2012-05-19T05:07:18Z Kent Tarver Copyright 2012, Kent Tarver SPHPBLOG
Aero Digest Article from 1944 describing the Aeromatic propeller.






]]> http://www.aeromatic.com/resources/index.php?entry=entry110516-130949 2011-05-16T00:00:00Z 2011-05-16T00:00:00Z
Well, here it is February 2011 and I am still waiting for his answers.]

Here is a copy of my letter of 4/4/2005.

Kent Tarver

TARVER PROPELLERS, LLC

1500 Rio Vista Dr. Hangar C-4

Fallen, NV. 89406

www. aeomatic. com

4/4/2006

Dear Mr. Montague,

I see that you are very critical concerning the Aeromatic propeller.

I would like you to answer a few more questions about your opinions, views and experience with them.

First I will quote you in some of your comments I find on the Swift website.

Quote 1 - "inefficient" Tell me what are the numbers you would consider as inefficient or efficient. Also tell me what the efficiency numbers are for the Aeromatic or any other propeller brand like Hartzell and McCaully.

Quote 2 - Again about efficiency - " The advantage to a controllable is to be able to turn the rpm UP, which is just where these props DON'T work.

Can you tell me why they DON'T work. Do you know how to set up and operate an Aeromatic? What is it that DON'T work? What proof can you offer?

"With the high maintenance and possibility of catastrophic failure that is why I don't like these props".

Tell me what propeller is immune to a catastrophic failure if not properly used and properly cared for.

Quote 3 - ".. very short TBO". Just what is the TBO for an Aeromatic? Where did you get the information that Aeromatics need a "$3500 overhaul every 200 hours?"

Quote 4 - With your Sensenich prop ".. Full throttle at 2000' msl indicated about 165 mph. Switching to my Aeromatic full throttle at 2000' indicated 135 mph".

It is clear that you don't know how to set up an Aeromatic propeller. And your little test is somewhat laughable.

Quote 5 - "They are a product of the '40s and obsolete today".

What makes them obsolete? If an Aeromatic if obsolete then how about all those props that were designed in the 20s and 30s and are still used today?

Quote 6 - "There was never a company named Flo-Torp that made Aeromatic blades". You make this statement as though you are damn sure of this "Flo-Torp" company's existence. Give me some information on this company.

Where do you get all you wonderful information? If Flo-Torp made Aeromatic blades they for darn sure were not certified blades. Maybe you have been flying around behind your Aeromatic that were fitted with "Homebuilt blades".

Quote 7 - "You can't get over 125 hp with that prop 'Aeromatic' unless you are at or below sea level".

This statement shows your gross ignorance not only of Aeromatic props but also your lack of understanding of engine performance in general. If you know this to be true then most everyone else can greatly benefit from your superior wisdom and expertise. I ask you to elaborate on this statement so we can learn from you.

Quote 7 - "The Aeromatic seems to require attention every one or two hundred hours".

I am here to tell you sir that any propeller requires attention every time you fly it. I get the impression that you just bolt a propeller and go. If you wait 200 hours between propeller pre-flight inspection then yes, you are flirting with a catastrophic failure.

OK, so again, give us some proof, how about some witnesses that can prove their support of your claims?

Now about T.J. Johnson's comments.

"I had my F200 Aeromatic overhauled at a cost of $1500... it lasted 23 hours!!" I sent it
back and one blade had 2 lag screws broken., the blade is no longer airworthy., they can't
simply replace the lag screws because when the old ones are removed part of the old
wood comes out and the new screws will not attain the torque requirements to meet
airworthiness requirements " etc.

The Aeromatic blades can be certified with up to 3 screws broken or missing under specified conditions See SB 2000-001A on ww v.aeromatic.com. Furthermore lag screws can and are routinely replaced, the old wood doesn't "come out" and yes the replacement screw will and does routinely take the required torque.

Now about the "Editor" who ever he is. "My two cents. When I became the caretaker of Swift N3307K in 1982, it had an Aeromatic prop. It was the variable pitch version not the two position 'flip-flop....', etc.

There is no such thing as a two position flip-flop Aeromatic.

I would like to know who is telling you guys that an Aeromatic needs overhauling ever 20 to 30 hours or every 200 hours or any other TBO for that matter?

Further quoting the "Editor" - "Additionally, people knowledgeable (Mr. Montague I assume,) on the subject were telling me that the Aeromatic prop blade was inefficient compared to metal bade props".

In some cases that is true and in some cases that is not true. See comments below.

"They'll (Aeromatic) look great all cleaned up and mounted on the wall in your hangar or den".

That is the first statement in all this diatribe I've quoted above that I can't criticize. They are very pretty when not neglected and when used properly and taken care of properly and understood properly. Not only that but they will also perform beautifully when not neglected and when used properly and taken care of properly and understood properly and maintained properly. But you have to seek out technical support data from someone other than rumor editors and victims of rumor editors.

