Mostly what others here have said, but I was involved in some of the flight testing of some twins that were being converted from diesels to 180 hp LL burners. The airplane manufacturer is/was in love with MT props and used those for a majority of the testing. They also looked at using Hartzell props. The Hartzell props had better performance (cruise, climb) but when there was a vibration survey of the prop and engine combination (Hartzell/Lycoming) as part of the certification there were some RPM ranges that had unacceptable vibration levels so there would need to have been limitations on operation.

Long story longer, some manufacturers don't want to have to have that limitation in their POH. Could have been fixed by getting the Lycoming with counterbalance on the crank, but they just chose to use the MT props.

I got the word from McCauley:

First thank you for buying McCauley, as we do think our product is a
superior product.

With both conditions <15"MP and 1900-2350RPM we are getting into a wind
milling condition (prop turning the engine). This wind milling can cause
a harmonic vibration, if continuously operated in this condition over a
period of time it can be detrimental to both the engine and propeller,
thus the placard to avoid. Please note that being aware of this
condition and avoiding when possible, McCauley has certified with the
operational practice of the placard that over the theoretical life of
the propeller there will be no problem from this condition.

McCauley's standard for "Continuous" is: the same as Aviation's engines
standard, 5 minute limitation in duration. You are correct it takes
both criteria to produce this condition.


Regards

Thanks for checking with the "source". Always the best bet to get things from the horse's mouth, so to speak.

MTV

There is nothing in my paperwork that mentions a Manifold Pressure anywhere. My Avcon Conversion was done in the early 70's so the larger RPM restriction range and MP setting might have been added later. Possibly I've missed an update somewhere along the way update. I'll look into it.

I will just avoid the restricted RPM's because I don't want to be forced to buy a new prop right now or worse. I think I will use the 1950 - 2350 scale as a self imposed restriction even though mine says 2000 - 2250. I don't usually cruise under 2350 anyway and pulling back to 1600 -1800 while landing works too.

Jaerl,

You have a DIFFERENT propeller. The restriction he's described apply to the O-360 engine with a McCauley prop, not a Hartzell.

MTV

It is interesting that the Hartzell prop restriction is across all power settings.
The <15" MP and anything above 1900 RPM will pretty much only occur when diving at low power settings.
Even when on steep approach, I am usually less than 1600 RPM at idle.
Jaerl, you should email Hartzell and see what they say - McCauley's reply to my querry was pretty illuminating.
If you have the Lycoming power chart, can you post it? Mine is glued on the visor in the plane...

Mike, I know AKclimber has a different prop now, I was thinking his placards were from the original STC with the Hartzell not the McCauley since he said he didn't know where the restriction came from. My mistake. I was thinking my conversion was and early one and the plane was inactive for 25+ years. I might have missed an AD on the Avcon conversion. I did write Hartzel and I'll post what they reply.

I'll get the Power chart out of my plane and I'll try to get it posted soon.

Here is the response I got from Hartzell, my placards are correct. The restrictions have nothing to do with anything except the engine/hub/blade combination. Link to the PDF at the bottom.

"The restriction comes from the interaction between the propeller & the engine. I’ve included a copy of the type certificate data sheet for your propeller. It’s 13 pages long, but the data you are looking for is in the “Note 9” data near the end of the Type Certificate. Find your engine /prop in the list, and you’ll see your restriction.

I’m not surprised that the McCauley prop has a restriction on their prop as well, and that it is different than that on the Hartzell prop, as it all has to do with induced resonance in the propeller.

If you have any additional questions, or if I can be of further assistance, please feel free to contact me at your convenience.

Regards,

Kevin M. Ryan
Product Support Representative
Hartzell Propeller Inc.
Phone: 937.778.4379
Fax: 937.778.4391
Email: [email protected]"

http://rgl.faa.gov/Regulatory_and_Guida ... /P-920.pdf

Interesting - the Hartzell RPM restriction is across all MP settings.
So according to your Lycoming power chart, can you even fly at 55% or 65% power settings without encroaching on those restrictions?

AKclimber wrote:Interesting - the Hartzell RPM restriction is across all MP settings.
So according to your Lycoming power chart, can you even fly at 55% or 65% power settings without encroaching on those restrictions?

Sure, just use different combinations of MP and RPM. The power charts the manufacturers provide simply give "general" power settings. In most cases, you can use whatever combination you like. So, you may be able to use a higher RPM and low MP to achieve, say 65%, but you also may be able to achieve 65% with a lower RPM and higher MP.

And, in fact, Lycoming allows a very wide range of RPM, many of which (lower RPM) are not listed on their power charts, even though they are approved.

Many folks with these engines run very low RPM settings, like 1900 or 1950, and slightly higher or sometimes somewhat higher MP settings.

Remember, most propellers are most EFFICIENT at relatively low RPM.

MTV

My engine/prop restriction are those RPM's in any manifold settings. These I found these interesting:

"Avoid continuous ground
operation in cross and tail
winds of over 10 knots
between 1700 and 2100
RPM".

"Avoid continuous operation
on the ground between
1900 and 2300 engine RPM
in winds above 15 MPH".

Call Avcon and ask them.

Don't expect much of a response--if there is one thing that Avcon does really, really well, it is avoiding responding. Their phone is often answered by a machine, so if you leave a message, they don't call back. If a live person answers, the person who knows the answer "...isn't here; he'll call you when he gets in" but "he", whoever "he" is, doesn't call back. Truly awful customer service, as bad as you can find anywhere. Yet the conversion itself was a pretty good one, according to several mechanics I've talked with, including my current IA, who has maintained my airplane for some 7 1/2 years now, so it's a shame that a good product isn't backed by decent customer service.

Cary

Cary wrote:

Call Avcon and ask them.

Don't expect much of a response--if there is one thing that Avcon does really, really well, it is avoiding responding. ......

That'd be Bob Williams in Kansas, aka Avcon aka Bush Conversions. Well known for poor (!!) customer service.

Fundamental rule of business: Please your customer, he'll tell someone else. Displease your customer, he'll tell 10 others. Amazing how many business people don't understand that rule.

Cary