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 Post subject: Cherokee 250?
PostPosted: 23 Apr 2021, 06:20 
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Company: Reliant Aircraft Service
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I am researching cylinder options for my Cherokee 235, and i came across a couple of past "for sale" advertisements, and these planes were touted as having "250 HP Upgrade"

I am perplexed by this because I find no STC to modify the engine, nor an airframe STC, which would be needed due to the higher octane requirement.

I would think a field approval would have been prohibitively expensive

I reached out to one of the current owners, but got no response.

Does anyone know how this HP increase could have been legally achieved?

Thanks


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 Post subject: Re: Cherokee 250?
PostPosted: 23 Apr 2021, 07:51 
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Back in the day a field approval was much easier and more lax. Of course, it may just not be legal. You could request a records check from the FAA.


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 Post subject: Re: Cherokee 250?
PostPosted: 23 Apr 2021, 08:34 
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Pretty much this. In the time of the GADO, field approvals were common.

Best,
Rich


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 Post subject: Re: Cherokee 250?
PostPosted: 23 Apr 2021, 21:39 
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the 235 is a low compression engine. Put in higher compression pistons and you get the extra HP the 250 is a std engine as I understand.


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 Post subject: Re: Cherokee 250?
PostPosted: 24 Apr 2021, 11:24 
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The Comanche 250 is a 250 HP 540 with a carburetor. I wonder what differences there are between it and the 235. Counterweights could be different. I didn’t care for flying a Cherokee 235, but have been in a couple Comanche 260s that I found to be quite smooth. Additional counterweights?


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 Post subject: Re: Cherokee 250?
PostPosted: 24 Apr 2021, 11:41 
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I am no expert at this, but I believe that A DER could be used and that is basically a Field Approval. I have heard 20% increase in HP is within the norm for a DER approval. The DER data applies to only one airplane, so it is not a general STC.


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 Post subject: Re: Cherokee 250?
PostPosted: 27 Apr 2021, 09:30 
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Username Protected wrote:
I am no expert at this, but I believe that A DER could be used and that is basically a Field Approval. I have heard 20% increase in HP is within the norm for a DER approval. The DER data applies to only one airplane, so it is not a general STC.



DER is a great idea, thanks


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 Post subject: Re: Cherokee 250?
PostPosted: 27 Apr 2021, 19:01 
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The biggest advantage of this mod is that even if you limit the HP to 225 you will have more HP available at altitude. and as this aircraft has no turbocharger that can be helpful.


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 Post subject: Re: Cherokee 250?
PostPosted: 27 Apr 2021, 22:40 
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Username Protected wrote:
I am no expert at this, but I believe that A DER could be used and that is basically a Field Approval. I have heard 20% increase in HP is within the norm for a DER approval. The DER data applies to only one airplane, so it is not a general STC.


Though I’ve heard you can reference somebody else’s DER approved FAA paperwork as a precedent making any follow on application a bit of an easier process.

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 Post subject: Re: Cherokee 250?
PostPosted: 29 Apr 2021, 19:49 
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Joined: 10/14/14
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Company: Corporate Air Technology
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After purchasing my 235 when the P28B website was still up and running I was compelled to post a April Fools spoof about the rebirth of the 235.

My edition utilized a turbo diesel for better performance at altitude greater available fuel source throughout the world.

viewtopic.php?f=49&t=98562&view=unread#unread

If you really wanted some extra umph I may suggest the MTU 20V 8000 series diesel a twenty cylinder engine rated at 10996 HP @ 1050 RPM.


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 Post subject: Re: Cherokee 250?
PostPosted: 18 Apr 2022, 06:48 
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Update, I was able to successfully obtain a field approval for installing the high compression pistons, so this type mod is still possible, but took about 9 months!


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 Post subject: Re: Cherokee 250?
PostPosted: 18 Apr 2022, 14:37 
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It is also quite possible the sellers listing the 250hp upgrade had no idea what they were talking about.

Another possibility on decades old airplanes is that something was upgraded without any approved data. Things were looser back in the day, approvals were easier. Also, some folks even today, don't bother getting paperwork...


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 Post subject: Re: Cherokee 250?
PostPosted: 18 Apr 2022, 15:09 
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Unless things have changed, a DER cannot approve a STC or field approval. A DER can approve compliance documentation in support of a design change, and can coordinate other aspects with the FAA. In the case at hand, the DER would need authorization for both engine and aircraft changes, which might be a little unusual.


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 Post subject: Re: Cherokee 250?
PostPosted: 18 Apr 2022, 15:30 
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Username Protected wrote:
It is also quite possible the sellers listing the 250hp upgrade had no idea what they were talking about.

Another possibility on decades old airplanes is that something was upgraded without any approved data. Things were looser back in the day, approvals were easier. Also, some folks even today, don't bother getting paperwork...

one might be surprised to find what pistons are actually installed in a lot of engines. By accident or on purpose. Joe Average IA gets a new-to-him airplane in for a 100hour. If compression and borescope look normal, and the logs have no hint, why would he go any further?


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 Post subject: Re: Cherokee 250?
PostPosted: 22 Apr 2022, 17:47 
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Username Protected wrote:
Update, I was able to successfully obtain a field approval for installing the high compression pistons, so this type mod is still possible, but took about 9 months!



Stephen, I must ask, what did it do for performance? If you have a fat wing 28 like mine I would not expect much more in cruise and a bit better take off and climb. Did you document before and after. No more auto gas STC and likely no 94UL with the high compression pistons.


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