TBM850 loosing power climbing around FL200

Everything is fine ,then all of a sudden I can see my speed start to drop.

I did notice the pitch trim being way out there.

I have to take off the autopilot, level out and re-start the autopilot once the plane is back in control

Thing is I am not sure if the autopilot is not working properly or If I am doing something wrong.

Anyone know what is happening?

 

 

 

 

Are you increasing your power as you climb? TurboProps torque decrease as you climb and you need to adjust it regularly to keep the climb performance you require.

R. 

100 percent even tried adding the turbo

 

 

It kind of sounds like you're expecting to maintain the same climb rate regardless of altitude, and you're setting an autopilot climb via the VS button.

When you do that, the autopilot will try to maintain whatever climb rate you were at when you pressed the button, but as you get higher power decreases, the prop has less air to push against, etc, meaning your climb rate needs to decrease or your airspeed does.

As your airspeed decreases you start climbing more slowly, which the autopilot tries to fix with the only tool in its box: Pitch up more. This, of course, just exacerbates the problem, but it's also an explanation for why your pitch trim is "way out there."

Once you get above FL200 in most turboprops, you can expect a pretty sluggish stable climb rate. The VS button is really more useful for descending. For climbing, you want the IAS button because that will tell the plane to climb at a specific speed, so it will automatically reduce the climb rate as power drops off with altitude.

 

As @eslader has touched on, what mode are you using to climb with?  If it's VS, that is operationally incorrect, will not provide speed protection and will certainly lead to speed bleeding off (unless VS is reduced during the climb).

It's possible you're also climbing in vertical basic mode, which with this AP is pitch hold.   This will also result in reduced speed as you climb - unless the pitch is reduced as you climb.

I fly this plane a lot - in the flight levels - and see no power loss over and above that which you correctly see in turbo props, in terms of reduced torque due to less dense air as you climb.

Edited March 20, 20242 yr by JYW

That makes sense.

Its what do with the Cessna 414.

I could not figure out how to adjust the pitch with the IAS for the TBM.

Will go at it again tonight.

Thanks

Most of the time I climb and descend in IAS mode for the speed protection and best climb rate. After takeoff I aim for 125kts (with best rate of climb speed being 123). Once I reach 125 kts I hit IAS and engage the autopilot. This seems to work really well for me. I rarely climb above 20,000ft (service ceiling is 31,000 - don't think I've ever been that high in the 850). 

Edited March 20, 20242 yr by Cpt_Piett

Just a note about climb and VS. Yes, IAS is the way to go and it affords speed protection, .....but. I haven't flown real world turbo props, but while flying real world jets, you will find that some of the IAS hold type of modes get squirrely/pitchy once you get into MACH change over. Now, turbo props normally don't get into these altitudes(FL280 to FL290). ...but, even below MACH change over, things can get squirrely/pitchy from gusts, temperature inversions and turbulence(you won't see this in flight sim). The thing is, you can climb in VS or IAS modes. I actually use VS above MACH change over to prevent porpoising and large speed variances because of it. The key is paying attention to the climb. If your climb speed schedule is 330KTS/MACH .825 and it's falling behind, reduce the VS to maintain the schedule. Even in jets, my last few thousands up to Optimum + 2000 is 800 to 1000FPM. You definitely have to watch your weights and speed schedule. If you are below 800FPM, you are either flying too fast in the climb or you are too heavy and above your optimum altitudes. Don't be afraid of VS, just pay attention as you should.      

Edited March 20, 20242 yr by G550flyer
Edit

In IAS mode set to 130kts and at 21,000ft I'm getting roughly 1100fpm. I intend to test whether I can reach service ceiling of 30,000, and what the climb rate will be. TRQ 90% PROP 1900rpm. 

25,000ft: just above 1000fpm. 

26,000ft: same

27,200: starting to fall below 1000fpm. 

28,000: around 900fpm

28,000-30,000: around 500fpm

...and just above the clouds (Northern Norway). Temp: -54C. GS 233kt. Winds: don't think I can see that in the 850. 

 

Edited March 20, 20242 yr by Cpt_Piett

Best to climb on FLC mode then.. so you set 125kts FLC and adjust torque as you climb.. at least this is how real M500 / M600 pilots operate on their turbos..

R.

1 hour ago, Cpt_Piett said:

In IAS mode set to 130kts and at 21,000ft I'm getting roughly 1100fpm. I intend to test whether I can reach service ceiling of 30,000, and what the climb rate will be. TRQ 90% PROP 1900rpm. 

25,000ft: just above 1000fpm. 

26,000ft: same

27,200: starting to fall below 1000fpm. 

28,000: around 900fpm

28,000-30,000: around 500fpm

...and just above the clouds (Northern Norway). Temp: -54C. GS 233kt. Winds: don't think I can see that in the 850. 

 

Pretty sure I was aiming for 1200 to 1400fpm. Could be where my problem started. its just weird how quickly things turned bad.

Are you using the 850 mode on the climb.

 

Data picked up from a real TBM shows a pretty interesting change in fpm as it climbs

0-5000  - 2400fpm

5000-15000 - 1500fpm

FL150 to FL 280 - 1000fpm

speeds up to 180 knots passed 5000ft.

 

Edited March 20, 20242 yr by Ron Lefebvre

1 hour ago, Ron Lefebvre said:

Are you using the 850 mode on the climb.

TBH I’ve completely forgotten about the 850 mode… used it a bit initially. Can’t remember the “criteria” for using it.

If I’m not mistaken, that’s pretty close to what I’ve been getting. At 30,000 I got up to GS 243kts. But I guess TAS is better to use when comparing.

Btw I nearly stalled the plane using VS mode on descent (while reading avsim lol)

Edited March 20, 20242 yr by Cpt_Piett

You should be climbing on IAS or FLC. Descending on VS.

7 hours ago, G550flyer said:

Just a note about climb and VS. Yes, IAS is the way to go and it affords speed protection, .....but. I haven't flown real world turbo props, but while flying real world jets, you will find that some of the IAS hold type of modes get squirrely/pitchy once you get into MACH change over. Now, turbo props normally don't get into these altitudes(FL280 to FL290). ...but, even below MACH change over, things can get squirrely/pitchy from gusts, temperature inversions and turbulence(you won't see this in flight sim). The thing is, you can climb in VS or IAS modes. I actually use VS above MACH change over to prevent porpoising and large speed variances because of it. The key is paying attention to the climb. If your climb speed schedule is 330KTS/MACH .825 and it's falling behind, reduce the VS to maintain the schedule. Even in jets, my last few thousands up to Optimum + 2000 is 800 to 1000FPM. You definitely have to watch your weights and speed schedule. If you are below 800FPM, you are either flying too fast in the climb or you are too heavy and above your optimum altitudes. Don't be afraid of VS, just pay attention as you should.      

Not sure which plane(s) you're referencing, but in the SETP's we fly are around 150 IAS initially and then 170 IAS in the climb. Routinely @ or above FL280 long range cruise. Shorter trips sure FL200-FL240. Never see squirrels or porpoises even with the awful AP we have... 🙂

Edited March 20, 20242 yr by Flyfaster_MTN002

4 hours ago, Cpt_Piett said:

TBH I’ve completely forgotten about the 850 mode… used it a bit initially. Can’t remember the “criteria” for using it.

 

After takeoff then basically on all the time.  I'm not sure about landing... you'd probably go back to 700 hp in case of a missed approach so you don't over torque.