TB20 2 blade to 3 blade prop change

Hi petakas,

I posted this in a different thread here before but as you asked specifically about the TB20, here are my experiences:

I exchanged the original 2-blade Hartzell metal prob on my TB20 against a 3-blade MT composite prop in October 2010 and have since flown about 250 hours with it. The prop I now have is an MTV-9 with the newer scimitar blades. MT does have a number of different prop-designs and not all prop/engine/-airframe-combinations work equally well, I understand. My personal experience is just with the TB20.

My old prop was due for overhaul in 2010 and I got an interesting offer from MT to trade in my old prop for a new MT-prop with a moderate cash payment on top. Before I decided to go that route I had the chance for test flights in two other TB20s, one with a 3-blade MT and one with a 3-blade Hartzell metal prop, in addition to my experience with the 2-blade.

My initial impressions were as follows, however, it needs to be said that conditions were not completely comparable as the ages and hours on airframes and engines of the planes were quite a bit apart, different headsets were used, weather was a rather gusting wind. Anyway, here goes

- the MT-prop has the German “erhoehter Schallschutz” (better noise certificate), excempting it from various operating restrictions on some fields in Germany, e.g. no take-offs between 12 and 2, no traffic circuits after 4 etc. and/or also triggering lower landing fees, in combination with a Gomolzig exhaust system. The 2-blade on my plane, also Gomolzig-equipped, or a 3-blade metal prop would not meet the noise threshhold any longer
- the MTV-9 MT-prop is rated for up to 450HP and continuous 2.700 rpm but needs to be downrated to 2400 rpm (standard high rpm on a TB20 for take-off is 2.575 rpm) in order to achieve the noise certificate. The plane I test flew had the higher noise certificate but miraculously ran at the standard 2.575 rpm. Neither the Gomolzig exhaust, nor the engine or the prop have a problem with this

- Runway acceleration/take-off roll: Felt quite a bit better with the MT over the metal props, but cannot really quantify this due to the conditions mentioned above
- Initial Climb: Also felt a bit better with the MT over the metal props but not as pronounced as take-off roll
- Cruise climb: No discernible difference between the 3 props
- Cruise: MT and Hartzell about 3 knots slower in IAS at same powersetting
- Noise/vibration: Quite a bit reduced with the MT and the sound has a “better feel” to it
- Looks: Definitely better with the 3-blade

My initial conclusion: I liked what I experienced with the MT and preferred it over the 3-blade Hartzell but it was not of the “Wow, I absolutely need to have the MT-prop”-kind.

The reasons why I finally went for the MT were:

- weight
- vibration and noise structure
- noise level certificate: The MT prop came with the higher noise certificate and my plane already had a Gomozig exhaust system
- maintenance: small nicks and dents to the prop from stones do not have to be filed out but can be repaired, if need be even by diy (allowed by the POH)
- Base Price of Hartzell prop was slightly more expensive than the MT at the time, further rebate after negotiations also better for MT
- MT offered a very attractive trade-in price for my 2-blade
- last but not least: MT’s offices and plant are just one airport over from the one where my plane is located. In case of any problems it is not emails or phone calls but a visit to their MD’s office which tends to resolve any potential issues far quicker

Per the handbook, the MT does produce pretty much the same take off-roll, climb and cruise figures as the original 2-blade prop albeit at a reduced max RPM of 2.400. The handbook says to add 3% to the book numbers of the original 2-blade on take-off roll, all other numbers remain unchanged. This difference is so small that I cannot really distinguish it in actual terms when handling the plane. However, I do not feel that performance is worse than the 2-blade in real life.

After the MT-prop was installed I tested my plane also with the original 2.575 max RPM which is technically ok, MT also have a POH for this, but would not give you the higher noise certificate. Here, the POH simply and rather unprecisely says “The performance will be at least equal to or better than the 2-blade. Use the performance numbers of the original 2-blade”. I saw a somewhat accelerated take-off run although I would not want to take a guess on any numbers. It is not a significant change, however. Initial climb is improved by maybe 150 ft/min but again this is a personal estimate based on my experience with the 2-blade and not backed-up by something even remotely resembling a proper flight test. All other numbers were unchanged.

