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High CHTs after TB21 turbo engine overhaul

Mooney_Driver wrote:

So the question would be to set take off power manually to the normal MP for climb and see what happens

That is not necessarily representative of what should happen if things were set right, since this requires a throttle position different from WOT, and throttle position affects fuel richness.

In other words: what Placido needs is correct richness at WOT, and not another throttle position, which is the standard take/off+climb regime. hence you are correct that he needs the MP setting of his wastegate to be correct, but at WOT, then he can figure whether FF is correct.

Also he needs to figure whether his FF indication is correct, which is easy to do if he has a fuel totalizer.

And even with correct baffling (a must, yes) , a 10% excess MP/pwr will drive your CHTs away as the design cooling capacity is exceeded. On air-cooled TSIO520 contis this is patently obvious, but perhaps liquid cooled ones like that of @Flyingfish are a bit more tolerant of MP excursions without a CHT impact

Antonio
LESB, Spain

Mooney_Driver wrote:

instead of experimenting, I’d get the overhauler and your maintenance involved ASAP

Yes, but in order to make their help as effective as possible, give them as much data as you can (is your FF verified as correct?, and share FF, MP and CHT data and insist that your procedures are the same as before the engine change)

Last Edited by Antonio at 19 Nov 20:45
Antonio
LESB, Spain

Just to add something else in as a consideration. Have you checked the timing accurately? being advanced can lead to increased CHT’s. This probably isn’t the issue. But it’s easy to pop a piston plug in with a protractor on the spinner and check where it is.

Antonio wrote:

That is not necessarily representative of what should happen if things were set right, since this requires a throttle position different from WOT, and throttle position affects fuel richness.

In other words: what Placido needs is correct richness at WOT, and not another throttle position, which is the standard take/off+climb regime. hence you are correct that he needs the MP setting of his wastegate to be correct, but at WOT, then he can figure whether FF is correct.

I agree Antonio. My suggestion was based on the question whether then excessive MP he gets is overboosting the engine, which by now we know it isn’t. However, if a faulty wastegate is the problem, it could help in a situation where he has to ferry the plane. I recall from planes with fixed wastegates (Seneca II, Arrow 3T) you have to set take off power manually (not WOT) in order not to overboost the engine. That was my thought process.

Antonio wrote:

And even with correct baffling (a must, yes) , a 10% excess MP/pwr will drive your CHTs away as the design cooling capacity is exceeded.

Exactly. So a power reduction at least after take off might be a temporary solution to that.

Clearly, if he is involving the overhauler as well as any maintenance, he needs to give them all the data he has, ideally the data from his analyzer. But the data he has shared here is sufficiently irregular that something must be amiss.

LSZH, Switzerland

I do have an insight avionics fuel totalizer and the fuel flow seems to be correct and it looks identical to before the overhaul. I have failed to look at TIT or EGT numbers in particular during take-off. I can surely say that TIT never exceeded its limits but I couldn’t tell you now whether the take-off TIT numbers are higher now than what they were before.

What is it that the mechanic should look at to correctly set MP/FF for take-off. It is the waste gate or the density controller or both?

LSZH

If MP increased and FF is at the same level as it was at the lower MP, you’re running leaner. High CHT might indicate too lean. I believe the FF is set at the fuel servo, the MP between the wastegate and density controller. As Antonio wrote, it is much better to be over rich than not rich enough. I thought your MP appears to not exceed limits, so if not broken, perhaps don’t fix. You get better feedback, but admittedly possibly spend more money chasing a problem, when you change one parameter at a time.

tmo
EPKP - Kraków, Poland

I agree with Off-Field, Timing directly affects CHT.
I can’t find it but last year an article regarding someone’s struggle with temps was written about the subject.
Maybe the overhaul is ‘smokescreening’ something straightforward as Timing.

United Kingdom

@THY also owns a TB21. Maybe he can also contribute with some values for comparison…

Good luck with troubleshooting!

EDLE

tmo wrote:

You get better feedback, but admittedly possibly spend more money chasing a problem, when you change one parameter at a time.

That is a good point. If @placido has good access to his mechanic, then the feedback may be of interest, but it may take several iterations.

If not, he just needs the problem fixed in one go.In such case, I would do ignition timing, MP and FF adjustments (since FF indication seems to be good) all in one go. Maybe we will not know what fixed it, but hopefully it will be fixed or at least mitigated.

Antonio
LESB, Spain

Dear all it will be a couple of weeks before my mechanic can work on the airplane so i won’t have any news short term. I will ask him to also look at timing but I don’t think this will be the issue as the magneto was not overhauled during the engine overhaul as I had replaced the magneto with a newly overhauled one just 6 months prior to the engine being overhauled. So I guess that nobody really touched the magneto but nevertheless I will ask the mechanic to also look at this.

I have talked to the overhauler on Friday and his take is to adjust the density controller so that it shows the correct values on the ground and to also close the gaps around the metal sheet that contours the engine case.

I will let you know if this will have fixed my issues. thanks to all for your valuable contributions.

LSZH
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