How to stabilize KIAS?

Villajota

Hi, It's difficult for me to maintain a stable KIAS when in cruise. No matter how delicately I set the throttle KIAS never stops; keeps on rising or lowering to dangerous levels. I've tried PMS/TGT with no success. Please note that I'm using a Honeycomb Bravo and a single lever for all 4 throttles.

The only way I've found to maintain KIAS stable is using IAS in cruise mode, once my CRZ ALT has been reached. But I'm not sure if this is an accepted procedure in the 146 or just a "trick" of the simulator. I would like to stabilize KIAS the way it is done in the real aircraft.

Thanks in advance,
Jesus

Mark

With the 146 having no autothrottle, it is up to the pilots to set and maintain the correct engine settings in the cruise to maintain airspeed.

The technique I personally use is once levelled off at cruise altitude, I'll rotate the speed reference bug on the ASI to my planned cruise speed (0.65 to 0.7 Mach). This will then bring the FAST/SLOW indicator to life on the ADI and it allows me to see how fast or slow I am compared to the reference speed, and if I am accelerating or decelerating. I'll then set SYNC mode on the TMS and reduce the throttles until the engines are indicating approximately 83% N1 (this varies depending on altitude, wind speed, etc). I will then monitor the FAST/SLOW indicator to get a feel of if the thrust I have set is too much, or too little and then adjust accordingly.

Try not to make any large and frequent adjustments to the throttles in the cruise, just make one small adjustment of 1% or 2% N1 at a time and let the aircraft settle at its new cruise speed before adjusting the throttles again.

Once you find the sweet spot and the aircraft starts to maintain the intended airspeed, you're usually good to leave the throttles where they are until a change in weather conditions necessitates a further change.

Once you've found the engine setting that allows you to maintain the desired speed, you could then adjust the TGT reference temperature on the TMS to match the current engine TGT and then engage TGT mode on the TMS. The TMS will then maintain the TGT reference temperature and small adjustments can be made to the TGT reference temperature to increase/decrease engine thrust in small increments without touching the throttles.

I hope that helps.

Mark - Just Flight

Avionic

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". I have assigned keybinds to "small throttle increase" (or something like that), which makes adjustments of less than 1 % to make it a bit easier to keep it under control.

It also means that the 146 produces very little thrust when flying slow and as such has an abysmal climb rate when slow. So doing an NADP1 procedure it takes an eternity before you reach acceleration altitude.
I don't know if it is perhaps a real life result of having 4 very small jet engines or if it might be a result of not quite getting the numbers right with the limits that the MSFS engine modelling provides. I guess it could be interesting to compare with real life numbers, but I haven't done that yet.

Villajota

Thanks for the help. And what do you think about using IAS in cruise to stabilze KIAS? It really works, but I feel that this is probably a consequence of how the simulator works and not a strategy that could be done in the real aircraft.

Mark

The IAS autopilot mode is only used during climb and descent, so it doesn't make sense to use it during a cruise.

When the IAS autopilot mode is engaged, the aircraft will adjust pitch to maintain the speed that IAS mode was engaged at. So if you want to climb at 250 knots, you would engage IAS mode when the ASI shows 250 knots and the autopilot will adjust the climb rate to maintain the speed.

If IAS mode were to be engaged in the cruise, this would disengage the altitude hold autopilot mode and the autopilot would pitch the aircraft up/down to maintain the speed it was engaged at, causing the aircraft to either climb or descend. This isn't the behaviour you would want to see in an aircraft in the cruise, as it would be deviating from the assigned altitude.

Engine management is the key to keeping on speed in the cruise in the 146.

Mark - Just Flight

Villajota

@Mark The procedure you describe works fine. Not only is the better solution but also makes this aircraft even more attractive and fun to fly. Thanks!