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By PeteBC
FLYER Club Member  FLYER Club Member
#1902918
Hi all, just idly wondering what is required to change the prop on a CofA plane for one with a different pitch, so from a climb prop to a cruise.

Does this require a specific STC for the aircraft? The engine? I assume the noise certificate will need to be reissued, but is it even possible without a plane specific STC?
Last edited by PeteBC on Thu Mar 10, 2022 10:50 am, edited 3 times in total.
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By Rob L
#1902951
I think the rules are the same (or at least similar) between CofA and PtF.
This is assuming a nominally fixed-pitch metal prop like a MacCauley or Sensenich.

You are allowed up to I believe two inches of cumulative pitch change (i.e. if you go 1/2 inch one year and then next year reverse it back to where it was; that's a total on One Inch of pitch change).

I'm no expert; just ask a prop shop.

I had CFS at Coventry repitch a MacCauley prop for me about 20 years ago; they let me watch...it was then a very visual process with a bloke on the end of a long lever arm bending the blades (I have no reason to believe the process has changed!)
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By PeteBC
FLYER Club Member  FLYER Club Member
#1902963
Thanks Rob, I never thought of bending a metal one! Do you know what the rules are for a wood or wood/composite where it would be a unbolt one and bolt another on?
By PeteBC
FLYER Club Member  FLYER Club Member
#1903054
Thanks Trent - I'm more wondering about the legality and paperwork process of such a change for a CofA aircraft, rather than the mechanics. I've dropped a line to Hercules, thanks again
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By GrahamB
FLYER Club Member  FLYER Club Member
#1903066
PeteBC wrote:Hi all, just idly wondering what is required to change the prop on a CofA plane for one with a different pitch, so from a climb prop to a cruise.

Does this require a specific STC for the aircraft? The engine? I assume the noise certificate will need to be reissued, but is it even possible without a plane specific STC?


My understanding is as follows:

You need to look at the original type certificate for the aircraft to see what prop or props were originally approved. If the one you want is there, your maintenance company/licensed engineer can just go ahead and carry out the change and document it.

If the prop you desire is not certified as original equipment on the TC, then you need an STC to fit a different one. The STC needs to specify your aircraft on its Approved Model List (AML). If it's not there on the AML, then the STC holder may be persuaded to add it, at cost no doubt. If not, you could seek a one-off approval but that's likely to be expensive and with the state the CAA is in at the moment may take a long time.
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#1906172
GrahamB is correct. For a Part 21 (CofA) aircraft you need to either already have the prop you want listed by the manufacturer, or get an STC to fit what you want. Good luck with that where the CAA are concerned!

I'm in the same boat. My Archer is a pre-78 model with a 60" prop. The post 78 models have a 62" cruise prop which, together with the fuller wheel pants gives the 5-8kt speed increase. I would like to put a 62" on mine but the POH clearly states that by serial number (i.e. Year of manufacture) only the 60" is approved.

The other aspect is that if you put a different prop on then all your performance graphs become voided as no one will have tested the take off and landing distances with your configuration. That's where the CAA are likely to have a field day making life difficult for you.
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