Engine thrust at Idle

[vonmar 8]

Just started using the Twin Otter in MSFS.

Nice to have it in MSFS now.

 

Spawn the Otter Floatplane on a lake (PALH , Lake Hood) and cannot idle (zero kts).

Always moving 7kts or more.

 

Note:

Same Otter in P3Dv4 idle thrust is ok , zero kts.

I use FSUIPC for axes and assignments.

 

[UnsealedKarma 52]

This behaviour seems true to life.

You can feather the props but it will create a bit of forward thrust. If you want to lay still move into the reverse (beta). Many Twotter floatplanes has a prop lock to keep the prop in beta during startup to avoid forward movement.

[vonmar 8]

4 hours ago, UnsealedKarma said:

This behaviour seems true to life.

You can feather the props but it will create a bit of forward thrust. If you want to lay still move into the reverse (beta). Many Twotter floatplanes has a prop lock to keep the prop in beta during startup to avoid forward movement.

Have you tested the problem I reported?

[EDNR-Cruiser 319]

3 hours ago, vonmar said:

Have you tested the problem I reported?

They can't! You would need to send them your computer or at least all information related to the problem - which is a lot!  
What you reported is most likely a bad configuration (that is a user problem) not a software issue.

If you want to go to zero thrust you need to go to BETA mode as UnsealedKarma has pointed out correctly. That's how turbo-props usually work and even though I'm not familiar with the Twotter I assume that it works the same.

Idle thrust in a turbo-prop still means 40 to 60 HPs, that will easily accelerate your plane to 30-40 kts. You can't go any lower without burning your precious turbines into lumps of metal.
If you want to go slow or stop, that's what BETA is for (has nothing to do with feathering): you change the angle of attack of the prop blades to a degree where they produce almost or no thrust anymore while the turbine is still rotating at a speed which allows the air inflow to provide sufficient cooling. If you go below BETA, the props will even provide negative thrust, generating enough power to slow down your plane after landing as good or better than your brakes. That's called reverse.

[vonmar 8]

I can only test the Otter with P3Dv4 / P3Dv5 and MSFS:

 

Spawn the Otter Floatplane on a lake (PALH , Lake Hood) and do nothing else.

 

Are your results the same with P3Dv4 / P3Dv5 and MSFS?

[Schemgg 6]

6 hours ago, vonmar said:

I can only test the Otter with P3Dv4 / P3Dv5 and MSFS:

 

Spawn the Otter Floatplane on a lake (PALH , Lake Hood) and do nothing else.

 

Are your results the same with P3Dv4 / P3Dv5 and MSFS?

 

I guess the 64 thousand dollar question here is ...

 

Which is correct?

 

One of them must be wrong, but why do you assume it's MSFS?

[taw1962 21]

Try these edits to make the Twin Otter stop at idle on land and water:

 

Open the ENGINES.CFG with Notepad and search for the line:

 

low_idle_n1 = 51 ;52.00 ; Idle N1 with minimal condition

 

Change it to:

 

low_idle_n1 = 21 ; 51 ;52.00 ; Idle N1 with minimal condition

 

Search for the line:

 

low_idle_n2 = 50 ;=1100 RPM 58.5

 

Change it to:

 

low_idle_n2 = 20 ; 50 ;=1100 RPM 58.5

 

You should also move the prop levers to full feather position; I mouse click and drag the levers in the VC but a key or button assignment is also possible.

 

For the floatplanes and amphibians only, if you also want invisible rudder steering:

 

Open the FLIGHT_MODEL.CFG with Notepad and search for these lines:

 

(Floater models)

point.3 = 4, -15.20,  -6.70, -6.20, 2800, 0,   0,  0, 0.6, 1.0, 0.50, 0, 0, 2, 0, 0, 1 ; Float rear left
point.4 = 4, -15.20,   6.70, -6.20, 2800, 0,   0,  0, 0.6, 1.0, 0.50, 0, 0, 3, 0, 0, 1 ; Float rear right

 

(Amphibian models)

point.6 = 4, -15.20,  -6.70, -6.20, 2800, 0,   0,  0, 0.6, 1.0, 0.50, 0, 0, 2, 0, 0, 1 ; Float rear left
point.7 = 4, -15.20,   6.70, -6.20, 2800, 0,   0,  0, 0.6, 1.0, 0.50, 0, 0, 3, 0, 0, 1 ; Float rear right

 

Change them to:

 

(Floater models)

point.3 = 4, -15.20,  -6.70, -6.20, 2800, 0,   60,  0, 0.6, 1.0, 0.50, 0, 0, 2, 0, 0, 1 ; Float rear left
point.4 = 4, -15.20,   6.70, -6.20, 2800, 0,   60,  0, 0.6, 1.0, 0.50, 0, 0, 3, 0, 0, 1 ; Float rear right

 

(Amphibian models)

point.6 = 4, -15.20,  -6.70, -6.20, 2800, 0,   60,  0, 0.6, 1.0, 0.50, 0, 0, 2, 0, 0, 1 ; Float rear left
point.7 = 4, -15.20,   6.70, -6.20, 2800, 0,   60,  0, 0.6, 1.0, 0.50, 0, 0, 3, 0, 0, 1 ; Float rear right

[vonmar 8]

Hello taw1962 ,


I modified the -100 float pax
Flight Idle / FSUIPC feathering 
0 to 1 Knot bounced back an forth

Then I tested the unmodified -300 floats pax
initially idled at 2 knots then 1 knot then 0 to 1 knot


What did your tests show?



Notes:

I really do not like editing these files but ok for testing.
An edited file would need re-editing / verifying with each product Update and the edit would need to be applied to each Otter (floats in this test) model.


The Otter in P3Dv4 loads with engines running and on Start Locks.
Maybe that would be possible with the MSFS Otter.

