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Automatic mechanical propeller (Aeromatic)

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homebuilderfan

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I will try to make a short summary about the thread (at least I will make less errors; I hope...;) )
I fly (have flown) always light aircrafts (european ultralight- similar to american LSA, just a bit lighter-); I have always been attracted by the variable pitch propellers; never used because of their cost, complexity, reliability -talking about non certified propellers- (a few hours behind a Ivoprop, past year).
Now I am understanding the huge importance of the pair engine/propeller (read carefully: "engine/propeller"; not only propeller).
Currently flying behind a Rotax 100hp; I have read about the Aeromatic brand:I find the idea of a fully automatic mechanical propeller exciting: exactly what I have dreamed about without knowing it has been existing since the WWII...
Now, is there among you, members, someone having a direct experience about it?
What about mounting the Aeromatic in front of a Rotax 100hp?
If you are wondering why I am thinking not to use an electronic device to control an electric VPP, well: worried about the reliability of the NON certified products.
Any (wise) advice/help will be greatly appreciated.
Thank you.
 

fredoyster

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My experience is limited to a ride in an old Bellanca with one of these, and a bunch of reading, so take this as a non-authoritative comment at best. An Aeromatic is not a fully automatic propeller that maintains rpm using a governor, but it comes close. As the airspeed increases, the blade pivots to change the effective pitch. It's a significant help, because the low-airpseed pitch can be optimized more closely for takeoff and the high-airspeed pitch can then be closer to optimum for cruise, even though it cannot compensate at high altitudes for loss of power. There are clear instructions for adjusting the stops and counterweights for optimal results. It has been a reliable solution although subject to the same environmental issues that apply to any wooden propeller. There is no existing Aeromatic intended for a Rotax, the smallest one weighs about 30 pounds -- this makes it highly unlikely that an Aeromatic would be within the rotational inertia limit for a Rotax. But if someone took this concept into the present century it could be very useful. In the US for light-sport compliance, you'd have to make sure that FAA agreed with the idea that it was a ground-adjustable propeller (which it is) since no aspect of the in-flight operation is accessible to the pilot. The current owner of the Aeromatic certificates, although he's apparently not a repair station for certificated planes anymore, is Kent Tarver in Nevada, Aeromatic Propellers: Introduction.
 

TFF

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The biggest problem with an Aeromatic is finding one. It would be perfect if a Rotax 912 one was developed, but there is no money in one unless a LSA airframe company would flip the bill. I have a friend looking for a 0-235 TypeII flange one. I dont know if a new one has been made in years. Tarver keeps up the fight.
 

bmcj

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I run an Aeromatic prop on my Starduster Too, but it is a bit too large for a Rotax (96" diameter and very wide and thick blades). They work great! The biggest drawback is that the airfoil sections are thick and wide chord, so that can be a bit limiting on RPM. My engine is 260 HP with an internal gear reduction, so it does fine, but an engine that gets its power from RPM rather than torque will have a tough time unless you've got a serious reduction drive. Plus, I am unaware of any small diameter Aeromatics for engines in 100 HP range.
 

TFF

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They made Aeromatics for Lycoming 0-235s. Most are the early hub Type 1 not Type 2. Type 2 is the modern standard. They made some 2s but not a lot. What made the Aeromatic disappear was the willingness for the engine builders make real constant speed prop engines. There are a lot of applications 99% are before 1950. As for no certified props, the FAA went to the little home business and essentially deemed that there was not enough money to handle being sued for ADs. Being able to afford fines and lawsuits is what the FAA cares about.
 

plncraze

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BMCJ please tell us more about that engine prop combo and how you decided to put that in your plane. Thanks!!
 

fredoyster

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Can anyone fill in more of this story?
TFF's comments about liabilty, and the expansion of requirements for QA/QC/continuing airworthiness paperwork systems are probably enough. That's sad but even absent any personality issues with the Seattle MIDO I can imagine it would be hard for a one- or two-man shop to satisfy bureaucrats who were accustomed to dealing with Boeing.

