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Derating engine to increase TBO?

Looking at the history of Mooney Ovation on AvWeb, I find it surprising that they got a higher TBO by de-rating engine max RPM?

I am at the moment looking at one Mooney O2 GX (280hp & 2000h TBO) with the O3 engine upgrade (310hp & 1700h TBO) following the MidWest Mooney STC (paper work mainly but also new prop, new tach redline and adjusting governor)

How common is this case? would most of flyer be happy with more TBO or more HP?
I guess the answer is Crystal clear if one accepts flying beyond TBO (in EASA land), ofc subject to Fuel Flow being a “finite number”

Also anyone in EuroGA flies an M20R Ovation and happy for a chat?

https://www.avweb.com/ownership/mooney-ovation/

Last Edited by Ibra at 05 Jan 10:14
Paris/Essex, France/UK, United Kingdom

First of all; Ovations are gorgeous ! Second; don’t stare yourself blind on TBO. Get yourself a proper engine monitor and fly the engine on condition, especially an atmosferic one.

My engine has a TBO of 1800hrs, but if I was to factory overhaul it now the new TBO would be 2000hrs. It’s an academic exercise.

EBST, Belgium

The Cessna 172R has the same engine as the Cessna 172S (Lycoming IO-360-L2A) but on the 172R it is derated from 180 hp to 160 hp. No difference in TBO.

I wonder what reason Cessna had to derate the engine on the 172R.

ESKC (Uppsala/Sundbro), Sweden

Ibra wrote:

I am at the moment looking at one Mooney O2 GX (280hp & 2000h TBO) with the O3 engine upgrade (310hp & 1700h TBO) following the MidWest Mooney STC (paper work mainly but also new prop, new tach redline and adjusting governor)

Not flying the O3, but I don’t think the midwest STC has been EASA validated (which is not important if you want to keep the aircraft N-reg).

Last Edited by Guillaume at 05 Jan 14:03

airways wrote:

My engine has a TBO of 1800hrs, but if I was to factory overhaul it now the new TBO would be 2000hrs. It’s an academic exercise.

The M20J, I used to fly was 2500h before getting a new engine (gave up after a nasty prop strike rather than something unexpected)

Airborne_Again wrote:

The Cessna 172R has the same engine as the Cessna 172S (Lycoming IO-360-L2A) but on the 172R it is derated from 180 hp to 160 hp. No difference in TBO.I wonder what reason Cessna had to derate the engine on the 172R.

I would have expected TBO to go up, but does the engine run on same propeller? or runs with a heavy combination (long & corase?) ?
Maybe physics of extending TBO using low rated RPM differs for fixed & variable propellers

Guillaume wrote:

Not flying the O3, but I don’t think the midwest STC has been EASA validated (which is not important if you want to keep the aircraft N-reg).

Yes it will be on N-reg

Last Edited by Ibra at 05 Jan 14:06
Paris/Essex, France/UK, United Kingdom

In Alaska they use a clothes peg on the Cessna 185/206, not sure if this is based on an OWT, and whether the clothes peg keeps the constant speed propeller (on full fine/max) tips from going supersonic, and being more neighbourly. @PilotDAR hopefully knows the answer.

In general these large normally aspirated displacement engines are happiest at 65%-75% power. Running them at 55% does not necessarily extend the engine life – see the Warrior used by the Rare Bear racing team – SOP was WOT all the time until landing.

Turbo charging changes this, in part because of the additional complexity of engine components. The largest HP output range that I can think of is the Lycoming -540, which goes from 235 HP (Pawnee) to the 425 HP output in the Navajo 31P. Interestingly there are probably more Pawnees around as a proportion of the original fleet, than 31P’s.

Oxford (EGTK), United Kingdom

Airborne_Again wrote:

The Cessna 172R has the same engine as the Cessna 172S (Lycoming IO-360-L2A) but on the 172R it is derated from 180 hp to 160 hp

How exactly do you derate identical engines?

The elephant is the circulation
ENVA ENOP ENMO, Norway

Ibra wrote:

I would have expected TBO to go up, but does the engine run on same propeller? or runs with a heavy combination (long & corase?) ?
Maybe physics of extending TBO using low rated RPM differs for fixed & variable propellers

The propellers are different.

ESKC (Uppsala/Sundbro), Sweden

LeSving wrote:

How exactly do you derate identical engines?

You use a 2400 rpm redline rather than 2700 rpm. And different propellers.

ESKC (Uppsala/Sundbro), Sweden

Perhaps fictionally derating an engine (just lowering the redline) doesn’t affect TBO. Like the 235hp of the 182 vs the 250hp of ie TB20.

Here is one partial clue from Lycoming SI1009 :

The F,G and J versions offer 125hp, slightly more than the others.

LFOU, France
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