then INCREASE power.

It is not always possible to discern how much actual thrust reduction was used by looking at the N1 used for takeoff power. I've seen an assumed temperature forty degees higher than actual yeild an N1 in the mid 90s.

Happiness is not seeing another trite Ste. Maarten photo all week long.
 
Luis777
Posts: 81
Joined: Sun Aug 29, 2004 3:16 am

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 12:00 am

Many operators use reduced thrust takeoff whenever performance limits and noise abatement procedures permit. Thrust reduction or derate lowers EGT and extends engine life.

The first method is Assumed Temperature Method (ATM), this method achieves a takeoff thrust less than the full rated takeoff thrust by using an assumed temperature that is higher than the actual temperature. The maximum thrust reduction authorized by most regulatory agencies is 25% below any certified rating, on the 767 PW4000 could be as low as 1.39 EPR and on 737NG as low as 89% N1. (GE and RR use N1 as reference and PW uses EPR)

The second method is fixed derate which uses a takeoff thrust less than full rated thrust for which complete and independent performance data are provided in the Airplane Flight Manual. Derated thrust is obtained by selection of fixed tkeoff derates from the Flight Management Computer (FMC). TO1/CLB1 provides a takeoff/climb limit reduced 3%N1 (approximately 10% thrust). TO2/CLB2 provides a takeoff/climb reduced by 6%N1 (approximately 20% thrust).

I hope this info could help you.

Regards

LG
 
G4Doc2004
Posts: 120
Joined: Thu Feb 19, 2004 7:49 am

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 12:22 am

Our G-IV with the RR Tay 611-8 engine uses EPR's calculated by the FMS. "Power for the Day" is the max EPR available for use, and is usually in the range of 1.72 to 1.74 depending on temp, etc. "Flex Power" is the de-rated EPR and is what we usually use more for the advantage of extending engine life and making mid-life and overhauls less costly. The de-rated EPR is around 1.53-1.54.
"Failure to prepare is preparing to fail"--Benjamin Franklin
 
sevenheavy
Posts: 927
Joined: Tue Mar 23, 2004 3:30 am

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 2:24 am

Thanks for all the responses- all great info and much appreciated.
I had no idea at GE and RR use N1 and PW use EPR for reference - I wonder why?

Thanks again.

SevenHeavy
So long 701, it was nice knowing you.
 
XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 2:33 am

SlamClick- an interesting tidbit about my little bird- whenever we flex, we actually DO increase power for climb thrust. You'll go from 85% to about 88-89% N1 when setting climb thrust. I always thought that was wierd- I guess that's the way the Canuck Jet works.
Chicks dig winglets.
 
lowrider
Posts: 2542
Joined: Wed Jun 30, 2004 3:09 am

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 4:28 am

XFSU,
That must be a company specific thing. For flex thrust takeoffs, if the N1 setting is below the climb setting, we leave it there until 10,000, If it was good enough to get you to 1000, the next 8-9 should be easy.
Proud OOTSK member
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 4:49 am

The first method is Assumed Temperature Method (ATM)...
The second method is fixed derate...


AA B738 operations utilize BOTH. The lowest N1 I recall seeing was 78%...had to look over the numbers more than twice, but everything matched up and that's what we used. Most often we'll be operating in the low 80% N1 range though.

*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 7:38 am

On the 744 you can and do use both methods. For example, at SQ, we ust TO-1 and assumed up to 52C. I know of other carriers who start at TO-2 and 52C.

To make a correction in Luis777's post, RR use EPR not N1. Only GE uses N1, PW, RR, IAE all use EPR.
Fly fast, live slow
 
rendezvous
Posts: 531
Joined: Sun May 20, 2001 9:14 pm

RE: Pilots: De-rated Take-offs - How Low?

Mon Aug 30, 2004 7:38 am

You should see the Emirates 777-300s leave Auckland. They go trans-Tasman so flights are 3-4 hours. They use as much runway as a fully loaded 747-400 going to Los Angeles.

Who is online

Users browsing this forum: AA777223, adiru777, Afstand, CMHChris, vc10, Yahoo [Bot] and 15 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos