Aeromatic RPM Consistency

D

dtreid

New member
I've been fine tuning the aeromatic on my 165 Cruisair. Field elevation is 4000'.

I adjusted the static RPM to 2800 w/o any weights on the prop as the manual suggests.

I adjusted flight RPM with weights as the manual outlines.

My static RPM with weights on now varies from 2500-2600 RPM.

What are other experiences with this prop? Is this much of a drop of static RPM after corrected for flight RPM to be expected?
Do others have static RPM vary a bit depending on the day?
 
dtried, look over our type certificate. There is a 2650 red line with an Aeromatic, on a 165. There is an Aeromatic AD that says 2650 on Stinsons, but it doesnt mention Bellancas. Bellanca went ahead and put it in the TC. ______Grant.
 
if this variation is due to changes in density altitude ( temp and humidity at same airport)
see what leaning will do for you .

otherwise no idea.

can you compare with one of those optical tachs ?
 
I was wondering if it might be a density altitude thing. I have installed and electronic tach, so I am confident of it's accuracy.
 
I've had the rpm discusion with Kent Tarver, among many, and the SB 22 clearly states that it applies to Stinsons model 108-2 & -3 airplanes using an aeromatic with 76" blades; the Bellanca uses 74" blades... the SB DOES NOT APPLY. The fact that the Feds never got around to fixing all their paperwork is the "distractor". I run using the Engines limits as a guide, there's no need for the tach marking either as far as I'm concerned.

I have the exact problem at my 2683 MSL airport when setting up the Aeromatic. I talk and email Kent quite a bit. I have found that if I adjust the weights to keep from overspeeding then my static and T.O. rpm drop to about 2650, maybe 2700 once climbing (at 800 fpm/80 mph indicated). If I adjust the weights to get 1750-2800 for T.O. the engine wants to run at just over 2900 rpm at full throttle, I don't. The problem is even more confusing when I try to make sense out of the corresponding manifold pressures for the power settings. Using the ballpark 1" per 1000 ' makes the MAP closer to book but it's still 1-2" shy of agreeing with the (factory otimistic?) charts in the engine book.

So, who else with a 165 on a Aeromatic has these problems? Any fixes?
 
Tailwheel, you are correct that the SB does not apply, but our type certificate certainly does. Even if the FAA is wrong about the RPM, it is in print, and any IA that signs off a Cruisair with an Aeromatic that goes to 2800 RPM is risking his ticket, not to mention the Insurance companies that would try to not pay out if you had an accident, even if the prop had nothing to do with it. The IA that does my annuals said that he has the gear to check for the destructive vibrations that made for the 2650 limit, but said it would be expensive and to try to get the FAA to change a Type Cert. that nobody owns would be pissing into the wind. I happen to be the person who told Kent about the 2650 limit. He had been advising Cruisair people that 2800 was OK, but had not looked at the TC. He looked up our TC while I was talking to him, and his response was OH Crap. There may or may not be any danger in our airframe/engine combination at 2800 RPM, but nobody, knows for sure. At one time I had plans to put a 165 in my Cruisair, with a 220 flywheel(technically an impulse absorber) and running the Aeromatic at 2800,(of course with the tack showing a 2650 red line). I doubt there would have been any trouble, but no-one knows for sure. I would put my Cruisair into experimental category in a heart beat if it were possible. Testing for destructive vibrations is not difficult in this day and age,but expensive, and the FAA makes everything into a congressional case, and we all know how well that works out. ______Grant.
 
Well, as pointed out here recently, you Can go experimental, but you will be in the exhibition category.

For airplanes that have been grounded and in storage for years because of the expense of repairs and inspections
as certified planes.. this is probably a better choice than not flying until the mice move in.

Curiously, and apropos of nothing, I had a guy try to sell me a T-crate project with no logs, no data plate, no nothing.
His plan was to build it up as a clip wing, fly it at airshows, and register it ex-ex.

Hell, anytime you see a cruisair flying, everybody knows it's an exhibition ! :twisted:
 
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