Speedbrakes

[B737]

Speedbrakes has a very poor effect during flight. Noise& vibration coming up but the speed reduction almost undetectable 

[Litjan]

Welcome to the real world of a 737 pilot!

In the real aircraft the speedbrake will increase the rate of descent by about 50% at 250kts (faster -> more, slower -> less).

So instead of descending with ca. 1500 feet per minute you will now descend with 2200 feet per minute.

Unlike in other aircraft, the speedbrake will not save your *ss when planning the descent poorly. In fact when I flew the 737 using the speedbrake was stigmatized as a sign of poor pilotage (unless you would get a completely unexpected shortcut or in an emergency, of course).

Cheers, Jan

 

[B737]

Thank you Jan,agree.

On Ng series guess bit higher due to 8 flt spoilers exists.

[B737]

Can  somebody make a cross check just to confirm  that the speedbrake does not do any brake action in the air...

Jan I can agree with you, but in the sim does not work

[Litjan]

I am sure it does...

Go ahead and display the "Aerodynamic forces" (field 64) in the DATA OUTPUT tab so you can see the little green numbers for "drag".

When I fly at 230 kts, the drag is roughly 6100 lbs. When I deploy the spoilers to the "Flight Detent" the drag goes to 7100 lbs, when I go further (not allowed in flight) to the "Full extend detent" the drag rises to 7700lbs.

N1 increases accordingly.

 

Edited April 6, 2021 by Litjan

[B737]

Actually I try  in descent mode by V/S. Choose the V/S high enough just to let the throttle at idle by A/T.

 

After all of these settings try to extend the spoiler and pls let me know what you saw.

Because I have not seen any difference.

 

In level flight I can confirm your answer but my personal opinion dictates to me should be more influence...

 

 

[Litjan]

I have tuned the flightmodel and the speedbrake effect to match my personal experience flying this aircraft. If you feel that it should be different, by all means go and  change the model in planemaker to your liking.

[B737]

Actually I try  in descent mode by V/S. Choose the V/S high enough just to let the throttle at idle by A/T.

 

After all of these settings try to extend the spoiler and pls let me know what you saw.

 

Pls check this, and will see surely what I am talking about. Zero effect

[Litjan]

It works as expected:

Fly with V/S at -1500fpm and then set MCP SPD to 210 kts.

At 15.000 feet (descending) the IAS will stabilize at ca. 231 kts IAS.

Now pull speedbrake to FLT DET.

Airspeed starts reducing (in my test it is 215kts by the time I reach 11.000 feet).

 

[B737]

Shall I use A/T and/ or A/ P when doing your test? How did you do exactly?

Marginal effect for me is only at the moment when N1 increasing and  the G/ S reducing just a little. IAS almost remain constant

 

But when comparing ixeg with other aircrafts in xplane the difference is quite big in drag.

I did not say you are not right, but not easy accept or detecting deceleration....

 

 

[B737]

Dear Jan!

I need help, possibly piloting issue.

Almost every time the fmc can not calculate the route without ,,required drag'' message.

Most of the time the A/ P can not handle the speed and vertical speed in the descent phase and usually overshooting everything even we can not capture the glide slope due to we still high enough with overspeed.

Where can I be wrong?

 

[B737]

[Litjan]

Not sure.

[Litjan]

Let me expand a bit on this:

The VNAV part of our descent calculation is not perfect yet. It can work on simple descents, but will not handle multiple or complex restrictions, nor will it factor in head- or tailwind.

This may cause the VNAV calculations/predictions to be erroneous and the pilot needs to monitor the distance/altitude/energy state of the aircraft and revert to selected modes (FL CHG, V/S, manual flight) as warranted. There is a "descent calculator helpsheet" included in the documents for the AviTab free add-on in the airplane to help with calculating the descent profile.

Here is some more reading regarding the state of the current version:

https://forums.x-pilot.com/forums/topic/8526-things-that-are-not-going-to-be-in-v133/

https://forums.x-pilot.com/forums/topic/18101-faq-for-new-users/

and some videos I made recently:

https://www.youtube.com/channel/UCJJ1M9epDJiGKmXConLp3Ew

[B737]

Thank you very much. I was thinking about wind also, due to fmc does not get wind data ahead.....

[Morten]

Regarding speedbrake drag, it was calibrated using the real drag data from boeing. (Jan might have adjusted it later)

It depends on Mach and Cl (aoa).  Gives an increase in Cd between 0,011 - 0,014 in the normal envelope, so not much..

Edited April 10, 2021 by Morten

[B737]

Thank you!