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German register query - Can I run my D reg propeller on condition?

My new prop, due to be installed next week

what is the reason for this prop change?

More blades typically means more drag

LSZK, Switzerland

Yes but it looks incredibly cool with the Lindberg sunglasses

Administrator
Shoreham EGKA, United Kingdom

No, the plane will (probably) be about 1-2 kts faster, but this is really not the reason.

- Better Cooling, lower CHTs in climb
- More thrust
- Turbine like operation almost without vibration (if it’s true what others say …)
- Strong braking effect and high descent rate when pulling power back (probably better short field performance … if I can handle it, that is)
- Blades, like all MT blades, can be repaired, Nickel leading edge can be changed if damaged

+ Better ground clearance due to shorter blades, good for grass strips (about 1 inch) (G2 Cirrus has lower landing gear than G3 model)

I am not even sure if it looks better, I actually like 3 blade props … we’ll see :-)

Last Edited by at 27 Feb 08:02

Is your current propeller an alumin(i)um one?

Before I overhauled my two blade aluminum one I researched this for my aircraft.

  • The current propeller seems to have an efficiency in the high 90ies % in cruise, so there’s unlikely any improvement possible
  • In climb, it’s in the 70ies, so there’s an improvement possible
  • Modern aluminum shapes (scimitar blades) might have a minor effect on noise, but not efficiency.
  • The MT has a lower diameter, which is nice for ground clearance and also for noise due to lower tip speed, but also means a much larger part of the prop disc is shadowed by the cabin
  • Fitting an MT 3 blade prop would reduce cruise speed by about 7% (according to the AFM supplement), and it is indeed significantly slower (according to pilots of other converted aircraft)
  • An aluminum prop mostly dissipates vibration energy by radiation. A composite prop also absorbs significant vibration energy (that’s in part why it is lower noise), but that also likely means that the structure is stressed much more, and likely damage in the long run. And AFAIK “overhaul” of a composite prop essentially means you get new prop blades with the old serial number plate.

So I remained with the 2 blade aluminum one. Even MT themselves strongly advised against fitting the 3 blade MT.

Last Edited by tomjnx at 28 Feb 07:51
LSZK, Switzerland

What I have heard is that the wooden MT props are – due to their stainless steel edges – better in withstanding damage from small stones (say 1cm across) which do a lot of gradual damage to aluminium props, but they shatter easily if touching a small piece of soil.

But then “touching a small piece of soil” is an official prop strike, with all that leads to… the difference with a metal prop is that you may never know about it.

There is a belief that shattering a wooden prop does not need an engine shock load inspection but this is not reflected in the engine manufacturers’ view.

A 7% loss of cruise speed is completely unacceptable IMHO. That is something like a 15% loss of engine power. The Hartzell 3B prop does not lose any cruise speed, so why does the MT one do that?

Administrator
Shoreham EGKA, United Kingdom

No, it does not scatter “touching a small piece of soil”, there is no evidence for that. On the other hand an MT blade can easily be repaired (they do that all the time) while an aluminum blade has to be changed.

The best part about the four blade MT is that it is smooth like a turbine.

Many SR22s were converted to the 4blade MT now, in the USA many are sold all the time. All owners report: at least the same speeds, better cooling and less vibration, shorter take-off run, better climb – and a great braking effect when you pull the power.

On this new version of the MTV-14 the leading edges are not stainless stell but Nickel, which is much harder.

Last Edited by at 28 Feb 21:06

The best part about the four blade MT is that it is smooth like a turbine

I find it hard to understand how a propeller could be smooth as a turbine when most of the vibration apparently comes from sources not related to the propeller but rather related to the frequency of the exhaust events.

On the other hand an MT blade can easily be repaired (they do that all the time) while an aluminum blade has to be changed.

Would that not depend on the damage? It is very difficult to repair a highly stressed composite structure while maintaining its shape.

Administrator
Shoreham EGKA, United Kingdom

I would say a lot of the vibration comes from the prop. After Jim Barker, a Cirrus specialist from Minnesota, balanced my Hartzell prop at least 50 percent of the vibration was gone …
About the 4 blade prop: I cannot explain it, but that’s what many of the owners say. Next week I can tell you more.

With the woodden core they repair all blades. I saw some where half of the blade was missing, and they repair those too.

Last Edited by at 28 Feb 22:14

@ Tomjnx

I researched this for my aircraft.

What aircraft do you fly – there is nothing mentioned in your profile? Would be nice to know which a/c loses 7% cruising speed when switching to a 3blade MT prop.
Tb20 e.g. does not lose any performance with a MT prop – see MT literature and Socata Users Group MT prop discussion.
Interesting now that the big US prop manufacturers come up with new composite products.

EDxx, Germany

From my experience, the “smaller” aircraft types (those with 160 to 200 hp, i.e. generally those originally designed for a two-blade prop) loose quite a bit of speed if switched to three blades. The small Mooneys and Piper Arrows cime to mind. Here in Germany, many of these have got shortish 3-bladers here in Germany for noise reasons and they are often about 5 knots shorter, so let’s say 3%.

The worst examples were two plain vanilla C172s in a club I was belonged to. The first was converted to a fixed pitch four blade (!) prop and the other to an electric constant speed three blade prop. Both aircraft lost about ten knots (from say 110 knots down to 100) for the same fuel flow.

With the biggish singles (230hp and more) it seems that going to three blades does not usually cost much in terms of cruise speed, but vibration is usually significantly less.

Frankfurt (EDFZ, EDFE), Germany
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