McCauley prop question. 'CF' vs. 'CM' differences

[N74DV]

I'm looking for a McCauley prop and have been told I need a 'CF' variant as opposed to a 'CM'. I'm having a hell of a time finding a prop in 'CF' version but have seen one on eBay which is a 'CM'.

[N74DV]

Re: McCauley prop question. 'CF' vs. 'CM' differences

Well... had I searched a few minutes longer before posting I'd have seen the difference is in the tips. CM is square, CF is rounded.

[fearofpavement]

Re: McCauley prop question. 'CF' vs. 'CM' differences

You can use any prop listed on your TCDS or that has an STC for the plane and engine combination you have. ie, Propellers are not just certified for the engine but for the airframe as well. Our T uses the "clip tip".

[woodmw]

Re: McCauley prop question. 'CF' vs. 'CM' differences

The important difference is that the CF is Model 1A90 and CM is 1B90. 1A90CMxxxx is on the TCDS. 1B90CMxxxx is not. I am sure a 1B90 would require an FAA-337, which I have been told, by an A&P/IA friend, are almost impossible to get approved, at least through FAA-Houston.

[Mark Julicher]

Re: McCauley prop question. 'CF' vs. 'CM' differences

Right on the money Mike!
I don't know the folks in Houston FSDO, but I have done two field approvals for the 1B90 on Taylorcraft with the San Antonio FSDO. It helps that I have a letter on McCauley letterhead stating that the 1A90 and 1B90 are identical in thrust and flutter characteristics. In truth, a 337 on this should be "no brainer" easy, but feds are feds and it is easier to say no.

[NY86]

Re: McCauley prop question. 'CF' vs. 'CM' differences

McCauley considers the 1A90CFxxx and 1B90CMxxx interchangeable.They specifically state so in the prop type certificate.

NOTE 6. Interchangeable blades. Models 1A90 series and 1B90-CM, or 1C90-ALM and 1C90-CLM are sufficiently
similar aerodynamically and vibrationwise to permit interchangeability in the same diameter and static r.p.m.
without a flight test.

Type certificates are approved data...

[Dano"T"]

Re: McCauley prop question. 'CF' vs. 'CM' differences

McCauley considers the 1A90CFxxx and 1B90CMxxx interchangeable.They specifically state so in the prop type certificate.



Type certificates are approved data...

Soooo bolt that puppy on there, scribble in the log book and go flying.

[Mark Julicher]

Re: McCauley prop question. 'CF' vs. 'CM' differences

This is the same discussion the tribe had a year or so ago.
You can bolt it on safely and it works fine, but Type Certificate 696 does NOT list the 1B90 propeller - so take that up with your IA. Personally I wouldn't sign it off with just a log entry, but somebody else might.

[Doc]

Re: McCauley prop question. 'CF' vs. 'CM' differences

Yes...the logbook entry is the answer as long as it references the 337 (LOL). Mark did this for me a couple of years ago and it sailed through without any problems...just a matter of having the correct paperwork (approved data from McCauley) as he stated. Doc

[dejh22]

Re: McCauley prop question. 'CF' vs. 'CM' differences

My project came with a 1B90CM/7445 72.5 inches. It was approved with a 337 dated Nov. 21 2003. I have no knowledge of what kind a performance one would get from this prop. It is on a A65-8.

[NY86]

Re: McCauley prop question. 'CF' vs. 'CM' differences

You (the IA) write the 337 referencing the TC as approved data and send it in. No (further) FAA involvement required, nothing to sail through.

[fearofpavement]

Re: McCauley prop question. 'CF' vs. 'CM' differences

It is important to realize that the type certificate for the propeller does not approve it for the aircraft. The aircraft's type certificate is what authorizes the use of a particular propeller. So I am sure a log entry will not be adequate without some "approved data" and a 337 and or an STC. A different propeller would never qualify as a "minor" alteration.

[NY86]

Re: McCauley prop question. 'CF' vs. 'CM' differences

Not sure if the above was aimed at my response or not, but, at the risk of beating a dead horse,

The aircraft specification authorizes use of the 1A90. The prop TC states the 1A90 and 1B90 are interchangeable without flight testing. This is approved data and can be used to justify a 337 for the airframe installing the 1B90 in place of the 1A90. Since the prop TC is approved data, the FAA does not need to be involved in the approval process; all you need to do is file the 337. It is a major alteration, but it does not require a field approval because there is existing approved data, i.e. the prop type certificate.

TMSAISTI!

[n6346m]

Re: McCauley prop question. 'CF' vs. 'CM' differences

I agree with John. Manufacturers quite often make a "new and improved" part with a different part number and state that the old parts and new parts are interchangeable. You would not need the FAA approval to use either part. I believe this falls in the same category.

[fearofpavement]

Re: McCauley prop question. 'CF' vs. 'CM' differences

I agree with John. Manufacturers quite often make a "new and improved" part with a different part number and state that the old parts and new parts are interchangeable. You would not need the FAA approval to use either part. I believe this falls in the same category.

Well, this isn't exactly the same scenario. Sometimes a manufacturer will change a part slightly and give it a new part number or sometimes just change the part number. Most often these are FAA/PMA parts and you are correct that the "new" part can directly replace the old part.

In the case of the propeller, these two props are NOT identical, one has rounded tips and one has the clipped tips (flat ends) so it is not a case of the same propeller with a different number. The other issue is that a propeller is considered to be a major component that is specifically called out in the type certificate. The same would apply to an engine. A TSIO-520C is not exchangeable with a TSIO-520M. Although they are similar they are not the same.

I am not insinuating that the 1B90 can't be used, I am just saying that it requires MORE than a logbook entry. Whether the type certificate of the propeller approves it for the airframe, I am unsure of at this time. I will have to check into that in more detail.