Start up animation of propellers

[nieto 0]

Hello,

What modification I could do in the aircraft cfg for having a true animation of propellers speed at start up ?... That means: when I clutch the start button , the propeller begins to spin slowly and the speed increases when I inject the fuel .

Many thanks in advance

Jean-Pierre

[Finn 873]

The props don´t start to spin when the starter turns.

The turbopropengines used on the Twin Otter are P&W PT6 free turbine engines.

In essense You have a core engine that works very much like a normal jet engine. This core engine is the one You are starting when turning on the starter and injects fuel.

The exhaust from this core engine is used to drive another turbinewheel - the free turbine, which via the gearbox drives the propeller.

A certain amount of thrust must be produced by the core engine before the propeller starts to move. Thats why You can the spin up and a whine from the engine allthough the propeller is standing still.

With FSX there is an issue though, and that is that the engine and afterwards the propeller spins up too fast, but this is hard to fix when You still want to have spinnning propellers in multiplayer.

Another issue is also related to the way spinning props are done in FSX. You got a real 3D animation of the propeller spinning, but this onlu looks right until a certain (low) RPM, thereafter it won´t look right anymore, mostly due to the limited FPS, even if You got more than 50 Fps, this won´t be enough. Therefore in FSX the true 3D animation is cut and the 3D propeller blades made invisible at a certain RPM and replaced with a pure texture sheet that refelects that of a spinning prop. Often this is even done twice, so You got 3 "layers" of animation/texturing 3D:Low, Texture1: medium, Texture2:high rpm.

Finn

[nieto 0]

Hello Finn,

Many thanks for your answer and explanation, I appreciate. Pitty, but I will survive !....

I am curious to know how Majestic Software, with the Dash8 Q400, has realized a real rendition of propeller spinning at start up...

Anyway, your Dash 6-300 remains an excellent model for me.

Best regards

Jean-Pierre

[Finn 873]

I´m not sure why You find it a pitty when generally the animation for the propeller is correct, apart from the too quick spin-up.

Majestic toatally bypasses FSX own flightmodel and engine simulation and do those in the background themselves.

While this certainly is a way to fix alot of the FSX limitations, it´s also alot more complex and requires far more developement time, something that only can be done economically sound by setting the price higher (35,- euro for 11 versions vs 50,- euro for 1 version) and/or having a second product lineup i.e having professional customers to help pay the developement.

Finn

[taguilo 12]

The props don´t start to spin when the starter turns.

The turbopropengines used on the Twin Otter are P&W PT6 free turbine engines.

In essense You have a core engine that works very much like a normal jet engine. This core engine is the one You are starting when turning on the starter and injects fuel.

The exhaust from this core engine is used to drive another turbinewheel - the free turbine, which via the gearbox drives the propeller.

A certain amount of thrust must be produced by the core engine before the propeller starts to move. Thats why You can the spin up and a whine from the engine allthough the propeller is standing still.

Actually in a PT6 engine the propeller does start to spin at a very low rate (10-20 rpm) when starter is engaged, as the air coming from the core engine has enough pressure to slowly rotate the free turbine.

With FSX there is an issue though, and that is that the engine and afterwards the propeller spins up too fast, but this is hard to fix when You still want to have spinnning propellers in multiplayer.

That is correct, but custom code (like using IS USER SIM variable) could be set to manage the rotation_slow animation. Anyway, I guess a still prop at startup is not a big issue to most users.

Tom

[Erikk 7]

I must to give equal to taguilo, last week I have been at TNCM, and I flew to times with Winair in the Twin Otter, and indeed the props are going to spin when the starter is on. Just before the fuel lever is set.

[MarkHurst 173]

Can I suggest that you need to make something of an effort to actually see the props from the cockpit?! I guess if you want to make a video from outside it might be significant.

[Erikk 7]

No It only will be nice if the developers could model it..

[Finn 873]

The Twin Otter project is regarded as finished and no further changes are planned.

While the propeller animation during startup doesn´t reflect 100% the reality, it makes little sense to change that.

1. My statement about how the turbine works, described in post 2 in this thread is still correct. Whether the props starts at the exact same time as the starter engages (Not very likely taking the inner workings into account) or it start very short after is probably a matter of conditions (warm engine and gearbox vs cold engine and gearbox, fitted with startlocks or not etc..)

2. Making custom animated propellers are not as easy as You might think. We have done that before on both the Dimona X and Robin X and the effort set in contrast to the end result is most often not worth it.

Custom propeller animation f.ex will not show up in multiplayer sessions for other players - the prop will simply be at a standstill. And in the case of the Twin Otter we are talking about maybe 10 sec of not full realistic look.

While I do understand what You longing for, I must still point out that FSX has it's limitations.

Even the PMDG J41 has totally wrong startup animation of the prop. (It simulates a geared turboprop where the prop is driven directly via the gearbox by the core engine, but the PMFG J41 still animates the prop standing still serveral seconds after the starter has started whining). So I gues PMDG came to the same conclusin that we did - it´s not worth the effort to do these complex animations, which would cause issues elsewhere, just for 10 sec anomality.

Finn