146 Cruise Speed
-
I cannot keep a stable cruise speed with a fixed throttle setting. I expect that the matching drag will determine the speed at a given throttle setting. If we're accelerating at a fixed altitude, there should be a point where, as speed increases with the increasing drag, the plane's speed should come to equilibrium and be stable. That works in other craft but not the 146. The only way I can hold a reasonable cruise speed is to use IAS and tolerate a bit of altitude variation. I use a Virpil controller with very stable output for any given setting. I noticed that N1 is not stable with a fixed throttle setting.
Is this the correct behavior for the 146 and if so can you explain it?
(I searched for a similar topic on the forum and did not find anything so I apologize if this has already been covered.)
-
There were some similar discussions had recently in a separate thread that I'll link here: https://community.justflight.com/topic/6687/how-to-stabilize-kias
That should cover the procedure for setting a throttle position in the cruise to achieve a stable cruise speed, but please do let us know if you have any further questions.
Mark - Just Flight
-
I was using SYNC on N1 as recommended. The same problem was mentioned in a post by Avionic in the linked discussion above:
"Compared to most other planes, the 146's engines seem more sensitive to airspeed.
So a bit too much throttle --> higher airspeed --> more power --> even higher airspeed until you overspeed. Same effects of course work in reverse when decreasing throttle.
The increase in drag would be the counteracting effect, but unlike most other planes the increase in drag doesn't seem to outweigh the increase in power, making it an "unstable system".It just seems too difficult to get it stable and runs counter to the idea that as drag increases with speed you should easily hit a limiting speed for any given throttle setting. Maybe that is just how it works on the 146, and I'd love to hear from an experienced BAE pilot
-
@Artpom said in 146 Cruise Speed:
Interesting - i thought that such basics of physics as 'higher speed = more drag' is already implemented...
The problem ist not drag, it's that N1 appears to be dependent on airspeed. You can observe that when flying level and accelerating. Or by watching N1 fluctuation when flying in turbulences. Faster IAS = higher N1 for a given throttle lever setting. I don't know if this is realistic for the real aircraft.
That why the workaround is to use TGT, which results in a constant N1 and thus stable airspeed. -
FYI, for correct target:
The 146-100 and -200 intermediate cruise speed is 0.65M.
The 146-300 intermediate cruise speed is 0.67M.
With AP engaged and ALT HOLD at FL280 and FL290 the total fuel burn would be about 2,000 kg/hr. TMS would normally be used in N1 sync mode during the cruise.
