The clear evidence from the TB20 camp is that a 3B prop doesn’t produce less vibration than a 2B prop, but nobody I know can think of why.
Certainly everybody I have known who installed a 3B prop had vibration issues, but those might have been due to Hartzell’s poor balancing.
The MT prop might work differently in that – by flexing – it absorbs more of the torque pulses thrown at it by the engine, which might have some beneficial effect.
But unless somebody does a proper measurement like I did (see the link I posted) I won’t believe it, because this stuff is incredibly subjective. I have “felt” a lot of vibration after say a prop OH but a measurement showed it was just an illusion. And I don’t know of anybody who has any objective data.
There are all kinds of theories on why matching the # of blades to the # of cylinders (or whatever) might affect vibration, but none of it makes sense to me.
I have re-read about 50 posts ons COPA about the MT 4-blade prop and found that …
… some owners report a gain of 1-2 knots TAS
… some others say they have not seen any difference
(no owner reports less speed)
But all of them write that the MTV-14 is extremely smooth and produces very much less noise.
Also the braking effect seems to be impressive, one guy reported descent rates of 4000 fpm without going over Vne.
Anything which gets you less vibration has to be worth having – all of our pistons planes vibrate like hell…
And anybody doubting how much comes from the slipstream only has to touch the front window. A 4B prop ought to generate less air disturbance than a 3B prop.
But what is “very much less noise”? Is there any data on this? One would think that with noise certificates being a big thing in Germany, some measurements would exist. Otherwise we could so easily be looking at a case of this (a better sound via gold plated mains power plugs, €700 interconnects, etc).
Of course, just look up the data sheet of the MTV-14, all on their website. Unfortunately the SR22 is still too loud to ge a german noise certificate, … results in € 30 landing fees at some airports.
EDIT: Sorry, no the noise data is not in the data sheet. I will make some measurements next week
Vibration two vs. three blades certainly makes a difference on a 300HP.
Two bladed props overtime start to vibrate pretty badly after some stone chips have been repaired.
On three bladed props the unbalance is evened out I guess. Lower tip speeds too on the three-blade due to smaller diameter for the same RPM, reducing noise.
Well, on the MTV-14 the blades are really only a little shorter … for me that’s a critical point because I find some of the 4-blad props so ugly! Especially the fixed pitch MT ones that Bosco mentioned really destroy every airplane design. A Cessna with that prop looks like a Playmobil toy… to me.
By the way: If anybody is interested, I could organize a tour through the MT production facility near EDMS. How about making that a trip? The EDMS airport even has some (simple but cheap) rooms above its restaurant (which is okay too) and we could also tour Avionik Straubing.
Peter, if you want me to organize that, let me know. This concept could be extended into visiting Munich (“Deutsches Museum” has a terrific aerospace collection).
Here’s the famous four-blader, made by Hoffmann:
And here’s the constant speed three-blader from mt:
Here’s the mt one for the SR22:
if you want me to organize that, let me know
Yes that would be fun How about later in March, after the Swiss meet-up on the 7th?
I will need a 24hr early warning of another Messerschmitt museum though
The German Museum (Deutsches Museum) collection at Oberschleissheim (one of the olderst civil airports in the world) is FAR from beeing a “Messerschmitt” museum ;-) You’d enjoy it, I’m sure.
Let me check my March dates, and I’ll get back to you later!
Just to add my 2 cents on the topic:
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. The picture of the 3-blade MT prop posted by Bosco above is the older design with the rounded tips. Likewise, there is also an older design of the MTV-14 4-blade scimitar prop shown on the Cirrus-pic with rounded tips, also labelled an MTV-14.
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:
- 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.