There is also a backlog of bad reputation from the time Aeromatics were serviced by a shop in California that couldn't seem to keep them from leaking oil. Apparently this wasn't a problem before or since.

I don't think there are any patents that still apply to the Aeromatic design. I'll bet a competent mechanical engineer with a good CNC shop could come up with an Aeromatic-style hub that would take the blades that are available from Whirlwind, Warp Drive, Powerfin etc. and prove it out in the experimental market.
 

TFF

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Back when all airplanes were parked outside, Aeromatics were not the prop to be left outside for 20 years. Keeping it airworthy with scarce and I bet expensive parts at the time did not help. Composite blades that can not rot at the blade retention would solve the really only part that causes problems. My frined wants to put one on a Grumman Yankee. He is not the first to do it but would be the second.
 

pwood66889

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From TCDS 718:
A-718
Page 3 of 6
4. Propeller - Koppers Aeromatic F200 hub with 00-73E or 00-73F blades.
28 lb.
(-32.5)

No change in parts list assembly may be permitted without
FAA engineering approval.
(a) With Continental C-75-12 engine
Diameter: not over 73 in., not under 71.5 in.
Pitch setting at 24 in. sta.: low 13°, high 20.3°
Parts list assembly No. 4305
(b) With Continental C-85-12 engine
Diameter: not over 73 in., not under 71.5 in.
Pitch settings at 24 in. sta.: low 11°, high 20° min.
Parts list assembly No. 4305A
Percy in SE Bama
 

bmcj

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Almost a month passed since I asked infos about this propeller. Are there so few of them around?
I think it was answered. TFF said he thinks they made an old style hub Aeromatic for the Lycoming O-235, but I doubt that would fit a Rotax. I am unaware of any that would fit the Rotax, but the best person to ask about it can be found at www.aeromatic.com, they might be able to tell you if one would fit. Rotax would know if the weight and mass moment of inertia is suitable.
 

Aviator168

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Yes. If you create fast spinning vortex on top of a surface, the surface will go up. This is due to air molecules in the vortex tend to go tangential so a partial vacuum is create at the center of vortex. Same principle a tornado sucks up stuff from the ground.

[video=youtube;KznKoh1-0eo]https://www.youtube.com/watch?v=KznKoh1-0eo[/video]
 
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fredoyster

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Can't use them on lsa.
Not so fast. I don't think there has been an interpretation that says that. While there is a pilot-controlled Aeromatic, the more common kind would be considered ground-adjustable, I think. Existing Aeromatics are at least 34 pounds and around 70" in diameter, certainly over the Rotax inertial moment limit.
 

Hot Wings

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Not so fast. I don't think there has been an interpretation that says that.
And not all countries have the same LSA standards as the US. Our pilot controllable limitation is from the FAA's regulations defining what we call an LSA - not due to limitations of the ASTM standards. There were some LSA's grounded in Australia because ASTM standards at the time did not have any standards for CS props. We had to develop additional standards - which IIRC are still in the ballot process.

Way back in the early days creating the original standards some of us spent time trying to make sure that the ASTM standard language non-pilot controlled variable pitch props, such as the Aeromatic and scimitar, would be acceptable.
 

blane.c

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I wonder if anyone who had the inclination and finance was to approach Mr Tarver about developing propellers for experimental aircraft what his reaction would be?

It seems to me that making new propellers from fresh materials to fit currently used popular prop hub and power configurations would fit a worldwide market niche.
 

bmcj

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I wonder if anyone who had the inclination and finance was to approach Mr Tarver about developing propellers for experimental aircraft what his reaction would be?

It seems to me that making new propellers from fresh materials to fit currently used popular prop hub and power configurations would fit a worldwide market niche.
Kent has no problem with experimentals, and given the latest legal imposition, I think experimentals are his only market allowed. He made my prop for my Starduster.

You'd have to ask him (or his son, who is now doing most of the work).
 
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