Free Wheel Turbine ?

[Jemiba]

The AE article about the Morane Saulnier Statodyne concepts mentioned, that for
those types, not equipped with twin engines (which eleminated torque due to their
installation face-to-face), the use of a "volant-turbine libre", translated as free-wheel
turbine was envisaged.
Anybodywho can explain to me, what was meant ? ???
I would assume, that the turbine would be fitted with a kind of additional stage, counter
rotating to the compressor/fan. But where could it be positioned ?

Generally, the term "free-wheel turbine" seems to have a different meaning .

 

[red admiral]

Maybe something like the Grim Vane Wheel as used on some ships? Its freely rotating and increases the efficiency of the installation though I'd think the increase in weight would preclude this for an aircraft installation.

 

[AeroFranz]

The only meaning of 'free turbine' that I know of is a turbine stage positioned aft of the gas generator and connected exclusively through the gas path, so that it is free to spin at a different speed compared to the gas generator spool.
Does this fit the case? ???

 

[Jemiba]

"...to spin at a different speed compared to the gas generator spool"

Yes, something like that was my thought, too, it just would have to spin in
the opposite direction to the other turbine stages. I'm just not sure, what
the penalty on weight and maybe engine efficiency would be and if it would
be worth the effort at all.
Perhaps I should add, that the mentioned article didn't speak of torque, but
of gyroscopic effects. I actually never thought of it with regards to jet
driven aircraft. ???

 

[red admiral]

Was it decided what sort of engine to use?

From reading it again it seems something more like the Pegasus might have been planned where the LP and HP spools contra rotate. With the contra-rotating turbine it is possible to remove the turbine stators and save some weight. Gyroscopic effects are quite large with jet engines (1000lb of metal going round at 8000rpm) and its more of a problem for VTOL aircraft for control at low speeds. I think the contra-rotating two spool engine is most likely.

 

[Jemiba]

"I think the contra-rotating two spool engine is most likely."

That sounds like the keyword, I was looking for, thank you!
The Morane Saulnier Statodyne designs (or better : concepts ..) probably
would have used the Turbomeca Marbore, in the case of the smaller ones and
Bristol Orpheus or SNECMA ATAR103 / 08 for the larger designs.

 

[AeroFranz]

From reading it again it seems something more like the Pegasus might have been planned where the LP and HP spools contra rotate. With the contra-rotating turbine it is possible to remove the turbine stators and save some weight.

Red admiral is right, in the case of the Pegasus, the LP spool spins in one direction and the HP in the other. The LP is heavier but spins at lower RPMs, while the HP spins at high RPMs but is lighter. Overall the gyroscopic effects are diminished.

 

[red admiral]

The Morane Saulnier Statodyne designs (or better : concepts ..) probably
would have used the Turbomeca Marbore, in the case of the smaller ones and
Bristol Orpheus or SNECMA ATAR103 / 08 for the larger designs.

Hmmm, I think it would be difficult to try and adapt an existing engine to the configuration as they're all single-spool types. There would have to be massive alterations to get a two spool engine from them.

 

[Jemiba]

"There would have to be massive alterations to get a two spool engine from them"

That would mean, back to the first idea, to something similar as the Grim Vane Wheel,
a gas driven gyroscope, counterrotating to the turbine.
As it would only be used for the single engined designs, which were intended for testing
and training only, maybe a loss of performance for the sake of better stability and easier
handling, would have been acceptable .

 

[AeroFranz]

I almost forgot...I only ever hear the term "free turbine" associated with turboshafts or turboprops, never with turbofans or turbojets. So maybe this is not the right explanation after all.

 

[Jemiba]

I think, the translation "free-wheel turbine" just didn't met the original
term and moreover it was, or is used for other principles.
I agree, that adapting an existing engine to a two spool design probably
means more or less designing a new engine, something that was precluded
by the specification for the VTOL interceptor, which should have been the
result. So a relatively simple solution had to be found and the additional
stage, "freely" rotating in the gas path could have done the trick.
The number of tailsitter VTOL jet aircrat, that actually flew, is quite
small, just the Ryan X-13 Vertijet and the SNECMA C.450 Coléopère came to
my mind, but I haven't read of problems, that could have been traced back
to gyroscopic effects. Maybe other manufacturers simply saw no need for
that solution, as there wasn't a problem !