Vibration and noise, however, are significantly reduced and personally I very much prefer the noise characteristics of the MT over the previous 2-blade.

Isn’t there also an MT 4-blade prop for the TB20?

The interesting thing about the max RPM is that there is no tolerance specified anywhere – see here

Yet the performance is hugely affected by this.

So it makes sense to go a little bit over the max figure (because as any engineer knows, there must be a tolerance on this) and verify it with an accurate electronic meter.

RXH – would you say that the 3B MT prop has a significantly different braking effect to the 2B Hartzell?

Hi Peter,
i think there is no TB20 STC for the MTV-14 four blade prop yet.

i think there is no TB20 STC for the MTV-14 four blade prop yet.

This is said elsewhere to be a 4B prop

And here you go

Only one was ever sold, to the above TB20 owner (D-EACX, at the time in Switzerland) whose plane was used to get the EASA-only STC, and reportedly MT don’t market it anymore.

Oh, i was wrong, sorry. I had asked one of the engineers about the TB20 last week and he said that there’s no STC yet … maybe he misunderstood my question … This one has the old style blades though

@ Petakas

are you sure that the governor has a 12y overhaul limit – so far I thought it was also 6y ?
I am in for a prop change with my TB20 to MT9 three bladed – MT need 2,5 months now to deliver. Think they were very busy with one guy’s 4 bladed prop

edited: I just found a reference by Hartzell which confirms the 12y

D. Governors
(1) Hartzell propeller governors are to be overhauled at the same time as engine
overhaul, but not to exceed 2400 hours of operation (there is no calendar limit
applicable to governors).

I changed prop on my TB20 about 18 months ago. In my case it was from a Hartzell 2 blade metal to a Hartzell 3 blade metal.

I definitely prefer the look of the 3 blade, so have no regrets. But I can’t really say I’ve seen a noticeable difference in performance. Perhaps a little better climb performance, particularly when climbing above 10,000 feet. And I like to think it’s a little smoother, but that’s only a subjective view.

So from my perspective, the change is worth it for the look of the prop, but any performance enhancements will be small.

RXH – would you say that the 3B MT prop has a significantly different braking effect to the 2B Hartzell?

Yes, it does. I made that experience for the first time during the test flight I described above with another TB20 which had the MT 3-blade installed before I made the call to install that prop on my own plane. Over the treshold I reduced the power to idle the way I was used to doing it with the 2-blade prop and the plane decelerated and dropped quite a bit more than I was expecting. The resulting landing was certainly not in the top three of my best landings.

As flyer59 has pointed out, the MT 4-blade prop STC’d for the TB20 has the older design round-tip blades. I asked MT about the 4-blade at the time I was thinking about getting a new prop. They did not actively recommend it and advised to go for the 3-blade prop with the newer design.

@ nobbi

Which spinner are you planning on getting?

To “sweeten the deal” MT included the HiGlo-spinner when they installed my prop. The HiGlo is their standard composite spinner (which can be painted in any colour) with a chrome cover and some colourless lacquer on top instead of paint. It does look very nice but the chrome cover (NOT the spinner) has developed some small cracks after about 4 years of use in certain areas and also some chips of chrome have come off at the edge of the spinner. The chrome covering of the spinner was not done by MT themselves but some other company they sourced this work to which obviously did not have this process under control as well as they should have.

I understand that MT has come off this particular product a bit and especially for higher powered planes being flown in weather do not actively recommend the HiGlo any longer (don’t quote me on this, this is hearsay I have from a third party). However, when I talked to MT about the cracking chrome cover they offered without any fuss to paint the spinner at the next prop overhaul in a colour of my choosing at their expense. I think this is more than fair.