How long should the engines last?

[xender 459]

Hi guys!

Im wondering, how long should the engines last in green before going yellow? I can manage to get like 10 hours or so (not in continuous operation but in multiple flights) and after that they start to get yellow.

Is that ok or im mismanaging them? (This is all manual, without AFE).

Also, lets say im climbing to FL200. At what point should i switch to auto lean mixture? Right now i leave the mixture at auto rich until i real cruise altitude and then switch to auto lean. Is that how it should be done?

Thanks!

[downscc 1,327]

3 hours ago, xender said:

Hi guys!

Im wondering, how long should the engines last in green before going yellow? I can manage to get like 10 hours or so (not in continuous operation but in multiple flights) and after that they start to get yellow.

Is that ok or im mismanaging them? (This is all manual, without AFE).

Also, lets say im climbing to FL200. At what point should i switch to auto lean mixture? Right now i leave the mixture at auto rich until i real cruise altitude and then switch to auto lean. Is that how it should be done?

Thanks!

Hi Juan:  The engines should give you hundreds of hours.  I'm not sure if they stay green for a typical TBO but it will be much greater than 10 hrs.  FL200 is an unusually high cruise altitude, why so high?  This isn't a jet that gets better performance and economy at altitude. I fly around 8000 or higher as required for terrain.  Make sure you power back from takeoff to METO after takeoff and power back to climb once at climb speed of 160-170 KIAS.  Keep it auto rich and in climb speed after you level off at cruise and let the excess power accelerate you to the book cruise value. Then set a power according to book and then auto lean and cowls 0.

Always stick to book values for power settings.  You have a choice of the original Douglas charts that use BMEP or you can use the additional charts PMDG added from operators flying her today that use MP.  Either one, but stick to the numbers.

[xender 459]

Thanks Dan.

I usually fly at FL200 because that's what pfpx tells me to do when i do my flight plans. Maybe that's killing them prematurely 

 

Thanks

[Chock 17,769]

It is not unknown for a Pratt & Whitney R-2800 Double Wasp to go 1,400 hours before it needed a major overhaul, but certainly it should last a 1,000 hours before needing anything really major doing to it if operated properly, but, if it has been mismanaged and damaged, then subsequently operating it properly will not mean it will then last for that length of time because the damage has probably already been done. Note that this is not true of all P&W Double Wasps, as there are very many different models of it and some are more resilient than others, but as a general guide, if you are getting problems after ten hours of operation, then that is indicative of it not being operated properly, actually at about ten hours the real thing probably won't even have been run in properly.

Like most air cooled engines, if it appears to be using a lot of oil, that's usually an indication that it has been operated incorrectly, so that's a good guide. It isn't just the settings you put it on for flight either which you have to watch, it's how you manage cooling it for a descent too, and since you've been taking it up to 20,000 feet, that means an air cooled radial like the R-2800 would be particularly at risk of shock cooling on the descent, this is where the engine gets throttle back and also goes down into thicker air, meaning more airflow goes over it and in combination with it being throttled back, it cools down too quickly, this leads to damage such as cooling fins cracking and cylinder heads warping, which then blows the cylinder head gasket, which reduces compression meaning it will develop less power and run unbalanced and it makes the oil leak too. To avoid shock cooling with radial air cooled engines, in addition to using the cooling gills, you may need to occasionally put the revs up even on the descent so it doesn't cool down too quickly. To be honest you should do that anyway occasionally as it helps to prevent the plugs fouling from oil build up on them when throttled back for extended periods.

[downscc 1,327]

2 hours ago, xender said:

Thanks Dan.

I usually fly at FL200 because that's what pfpx tells me to do when i do my flight plans. Maybe that's killing them prematurely 

 

Thanks

Don't let PFPX select your cruise altitude. That alone will not injure the engines but never go that high unless there is a really good reason.  This isn't a jet.

[CrashTronic 3]

20 hours ago, Chock said:

...that means an air cooled radial like the R-2800 would be particularly at risk of shock cooling on the descent...

If shock cooling is a risk then are those effects also seen in cold climates sub zero temperatures on shutdown? It appears that would be the greatest shock cooling area because of no heat production. And with a massive fleet of piston powered airlines we have yet to see any evidence which is statistically relevant to support shock cooling. Yes damage can happen if there are flaws in the metallurgy but that is the root cause not the high cooling rate theory.

I highly suggest reading Pelican's Perch by Jonn Deakin https://www.avweb.com/news/pelican/182102-1.html

He has a wealth of information and we used it at our flight school as a foundation to engine management, especially for those looking to get into the big bore high performance engines.

[downscc 1,327]

2 hours ago, CrashTronic said:

If shock cooling is a risk then are those effects also seen in cold climates sub zero temperatures on shutdown? It appears that would be the greatest shock cooling area because of no heat production. And with a massive fleet of piston powered airlines we have yet to see any evidence which is statistically relevant to support shock cooling. Yes damage can happen if there are flaws in the metallurgy but that is the root cause not the high cooling rate theory.

Agree, while shock cooling is a concern in our TSIO-520s on the Chancellor, there is little concern for that in the big round ones. Primary emphasis is on keeping a positive BMEP indication which means the props are not turning the engine.  Typical descent is at 25 inHg MP.

[xender 459]

@downscc What's the problem with the props turning the engines? Isn't that the same as a car going downhill in low gear?

[downscc 1,327]

31 minutes ago, xender said:

@downscc What's the problem with the props turning the engines? Isn't that the same as a car going downhill in low gear?

Good question.  No it is different. In general, geared aircraft engines will be damaged if the prop turns the engine.  They are not designed for the negative torque.  In some cases you will see damage very quickly.  Even the geared turboprops like the J41 keep the torque positive.

[xender 459]

Then that must be my problem. I use idle power. I even have to push the gear button to silence the gear horn. That must be it.

thanks!

[metzgergva 28]

You will have more fun flying the aircraft after reading through the manual and look at the traffic patterns to give you a feel.

[CrashTronic 3]

Solution to the negative torque problem....hang jets on them wings

[CrashTronic 3]

Oh and I should add, below ~17" mp the prop drives the engine according to AFSD.

[metzgergva 28]

The rule is to keep MAP min equal RPM/100 as a wind change may change the load on the props. The faster you fly the better to keep an additional margin like 22 over 2000.

[Claudius_ 323]

1 hour ago, metzgergva said:

The rule is to keep MAP min equal RPM/100 as a wind change may change the load on the props. The faster you fly the better to keep an additional margin like 22 over 2000.

Can you explain better this interesting rule? Thanks.