adamant365

Thrust Decrease After Takeoff

Recommended Posts

Quote

We still haven't established if the reference thrust should change during this period.

 

(Real world) I think the green target thrust may only vary with TAT changes if the actual TAT is over 30C. 747-400 engines are "flat-rated" to 30C (at sea-level). Similarly, you might only see assumed temperature derate entries changing target thrust when the entries are over 30C. The video does show a target thrust change of 0.1% without a TAT change during taxi, but there are a number of factors/parameters which influence the target. 

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

John, thanks for your help and your great knowledge, but please, let me say that this is clearly a major bug and it's strange that it hasn't been discovered during beta testing. It's not possible that (see screenshots by MauB a couple of posts above but it happens in any takeoff) the takeoff reference N1 is 102.1 and before V1 the actual thrust is already 103.5! Even more, a few feet after lift off it's 104.5! The actual thrust must be 102.1, and can increase slightly after lift off, but I wouldn't say more than 102.2-102.3... There is an unwanted creep in thrust that must be fixed...

Share this post


Link to post
Share on other sites

I was just hoping someone knew for sure how it really works. My books are hopeless... I'm still mostly guessing. I assumed thrust target and thust control was based on TAT (my books seem to say control is based on TAT), but did you see the latest update in that other sim?  :laugh:

I think I'll keep my silence on this issue until we get some concrete evidence. Now I'm doubting my flat rating theory.

Share this post


Link to post
Share on other sites

Yes, I'm not saying this is a bug, but just reporting what I'm seeing. My flights are mostly with the ERF variant.
I did a flight some minutes ago with the BCF (PW engines) and noticed that the EPR didn't rise above green mark and didn't drop either, it remained right on the mark all the time during takeoff roll and climb until thrust reduction.

Share this post


Link to post
Share on other sites
59 minutes ago, MauB said:

I did a flight some minutes ago with the BCF (PW engines) and noticed that the EPR didn't rise above green mark and didn't drop either, it remained right on the mark all the time during takeoff roll and climb until thrust reduction.

Yes, indeed the EPR is ok, but if you look at N1, you'll se it increases like in the GE engines.

Share this post


Link to post
Share on other sites

I don't have idea, but i had the same issue with GE engine. Departing from OTHH to Frankfurt, runway 34R, the takeoff was D-TO2, FLX 66º with 94,8% of N1. Even with the AT in "hold", a few seconds after takeoff, the thrust decrease around 5% and then came back to 94,6%. I noted because of the sound decreasing way before 1.500ft and then rising up again. The throttle on my joystick is always at idle, only used for taxi.

The same issue was noted on the next flight, departing from Frankfurt. Rwy 25c, D-TO1, FLX 52º with 95% of N1.

I will eliminate the throttle from command menu in FSX and test only using the F2 / F3 in a few hours, on the return leg to Frankfurt.

 

Renato Roberto

SBGR / Brazil

Share this post


Link to post
Share on other sites
On 27/2/2017 at 9:54 PM, adamant365 said:

It makes some sense, but you'll notice the EPR in the RR/PW versions is decreasing away from the green target when THR REF engages, not decreasing to meet it like you're explaining. I'm not seeing an increase in EPR during the TO, it is staying stable.

EDIT: I see what you're saying now. Just did a quick test with the PW variant. While EPR stays stable throughout the TO run, N1 does increase by 2-3%. Then at THR REF (400'), N1 decreases to the original TO value but that causes EPR to decrease away from the target TO value. In my recent test EPR dropped from 1.44 to 1.39.

Yesterday I tried with a RR engines for the first time. During takeoff run, when HOLD engages, the EPR correctly stays at the green reference value, while the N1 starts increasing erroneously like in the GE engines. At 400 ft, when THR REF engages, it's not clear what the A/T wants to do, it seems that it wants to bring the N1 back to the one matching the reference EPR (even if the EPR has not moved from the reference value). The result is a decrease in EPR to a lower value than the reference one. Clearly this behaviour needs to be corrected as well...

Share this post


Link to post
Share on other sites

As best as I could tell, N1 stayed within 0.1 of target throughout. Interesting that they had a D-TO 2 with +55C AT, but used normal CLB. There was a 6+% bump in thrust at "thrust reduction" altitude. I don't think I have seen that before.

Share this post


Link to post
Share on other sites
12 minutes ago, adamant365 said:

There was a 6+% bump in thrust at "thrust reduction" altitude. I don't think I have seen that before.

Indeed, it should be "thrust increase" altitude :biggrin:

Share this post


Link to post
Share on other sites

Any news in that matter? This bug is still there and especially on long take off runs you can see a great discrepancy between the green reference thrust and the actual thrust.

Share this post


Link to post
Share on other sites
On 17/03/2017 at 2:34 PM, adamant365 said:

As best as I could tell, N1 stayed within 0.1 of target throughout. Interesting that they had a D-TO 2 with +55C AT, but used normal CLB. There was a 6+% bump in thrust at "thrust reduction" altitude. I don't think I have seen that before.

Hi,

Considering the rampie with the KLM jacket and the airport alitude, it looks like a KLM freighter flight from Nairobi to Amsterdam (HKJK-EHAM).

NADP2 as with an aircraft probably quite heavy.

In the sim no matter what the take off thrust is, anyweight over 300T, I would use CLB1 or CLB even if TO thrust is T/O2 + temp. 

Otherwise the climb rate at CLB2 above 300T is disastrous...

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now