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Mooney PM20K (Porsche) (also composite propellers)

Very interesting about the MT prop, I did not know that!

achimha wrote:

The PFM was also instrumental to the rise of MT. The original McCauley aluminium props would destroy the Porsche gearbox and they had to replace all delivered props with the lighter and better shock absorbing MT props at Porsche’s expense. The props were quite exotic back then. Later the diesel engines would also require MT props for the same reason.

Maybe the dual mass flywheel currently included in the Continental and Austro diesels allows heavier metal props?

EFHF

AirV wrote:

Maybe the dual mass flywheel currently included in the Continental and Austro diesels allows heavier metal props?

But why? Nowadays the market seems to have understood that wooden composite props are superior. For conversions they still partially offset the extra weight of the diesel engine. They are also quieter and generate less vibration with unlimited repair/overhaul. Even turboprops are going in that direction with a lot of conversions to wooden composite. There are also carbon fiber composites but they are much more expensive. The A400M is equipped with those.

Metal props are more durable and need less maintenance? You can have 3 bladed metal prop for reduced vibration and noise? Maintenance is expensive and so are the propellers.

Last Edited by AirV at 29 Aug 14:00
EFHF

A wood prop provides a high level of damping at the cost of low strength, which compromises the aerodynamic efficiency of the blades. Also a wood constant speed prop requires using lag screws glued into the end grain of the blades to retain them, 1930s technology which works… but for me as the owner and operator of a wood MT prop, and as an engineer working in roughly the same field is a bit scary. I am very careful with my prop, particularly avoiding over-revving it with my (slow response) electric governor.

Aluminum props also have disadvantages, most things do, but wood props in my opinion are an unfortunate compromise. Wood’s high level of structural damping isn’t very relevant for any engine I’d own. I think the best prop in 2017 is Whirlwind with hollow carbon fiber blades and electroformed nickel leading edges – both of which promote aerodynamic efficiency. Unfortunately for me and my aircraft, since I’d replace my MT with one were it otherwise, the founder (a friend) is not interested in the certified market – the money and freedom of developing & selling uncertified props in volume appeals to him more, and as I understand it he’s not sufficiently interested in licensing the technology to certified prop manufacturers for a small increase in revenue. He sells plenty of props regardless, at roughly the same price as the wood bladed MT.

The first props Whirlwind made 20 years ago were roughly the same technology as the MT, ultra-thin weather shield, lag screws and wood blades included. Since then the design has changed completely through ongoing development.

Last Edited by Silvaire at 29 Aug 14:40

Silvaire wrote:

I think the best prop in 2017 is Whirlwind with hollow carbon fiber blades and electroformed nickel leading edges – both of which promote aerodynamic efficiency. Unfortunately for me and my aircraft, since I’d replace my MT with one were it otherwise, the founder (a friend) is not interested in the certified market

I have a Whirlwind GA-200L and you can tell Jim and Patti that I am very pleased with it. The only problem is that I have been waiting four months to get official approval for it in France.
Simon

I find it funny how people say “the PFM was slower due to cooling drag” when in fact nobody has an idea of Lyco / Conti cooling that is actually quantifiable beyond “it works”.

simon32 wrote:

you can tell Jim and Patti that I am very pleased with it.

I’ll do so

I don’t think you can call the MT products “wooden” props. The core is wood but there’s many layers of glass and carbon fiber around, so that the end product it not a “wooden” propeller. Also I do not recall that there have ever been problems with the strngth or maintenance. MT props are used on TBMs and King Airs and even on much larger transport aircraft without problems. Also the price is much lower than the full carbon props. The 4-blade MTV-14D for the SR22 is around € 19K, with TKS, spinner and bulkhead incl. installation, the Hartzell 3-blade carbon prop is over $ 30 K.

My MT prop has a very thin layer of composite on top of the wood that serves no structural purpose, just one layer. You can see the grain of the wood through the composite. It’s there to prevent water getting to the wood. The reason for it being so thin is that if it were thicker the bond to the wood would fail in shear under centfugal loading and it would come off.

One issue with the weather shield composite is sealing that thin layer to the hub at the root of the blades. It seems to separate there and require repair. With an all composite blade that is a non-issue.

All composite propellers are more expensive for certified applications but about the same uncertified, as mentioned above.

Last Edited by Silvaire at 29 Aug 16:07
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