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Aeromatic Props

Posted By:
Keith Leitch
23
Posts
2
#1 Posted: 3/6/2010 12:28:28

 

I have access to an Aeromatic prop that was previously installed on a PA-12 with an O-235.
I have a Champ (7AC-CONV) that has an O-235c2c installed via the Buzz Wagner STC and would like to try this prop on my plane. I have found out that it is legal on the O-235 and legal on a Champ(original engine), but can't find where it would be legal on my Champ with the O-235.
Can I just install this prop using the list of engines it is legal for? Field Approval maybe?
I'm stumped!!!
Thanks,
WW

 



Jim Rice
Vintage Aircraft Association Member
12
Posts
9
#2 Posted: 3/6/2010 13:59:17

I can't answer your question regarding the Champ.  Have you dealt with an Aeromatic before?  They are very expensive to overhaul and maintain.  Old blades are prone to broken lag screws which hold the blade to the flange.  This can lead to a loss of a blade.  While new blades are available, hubs are not.  The F200 hubs (what you would need on the O-235, IIRC) are around used, but the F220 is scarce. 

I flew an Aeromatic on my Swift.  While it did help some with allowing the engine to turn up on takeoff, it didn't really cruise any better than with a fixed pitch prop.  Many Swifts came from the factory with the Aeromatic.  Today, the Swift Association recommends against the use of the Aeromatics.  Others praise them.

I'm not necessarily trying to stop you, just wanted to let you know there are some issues with Aeromatics.   They aren't the equivalent to an "automatic constant speed prop" some folks seem to believe.

Jim



Jim Rice Collierville, TN Globe Swift N3368K Piper J-3 Cub N7155H
Keith Leitch
23
Posts
2
#3 Posted: 3/6/2010 14:35:21

Jim,

Thank you for your response. I have read about the lag bolt issue and know of the proceedure on how to check for this particular problem.  I have spoken in depth with Tarver (current holder of the Aeromatic STC) and he has new blades. Granted as you state...they are not cheap.  I have access to a complete prop that was removed from a PA-12, a spare hub, and the friend that has these also has a couple of the F220 hubs.
happy

I guess some guys just seem to find all kinds of things!!

I have corresponded with several guys that have had these on Champs, Cubs, and Taylorcrafts and they all seemed to really like the additional performance the prop offered. One gentleman in particular was very impressed with it and wants one for his Champ, he would also like to have one on his Super Cub.

The reason I am wanting this is because I fly floats and would like to get ANY added performance since I am very limited to the props I can put on my plane with the STC that was used in the conversion.

Thank you,

Keith

PS. Just curious....is this the same Jim from J3 site?



Pierre D'Entremont
Homebuilder or Craftsman
131
Posts
37
#4 Posted: 3/7/2010 11:56:57

Was just on the horn with Don Browett  who has an Aeromatic on his Great Lakes ...read off your situation...He seemed to think you would be declined by those who would help you... thats sorta what he said...lol

He is not one to rest his fingertips on a computer keyboard but will talk on the phone happily...816-373-1916



Tooky or Pierre
Kent Tarver
Homebuilder or Craftsman
7
Posts
1
#5 Posted: 3/11/2010 22:28:09

The blades for the Aeromatic F200 are $3200 installed on a hub that needs no OH or repair.  Check the new price installed on any other brand of variable pitch props like MT, Hoffman, Hartzell, McCaully.

The lag screw issue:  The propellers made by those before me torqued the lag screws to 150 in/lb.  I see no data in my engineering or procedures that told them to torque each screw at least 7 or 8 times.  If they put 150 in/lb on each screw and mounted  the blade on a prop they it is fairly certain that those props went on airplanes with less than half of the 15 screws carrying the centrifugal load.  Since there is no history of blade failures then that whould be good indication that the lag screw method of retention is not an issue.  Analysis and pull test prove that the failure of lag screws occurs at 4 to 5 times the calculated load.  The FAR states that the blade shall be subjected to twice the calculated centrifugal load and it shall not fail.  I doesn't say how much above twice the load it is allowed to fail.  The calculated centrifugal load on a typical blade of a 74" prop turning 2800 rpm is about 19,000#.  Pull tests have proven that the failure of 15 screws happens at between 90,000 and 120,000# of force. 

I have found that each time I go around and torque all the screws that the screw will show some more "take".  Typically, I torque all 9 bolts in the outside row, then torque the inside 6 bolts to 150"/lb, then go back to the outside row and find that they are not torqued to spec, so, I torque them to 150in/lb then go back to the inside row and find them not to spec, they "take" more torque.  I do this on all screws until no screw "takes" any more torque.  Now, that is the way to make all the screws do their job.

It is my judgement that all those broken screws I've found in old Aeromatic blades were not properly torqued. 

I have one confirmed blade failure on a RV-4 with an 0-320 engine.  One of my friends had an Aeromatic for many years.  It looked very good, no dings in LE, pretty shinny paint, no rust.  They put it on my other friend's RV-4 and flew it.  Got only 2150 rpm, they landed, tweeked the counterweights, took off and climbed to about 2500' above his airport (which is above 4000' MSL).  This time a blade separated, the pilot made a sucessful landing, broke the engine and firewall.  They gave me the prop for analysis.  The separated blade was never found. 