[taw1962 21]

27 minutes ago, vonmar said:

 

I modified the -100 float pax
Flight Idle / FSUIPC feathering 
0 to 1 Knot bounced back an forth

Then I tested the unmodified -300 floats pax
initially idled at 2 knots then 1 knot then 0 to 1 knot


What did your tests show?

 

My tests were done in real weather with 4 knots wind, which gave 2-3 knots airspeed even though the plane was visibly stationary.

[vonmar 8]

Hello taw1962 ,

Just to verify.

With no engine.cfg edits.

If you just spawn the Otter Floatplane on a lake (PALH , Lake Hood).
Thrust flight idle.
Props full forward.

Are you moving 7kts or more no matter which heading?

 

Edit:

For my tests :

No live weather

No wind layer

[taw1962 21]

38 minutes ago, vonmar said:

If you just spawn the Otter Floatplane on a lake (PALH , Lake Hood).
Thrust flight idle.
Props full forward.

Are you moving 7kts or more no matter which heading?

 

Yes of course, because the prop levers are full forward. When I pull them back to full feathered, the plane slows down to 1 knot. Prop pitch has never been modelled as accurately as this in other sims, that's why the P3D version doesn't behave this way.

With the engine.cfg edits I suggested above, the plane will stop at idle thrust with the props feathered.

[vonmar 8]

Hi taw1962,

"prop levers are full forward. When I pull them back to full feathered, the plane slows down to 1 knot."

"Prop pitch has never been modelled as accurately as this in other sims, that's why the P3D version doesn't behave this way. ?

 

That is what I was looking for in the Otter msfs manual and checklists.

 

Where did you find that Twin Otter (MSFS) information documented?

[taw1962 21]

1 hour ago, vonmar said:

That is what I was looking for in the Otter msfs manual and checklists.

 

Where did you find that Twin Otter (MSFS) information documented?

 

It's an MSFS feature which was included in SU8: https://www.flightsimulator.com/release-notes-1-23-12-0-sim-update-viii-now-available/

 

"New optional propeller simulation system with hundreds of moving surfaces covering the propeller realistically simulated has been implemented on 3 planes Cessna 152, Cessna 208 B Grand Caravan EX and Beechcraft King Air 350i now use the new propeller simulation system. This improves propeller effects such as p-factor as well as feathering, prop drag, etc…"

 

Twin Otter update 1.0.5.0 included 7 new prop improvements enabled by SU8: https://forum.aerosoft.com/index.php?/topic/171404-aerosoft-aircraft-twin-otter-update-to-1050/

 

Version 1.0.5.0

Changelog

- Reworked propeller animations (all models)

- Updated exterior for all models

- Prop Section clean up

- Fine tuning prop to meet climb and cruise data

- Spoiler with 60 degrees angle to simulate additional drag when blade angle is below 12 degrees (happens in idle flight situations)

- Different ski settings to allow sliding with less power

- Added control code for spoiler

- Centralized propeller animation code

- Animated "slow" propeller blades

- Fixed: Wrong TQ indicator background textures for some models

- Fixed: CL Ignition Switch normal highlighting pitot heat switch instead

- Added: Missing pop-out clickspots for GPSes and other displays

- Fixed: "Position Light ON" on before startup checklist switching anti-coll light instead

- Fixed: Switched BOTH ON AFT / BOTH ON FWD labels

- Added: Full-range propeller blade animation

- Fixed Generator 2 annunciator not lit when engine 2 is off

[vonmar 8]

Hi taw1962,

 

Thanks for the additional information / links.

 

I read it but I did not see where it mentions i.e., correcting for zero Kts by feathering?

 

Before this update 1.23.12 (2-28-22) / Aerosoft Twin Otter update 1.0.5.0 included 7 new prop improvements

was the feathering problem existing as in the Twin Otter Advanced for P3Dv4 or FSX?

 

Note:

Aerosoft Twin Otter version 1.0.5.0 is what I purchased on 3-24-22 so it is very new for me.

 

[taw1962 21]

14 hours ago, vonmar said:

I read it but I did not see where it mentions i.e., correcting for zero Kts by feathering?

 

No need to mention what feathering does, most simmers already know: When a prop is feathered it is "windmilling" and producing no thrust: https://skybrary.aero/articles/feathering

The prop feathering effect is new and so far unique to MSFS. Older sims couldn't model it so the workaround was for constant speed props to produce no thrust at engine idle, which is incorrect.

[EDNR-Cruiser 319]

Not quite correct!    Now I actually believe it's time to explain what feathering does... 

Feathering is used when an engine is NOT running to reduce the drag of a windmilling (spinning) prop which means that the prop does NOT ROTATE any more, RPM is zero! If an engine fails, the props continue spinning thru the windmilling effect which causes a massive drag in multi-engine aircraft on the side of the defective engine, i.e. you have a lot of thrust on one side of the plane and a lot of drag on the other side. Now guess if that is a healthy situation or not...
Sure, feathering produces no thrust any longer but it is basically the same effect as shutting down your engine.
If you want to go slow and adjust your speed in fine steps you have to use the BETA range (it is called range for a reason! ) and I can easily adjust the taxi speed of all my turbo props in XP11 in very fine steps from crawling backwards to slow walking speed up to 30 kts speed taxiing.

[UnsealedKarma 52]

To elaborate on the post above, as feathered props does provide a bit of forward thrust, Twin Otter seaplanes are often fitted with prop locks or blade latches. These are installed to prevent the prop from going into feather position when the oil pressure falls on power off. As described in the POH it takes a special startup procedure (see p. 4-17 in the link below).

 

https://dokumen.tips/documents/pilot-operating-handbook-and-aircraft-flight-manual-dhc-6-series-300-twin-otter.html