OK, Mr. Montague how about a response to this letter?

I want to hear from you how many catastrophic failures you know about. I also ask you to provide the names of the people that have had catastrophic failures along with the results of the NTSB details of the accident. I'll even give you a couple of places to start. The first one is the claimed blade separation off a Fairchild on 1 April 2000. The next one is the crash of a Monocoupe near St. Louis in late 04 or early 05.

After your answers to my letter I will give the details of a real blade separation from an Aeromatic that was being flown on an 0-320.

Neither you nor your co-harts have mentioned anything about the proper installation and operating instructions on Aeromatic props. There is a definite sequence the must be followed in order to get the performance from an Aeromatic. From what I read on your website "The Answer Man" leads me to the conclusion that you Swift/Aeromatic "experts" think you can just bolt on an Aeromatic propeller just like you do all those metal clubs and go flitting about in the atmosphere without a care in the world.

Whether you know it or not the FAA considers propellers to be "critical" item on par with engines and airframes. They do need someone knowledgeable to install them and then someone equally knowledgeable of how to use them. Your diatribe sends the message to any technically qualified person, that you can treat an Aeromatic prop just like you treat the metal clubs you so admire.

LASTLY, — I ASK YOU TO BACK UP YOUR CRITICISM WITH SOME TANGEABLE DATA AND GIVE ME EVIDENCE THAT YOU ARE AN AUTHORITY ON THE SUBJECT.

Quite frankly sir, you don't impress me with your technically expertise.

OK, 'nuf of all this. I promised to comment on the efficiency subject.

The term efficiency as applied to propellers should be defined when one starts talking about the subject. There are a number of different kinds of efficiency. One is how efficient is the match of the propeller to the engine. Explained this way. If an engine is producing 100 shaft-hp and the propeller provides a 100 hp load to the shaft, the source and the load is matched to 100%. There are cases in which this is true and as a matter of fact it can be and sometime is, theoretically, more than 100% efficient. Next then there is how efficient the propeller transfers the 100 hp from the engine to the air. In other words does the air acting on the propeller absorb 100 hp? The answer is no and it never does. There are no 100% efficient propellers. Next this thing called Advance Ration is the final word of efficiency and this includes not only the engine/propeller but also the airframe.

But I will assume you mean efficiency as applied to Advance Ratio. I do not plan to get too technical with you because it may loose you.

When a propeller blade tip is moving at Mach 1 and higher, efficiency begins to suffer, however of little concern. It is the section speed that is important. There are some propellers that operate at these tip speeds during maximum rpm, like during takeoff and climb. An example is a 9.5' prop turning at 2640 rpm. The tip travels in one revolution 29.8'. 29.8 times 2640 rpm * 78672 1pm, divided by 60 - 1311.2 fps. Mach 1 at sea level in standard atmosphere is 1120 fps. So it is clear that this example of tip speed is Mach 1.17. A propeller does most of it's work at and around the 70 to 75 percent of it's diameter. So, if we do the numbers again on this prop we get a section speed of 984 fps. This is the speed where the propeller begins to show some degradation of efficiency, but again it small. But in these numbers the thickness, or better yet, the thickness ratio becomes more important.

Back to our world. The most often criticism that is batted around about inefficiency of Aeromatic blades goes like this, "them things are too thick and are not efficient". A typical 74" propeller's section speed at 2600 rpm calculated out to be about 630 fps. This is a speed where efficiency suffering is not discernable, especially to a pilot.

It is also proven by tests that the loss in efficiency of a practical "thick" blade does not suffer until it gets up around 800-900 fps and then it is very little.

So to talk about the Aeromatic being inefficient is like arguing about the speed of light.

Oh, yes. If you want to know where 1 get my information and if anyone wants to look into this subject for themselves, pick up a copy of ANC-9. In it you can learn just about anything you ever wanted to know about propellers. Then add to your reading list ANC-18 and ANC-19. The latter two documents deals quite thoroughly with wood airplane construction and wood blade propellers from the fabrication, selection and inspection point of view whereas ANC-9 will increase your smarts on the engineering aspects of propellers.

Between the Koppers company and Univair there were more than 14,000 pairs of blades made for the Aeromatic, virtually all of them have seen service. There is only one AD note against these blades. And there is only two against the hub, none of which apply to hubs that I assemble or blades that I manufacture, Name the other propeller brands that have a track record to match this.

It is evident to me that your bad experience is related to two possible causes. First you may have tried to use an Aeromatic that wasn't set up for your airplane. You may have gotten a propeller that was misused of one that, has been neglected. Second, you knowledge on how to set one up evidently is grossly lacking.

Now, Mr. Montague put up or shut up. I await your answer.

Kent Tarver.
]]> http://www.aeromatic.com/resources/index.php?entry=entry110302-130223 2011-03-02T00:00:00Z 2011-03-02T00:00:00Z