The ferule was still in the hub.  Of the 15 screws, 10 of them had old rusty breaks, two of them has fresh shinny breaks and 3 of them pulled out of the wood.  So, it is clear that both flights were made on only 5 screws and it is most likely that those 5 were not sharing equally the load. 

It then is logical that with the 15 screws properly torques that this would not happen.  I would guess that there are a whole bunch of Aeromatics flying around out there with half the screws going along for the ride.

Early Messerschmidts, Hawker Hurricanes and Spitfires used this design of wood blades using lag screws to hold them together.

I am working on a patent that will allow higher rpm at high altitudes.  This will allow the Aeromatic to give you everything a CS prop will give, it just will not have the closed loop control of rpm like the CS has. 

The prop is approved for PA-12 and the PA-12S.  Also the Aeronca 7AC, S7AC, 11AC, S11AC and 15AC.

 

 



Stan Comer
3
Posts
0
#6 Posted: 3/11/2010 23:31:02

Keith,

I have owned two Bellanca 1413 airplanes.  Both had the Aeromatic propeller.  I really like the propeller.  It made the Cruisaire in my opinion.  I did have two instances, both really one. that could have beween bad.  I was flying back to Washington from Arizona and stopped at Meadow's Field in Bakersfield, California, for fuel.  While waiting for the fuel truck to arrive (they did pump gas for you in those days!) I noticed a split in one of the blades.  There was a shop on the airport that had a metal propeller that was approved for the Cruisaire.  I made arrangement to have the Aeromatic propeller shipped to my home and left for home.The airplane did not fly the same with the metal propeller.  It wasn't nearly as smooth and when I got it 'on the step' it gave me about 135 mph indicated.  I was used to 145-150 mph.

I sent the propeller to Univair to have a new blade put on and to have done what else was needed to make the propeller airworthy.  It took about three weeks to get my prop back. I don't recall what the bill was for getting the prop overhauled, but my memory is that it was not outrageous.  I was anxious to get the prop back on the Cruisaire so I put it on right away.  Everything looked, sounded and felt OK so I took off.  Boy!  What a joy.  That prop is so smooth   
happy    Then it happened.  I felt a very slight bump.  The prop did not feel right.  Only a person who hs experienced the smoothness of the Aeromatic propeller would notice anything wrong.  I landed right away.  I removed the prop and sent it back to Univair.  They said a nut or bolt or something inside of the hub had come off.  It took another three weeks to get my prop back again.  I had no other problems after that.  I just enjoyed the smoothness of the propeller.  The Aeromatic propeller does enhance the perfoemance of the Bellanca Cruisaire and probably any other airplane upon which it is put.

Best wishes,

 

Stan Comer



scomer
Keith Leitch
23
Posts
2
#7 Posted: 3/12/2010 06:48:58

Kent,

Thank you for the reply. I am an ardent believer in the Aeromatic!!! Thanks for stating again how the lags are torqued. I am going to recheck this particular prop and have another look at it.

I remember talking to you about a year ago on the legalities of putting it on my plane. I know it is legal on the Champ and on the O-235 on the PA-12 but if I remember correctly the issue was being able to put it on my plane because it has an O-235 installed via the Buzz Wagner STC. I guess I need to speak more to my IA and see if possibly I can get it approved with a field approval.

Thanks again everyone.

Keith



Kent Tarver
Homebuilder or Craftsman
7
Posts
1
#8 Posted: 3/12/2010 20:23:31

It's certified on the J-3C  with C-85, PA-11 with C-90, PA-12, PA-12S with 100 hp and J-5C with 100hp.

I see no reason why you can't get a field approval.



Keith Leitch
23
Posts
2
#9 Posted: 3/13/2010 08:36:35

Thanks again Kent. That is the avenue I am going to take. I have seen your props and they are georgous!!! Are they okay to use on a floatplane? This one has a metal leading edge.

Hopefully it won't need new blades. But if it does I guess I'll be getting it touch with you.
happy

Keith



Scott Thomas
Vintage Aircraft Association MemberYoung Eagles Pilot or VolunteerHomebuilder or CraftsmanAirVenture Volunteer
3
Posts
0
#10 Posted: 1/21/2011 09:24:32

So, how does the tale end? Did you get the Aeromatic  mounted (legally)? how do you like it?

I have owned/flown my Cruisair with an Aeromatic since 1987 and like it  a lot. There were "issues" about support and service while the ownership traveld from Univair to Kenitics, briefly to another family, the courts, and finally to Kent Tarver but now there are no service/reliability problems. I have flown other Cruisairs with both metal and wood props and think that the Aeromatic is the best. I always assumed it gave similar performance to other planes as well.

My father flew Cessnas with and without Aeromatics in the 50s and was always complimentary about the performance difference.



Ray Myers
Vintage Aircraft Association Member
1
Post
0
#11 Posted: 2/5/2011 11:53:53

Keith 

Does your friend still have the F220 hubs?  Would he be interested in selling one?


Ray Myers